Landscapes and Landforms of Portugal [1st ed.] 9783319036403, 9783319036410

Citation preview

World Geomorphological Landscapes

Gonçalo Vieira José Luís Zêzere Carla Mora   Editors

Landscapes and Landforms of Portugal

World Geomorphological Landscapes Series Editor Piotr Migoń, Institute of Geography and Regional Development, University of Wrocław, Wrocław, Poland

More information about this series at http://www.springer.com/series/10852

Gonçalo Vieira
José Luís Zêzere
Carla Mora Editors

Landscapes and Landforms of Portugal

123

Editors Gonçalo Vieira Centre of Geographical Studies Institute of Geography and Spatial Planning University of Lisbon Lisbon, Portugal

José Luís Zêzere Centre of Geographical Studies Institute of Geography and Spatial Planning University of Lisbon Lisbon, Portugal

Carla Mora Centre of Geographical Studies Institute of Geography and Spatial Planning University of Lisbon Lisbon, Portugal

ISSN 2213-2090 ISSN 2213-2104 (electronic) World Geomorphological Landscapes ISBN 978-3-319-03640-3 ISBN 978-3-319-03641-0 (eBook) https://doi.org/10.1007/978-3-319-03641-0 © Springer Nature Switzerland AG 2020 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

Series Editor Preface

Landforms and landscapes vary enormously across the Earth, from high mountains to endless plains. At a smaller scale, Nature often surprises us by creating shapes which look improbable. Many physical landscapes are so immensely beautiful that they have received the highest possible recognition—they hold the status of World Heritage properties. Apart from often being immensely scenic, landscapes tell stories which not uncommonly can be traced back in time for tens of million years and include unique events. In addition, many landscapes owe their appearance and harmony not solely to natural forces. For centuries, or even millennia, they have been shaped by humans who modified hillslopes, river courses, and coastlines, and erected structures which often blend with the natural landforms to form inseparable entities. These landscapes are studied by Geomorphology—‘the Science of Scenery’—a part of Earth Sciences that focuses on landforms, their assemblages, the surface and subsurface processes that moulded them in the past and that change them today. The shapes of landforms and the regularities of their spatial distribution, their origin, evolution, and ages are the subject of research. Geomorphology is also a science of considerable practical importance since many geomorphic processes occur so suddenly and unexpectedly, and with such a force, that they pose significant hazards to human populations and not uncommonly result in considerable damage or even casualties. To show the importance of geomorphology in understanding the landscape, and to present the beauty and diversity of the geomorphological sceneries across the world, we have launched a new book series World Geomorphological Landscapes. It aims to be a scientific library of monographs that present and explain physical landscapes, focusing on both representative and uniquely spectacular examples. Each book will contain details on geomorphology of a particular country or a geographically coherent region. This volume covers Portugal—a country which is not large in terms of area, but extremely endowed with magnificent landscapes. Its territory integrates all aspects of geomorphology, from varied coastal sceneries, including spectacular coves and rock arches of Algarve, through denudational plains and karstic massifs, residual mountain ranges and inselbergs, deeply entrenched valleys, to wild mountain environments of Serra da Estrela and Serra do Gerês which both host impressive evidence of Pleistocene glaciation. Some of them are better known to the international community than others, but all deserve to be shown to the world and this goal is fulfilled by this latest addition to the World Geomorphological Landscapes series. The World Geomorphological Landscapes series is produced under the scientific patronage of the International Association of Geomorphologists—a society that brings together geomorphologists from all around the world. The IAG was established in 1989 and is an independent scientific association affiliated with the International Geographical Union and the International Union of Geological Sciences. Among its main aims are to promote geomorphology and to foster dissemination of geomorphological knowledge. I believe that this lavishly illustrated series, which sticks to the scientific rigour, is the most appropriate means to fulfill these aims and to serve the geoscientific community. To this end, my great thanks go to the editors of the volume, Profs. Gonçalo Vieira, José Luís Zezêre and Carla Mora, who agreed to coordinate the book and ensured that the final product is of high quality. I am also v

vi

Series Editor Preface

grateful to all individual contributors who agreed to add the task of writing chapters to their busy agendas and delivered excellent final products. On more a personal note, I am particularly pleased to see the Portugal volume joining the series. I had the privilege to work in Portugal myself, exploring geomorphology of Serra da Estrela—the highest mountains of the country—in the stimulating company of Prof. Gonçalo Vieira. He was also kind enough to show me many other places and these trips leave no doubt that Portugal is a geomorphological destination not to be missed. Wrocław, Poland

Piotr Migoń Series Editor

Preface

Landscapes and Landforms of Portugal volume presents, for the first time, a series of synthesis chapters on landscape highlights of mainland Portugal, covering a wide diversity of geomorphological settings. These are presented with language and graphic styles that try to bridge-the-gap from professional scientists to undergraduate students, while being also accessible to all those interested in the earth sciences, to help for a better understanding of landscape evolution and specific features of the Portuguese landforms. The authors are physical geographers and geologists, mostly from Portuguese research institutions, all of them having had conducted research in the regions which they present. The main objective of the book is to provide a good overview of the geomorphology of Portugal, but also of its links with human occupation of the territory, geohazards and geoheritage management. This book is a tribute to Prof. António de Brum Ferreira, who has been an inspiration for generations of geomorphologists and students. Landforms and Landscapes of Portugal volume is organized in five thematic parts, i.e. 1. geomorphological setting, dynamics and hazards, 2. coasts, 3. mountains and valleys, 4. urban areas, 5. geoconservation and geoparks. In each part, chapters are ordered geographically from north to south, covering most of mainland Portugal (Fig. 1). Part I (Geomorphological Setting, Dynamics and Hazards) aims at presenting an introduction to the landscapes of Portugal, starting with a geomorphological synthesis by C. Ramos and A. R. Pereira (University of Lisbon, Chap. 1), followed by an overview of climate of Portugal by C. Mora and G. Vieira (University of Lisbon, Chap. 2), aiming to better understand geomorphological dynamics, especially the present-day one, but also providing a glimpse into Pleistocene and Holocene environmental conditions. J. L. Zêzere (University of Lisbon) presents a synthesis of geomorphological hazards at the national level (Chap. 3), while R. A. C. Garcia and S. C. Oliveira (University of Lisbon) present two examples of landslide hazardscapes (Chap. 4). Finally, S. C. Oliveira and co-authors (University of Lisbon) present a synthesis on land use planning and emergency management associated with geomorphological hazards in Portugal (Chap. 5). Part II (Coasts) includes reviews of several important sectors of the Portuguese coastline, its geomorphological characteristics and evolution. M. A. Araújo (University of Oporto) presents interesting features of the coast north of the city of Espinho, covering the morphostructure, rock control on landforms, the littoral platform and also the Cenozoic deposits and geomorphological evolution (Chap. 6). C. Neto and colleagues (University of Lisbon) focus their review on the Tróia Peninsula, a sand spit located at the Sado Estuary, close to Setúbal, and discuss its geomorphological characteristics and dynamics, linking it to the littoral drift and Holocene sea-level change (Chap. 7). Moving southwards, A. R. Pereira (University of Lisbon) presents the remarkable southwest coast of Portugal, marked by its littoral platform, tectonics and sediments (Chap. 8). Finally, D. Moura (University of Algarve) and colleagues introduce the rocky section of the Algarve, marked by its scenic cliffs, but also depositional environments and karstic terrains (Chap. 9). Part III (Mountains and Valleys) covers most interior Portugal and also some coastal mountains. P. Pereira and D. I. Pereira (University of Minho) present the landforms of the Peneda and Gerês mountains, located in the only National Park in Portugal and focus on vii

viii

Fig. 1 Approximate location of the areas presented in the book with indication of the chapter numbers. Black—coasts (Chaps. 6–9) and mountains and valleys (Chaps. 10–21), red—urban areas (Chaps. 22–23), blue—geoparks (Chaps. 24–28). The limits are not exact, and especially in the geoparks, boundaries are irregular and correspond to administrative limits

granite and glacial landforms (Chap. 10). The same authors provide an overview of geomorphological landscapes of Trás-os-Montes and Alto Douro in north-east Portugal, focusing on long-term geological and landform evolution and on the interplay between planation, tectonics and fluvial erosion (Chap. 11). S. Pereira (University of Lisbon) presents geomorphology and its interplay with anthropogenic action in the scenic Alto Douro valley, with its impressive terraces associated with the famous vineyards of this UNESCO World Heritage (Chap. 12). S. Daveau (University of Lisbon) zooms in at the Vilariça and Longroiva tectonic basins, discusses their genesis and significance of landforms for the evolution of the human settlement in the territory, comparing both basins (Chap. 13). P. P. Cunha and colleagues (University of Coimbra and San José State University) show the geomorphology of the Mondego river valley, including its hydrological dynamics and fluvial terraces (Chap. 14). G. Vieira and A. Nieuwendam (University of Lisbon) discuss the main features of glacial and periglacial landforms and deposits of the Serra da Estrela, a landscape which surprises all geomorphologists due to the clear imprint in the landscape of cold Pleistocene dynamics (Chap. 15). P. P. Cunha and colleagues (Universities of Coimbra, Évora, Porto and Durham) introduce landforms of the Beira Baixa, mainly between Sarzedas and Monfortinho, a region with a very interesting evolution linking planation, tectonics, fluvial dynamics, Cenozoic deposition and residual relief (Chap. 16). The Sicó massif is presented by P. P. Cunha and colleagues (University of Coimbra), evidencing the significance of limestones, dolomites and marls, together with tectonics, for the evolution of the mountains, as well as of numerous landforms and deposits, which include fluvial and karstic phenomena, as well as marginal periglacial deposits (Chap. 17). M. L. Rodrigues (University of Lisbon) presents the limestone

Preface

Preface

ix

massif of Estremadura, its morphostructures and karstic landforms at different scales, showing also evidence of different generations of slope deposits and examples of geomorphosites (Chap. 18). M. C. Kullberg and J. C. Kullberg (University of Lisbon and New University of Lisbon) discuss the geological evolution and landforms of the Serra de Sintra, resulting from an igneous body intrusion and subsequent uplift deforming the surrounding, predominantly Mesozoic sedimentary rocks (Chap. 19). The area also shows significant testimonies of its Quaternary dynamics, including raised beaches and aeolianites, as well as excellent examples of granite landforms. J. L. Zêzere presents the geomorphology of the north of Lisbon region, a typical cuesta landform area, developed in Mesozoic and Cenozoic sedimentary terrains (Chap. 20). The author presents its geomorphological evolution dominated by fluvial incision and differential erosion and also the present-day contemporary geomorphological dynamics, dominated by mass movements triggered by earthquakes and, more frequently, by different types of rainfall events. Finally, the Arrábida Chain, presented by Fonseca and co-authors (University of Lisbon), is dominated by the small but very interesting Serra da Arrábida, a limestone massif showing an almost perfect structural control, coinciding with an anticline, southbound by a fault scarp (Chap. 21). This mountain has been described as one of the finest examples of the Alpine orogenesis in Portugal. Part IV is dedicated to the geomorphology of the two largest cities in Portugal: Lisbon and Oporto. In Oporto, L. Soares and C. Bateira (University of Oporto) discuss the geomorphological setting of the town, built over granites associated with a narrow belt of metasediments, and marked by the deep incision of the Douro valley (Chap. 22). These conditions favour the occurrence of slope movements, major river flooding and erosion associated with ocean dynamics. T. Vaz and J. L. Zêzere (University of Lisbon) present the geomorphic setting of Lisbon and discuss the main geohazards affecting the urban area, which are dominated by earthquakes and also by landslides induced by earthquakes (Chap. 23). Part V aims at covering geoconservation in Portugal and includes chapters on UNESCO Global Geoparks of mainland Portugal, as well as on the recent candidate that will be classified in early 2020. Portugal has been one of the leading countries in the promotion of UNESCO Global Geoparks, and although not all focusing on geomorphological phenomena per se, Geoparks always include geomorphic geosites. Their role in regional sustainable development and promotion of geology and geomorphology, and geoconservation makes them excellent examples of the applicability of the science of geomorphology. Part V initiates with an overview of geoconservation in Portugal, mainly targeting at geomorphological heritage, by J. Brilha and P. Pereira (University of Minho, Chap. 24). This initial chapter is followed by four chapters on the Geoparks, which are, from north to south: the Terras de Cavaleiros Global Geopark: A UNESCO Global Geopark by D. I. Pereira and P. Pereira (Chap. 25), the Arouca UNESCO Global Geopark: Geomorphological Diversity Fosters Local Development by A. Sá (University of Trás-os-Montes and Alto Douro Chap. 26), The Estrela Geopark— From Planation Surfaces to Glacial Erosion by G. Vieira and colleagues (University of Lisbon and Association Geopark Estrela, Chap. 27), and the UNESCO Naturtejo Global Geopark: The Culture of Landscape by C. N. Carvalho and J. Rodrigues (Geopark Naturtejo da Meseta Meridional, Chap. 28). Lisbon, Portugal November 2019

Gonçalo Vieira José Luís Zêzere Carla Mora

Acknowledgements

This book was only possible to prepare thanks to the invitation and continuous support provided by Prof. Piotr Migoń, who visited Portugal several times and is, clearly, a friend of the Portuguese geomorphology. We are sincerely thankful for this opportunity. The numerous co-authors of the chapters are the soul of the book and have openly accepted to collaborate in this challenge, which took significantly longer to prepare than we envisaged. They have been patient and understood well the challenges associated with bringing together so many different authors, in hectic times for most scientists. We are thankful for their contributions and support. Mr. Duarte Fernandes Pinto has agreed to provide, free of charge, his excellent aerial photographs from Portugal, which he makes available at the blog “A Quinta Dimensão” (http://portugalfotografiaaerea.blogspot.com). We are extremely thankful for his contribution to several chapters of the book. Finally, we thank Springer for their continuous editorial support during the preparation of the manuscripts and editorial work. Lisbon, Portugal November 2019

Gonçalo Vieira José Luís Zêzere Carla Mora

xi

In Memoriam—António De Brum Ferreira

Prof. António de Brum Ferreira at a till outcrop in the Serra da Estrela in June 2001

António de Brum Ferreira (1941–2013) was born in the island of São Miguel (Azores) in February 1941. In 1960, he started studying geography at the University of Lisbon and was part of a generation of prestigious Portuguese geographers. In 1966, he began his career as assistant in the Department of Geography, at the Faculty of Letters of the University of Lisbon, and went through all academic categories until he was appointed Full Professor of Physical Geography in 1990. António de Brum Ferreira was Director of the Research Area on Physical Geography and Environment at the Center of Geographical Studies, and was a founding member and the first President of the Portuguese Association of Geomorphologists. In addition, he was a founding member of the European Center on Geomorphological Hazards (CERG), supported by the Council of Europe. He authored numerous scientific papers, including tens of articles in international and national journals, in the fields of landform evolution, morphotectonics, glacial and periglacial geomorphology, slope movements, natural hazards, climatology and regional geography. In 1966 he wrote “The Graciosa Island”, his dissertation of graduation, still very influenced by the Regional Geography methods of the 1960s. From 1968 to 1970, António de Brum Ferreira had an internship at the Universities of Toulouse and Clermont-Ferrand in France and became interested in detailed geomorphological mapping, bringing to Portugal the concept and the methodology. In 1978, he published “Plateaus and mountains of the North of Beira. Study of Geomorphology”, his Ph.D. thesis, a work on evolutionary geomorphology that is still a reference work in Portugal, followed by geographers, geologists and other Earth scientists. In the 1980s and 1990s, António de Brum Ferreira became interested in periglacial and glacial morphogenesis, coordinating a large survey on the Pleistocene glaciation of Serra do Gerês, published in 1999 (in co-authorship with Juan Ramón Vidal Romani, José Luís Zêzere and Maria Luísa Rodrigues). He also coordinated the Portuguese Science and Technology funded project (Program Praxis XXI) “Estrela—Geomorphological and Biophysical Processes

xiii

xiv

In Memoriam—António De Brum Ferreira

and Landscape Units in Mediterranean Mountain Environment. Application to Serra da Estrela”, which started in 1998. In 1979 António de Brum Ferreira accompanied and surveyed the events of slope instability in the region north of Lisbon, namely at Calhandriz and Adanaia, and deepened research on the subject since the mid-1980s. This topic, including issues of hazard and risk, focused his attention until the end of his scientific career. In 1984 he presented “Mouvements de terrain dans la Région au Nord de Lisbon” at the first major world conference dedicated to the subject, held in Caen (France). Integrated in a network of European researchers structured around the CERG, António de Brum Ferreira was the coordinator of a Portuguese team that participated in several European projects, which resulted in many publications in international reference journals. The list of projects includes the TESLEC—The temporal stability and activity of landslides in Europe with respect to climatic changes (1994–1996), the Newtech—New technologies for landslide hazard assessment and management in Europe (1996-98) and the ALARM—Assessment of Landslide Risk and Mitigation in Mountain Areas (2001–2004). Still within the scope of the CERG, António de Brum Ferreira involved the Department of Geography of the University of Lisbon in an ERASMUS network consisting of major European universities, promoting high-level teaching and internationalization of several generations of young researchers of the Center of Geographical Studies. Within the framework of this ERASMUS network, the “Fifth European intensive course on Applied Geomorphology: Mediterranean and urban areas” was organized in Lisbon in 1996, with 46 participants from 10 European universities. António de Brum Ferreira’s involvement in advanced training is evident in the list of his doctoral students which pursued academic careers in physical geography: Maria João Alcoforado, Ana Ramos Pereira, Catarina Ramos, José Eduardo Ventura, José Luís Zêzere, Maria Luísa Rodrigues, António Martins, and Gonçalo Vieira. Those who had the privilege of working with António de Brum Ferreira, have strong and good memories of him as an extremely rigorous and demanding researcher and professor with a remarkable intellectual honesty and an enormous passion for geomorphology. The ability to create a school, based on solid scientific knowledge, is an invaluable legacy that Prof. Brum Ferreira left to the Portuguese Geomorphology and this book is a tribute to him from a large number of Earth Scientists who have either directly collaborated with him, or benefited directly or indirectly from his influential work.

Contents

Part I 1

Geomorphological Setting, Dynamics and Hazards

Landscapes of Portugal: Paleogeographic Evolution, Tectonics and Geomorphology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Catarina Ramos and Ana Ramos-Pereira

3

2

The Climate of Portugal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Carla Mora and Gonçalo Vieira

33

3

Geomorphological Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . José Luís Zêzere

47

4

Portugal Landslide Hazardscapes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ricardo A. C. Garcia and Sérgio C. Oliveira

63

5

Geomorphological Hazards, Land Use Planning and Emergency Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sérgio C. Oliveira, Ricardo A. C. Garcia, and José Luís Zêzere

Part II 6

73

Coasts

The Northwest Portuguese Coast: A Longitudinal Coastline and Its Diversity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Maria Assunção Araújo

83 99

7

The Tróia Peninsula—An Aeolian Sedimentological Legacy . . . . . . . . . . . . . Carlos Neto, Miguel Geraldes, and Diana Almeida

8

The Southwest Coast of Portugal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 Ana Ramos-Pereira and Catarina Ramos

9

The Rocky Coast of Western Algarve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 Delminda Moura, Sónia Oliveira, and Tomasz Boski

Part III

Mountains and Valleys

10 The Granite and Glacial Landscapes of the Peneda-Gerês National Park . . . 127 Paulo Pereira and Diamantino Insua Pereira 11 The Geomorphological Landscape of Trás-os-Montes and Alto Douro . . . . . . 139 Diamantino Insua Pereira and Paulo Pereira

xv

xvi

Contents

12 The Terraced Slopes of the Douro Valley . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 Susana Pereira 13 The Longroiva and Vilariça Depressions: Two Narrow Tectonic Basins with Different Impacts on the Human Occupation . . . . . . . . . . . . . . . . . . . . . 163 Suzanne Daveau 14 The Mondego River and Its Valley . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 Lúcio Cunha, João Santos, and Anabela Ramos 15 Glacial and Periglacial Landscapes of the Serra da Estrela . . . . . . . . . . . . . . 185 Gonçalo Vieira and Alexandre Nieuwendam 16 Landscapes and Landforms of the Beira Baixa Region (Sarzedas–Monfortinho, Eastern Central Mainland Portugal) . . . . . . . . . . . . 199 Pedro P. Cunha, António A. Martins, Alberto Gomes, and David R. Bridgland 17 The Sicó Massif: Morphostructural Aspects, Hydrology and Karstification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211 Lúcio Cunha, Luca Antonio Dimuccio, and Isabel Paiva 18 The Limestone Massif of Estremadura . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229 Maria Luísa Rodrigues 19 Landforms and Geology of the Serra de Sintra and Its Surroundings . . . . . . 251 Maria Carla Kullberg and José Carlos Kullberg 20 The North of Lisbon Region—A Dynamic Landscape . . . . . . . . . . . . . . . . . . 265 José Luís Zêzere 21 The Arrábida Chain: The Alpine Orogeny in the Vicinity of the Atlantic Ocean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273 André F. Fonseca, José Luís Zêzere, and Mário Neves Part IV

Urban Areas

22 Geomorphology in a World Cultural Heritage Site: The City of Porto . . . . . 281 Laura Soares and Carlos Bateira 23 The Urban Geomorphological Landscape of Lisbon . . . . . . . . . . . . . . . . . . . . 295 Teresa Vaz and José Luís Zêzere Part V

The UNESCO Global Geoparks of Mainland Portugal

24 Geoconservation in Portugal with Emphasis on the Geomorphological Heritage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307 José Brilha and Paulo Pereira 25 Terras de Cavaleiros Geopark: A UNESCO Global Geopark . . . . . . . . . . . . 315 Diamantino Insua Pereira and Paulo Pereira 26 Arouca UNESCO Global Geopark: Geomorphological Diversity Fosters Local Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329 Artur Abreu Sá and Daniela Rocha

Contents

xvii

27 The Estrela Geopark—From Planation Surfaces to Glacial Erosion . . . . . . . 341 Gonçalo Vieira, Emanuel de Castro, Hugo Gomes, Fábio Loureiro, Magda Fernandes, Filipe Patrocínio, Gisela Firmino, and João Forte 28 Naturtejo UNESCO Global Geopark: The Culture of Landscape . . . . . . . . . 359 Carlos Neto de Carvalho and Joana Rodrigues Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377

About the Editors

Gonçalo Vieira is Associate Professor of physical geography at the Institute of Geography and Spatial Planning of the University of Lisbon, specializing in geomorphodynamics of polar and mountain environments, permafrost and periglacial geomorphology and remote sensing. He is Member of the research group on Climate Change and Environmental Systems (ZEPHYRUS) of the Centre of Geographical Studies and Scientific Coordinator of the Estrela Geopark. He is Author or Co-author of numerous papers in peer-reviewed international journals. José Luís Zêzere is Professor of physical geography at the Institute of Geography and Spatial Planning of the University of Lisbon, specializing in applied geomorphology, landslide hazard assessment and risk analysis. He is Vice-President of the CERG—European Centre on Geomorphological Hazards, Council of Europe, and Head of RISKam—Research Group Environmental Hazard and Risk Assessment and Management within the Centre of Geographical Studies. He is Author or Co-author of numerous papers in peer-reviewed international journals. Carla Mora is Assistant Professor at the Institute of Geography and Spatial Planning of the University of Lisbon, specializing in mountain climatology and remote sensing applications in cold environments. She is Member of the research group on Climate Change and Environmental Systems (ZEPHYRUS) of the Centre of Geographical Studies and Coordinator of the research group on climate change and territory at the Estrela Geopark. She is Author or Co-author of numerous papers in peer-reviewed international journals.

xix

Part I Geomorphological Setting, Dynamics and Hazards

1

Landscapes of Portugal: Paleogeographic Evolution, Tectonics and Geomorphology Catarina Ramos and Ana Ramos-Pereira

Abstract

This chapter synthesizes the most relevant aspects of geology, tectonics and geomorphology of Portugal. Its main purpose is to frame, in a morphostructural point of view, the more specific chapters on Portuguese geomorphological landscapes. It includes a summary of (i) the main evolutionary stages of the Portuguese territory, as well as the present tectonic framework of Portugal’s mainland, Azores and Madeira archipelagos, and (ii) the main regional features of the geomorphological units. The synopsis is based on the scientific publications of many colleagues, physical geographers and geologists, who with their work contributed, over the years, to the geomorphologic knowledge of the country. Professor António de Brum Ferreira was the “greatest teacher” of Portuguese geomorphologists, to whom many of us owe the taste, rigour, the practice and the knowledge of geomorphology. Keywords








Portugal Paleogeographic evolution Geotectonical framework Regional geomorphological units

1.1

Introduction

Over time, there have been many publications, of both Portuguese and international researchers, on the geological and geomorphological characteristics of Portugal and its geodynamics, in both the fields of geology and physical geography. The majority are related to specific subjects and limited areas of the country, whose contributions to the C. Ramos
A. Ramos-Pereira (&) Centre of Geographical Studies, Institute of Geography and Spatial Planning, University of Lisbon, Lisbon, Portugal e-mail: [email protected]

geomorphology of Portugal were, over time, compiled in synthetic works, published in different languages. The first synthesis on the scientific Geography of Portugal (with emphasis on geomorphology) is due to the German geographer Hermann Lautensach (volume I 1932 and volume II 1937). This work, written in German, was poorly disseminated among Portuguese scientists, given the language barrier. Volume I, with some updates by Lautensach in 1944, was translated into Portuguese and later included in another synthesis by Ribeiro et al. (1987). Almost 20 years after Lautensach, in 1955, the Portuguese geographer Orlando Ribeiro updated and synthesized the geographical knowledge of Portugal, giving particular emphasis to geomorphology, in a book written in Spanish, included in the series of volumes on the Geografia de España y Portugal, edited by Manuel de Terán. Two decades later, nine geologists (eight Portuguese and one Polish) published, in French, in Ribeiro et al. (1979), the first synthesis of the evolution and geological characteristics of Portugal. In 1981, the first geomorphological map of mainland Portugal, at a 1:500,000 scale, and explanatory report were published in French by Ferreira (1981), with a major contribution from António de Brum Ferreira. In the same decade, the French–Portuguese geographer Suzanne Daveau compiled the texts of Lautensach and Ribeiro introducing what she called “Comments and Updates” in a Portuguese four-volume compilation, on the Geography of Portugal, of which Volume I (Ribeiro et al. 1987) relates to geomorphology. In 2004, with the coordination of Feio and Daveau (2004), the Portuguese Association of Geomorphologists published a compilation of several works, from physical geographers and geologists, on the major regional relief units of mainland Portugal. The great advance of scientific knowledge on the paleogeographic evolution of Portugal and on the recent and present-day dynamics of its physical environment led to recent publications in the twenty-first century. There are two main syntheses written in Portuguese: “Geografia de Portugal - O Ambiente Físico” (Ferreira 2005) and “Geologia de

© Springer Nature Switzerland AG 2020 G. Vieira et al. (eds.), Landscapes and Landforms of Portugal, World Geomorphological Landscapes, https://doi.org/10.1007/978-3-319-03641-0_1

3

4

C. Ramos and A. Ramos-Pereira

Portugal” (Dias et al. 2013a, b). The first, written by physical geographers and coordinated by António de Brum Ferreira, is a volume included in a wider “Geography of Portugal” directed by Carlos Alberto Medeiros. Volume I devotes particular attention to the geomorphology of Portugal, gathering for the first time in one book, the most relevant aspects of physical geography of mainland Portugal and the Azores and Madeira archipelagos. The volume presents paleogeographic evolution of Portugal, geomorphologic contrasts, recent and present-day dynamics, as well as natural resources and risks. The other synthetic publication (Dias et al. 2013a, b) is written mainly by geologists and was published in two volumes: volume I, on the pre-Mesozoic Geology of Portugal, and volume II, on the Meso-Cenozoic Geology of Portugal. Pereira et al. (2014) presented a hierarchical classification of the geomorphological units of mainland Portugal, with a distinct methodology from previous authors. They define three hierarchical levels of geomorphological landscapes: (i) the first level is the morphostructural units (platforms, sedimentary basins and young Alpine mountain ranges, the latter not represented in mainland Portugal), (ii) the second level includes 10 regional geomorphological units, which are subordinate to the previous gross division, and (iii) the third level corresponds to the 56 major sub-units that subdivide the second level. This classification of the geomorphological landscape was based on a three-step methodology: (i) identification of relief patterns in 2008 SRTM (Shuttle Radar Topography Mission) radar images, with 90 m resolution, (ii) fieldwork for validation, correction or redefinition of the sub-units and (iii) analysis of quantitative parameters for each unit. This chapter is mainly based on a review of Feio and Daveau (2004), Ferreira (2005), Dias et al. (2013a, b) and Pereira et al. (2014) and has two main objectives: (i) to present the key stages and the main geological features of Portugal, as well as to provide the background to the present geotectonic setting and, and (ii) to characterize the diversity of Portugal’s large regional relief units. It is a summary of the main geological and geomorphological characteristics of the Portuguese territory, leaving further analysis of the geomorphological landscapes of Portugal to the following chapters.

1.2

Paleogeographic Evolution and Geomorphology of the Portuguese Mainland

The Portuguese territory, with an area of 92,225 km2, comprises mainland Portugal and the Azores and Madeira archipelagos (Fig. 1.1). The mainland (89,102 km2) is

located between 37 and 42° N in the west of the Iberian Peninsula, bordered by Spain to the north and east, and the Atlantic Ocean to the west and south. In the North Atlantic, the archipelago of the Azores (2322 km2) is set between 37 and 40° N, about 1500 km to the west of the mainland, and the archipelago of Madeira (801 km2) lies between 30 and 33° N, 800 km southwest of the mainland. From a morphostructural point of view, mainland Portugal consists of three units (Fig. 1.2): (i) the Iberian or Hercynian Massif (also known as the Hesperic Massif), mostly of Paleozoic age, (ii) the slightly deformed Meso-Cenozoic sedimentary borderlands of the Iberian Massif, forming the western or Lusitanian Basin and the southern or Algarve Basin and (iii) the Lower Tagus and Alvalade Sedimentary Basins, of Cenozoic age. The islands of the Azores and Madeira form a separate unit and represent the highest points of submarine mountains that rise above the ocean surface, being of volcanic origin and of Cenozoic age.

1.2.1 The Paleozoic Evolution Portugal’s geological and geomorphological characteristics are mainly due to two Wilson cycles, according to the theory of plate tectonics: the Variscan (540–270 Ma) and the Tethys/Atlantic (250–0 Ma) (Ribeiro 2013a). Although pre-Cambrian terrains outcrop in Portugal, they are of limited extent, as Variscan deformation reached a great intensity in Iberia, which somehow attenuated ante-Hercynian remains. Therefore, in the area presently occupied by Portugal, only one large orogenic cycle can be considered during the Paleozoic era (Ribeiro et al. 1979; Ferreira 2005). It is responsible for the origin of the Hercynian Massif, which resulted from the destruction of the western sector of the Hercynian or Variscan chain, at the end of the Paleozoic, which in morphostructural terms corresponds to a platform. The Iberian Massif, extending from north to south, covers about 70% of mainland Portugal (Fig. 1.2). It is composed of magmatic and metamorphic rocks, with prevailing granitoid rocks and various types of schist and shales with varying grades of metamorphism. The latter are distributed throughout the Iberian Massif in Portugal, although with a much lower grade in the far south, while the granitoid rocks are located mainly in the northwest and central-north of the country, albeit with some outcrops in the Alentejo (Figs. 1.2 and 1.3). In Portugal, the Variscan structures have a general NW– SE direction. The zones which show similar evolution of stratigraphy, geometry of tectonic deformations, nature of magmatism and intensity of metamorphism are arranged perpendicular to this direction. Thus, in general terms, from NE to SW, the following zones occur (Fig. 1.2): the Central Iberian Zone (CIZ), the Ossa Morena Zone (OMZ) and the

1

Landscapes of Portugal: Paleogeographic Evolution …

5

Fig. 1.1 Location of the Portuguese territory (mainland Portugal and the Azores and Madeira archipelagos). Islands of Azores: C (Corvo), F (Flores), Fa (Faial), G (Graciosa), P (Pico), SJ (São Jorge), SM (São

Miguel), SMa (Santa Maria), T (Terceira). Islands of Madeira: D (Desertas), M (Madeira), PS (Porto Santo), S (Selvagens)

South Portuguese Zone (SPZ). The CIZ corresponds to the axial zone of the Variscan chain and together with the OMZ composes the inner part of the Variscan Orogen. In these two zones, the rocks are older, more deformed and more intensely metamorphized, showing also extensive magmatic intrusions. The SPZ corresponds to the external part of the Variscan Orogen, with the most recent and lower-grade metamorphic Paleozoic sedimentary series, with fewer magmatic intrusions. The Variscan cycle in Iberia consisted of four phases (Ribeiro 2013a): Phase 1 (540–420 Ma, Cambrian, Ordovician and Silurian) was dominated by a plate divergence regime that led to the opening of Paleozoic oceans, bordered by passive margins; Phase 2 (420–390 Ma, Upper Silurian to Middle Devonian) showed the beginning of subduction in the margins of the Paleozoic oceans; obduction of ophiolitic blades and high-pressure thermal metamorphic events occurred; Phase 3 (390–300 Ma, Middle Devonian to Upper Carboniferous) showed continental

collision and orogenesis, with abundant granitoids and high-temperature metamorphism; Phase 4 (300–270 Ma, Upper Carboniferous to Middle Permian) showed intracontinental transcurrent deformation followed by orogenic collapse. The lithostructural characteristics of the Hercynian Massif depend on the various phases of the Variscan cycle. Phase 1 (540–420 Ma) was dominated by extensional regime, with expression in the sedimentary record and in the magmatism. The lithospheric stretching process formed deep basins in the CIZ that were filled by thick marine facies formations, which integrate the Dúrico-Beirão Supergroup (Ferreira 2005), previously known as ante-Ordovician Schist–Greywacke Complex (Ribeiro et al. 1979). This deposition of turbidite and interturbidite sediments is typical of deep marine and continental margin (shelf and slope) environments. At the same time, but further south, in the Ossa Morena Zone, several shallow basins formed, which were filled over time by sediments of different facies: terrigenous at the base,

6

Fig. 1.2 Morphostructural units and lithology of mainland Portugal. 1 Cenozoic sedimentary rocks (mainly sands, sandstones, clays, limestones and marls), 2 Mesozoic sedimentary rocks (mainly limestones, marls, sandstones and clays), 3 Mesozoic igneous rocks (mainly granites and syenites), 4 Paleozoic metasediments, 5 Paleozoic plutonic rocks (mainly granites), 6 Paleozoic volcanic rocks (porphyry and others), 7 main faults, 8 Variscan unit boundary of the Iberian Massif, B Berlengas islands location, AB Algarve Basin, AvB Alvalade Basin, CIZ Central Iberian Zone, LB Lusitanian Basin, LTB Lower Tagus Basin, OMZ Ossa Morena Zone, SPZ South Portuguese Zone, F fault

carbonates and terrigenous again at the top. It shows an evolution from a clearly continental environment to a coastal carbonate platform and then again to a continental environment (with sandstones and mudstones; Mata et al. 2006). In some of the OMZ basins, intense magmatic activity also occurred (in the Cambrian), giving rise to volcanic rocks and volcano–sedimentary complexes. In the Cambrian, the CIZ basins were deeper than those of the OMZ, but in the Ordovician the situation was reverse, increasing the depth of

C. Ramos and A. Ramos-Pereira

Fig. 1.3 Localities mentioned in the text: dots—localities and places, numbers—mountains; lines—main rivers. Mountains: 1 Açor, 2 Aire, 3 Alvaiázere, 4 Alvão, 5 Alvelos, 6 Amarela, 7 Arada, 8 Arrábida, 9 Barroso, 10 Boa Viagem, 11 Bornes, 12 Cabreira, 13 Caldeirão, 14 Candeeiros, 15 Caramulo, 16 Cercal, 17 Coroa, 18 Estrela, 19 Freita, 20 Gardunha, 21 Gerês, 22 Grândola, 23 Larouco, 24 Lousã, 25 Marão, 26 Mesquita, 27 Monchique, 28 Monte Figo, 29 Montejunto, 30 Montemuro, 31 Montesinho, 32 Muradal, 33 Nogueira, 34 Peneda, 35 Portel, 36 S. Mamede, 37 Sicó, 38 Sintra, 39 Vigia

the latter relatively to the CIZ basins (Ribeiro et al. 2007). From the Cambrian to the Ordovician, the crustal stretching process intensified in the OMZ but, on the contrary, practically ceased in CIZ, with a decrease in basin subsidence. The deep sea that existed during the Cambrian became narrower

1

Landscapes of Portugal: Paleogeographic Evolution …

and lost depth. It then began receiving quartz sands, usually deposited in continental shelf environments (passive margin). These would undergo metamorphism by the end of the Variscan cycle, so that the well-known Armorican quartzites, outcropping in different areas in Portugal, came into being (Bolacha 2014). These quartzites presently form higher relief due to its resistance against erosion. In the Lower Ordovician, a transition to coastal facies occurred from southwest to northeast, from a distal and deeper continental shelf of the OMZ to a shallower one in the NE sector of the CIZ. During the Lower Paleozoic “alternating ridges and grooves were created, where the thickness (and type) of sediments may vary considerably; there are also indications of tectono-sedimentary instability that produced gaps in the Paleozoic series” (Ribeiro 2013a: 25). In the Silurian, the increase in paleogeographic differentiation is shown in the sedimentary and magmatic records. The various sedimentary gaps recorded during the Silurian seem to reflect tectonic instability, preceding the Variscan tectonogenesis (Ferreira 2005). Phase 2 of the Variscan cycle (420–390 Ma, Upper Silurian to Middle Devonian) was dominated by the closing of the Paleozoic oceans (Rheic and Paleo-Tethys), resulting in the area now occupied by the Portuguese territory in the transformation from passive to active continental margins. The autochthonous sediments of the Dúrico-Beirão Supergroup were the first to deform and to be subjected to metamorphism. Being a continental margin deposit, it forms a thick sequence of shales and metagreywackes, which make up a large part of the CIZ substrate (Fig. 1.2). Subduction is widespread in all active margins, and obduction occurred in restricted segments of these margins. As a result, intrusive magmatic rocks formed, with which volcanic activity episodes were also associated, as well as ophiolite complexes linked with obduction (Bolacha 2014). Phase 3 (390–300 Ma, Middle Devonian to Upper Carboniferous) was essentially dominated by continental collision processes and subsequent orogenesis (Hercynian or Variscan Cordillera Formation), albeit with considerable regional asymmetries. The sedimentary records, predominantly marine and of continental margin, evolved to molasses deposited in intra-mountain basins (e.g. Ribeiro et al. 1979; Ribeiro 2013a) in the north and centre of Portugal. This is the case of the Douro Carboniferous groove, which is important for the quality of its anthracite content. Concomitantly, abundant synorogenic magmas, mostly of granitoid composition, between 320 and 310 Ma old, were produced (Ribeiro 2013a). In the south of the territory, the subduction (of the Rheic Ocean) continued along the margins of the OMZ, leading to the formation of igneous complexes in the Beja region of OMZ (Figs. 1.2 and 1.3)

7

and marine volcano–sedimentary complexes in the SPZ. In the latter, the Iberian Pyrite Belt stands out, important for its polymetallic sulphide deposits. Marine sedimentation continued in the SPZ, up to the Carboniferous, and is thus synorogenic, becoming younger from NE to SW. The last marine sediments (pelites and greywackes of the Baixo Alentejo Flysch Group; Figs. 1.2 and 1.3) are derived from erosion of inland formations, i.e. located N and NE (Oliveira 1983; Oliveira et al. 2006, 2013). Metamorphism and deformation of these formations also decreased gradually to the SW, showing the progression of the orogenic wave (Araújo 2013). In Phase 4 (300–270 Ma, Upper Carboniferous to Middle Permian), transcurrent intracontinental deformation followed by orogenic collapse (Ribeiro 2013a, b) occurred. The persistence of compression due to the continental collision between the continents of Laurasia and Gondwana (in the north of which Iberia was located) led to: the formation of the supercontinent Pangea and the spread of deformation to the interior of Iberia. In the north and the south, Iberia was affected by E–W strike-slip faults (North Pyrenean Fault and Azores–Gibraltar Fault; Ribeiro 2002), while inland, predominantly NNE–SSW strike-slip faults were formed (Verín–Penacova, Bragança–Manteigas, Messejana faults; Ribeiro 2002, 2013a) (Fig. 1.2). This corresponds to the Late Variscan deformation (Mateus and Noronha 2010). The synorogenic magmatism, between 310 and 320 Ma, was followed by late magmatism. The granitoids of this late stage often formed zoned massifs, surrounded by aureoles of contact metamorphism (Azevedo and Aguado 2013). Over circa 70–90 Ma at Permian–Triassic boundary, there is sedimentary gap in the west of Iberia. During part of this period, the Variscan chain was razed and a platform formed: the Iberian Massif (Fig. 1.4). This platform was affected later by tectonic movements of the subsequent cycle (Thetis/Atlantic), which completely changed its geomorphologic features.

1.2.2 The Mesozoic Evolution During the Mesozoic Era (251–65 Ma), the paleogeographic evolution of Portugal was marked by the beginning of a new Wilson cycle (Tethys/Atlantic or Alpine) and by a predominantly distensive tectonics that led to the formation of the Lusitanian (west of the Iberian Massif) and Algarve (to the south) Sedimentary Basins. These basins were infilled by sediments of Mesozoic and Cenozoic ages (Fig. 1.2). Presently, the Algarve Sedimentary Basin comprises the extreme south of mainland Portugal and extends in a W–E direction over about 140 km, with the width varying from 3

8

C. Ramos and A. Ramos-Pereira

Fig. 1.4 Angular unconformity with stratigraphic hiatus between the Paleozoic (Carboniferous pelites and greywackes) and the Mesozoic rocks (Triassic fluvial sandstones) at Telheiro Beach (western Algarve) (photograph by Diamantino Ínsua Pereira, University of Minho, Portugal)

to 25 km. It corresponds to an ENE–WSW sedimentary continental slope faulted by submeridian tectonic lines, which differentiated sedimentary conditions between the western and eastern Algarve. In general, the sedimentary series are thicker and deeper to the SSE (Ferreira 2005). The Lusitanian Basin corresponds to a continental margin distensive basin of Atlantic-type non-volcanic rift. It extends over 200 km, following roughly NNW–SSE direction, and reaches 100 km wide, 2/3 of which are emerged. Sedimentation reaches a maximum thickness of about 5000 m (Kullberg et al. 2013). The reconstruction of the key Mesozoic events in Portugal is based on evidence from this basin. At the beginning of the Mesozoic, the Iberian Massif was part of Pangea. The lithospheric stretching and faulting affecting this supercontinent led to its fragmentation and opening of the Tethys and Atlantic oceans. Iberia was located in a hinge position regarding the new boundaries of the lithospheric plates and the two oceans. A triple junction connecting the opening of the two oceans developed in the intersection of the southern (Tethys) and western (Atlantic) margins (Ribeiro 2013b). Consequently, the formation of the western Portuguese margin depended on the divergence between the Eurasian and American plates, associated with the opening of the Atlantic; in turn, the formation of the southern margin was controlled by differential movement between the African, Eurasian and American plates, associated with the opening of the Tethys (Fig. 1.5A). “The boundary between the African and Eurasian plates in the Iberian region began to develop from the Triassic as a left-lateral transtensional boundary due to the approximately E–W movement between Eurasia and America and NW–SE between Africa and America” (Terrinha et al. 2013: 126). In

the case of the Algarve Basin, the normal faults, associated with the break-up of Pangea, are E–W directed, as the Azores–Gibraltar Fault, and dip southwards, interfering with the NNE–SSW normal faults and controlling the sedimentation in the western Algarve zone (Ribeiro et al. 1996). The normal fault system is sub-parallel to the Porto–Tomar Fault in the centre and north of Portugal (Fig. 1.2), which guides the Lusitanian Basin individualization. These large Variscan tectonic lines were thus reactivated as normal faults. The opening of the Atlantic Ocean took place in stages, from south to north, through the formation of several basins, which preceded oceanization (Terrinha et al. 2005; Kullberg et al. 2013). Kullberg et al. (2013) distinguished 4 phases of rifting (crustal swelling followed by thermal subsidence and distension) in the Iberian western margin (IWM) between the Triassic and Lower Cretaceous, which had extreme consequences on the structure and infilling of the basins. In the IWM, rifting began in the Late Triassic (*210 Ma). As a result, between 200 and 180 Ma the Iberian Massif was crossed by dykes (e.g. along the Messejana Fault; Fig. 1.2). The distension caused the formation of grabens and half-grabens, where a detrital complex forms the base of the Mesozoic formations. These are the so-called Grés de Silves (Silves Sandstones) and the Margas de Dagorda (Dagorda Marls), deposited in semi-arid or subtropical climate conditions with a pronounced dry season (Ferreira 2005). The former are essentially red siliciclastic formations of alluvial fan type and eolianites. Evaporites (rock salt and gypsum) deposited in the centre of the lagoons are frequent in the Dagorda Marls. These formations are followed by dolomites, marls and limestones. The progressive enrichment in carbonates and evaporites is interpreted as the transition from a continental to marine

1

Landscapes of Portugal: Paleogeographic Evolution …

9

Fig. 1.5 Paleogeography of Iberia in the Upper Jurassic (A) and Lower Miocene (B). 1 Submerged areas, 2 emerged areas, 3 present continental boundaries, 4 cordilleras (continental collision), 5 tectonic

plate movement: (a) divergence, (b) lateral movement, (c) convergence, AGFZ Azores–Gibraltar Fracture Zone, GA Gibraltar Arc (from Ribeiro, 2013b, simplified)

environment, with fluvial–lacustrine deposits and episodes of marine invasions. In the second rifting phase in the Early Jurassic, the Western Basin began transforming into a westward tilted half-graben, whose western boundary is the granite-gneiss Berlengas Horst (an element of the Iberian Massif; Kullberg et al. 2013). The formation of limestones intensified at the end of the Early Jurassic and started to dominate the sedimentary sequences (Kullberg et al. 2006, 2013; Terrinha et al. 2013). The meridian faults were mainly responsible for the subsidence of the Western Basin, and significant variations of facies and thicknesses controlled by ENE–WSW to E–W faults define different compartments in the basin. Among them is the Nazaré Fault (Fig. 1.2) that separates the basin into sectors with different crustal stretching and sedimentation types (thickness and associated facies). The marine environment was predominant until the end of the Middle Jurassic, depositing thick limestone layers. The Upper Jurassic shows several discontinuities in sedimentation and depositional environments varied in time and space, from an open sea to a lagoon or fully terrestrial. In the third rifting phase in the Late Jurassic and at the beginning of Early Cretaceous (Fig. 1.5A), there was, for the first time, evidence of continental break-up in the North Atlantic with oceanic crust formation (*142 Ma). The Lusitanian Basin showed again a central graben with peripheral half-graben morphology. Tectonic changes in the basin, which included uplift of the Berlengas Horst, allowed for the accumulation of detrital and carbonate materials which formed important submarine deltaic fan systems in a

carbonate–terrigenous platform domain, both from the W and E (Kullberg et al. 2013). The fourth rifting phase in the Early Cretaceous is associated with magmatism (*135 Ma). It corresponds to the main phase of oceanic crust formation in the area of the Tagus Abyssal Plain, which may have favoured the progressive tilting of the Lusitanian Basin to the south, where marine influence remained (Kullberg et al. 2013). Thus, during the Early Cretaceous in sedimentary syn-rifting sequences the deposition of fluvial sands occurred, grading in the southerly direction into marine marls and limestones. This differentiation continued during the Early–Late Cretaceous, in post-rift sequences that are carbonate to the SW and fluvial to the N and E (Ribeiro 2013b). From the Cretaceous onwards, stretching took place west of the present-day Berlengas archipelago (Fig. 1.2), separating the Lusitanian Basin from the Atlantic Ocean Basin (Bolacha 2014). The formation and spreading of the oceanic lithosphere west of Iberia and the opening of the Gulf of Gascony in the north, during most of the Cretaceous, have led to an approximate 35° anticlockwise rotation of Iberia. This rotation led to the individualization of the Iberian microplate (about *110 Ma; Ribeiro 2013b). In turn, the rotation of the African Plate relative to the Eurasian Plate led to the closure of the Tethys at the end of Mesozoic by subduction of the oceanic crust (NE Africa/Arabia region). The compression between the African Plate (mainly in the northwest sector—Nubian Plate) and the Eurasian Plate became dominant. This compression (N–S) started in the Late Cretaceous and reactivated a deep fault

10

zone that extends from the submarine Tore Seamount (300 km west of Peniche) to the Gulf of Cadiz (Ribeiro 2013b). The fault acted as a dextral strike-slip, where magma ascended in zones of decompression (Kullberg et al. 2013), leading to the intrusion of the magmatic massifs of Monchique, Sines and Sintra by 74–72 Ma ago (Figs. 1.2 and 1.3). Almost contemporary is the volcanic complex of Lisbon (basalts and pyroclasts) and other volcanic occurrences that also affected the Algarve Basin. The drastic tectonic change from predominantly extensional to compressional at the beginning of the Late Cretaceous resulted from the “rotation of the displacement vector of the trajectory of Africa relatively to Eurasia, from approximately NW-SE to SW-NE, according to the present coordinates” (Dewey et al. 1989, in Terrinha et al. 2013: 30). The Cenozoic was thus characterized by widespread compression in Iberia.

1.2.3 The Cenozoic Evolution During the Cenozoic Era (65–0 Ma), the paleogeographic and geomorphological evolution of Portugal was mainly marked by the following factors: (i) compressive tectonic phases due to convergence between the Eurasian and African plates that affected the Iberian microplate, located between them, (ii) climate changes between the Tertiary and the Quaternary, with important consequences on the morphogenesis, and (iii) continuation of the opening of the Atlantic Ocean with the emersion of the Madeira and Azores archipelagos (see Sects. 1.3.11 and 1.3.12). In mainland Portugal, there are no significant mountain ranges (interplate), as the territory was far from intense tectonic inversion that occurred during the Alpine orogeny (Cantabrian–Pyrenean chain in northern Iberia and Betic Chain, in the south; Fig. 1.5). Hence, it has only experienced long-distance effects of the Alpine compression (Ribeiro 2013b). From a geomorphological point of view, the Cenozoic evolution of mainland Portugal was marked by the appearance of a third morphostructural unit—the Lower Tagus and Alvalade Sedimentary Basins and by the regional differentiation of the main relief units (or regional geomorphological units; see Sect. 1.3). Today, the Lower Tagus and Alvalade Sedimentary Basins (also called the Tagus and Sado Sedimentary Basins) show a general NE–SW trend, occupying 15% of the territory (Fig. 1.2). The Lower Tagus Basin is about 150 km long and has an average width of 75 km, with the maximum sediment thickness reaching 1400 m in the Setúbal Peninsula. The Alvalade Basin is about 75 km long and 35 km wide, and the maximum sediment thickness is less than 500 m (Ferreira 2005). The two basins formed in the Paleogene and were separated by the Valverde-Senhor das

C. Ramos and A. Ramos-Pereira

Chagas Horst (cut into Paleozoic rocks) until the Late Pleistocene. It was then that the Sado River that drains the Alvalade Basin crossed the horst and entered the Lower Tagus Basin (Pais et al. 2013). The Cenozoic sedimentary formations of the basins, spanning the period from the Middle Eocene to the Upper Pliocene, are mostly continental detrital (gravels, sandstones and lutites), with lacustrine limestones of the Upper Miocene in the Santarém region. In the Miocene and Pliocene, there were several marine transgressions in the downstream sector of the Tagus Basin and in the Alvalade Basin at the end of Late Miocene (Pais et al. 2013), leading to the deposition of lutites, sandy lutites and marine biocalcarenites. The detrital infilling phases ended with coarse material spills that make up the bulk of the basins’ infill, generating the so-called culminating surfaces. In the beginning of the Cenozoic, Iberia moved together with Africa (Ribeiro 2013b), being separated from Eurasia by the Cantabrian and Pyrenean margin. The convergence between Africa/Iberia and Eurasia trended NNE–SSW, leading to the subduction of the Tethys oceanic lithosphere near that margin. The secondary traction in the interior of the Iberian microplate generated strike-slip basins which followed this trend, among which the Tagus and Sado Basins (Fig. 1.2) between Messejana and Lower Tagus Valley Faults stand out due to their dimensions (Ribeiro et al. 1979; Ribeiro 2013b). During the Eocene/Oligocene, continental collision occurred, with the formation of the Cantabrian– Pyrenean mountain chain in northeast Iberia (Fernández-Lozano et al. 2011). As a consequence, from the Late Oligocene on, Iberia began to enclose the Eurasian plate and to converge, in the south, with Africa (Nubian sub-plate) along the Azores–Gibraltar boundary (Ribeiro 2013b; Figs. 1.5B and 1.6). The Pyrenean compressive orogenic wave had repercussions mainly in the north and the centre of Portugal, with its effects decreasing southwards. During the Paleogene until the beginning of the Late Miocene, the Iberian Massif experienced the effects of continued compressive tectonics (emphasizing the Pyrenean phase) under climatic conditions favouring erosion. During the Paleogene, the climate in Iberia became progressively less humid, partly due to the closing of the Tethys (Jiménez-Moreno et al. 2009), evolving to subtropical, with a long dry season, and hot semi-arid. These conditions favoured planation, with the formation of a Paleogene erosion surface and transport of feldspar sands to the basins (Pais et al. 2012, 2013). During the Miocene (Fig. 1.5B), an important change of the convergence vector between Eurasia/Iberia and Africa took place, rotating from NNW–SSE to NW–SE (Ribeiro 2013b; Pais et al. 2012, 2013). It was during that period (Late Miocene) that the maximum compression was reached in Portugal, corresponding to the Betic tectonic phase. The main fault systems that were reactivated resulted in: (i) NE– SW to ENE–WSW thrusts, (ii) NNE–SSW left-lateral

1

Landscapes of Portugal: Paleogeographic Evolution …

11

Fig. 1.6 Geotectonic setting of mainland Portugal and the Azores and Madeira archipelagos. 1 Relative movement of the tectonic plates, 2 plate boundary faults (known location), 3 plate boundary faults (approximate location), 4 diffuse plate boundaries (continental

collision). Gb Gibraltar, HF Horseshoe Fault, MPF Marquês de Pombal Fault. Seamounts AS Ampére, CPS Coral Patch Seamount, GB. Gorringe Bank, SS Seine, TS Tore, TAP Tagus Abyssal Plain

strike-slip faults and (iii) NW–SE right-lateral strike-slip faults (Pais et al. 2012). In Iberia, the Betic Mountain Range formed (Fig. 1.6), and in Portugal, there was the uplift of important mountains, with the main examples being the mountains of the northwest and the central massif belonging to the Central Iberia Cordillera (Figs. 1.6 and 1.7), uplifted in a pop-up structure (Ribeiro 2013b). The intraplate Central Iberia Cordillera was affected by the interferences of the induced compressions in the north of Iberia during the Paleogene and in the south during the Miocene (Ribeiro 2013b). The tectonic inversion of the Lusitanian Basin (that had been going on since the Late Cretaceous) was accentuated during the Miocene, reactivating various structures such as the Nazaré and Arrife–Montejunto Faults, delimiting in the NW and SE an uplifted tectonic compartment (Fig. 1.7), which is an extension of the central massif pop-up structure. The inversion of the Lusitanian Basin transformed the Lower Tagus Basin into a foreland basin in contact with the basement (Ribeiro 2002). This process led to an increased subsidence of the Lower Tagus Basin, expressed by a thick Miocene sedimentation (most of the infilling of the basin), with the occurrence of several sedimentary cycles. During the Middle and Late Miocene, there was an important climatic change in Iberia, with cooling, but mainly with a series of arid phases that intensified to the end of the Miocene (Jiménez-Moreno et al. 2009). In the Pliocene

(3.4 Ma), a Mediterranean-type subtropical climate was established, with summer drought (Jiménez-Moreno et al. 2009). In the Late Pliocene and the beginning of the Pleistocene, various events of climatic and tectonic nature will be crucial for the definition of the geomorphological contrasts of the Portuguese territory. From these, the following stand out: the occurrence of a wet period in the Late Pliocene—the Piacenzian (Pais et al. 2013), the submergence of the coastal zone—Piacenzian transgression (Ferreira 2005), the Ibero-Manchega compressive tectonic phase with important vertical movements in the Late Pliocene to the onset of the Pleistocene (Pais et al. 2013) and the last pre-Quaternary erosional phase extending to the beginning of the Lower Pleistocene, due to a drier and, in the Gelasian, cooler climate. As a result of intensification of the tectonic uplift and greater availability of water in the Piacenzian wet period, there were several fluvial captures. In particular, the Tagus and Douro River systems evolved, extending into and capturing the former interior drainage systems of Iberia, giving rise to major exorheic river basins open to the Atlantic Ocean. After that, a more arid phase, but with concentrated heavy rains, during the Plio-Pleistocene transition, was associated with torrential run-off, with the resultant debris flow deposits with dominant quartz clasts and quartzite (many supplied by

12

Fig. 1.7 Relief of mainland Portugal and active faults. 1 Active fault, 2 geological lineaments which may correspond to an active fault (from Cabral 1993, 2012 and Silva et al. 2008). Faults AF Arrife, MF Montejunto, SF Sobreira Formosa–Grade–Sobral do Campo, SQF S. Marcos–Quarteira. Regional geomorphological units: A mountains of the northwest, B central-northern plateaux, C Northern Meseta, D mountains of the central massif, E Southern Meseta (E1 Castelo Branco planation surface, E2 Alto Alentejo planation surface, E3 Baixo Alentejo planation surface), F south and southwest low mountains, G small mountains, hills and interior plateaux of the Lusitanian Basin, H low mountains, inland plateaux and depressions of the Algarve Basin, I plateaux and plains of the Lower Tagus and Alvalade Basin, and J Littoral Platform

the quartzite ridges of the Iberian Massif) in a clayey matrix, forming the so-called Rañas and correlative deposits (Martín-Serrano 1988). This phase led to the establishment of the Villafranchian planation surface in areas undergoing erosion (Ferreira 2005) and to the last pre-Quaternary infilling phase of the sedimentary basins, which constitutes the bulk of their current interfluves. Climate variations observed in mainland Portugal during the Cenozoic were favourable to

C. Ramos and A. Ramos-Pereira

pediplanation. These were responsible for individualization of inselbergs (especially in granitic areas), which stand out within planation surfaces in the drier interior of the country, where tectonic movements were less intense. In these areas, vast polygenic surfaces developed, which were consecutively retouched during the subsequent erosive phases (Ferreira 1996). In regions where vertical tectonic movements were more intense and where different tectonic compartments were defined, the erosive phases were imprinted in the relief by stepped planation surfaces at various altitudes. In the Quaternary, the combined effect of continued regional tectonic uplift and climate changes, associated with the alternation of glacial and interglacial periods, led to profound changes in the mountains, in the valleys and on the coast. A progressive degradation of Tertiary planation surfaces occurred, with the incision of the fluvial systems, promoted by tectonic uplift and by periods of lower sea levels. Quaternary fluvial terraces and raised beaches provide the evidence of this geomorphological dynamics. The Littoral Platform present along the Portuguese coast, which is a polygenic surface due to continental and marine erosion in the Piacenzian, was also submitted to differential effects of regional tectonics that deformed it. This tectonic differentiation allowed for local marine transgressions in subsided tectonic compartments during the Early Pleistocene (probably Calabrian). The current geotectonic framework of Portugal (2.6 Ma to present) is thus defined as follows (Cabral 2012: 72): “The Eurasia-Nubia plate boundary is clearly discernible at the western and central parts of the Azores–Gibraltar fracture zone, represented by the Terceira Ridge leaky transform, near the Azores archipelago, and by the Gloria transform fault, eastwards up to the Tore Madeira Rise (*20° W). East of the Gloria fault, the plate boundary is poorly established and its nature is matter of debate, as the interplate deformation is apparently distributed across a broad area, over 200 km wide” (Fig. 1.6). The tension trajectories in Iberia are different in space and time. Thus, in the interior of Iberia, maximum compression is NNW–SSE, gradually turning to WNW–ESE in the west and southwest margins. Ribeiro (2013b: 18) states that “the satellite geodesy data show that the current movement of Iberia relative to Nubia is directed nearly E–W; it is therefore distinct from the movement given by the kinematic model NUVEL 1A, based on the circa 3 Ma magnetic anomaly 2A, which was NW-SE”. The research carried out by several authors in the Portuguese South Atlantic and SW continental margin, south of the Algarve and west of the Alentejo, reported by Cabral (2012) and Ribeiro (2013b), using neotectonic, seismotectonic and morphotectonic data, provides strong evidence that the Atlantic continental margin of mainland Portugal is in transition from a passive margin to an active margin. In the submerged area, seismic tomography allows to follow a

1

Landscapes of Portugal: Paleogeographic Evolution …

subduction zone down to about 100 km deep below the Marquês de Pombal—Horseshoe active thrust fault system (Fig. 1.6), with a rupture and displacement area capable of generating high-magnitude earthquakes, such as the Lisbon Earthquake of 1755. Hence, in the W and SW of the Algarve, the subduction process of the Atlantic Ocean floor beneath Iberia (the Marquês de Pombal Fault System) and of Africa over the Atlantic in the Horseshoe Fault System (Ribeiro 2013b) will have started. “According to this model, Iberia is behaving as a microplate that is rotating clockwise between Africa and Eurasia, inducing convergence across the west Iberia margin at *1 mm/year” (Cabral 2012: 72).

13

In general, it can be stated that in mainland Portugal the areas of low altitude prevail, since over 70% of the territory is below 400 m and less than 12% is above 700 m. Another important aspect is the elevation asymmetry between the north and the south (Fig. 1.7). The area north of the Tagus River comprises 95% of the areas above 400 m, while the area south of the Tagus shows 62% of the lowlands below 200 m. In the north, most of the mountains show altitudes above 1000 m, but in the south only one, the Serra de São Mamede, reaches this altitude.

1.3.1 Mountains of the Northwest

1.3

The Regional Geomorphological Units of Portugal

The major morphostructural units of Portugal define the main contrasts relating to lithological assemblies and their geological structure, but they do not reflect the relief differences at the regional scale. These depend mainly on the combination of: (i) the different regional impacts of the Cenozoic tectonics, (ii) the regional asymmetries of climate in the Tertiary and Quaternary, and (iii) the response of the different regional lithostructural characteristics to the internal and external Cenozoic geodynamics that affected the territory. Thus, for the analysis of the geomorphological landscapes of Portugal, the first-order morphostructural units are subdivided into large regional relief units or regional geomorphological units (Table 1.1). The main features of these units are summarized for mainland Portugal (with a brief mention to the Azores and Madeira archipelagos).

The region occupied by the mountains of the northwest develops mainly on granitic rocks and is triangular in shape, due to its control by two large tectonic zones: the NNW– SSE to N–S Porto–Tomar Fault in the southwest and the NNE–SSW Verín–Penacova Fault in the east (Fig. 1.7). The relief is intensely fragmented by tectonic compartments, and horst and graben structures stand out. The mountains of the northwest contact in the west with the Littoral Platform and in the east with the central-northern plateaux. The mountains of the northwest show altitudes between 1000 and 1600 m and are composed of the following mountain massifs (Figs. 1.3 and 1.7): (i) Peneda (1416 m), Amarela (1362 m), Gerês (1545 m), Larouco (1535 m), Barroso (1279 m), Cabreira (1262 m), Alvão (1283 m) and Marão (1415 m) north of the River Douro, and (ii) Montemuro (1382 m), Freita (1085 m), Arada (1071 m) and Caramulo (1076 m) south of the River Douro. South of the River Douro, the mountains were uplifted along the Verín–Penacova Fault that borders them to the

Table 1.1 Classification of the regional geomorphological units of Portugal Morphostructural units (at the global scale)

Morphostructural units of Portugal

Regional geomorphological units of Portugal

Platforms

Iberian Massif or Hercynian Massif

Mountains of the northwest Central-northern plateaux Northern Meseta Mountains of the central massif Southern Meseta South and southwest low mountains

Sedimentary basins

Oceanic mountain ranges

Lusitanian and Algarve Meso-Cenozoic Basins (slightly deformed)

Low mountains, hills and inland plateaux of the Lusitanian Basin

Lower Tagus and Alvalade Cenozoic Basins

Plateaux and plains of the Lower Tagus and Alvalade Basin

Mountain ranges (summits of volcanic submarine ranges)

Archipelago of Madeira

Low mountains, inland plateaux and depressions of the Algarve Basin

Archipelago of Azores

Littoral Platform

14

east, and tilted to the NW (Montemuro) and to the W (Caramulo). North of the River Douro, the relief resembles a grid of compartments individualized by an orthogonal network of fractures, which feature two main directions: ENE– WSW, seized by major rivers (Minho, Lima and Cávado), and N–S to NW–SE, seized by their tributaries or smaller rivers (Figs. 1.3 and 1.7). These relief compartments elevate from the coast inland, inducing the successive rising of Atlantic moist air masses and their progressive destabilization. This orographic effect is reflected in the regional climate, giving the mountains of the northwest a hydroclimatic specificity unique in mainland Portugal, being the region with more rain and more rainy days. The average annual rainfall is larger than 1200 mm, and on the summit of the highest mountains it exceeds 3000 mm. The abundance of water and the entrenchment of the hydrographic network cause intense dissection of the relief. The short dry summer season (1–2 months) combines the edaphic humidity at the base of the slopes (and in valley floors) with high temperatures, leading to chemical weathering of the base of the granitic slopes, which induces their parallel retreat, maintaining steep profiles (Ferreira 2005). The main valleys are thus wide with flat bottoms and steep slopes. Even though dendritic drainage patterns dominate, fracturing of granitic bedrock defines fracture valleys along lineaments, with parallel to rectangular drainage patterns (Fig. 1.8). The valleys consist of alternating narrow and wide sections due to phenomena of differential erosion between various types of granitoid rocks or between these and Paleozoic metasediments. Some cross almost closed

Fig. 1.8 Typical landscape of the NW mountains: tectonic compartments and dominant granite landforms. The dotted white line represents fracture lineaments, sometimes seized by rivers (fracture

C. Ramos and A. Ramos-Pereira

depressions (alveoli) due to chemical weathering and differential erosion processes within the granites.

1.3.2 Central-Northern Plateaux The central-northern plateaux are comprised between two major NNE–SSW tectonic lines: the sinistral strike-slip faults of Verín–Penacova in the west and Bragança–Manteigas Zone in the east (Fig. 1.7). These are Late Variscan strike-slip faults reactivated during the Neogene and Quaternary, leading to vertical displacements of hundreds of metres. Along these lineaments, tectonic depressions have developed. The central-north plateaux correspond to planation surfaces with dissimilar development and different altitudes, the so-called stepped surfaces and the polygenic surfaces. The stepped surfaces (also found in the mountains of the northwest, although with less morphologic expression) prevail and have been formed due to planation phases and periods of increased tectonic dynamics that shifted them vertically between the Late Cretaceous and the Plio-Quaternary (Ferreira 1978; Ribeiro 2004). The stepped surfaces are: (i). the culmination surface, between 900 and 1200 m asl, (ii) the fundamental surface (more extensive) between 800 and 900 m asl, and (iii). one or two lower levels (depending on the area) between 500 and 700 m asl. The preservation of these landforms depends not only on the density of fractures (if they are denser, the planation levels are reduced to narrow interfluves, Fig. 1.9), but also on mineralogy, particularly within granites. In turn, the

valleys). Photograph credits Duarte Fernandes Pinto, A Terceira Dimensão, http://portugalfotografiaaerea.blogspot.com

1

Landscapes of Portugal: Paleogeographic Evolution …

15

Fig. 1.9 Central-northern plateaux with flat surfaces on interfluves at different altitudes. In the foreground, one of the lower levels, tilted towards the River Douro, is dash marked. Photograph credits Duarte Fernandes Pinto, A Terceira Dimensão, http://portugalfotografiaaerea.blogspot.com

lower levels are well developed in soft rocks, such as shales and greywackes, especially along the valleys of the Douro and its main tributaries. In the extreme south of the central-north plateaux, a polygenic surface developed—the Mondego Platform— showing that the legacy of tectonic deformations was successively obscured by various erosive phases that retouched them, keeping the general profile of the planation surface. The Mondego Platform is a low area that separates the mountains of the northwest from the mountains of the central massif (Fig. 1.3), with its limits bounded by major active fault zones: Verín–Penacova to the northwest and Seia– Lousã to the southeast (Fig. 1.7). To the north, on the contrary, it contacts with the stepped surfaces of the plateaux through an erosive margin and, like the fundamental surface, is tilted towards SSW. In the central-northern plateaux, it is still to be noted: (i) the large number of fracture-controlled valleys, whose direction follows, in general, the course of tectonic lines that border them (Verín–Penacova and Bragança–Manteigas) and (ii) the area occupied by the Mirandela depression, a half-graben situated at an altitude of 400– 450 m asl, north of the Douro River (Fig. 1.3).

1.3.3 Northern Meseta Mainly eastwards of the Bragança–Manteigas Fault, and partly in continuity with the fundamental surface of the central-northern plateaux, a polygenic surface named the

Northern Meseta occurs (Fig. 1.7). It is at an average altitude of 800 m, but is far from being horizontal, as north of the River Douro it is tilted to SSW (between 1000 and 700 m asl), to the south of this river and to NNW (between 1000 and 400 m asl). In Portugal, the Northern Meseta is an erosional surface, which truncates different types of bedrock (granites, granodiorites, shales, greywackes, pelitic hornfels, schist– migmatite complexes), but in Spain, where it reaches its greatest extent, it connects to the River Douro Sedimentary Basin, being in geomorphological continuity with the Castilla la Vieja Plateau. Ferreira (1978) and Pereira (1997, 1999) showed that the surface of the Northern Meseta developed during the Neogene and the Early Quaternary through various erosional events, due to an endorheic drainage directed to the sedimentary basin of the River Douro (Castilla la Vieja). Subsequently, the endorheic drainage of the upper Douro was captured by the lower Douro, east of the Bragança–Manteigas Fault Zone, about 2.4–1.6 million years ago (Ribeiro 2004 and Ferreira 2005). This capture, responsible for the exoreic drainage towards the Atlantic Ocean, is witnessed in the international sector of the Douro River valley, which divides Portugal and Spain, by the incision of the river in a gorge, which deeply cuts the Meseta (Fig. 1.10). The Northern Meseta is particularly well preserved near the Spanish border, east of the rivers Sabor and Côa (northern and southern tributaries of the River Douro, respectively; Fig. 1.3). West of these rivers, the Northern Meseta is less well preserved due to the increased fluvial dissection and, especially, to the Cenozoic tectonics that

16

C. Ramos and A. Ramos-Pereira

Fig. 1.10 Northern Meseta in the border area between Portugal and Spain (International Douro–Aldeadávila Dam). The incision of the River Douro into the Northern Meseta, due to the capture of the former

endorheic drainage of the upper Douro, is visible. Photograph credits Duarte Fernandes Pinto, A Terceira Dimensão, http:// portugalfotografiaaerea.blogspot.com

affected it along the Bragança-Manteigas Fault. In the area of the Northern Meseta, interrupting its general flatness, there occur some hills, which are according to Ribeiro (2004): (i) circum-denudation remnants (Coroa and Montesinho mountains; Fig. 1.3), (ii) lithology-controlled, reflecting elevated resistance of quartzite ridges and mafic and ultra-mafic rock, and (iii) half-horsts (Nogueira and Bornes mountains). The negative landforms within the Northern Meseta follow the Bragança–Manteigas strike-slip fault, along which several tectonic depressions are aligned (Bragança, Macedo de Cavaleiros, Vilariça and Longroiva) that mark a deep linear trough in the landscape (Figs. 1.3 and 1.7).

arranged in steps, along which is the passage of the mountains of the central massif to the Southern Meseta. In a regional context, the Sobreira Formosa–Grade–Sobral do Campo fault (Fig. 1.7) “is the recognized structure that more strictly defines the southern boundary of the reliefs of the Central Cordillera” (Cabral 1993: 200). The mountains of the central massif are essentially composed of two compartments: (i) the NW compartment, which is higher, between 1200 and 2000 m altitude, of which the Serra da Estrela (1993 m; Fig. 1.11), Açor (1418 m) and Lousã (1205 m) are part of, and (ii) the SE compartment, which is lower, between 1000 and 1200 m, comprising the mountains of Gardunha (1227 m) and Alvelos (1084 m). Between the two lies an intra-mountain depression, interpreted as a narrow graben drained by the River Zêzere (Ferreira 2005; Figs. 1.3 and 1.7). Although this mountainous alignment consists of tectonic compartments, fragmented into blocks tilted in different directions, the lithological composition imprints specific features to the relief. The dominant rocks are granitoids and pre-Mesozoic metasediments, interspersed by narrow outcrops of quartzite. In the granites, the old planation surfaces are better preserved, as is the case of the Torre plateau, the highest point of the Serra da Estrela mountains. In shale rocks, strong dissection of relief dominates, and the valleys have a sinuous profile, as in the mountains of Açor and Lousã. Quartzites support elongated ridges, according to the Variscan structures (NW–SE), perpendicular to the general alignment of the mountains of the central massif, as in the Moradal mountains (Muradal, Fig. 1.3).

1.3.4 Mountains of the Central Massif The mountains of the central massif in Portugal, also referred to by some authors as the Central Cordillera (Daveau 2004), form an alignment of tectonic origin and are part of the Iberian Central System. Its uplift, with significant episodes at the end of the Miocene, separated the Iberian Meseta into two distinct geomorphological units: the Northern Meseta and the Southern Meseta. In Portugal, the mountains of the central massif follow a general NE–SW direction (Fig. 1.7), being bounded in the NW by the Seia–Lousã Fault and in the SE “by a complex geometry fault set, although generally subparallel, with a mean NE-SW to ENE-WSW direction, with important sinuosities and submeridian ramifications” (Cabral 1993: 199). These faults define a set of levels

1

Landscapes of Portugal: Paleogeographic Evolution …

17

Fig. 1.11 Estrela mountain in the Loriga area (western slope), a valley where a small glacier flowed down to about 800 m asl in the Last Glacial Maximum. Photograph credits Duarte Fernandes Pinto, A Terceira Dimensão, http://portugalfotografiaaerea.blogspot.com

It should also be noted that in Serra da Estrela—the highest mountain of mainland Portugal (Fig. 1.11)—geomorphological remnants of the last Quaternary glaciation were found for the first time in the nineteenth century. Of these, the Zêzere glacial valley stands out, where the valley glacier reached a length of 11 km and attained a thickness of 300 m at maximum glaciation (Vieira 2008). Subsequently, landforms and glacial deposits have also been recognized in the highest parts of the mountains of the northwest, in both Peneda and Gerês.

1.3.5 Southern Meseta The Southern Meseta is a Cenozoic extensive polygenic planation surface that cuts the bedrock consisting mainly of metasediments, secondarily of granitoids and sporadically of mafic rocks (Pereira et al. 2014). The Southern Meseta extends southeast of the mountains of the central massif towards the south and southwest low mountains, confining to the west with the Lower Tagus and Alvalade Sedimentary Basins. To the east, it continues in Spain, where it reaches its widest dimension. The Southern Meseta is much lower than the Northern Meseta as it develops between 200 and 400 m asl. At a regional scale, its continuity is disrupted by two active faults, the Pônsul and the Vidigueira, which divide it into three

compartments, decreasing in altitude from north to south (Fig. 1.6): (i) the Castelo Branco surface, at an altitude of 400–450 m asl, (ii) the Alto (high) Alentejo surface, about 250–350 m asl, and (iii) the Baixo (low) Alentejo surface, about 200–250 m asl (Fig. 1.2). The Pônsul Fault is a Late Variscan structure, with a NE– SW direction, whose reactivation in the Plio-Quaternary produced a fault-generated escarpment (Cabral 1993), southeast of which Cenozoic deposits lying discordantly over the Hercynian Massif are preserved. The E–W to WNW–ESE direction Vidigueira Fault is also a Variscan structure, whose Cenozoic history involved several phases which occurred between the Early or Middle Miocene and the Early Quaternary (Silveira 1990 in Ferreira 2005). Its reactivation caused an escarpment, which in addition to separating the Alto Alentejo surface from the Baixo Alentejo surface limits, in one of its sections, the southern slopes of the Portel Horst (Fig. 1.7), one of the tectonic landforms that rise above the Southern Meseta. The Southern Meseta is differently preserved, depending on the type of rock, the faults that cross it and the Quaternary incision of the river systems. The planation is almost perfect (Fig. 1.12), as within the Castelo Branco surface, Alto Alentejo surface, south of the Tagus River (Nisa area), south of Évora and Baixo Alentejo surface, in the Beja area. However, in the areas dominated by shales and drained by the Guadiana River and its main tributaries, the polygenic

18

C. Ramos and A. Ramos-Pereira

Fig. 1.12 Southern Meseta with the polygenic planation surface of Alto Alentejo. Photograph credits Duarte Fernandes Pinto, A Terceira Dimensão, http://portugalfotografiaaerea.blogspot.com

surface is heavily dissected and lowered. North of Évora, the Southern Meseta is also fragmented by multiple faults, locally with altitude differences of only tens of metres, but in some places reaching hundreds of metres (Ferreira 2005). The flatness of the Southern Meseta is thus interrupted by elevations of tectonic origin, among which the São Mamede mountain stands out (Fig. 1.3). São Mamede is the highest mountain in the south of Portugal (1027 m), formed by granites and shales, intercalated with quartzites that support the highest peaks. The residual hills due to rock resistance, which also interrupt the polygenic planation surface, are essentially quartzite ridges, which constitute the most important and most frequent residual relief rising from the planation surfaces in Portugal (Ferreira 2005). The quartzite ridges may be several tens of kilometres long and can reach a few hundred metres high. Quartzites were subjected to Variscan folding, showing therefore a NW–SE to W–E orientation. Sometimes, they appear as double ridges, corresponding to the flanks of hanging synclines (Fig. 1.12). In Alentejo, residual hilly relief also occurs due to intercalations of marble and dolomitic limestones. Finally, in the granitic areas of the Castelo Branco surface a unique geomorphological landscape in Portugal is found, dominated by inselbergs (Fig. 1.13). These hills rise a few hundred metres above the planation surface and were inherited from the dominant climatic conditions in the Cenozoic, whereas the dryness of the region contributed to their persistence to the present day.

1.3.6 South and Southwest Low Mountains At a regional scale, the low mountains of the south and southwest show a L-shape arrangement, in two main directions: north–south (Grândola, 326 m, and Cercal, 378 m) and west–east, transverse to the former (Monchique, 902 m, and Caldeirão, 589 m; Fig. 1.3). The Serra do Caldeirão separates the Southern Meseta and the Algarve Sedimentary Basin, while the Serras de Grândola and Cercal are located between the Alvalade Sedimentary Basin and the Littoral Platform (Figs. 1.3 and 1.7). Also, part of the south and southwest low mountains is Mesquita (517 m), a NW–SE quartzite ridge, located north of Monchique mountain, and Vigia (393 m), which seems to extend to the NW the Caldeirão mountains, being separated from it by the incision of the River Mira (Fig. 1.3). Even though they constitute high relief in relation to the surrounding areas, these low mountains show different geneses and ages. The mountains of Grândola, Vigia and Caldeirão are carved in the formations of the Baixo Alentejo Flysch Group (turbidites, greywackes and pelites). The Cercal mountain, in addition to the Flysch Group, also consists of more resistant volcanic–siliceous complexes. The Monchique mountain is composed of a core of igneous rocks (mostly nepheline syenite, dated for the Upper Cretaceous), by a contact metamorphism zone and the surrounding shales. The Monchique mountain is an impressive relief that stands out in the extreme southwest of the Portuguese

1

Landscapes of Portugal: Paleogeographic Evolution …

19

Fig. 1.13 Castelo Branco polygenic planation surface at the Southern Meseta interrupted by residual relief: (i) the Penha Garcia double quartzite ridge (within which springs the River Pônsul) and (ii) the Monsanto and Moreirinha inselbergs. The mountains of the central

massif are visible in the background. Photograph credits Duarte Fernandes Pinto, A Terceira Dimensão, http://portugalfotografiaaerea. blogspot.com

territory, causing, by its orographic effect, annual rainfall exceeding 1000 mm, well above 400–700 mm recorded in the Algarve. The moisture and freshness of the mountain, along with the type of substrate, form “a world apart” in the Algarve context. The igneous rocks and those belonging to the metamorphic aureole, more resistant to erosion, emphasize the mountain which rise above the vast plateau carved in shales, themselves considerably dissected by fluvial incision (Fig. 1.14). However, there is evidence that this relief has been raised by several tectonic pulses, at least since the Miocene (Feio 1952; Terrinha et al. 2013). The Caldeirão mountain represents the southern swell of the Baixo Alentejo surface and is separated from the Monchique mountain by the São Marcos–Quarteira depression, which develops along the active strike-slip fault of the same name (Fig. 1.7). This deformation of general W–E direction began in the Neogene. It is set according to an asymmetrical dome, whose southern flank is steeper than the northern one and where several fault and fold escarpments are recognized. The Grândola and Cercal mountains lie below 400 m asl, perhaps due to their youth, since the beginning of uplift is assigned to the Late Pliocene (Cabral 1993). They rise in parallel to the Alentejo coast along a meridian fault (Fig. 1.7), responsible for the escarpment that forms the

western slope of these mountains and separates them from the Littoral Platform (Fig. 1.15). The Grândola mountain is also bound by the WNW–ESE Grândola Fault in the north. Vertical displacement along this fault created another impressive escarpment that separates this minor elevation from the Alvalade Sedimentary Basin. These low mountains are interpreted as half-horsts tilted to the east and ESE.

1.3.7 Low Mountains, Hills and Inland Plateaux of the Lusitanian Basin At a regional scale, a simple view of the relief map of Portugal shows that the alignments of higher ground belonging to the mountains of the Central Iberian Massif, as well as to the extreme south of the mountains of the northwest, seem to extend into the Lusitanian Basin (Fig. 1.7). Kullberg et al. (2013) showed the existence of a tectonic compartment, with a NE–SW direction, bounded by the Nazaré (NW) and by the Arrife and Montejunto (SE) faults, responsible for its uplift in the Cenozoic. This compartment coincides roughly with the geomorphological unit of low mountains, hills and inland plateaux of the Lusitanian Basin.

20

C. Ramos and A. Ramos-Pereira

Monchique Mountain Iberian Massif

Algarve Basin

Silves

Fig. 1.14 Contact between the Iberian Massif and the Algarve Sedimentary Basin in the Silves area. In the background, the Serra de Monchique stands out, rising from a planation surface cut in shales and highly dissected by fluvial erosion (gipfelflur). In the foreground,

the peripheral depression, incised in the Silves sandstones of the Algarve Basin. Photograph credits Duarte Fernandes Pinto, A Terceira Dimensão, http://portugalfotografiaaerea.blogspot.com

Fig. 1.15 Cercal mountain and its western fault scarp, overlooking the Littoral Platform, southwest of Vila Nova de Milfontes (Alentejo). Photograph credits: Duarte Fernandes Pinto, A Terceira Dimensão, http://portugalfotografiaaerea.blogspot.com

1

Landscapes of Portugal: Paleogeographic Evolution …

21

Fig. 1.16 Lusitanian Basin southwest of Nazaré with the low mountain ranges and hilly relief, as well as the Littoral Platform interrupted by the diapiric depression of Caldas da Rainha. Photograph

credits Duarte Fernandes Pinto, A Terceira Dimensão, http:// portugalfotografiaaerea.blogspot.com

Thus, this unit is bounded: (i) by the Littoral Platform on the ocean side (NW, W and S), (ii) by the Porto–Tomar Fault that separates them from mountains and plateaux of the Iberian Massif, in the east, (iii) by Arrife and Montejunto faults, responsible for its thrust over the Lower Tagus Sedimentary Basin in the southeast (Fig. 1.7). Still belonging to this unit, although separated by the Littoral Platform, there are two low mountain ranges that rise above the platform (Boa Viagem, north of the Mondego River, and Arrábida, south of the Tagus River) and the diapiric depression of Caldas da Rainha that interrupts the Littoral Platform (Figs. 1.3 and 1.16). The region of low mountains, hills and inland plateaux of the Lusitanian Basin is the most difficult to summarize in respect of their main geomorphological characteristics. This is due to the combination of several factors: (i) lithological diversity (dolomites, limestones, marls, evaporitic complexes, sandy and clayey detrital formations and igneous rocks), (ii) considerable lateral variation of facies, (iii) different directions of active faults and (iv) combination of regional tectonics with salt tectonics, the latter induced by the presence of the evaporitic complex (Lower Jurassic) at the base of the sedimentary infilling of the basin. This may have caused the “detachment” of the basement in relation to the sedimentary cover, favouring the origin of deformed structures, regardless of the movements of the basement. The interconnection of all these factors is responsible for the origin of the complicated pattern of low mountains, hills, plateaux and depressions. Structural forms that develop in monoclines, and folded and faulted structures prevail. The

low mountains that stand out most in the landscape have altitudes between 500 and 680 m asl, except for the one north of the Nazaré Fault. From north to south, there are limestone mountains of Boa Viagem (262 m), Sicó (553 m), Alvaiázere (618 m), Candeeiros (610 m; Fig. 1.16), Aire (679 m), Montejunto (666 m) and Arrábida (501 m) (Fig. 1.3). Their cores consist of Jurassic limestones in an anticline folds or semi-folds, bounded by faults (sometimes thrusts) on one or both flanks. The only non-calcareous low mountain massif is Sintra, culminating at 529 m (WNW of Lisbon; Fig. 1.3). It is a subvolcanic massif whose rocks (granite, syenite and gabbro) date from the Upper Cretaceous (correlative of Monchique). The discontinuous mountainous alignment of Sintra– Montejunto–Candeeiros–Estrela (Figs. 1.3 and 1.7) constitutes one of the most important climatic limits in Portugal. To the north of this alignment extends the Atlantic Portugal with a more rainy and cool weather, whereas the Mediterranean Portugal, with a drier and warmer climate, is located in the south. The hilly relief is very common. The hills have developed in particular: (i) in monocline structures with alternating hard (limestone) and soft (marl and sandy clay) rocks, usually forming cuestas, for example, in the region north of Lisbon and (ii) in Mesozoic volcanic rocks, especially from the Upper Cretaceous (basalts, dolerite, volcanic breccias), often corresponding to volcanic chimneys. The most interesting depression within the entire geomorphological unit is the Caldas da Rainha, with a NNE– SSW trend and the bottom at an average altitude of 30–

22

40 m asl. It is a diapir that during the Quaternary may have functioned as a graben bounded by reverse faults (Ribeiro 1984). The rocks of the evaporitic complex outcrop in the floor of the depression and are only interrupted by isolated hills in dolerites and more resistant limestones (Fig. 1.16). Karst landforms, which present a great variety of types and sizes, are a fundamental aspect of the unit. The most spectacular ones, both at the surface and underground (caves), are located in the Estremadura Limestone Massif (NW of the Arrife Fault; Fig. 1.7).

1.3.8 Low Mountains, Inland Plateaux and Depressions of the Algarve Basin The low mountains, inland plateaux and depressions of the Algarve Basin are limited to the north by the Monchique and Caldeirão mountains of the Iberian Massif and by the Littoral Platform to the west, south and east. This small geomorphological unit is only 15 km wide at maximum (in the Albufeira meridian), extending across 95 km in W–E direction, from the meridian of Lagos to Tavira (Figs. 1.3 and 1.7). Together with the Littoral Platform, it forms the emerged Algarve Sedimentary Basin and constitutes a typical landscape unit of the Algarve interior, corresponding roughly to the so-called Barrocal. The region comprises mainly Jurassic rocks, with evaporite, volcano–sedimentary, carbonate and detrital formations. The landforms are conditioned by the same factors as mentioned in the Lusitanian Basin. The so-called peripheral depression has developed in contact with the Iberian Massif (Fig. 1.14), due to differential erosion between the Silves Sandstones (Grés de Silves) (more ductile) and Jurassic dolomites and limestones. This depression belongs to the northern sector of the unit that shows up north of the Sagres–Algoz flexure (Fig. 1.7). Tabular relief, which is not exactly structural as it has been retouched by erosion, prevails here. Plateaux alternate with depressions, the latter usually of karst or fluviokarst origin. In the southern sector of the unit, between the Sagres–Algoz and Albufeira flexures, the complexity of the sedimentary structure is higher, with folds and fold–faults with associated thrusts (Ribeiro 1984), also implying higher geomorphological complexity. “The structures that are more clearly reflected in the relief (…) are in fact anticline folds, but these, besides being affected by displacements in faults they are already well-dismantled by erosion“ (Ferreira 2005: 113). This is the case of the alignment of higher grounds that stand out in the area north of Faro, of which the low mountain massif of Monte Figo (410 m), with a W–E direction, is noteworthy (Figs. 1.3 and 1.7).

C. Ramos and A. Ramos-Pereira

1.3.9 Plateaux and Plains of the Lower Tagus and Alvalade Basins The plateaux and plains of the Lower Tagus and Alvalade Basins are a regional geomorphological unit almost coincident with the Lower Tagus and Alvalade Cenozoic Sedimentary Basins. The exception is in its terminal sector, in the area occupied by the Littoral Platform, with which it contacts (Figs. 1.2 and 1.7). The limits of this unit are quite varied: (i) the downstream sector connects imperceptibly with the Littoral Platform, which is an extension of the plains of the basin, (ii) to the east, it connects with the Southern Meseta, which extends into the sedimentary basin by the culminating surface of the plateaux; (iii) to the southeast, the contact with the Southern Meseta, on the contrary, is very clear, through an escarpment 100 m high, due to the Late Variscan Fault, reactivated in the Cenozoic—the Messejana Fault—of NE– SW direction, (iv) in the southwest sector, it contacts with the Grândola mountain massif that rose along the Grândola Fault, isolating the unit from the ocean, (v) to the northeast, it contacts with the terrains of the Lusitanian Basin which form higher ground due to either a fault (Arrife, Montejunto and Lower Tagus Valley) or a flexure (Fig. 1.7). The unit comprises extensive flat landscapes, with altitudes under 100 m asl in the Lower Tagus Basin and under 150 m asl in the Alvalade Basin. The plateaux are predominantly carved in coarse sand formations with conglomeratic and argillaceous intercalations, pre-Quaternary and Pleistocene lacustrine limestones. The structure is almost horizontal, reflected in the extensive flat interfluves. Nevertheless, in the NW border, near the contact with the Lusitanian Basin, on the Tagus right bank, the structure tilts to southeast, and a succession of monocline ridges (cuestas) occurs. The plains are at altitudes below 20 m asl and are composed of Holocene alluvium (alluvial plains), deposited during the floods of the Tagus and Sado rivers. The plains create a great contrast in the landscape with the plateaux. The plateaux, occupied by heath, pine and eucalyptus trees, have low fertility sandy soils, while the plains support an important agricultural activity, taking advantage of the great fertility of the soils, namely the Tagus alluvial plain (Fig. 1.17), thus constituting, according to Gaspar (1993) “the greatest natural heritage of Portuguese agriculture”.

1.3.10 Littoral Platform The Littoral Platform is a separate relief unit. It is a name given to the flat area adjacent to the sea, which follows the shoreline and is often covered with sediments of different facies, whose inland boundary may be sharp or transitional (Fig. 1.18). This boundary is often sharp of tectonic origin

1

Landscapes of Portugal: Paleogeographic Evolution …

23

Fig. 1.17 Plateaux and plains of the Lower Tagus. Standing out in the foreground is the Tagus alluvial plain near Valada; in the background, the plateaux. Photograph credits Duarte Fernandes Pinto, A Terceira Dimensão, http://portugalfotografiaaerea.blogspot.com

Fig. 1.18 Littoral Platform in central Portugal. Example of a wide platform and ill-defined inner rim, developed in the Lusitanian Basin rocks. Photograph credits Duarte Fernandes Pinto, A Terceira Dimensão, http://portugalfotografiaaerea.blogspot.com

24

Fig. 1.19 Characteristics of the Littoral Platform in mainland Portugal. 1 Dominant accumulation, 2 dominant erosion, 3 ill-defined limit, 4 tectonic rim. Localities A Aveiro, La Lagos, S Sintra, Sa Sagres and Si Sines

(Fig. 1.15), although locally the Littoral Platform can connect to the inland flat surfaces (Fig. 1.19). The Littoral Platform may be subdivided into two units: (i) an erosional surface, which extends from a few metres to about 200 m above sea level, and (ii) a more regular and lower surface constructed by the accumulation of sediments (Fig. 1.19). The former is the true rasa (coastal plateau), according to the terminology of Guilcher (1974), with examples in the northwest platform, around the Sintra

C. Ramos and A. Ramos-Pereira

mountain massif or along the coast of Alentejo (Fig. 1.15) and western Algarve. The latter is the false rasa (coastal plain), occurring particularly in the Aveiro region and central Algarve (Fig. 1.7). This distinction is related to the regional tectonic regime. In the uplifted areas, the Littoral Platform is more or less stepped, represented by horizontal and tilted levels that descend towards the sea, reaching 19 km in width. This form truncates rocks regardless of their resistance and structure. On the other hand, the built-up Littoral Platform can reach 38 km wide, resulting from the filling of graben-type tectonic structures, such as the Aveiro graben (Lauverjat 1982). The low altitude favours its preservation, since it is not dissected by the hydrographic network. The morphological simplicity of the platform hides its complex origin, varying from one region to another and revealed by the diversity of deposits, which can be marine, fluvial or transitional. In the northwest of Portugal, the Littoral Platform is relatively narrow (Fig. 1.20), never exceeding 6 km, from a few metres above the current sea level to about 140 m asl. Marine deposits are limited to a narrow strip along the shoreline to about 40 m asl. Inland, the deposits show fluvial facies (Ramos-Pereira 2004). The step that separates fluvial from marine deposits presents generally a meridian and rectilinear outline, and is of tectonic origin. In the Lusitanian Basin, the Littoral Platform elements are not always well preserved due to the variety of rocks present. However, it is worth mentioning the platform around the Serra de Sintra and the staircase of terraces, suggesting a number of episodes of marine reworking, probably due to regional uplift, coupled with the rise of the Sintra Massif (Ribeiro 1941; Ferreira 1984; Kullberg and Kullberg 2000). Ferreira (1984) identified a beach deposit on a 180 m level (Ulgueira), which highlights the regional uplift. Also, in the Portuguese southwest, south of Sines, the Littoral Platform occurs at different altitudes, from about 14 m in the north to 150 m in the south. It also shows a mixed genesis. It is built up by sediments in the northern part, whose thickness reaches 14 m, transforming southward into a predominantly erosive form truncating various rocks of the Iberian Massif, such as turbidites, metavolcanic rocks and quartzites (Ramos-Pereira 2004). In summary, it can be said that the Littoral Platform is polygenic, having been subjected to successive continental and marine reworking. It probably derives from an ancient Cenozoic erosion surface, subjected to tectonic movements responsible for the fragmentation of the planation surface and uplift of the marginal elevations, which limit the Littoral Platform on the inland side. The lower compartments have been reworked either by the sea or by fluvial processes, due to climatic fluctuations, eustatic variations and tectonics. The tectonic–eustatic behaviour varied regionally and cannot

1

Landscapes of Portugal: Paleogeographic Evolution …

25

Fig. 1.20 Northwestern Littoral Platform. Example of a narrow platform and well-defined inland rim, developed in the Iberian Massif rocks. Photograph credits Duarte Fernandes Pinto, A Terceira Dimensão, http://portugalfotografiaaerea.blogspot.com

therefore be extrapolated over the whole coast of Portugal. In addition, the significance of Quaternary tectonics in the deformation of the Littoral Platform is evident.

1.3.11 The Madeira Archipelago The Madeira archipelago (801 km2) lies between latitudes 30 and 33° N, 800 km southwest of mainland Portugal (Fig. 1.1). It is comprised by the island of Madeira, with 92% of the archipelago’s area (737 km2), the island of Porto Santo (42 km2) and small islands clustered into two distinct groups: the Desertas, in the SW extension of the island of Madeira, and the Selvagens Islands, further away, 280 km to the southwest, and closer to the archipelago of the Canaries (165 km away). All the islands are volcanic, but belong to different morphostructural domains and distinct volcanic provinces (Mata et al. 2013). The small Selvagens Islands are part of the Canaries volcanic province, located between the oceanic and the continental domains of the African plate. They are the oldest islands (the emerged base of the volcanic complex of the Selvagem Grande is over 20 Ma old) and have a greater variety of volcanic rocks, relative to the islands of the Madeira, Porto Santo and Desertas group, where the abundance of acid volcanics stands out. The Madeira, Porto Santo and Desertas group, which comprise the essential of the archipelago, belong to the

Madeira volcanic complex, in a clear oceanic domain. The archipelago is located in the extreme south of the intersection of two sets of elevations that rise from the ocean floor, consisting of: (i) the Madeira–Tore submarine ridge, which stretches for more than 1000 km in a NNE–SSW direction, and (ii) an alignment of seamounts, which stretches for about 700 km and begins at the Ormonde Peak (belonging to the Gorringe Bank, WSW of the Algarve), through the Ampere and Coral Patch Seamounts, Seine, to the Porto Santo and Madeira Islands (Figs. 1.1 and 1.6). The Madeira–Tore ridge, “will have initially been generated along the Mid-Atlantic Rift, by the interaction of the Canary mantle plume with the rift, which coincided spatially, at the time (lower Cretaceous)” (Mata et al. 2013: 697). On the other hand, the alignment of seamounts is a hotspot track and shows the activity of a mantle plume during the last 70 Ma. In fact, the age of the volcanic formations of these mounts reduces progressively from NE to SW: Ormonde (65– 67 Ma), Ampére and Coral Patch (31 Ma), Seine (22 Ma), Porto Santo (14 Ma) and Madeira (>5 Ma). The good correlation between the age and the distance between these formations allows for determining the speed of the African plate movement over the hotspot, which is 1.2 cm/year. The most recent volcanic activity on the island of Madeira dates to circa 6500 years ago. This hotspot is at present slightly south of the island (Ferreira 2005). The two main islands of the Madeira archipelago have distinctive geomorphological characteristics, but one

26

common feature: advanced erosion of the volcanic landforms. Madeira Island formed in three distinct phases (Mata et al. 2013): (i) the emersion phase (>5.6 to >2.5 Ma), in which volcanism has subaerial expression, with volcanic breccias, pyroclastic deposits and small intercalated lava flows being dominant, (ii) the main phase of formation (shield volcano), when the island came close to its present-day dimensions (2.5 to circa 1 Ma), with the predominance of thick lava stacks in comparison with pyroclastic deposits; at the end of this phase, with the decline in volcanic activity erosion became prevalent in morphogenesis through the intense fluvial dissection, and (iii) the final phase (25°) valley slopes, particularly along highly fractured zones that are subject to rockfalls. The residual soils associated with granite

weathering vary in thickness typically from 1 to 3 m and are susceptible to debris flows that can be initiated both by small slides or overland flow (Fig. 3.7). The mountainous slopes carved in metasediments (particularly in schists and shales) along the central and northern parts of the country are usually affected by landslides affecting shallow regolith and slope deposits. Discontinuities within schists and shales (e.g. layering, foliation and fracture

Fig. 3.7 Debris flows affecting the granitic weathering mantle in the Alforfa valley (Estrela Mountain)

54

J. L. Zêzere

planes) are explored as rupture surfaces for planar slides along moderate slopes (10–15°). When the hillslope angle is higher, the initial slip movement can evolve to rapid debris flows and mudflows that can be highly destructive. Movements of this type occurred, for example, along the Douro valley in January 2001. Landslides within the western and southern Meso-Cenozoic Borderlands are mainly controlled by lithology, geological structure and hydrogeological conditions, while slope angle is a secondary factor. Lower and Middle Jurassic limestones are relatively stable. However, the corresponding lithologic units can be affected by rockfalls along cliffs and hillsides with steep slopes (>25°). On the contrary, landslides are more frequent along the contact between the former geologic formations and the evaporitic complex of Triassic-Hettangian age, namely along the peripheral depression that borders the Hercynian Massif in the Algarve. From the Middle Jurassic upwards, the lithologic units show contrasting resistance and permeability, which increases the geomorphological susceptibility to slope instability. In this context, three lithologic units are very prone to landslides, essentially rotational slides, translational slides and complex slope movements (Rodrigues and Coelho 1989, Ferreira and Zêzere 1997): (i) marls and marly limestones of Upper Jurassic age, mainly along southern Estremadura, north of Lisbon and south of the Serra de Montejunto (Fig. 3.7), (ii) marls and limestones of Cretaceous age, particularly in the areas of Lisbon—Cascais—Ericeira and Nazaré—Leiria—Vila Nova de Ourém, and (iii) sequences of marls, clays, sands and sandstones of Upper Cretaceous age, particularly along the area of Pombal—Condeixa—Soure—Aveiro. Landslides within the Tagus and Sado Basin are typically shallow translational slides, mudslides, topples and rockfalls. These landslides are strongly associated with the presence of overconsolidated clays of Miocene age in the Lisbon region and detrital formations of the same age that occur along the Santarém region (Rodrigues and Coelho 1989).

3.4

Coastal Erosion

The Portuguese mainland coastal zone extends along 830 km and includes three major geomorphologic units: Beaches, Coastal Cliffs and Low Rocky Coasts. Additional details on the geomorphological characteristics of the Portuguese coastal zone can be found in Abecasis (1997), Andrade et al. (2002) and Ferreira and Matias (2013). Coastal erosion has been recognized as a problem in Portugal since the late nineteenth century as a consequence of the regressive trend of the coastline. The first coastal defences were built in the early twentieth century to protect the Espinho village, located south of Oporto, but were

inefficient to protect houses and streets that were destroyed along a 1000 m zone (Valle 1989). Nowadays, the Portuguese coastal zone faces two major geomorphological threats: the accelerated erosion along coastal cliffs (Fig. 3.8) and the poor sand supply on sandy beaches (Fig. 3.9). In a recent study, Lira (2014) estimated an average retreat rate of the coastline for 0.23 m/year from 1958 to 2010 for the entire low-sandy coastal zone of mainland Portugal. The coastal erosion phenomena in Portugal have been assigned to four major reasons (Dias 1993; Ramos-Pereira 2004; Teixeira 2014): – The rise of the sea level due to thermal expansion. The study of the secular tide gauge series at Cascais shows an average sea level rise of 1.9 mm/year for 1920–2000 and 3.6 mm/year during the first decade of the twenty-first century (Antunes 2011). Whether the extent of this recent increase in the rate of sea level rise is related to climate change is currently under analysis. – The low sediment supply since the 1950s. The decrease in the influx of continental sediments to the coastal zone has been linked to dredging operations and inert extraction along the rivers and estuaries, and especially to the construction of dams along the main Iberian rivers since the mid-twentieth century (Dias 1993; GTL 2014). For the major Iberian rivers, Dias (1993) estimated 85% reduction in sediment supply on the hydrographic basin net area for due to dams. In addition, it is estimated that dams are currently responsible for retaining more than 80% of the sand volume that was carried by rivers to the coastal zone before their construction (Dias 1993; Valle 2014). Consequently, there is a deficit of sand to be redistributed by the littoral drift that runs typically form north to south along the west coast and from west to east along the south coast. Along the west coast, the volume of mobilized sediments was estimated as 1 million m3/ year from the mouth of the Douro to Nazaré (Veloso-Gomes et al. 2006). – The construction of houses and infrastructures along the coastal zone. The Portuguese coastal zone has been subjected during decades to very high pressure associated with the progressive urbanization and construction of harbours, industrial and tourism facilities, which led to the disruption of the coastal biophysical systems, and in some extreme cases to their disappearance (Ramos-Pereira 2004). This is the case of some fragile beach-dune systems. – The implementation of heavy coastal engineering works. As a rule, the works of coastal engineering have harmful consequences to the coastal stretch where they are deployed. According to Dias (1993), the contrast between the rigid character of engineering structures and the high

3

Geomorphological Hazards

55

Fig. 3.8 Coastal cliff erosion in Algarve (Senhora da Rocha)

Fig. 3.9 Accelerated erosion on sandy beaches in Vagueira (Central Portugal). Photograph credits Duarte Fernandes Pinto, A Terceira Dimensão, http://portugalfotografiaaerea.blogspot.com

56

J. L. Zêzere

Coastal sections subject to the most intense coastal erosion are the low-sandy coasts in Central Portugal, form Oporto to Nazaré, as well as the zone of Costa da Caparica, where the coastal erosion hazard is classified as very high (Fig. 3.10). In addition, the cliff and beach-cliff coastal systems located from Nazaré to Peniche are subject to very high hazard as they are very prone to rockfalls and rockslides that affect stratified rocks (limestone, marl, sandstone, clay) of Jurassic and Cretaceous age. The coastal cliffs in Algarve, spanning from Alvor to Olhos de Água, are subject to a high hazard regarding coastal erosion, and the same occurs along the sandy coast along the eastern part of the Algarve. The low rock coastal zone of NW Portugal that also includes some few narrow sandy beaches is also classified as presenting high hazard regarding coastal erosion (Fig. 3.10).

rivers, especially if they occur in highly urbanized areas. More than half of total deaths due to hydrologic disasters in Portugal’s mainland in 1865–2010 occurred during a single flash flood event in the Lisbon region on 25–26 November 1967 (Fig. 3.12), causing 522 fatalities (Zêzere et al. 2014). Additional details on this flash flood can be found in Trigo et al. (2016). The reduced concentration time within small catchments and the typically high peak discharge and high sediment content make flash floods a major threat in the country. The flash floods are driven by very intense rainfall episodes concentrated in a few hours, and most often occur in fall and spring. The absence of an appropriate early warning system for flash floods is an additional source of risk to people and properties. Floods of major rivers like the Tagus (Fig. 3.13) and Douro occur progressively in time as a result of rainy periods extending over several weeks during winter. Nowadays, the management of dam discharge is used to prevent most floods. However, dams can also increase the exceptional floods if the reservoirs reach their full capacity, implying their opening during periods of long-lasting heavy rainfall. Apparently, this was the case of the Tagus flood in March 1978 that was produced by massive discharges from the Spanish dams of Alcantara and Cedillo (Daveau et al. 1978).

3.5

3.6

dynamics of the coastal system is sufficient to enter disturbance into the system. In particular, the construction and expansion of harbour structures result in artificial obstacles to the circulation of sediments mobilized by the littoral drift. The same effect is noted along engineered coastal groins, where sediments typically accumulate updrift of the groin, whereas erosion accelerates downdrift.

Floods and Flash Floods

Floods and flash floods are important sources of hazard and risk in Portugal’s mainland. The zones subjected to flooding, including critical stretches and critical points, were mapped in an early work performed for the 1st National Water Plan (INAG 2001) (Fig. 3.11). Recently, 1621 hydrologic disaster cases that generated human consequences during the period 1865–2010 were inventoried in the DISASTER database (Zêzere et al. 2014). These floods and flash floods were responsible for 1012 deaths (average of 6.9 per year), 13,372 displaced and 40,283 homeless people. Hydrologic disasters were widespread along the country (Fig. 3.6), but more critical areas with high density of flood cases are located in the Lisbon region and the Tagus valley, in the Oporto region and the Douro valley, in the Coimbra region and the Mondego valley, and along the Vouga River valley (Fig. 3.11). Floods occur along the major rivers (e.g. the Tagus, Douro, Mondego, Sado and Guadiana rivers), whereas flash floods occur in small catchments, mainly within the Lisbon Metropolitan Area, the West Alentejo and the Algarve. Flash floods are potentially more dangerous than floods in major

Conclusions

Figure 3.14 summarizes the spatial incidence of five major geomorphological hazards in the Portuguese mainland. These hazards have a significant impact in the country and need to be accounted for by urban planning and civil protection stakeholders. The western and southern coastal zones are exposed to a larger number of threats, whereas the interior is essentially susceptible to landslides. The inner Alentejo is the safest zone of Portugal’s mainland, whereas the Lisbon region, the Lower Tagus Valley and the Algarve are zones subject to high level of geomorphologic hazard, namely to earthquakes, tsunamis, coastal erosion, floods and flash floods and, to a certain extent, landslides. These high hazard zones partly coincide with the most densely inhabited zones of the country and include the major part of economic activities and critical infrastructures of Portugal. The very high exposure to geomorphological hazards has been taken into account by civil protection stakeholders, especially regarding earthquake and tsunami hazard for which detailed studies have been made for both the Lisbon Metropolitan Area and the Algarve.

3

Geomorphological Hazards

57

Fig. 3.10 Simplified geomorphology of the Portuguese coastal zone and assessment of coastal erosion hazard (based on: Instituto do Ambiente 2005; Andrade et al. 2006; Zêzere et al. 2007; Ferreira et al. 2008; Lira 2014)

58

Fig. 3.11 Flood prone areas in the Portuguese mainland (Source of data INAG 2001; Zêzere et al. 2014)

J. L. Zêzere

3

Geomorphological Hazards

59

Fig. 3.12 Bridge destroyed by the 1967 flash flood in the Trancão valley (north of Lisbon)

Fig. 3.13 The 2013 Tagus flood in Reguengo do Alviela. Photograph credits Duarte Fernandes Pinto, A Terceira Dimensão, http:// portugalfotografiaaerea.blogspot.com

60

Fig. 3.14 Multi-geomorphological hazard map of mainland Portugal

J. L. Zêzere

3

Geomorphological Hazards

References Abecasis F (1997) Caracterização geral geomorfológica e aluvionar da costa continental portuguesa. Associação Eurocoast Portugal, Porto, pp 9–24 Andrade C, Freitas MC, Cachado C, Cardoso AC, Monteiro JH, Brito P, Rebelo L (2002) Coastal zones. In: Santos FD, Forbes K, Moita R (eds) Climate change in Portugal. Scenarios, impacts and adaptation measures. Gradiva, pp 173–219 Andrade C, Freitas MC, Brito P, Amorim A, Barata A, Cabaço G (2006) Zonas Costeiras. In: Santos FD, Miranda P (eds) Alterações Climáticas em Portugal: Cenários, Impactos e Medidas de Adaptação. Projecto SIAM II, Lisboa, Gradiva, pp 169–208 Antunes A (2011) Variação actual do NMM em Cascais. In: VII CNCG – Conferência Nacional de Cartografia e Geodesia, Porto, 11 p Baptista MA (1998) Génese, propagação e impacto de tsunamis na costa portuguesa. PhD dissertation, University of Lisbon Baptista MA, Miranda JM (2009) Revision of the Portuguese catalog of tsunamis. Nat Hazards Earth Syst Sci 9(1):25–42 Bezzeghoud M, Borges JF, Caldeira B (2011) Ground motion simulations of the SW Iberia margin: rupture directivity and earth structure effects. Nat Hazards 69:1229–1245 Cabral J (1995) Neotectónica em Portugal Continental. Memórias do Instituto Geológico e Mineiro 31, Lisboa Cabral J (1996) Sismotectónica de Portugal. Colóquio/Ciências: revista de Cultura Científica, 18. Fundação Calouste Gulbenkian, pp 39–58 Cabral J (2012) Neotectonics of mainland Portugal: state of the art and future perspectives. J Iber Geol 38:71–84 Cabral C, Ribeiro A (1989) Carta Neotectónica de Portugal. Nota Explicativa. Serv. Geol. Portugal Canora C, Vilanova S, Besana-Ostman G, Carvalho J, Heleno S, Fonseca J (2015) The Eastern Lower Tagus Valley fault zone in central Portugal: active faulting in a low-deformation region within a major river environment. Tectonophysics 660:117–131 Cunha TA, Matias LM, Terrinha P, Negredo AM, Rosas F, Fernandes RMS, Pinheiro LM (2012) Neotectonics of the SW Iberia margin, Gulf of Cadiz and Alboran Sea: a reassessment including recent structural, seismic and geodetic data. Geophys J Int 188:850– 872 Daveau S, Almeida G, Feio M, Rebelo F, Silva R, Sobrinho A (1978) Os temporais de Fevereiro/Março de 1978. Finisterra 30:236–260 Delgado J, Garrido J, López-Casado C, Martino S, Peláez JA (2011) On far field occurrence of seismically induced landslides. Eng Geol 123:204–213 Dias JA (1993) Estudo de Avaliação da Situação Ambiental e Proposta de Medidas de Salvaguarda para a Faixa Costeira Portuguesa (Geologia Costeira), Liga para a Proteção da Natureza/Ministério do Ambiente, Lisboa Duarte JC, Rosas F, Terrinha P, Schellart WP, Boutelier D, Gutscher M-A, Ribeiro A (2013) Are subduction zones invading the Atlantic? Evidence from the southwest Iberia margin. Geology 41:839–842 Ferreira Ó, Matias A (2013) Portugal. In: Pranzini E, Williams A (eds) Coastal erosion and protection in Europe. Taylor & Francis, London, pp 278–293 Ferreira AB, Zêzere JL (1997) Portugal and the Portuguese Atlantic Islands. In: Embleton C, Embleton-Hamann C (eds) Geomorphological hazards of Europe, developments in earth surface processes, vol 5. Elsevier, Amsterdam, pp 391–407 Ferreira Ó, Dias JA, Taborda R (2008) Implications of sea-level rise for Continental Portugal. J Coast Res 24(2):317–324

61 García-Mayordomo J, Insua-Arévalo JM, Martínez-Díaz JJ, Jiménez-Díaz A, Martín-Banda R, Martín-Alfageme S, Alvárez-Gomez JA, Rodríguez-Peces M, Pérez-López R, Rodríguez-Pascua MA, Masana E, Perea H, Martín-González F, Giner-Robles J, Nemser ES, Cabral J, QAFI Compilers Working Group (2012) The quaternary active faults database of Iberia (QAFI v.2.0). J Iber Geol 38(1):285– 302 Grandin R, Borges JF, Bezzeghoud M, Caldeira B, Carrilho F (2007) Simulations of strong ground motion in SW Iberia for the 1969 February 28 (MS = 8.0) and the 1755 November 1 (M * 8.5) earthquakes–II. Strong ground motion simulations. Geophys J Int 171:807–822 GTL – Grupo de Trabalho para o Litoral (2014) Gestão da Zona Costeira. O desafio da mudança, Lisboa Guha-Sapir D, Below R, Hoyois P (2016) EM-DAT: the CRED/OFDA international disaster database. www.emdat.be. Université Catholique de Louvain, Brussels, Belgium INAG (2001) Plano Nacional da Água. Ministério do Ambiente, do Ordenamento do Território e do Desenvolvimento Regional, Lisboa Instituto do Ambiente (2005) Relatório do Estado do Ambiente 2003. Portugal, Amadora Lira C (2014) Análise da evolução da linha de costa em litoral baixo arenoso nos últimos 50 anos. Relatório técnico de apoio ao estudo do grupo de trabalho do litoral – GTL, Lisboa Martins I, Mendes-Victor LA (2001) Contribuição para o Estudo da Sismicidade da região Oeste da Península Ibérica, 25. Instituto Geofísico Infante D. Luís, Universidade de Lisboa Oliveira CS (1986) A Sismicidade Histórica e a Revisão do Catálogo Sísmico. Laboratório Nacional de Engenharia Civil, Lisboa Omira R, Baptista MA, Matias L (2015) Probabilistic tsunami hazard in the Northeast Atlantic from near- and far-field tectonic sources. Pure Appl Geophys 172:901–920 Peláez JA, López-Casado C (2002) Seismic hazard estimate at the Iberian Peninsula. Pure Appl Geophys 159:2699–2713 Ramos-Pereira A (2004) O espaço litoral e a sua vulnerabilidade. Geoinova 9:33–43 Ribeiro A (2005) O sismo de 1755 e a Geodinâmica da Ibéria e Atlântico. In: O Grande Terramoto de Lisboa, vol I—Descrições. FLAD e Público, pp 219–236 Ribeiro A, Cabral J, Baptista R, Matias L (1996) Stress pattern in Portugal mainland and the adjacent Atlantic region, West Iberia. Tectonics 15:641–659 Rodrigues LF, CoelhoAG (1989) Landslides in Portugal—extent and economic significance. In: Brabb EE, Harrod BL (eds) Landslides: extent and economic significance. Balkema, Rotterdam, pp 179–189 Santos A, Koshimura S (2015) A criterion for tsunami hazard assessment at the local scale. J Geodesy Geomatics Eng 2:87–96 Santos A, Zêzere JL, Agostinho R (2011) O tsunami de 1755 e a avaliação da perigosidade em Portugal continental. VIII Congresso da Geografia Portuguesa, Repensar a Geografia para Novos Desafios, Comunicações, APG, Lisboa, 6 p Silva HG, Bezzeghoud M, Rocha JP, Biagi PF, Tlemc¸ani M, Rosa RN, Salgueiro da Silva MA, Borges JF, Caldeira B, Reis AH, Manso M (2011) Seismo-electromagnetic phenomena in the western part of the Eurasia-Nubia plate boundary. Nat Hazards Earth Syst Sci 11:241–248 Teixeira T (2014) Obras costeiras e gestão da posição da linha de costa do litoral de Espinho ao Cabo Mondego. Ingenium II, 141 Teves-Costa P, Borges JF, Rio I, Ribeiro R, Marreiros C (1999) Source parameters of old earthquakes: semiautomatic digitization of analog records and seismic moment assessment. Nat Hazards 19:205–220

62 Trigo R, Ramos C, Pereira S, Ramos A, Zêzere JL (2016) The deadliest storm of the 20th century striking Portugal: flood impacts and atmospheric circulation. J Hydrol 541(A):597–610 Valle AS (1989) As obras de protecção e de reconstituição das praias de Espinho (Tema IV). Recursos Hídricos 9(3):57–67 Valle AS (2014) Perda de Território por Ação do Mar: Uma Questão Nacional. Ingenium II, 141 Vaz T, Zêzere JL (2015) Landslides and other geomorphologic and hydrologic effects induced by earthquakes in Portugal. Nat Hazards 81:71–98 Veloso-Gomes F, Taveira-Pinto F, Pais-Barbosa J, Costa J, Rodrigues A (2006) Estudos e intervenções na Costa da Caparica. Atas das 1ªs Jornadas de Hidráulica, Recursos Hídricos e Ambiente, FEUP/SHRHA, pp 27–35 Zêzere JL, Pereira AR, Morgado P (2005) Perigos naturais e tecnológicos no território de Portugal Continental. Actas do X

J. L. Zêzere Colóquio Ibérico de Geografia “A Geografia Ibérica no contexto europeu”, Évora, 17 p Zêzere JL, Ramos-Pereira A, Morgado P (2007) Perigos Naturais em Portugal e Ordenamento do Território. E depois do PNPOT? Geophilia - O sentir e os sentidos da Geografia, CEG, Lisboa, pp 529–542 Zêzere JL, Pereira S, Tavares AO, Bateira C, Trigo RM, Quaresma I, Santos PP, Santos M, Verde J (2014) DISASTER: a GIS database on hydro-geomorphologic disasters in Portugal. Nat Hazards 72:503–532 Zitellini N, Gràcia E, Matias L, Terrinha P, Abreu MA, DeAlteriis G, Henriet JP, Dañobeitia JJ, Masson DG, Mulder T, Ramella R, Somoza L, Diez S (2009) The quest for the Africa-Eurasia plate boundary west of the Strait of Gibraltar. Earth Planet Sci Lett 280:13–50

4

Portugal Landslide Hazardscapes Ricardo A. C. Garcia and Sérgio C. Oliveira

Abstract

The diversity of geological and geomorphological landscapes in mainland Portugal is responsible for the occurrence of different landslide types. The present chapter illustrates three examples of destructive landslide hazardscapes responsible for recent hillslope evolution: in a granitic context, the Frades landslide, a lethal debris flow; and in sedimentary contexts, the Calhandriz landslide, the biggest rainfall-triggered landslide that occurred in Portugal in the last 50 years, and the Grande da Pipa River basin, the major landslide-prone area within the north of Lisbon region. Keywords







Landslides Hazardscapes Deep-seated landslides




Debris flow




Shallow slips

such as destruction of the vegetation cover, introduction of artificial cuts affecting slope stability and neglect of existing evidence of slope instability. Their combinations make landslides one of the most frequent and dangerous hazards in Portugal (Ferreira 1984; Ferreira et al. 1996). Indeed, landslides caused c. 236 deaths and affected more than 2800 people in Portugal’s mainland in the period 1865–2010 (Zêzere et al. 2014; Pereira et al. 2015). This chapter presents three case studies to show different landslide occurrences and their relations to landscape types of the Portuguese mainland. These are the Frades landslide, as an example of a lethal debris flow in a granite context; the Calhandriz landslide, which is the biggest known landslide that occurred in Portugal in the last 50 years, and the Grande da Pipa River basin, as an example of an inactive sedimentary basin setting where shallow and deep-seated landslides frequently occur (Fig. 4.1).

4.2 4.1

The Frades Landslide

Introduction

Landslides in Portugal are among the hazards for which susceptibility assessment is mandatory in spatial planning and emergency plans (for more details see Chap. 5). Despite the generally small dimensions of landslides in Portugal (e.g. Garcia et al. 2014), they occur frequently and account for significant economic losses due to infrastructure and property damage (e.g. Zêzere et al. 2007, 2008). The alternation of rock layers with very different permeability, plasticity and/or degree of weathering associated with steep slopes, as well as irregular precipitation distribution are natural conditions favouring landslide occurrence (e.g. Ferreira et al. 1987). These natural factors coexist with human factors, R. A. C. Garcia (&)
S. C. Oliveira Centre of Geographical Studies, Institute of Geography and Spatial Planning, University of Lisbon, Lisbon, Portugal e-mail: [email protected]

Located near the town of Arcos de Valdevez, the Frades landslide (41°57′ 21.71″ N; 8°27′ 37.01″ W) (Fig. 4.2) took place on 7th December 2000, affecting the Frades village, where economic damage (including four destroyed houses) and four deaths were registered (Bateira et al. 2014). As usual for debris flows in the north of Portugal, the phenomenon was triggered on a very rainy day (170 mm in 5:30 h, the second highest value in 41 years), preceded by antecedent rainfall of 928 mm in 17 days (Soares 2008; Soares and Bateira 2013; Bateira et al. 2014). The movement occurred in a concave slope with an average slope angle of 30° cut in Carboniferous granite bedrock, showing a shallow but highly weathered (clay formation) mantle and dense jointing in the upslope sector, where the main scar developed (Fig. 4.2, Bateira et al. 2014). The slope is sparsely covered by vegetation rooted in the shallow weathering mantle and slope deposits with a

© Springer Nature Switzerland AG 2020 G. Vieira et al. (eds.), Landscapes and Landforms of Portugal, World Geomorphological Landscapes, https://doi.org/10.1007/978-3-319-03641-0_4

63

64

R. A. C. Garcia and S. C. Oliveira

4.3

Fig. 4.1 General setting of landslide hazardscapes. Grande da Pipa River (GPR) basin (Source Rivers and hillshade, European Environmental Agency)

clayey matrix. The clay fraction, with their high absorption and plastic characteristics, had an important role as a landslide conditioning factor (e.g. Oyagi 1984; Sharma et al. 2013). Such materials, when exposed to intense rainfall, frequently saturate reaching the plasticity and liquid limit and favouring flow phenomena, as was the case in Frades (e.g. Bateira et al. 2014). The landslide started in the upper part of the slope as a small rotational slide and evolved downslope into a rapid debris flow. Figure 4.3 shows the debris flow path, c. 1.5– 2 m deep and 20–25 m wide (Barra 2003), mobilizing the surface regolith and deposits. The flow showed a run-out of about 800 m, with the coarsest debris and boulders showing a 380 m long displacement in 180 m of elevation (Bateira et al. 2014), ceasing their movement upon hitting and destroying the houses and reaching the road (EM 505).

The Calhandriz Landslide

The Calhandriz landslide is located 25 km NNE of Lisbon (38°55′ 24.42″ N; 9°4′ 17.20″ W) (Fig. 4.4) and took place on 9–10th February 1979 after a very rainy late autumn and winter (Ferreira 1984). As usual in the North of Lisbon region for deep-seated landslides, the movement was prepared and triggered by the accumulated rainfall and in the Calhandriz case, it started on a very wet day showing 102 mm of rain (Ferreira et al. 1996), with the critical rainfall intensity/duration estimated at 694 mm/75 days, which corresponds to a return period of about 22 years (Zêzere et al. 2015). Such a significant antecedent rainfall induced soil saturation associated with the rise of the water table level up to the topographical surface, which showed pooling (Ferreira et al. 1996). The presence of a high amount of water in the terrain contributed to the landslide movement that lasted approximately 36 h (Ferreira et al. 1996). The Calhandriz landslide is a singular case in Portugal concerning the landslide size and damage. The landslide-affected area has a maximum length of about 1 km, covers a surface of 180,000 m2 and the volume of material involved was estimated as 1,300,000 m3 (Ferreira et al. 1996), which is the largest volume of a rainfall-triggered landslide registered in Portugal. In addition, the landslide affected 16 houses, some of them recently constructed (Coelho 1979; Ferreira et al. 1996), being one of the most damaging landslides in Portugal, although without victims. This complex mass movement (with translational, rotational and flow components) took place on a gentle slope (9°) affecting marls and marly limestones of upper Jurassic age (known in this region by their high plasticity when saturated) and thick deposits resulting from previous landslides (Ferreira et al. 1996—Fig. 4.5). The coincidence between the geological dip and topography is almost perfect. According to Ferreira et al. (1996), the Calhandriz landslide contains two main sectors. The upslope sector comprises the main scar (1–3 m high) and was less active, being dominated by depletion and a mean horizontal displacement of 30 m. In this sector, seven houses were totally destroyed and four other houses were seriously affected. Although these houses had been repaired, they still show back-tilting as the evidence of rotational deformation. The downslope sector was the most dynamic and complex. Although it contains a local depletion zone of 6 m depth, this sector is the major accumulation zone of the landslide, where the accumulation lobes (still visible in landscape) reached more than 10 m high above the original topographic surface. The recorded mean horizontal displacement reached 45–50 m, but two houses showed horizontal dislocations of 170 and 230 m. These unusual displacements could be explained by

4

Portugal Landslide Hazardscapes

65

Fig. 4.2 Frades landslide location

the poor foundations of the houses, which allowed them to slip over the landslide mass. In total, seven houses were destroyed in the downslope sector of the landslide. In the lower part of the landslide, the slide evolved to a flow and the affected mass blocked the valley floor of the River Pequeno. The river channel is nowadays carved in the displaced material and shifted southwards 28–30 m (Ferreira et al. 1996).

4.4

The Grande da Pipa River Basin Landslides (Arruda dos Vinhos)

The Grande da Pipa River basin (GPR) is a small basin of 110 km2 (Fig. 4.6), which is recognized as a major landslide prone area within the north of Lisbon region (Oliveira 2012). Landslides are regionally called quebradas (hummocky

morphology) and fervidas (boiling water/soils) due to the water flow towards the landslide surface as a consequence of the pore-water pressure increase within the sliding mass. Landslides in the GPR basin are frequent both in space and time (Oliveira 2012) and are typically triggered by both intense and long-lasting rainfall events (Zêzere et al. 2015). The GPR basin is elongated 15 km in the west–east direction. The elevation ranges from 440 m in the west, in the vicinity of the fortification of Alqueidão (military defensive system to face the Napoleonic invasions) constructed over a techenite batholith and 5 m in the east, near the confluence of the Grande da Pipa River mouth with the Tagus River alluvial plain. The regional geology is dominated by clays, marls, sandstones and limestones of Upper Jurassic age, which are deformed by a wide curvature angle tectonic rebound that generated an anticline whose axis is located in the centre of

66

R. A. C. Garcia and S. C. Oliveira

Fig. 4.3 Frades debris flow: a main scar, b main flow path and surface non-sorted deposit and c accumulation of the finer material downslope of the main road (Photograph credits: Laura Soares)

the Arruda dos Vinhos region (Zbyszewski and Assunção 1965). The dominance of 800 m thick soft rocks (clays, marls with few sandstone intercalations) (Zbyszewski and Assunção 1965), results in a gentle hilly relief of the basin. Lithology shows an important role in landform evolution, mainly through differential erosion promoting structural relief inversion and the development of an erosional basin along the axis of the anticline (Fig. 4.7), where the older and softer rocks (clays and marls of the Abadia complex) outcrop. Within the GPR basin, slopes tend to be gentle (less than 15°), while overlying clays and marls of the Abadia complex, but a 10–20 m high rock face occurs in limestones of Amaral formation, forming the steepest slopes of the region (Fig. 4.8). The historical landslide inventory for the Grande da Pipa River basin includes 1434 landslides (Fig. 4.6), mainly of the slide type (96% of the total landslide inventory),

affecting 5.9% (6,484,402 m2) of the basin (Oliveira 2012; Oliveira et al. 2015). The landslide density is of 13 landslides/km2, and the highest in the north of Lisbon region. Landslides are typically small (from 7 to 262,000 m2) with a mean area of approximately 4500 m2. The largest and most destructive landslides are deep-seated rotational slides with a slip surface depth >1.5 m. 570 landslides of this type were inventoried (Fig. 4.9), representing 93% of the total unstable area in the GPR basin. The shallow slides (slip surface depth  1.5 m) are dominant in number (799 shallow rotational and translational slides, both in natural and artificial slopes—cuts and fills) but represent only 6% of the total unstable area in the basin. The causes of the landslides affecting the clays and marls of the Abadia complex (LU9) were summarized by Alonso et al. (2010) and are mainly related to changes in water content (effective stresses) and changes in soil suction, in particular after heavy rain periods. The same authors verified

4

Portugal Landslide Hazardscapes

67

Fig. 4.4 Calhandriz landslide location (Source of image: World imagery, ESRI)

Fig. 4.5 Schematic profile of the Calhandriz landslide. 1. Old landslide scars in marls and marly limestones; 2. Calhandriz landslide mass and affected houses (adapted from Ferreira 1984)

that the soil suction changes degrade the clays and marls in terms of their mechanical properties (strength, cohesion, loss of cementation, bonding and stiffness). This physical disaggregation, together with the succession of wetting and

drying cycles that induce plastic deformation, promotes the water entering the rock, thus reducing shear strength. In addition, modifications of surface run-off, subsurface drainage (e.g. use of drains) and topography (e.g. terrain landfills

68

R. A. C. Garcia and S. C. Oliveira

Fig. 4.6 Geological context and landslide inventory at the Grande da Pipa River (GPR) basin. Lithological units are classified according age criteria: LU1—Alluvium; LU2—Limestone intercalations; LU3—Conglomerates, sandstones and mudstones; LU4—Sandstones, marls and limestones; LU5—Limestones and marls; LU6—Mudstones,

sandstones, marls and limestones; LU7—Coralic limestones; LU8— Limestones; LU9—Marls, mudstones and sandstones; LU10—Conglomerates; and LU11—Dykes and magmatic intrusions (Oliveira 2012)

and excavations) in the unstable surrounding areas are common practices in the region and contribute to the occurrence of new landslides or reactivation of the old ones. Most of the landslides inventoried in the GPR basin were triggered by rainfall. However, the landslides are not more frequent in the lower part of the slopes, where the ground water table is typically higher. The largest landslides show their main landslide scarp near the contact between the clays and marls of the Abadia complex (LU9) and the limestone of the Amaral formation (LU7) that outcrops in the upper part of the slopes. The intense fracturing that exists in the ductile limestone formation allows for their high permeability,

whereas slow percolation of water along the clays and marls underneath it allows for deep soil saturation in the upper part of the slope after long-lasting rainfall events.

4.5

Conclusions

Landslide hazardscapes shown in the present section are far from representing the landslides full geoenvironmental conditions in Portugal but allow exemplifying some of the main geomorphological contexts and scales for potentially harmful landslides occurrence: (i) as single phenomena,

4

Portugal Landslide Hazardscapes

69

Fig. 4.7 GPR basin, an erosional depression forming a relief inversion on the marls and clays of the Abadia complex (exposed at Monfalim, Sobral de Monte Agraço). Note the controls of volcanic dykes and masses on the basin morphology. Credit: S.C. Oliveira

Fig. 4.8 Typical slope within the Grande da Pipa River basin: limestone rock face on the upper slope section and gentle topographic gradient on the clays and marls outcropping in the medium and bottom slope sections. Credit: S.C. Oliveira

associated with high plasticity marls and clays materials affecting huge area and volume (Calhandriz landslide); or associated to high velocity flows (Frades landslide), occurring in steep and weathered granite slopes; (ii) as regional high-density historical landslide inventories (GPR basin). In

this case, slow moving deep-seated and shallow rotational slides are dominant and are mainly associated to the outcropping of softer and plastic rocks such as clays and marls contributing to the definition of one of the most important landslide prone areas.

70

R. A. C. Garcia and S. C. Oliveira

Fig. 4.9 Complex landslides in the Grande da Pipa River basin. Credit: S.C. Oliveira

References Alonso EE, Pineda JA, Cardoso R (2010) Degradation of marls; two case studies from the Iberian Peninsula. In: Calcaterra D, Parise M (eds) Weathering as a predisposing factor to slope movements. The Geological Society of London, vol 23, pp 47–75 Barra A (2003) Cartografia de susceptibilidade de vertentes. Aplicação ao concelho de Viana do Castelo, Braga. Master thesis, 135p Bateira C, Soares L, Rodrigues D, Moura R, Teixeira M, Santos M (2014) Movimentos de vertente no norte de Portugal: importância do comportamento hidrológico das formações superficiais. Revista Brasileira de Geomorfologia 15(4):551–565 Coelho AG (1979) Análise cartográfica da estabilidade de taludes naturais para o planeamento urbano. Geotecnia 26:75–89 Ferreira AB (1984) Mouvements de terrain dans la région au nord de Lisbonne. Conditions morphostructurales et climatiques. In: Flageollet JC (ed) Mouvements de Terrain: Communications du Colloque, Caen 22-23-24 mars. Documents du BRGM, vol 83, pp 485–494 Ferreira AB, Zêzere JL, Rodrigues ML (1987) Instabilité des versants dans la région au Nord de Lisbonne. Essai de cartographie géomorphologique. Finisterra XXII 43:227–246

Ferreira AB, Zêzere JL, Rodrigues ML (1996) The Calhandriz landslide (Metropolitan area of Lisbon). In: Chacón J, Irigaray C, Fernández T (eds) Landslides: proceedings of the 8th international conference and field workshop, Granada 27–28 Sept, pp 31–38 Garcia RAC, Oliveira SC, Zêzere JL (2014) Distribuição da densidade de probabilidade da magnitude de deslizamentos na região norte de Lisboa, Portugal. Comunicações Geológicas 101(Especial II):897– 901 Oliveira SC (2012) Incidência espacial e temporal da instabilidade geomorfológica na bacia do rio Grande da Pipa (Arruda dos Vinhos). PhD thesis in Physical Geography, IGOT, Universidade de Lisboa, 452p Oliveira SC, Zêzere JL, Catalão J, Nico G (2015) The contribution of PSInSAR interferometry to landslide hazard in weak rock-dominated areas. Landslides 12(4):703–719 Oyagi N (1984) Landslides in weathered rocks and residual soils in Japan and surrounding areas: a state-o-the-art report. In: Proceedings of the IVth international symposium on landslides, Toronto, vol 3, pp 1–31 Pereira S, Zêzere JL, Quaresma I, Santos P, Santos M (2015) Mortality patterns of hydro-geomorphic disasters. Risk Analysis (published online)

4

Portugal Landslide Hazardscapes

Sharma R, Metha B, Jamwal C (2013) Cut slope stability evaluation of NH-21 along Nalayan-Gambhrola section, Bilaspur district, Himachal Pradesh, India. Nat Hazards 66(2):249–270 Soares L (2008) A importância das formações superficiais no âmbito dos processos de erosão hídrica e movimentos de vertente no NW de Portugal. Dissertação de doutoramento em Geografia Física, Fac. Letras, Universidade do Porto, 850p Soares L, Bateira C (2013) Movimentos de masse em vertentes no norte de Portugal. Retrospectiva e actualização. In: Lourenço LF, Mateus MA (Coord.) Riscos naturais, antrópicos e mistos. Homenagem ao Professor Doutor Fernando Rebelo, pp 367–383 Zbyszewski G, Assunção CT (1965) Notícia explicativa da folha 30-D (Alenquer). Carta Geológica de Portugal, Serviços Geológicos de Portugal, Lisboa, 104p

71 Zêzere JL, Garcia RAC, Oliveira SC, Reis E (2008) Probabilistic landslide risk analysis considering direct costs in the area north of Lisbon (Portugal). Geomorphology 94(3–4):467–495 Zêzere JL, Oliveira SC, Garcia RAC, Reis E (2007) Landslide risk analysis in the area north of Lisbon (Portugal): evaluation of direct and indirect costs resulting from a motorway disruption by slope movements. Landslides 4:123–136 Zêzere JL, Pereira S, Tavares AO, Bateira C, Trigo RM, Quaresma I, Santos PP, Santos M, Verde J (2014) DISASTER: a GIS database on hydro-geomorphic disasters in Portugal. Nat Hazards 72:503–532 Zêzere JL, Vaz T, Pereira S, Oliveira SC, Marques R, Garcia RAC (2015) Rainfall thresholds for landslide activity in Portugal: a state of the art. Environ Earth Sci 73(6):2917–2936

5

Geomorphological Hazards, Land Use Planning and Emergency Management Sérgio C. Oliveira, Ricardo A. C. Garcia, and José Luís Zêzere

Abstract

In the last decades, Portugal was affected by several geomorphological hazards that produced high levels of destruction and disruption on human activities, particularly due to the inappropriate occupation of areas where natural hazardous phenomena occur. To cope against the consequences of these hazards, a set of legal instruments has been implemented in the last 30–40 years by national initiative or by transposition to the national law of European Directives within the thematic of risk assessment and management. This chapter broadly presents the planning and emergency management legal framework in Portugal, as well as the specific normative instruments for the major geomorphological hazards that influence land use regulation. Keywords





Geomorphological hazards Lands use planning Emergency management Civil protection

5.1




Introduction

Geomorphological hazards are among the environmental processes that cause higher disruption on human activities worldwide. Panizza (1996) pointed out the concept of “unstable landform,” which can be described as a landform which is not in equilibrium with the natural environment and therefore tending to reach a balance by modifying itself. Such modification may generate the hazard that can threaten people and assets.

In the last decades, Portugal was affected by several hydro-geomorphologic disasters that caused deaths, injuries, homelessness and high levels of destruction and disruption on human activities (Zêzere et al. 2014), as well as other types of natural hazards (Ferreira and Zêzere 1997). Social and economic impacts resulting from the increase of human exposure to natural hazards lead to the development and implementation of effective prevention and mitigation measures, mainly concerning spatial planning and civil protection emergency management. Spatial planning is recognized as a major contributor to Disaster Risk Reduction (Prenger-Berninghoff et al. 2014) and hazard mapping is a core component of successful spatial planning (OECD 2010). Nevertheless, according to Zêzere et al. (2007) and taking as example the Portuguese Municipal Master Plans, hazard maps only become effective followed by the regulation of possible land uses. In the past, the Portuguese legislation and practice regarding territorial planning and its coordination with civil protection policy did not ensure effective prevention policies to face the adverse effects of natural hazards (Zêzere 2007). Major advances in this respect were achieved in 2007 with the approval of the National Program on the Territorial Planning Policy (PNPOT, Law 58/2007) built upon three strategic pillars: (i) the prevention and risk management system, (ii) the conservation and sustainable management of natural resources and agro-forest areas, and (iii) the urban system and accessibilities. With the first version of the PNPOT, the preventive risk management was assumed as a priority for the spatial planning policy and the hazard and risk assessment became a compulsory part within the complete territory planning instruments. The recent changes to the PNPOT (Extraordinary Council of Ministers 14/7/20018) place the focus on the prevention of risks and on the adaptation of the territory to climate change.

S. C. Oliveira (&)
R. A. C. Garcia
J. L. Zêzere Centre of Geographical Studies, Institute of Geography and Spatial Planning, University of Lisbon, Lisbon, Portugal e-mail: [email protected] © Springer Nature Switzerland AG 2020 G. Vieira et al. (eds.), Landscapes and Landforms of Portugal, World Geomorphological Landscapes, https://doi.org/10.1007/978-3-319-03641-0_5

73

74

5.2

S. C. Oliveira et al.

The Land Use Planning System

The most recent changes regarding natural hazards prevention and effective reduction of their effects through land use planning in Portugal were introduced by the law of the land use planning and urbanism (Law 31/2014) and by the juridical regime of the territorial planning instruments (RJIGT, Decree-Law 80/2015). The territorial management system considers four spatial planning levels: national, regional, intermunicipal, and municipal. Within the purposes of public policy on land use planning and urban planning are: (i) preventing collective risks and reducing their effects on people and assets; (ii) safeguard and enhance the coastal zone, riverbanks, and reservoirs; and (iii) increase the resilience of the territory to the effects of extreme weather events and mitigate the effects of erosion. In addition, the territorial plans should assess the hazardous and risk zones as well as the location of exposed elements. Moreover, each plan should establish rules and measures for the prevention and minimization of risks, depending on the degree of hazard, exposure, and vulnerability. Every municipality in Portugal has to define the National Ecological Reserve (REN, Decree-Law 166/2008, modified by the Decree-Law 239/2012), which is a public utility restriction where, as a rule, the development is forbidden. The main objectives of the REN include the prevention and reduction of the degradation of aquifer recharge, the risks of coastal flooding, floods, landslides, and soil erosion, contributing to climate change adaptation and safeguarding environmental sustainability and the safety of people and assets.

5.3

The Civil Protection and Emergency Management System

The Law 27/2006 describes the main objectives of civil protection that include: (i) to prevent risks and the occurrence of a major accident or catastrophe resulting therefrom; (ii) to mitigate risks and limit their effects; (iii) to assist people in danger, to protect cultural, environmental and public goods and values; and (iv) to support the restoration of living conditions in areas affected by major accidents or catastrophes. The concern for prevention is expressed when describing the areas on which the civil protection activity should be carried out (e.g., collecting, forecasting, evaluating and preventing risks, the analysis of vulnerabilities, information and population formation, aiming at their awareness of self-protection and collaboration with the authorities).

However, civil protection policies and operations are virtually omitted on the subject in the Law 27/2006. The Portuguese civil protection response has been naturally reactive and that is expressed clearly in their objectives and action fields, which pointed out the rescue and assistance of people as the priority of civil protection services. At the municipal scale, the reactive activity of civil protection is guided by the Municipal Emergency Plan. The civil protection assures also the support of the restoration of peoples’ life routines in areas affected by a severe accident or catastrophe (Fig. 5.1).

5.4

Legal Framework for Specific Natural Hazards

The geomorphological hazards with more relevance in the context of land use planning and emergency management within the Portuguese territory are earthquakes and tsunami, landslides, coastal erosion, floods and flash floods.

5.4.1 Earthquakes and Tsunami In Portugal, the legal framework considering the seismic hazard was defined by the Regulation of Safety and Actions for Building and Bridge Structures (RSA, Decree-Law 235/83) approved in 1983, which defines four seismic areas (A–D, by descending order of seismicity, Fig. 5.2a). More recently, the seismic zonation for Portugal (Figs. 5.2b, c) considering the seismic actions of Type I (seismicity in the tectonic boundary plates) and Type II (intra-plate seismicity sources) was redefined by the NP EN 1998-1 2010 (Eurocode 8 Design of structures for earthquake resistance). This regulation aims to ensure that human lives are protected, the damages in infrastructures are limited, and the important structures with civil protection purposes are operational, in case of earthquake occurrence. Two fundamental requirements are considered: (i) non-occurrence of collapse and (ii) damage limitation (probability of exceedance of 10% in 10 years, return period of 95 years and exceedance ability of 10% in 50 years or return period of 475 years). For the tsunami hazard, there are no specific guidelines nor regulations. Nevertheless, the identification of tsunami inundation areas and the assessment of vital exposed elements have been included in the recent revisions of Regional and Municipal Master Plans (Fig. 5.3).

5

Geomorphological Hazards, Land Use Planning and Emergency …

75

a

b

Fig. 5.1 Flash floods affecting the Lourinhã city center, west Portugal (39°14′ 37″ N; 9°18′ 44″ W): a clay deposit resulting from the flash flood of 23 September 2014, b restoring works by civil protection agents

5.4.2 Landslides

5.4.3 Coastal Erosion

The identification and delimitation of unstable slopes (landslide inventory, Fig. 5.4) and the assessment of areas susceptible to landslide occurrence, considering different landslide types is mandatory at the municipal scale and integrates the National Ecological Reserve. The criteria for the definition of landslide-prone areas are defined at the national and regional levels through a set of strategic guidelines, including the delimitation of scarps (gradient higher than 45°) with a protection buffer to the scarp upper and lower limit; the complete landslide inventory and a surrounding protection area of 10 m bounding each landslide; and the landslide susceptible area obtained with a data-driven method, which ensures the validation of a fraction of not less than 70% of the total landslide areas included in the municipal landslide inventory.

Coastal erosion is a worldwide problem and Portugal with its 830 km of coastline is no exception (Fig. 5.5). In 2009, the National Strategy for Integrated Coastal Zone Management (ENGIZC, Ministries Council Resolution 82/2009) defined the strategic framework of the management, integrated and participatory actions in the coastal zone, in order to ensure the sustainable development. With respect to coastal hazards, the strategy defines climate change as a major threat for the coastal susceptibility to erosion, namely through sea level rise, storms, and extreme weather events. The coastal zone has specific plans in the framework of spatial planning (the Coastal Zone Program—POC) and it also included in the National Ecological Reserve, at the municipal scale. The Coastal Zone Program (POC) covers a strip along the coast, which is 500 m wide onshore (can

76

S. C. Oliveira et al.

2 3

Spain

Type 2

B

4

1

C

5

2

D

6

3

km 100 8°0'0"W

1

Oporto

Lisbon

Type 1

38°0'0"N

38°0'0"N

A

Atlantic Ocean

40°0'0"N

Spain

Lisbon

Lisbon

0

Oporto

38°0'0"N

Atlantic Ocean

Spain

c

42°0'0"N

b

42°0'0"N

Oporto

40°0'0"N

Atlantic Ocean

40°0'0"N

42°0'0"N

a

0

km 100

0

8°0'0"W

6°0'0"W

km 100 8°0'0"W

6°0'0"W

6°0'0"W

Fig. 5.2 Seismic zonation for Portugal according to the RSA (1983) (a) and EUROCODE 8 regulation Type I (b) and Type II (c) actions. The letters and numbers represent each seismic zone by descending order of seismicity

Fig. 5.3 Regional tsunami inundation susceptibility map for the Lisbon Metropolitan Area. Adapted from Ramos et al. (2010)

Lisbon

Setúbal Tsunami inundation susceptibility High Moderate

5

Geomorphological Hazards, Land Use Planning and Emergency …

77

Fig. 5.4 Rotational slide affecting the VCI (internal route belt) Alcobaça, western Portugal (39°32′ 22.79″ N; 8°58′ 43.94″ W)

reach 1000 m, if justified by the need to protect coastal biophysical systems) and a maritime range up to the bathymetric of 30 m, including the areas under port jurisdiction. The National Ecological Reserve includes, in the coastal zone: (i) the maritime and the terrestrial coastal protection zones; (ii) the coastal protected landforms (beaches, spits, barrier welded and barrier islands, tombolos, salt marshes, sea stacks, coastal and fossil dunes, and cliffs and respective protection zones); (iii) the transition waters and respective margins and buffer protection zones; and (iv) the areas threatened by the sea, which are subjected to coastal overwash.

5.4.4 Floods and Flash Floods The Decree-Law 468/71 is one of the first legal acts establishing restrictions to land use in areas affected by floods, which was approved a few years after the catastrophic flash flood that affected the Lisbon region on November 1967. In 1987, in the sequence of the 1983 flash floods affecting again the Lisbon region, the areas threatened by floods, named “adjacent areas” in the legislation, were redefined and the construction was forbidden or strongly conditioned in such areas. In 1998, the Decree-Law 364/98 imposes the mapping of inundation zones at the municipality scale, and the

establishment of land use restrictions necessary to face the flood risk (Fig. 5.6b) The delineation of zones threatened by floods and adjacent zones is also considered in the Portuguese Water Law 58/2005 (amended and republished by the Decree-Law 130/2012), which transposes to the national legal order the European Directive 2000/60/CE. These legal documents are coordinated with the juridical regime of the REN approved by the Decree-Law 239/2012. With this legal framework, the zones threatened by floods are defined as the limit of the flood with a 100-year return period, or the limit of the highest flood record. More recently, the Decree-Law 115/2010 transposes into the national law the European Directive 2007/60/CE, which aims to establish a framework for the assessment and management of flood risk and to minimize the consequences of floods. For each hydrographic region, this law considers the construction of inundation zone maps and inundation risk maps. The former contains the definition of the physical characteristics of the floods as well as the inundation extent of low, medium, and high probability areas, whereas the latter indicates the potential harmful consequences associated to inundations (e.g., number of inhabitants potentially affected and sensitive buildings). The inundation risk management plan includes the management of the flood risks and is focused on prevention, protection, and preparedness, including prevision and early warning systems adapted to each basin characteristics (Fig. 5.6).

78

S. C. Oliveira et al.

a

b

Fig. 5.5 Coastal erosion and implementation of soft coastal protection measures. a Trafal cliff coast in poorly consolidated Plio-Pleistocene red sandstones (37°3′ 26.00″ N; 8°4′ 49.00″ W); b Improvement of the

stability conditions of the Costa da Caparica coastline and protection of heavy coastal engineering works, January 2007, (38°38′ 40.00″ N; 9°14′ 31.00″ W)

5

Geomorphological Hazards, Land Use Planning and Emergency …

79

a

15 - 10 - 1987

b

Fig. 5.6 Lima River floods at Ponte de Lima village, northwest of Portugal (41°46′ 5.57″ N; 8°35′ 4.69″ W). a Historical flood levels marks inscribed on riverside buildings; b Compatible land uses with flood prone areas in the river Lima margins

5.5

Conclusions

The major geomorphological hazards affecting the mainland Portugal are covered directly or indirectly by one or more legal instruments, which allow to conclude that natural hazards assessment and the corresponding regulation of land use are, at least theoretically, well framed in the Portuguese

legislation. The partial overlap of the scope of many programs and plans has been generating different versions of models on the same topic, at a similar scale for the same region, which revealed to be not fully compatible. Such situation is not desirable for spatial planning, neither for emergency management. Nonetheless, the current legal framework, which imputes the responsibility to define land use rules only to the municipal plans, may solve this problem in the midterm.

80

References Ferreira AB, Zêzere JL (1997) Portugal and the Portuguese Atlantic Islands. In: Embleton C, Embleton-Hamann C (eds) Geomorphological hazards of Europe, developments in earth surface processes, vol 5. Elsevier, Amsterdam, pp 391–407 OECD (2010) Policy handbook on natural hazard awareness and disaster risk reduction education. International network on the financial management of large scale catastrophes Panizza M (1996) Environmental geomorphology. Developments in earth surface processes, vol 4. Elsevier, 268p Prenger-Berninghoff K, Cortes VJ, Sprague T, Aye ZC, Greiving S, Głowacki W, Sterlacchini S (2014) The connection between long-term and short-term risk management strategies for flood and landslide hazards: examples from land-use planning and emergency

S. C. Oliveira et al. management in four European case studies. Nat Hazards Earth Syst Sci 14:3261–3278 Ramos C, Zêzere JL, Reis E (2010) Avaliação da suscetibilidade aos perigos naturais da região de Lisboa e Vale do Tejo. Prospectiva e Planeamento 17:57–73 Zêzere JL (2007) Riscos e ordenamento do território. Inforgeo, Julho, pp 59–63 Zêzere JL, Pereira S, Tavares AO, Bateira C, Trigo RM, Quaresma I, Santos PP, Santos M, Verde J (2014) DISASTER: a GIS database on hydro-geomorphologic disasters in Portugal. Nat Hazards 72:503–532 Zêzere JL, Ramos-Pereira A, Morgado P (2007) Perigos naturais em Portugal e ordenamento do território. E depois do PNPOT? Geophilia – O sentir e os sentidos da Geografia. Lisboa, C.E.G., pp 529–542

Part II Coasts

6

The Northwest Portuguese Coast: A Longitudinal Coastline and Its Diversity Maria Assunção Araújo

Abstract

The coastline of northwest Portugal shows a remarkable regional homogeneity with a very consistent NNW-SSE orientation from Cape Silleiro in Galicia to Espinho, 14 km south of Oporto. It is a ca. 122 km stretch of rocky coast covered, in most places, by recent beach and dune sands. Besides its straight appearance, another important feature is the presence of the so-called littoral platform, which develops as an erosional surface adjacent to the coast, generally separated from the interior by an abrupt escarpment. The littoral platform shows several outcrops of Plio-Quaternary deposits, which may be the key to understand its origin and evolution. In this chapter, the general evolution of the coastline of northwest Portugal is discussed. The area between the rivers Leça and Espinho is analysed in more detail. Along these 39 km of coastline, Cenozoic deposits covering the coastal platform are frequent and well exposed, which make it an interesting area for the understanding of its paleogeographical and geomorphological evolution. Keywords









Littoral platform Cenozoic deposits Neotectonics Coastal erosion Iberian Massif Porto-Tomar fault

6.1




Introduction

This chapter presents a section of the Portuguese coast between the mouth of the river Minho, on the border with Galicia in Spain, and the city of Espinho (Fig. 6.1). It will be specifically focused on the area from the river Ave to M. A. Araújo (&) Faculty of Arts and Humanities, Centre of Studies in Geography and Spatial Planning (CEGOT), University of Porto, Porto, Portugal e-mail: [email protected]

Espinho, 14 km south of Porto, where many deposits occur providing a good insight into Quaternary landscape evolution. The northern Portuguese coastline is generally rectilinear, showing a very consistent orientation in NNW-SSE direction, beginning at Cape Silleiro (near Baiona, still in Galicia), southwards to Espinho. To the north of the Cape Silleiro, up to the border between Galicia and Asturias, a deeply indented coast, oblique to the general direction of the shoreline, occurs—the so-called Rias of Galicia. This contrast is the most striking aspect of the north-western Iberian coastline. The reasons for this have been long discussed by several authors, since Teixeira (1944). He suggested that Galicia has been subsiding and that submergence and consequent coastline indentation are the responses to the tectonic behaviour of different compartments in which the Galician one is subsiding, while the Oporto compartment is uplifting. However, since the works of Nonn (1966) several possible origins for the Galician “Rias” have been identified. Drowned river valleys seem the most obvious explanation, although a bit simplistic, because most of the world’s coasts are effectively drowned by postglacial transgression. The “Rias” may also correspond to tectonic depressions (grabens) invaded by the Holocene transgression. Another hypothesis suggests that during the Tertiary, crystalline rocks were deeply weathered along fractures, then, during the Quaternary, the fractures were cleared off the regolith, generating valleys, later invaded by postglacial transgression. Nonn also suggested that the rectilinear coastline from Cape Silleiro to Espinho results from a structural control by the Porto-Tomar fault and of its extensions to the north. This is very likely, considering the parallelism between the Porto-Tomar fault and the rigidity of this coastal stretch (Fig. 6.2). A closer analysis using maps and aerial photographs at several sections of the coast also shows lineaments with a clear structural influence (Figs. 6.4 and 6.5),

© Springer Nature Switzerland AG 2020 G. Vieira et al. (eds.), Landscapes and Landforms of Portugal, World Geomorphological Landscapes, https://doi.org/10.1007/978-3-319-03641-0_6

83

84 Fig. 6.1 Topography of north-western Iberian Peninsula: location of the places and rivers mentioned in the text (Global Mapper, version 19.01). The frontier between Portugal and Spain partially coincides with the last part of Minho River; P-P’: Padrón fault. Porto-Tomar fault can be seen in Fig. 6.2

M. A. Araújo

6

The Northwest Portuguese Coast: A Longitudinal Coastline …

Fig. 6.2 Western Peninsula with some of the most evident tectonic lineaments in black (Topography: Global Mapper 19.1). Besides the Padrón fault (P-P’), the Porto-Tomar fault (P-T) is clear. The latter gives rise to the N-S general trend of the coastline from Cape Silleiro to Espinho. Map inset shows the Iberian Peninsula (Google Earth Pro)

85

86

M. A. Araújo

and also many beaches that are gently arched, masking the bedrock located at different depths. To the south of Espinho, the coastline orientation changes to NNE-SSW and is quite regular until the promontory of Nazaré, ca. 156 km to the south. This contrast between the northern (until Espinho) and central coastlines of Portugal has a major structural reason. North of Espinho, the coast is sculpted over the rocks of the Iberian Massif, which consists of Precambrian and Paleozoic igneous and metamorphic rocks, folded and metamorphized with granitization during the Variscan orogeny. This orogeny took place between the middle Devonian and the Permian, with the main stage in the late Carboniferous. To the south of Espinho, a new structural region, the Lusitanian basin, begins as the result of the opening, during the Mesozoic, of a rift that became an aulacogen, an aborted rift. During the Middle to Late Jurassic a new rift located further west began separating Eurasia from the North American plate. The Variscan basement is hence covered by formations of Mesozoic and Cenozoic age in the Lusitanian basin. The northern part shows recent sediments from the Holocene back to the Upper Pleistocene, while around Aveiro Mesozoic (Cretaceous) formations occur. It is noteworthy that from the 1990s onwards, there was a significant increase of publications about the coastline from Cape Silleiro to Espinho, including several doctoral theses (Granja 1990; Araújo 1991; Alves 1996; Blanco Chao 1999; Carvalhido 2012). In this chapter, the focus is on presenting a synthetic analysis of this coastal strip, especially in the area where Quaternary deposits are best exposed and are more frequent, which is from the Ave River mouth to Espinho.

6.2

Geological and Geographical Setting

The direction of the coastline between the Cape Silleiro and Espinho is guided by an important structural feature, the Porto-Tomar strike-slip zone that enters the mainland near Oporto, with a prolongation to Cape Silleiro (Fig. 6.2). NNW-SSE is also one of the most evident structural directions in the old Variscan folds, the northern part of Valongo anticline (Fig. 6.1). Although the main Variscan direction (NNW-SSE to NW-SE) shows a great importance in the geomorphological development of the northern Iberian Massif, some large-scale geomorphological features are related to other orientations. The most important structures are the late Variscan strike-slip faults, mostly of NNE-SSW direction

(Gerês: 43 km, Verín-Penacova: 217 km and Vilariça: 203 km long, Fig. 6.2). These faults are responsible for the main units of the territory of northern Portugal (Ferreira 1991). The N-S direction is very significant too, exemplified by the Padrón fault (Figs. 6.1 and 6.2), which is more than 130 km long, creating a meridian corridor across Galicia and northern Portugal. Another important direction is the ENE-WSW, controlling courses of most northern Portuguese rivers (Fig. 6.2). One of the main features of the Iberian Massif is its organization in large areas with similar paleogeography and lithologic characteristics: the Iberian Massif zones. The area discussed in this chapter is integrated in two of the tectono-stratigraphic zones of the Iberian Massif: Central Iberian Zone and a small outcrop of the Ossa-Morena Zone (Chaminé 2000). The Ossa-Morena Zone materials occur in a very narrow area, partially covered by beach sands along the Oporto coastline and the south of the Douro mouth, from Lavadores to Espinho, bordering the Porto-Tomar fault to the west. It is composed of very old rocks of Neoproterozoic age (Chaminé 2000). The Central Iberian Zone is the central part of the Variscan orogen, where the tectogenesis was more intense. Therefore, different kinds of granites and metamorphic rocks are the most common outcrops in a significant part of this area. The granites intruded, mostly during the Carboniferous, a lower Paleozoic sequence that begins with a Cambrian flysch, made up of monotonous schists and greywackes (Ribeiro et al. 1979). Upon this sequence, the alternation of Ordovician quartzites/slates forms currently the Appalachian-style ridges visible in Fig. 6.1. The Valongo anticline is one of the most important Variscan structures in northern Portugal. Its western flank is about 100 km long, with the quartzites reaching the coastline near the Cávado River mouth. Due to their resistance to marine erosion, the quartzites form the so-called Fão “Horses”, rocky outcrops that make the approach to the Cávado River mouth quite hazardous. At São Félix the quartzite ridge structure is quite notorious, dominating the coastal landscape (Figs. 6.1 and 6.3-D). The entire north-western Iberian coastline is developed upon Iberian Massif bedrock. From Caminha (river Minho mouth) to Espinho, almost half of the coastline is mapped as bedrock outcrops, contacting directly with the sea. Some of them correspond to low cliffs, while high cliffs are quite rare. About 52% of the coastline length corresponds to beach sands and, more rarely, to coarser sediments. The accumulation covering bedrock is thin, and sometimes during winter

6

The Northwest Portuguese Coast: A Longitudinal Coastline …

87

Fig. 6.3 The differential development of the littoral platform in the northwest coast of Portugal (maps and profiles: Global Mapper, version 19.1)

and stormy weather, marine erosion removes the sand cover, revealing the otherwise hidden rocky outcrops. In resistant metamorphic rocks, marine erosion guided by fractures and faults can create some spectacular notches (Fig. 6.4). The rocky outcrops are extremely fractured and

some of the lineaments are not simply the result of weak rock scouring by the marine action. In some places, recent vertical movements, along old Late Variscan directions, seem to have uplifted marine platforms associated to the last interglacial (Fig. 6.5).

88

M. A. Araújo

Fig. 6.4 Panoramic view of the Vila Chã tidal notch (locally called “Pedra do Bispo”). This notch is controlled by an ENE-WSW fracture

Fig. 6.5 Google earth view of the S. Paio area. The culmination of “A” platform is ca. 10 m asl. “B” culminates at 21 m. At “C”, the granite base is 5 m asl (see also Fig. 6.13). D represents the position of

6.3

Littoral Platform: Concept and Development

Beyond its rectilinear appearance, the northern Portuguese coast is characterized by the presence of a platform of varying width accompanying the coastline, showing a steep escarpment separating it from the interior (the so-called marginal relief—Araújo 1991). This platform is generally called littoral platform (Ferreira 1983, 1991; Araújo 1991). The existence of cover deposits, generally considered Plio-Quaternary in age, is another key feature of this platform. Initially interpreted as a fossil cliff, the marginal relief

the fossil tidal notch (Fig. 6.14). The most evident fractures are underlined in white. Image: Google earth

was later interpreted as an escarpment of tectonic origin affecting the oldest deposits covering the littoral platform (Ribeiro et al. 1991; Araújo 1991). The littoral platform has a very unequal development, reaching different altitudes and widths. Figure 6.3 shows its development in several stretches of the north-western coast. It is very narrow in southern Galicia (Fig. 6.3-A), with a high marginal relief on the inland side, attaining 500 m asl. In the middle of the area, at Viana do Castelo (Fig. 6.3-B), a narrow platform up to 50–60 m asl and a pronounced escarpment more than 300 m high occurs. Southwards, the littoral platform widens, culminates at around 50 m and the marginal relief is lower, attaining only ca. 220 m asl

6

The Northwest Portuguese Coast: A Longitudinal Coastline …

(Fig. 6.3-C and D). At the Ave-Leça interfluve, the littoral platform is wider and rises to 75 m asl (Fig. 6.3-E). South of the Leça River mouth, the littoral platform reaches 125 m. This is the area where the Cenozoic deposits are better exposed and where most of the deposits described below are located (Fig. 6.3-F). The position of the littoral platform close to the coast encouraged researchers to assign it to marine erosion. However, to prove marine origin, geomorphological or sedimentary evidence is needed. Yet, the cover deposits are rare, generally poorly preserved and most of them do not show marine characteristics. This is the case of the Oporto area, where only the deposits located under 40 m asl show a clear marine origin. The widespread deposits that occur above this elevation until the bottom of the marginal escarpment (ca. 125 m) are fluvial. Fossil beaches from at least the three last marine isotopic stages (MIS) occur below 40 m asl.

Fig. 6.6 Old outcrop at Rasa already destroyed. The top of the deposit was 124 m and showed a gentle slope to the east. A. Very weathered granite basement, exploited for kaolinite, B. Regular eroded surface

89

6.4

Cenozoic Deposits and the Geomorphological Evolution

The area between the Leça River and Espinho shows abundant Cenozoic deposits covering the littoral platform (Araújo 1991). Inside this sector, which corresponds to a coastal stretch about 20 km long, several types of Cenozoic deposits occur.

6.4.1 Fluvial Deposits Fluvial deposits occur above the altitude of 40 m asl and can be subdivided as follows. Above 100 m, they are probably of Pliocene (Piacenzian?) age. In Rasa (Fig. 6.6), at 124 m asl, there was a deeply weathered and very regular granite basement with a gentle slope to the east (Fig. 6.6-A). This outcrop was explored for kaolinite extraction and was

with granite boulders, C. Greyish silt layer, D. Cross-bedded layer, 1. Alkaline granite, 2. Calc-alkaline granite

90

M. A. Araújo

Fig. 6.7 Non-sorted alluvial fan deposits probably from the Gelasian over very irregular granite basement. Near the base it is possible to see alkaline granite (A) and older sediment (B, Piacencian?) boulders

already destroyed by 1991. Over the bedrock, some deeply weathered granite boulders, sometimes more than 50 cm long, were present (Fig. 6.6-B). The boulders were allochthonous since some of them were calc-alkaline (porphyritic, coarse-grained biotitic granite with mega feldspar crystals, Fig. 6.6-2), while the bedrock was alkaline medium-grained granite (Fig. 6.6-1). The boulder unit was covered by a silt layer more than 2 m thick (Fig. 6.6-C) and, in the top, a cross-bedded sandy layer was present (Fig. 6.6-D). The correlation with other deposits from north-western Portugal suggests a Piacenzian age (Pereira et al. 2000). Below, from 50 to 100 m asl, alluvial fan deposits occur. These are very heterometric, with a very irregular contact with bedrock. Sometimes, close to the bedrock, boulders from the older “Piacenzian” deposits occur (Fig. 6.7). These alluvial fan deposits may correspond to the Gelasian and are affected by compressive tectonics (Fig. 6.8).

These marine deposits were also recognized in other places along the coastline between Rio Ave and Espinho. The lowest level found in Lavadores, like many other small outcrops along the studied coastline, should correspond to the last interglacial MIS 5e, because the obtained age for an overlying aeolian deposit at S. Paio beach is 84 k BP (Fig. 6.13). Since there are at least two levels situated above this one, they may represent earlier stages, such as the MIS 7 for the level II and MIS 9 for the level I.

6.4.2 Marine Deposits

6.4.3 Eemian Beaches

Marine deposits are present below the altitude of 40 m asl and arranged as a staircase, representing successive Quaternary sea level stills-stands. The most complete sequence

Marine undercutting of the small cliffs backing the actual beaches revealed several outcrops of the last interglacial marine deposits. The analysis of the altitude of these

occurs in Lavadores, immediately south of the Douro mouth. There, within a short distance, three different levels are present: • Level I at ca. 29 m asl (Fig. 6.9), • Level II—from 17 to 19 m asl (Fig. 6.10), • Level III—from 5 to 7 m asl (Fig. 6.11).

6

The Northwest Portuguese Coast: A Longitudinal Coastline …

91

lower marine deposits, generally iron cemented, and typically covered by solifluction deposits. They are exposed whenever coastal erosion attacks younger formations (Last Glacial or Holocene) and reveals some old shore platforms and their correlative deposits. At S. Paio beach, just 100 m to the south of the previous outcrop (Fig. 6.5-D) a fossil notch, carved in fresh granite hanging at 9–10 m asl and fossilized by a marine pebble deposit can be found (Fig. 6.14). Between the notch and the former outcrop, there is a steep scarp with a straight NNE-SSW direction (see also Fig. 6.5). This last site represents the highest point in Fig. 6.12. If the 5 m and the 9– 10 m deposits are to be proven correlative, then this situation supports the hypothesis of local differential uplift (Figs. 6.13 and 6.14) At the Oporto coast, the lower marine deposits appear at 3–4 m asl (Fig. 6.11). To the south, near Espinho, at Aguda beach the Eemian marine deposit is at only 1 m asl (Fig. 6.15). If we assign all these outcrops to the last interglacial, the hypothesis of a coastal area gently subsiding to the south, towards the Lusitanian basin, seems quite plausible.

6.5

Fig. 6.8 Compressive fault (NNW-SSE direction) affecting the alluvial fan type deposit at Juncal, near Espinho

deposits across the studied coastal section shows a general decrease in elevation from north to south which may reveal vertical tectonics (Fig. 6.12). At S. Paio beach (Figs. 6.5-C and 6.13), a complex sequence is found. The base at ca. 5 m asl is a marine deposit, overlain by a solifluction unit and above it by an aeolian deposit. The later was TL dated for 84 k BP, showing that the underlying marine deposit may indeed be from the last interglacial (MIS-5e, often designed as Eemian). Hence, we assume a last interglacial age for the outcrops with a similar position throughout the studied coastline, i.e. the

Cenozoic Evolution: A Synthesis

Figure 6.16 tries to synthetize the main geomorphological features and the Cenozoic evolution of the area. The initial landscape was probably a Late Cenozoic polygenic surface upon which a braided river network, quite different from its current configuration, was present. This old fluvial network was responsible for extensive alluvial formations, at elevations probably close to the sea level (Fig. 6.6-D). Post-depositional tectonics would have created the marginal relief (inland escarpments) and hence, the topographic conditions for alluvial fan development (Fig. 6.7). After this, tectonic movements affected the alluvial fan deposits (Fig. 6.8) and possibly created the step between the continental and marine deposits. According to Cabral (1995), in the Porto area a general uplift of about 100 m occurred since the Pliocene. This uplift is one of the primary causes for the antecedence of the Douro River (Rebelo 1975; Araújo 1991). The deep down-cutting of the river reflects this antecedence of more than 70 m at the Arrábida bridge, some 2.9 km from the Douro mouth. The slopes around Arrábida and Dom Luís bridges reach 40% of declivity, this being the primary reason for the astonishing urban landscape of Oporto. The heterometric alluvial fans (Gelasian?) seem to have been affected by tectonics (Fig. 6.8). This movement, depressing the external part of the littoral platform, could be responsible for the clear separation between the fluvial deposits, which are older and higher, from the fossil beach

92

M. A. Araújo

Fig. 6.9 The oldest marine deposit with the top surface is about 29 m asl. This marine deposit is covered by solifluction deposits (Rampa Sub Ribas, Lavadores)

deposits, present below 40 m asl. The western area of the littoral platform could have been affected by the regional uplift (Cabral 1995), amplifying the eustatic variations and resulting in a staircase development (Figs. 6.9, 6.10 and 6.11). Recent tectonic movements could be responsible for the vertical displacement of the last interglacial fossil beaches (Fig. 6.12). An overall subsiding trend could explain the lower elevations that these marine platforms and deposits exhibit in the south, towards Espinho and the Meso-Cenozoic Lusitanian basin.

6.6

the remobilization of the aeolian sands, since they contain large percentage of rounded and frosted grains. These deposits are designated in geological maps as the “sandy-pelitic coverture formation”, that overlies the Eemian deposits mentioned above, corresponding to the period subsequent to the last interglacial (MIS 5e). This alternation between dunes and mass-wasting deposits is recurrent. The oldest mass-wasting deposit was 14 C dated for more than 40 k BP (Araújo 1995), while the last of such deposits found at Labruge beach and corresponding to a humid period was 14C dated for 7.8 k BP.

The Post-Eemian Remains 6.7

Cover formations deposited during the Last Glacial occur over much of the coast of northwest Portugal, mainly in the best-preserved geomorphological surfaces. During the dry periods, geomorphological activity should have been dominated by the construction of dunes (Fig. 6.13). During moister periods, part of the dune sand was remobilized to form mass-wasting solifluction-like deposits, generally rich in Paleolithic remains (Figs. 6.9 and 6.10). The microscopic analysis of the included sands confirms that they result from

Recent Coastal Dynamics: Tides, Sea Level Change and Wave Climate

Tides along the Portuguese coast are semidiurnal. The maximum tidal range at Leixões harbour, situated at the Leça River mouth, is about 3.8 m. At neap tides, the tidal range is substantially lower and equals 0.8 m. Low spring tides are very good times to explore the marine platforms and rocky notches the sea excavates, exploiting fractures and faults in hard granitic and metamorphic rocks (Fig. 6.4). In

6

The Northwest Portuguese Coast: A Longitudinal Coastline …

Fig. 6.10 Marine deposits, culminating at ca. 18 m asl, covered by solifluction deposits with vertically standing pebbles, indicating periglacial conditions during its evolution

fact, between Caminha (river Minho mouth) and Espinho, the bedrock is present below beach sands and in almost half of the area it contacts directly with the sea or outcrops beneath beach deposits. The Douro is the mightiest river in the Iberian Peninsula. It benefits from the high rainfall of northern Portugal and the peripheral mountains encircling the northern Meseta (Cantabrian Mountains, Léon Mountains and Central Iberian System). The construction of several dams for hydroelectric use retained about 86% of the sediments transported by the

93

northern Iberian rivers (Mota-Oliveira 1990). Anthropic constructions (harbours, sea defences, Fig. 6.17) also contribute to sediment deficit that affects most of the northern and central Portuguese coast, mainly to the south of Espinho, where the Variscan bedrock disappears under soft Quaternary deposits. Sea level changes have been over emphasized as the cause of beach erosion. However, it seems that only 10% of beach erosion can be attributed to sea level rise (Dias et al. 1997). Furthermore, at Leixões harbour the relative sea level appears not to be rising. On the contrary: “the mean rate of sea level change between 1906 and 2008 is −0.70 ± 0.27 mm yr−1, which does not agree with the global mean sea level rise of 1–2 mm yr−1” (Araújo et al. 2013). It means that, in a hundred years, sea level seems to have dropped by some centimetres at Leixões. The reason for that is still uncertain but the authors suggest that it is probably related to weather system and pressure changes in the North Atlantic. However, a very slow uplift may be present, as Cabral (1995) suggested for the Douro area. The sediment deficit, the soft Quaternary bedrock and possible subsidence towards the south (Fig. 6.12; Araújo 2002) might explain the dramatic erosion in most of the Portuguese coastline from Espinho to Aveiro. Wave climate has a great influence on littoral dynamics. Prevailing winds are from the NW, with resulting longshore drift being generally southwards. This creates a dissymmetry at the coastline when human constructions (harbours, littoral defences) are present, generating strong erosion south of the constructions. For example, the breakwater on Fig. 6.17 was projected to be detached from the coast to help artisanal fishing activity in the Aguda harbour. However, in some months’ time, it became connected to the beach. The accumulation against its northern face implied the downdrift erosion that undermined most of the aristocratic Granja beach summer leisure amenities (Fig. 6.17-C). The Atlantic facing northern Portuguese coastline is very energetic. From 1999 to December 2013, the Leixões wave buoy registered a maximum 16 m wave six times and almost

Fig. 6.11 Lower level marine deposit (MIS 5e) at Circunvalação beach, preserved upon Neoproterozoic gneisses and migmatites (Ossa-Morena Zone). 3–4 m asl

94

M. A. Araújo

Fig. 6.12 Elevation above the mean sea level of the Eemian marine deposits along the NW coast of Portugal, from Ave River till Espinho. Significant places discussed in the text are indicated

Fig. 6.13 Outcrop at S. Paio (C in Fig. 6.5). 1. Beach deposit, 2. Solifluction deposit (dark colour), 3. Aeolian deposit (ca. 84 k sequence suggests an Eemian age for the beach deposit

BP).

This

6

The Northwest Portuguese Coast: A Longitudinal Coastline …

95

Fig. 6.14 Paleo tidal notch at S. Paio (D, Fig. 6.5, elevation = 9 m). Right: detail of the marine deposit found a few metres to the NE, at a similar height

Fig. 6.15 The Eemian deposit at its lowest altitude, resting upon an old marine platform excavated in soft metamorphic rocks: Aguda beach ca. 1 m asl (cf. Fig. 6.12)

96

M. A. Araújo

Fig. 6.16 Proposal for the geomorphological framework in the Oporto coastal area

every year, 8 m significant-height waves occur. When the warm sectors of the polar front are active, SW winds can be very strong and can create an inversion of the littoral drift, eroding the southern areas in the lee of groins and inducing an aggravated sand-impoverishment. This happened with a great intensity in January 2014 at Furadouro, due to the Hercules storm, destroying a part of the existing defences. Long-period waves, coinciding with high spring tides climbed the coastal defences and the marginal road. Thus, the seawater invaded the village, which is situated between 3 and 5 m asl.

6.8

Conclusions

The contrast of the northern Portuguese coast with the Galician coastline, north of Cape Silleiro, is one of the most striking aspects of the north-western Iberian coast. It is a geomorphological problem that intrigues researchers from each side of the political border. The different development of the littoral platform from Cape Silleiro to Espinho also

suggests a different tectonic evolution. However, rather than the simplistic explanation of the subsidence of the Galician coast, it is thought that these stretches may have worked as slowly moving blocks during the Quaternary. They interacted with sea level changes creating several models of staircase development in the different stretches of the north-western coastal area of Portugal. At the end, an old idea of Carlos Teixeira (1944) is brought back into spotlight, but the blocks we consider are quite different from the original simplistic model. There are probably smaller blocks that result from the interference of transverse and longitudinal fault directions, reactivated during the Cenozoic (Fig. 6.2). The longitudinal directions linked to Porto-Tomar fault predominate to the south of Cape Silleiro (Fig. 6.2). To the north, the Galician coastline is mostly shaped by transverse and oblique faults (Fig. 6.2). The movement of these blocks continued throughout the Quaternary, interfering with eustatic sea level changes. So, the generalization about the origin “of regularly staircase arranged deposits following the ‘classic’ altitude for the Mediterranean”, still present in geological maps more than

6

The Northwest Portuguese Coast: A Longitudinal Coastline …

97

Fig. 6.17 Aguda-Granja beach (Google Earth Pro images, a 07/09/2003; b 22/06/2012). The beach erosion produced by the Aguda breakwater construction. c The cliff, more than 2 m high on the Granja beach, October 2006

50 years old (Costa and Teixeira 1957; Teixeira et al. 1962) is definitely outdated. Acknowledgements We deeply acknowledge the kindness and the 14 C dating performed by Professor Monge Soares (Instituto Superior Técnico, Campus Tecnológico e Nuclear) from Labruge beach solifluction coverture. We are also deeply grateful for editors’ revision of the text.

References Alves A (1996) Causas e processos da dinâmica sedimentar na evolução actual do litoral do Alto Minho. Ph.D. thesis, Minho University, p 438 Araújo MA (1991) Evolução Geomorfológica da Plataforma litoral da região do Porto. Ph.D. thesis, Physical Geography, FLUP, Porto University, p 534 Araújo MA (1995) Os fácies dos depósitos würmianos e holocénicos e as variações climáticas correlativas na plataforma litoral da região do Porto. VI Colóquio Ibérico de Geografia, proceedings, vol II, pp 784–794 Araújo MA (2002) Relative sea level, diastrophism and coastal erosion: the case of Espinho (Portuguese NW coast). In: “Littoral 2002”, proceedings, vol 2. Associação Eurocoast, Portugal, pp 125–132

Araújo IB, Bos MS, Bastos LC, Cardoso MM (2013) Analysing the 100-year sea level record of Leixões, Portugal. J Hydrol 481:76–84 Blanco Chao R (1999) Formas e procesos geomorfológicos diferenciados en las costas de Galicia: morfodinnámica y evolución de un sector de costa rochosa: cabo Silleiro-A Garda (Pontevedra). Ph.D. thesis, Universidade de Santiago de Compostela, p 192 Cabral J (1995) Neotectónica de Portugal Continental, vol 31. Memórias do Instituto Geológico e Mineiro, Lisboa, pp 1–251 Carvalhido R (2012) O Litoral Norte de Portugal (Minho-Neiva): evolução paleoambiental quaternária e proposta de conservação do património. Ph.D. thesis, Minho University, p 606 Chaminé HI (2000) Estratigrafia e estrutura da faixa metamórfica de Espinho–Albergaria-a-Velha (Zona de Ossa-Morena): implicações geodinâmicas. Ph.D. thesis, Porto University, p 497 Costa JC, Teixeira C (1957) Carta Geológica de Portugal na escala de 1:50000, notícia explicativa da folha 9-C (PORTO). Serviços geológicos de Portugal, Lisboa, p 38 Dias JMA, Rodrigues A, Magalhães F (1997) Evolução da linha de costa, em Portugal, desde o último máximo glaciário até à actualidade: síntese dos conhecimentos. Estudos do Quaternário, 1. APEQ, Lisboa, pp 53–66 Ferreira AB (1983) Problemas de evolução geomorfológica quaternária do noroeste de Portugal, Cuadernos do Laboratorio Xeoloxico de Laxe, nº 5. VI Reunion do Grupo Español de Traballo de Quaternario, A Coruña, pp 311–330 Ferreira AB (1991) Neotectonics in Northern Portugal—a geomorphological approach. Z Geomorph NF (Supl-Bd 82):73–85

98 Granja H (1990) Repensar a geodinâmica da zona costeira. O passado e o presente. Que futuro? (O Minho e o Douro Litoral). Ph.D. thesis, Minho University, p 347 Mota-Oliveira IB (1990) Erosão costeira no litoral Norte: considerações sobre a sua génese e controlo, Actas do 1º Simpósio sobre a protecção e revalorização da faixa costeira do Minho ao Liz. Inst. Hidráulica e Recursos Hídricos, Porto, pp 201–221 Nonn H (1966) Les régions cotières de Galice (Espagne) - Étude géomorphologique. Pub. Fac. Lettres Univ. Strasbourg, p 584 Pereira DI, Alves MIC, Araújo MA, Proença Cunha P (2000) Stratigraphy and paleogeographic interpretation of the north Portugal continental Cenozoic, vol 14. Ciências da Terra, UNL, pp 73–84 Rebelo F (1975) Serras de Valongo - Estudo de Geomorfologia, Suplemento de “Biblos”, vol 9. University of Coimbra, 194 p

M. A. Araújo Ribeiro A, Antunes MT, Ferreira MP, Rocha RB, Soares AF, Zbyszewski G, Moitinho De Almeida F, Carvalho D, Monteiro JH (1979) Introduction à la Géologie générale du Portugal. Serviços Geológicos de Portugal, Lisboa, p 114 Ribeiro O, Lautensach H, Daveau S (1991) Geografia de Portugal. I. a posição geográfica e o Território, Lisboa, Ed. Sá da Costa, 2ª edn., p 334 Teixeira C (1944) Tectónica plio-pleistocénica do Noroeste peninsular, Bol. Soc. Geol. de Portugal, vol IV. Fasc. I e II, Porto, pp 1–25 Teixeira C, Perdigão J, Assunção CT (1962) Carta Geológica de Portugal à escala de 1/50000. Notícia explicativa da folha 13-A (Espinho). Serviços Geológicos de Portugal, Lisboa, p 28

7

The Tróia Peninsula—An Aeolian Sedimentological Legacy Carlos Neto, Miguel Geraldes, and Diana Almeida

Abstract

7.1

The integration of studies from fields, such as geomorphology, palynology, history, archaeology and phytogeography, enables assessing the genesis and evolution of the most prominent Portuguese sand spit—the Tróia Peninsula. Data suggests that the spit has formed from Grimaldian dunes converted into barrier islands during the Holocene transgression, and coalesced by the accumulation of sediments transported by the northbound longshore drift. The Tróia Peninsula is integrated in one of the most important Portuguese natural protected areas. It holds a set of flora and vegetation of paramount relevance towards protection and conservation in accordance with the Natura 2000 Network. Its position acts as a barrier against the Atlantic Ocean, having allowed the development of the Sado estuary lagoon, which contains mud flats and salt marsh ecosystems, habitats for a wide range of flora and fauna, some of which with special protection status. The Tróia Peninsula forms indeed a natural protective barrier for the Natural Reserve of the Sado Estuary. The genesis of the peninsula, discussed in the present work, combined with the fact that it is made up exclusively of sand, make it very vulnerable to environmental changes, including sea level rise. Keywords




Sand spit Coastal drift Barrier islands




Holocene




Sea level rise

C. Neto (&)
M. Geraldes
D. Almeida Centre of Geographical Studies, Institute of Geography and Spatial Planning, University of Lisbon, Lisbon, Portugal e-mail: [email protected] M. Geraldes e-mail: [email protected] D. Almeida e-mail: [email protected]




Introduction

With a length of 27 km, a maximum width of 1.8 km and 27 m of maximum altitude, the Tróia Peninsula corresponds to the northern sector of the Tróia-Sines coastal arc (Fig. 7.1). It shows a NNW–SSE direction in the southern sector and a NW–SE in the northern sector and is made up of sandy sediments in the form of beaches and dunes, which enclose the salt marshes of the Sado estuary eastwards. It is the longest peninsula of the Portuguese coast and is embedded in a territory of greater ecological value in south-western Europe. The structure of the peninsula forms a natural barrier against the penetration of oceanic waves, generating a lagoonal estuary in the terminal section of the Sado River. The estuary stretches from Alcácer do Sal to Setúbal-Outão and Tróia, where it reaches the sea through the outlet named Barra do Sado (Figs. 7.1 and 7.2). Due to biogeographic, geomorphological and climatological reasons, the Sado region, which includes the Tróia Peninsula, has three protected areas (the Arrábida Natural Park, the Sado Estuary Natural Reserve and the Natura 2000 Site Comporta/Galé). Together, these three protected areas contain an important part of the Portuguese floristic and faunal heritage, being thus of major significance for protection and conservation. Albeit being on the beaches and dunes with high biological values for protection and conservation (including a high number of Lusitanian endemic species), only a small portion of the Tróia Peninsula is protected and included in the Sado Estuary Natural Reserve (Figs. 7.3, 7.4 and 7.5). The remaining area is reserved for tourism estate projects that started during the 1970s and that, being prior to the establishment of the Reserve (1980), could not be avoided. Associated with its natural wealth, now largely obliterated, the Tróia Peninsula stands as a fragile territory, because once it is solely constituted by sands, it critically depends on maintaining a balance in the sedimentary budget that current and near-future environmental changes seem to put in jeopardy, enhancing a trend of

© Springer Nature Switzerland AG 2020 G. Vieira et al. (eds.), Landscapes and Landforms of Portugal, World Geomorphological Landscapes, https://doi.org/10.1007/978-3-319-03641-0_7

99

100

C. Neto et al.

Fig. 7.1 Tróia Peninsula location and its insertion into the Sado estuary region

Fig. 7.2 Northern tip of the sand spit of Tróia and the Barra do Sado channel where the lagoonal estuary waters of the vestibular section of the River Sado flow into the Atlantic Ocean

7

The Tróia Peninsula—An Aeolian Sedimentological Legacy

101

Fig. 7.3 Eastern sector of Tróia Peninsula and the contact between the sand spit with grey and green dunes and the salt marshes of the Sado estuary

erosion that has been installed on most of the sandy coastline of mainland Portugal. According to Ferraz et al. (2010), the oceanic sector of the northern tip of the peninsula, that extends for 2.5 km, is a prograding coast (data for 1947– 2005). However, south of this sector the coastal dynamics becomes erosional, a trend which increases southward. In the northern part of the Tróia Peninsula, but in the estuary sector (Ponta do Adoxe), the sedimentary dynamics is also erosional, with 5 m of foredune recession between 2002 and 2005 (Silveira et al. 2011). These erosional processes on the estuarine bank led to the implementation of artificial sand nourishment measures with sand carried from the beach and the foredune with 286,000 m3 of sand placed alongshore for 1700 m in 2006 and 2007. Among others, these measures aimed to protect the Tróia Roman archaeological site (Silveira et al. 2011).

7.2

The Littoral Drift and the Formation of the Tróia Spit

The building up of sand spit and coastal dune ridges in the terminal sectors of the rivers along the Portuguese west coast typically obstructs stream flow and shifts the rivers either north- or southwards. Such a process leads to the

rectilinearization of the coastline (Moreira 1985). During the Holocene, the trend towards rectilinearization is especially evident after 4000–5000 BP, when the rates of sea level rise were strongly attenuated (Bao et al. 1999; Day et al. 2000; Psuty and Moreira 2000; Andrade et al. 2007) (Table 7.1). Sand spit formation is due to the dynamic imbalance between the longshore drift and fluvial-estuarine currents, which ultimately lead to sediment deposition (Moreira 1985). In the Portuguese west coast, the longshore drift shows a predominant north–south direction during most of the year (Moreira 1985), which is a result of the dominance of ocean waves arriving from northwest (Carvalho and Barceló 1966). In fact, according to Costa et al. (2001), the prevailing wave directions are northwest and west (97%), with southwest representing only 3% of the events. The north–south drift is morphogenetically effective in the straight sectors of the shoreline, mainly to the north of Cape Carvoeiro (Moreira 1985). It is noteworthy that in the capes, northwest waves undergo diffraction and thus propagate ashore from west to southwest, with the resulting longshore drift from south to north, but with weaker morphogenetic power (Quevauviller 1985). Southwest events are more frequent during winter and spring, inducing a south to north longshore drift with strong morphogenetic power. However, independently of the drift direction, the sheltered coastal

102

C. Neto et al.

Fig. 7.4 Peninsula of Troia in the Atlantic sector. We can see the embryonic dunes (nekas) in the high beach with Elymus farctus subsp. boreo-atlanticus (Simonet & Guin.) Melderis. To the interior the white dunes (instable dunes) with Ammophila

arenaria subsp. arundinacea H.Lindb. and the grey dune in the innermost sector dominated by two important endemism’s (Thymus carnosus Boiss. and Armeria pungens (Link) Hoffmanns. & Link)

sections south of the Espichel and Roca capes always show a northwards longshore drift (Moreira 1985; Moreira 1988; Day et al. 2000; Silva et al. 2007; Andrade et al. 2007). The formation of the Tróia Peninsula is related to the northerly longshore drift, whose erosion-accumulation balance varies seasonally (Moreira 1985). According to this author, winter and spring are dominated by erosion of the sandstone cliffs occurring south of Praia do Pego (Fig. 7.1), of the beaches and sand spit and by the offshore migration of the longshore bars. From spring to late autumn, the morphogenetic balance tilts towards accumulation and thus sand spits and longshore bars tend to grow. This process led to the formation and growth of the Tróia Peninsula and to the transportation of mostly sandy sediments, up to the northern tip of the peninsula and is responsible for its hook form and for sediment accumulation in the channel of the Barra do Sado, which needs cyclical dredging to keep the port of Setúbal open (Loureiro 1904). Miranda et al. (2007) emphasized the importance of the northerly longshore drift current in sediment transport along the Tróia-Sines arc and, based on 72 profiles, identified the main sediment sources: the inner-shelf, the Mio-Pliocene coastal cliffs, the Sines

subvolcanic massif and bivalvia communities existing in the Tróia Peninsula and Sado estuary (Miranda et al. 2007).

7.3

Holocene Sea Level and the Formation of the Tróia Peninsula

7.3.1 The Contribution of Geomorphology and Palynology The exact age of the Tróia Peninsula remains uncertain. However, several studies based on geomorphology (Moreira 1985; Dias et al. 2000; Psuty and Moreira 2000; Andrade et al. 2007; Rebêlo et al. 2013), archaeology (Étienne et al. 1994; Étienne and Mayet 1997; Almeida 2009), palynology (Mateus 1992) and biogeography (Neto 2002; Neto et al. 2009) underline that a configuration close to the current one has been reached in between 2000 and 3000 years BP. However, as argued by Moreira (1987), the Tróia Peninsula was being assembled from pre-existing barrier islands, some of which would be submerged during high tide. There was a moment of special significance at 2600 BP,

7

The Tróia Peninsula—An Aeolian Sedimentological Legacy

103

Fig. 7.5 Grey dune in the central sector of the Troia Peninsula. The grey dune has a high number of endemic species and is therefore considered a priority habitat of the Natura 2000 Network [2130 *Fixed coastal dunes with herbaceous vegetation (grey dunes)].

a date that, after Psuty and Moreira (2000), pinpoints the end of the period of regular rate of sea level rise (2 mm/year) that occurred from 6300 to 2600 BP (Table 7.1). Cores from different parts of the Sado estuary have shown evidence that the rate of sea level rise slowed down and ‘the horizontal expansion of high marsh could have begun at about 2600 years ago’ (Psuty and Moreira 2000, p. 136). This is the date determined as the beginning of the marsh expansion inside the estuary, which agrees with core data by Mateus (1992) in some of the Sado mires (Travessa and Formosa lagoons—Fig. 7.1) showing an increase of freshwater plants. Yet, given the extent of the peninsula, its formation may not accurately coincide with that time, but there are several indications that put forward the hypothesis that at least in some sectors sediment deposition and its emersion were older (Moreira 1985). Indeed, in the southern sector, where the peninsula roots into the mainland, the same author identified sandy deposits of cold and dry periods of the last glaciation in the banks of the Formosa and Travessa lagoons (Fig. 7.1). These poorly sorted medium-size sands,

subangular to sub-rounded, yellow ochre grained, form the bulk of some sectors of the Tróia Peninsula. In the southern sector, the Formosa and Travessa lagoons (located east of the coastal dunes) show peat-rich structures (Mateus 1992). The deepest levels of the cores, aged 7580 ± 70 years, unveil vegetation dominated by willows (Salix spp.), alders (Alnus glutinosa), sweet gale (Myrica gale), and mosses (Sphagnum spp.), identical to that which currently characterizes the sub-littoral mires in the region of Sado. This shows that at the time, the sea water did not affect the region. Despite that, the rapid rise in sea level during the early Holocene transgression left a signature in the type of vegetation that colonizes the two lagoons. During the phases with highest rates in sea level rise, the ascent of the saline groundwater table was faster than the mire growth, with small flood episodes appearing in the record, coeval with the expansion of typical deep-water communities (Potametea, Lemnetea). In the periods when the ocean waters entered the valley of the Carvalhal creek (especially during the estuary stage, between 5750 and 4100 BP), there was an expansion of

104 Table 7.1 Summary of the main periods and events of Tróia Peninsula formation

C. Neto et al. Cold and dry periods of the last glaciation

Sandy deposits of the banks of the Formosa and Travessa lagoons and Caldeira with yellow ochre colour (ferric iron enrichment— podzolization processes)

Moreira (1985, 1992), Neto (2002)

7580 ± 70 years

Vegetation dominated by willows (Salix spp.), alders (Alnus glutinosa), sweet gale (Myrica gale) and mosses (Sphagnum spp.), identical to that which currently characterizes the sub-littoral mires in the region of Sado

Deepest levels of the palynological cores of Mateus (1992) in Travessa and Formosa mires Neto (2002)

6300–2600 BP

Period of regular rate of sea level rise (2 mm/year) Barrier islands formed by the highest ancient dunes of cold and dry periods of the last glaciation Island mentioned in the Ora Maritima based on the sea traders’ handbook Massiliote Periplus

Cores from different parts of the Sado estuary. Psuty and Moreira (2000) Sea traders’ handbook Massiliote Periplus dated from the last quarter of sixth century BC

5750–4100 BP

Estuary stage (outpour of salt water over the entire area occupied by the current Sado estuary) Expansion of halophile vegetation (replacing the fresh water vegetation) in the Palynological cores of Mateus (1992)

Palynological cores of Mateus (1992) in Travessa and Formosa mires Psuty and Moreira (2000), Andrade et al. (2007)

4000–5000 BP

Trend towards rectilinearization is especially evident

Psuty and Moreira (2000), Andrade et al. (2007), Bao et al. 1999)

4100 BP

Holocene grey sands (recent dunes) have begun to accumulate, and spit formation start Replacement of the salty series by peatland vegetation in mire lagoons

Palynological cores of Mateus (1992) in Travessa and Formosa mires Cores from different parts of the Sado estuary (Psuty and Moreira 2000)

2600 years BP

Sea level rise slowed down, and the horizontal expansion of high marsh have begun

Cores from different parts of the Sado estuary (Psuty and Moreira 2000) Palynological cores of Mateus (1992) in Travessa and Formosa mires

2000 and 3000 years BP

Configuration of the spit close to the current one

Increase of freshwater plants. Palynological cores of Mateus (1992) in Travessa and Formosa mires

Currently

Tendency of erosion in much of the extent of the Tróia Peninsula and erosion of salt marshes in the Sado estuary (Shortage of sediment and sea level rising)

Moreira (1985, 1986, 1992), Moreira and Psuty (1993), Psuty and Moreira (2000), Miranda et al. (2007)

halophile vegetation. The outpour of salt water over the entire area occupied by the current Sado estuary led to a drastic change in the cores (Mateus 1992), so that the mire freshwater vegetation was replaced by a salty series (of salt marshes) dominated by Chenopodiaceae. At the end of this period, there was again a replacement of the salty series by peatland vegetation. This shows that since 4100 BP, a line of dunes settled on the ocean side of the peninsula, preventing the direct input of ocean waters. This process enabled the Formosa and Travessa lagoons to turn into coastal lagoons first and later to be

converted into peaty depressions cut off from the sea and experiencing peat accumulation until the present day.

7.3.2 The Contributions of History and Archaeology According to Moreira (1985) and Psuty and Moreira (2000), during the estuary phase reported by Mateus (1992), the Tróia Peninsula developed from a set of barrier islands

7

The Tróia Peninsula—An Aeolian Sedimentological Legacy

105

Fig. 7.6 Ancient dunes of cold and dry periods of the last glaciation near Caldeira de Tróia close to the northern tip of the Troia Peninsula. These old dunes present a yellow ochre colour (ferric iron enrichment due to podzolization processes) and are colonized by an important

endemism from Sado region (Juniperus navicularis Gand.) which forms a priority habitat of the Natura 2000 Network (2250 *Coastal dunes with Juniperus spp.)

formed by the highest ancient Grimaldian (dunes deposits of cold and dry periods of the last glaciation), which, by the action of longshore drift, merged bit by bit through the deposition of sediments. Besides the outcrops that can be observed on the flanks of the Travessa and Formosa lagoons, the Grimaldian sands are also visible in the northern tip of the Tróia Peninsula, near Caldeira (Figs. 7.1 and 7.6) (Moreira 1985). These deposits may have constituted an island during the estuary stage (5750–4100 BP). The existence of this island is mentioned in the Ora Maritima (The Maritime Shores) written by the Roman poet Rufus Avienus, an author of the fourth century AD, which was based on the sea traders’ handbook Massiliote Periplus for cabotage navigation, dated from the last quarter of sixth century BC (now lost), in which the sea routes around Iron Age Europe were described by Phoenician traders in their journeys. Avienus’ text contains an account of a sea voyage from Massilia (Marseille) along the western Mediterranean, describing seaways going northwards from Tartessus (Southern Spain) along the coast (the Atlantic Façade of the European coast), reaching as far as the British Isles. In the

littoral corresponding to the coast of the Sado estuary, he described an island and also the ‘dirty water, which become thick’, but currently there is no island in the littoral of Sado. Should such an island exist at 2600 years BP, it would have corresponded to the Grimaldian sands that, due to rapidly rising sea level, would have constituted a barrier island during the estuary stage reported by Mateus, which, in turn, would have been incorporated into the structure of the Tróia Peninsula in the early first century AD (Quevauviller 1985; Étienne et al. 1994).

7.3.3 The Contributions of Phytogeography Another argument in favour of the existence of the above-mentioned island and supporting the hypothesis that ancient Grimaldian dunes, converted to barrier islands by the Holocene transgression, formed the skeleton of the Tróia Peninsula, comes from phytogeography. Actually, the Grimaldian deposits near Caldeira de Tróia close to the northern tip as reported by Moreira (1987) are occupied by

106

an endemic juniper distributed along the Sado and Costa da Galé (Portugal). This is the only place where this plant occurs on the Tróia Peninsula (between Comporta village and the northern tip). The same juniper occurs also in outcrops of Grimaldian sands in the southern sector (Fig. 7.4). The association between the occurrence of Grimaldian sands and populations of Juniperus navicularis happens all over the Sado and Costa da Galé. J. navicularis is a relict species that is clearly not adapted to current climate conditions, not being able to multiply in nature by seed, but only under the vegetative form (by rhizome). The existing populations are thus protected by the Natura 2000 legislation, according to which it was towered as a species of priority protection. The existence of this plant on the Tróia Peninsula associated with the Grimaldian deposits allows for hypothesizing that its colonization must have occurred in relatively dry and cold stadials of the Pleistocene. The genus Juniperus has about 80 species throughout the world, mainly distributed in semi-arid regions (Loureiro et al. 2007), generally needing cold conditions for a certain time span for its seeds to break dormancy and hence germinate (Adams 2004; Broome 2003; Van Auken et al. 2004; Tilki 2007). To this extent, J. navicularis should have had its optimum during

C. Neto et al.

the cold and dry climate stadials of the Pleistocene; therefore, its expansion is no longer possible due to lack of conditions for seed germination. The present-day populations are thereupon virtually restricted to the Grimaldian sands (podzolized during the ‘Atlantic’ Holocene climatic chron with acidophilus heather/gorse vegetation) and are absent on the Holocene grey sands, which have begun to accumulate at 4100 BP (according to Mateus 1992), from south to north and gradually united the barrier islands formed by the ochre coarse Grimaldian sands. Despite lacking genetic studies to support this hypothesis, the Sado juniper (J. navicularis) seems to have evolved from J. oxicedrus of Trás-os-Montes region (NE of Portugal). Franco described in 1963 the population of Sado as a subspecies of J. oxicedrus of NE Portugal (Juniperus oxicedrus subsp. transtagana meaning beyond the Tagus River (south of Tagus). The subsp. oxicedrus colonizes the quartzite ridges of Vila Velha de Rodão in central Portugal in what is probably a migratory route to the south, through which the species has reached the far-off sandy Sado estuary. Given the ecological characteristics of the species optimum (especially the need of cold temperatures during the winter) and its particular resistance to dry conditions, it is possible to state

Fig. 7.7 Horizontal and vertical retreat of the salt marsh (in Sado estuary) in Carrasqueira (fishing palaphitic harbour) due to the combined effect of sea rise level and fishermen activity

7

The Tróia Peninsula—An Aeolian Sedimentological Legacy

that the colonization of the Sado dune fields would have occurred during the Quaternary cold and dry stadials whilst habitat availability was immense.

7.4

Final Remarks

The integrated analysis of all the information available from studies in several scientific areas (geomorphology, palynology, history, archaeology and phytogeography) made it possible to picture how the Tróia Peninsula’s build-up process occurred, included in one of the most important and sensitive natural areas in mainland Portugal. The understanding of how the Tróia Peninsula was formed and its recent dynamics are key factors affecting the level of resilience that it can have against the expected environmental changes in the next decades, which will reflect a strong local impact due to rising sea level (Ferreira et al. 2008). The Tróia sand spit is a natural barrier to protect one of the most important Portuguese wetlands (the Sado estuary). The knowledge of the Tróia Peninsula forming process enables stakeholders to design, with greater certainty, land-use masterplans and is the basis for the territorial planning of this meaningful natural area. On the other hand, the study of

107

how the Tróia sand spit evolved during the Holocene helps sustaining the conception of its great weakness and, therefore, justifies its high value towards protection and conservation. The major importance that the Tróia Peninsula had in mitigating the tsunami associated with the 1755 earthquake must be emphasized. The study by Rebêlo et al. (2013), using optical stimulated luminescence to determine the age of the sand dunes of the northern tip of the Tróia Peninsula, concluded that the tsunami destroyed a part of the dune fields, which were about 1000 years old, but part of the inner sector in contact with the estuary and salt marshes remained intact. In this way, the nonexistence of tsunami impact traces in inner Sado estuary becomes coherent. This work explains the importance of the Tróia Peninsula in the mitigation of extreme events and is therefore very important in protecting the inland ecosystems. These include not only the salt marshes (Figs. 7.7 and 7.8), but also marshes and rich fen complexes (sub-littoral mires), relict and rare ecosystems in southern Europe whose study has been of utmost importance in the understanding of climate fluctuations associated with the last glaciation stadials and the wetter early chrons of the Holocene (Neto et al. 2009).

Fig. 7.8 Retreat of the high salt marsh (the low salt marsh has been eroded) by gulleying followed by collapse of blocks of peat in the salt marsh of Sado estuary

108

References Adams RP (2004) Junipers of the World: the genus Juniperus. Trafford Publishing, Vancouver, BC Almeida JPL (2009) A necrópole romana da Caldeira, Tróia de Setúbal. Escavações de Manuel Heleno das décadas de 40-60 do século XX. Master Dissertation. Pré-História e Arqueologia, Faculdade de Letras. University of Lisbon Andrade C, Pires HO, Taborda R, Freitas MC (2007) Projecting future changes in wave climate and coastal response in Portugal by the end of the 21st century. J Coast Res SI 50:253–257 Bao R, Freitas MC, Andrade C (1999) Separating eustatic from local effects: a late-Holocene record of coastal change in Albufeira Lagoon, Portugal. The Holocene 9:341–352 Broome A (2003) Growing juniper: propagation and establishment practices. Forestry Commission Information Note 50:1–12 Carvalho JR, Barceló JP (1966) Agitação marítima na costa W de Portugal metropolitano. Memórias do LNEC 290:1–34 Costa M, Silva R, Vitorino J (2001) Contribuição para o estudo do clima de agitação marítima na costa portuguesa, 2nd Jornadas Engenharia Costeira Portuguesas, Sines, 20 pp (CD-ROM) Day J, Psuty N, Perez B (2000) The role of pulsing events in the functioning of coastal barriers and wetlands: implications for human impact, management and the response to sea level rise. In: Weinstein M, Kreeger D (eds) Concepts and controversies in tidal marsh ecology. Kluwer Academic Publishers, Dordrecht, pp 633–660 Dias JMA, Boski T, Rodrigues A, Magalhães F (2000) Coast line evolution in Portugal since the Last Glacial Maximum until present —a synthesis. Mar Geol 170:177–186 Étienne R, Makaroun Y, Mayet F (1994) Un grand compléxe industriel à Tróia (Portugal). Diff. E. de Boccard, Paris Étienne R, Mayet F (1997) La place de Tróia dans l’industrie romaine des sailasons de poisson. Itinéraires Lusitaniens. Paris [s.n.], pp 195–120 Ferraz M, Rebêlo L, Brito P, Costas S (2010) Tróia peninsula north sector evolution. Geosci On-line J 12(3):1–4 Ferreira Ó, Dias JÁ, Taborda R (2008) Implications of sea-level rise for continental Portugal. J Coastal Res 24(2):317–324 Loureiro A (1904) Os Portos Marítimos de Portugal e Ilhas Adjacentes. Lisboa. Imprensa Nacional, Vol I e II Loureiro J, Capelo A, Brito G, Rodrigues E, Silva S, Pinto G, Santos C (2007) Micropropagation of Juniperus phoenicea from adult plant explants and analysis of ploidy stability using flow cytometry. Biol Plant 51(1):7–14

C. Neto et al. Mateus JE (1992) Holocene and present-day ecosystems of the Carvalhal region, southwest Portugal. Ph.D. Dissertation, University of Lisbon Miranda P, Jesus C, Bernardes C, Rocha F (2007) Interpreting beach sedimentary dynamics between Tróia and Sines (SW Portugal) using heavy minerals and textural analysis. J Coast Res SI 50: 599–603 Moreira ME (1985) A evolução do litoral a partir da análise da rede hidrográfica. O exemplo da Ribeira da Comporta. Lisboa. Actas da 1ª Reunião do Quaternário Ibérico, Vol I Moreira ME (1986) Man-made disturbances of the Portuguese salt-marshes. Thalassas 4(51):43–47 Moreira ME (1987) Estudo fitogeográfico do ecossistema de sapal do Estuário do Sado. Finisterra 22(44):247–303 Moreira ME (1988) Seasonal processes of the beach-dune system on the western coast of Portugal. J Coast Res SI 3:47–51 Moreira ME (1992) Recent salt marsh changes and sedimentation rates in the Sado Estuary. J Coastal Res 8(3):631–640 Moreira ME, Psuty N (1993) Sedimentação Holocénica no Estuário de Sado. Nota preliminar. Actas da 3ª Reunião do Quaternário Ibérico, Coimbra, pp 289–297 Neto C, Arsénio P, Monteiro-Henriques T, Sérgio C, Costa JC (2009) Novas ocorrências de Spagnum auriculatum no Sul de Portugal. Acta Bot Malacitana 34:210–215 Neto C (2002) A Flora e a Vegetação do superdistrito Sadense (Portugal). Guineana 8:1–269 Psuty N, Moreira ME (2000) Holocene sedimentation and sea level rise in the Sado Estuary. Portugal J Coast Res 16(1):125–138 Quevauviller P (1985) Estuário do Sado – Costa da Galé. Análise Geomorfológica e estudo de alguns aspectos sedimentológicos. Internal report for the Direcção Geral de Ordenamento, p 85 Rebêlo L, Costas S, Brito P, Ferraz M, Prudêncio MI, Burbidge C (2013) Imprints of the 1755 tsunami in the Tróia Peninsula shoreline, Portugal. J Coast Res SI 65:814–819 Silva A, Taborda R, Rodrigues A, Duarte J, Cascalho J (2007) Longshore drift estimation using fluorescent tracers: new insights from an experiment at Comporta Beach, Portugal. Mar Geology 240 (1–4):137–150 Silveira T, Kraus N, Psuty N, Andrade F (2011) Beach Nourishment on Tróia Peninsula Portugal. J Coast Res SI 59:173–180 Tilki F (2007) Preliminary results on the effects of various pre-treatments on seed germination of Juniperus oxycedrus L. Seed Sci Technol 35(3):765–770 Van Auken OW, Jackson JT, Jurena PN (2004) Survival and growth of Juniperus seedlings in Juniperus woodlands. Plant Ecol 175: 245–257

8

The Southwest Coast of Portugal Ana Ramos-Pereira and Catarina Ramos

Abstract

The southwest coast of Portugal is rich in natural heritage and is framed within the Southwest Alentejo and Vicentine Coast Natural Park since 1995. Its complex geomorphological evolution reflects the geostructural position near the contact of the African plate and the Iberian microplate, and the relative sea-level changes and characteristics of the coastal systems. The major landform of the region is the Littoral Platform, tilted to the northwest and folded by meridian normal tectonic faults. These accidents cross a left lateral strike-slip fault—the longest NE–SW tectonic Iberian fault structure extended from Ávila (Placencia) to Messejana and to the continental margin. The Pliocene and Pleistocene sediments occurring in the Littoral Platform show a composite evolution. Seaward, the platform is undercut by the coastal cliff, which is the prevailing present-day coastal feature, with narrow beaches, in a coast with sedimentary deficit in the longshore drift. Keywords

Littoral platform sea-level change

8.1








Sediments Tectonics Natural park




Relative

Regional Setting

The Portuguese southwest coast extends from Porto Covo (Sines, 90 km south of Lisbon) to the southern coast of Portugal, being here included until the city of Lagos (Fig. 8.1). It is a predominantly rural area with low population density ( 7 earthquakes during the last 14.5 ka and estimated a slip rate of 0.3–0.5 mm/year and 2–3 m of displacement per event. The slip rate is consistent with the estimation of 0.2–0.5 mm/year in the last *2 Ma based on the geomorphological displacement and the stratigraphic references (Cabral 1989, 1995, 2012; Cabral et al. 2010; Perea et al. 2010). The small Bragança, Vilariça, and Longroiva Cenozoic basins are associated with the Vilariça left-lateral strike-slip fault and related to transpressional tectonic regimes (De Vicente et al. 2011; Pais et al. 2012). To the west, the borders of the larger Mirandela basin are imprecise (Fig. 11.1), though a wider interpretation suggests a tectonic basin developed between the referred main faults. According to Pais et al. (2012), all these small basins could be seen as tectonically preserved outcrops in the vicinity of transtensional/transpressional faults that crosscut the large domain of the Douro Cenozoic basin.

The Vilariça basin is the largest of the strike-slip basins, 20 km long and 3 km wide. The depression closes in the north against the Bornes push-up. In the south, the Vilariça fault controls the Douro River path generating the Vale Meão incised meander (Fig. 11.4). The basin’s flat bottom is tilted eastwards to the Vilariça scarp, which imposes a difference of 300–400 m relative to the Iberian Meseta surface (Pereira and Azevêdo 1995) (Fig. 11.5). The Serra de Bornes is the clearest compressive structure interpreted as a push-up developed on the restraining bends of the Vilariça fault (Cabral 1989, 1995, 2012) (Figs. 11.1 and 11.6). It has maximum altitude of 1200 m and an asymmetric shape caused by the fault scarp on the western border (Cabral 1985; Pereira 1997; Pereira et al. 2000). The Serra da Nogueira, with a similar NNE-SSW disposition (Fig. 11.1), though located on the western margin of the Vilariça fault, is also interpreted as a compressive structure. It reaches 1320 m asl and also presents an asymmetric profile, limited by the Vilariça fault scarp in the east and by a smooth surface slightly incised by rivers in the west. The Vilariça strike-slip basin is one of the geosites of the “Iberian Massif Landscape and Fluvial Network in Portugal” framework, in the context of the Portuguese inventory of the geological heritage (Pereira et al. 2015). It is the best example of a strike-slip basin including sediments, a clear scarp fault and the tectonic control of the drainage system in Portugal. The Longroiva strike-slip basin, located south of the Douro River, is also induced by the Vilariça fault. Despite

144

D. I. Pereira and P. Pereira

Fig. 11.4 Panoramic view of the Vilariça basin to the south, where the Vilariça fault controls the Douro River course

Fig. 11.5 Vilariça fault scarp limiting the Vilariça basin to the east and imposing a difference of 300–400 m between the flat valley and the Iberian Meseta surface

11

The Geomorphological Landscape of Trás-os-Montes and Alto Douro

145

Fig. 11.6 Bornes Mountain, a push-up relief developed on the restraining bends of the Vilariça fault

being smaller, 6 km long and 600 m wide, the NNE-SSW basin has similarities with the Vilariça basin regarding landforms and deposits. It is bounded by steep granite slopes in the east and by a shale slope that expresses the western part of the Meseta surface in the west (Ferreira 1978). A clear NW-SE fault scarp also limits the Longroiva basin to the south (Cunha and Pereira 2000). These small basins preserve Cenozoic sediments, mostly accumulated in response to tectonic movements that occurred between the Tortonian and the Gelasian. Older sediments, probably of Paleogene age, are referred to in the Vilariça and Longroiva basins by the designation of Vilariça Formation (Cunha and Pereira 2000; Pereira and Azevêdo 1995; Pais et al. 2012). It is assumed that the Vilariça Formation reflects the inefficient drainage towards the large Douro Cenozoic Basin in Spain. These alluvial mantles were supplied by a granite source and developed on low-gradient surfaces, whose exhumation is represented by the Iberian Meseta surface (Ferreira 1978; Cunha and Pereira 2000; Pais et al. 2012). In the Vilariça and Longroiva basins, this unit can display pronounced tectonic tilting, and in the basin borders, there is an over-thrust of the Variscan bedrock through faults with both reverse and horizontal components (Cunha and Pereira 2000) (Fig. 11.7). These characteristics are compatible with very intense regional Tortonian compression (Betic episode) and are responsible for the conservation of the Vilariça Formation in the depressions (Pereira 1997; Cunha and Pereira 2000; Pais et al. 2012).

11.6

The Douro Valley

The natural and cultural heritage on the Douro Valley is remarkable and has already deserved attention and international recognition. The World Heritage sites of the Cultural Landscape of Alto Douro Wine Region, related to the Port wine vineyards and the Palaeolithic rock art of Côa Valley Archaeological Park, near Vila Nova de Foz Côa, are the best examples of that recognition (Pereira 2004). Specific characteristics of the Douro River in the Portuguese territory and geology of its valley were decisive for the social and cultural evolution of local populations. In general, these singularities are due to deep fluvial incision into the hills and plateaus and are the reason for the sequence of dams in the valley and for distinctive historical floods. In the Portugal–Spain border region, steep cliffs, locally named “Arribas do Douro”, are the major fluvial landscape features (Fig. 11.8). This canyon-type valley is about 600 m deep and is carved mostly in granite into the well-preserved surface of the Northern Iberian Meseta (Antón et al. 2012). The canyon sidewalls host diverse flora and fauna habitats that justified the designation of the area as a Natural Park in 1998 (Alves et al. 2004; Pereira 2004). This section of the Douro River, with a steep longitudinal profile and numerous rapids and waterfalls, currently not visible due to the dams, establishes the link between an older Atlantic Douro and a previous endorheic basin, the Douro

146

D. I. Pereira and P. Pereira

Fig. 11.7 Outcrop at the southern limit of the Longroiva basin documents the reverse movement of the Vilariça fault, with the Variscan bedrock (Cambrian) over the Vilariça Formation (Paleogene)

Cenozoic Basin, located in the east (Galve et al. 2020). The transition from the former internal drainage (endorheic stage) to Atlantic Douro drainage (exorheic stage) is best explained by a combination of two drivers: i. increasing intraplate compression, that progressively tilted the Douro Cenozoic Basin towards the west and ii. a major climate change by *3.7 Ma (transition to a wetter climate stage), from the generally dry and hot climate during the Miocene and Zanclean to the humid and hot climate of the late Zanclean to Piacenzian. A latest stage (last *2 Ma), marked by enhanced fluvial incision, is related to continuous regional low crustal uplift, cooler climatic minima and associated lowering of sea level (Cunha et al. 2019). In the intermediate sector of the Alto Douro, Cambrian schists and greywackes induced a slightly wider valley, but

still with steep slopes. Here, the fluvial network promoted extensive erosion of the Meseta surface, which only remains preserved in small areas. Occasionally, the Douro River carves down to granite bedrock, resulting in small sections of canyon-type valley and waterfalls at the granite-schist contacts. The Alto Douro landscape, involving the Douro Valley and its tributaries, is characterised by terraces, built row upon row with retaining walls—the so-called socalcos. In this cultural landscape developed by the local population over decades of hard work, vineyards prevail next to olive and almond groves (Fig. 11.9). The steep valley, the tough schist and the scarcity of water do not appear to be obstacles in the creation of such a cultural landscape (Andresen et al. 2004; Pereira 2004).

11

The Geomorphological Landscape of Trás-os-Montes and Alto Douro

Fig. 11.8 Douro River canyon in São João das Arribas, Miranda do Douro

Fig. 11.9 Vineyards of the Cultural Landscape of Alto Douro Wine Region, a World Heritage site

147

148

11.7

D. I. Pereira and P. Pereira

Conclusions

The landforms that make up the north-east region of mainland Portugal cannot be grouped into a single landscape model. In fact, at least two distinct types of geomorphic landscape are represented. In the easternmost sector, the contrast of three different types of landforms is evident: the continuous surface of the Iberian Meseta, the residual ridges and the incised valleys. After a long period of continuous and slow uplift that allowed the preservation of the Meseta and the residual crests, the Douro River canyon was quickly cut during the Quaternary in a process that connected the Atlantic drainage and the inner sector of the Iberian Peninsula. Towards the west, the relief becomes more complex, with the Meseta surface losing regularity and dome blocks reaching around 1000 m asl near the Vilariça fault. Along the fault, the tectonic origin of landforms is clear, shown by the push-up reliefs and small depressions limited by steep scarps and filled by Cenozoic sediments. Several of the mentioned landforms have high scientific value and were selected as part of the inventory of the Portuguese geological heritage, especially the ones related to the Vilariça fault and the Douro River canyon (Pereira et al. 2015). Some landforms also show remarkable educational and aesthetic values, important for human well-being and for the development of tourism activities based on the unique natural characteristics of the region. Acknowledgements This work was co-funded by the European Union through the European Regional Development Fund, based on COMPETE 2020 (Programa Operacional da Competitividade e Internacionalização), project ICT (UID/GEO/04683/2013) with reference POCI-01-0145- FEDER-007690 and Portuguese national funds provided by Fundação para a Ciência e Tecnologia.

References Alves MI, Monteiro A, Ferreira N, Dias G, Brilha J, Pereira D (2004) Landscape as a support for biodiversity: the Arribas do Douro case study. In: Parkes MA (ed) Natural and cultural landscapes—the geological foundation. Royal Irish Academy, Dublin, pp 65–68 Andresen T, Aguiar FB, Curado MJ (2004) The Alto Douro Wine Region greenway. Landscape Urban Plan 68:289–303 Antón L, Rodés A, de Vicente G, Pallàs R, Garcia-Castellanos D, Stuart FM, Braucher R, Bourlès D (2012) Quantification of fluvial incision in the Duero Basin (NW Iberia) from longitudinal profile analysis and terrestrial cosmogenic nuclide concentrations. Geomorphology 165–166:50–61 Arthaud F, Matte Ph (1975) Les decrochements tardi-hercyniens du sud-ouest de l l’europe. Géometrie et essai de réconstitution des conditions de la déformation. Tectonophysics 25:139–171 Brilha J, Pereira P (2020) Geoconservation in Portugal with emphasis on the geomorphological heritage. In: Vieira G, Zêzere JL, Mora C (eds) Landforms and landscapes of Portugal, World Geomorphological Landscapes series, Springer (in this volume)

Cabral J (1985) Estudos de Neotectónica em Trás-os-Montes oriental. Provas A.P.C.C., Departamento de Geologia da Faculadade de Ciências, Universidade de Lisboa Cabral J (1989) An example of intraplate neotectonic activity, Vilariça basin, Northeast Portugal. Tectonics 8:285–303 Cabral J (1995) Neotectónica em Portugal Continental. Mem Inst Geol e Min 31, Lisboa, 265p Cabral J (2012) Neotectonics of mainland Portugal: state of the art and future perspectives. J Iberian Geol 38(1):71–84 Cabral J, Perea H, Figueiredo PM, Besana-Ostman GM, Silveira AB, Cunha PP, Gomes A, Lopes FC, Pereira D, Rockwell T (2010) Preliminary results of a paleoseismological study of the Vilariça fault (NE Portugal). Resumenes de la 1a Reunión Ibérica sobre Fallas Activas y Paleosismología, Siguenza, Spain, pp 41–44 Cloetingh S, Burov E, Beekman W, Andeweg B, Andriessen P, Garcia-Castellanos D, de Vicente G, Vegas R (2002) Lithospheric folding in Iberia. Tectonics 21:1041–1067 Conway-Jones BW, Roberts GG, Fichtner A, Hoggard M (2019) Neogene epeirogeny of Iberia. Geochem Geophys Geosyst (in press) Cunha PP (1992) Estratigrafia e sedimentologia dos depósitos do Cretácico Superior e Terciário de Portugal Central, a leste de Coimbra. PhD thesis, Univ. Coimbra Cunha PP, Pereira DI (2000) Evolução cenozóica da área de Longroiva-Vilariça (NE Portugal). Ciências da Terra (UNL) 14:89–98 Cunha PP, Pimentel NL, Pereira DI (2000) Assinatura tectonosedimentar do auge da compressão bética em Portugal - a descontinuidade sedimentar intra-Valesiano terminal. Ciências da Terra (UNL) 14:61–72 Cunha PP, Martins A, Gomes A, Stokes M, Cabral J, Lopes FC, Pereira D, de Vicente G, Buylaert JP, Murray AS, Antón L (2019) Mechanisms and age estimates of continental-scale endorheic to exorheic drainage transition: Douro River, Western Iberia, Global and Planetary Change, 181 De Vicente G, Vegas R, Muñoz Martín A, Silva PG, Andriessen P, Cloetingh S, González Casado JM, Van Wees JD, Álvarez J, Carbó A, Olaiz A (2007) Cenozoic thick-skinned deformation and topography evolution of the Spanish Central System. Global Planet Change 58:335–381 De Vicente G, Cloetingh S, Muñoz-Martín A, Olaiz A, Stich D, Vegas R, Galindo-Zaldivar J, Fernandez-Lozano J (2008) Inversion of moment tensor focal mechanisms for active stresses around the microcontinent Iberia: tectonic implications. Tectonics 27:TC1009 De Vicente G, Cloetingh S, Van Wees JD, Cunha PP (2011) Tectonic classification of Cenozoic Iberian foreland basins. Tectonophysics 502:38–61 Ferreira AB (1978) Planaltos e montanhas do Norte da Beira. Estudo de Geomorfologia. Memorias do Centro de Estudos Geográficos, 4, Lisboa, 210p Galve JP, Pérez-Peña JV, Azañón JM, Pereira DI, Cunha PP, Pereira P, Ortuño M, Viaplana-Muzas M, Prieto FJG, Remondo J, Jabaloy A, Bardají T, Silva PG, Lario J, Zazo C, Goy JL, Dabrio CJ, Cabero A (2020) Active landscapes of Iberia. In: Quesada C, Oliveira J (eds) The geology of Iberia: a geodynamic approach. Regional geology reviews. Springer, Cham García-Cortés A (ed) (2008) Contextos geológicos españoles. Uma aproximación al patrimonio geológico español de relevancia internacional. Instituto Geológico y Minero de España, Madrid Martín-Serrano A (1988) El relieve de la región occidental zamorana. La evolución geomorfológica de un borde del Macizo Hespérico. Ed. Instituto de Estudios Zamoranos Florian de Ocampo, Zamora Martín-Serrano A (2004) El borde occidental de la cuenca del Duero. In: Araújo MA, Gomes A (eds) Geomorfologia do NW da Península Ibérica. Faculdade de Letras da Universidade do Porto, pp 53–70

11

The Geomorphological Landscape of Trás-os-Montes and Alto Douro

Meireles C (2000) Carta Geológica de Portugal à escala 1/5000. Notícia explicativa da folha 3D (Espinhosela). Instituto Geológico e Mineiro, Alfragide, 64p Pais J, Cunha PP, Pereira DI, Legoinha P, Dias R, Moura D, Brum da Silveira A, Kullberg JC, González-Delgado JA (2012) The Paleogene and Neogene of Western Iberia (Portugal). A Cenozoic record in the European Atlantic domain. Springer Briefs in Earth Sciences, Springer, 158p Perea H, Cabral J, Figueiredo PM, Besana-Ostman G, Brum da Silveira A, Cunha PP, Gomes A, Lopes FC, Pereira D, Rockwell T (2010) Quaternary seismic activity of the Vilariça fault (NE Portugal): Preliminary results of a paleoseismological study. Actas do VIII Congresso Nacional de Geologia, e–Terra, 11, 4 p Pereira DI (1997) Sedimentologia e estratigrafia do Cenozóico de Trás-os-Montes oriental (NE Portugal). PhD thesis. University of Minho Pereira DI (2004) Dos aspectos gerais a algumas particularidades da geomorfologia do Nordeste Transmontano e Alto Douro. In: Araújo MA, Gomes A (eds) Geomorfologia do NW da Península Ibérica, Faculdade de Letras da Universidade do Porto, pp 71–91 Pereira P (2006) Património geomorfológico: conceptualização, avaliação e divulgação. Aplicação ao Parque Natural de Montesinho. PhD thesis, Earth Sciences Department, University of Minho, 370 p Pereira DI (2010) Landscape and drainage evolution in Northern Portugal. In: Cotelo Neiva JM, Ribeiro A, Mendes Victor L, Noronha F, Magalhães Ramalho M (eds) Ciências Geológicas: Ensino, Investigação e sua História. Associação Portuguesa de Geólogos, Vol I, pp 491–500 Pereira DI, Azevêdo T (1995) Evolução quaternária do graben da Vilariça (Trás-os-Montes, NE Portugal). Cadernos do Laboratório Xeolóxico de Laxe 20:123–137

149

Pereira DI, Pereira P (2020) Terras de Cavaleiros Geopark: a UNESCO Global Geopark. In: Vieira G, Zêzere JL, Mora C (eds) Landforms and landscapes of Portugal, World geomorphological landscapes series. Springer (in this volume) Pereira DI, Alves MI, Araújo MA, Cunha PP (2000) Estratigrafia e interpretação paleogeográfica do Cenozóico continental do norte de Portugal. Ciências da Terra (UNL) 14:73–84 Pereira P, Pereira DI, Alves MI, Meireles C (2002) Património Geomorfológico do sector oriental do Parque Natural de Montesinho (NE Portugal). In: Serrano E, García A, Guerra J, Morales C, Ortega M (eds) Estudios recientes en Geomorfología (2000–2002). Património, montaña y dinámica territorial, Sociedade Española de Geomorfología, Valladolid, pp 423–430 Pereira P, Pereira DI, Alves MI (2005) Particularidades da morfologia granítica da Serra de Gamoneda-Montesinho (Espanha-Portugal). Actas do X Colóquio Ibérico de Geografia, Universidade de Évora, CD-Rom, 10 p Pereira DI, Pereira P, Santos L, Silva J (2014) Geomorphological Units of Mainland Portugal. Revista Brasileira de Geomorfologia 15:567– 584 Pereira DI, Pereira P, Brilha J, Cunha P (2015) The Iberian Massif Landscape and Fluvial Network in Portugal: a geoheritage inventory based on the scientific value. Proc Geol Assoc 126(2):252–265 Ribeiro A, Kullberg MC, Kullberg JC, Manuppella G, Phipps S (1990) A review of Alpine tectonics in Portugal: foreland detachment in basement and cover rocks. Tectonophysics 184:357–366 Rockwell T, Fonseca J, Madden C, Dawson T, Owen LA, Vilanova S, Figueiredo P (2009) Paleoseismology of the Vilariça Segment of the Manteigas-Bragança Fault in Northeastern Portugal. Geol Soc Lond 316:237–258 (Special Publication)

The Terraced Slopes of the Douro Valley

12

Susana Pereira

Abstract

12.1

The Douro Valley is widely known because of the oldest demarcated wine region in the world dating from 1756, the Alto Douro Wine Region. The landscape of the Douro Valley was transformed by human activities and reflects the evolution of winemaking for nearly two thousand years. The Alto Douro Wine Region was classified as World Heritage by UNESCO in 2001. Since Romans introduced wine in the Iberian Peninsula in the first century AC, the Douro inhabitants planted vineyards in steep slopes. In these bare slopes, soils were artificially created using manual techniques, crushing Cambrian metamorphic rocks and building terraces supported by schist stone walls, to prevent soil erosion. The Douro Valley presents a temperate climate with a dry and hot summer, which is crucial for vine growth and grapes maturation. Local topographical characteristics, such as elevation, slope and aspect, are important factors affecting the viticulture and oenological characteristics of this specific region. In the Douro Region, slope angle controlled the land management practices, imposing the construction of terraces with schist stone walls. More recently, land embankments have been built in order to create flat surfaces to plant the vines. These structures originated a unique terraced landscape. The geomorphological features of the Douro Valley are described, including specific climatic, geologic, tectonic, soil and anthropogenic aspects that distinguish this region, unique to produce the famous Port wine and UNESCO World Heritage. Keywords

Douro valley




Terraced slopes




Anthrosols

S. Pereira (&) Centre of Geographical Studies, Institute of Geography and Spatial Planning, University of Lisbon, Lisbon, Portugal e-mail: [email protected]

Introduction

The Alto Douro Wine Region was included in the list of the UNESCO World Heritage in 2001. There are three main reasons that support the inscription: (i) the Alto Douro Region has been producing wine for nearly two thousand years and its landscape has been transformed by human activities, (ii) the components of the Alto Douro landscape are representative of the full range of activities associated with winemaking, and (iii) the cultural landscape of the Alto Douro is an outstanding example of a traditional European wine-producing region, reflecting the evolution of this activity over time. The Alto Douro Wine Region is the oldest demarcated wine region in the world, dating from 1756 (Pereira 2003). The area where Port wine production (red wine) is authorized covers, however, only 24,600 ha of the 250,000 ha of the Douro Region, whereas the remaining area produces table wines (red, white and rosés), classified as Denomination of Controlled Origin (DOC). Since the eighteenth century, the Port wine has been world famous for its quality. This long tradition of viticulture has produced a cultural landscape of outstanding beauty that reflects technological, social and economic evolution. For centuries, vineyards have been established on terraced slopes supported by schist stone walls, and the soils developed over the metamorphic formations have been significantly changed by direct human action, turning into anthrosols. Recently, land embankments were constructed for the same purpose using machinery, to create flat surfaces and enable vine plantations. In this chapter, an integrated analysis of climatic, geological, soil and topographical conditions of the Douro Region will be carried out, as a contribution to a better understanding of this distinctive landscape sustained by terraced slopes, which are used to produce the original Port wine, making it worth the UNESCO World Heritage recognition.

© Springer Nature Switzerland AG 2020 G. Vieira et al. (eds.), Landscapes and Landforms of Portugal, World Geomorphological Landscapes, https://doi.org/10.1007/978-3-319-03641-0_12

151

152

12.2

S. Pereira

Geographical and Climatic Setting

The Douro Region is located in the north-east of Portugal along the Douro River Valley (Fig. 12.1). The Douro River is one of the largest rivers of the Iberian Peninsula, c. 930 km long. It originates in Spain (Urbión Mountain) at 2080 m asl and flows into the Atlantic Ocean (Oporto, Portugal), within a hydrographic basin with 97,290 km2 and having stream flow of 21,992 hm3, year−1 (Morán-Tejeda et al. 2011). The Portuguese sector of the Douro basin covers 19% of the total area of the catchment and is characterized by deeply incised valleys surrounded by mountains (Fig. 12.1). The Western Mountains (Marão, Montemuro and Freita) block the flow of moist air coming from the Atlantic Ocean, and for this reason, lower humidity conditions occur in the Douro Valley. As a result, the Douro Valley is very hot in the summer and cold in the winter. The mean annual temperatures range from 11.8 °C in Barca de Alva (eastern area) to 16.5 °C in Peso da Régua (western area), reflecting the influence of continentality (Ribeiro et al. 1988). The annual precipitation in the Douro Valley decreases from the west to the east, ranging from 400 mm in the lower parts of the eastern valleys to 1200 mm in Serra do Marão. Precipitation occurs mainly during autumn and winter, with the summer drought typically lasting for three months. Climate is a major driving factor of wine productivity and, generally, wine quality is the highest in temperate climates. According to the Köppen-Geiger climate classification system (Köppen 1936), the Douro Region shows a

Fig. 12.1 General setting of the Douro Region in North-East Portugal

temperate climate with dry and hot summer (Csa). In these climatic conditions, vineyards normally grow in marginal conditions for agricultural production (Gouveia et al. 2011). Climatic parameters, such as air temperature, influence vine growth and the quality of the grapes. At the global scale, grapevines normally grow in areas with mean temperatures between 12 and 22 °C during the growing season, and daily average temperature values ranging from 20 to 35 °C allow for an optimal vegetative response. Heat or cold extremes may disrupt the optimum growth cycle of the grape or result in crop losses. Temperature also plays an important role in grape maturation which is relevant for the final characteristics of wines (aroma and colouration) (Jones and Davis 2005). Moreover, vineyards also depend on water availability, especially during critical growth stages that can affect grape and wine quality (Conradie et al. 2002). A surplus of precipitation and humidity can drown vines, lead to excess vegetation and the development of diseases (e.g. downy or powdery mildew). For centuries, the natural vegetation of the Douro Region was replaced by vineyard culture, leaving only a few traces of climax forests or primitive vegetation in abandoned vineyards after the phylloxera crisis in the late nineteenth century. Natural vegetation includes cork trees (Quercus suber), holm oaks (Quercus ilex), Douro Valley oaks (Quercus coutinhoi and Quercus henriquesii) and numerous exclusive endemics of the Douro Region (Digitalis amandiana or Trigonella amandiana, among others) (Costa et al. 1998). The Douro Region is divided into three winegrowing sub-regions: Lower Corgo, Upper Corgo and Upper Douro.

12

The Terraced Slopes of the Douro Valley

The Lower Corgo sub-region is located further west, closest to the Serra do Marão (Fig. 12.1), covering an area from Peso da Régua to Corgo River with around 14,501 ha of vineyards. In this area, where the rainfall and vineyard yields are the highest, the lighter and early maturing styles of Port are produced. To the east of this sub-region is the Upper Corgo, a drier area, where the finest vineyards are located and where the more concentrated and long-lasting wines are produced (20,914 ha of vineyards). The Upper Douro is the easternmost sub-region, including the area from Pinhão to Barca de Alva (10,197 ha of vineyards) and also the driest area, where the finest vintage wines are produced (IVDP 2016).

12.3

Geological Framework

The Douro Region is located in the Variscan Massif, a morphostructural unit of the Iberian Peninsula characterized by Pre-Cambrian and Palaeozoic formations which have been subject to metamorphism, deformation and granitic intrusions during the Variscan orogeny (Ribeiro et al. 1979; Dias 2001). The region shows four main geological units (Fig. 12.2b): (i) metamorphics of the Douro Group of Cambrian age, (ii) metamorphics of Ordovician–Silurian age, (iii) granitic rocks related to the Variscan orogeny that intruded the pre-existing metamorphic rocks and (iv) Cenozoic deposits. The Iberian Peninsula was part of the Armorican micro-plate, framed in the supercontinent Gondwana during the Cadomian orogeny (late Neoproterozoic, 650–550 Ma), which in a late collision phase originated the Central Iberian graben. This basin was filled in a deep marine environment with turbidites during the Proterozoic–Cambrian, forming the Douro Group geological formations (Sousa 1983) that are found in the Douro Region. These formations compose a continuous and elongated area following a W–E direction (Fig. 12.2b), where the Douro River excavated its valley. From bottom to top, the Douro Group presents the following formations (Sousa 1983; Pereira 2006b): a. The Bateiras Formation is composed of layers of laminated phyllites with metagreywackes and interbedded limestone, black phyllites and quartz metagreywackes dating from the Upper Proterozoic, b. The Ervedosa do Douro Formation is composed of stratified levels of green phyllites and quartz metagreywackes dating from the Lower Cambrian, c. The Pinhão River Formation is constituted by stratified metagreywackes with schist intercalations and microconglomerates of the Lower Cambrian,

153

d. The Pinhão Formation is composed of stratified levels of green phyllites, quartz metagreywackes and schists dating from the Middle Cambrian, e. The Desejosa Formation is characterized by the presence of phyllites with parallel and thin lamination, intercalated with metagreywackes and quartz metagreywacke inliers. It occupies the largest area in the Alto Douro Wine Region and dates from the Middle Cambrian, f. The São Domingos Formation is made of stratified levels of conglomerates, quartz metasandstones and metagreywackes dating from the Upper Cambrian. After the Cadomian orogeny, rocks were eroded and the Gondwana continent fragmented. In the Lower Ordovician, crustal stretching developed, and the rifting process begun with the deposition of large volumes of detrital sandy sediments in a shallow marine environment originating the Armorican Quartzite Formation (Ribeiro et al. 1979). The Ordovician–Silurian rocks are distributed in five main geological formations, from the oldest to the most recent (Pereira 2006b) (Fig. 12.2b): a. The Quinta da Ventosa Formation is composed of quartz phyllites and quartzites with dispersed conglomeratic levels dating from the Lower Ordovician, b. The Armorican Quartzite Formation is constituted by quartzites intercalated with schists with variable thickness dating from the Lower Ordovician, c. The Pardelhas Formation is composed of slates and carbonaceous schists of Middle Ordovician age, d. The Quartzitic-Phyllite Formation is composed by quartz phyllites and schists with quartzite levels from the Upper Ordovician, e. The Campanhó/Ferradosa Formation is composed by silicate-carbonate grey schists with quartzite and limestone levels, quartzite and thick levels of phyllites of Silurian age and intrusions of basic rocks. The oceanic expansion reached its peak in the Lower Devonian and in the Middle Devonian, the closing of the basin started with plate convergence associated with the Variscan orogeny. This has led to the deformation and metamorphism of the previous deposits, generating diverse tectonic structures such as faults and folds, prevailing until the end of the Carboniferous (Ribeiro 2006). During the Variscan orogeny, granitic magmas resulting from partial melting of the continental crust, with possible interaction of mantle magmas, intruded. In this context, very different granitic rocks formed (Ferreira et al. 1987; Noronha et al. 2006), presenting diverse texture, grain size, chemistry and mineralogical facies of different ages (Pires 2003).

154

S. Pereira

Fig. 12.2 Neotectonic and morphostructural framework of the Douro Region (Source Cabral and Ribeiro 1988; Ferreira 1991) (a) and simplified geological units of the Douro Region (Source Geological Maps of Portugal scale 1: 50,000) (b)

Syn-tectonic Variscan granites are frequent in the Douro Region, but also small late-tectonic granitic massifs can be found. According to Martin-Serrano (1988), at the end of the Mesozoic, the Variscan basement must have been razed and deeply weathered, under a tropical climate. In the transition from the Mesozoic to the Cenozoic, as a result of tectonic movements and climate change—which became tropical with a dry season—lateritic weathering profiles were eroded and gave rise to the Palaeocene sediments, which fossilized part of the quartzite ridges and constitute the basis of the Meseta Fundamental Surface, which occurs between 600 and 800 m asl (Martin-Serrano 1988). The residual reliefs with elevations close to 900–1000 m correspond to the top of the so-called Initial Surface (Martin-Serrano 1988). This surface is best preserved at quartzite ridges rising typically between 200 and 300 m above the Meseta Fundamental Surface (Pereira et al. 2000; Pereira 2006a). In the Neogene, fluvial network was slightly incised into an older surface. At that time, the Douro basin was endorheic, but with the alpine readjustments in the Late Pliocene,

the Atlantic fluvial drainage captured the Douro network, transforming it into an exoreic basin (Pereira et al. 2000; Pereira 2006a). Continued vertical movements uplifted the planation surface to 700 m asl in the NE of the Douro Valley in Portugal, causing the individualization of the Planalto (plateau) Mirandês (Cabral 1995) and resulting in the deep entrenchment of the present rivers, with slopes reaching several hundred metres (Ferreira 1991). Fluvial canyons turned into gorges of hundreds of metres depth, adapted to the course of tectonic lineaments (Ferreira and Ferreira 2004). Most faults are late Variscan in age, and some were reactivated during the Alpine orogeny. Near the end of the Variscan tectogenesis, the chain was affected by intense fracturing associated with a maximum compression direction close to N–S that gave rise to a left strike-slip fault system of N20 to N45 direction, which is the most important, and N120 to N140 right strike-slip faults (Pires 2003) (Fig. 12.2a). Locally, the valley was controlled by NW–SE, N–S and E–W faults that resulted in the incised meanders of the Douro River and its main tributaries (Pires 2003) (Fig. 12.2b).

12

The Terraced Slopes of the Douro Valley

The deep incision of the Douro occurred in both the Pliocene peneplain located to the east and the mountainous barrier in the west. With the rejuvenation of the drainage system, the Douro tributaries were affected by headward erosion and deep valleys developed as adaptations to the new base level. Longitudinal staircase-like profiles reflect the penetration of successive regressive erosion levels (Ribeiro et al. 1988). Cenozoic deposits are mainly located along the Douro Valley and main tributaries (e.g. Sabor, Côa, Tua, Corgo) (Fig. 12.2b), sometimes at different elevations.

155

12.4

Landforms and Structural Control in the Douro Valley

The landscape of the Douro Region is influenced by the presence of metamorphic rocks versus granitic rocks and also by tectonics (Fig. 12.3). The landforms show irregular and rugged surfaces in the granite areas (Ribeiro et al. 1988) and are influenced by the style of jointing and faulting (Twidale and Romani 2005). Granites show generally a complex network of orthogonal fractures and faulting associated with regional tectonics

Fig. 12.3 Extract of the geomorphological map of Portugal in the Douro Region (Ferreira 1980)

156

S. Pereira

Fig. 12.4 Typical landscape of the Douro Group geologic formations excavated by the Douro River in Covas do Douro (Alijó municipality). Photograph credits Duarte Fernandes Pinto, A Terceira Dimensão, http://portugalfotografiaaerea.blogspot.com

(NNE–SSW, N–S directions) or reflecting local styles (Pires 2003). Differential erosion was strong along densely fractured zones with deep weathering, forming narrow valleys with steep slopes and irregular thalwegs (e.g. Tua River near its mouth and Douro River in Miranda do Douro). Longitudinal profiles show steps associated with differential granite hardness. At the local scale, erosion along discontinuities, joints and fractures created sets of rounded boulders, which may appear isolated or form chaotic accumulations. The landforms developed within the Douro Group metamorphic rocks are characterized by narrow and steep valleys with rounded interfluves (Fig. 12.4), with the main topographical controls being lithology, folds, schistosity and fractures. Interstratification of metamorphic rocks (e.g. schist, conglomerates and greywackes) of different hardness provide different resistance to erosion, with more resistant lithologies, such as metagreywackes and conglomerates forming higher elevations. In the contact zone between granites and the Douro Group geological formations, significant altitude differences can be found, with steep slopes reaching 300 m in the north of the Alto Douro Wine Region and 150 m in the south. According to Ferreira (1978), these differences result from a tectonic unevenness predating the development of the lower

planation levels. In granitic areas, these levels are the result of differential erosion along tectonic lineaments (Pires 2003). On the west side of the Douro Region, the levels end where the Douro Group geological formations contact with the Ordovician rocks. There, the Douro River excavated a deep gorge in quartzites of the Serra do Marão (Fig. 12.3). According to the geomorphological map of Portugal (Ferreira 1980), residual elevations found in Douro are usually associated with harder lithologies, such as quartzite and schists with quartzite intercalations (Fig. 12.3). After the planation phase, rapid incision of the Douro River occurred in schists, causing headward erosion of its tributaries. The erosion process found some resistance when it reached granites and schists hardened by contact metamorphism, therefore developing longitudinal staircase-like profiles on the Douro tributaries, reflecting the penetration of successive regressive erosion levels (Ribeiro et al. 1988) (Fig. 12.3). In the Douro Valley, the western limit of the Meseta surface corresponds to a complex mountainous edge, which roughly follows the long late Variscan strike-slip fault of Bragança-Manteigas (Fig. 12.2a) with a NNE–SSW direction and approximately 220 km in length (Ferreira 1991; Perea et al. 2010). This edge is clear-cut to the south of the

12

The Terraced Slopes of the Douro Valley

Douro River, forming a fault scarp bounding the Meseta surface (Martin-Serrano 1988), and the Central Plateau in Portugal (Ferreira 1991). In the north of the Douro, the edge becomes less clear-cut, mainly due to more complex tectonics (Ferreira 1991). According to Cabral (1995), the strike-slip fault of Bragança-Manteigas may have been reactivated in the Miocene and the Quaternary as a left strike-slip fault, as a result of NNW–SSE compression. In the central part of the Vilariça graben, the strike-slip fault reaches 9 km in width as a result of several tectonic phases since the Variscan orogeny (Ribeiro et al. 1990; Cabral 1995). The Plio-Quaternary activity of the Bragança-Vilariça fault shows regional geomorphological expression and is supported by the presence of faulted sediments (Cabral 1995; Rockwell et al. 2009). Accumulated vertical displacements over the Neogene and Quaternary periods often reach 250– 300 m in both horsts and grabens, which are still visible in escarpments (Ferreira 1991; Pereira and Azevedo 1995). These are more evident in the schist-granite contact zones. On the granite side, the relief changes are abrupt, while on the schist side, the passage from the valley to the plateau is gradual. The bending of the Douro Valley at Pocinho reflects the presence of the Bragança-Manteigas strike-slip fault (Fig. 12.5).

157

The Verín-Penacova lineament is also a late Variscan strike-slip fault with a NNE–SSW direction (Fig. 12.2a). Horsts and grabens were formed along this lineament in the Tertiary and Quaternary (Ferreira 1991). South of the Douro (Northern Beira), this line has a clear morphological relevance, corresponding to the contact between the Central Plateau and the Western Mountains (Ferreira 1991). North of the Douro, a complex basin, about 90 km long, formed along this late Variscan fault zone, from Régua to the north of Verín, in Spain. The basin is not continuous and shows several independent sectors, such as the Chaves depression (Ferreira 1991). The Verín-Penacova fault is responsible for the bending of the Douro Valley at Peso da Régua. Most of the finest vineyards are planted on the steep slopes bordering the Douro River and its tributaries, among which are the Corgo, Pinhão, Tua and Côa Rivers (Fig. 12.4). Topographical characteristics such as elevation, slope angle and aspect are important factors influencing the viticulture and oenological characteristics (Fraga et al. 2014). Elevation can have an important impact on vineyard temperatures (e.g. air temperature lapse rate) and exert a strong influence on the selection of sites and grape varieties. Slope angle is important for soil erosion, water drainage and viticulture management, whereas aspect, influencing solar radiation, affects microclimate (Fraga et al. 2014). In the

Fig. 12.5 Douro River at the Pocinho Dam (Torre de Moncorvo municipality). Photograph credits Duarte Fernandes Pinto, A Terceira Dimensão, http://portugalfotografiaaerea.blogspot.com

158

S. Pereira

Douro Region, slope aspect is a key factor for site selection and grape varieties. For example, the Touriga Nacional vine demands more sun exposure and is used on predominantly south-facing slopes, whereas the Barroca vine produces better results on cooler slopes with reduced exposure to sunlight and thus, thrives on northern or eastern aspects. On the contrary, slope angle controls land management practices, such as the implementation of terraces on steep slopes to prevent soil erosion. Also, vineyard row orientation tends to be projected according to the aspect of the terrain in order to optimize solar radiation intercepted by vines (Fraga et al. 2014).

12.5

Soils of the Douro Region

Soil is one of the most important factors for viticulture because it supports the root system, which accumulates carbohydrates, absorbs water and other nutrients, thus being crucial for grapevine growth, physiology and yield attributes (Morlat and Jacquet 2003). In grapevines, nutrient and water uptake occur mostly within 0.5–1.0 m depth in the soil profile (Keller 2010). Therefore, deep soils with good drainage are more suitable for vineyard installation. Soil water retention properties can also affect grapevine performance, especially in Mediterranean regions where grapevines are subject to excessive heat and water stress (Fraga et al. 2014). In the Douro Region, foliated metamorphic rocks generate soils that can retain moisture, sometimes just enough to allow the vine to prosper in the arid conditions that occur during most of the summer. During several centuries, the population of the Douro planted vineyards even on steep slopes. On these bare slopes, soils were artificially produced by crushing rocks and by building stone wall terraces, in order to prevent erosion. Where metagreywackes or conglomerates occur (Rio Pinhão and São Domingos Formations), land clearing works were hard to perform, since these formations show increased hardness and disaggregation is arduous, with resulting soils showing high stoniness. Where phyllites dominate (Pinhão, Ervedosa do Douro and Desejosa Formations), the land clearing was easier since this rock type shows higher weathering and disintegrates easily, producing soils with low stoniness. In the Douro Region soils derived from the Douro Group formations and granitic rocks are classified into two groups (Agroconsultores and Coba 1991): 1. Soils formed by human activities (Aric AnthrosolsFAO/UNESCO, 1988), occupying 27% of the Douro Region on steep slopes. These soils result from deep soil mobilizations with forced rock disaggregation or material mobilizations, which resulted from cuts or fills with

consequent profile deepening, changes in the original soil horizons and incorporation of fertilizers. Most vineyards grow in Aric Anthrosols that can be found in terraced slopes. 2. Soils with a preserved original profile where human action changed only the superficial horizons. In this group, there are three main soil classes, according to the FAO/UNESCO soil classification: (a) Leptosols: soils with shallow depth (100 m), 5 fault scarp (30 m deep)

The Rabaçal depression (Figs. 17.3, 17.4 and 17.6), 12 km long, is crossed by the upper Mouros River (tributary of the Mondego River) and is a flat orthoclinal valley, ranging from 1 to 2.5 km in width. This marly-limestone depression was incised below the Serra da Villa surface (*300 m), the erosive palaeosurface present in the dolomitic hills to the east, and only hinted on the Degracias-Alvorge plateau to the west (Fig. 17.4). Therefore, it is plausible that this elongated and incised valley has a recent genesis (Quaternary?) with fluvio- and tectono-karstic origins (polje, in Cunha 1990), despite the lack of deposits to prove it. Between the southern flank of the Torre Vale de Todos anticline and the homonymous transpressive fault system, four marly-limestone depressions occur, corresponding to a zone of tectonic deformation of the Pliensbachian and Toarcian units affected by fluvio-karstic processes. While the three western depressions are open by recent fluvial erosion, the easternmost one (Várzea da Póvoa) is still closed and maintains an active karst with water being lost in a ponor (Algar do Caçador or da Várzea) and subsequently integrated in the local endokarst system (Fig. 17.4). To the south of Torre Vale de Todos structures, the Campo and Camporez marly-limestone depressions correspond to an outcrop of the Pliensbachian-Toarcian units, i.e. the core of an N-S gutted anticline affected by numerous fractures on the western flank. Also, in this case, the marly-limestone depressions are incised into a flat-surface around 300 m in altitude, which today constitutes watershed where the northernmost Camporez depression drains into the Dueça River (then to the Mondego River) and the southernmost Campo depression into the Zêzere River (then to the Tagus River) (Fig. 17.4).

17.2.3 Limestone Mountains/Plateaus According to the internal structure of the Sicó massif, its main body is dominated by a set of limestone mountains and plateaus supported by the well-karstified Middle Jurassic units (Fig. 17.7). In the structurally controlled

218

L. Cunha et al.

Fig. 17.5 Dissolution shafts in the dolomitic hills (Mesura-Santa Clara, Coimbra), filled by Meso-Cenozoic siliciclastics (palaeokarst)

Fig. 17.6 Most spectacular marly-limestone depression of the Sicó massif (i.e. the Rabaçal depression)

17

The Sicó Massif: Morphostructural Aspects, Hydrology …

219

Fig. 17.7 Typical karst landscape of the Sicó massif (Casmilo village)

Condeixa-Sicó block, the northern mountains show up, with particular expression for the Serra do Circo (406 m), Serra do Rabaçal (532 m), with a large asymmetric anticline structure oriented approximately E-W and marked by a thrust fault in its southern flank (Fig. 17.4), and Serra de Sicó (553 m). Linked also to the widespread presence of erosive palaeosurfaces, the central sector of the massif is dominated by a low-relief plateau-like morphology (Degracias-Alvorge plateau), slightly tilted towards the east, with altitudes ranging from 280 to 350 m asl and cut by deep structurally controlled valleys on its western flank (Fig. 17.4). In the south-eastern sector of the Sicò massif, the Penela-Alvaiázere block shows a submeridian fault system that marks its eastern border, while the conjugated fractures divide this narrow relief in a set of small limestone mountains (Castelo do Sobral, Serra de Mouro and Ariques), which progressively rise southwards, reaching 618 m asl in the Serra de Alvaiázere, the highest peak of the Sicó massif (Fig. 17.4).

17.3

Meso-Cenozoic Siliciclastic Cover and Geomorphological Evolution

In addition to a Jurassic syndepositional karstification (intraSinemurian and Middle-to-Upper Jurassic transition phases; Cunha and Soares 1987; Dimuccio et al. 2014b) confirmed by local and regional unconformities in the carbonate succession resulting from tectonic and eustatic effects (Dimuccio 2014), most of the karstification of the Sicó massif with impacts in the current landscape is, at least, from the Cretaceous. During the Early Cretaceous, most of the Sicò massif, already exposed due to a generalized and spatially differentiated tectonic uplift, was buried by a siliciclastic cover (Figueira da Foz Formation; Diniz 2001). Indeed, remains of these muddy-sandy and conglomerate siliciclastics, discordantly overlaying the Jurassic carbonates, can be found within the Sicó massif. The subsequent Cenozoic palaeoclimatic conditions, coupled with new tectonic arrangements, were

220

L. Cunha et al.

both responsible for intense pedogenesis and strong erosion phases. The progressive remobilization of the existing siliciclastic cover gave rise to the polygenic red sands (Cunha 1990). Later detrital deposits, such as those related to Pliocene marine transgressions, may have partially reached some of the western sectors of Sicó massif, although most of its western front was already uplifted and individualized, functioning as a barrier to the marine incursions (Cunha 1990). Quaternary climatic oscillations are marked by two groups of forms and associated deposits in the study area. The first one corresponds to a set of exposed karstified calcareous tufa/travertine covering an area of *10 km2 in the Condeixa region and related to warm interglacial periods (Mendes 1985; Cunha 1990; Soares et al. 1997, 2007). These continental carbonates show variable thickness reaching 50 m and are responsible for the construction of a platform at an altitude of 100–110 m, today cut into three small plateaus (Cernache, Eira Pedrinha and Condeixa). Moreover, the Condeixa tufa/travertine outcrops support the notorious Roman ruins of Conímbriga. The colder periods of the Quaternary were marked by the epigenetic incision of the hydrographic network, possibly favoured by the presence of the siliciclastic cover. The rigid walls of the fluvio-karst canyons often show the marks of these cold periods, particularly through different generations of relict cryonival slope deposits (see Cunha 1990, 1999). Therefore, in general terms, the landscape of the Sicó massif basically corresponds to a karst that was covered during most of the Cretaceous and Cenozoic (i.e. a palaeokarst), which today is partially exhumed. This exhumation is particularly noticeable in the highest and exposed sectors of the massif (Serra do Circo, Serra das Janeanes, Serra do Rabaçal, Serra de Sicó, Serra de Ariques and Serra de Alvaiázere, as well as in the western sectors of the Degracias-Alvorge plateau), where the uncovered carbonate rock and the surface/subsurface karst features are more abundant (Fig. 17.4). In contrast, in most of the Degracias-Alvorge plateau, as well as in the other lower sectors of the massif, the remains of the siliciclastic cover still mark a landscape with fluvial characteristics (whose valleys are dry and abandoned), to which some small dolines are added (mainly bowl-shaped) and even uvalas—both with evident cryptokarstic evolution.

17.4

Surface Karst and Fluvio-Karst Landforms

In the Sicó massif, it is possible to find almost all kinds of surface karst landforms that characterize the classical karst terrains. With the exception of contemporarily active poljes, among the superficial karst and fluvio-karst forms are isolated karren, karren fields, sinkholes (dolines and ponors),

uvalas, well- and not well-defined karst depressions (closed and open), dry valleys, blind valleys and deep canyons (Figs. 17.4, 17.8, 17.9, 17.10 and 17.11a). A great variety of karren of different types and generations appears particularly in the most exposed and uncovered surfaces, i.e. areas where the limestones are partially exhumed from the siliciclastic cover, although sometimes denote in its morphology aspects of an evolution under cover (rounded karren). Indeed, in the case of the dolomitic hills, many of these forms also appear beneath the siliciclastic cover in the shallow subsurface zone (i.e. the epikarst). The dolines are not very abundant (just over 500 in the whole massif; Cunha 1990), but there are several types (solution, collapse and subsidence). The depressions vary in terms of shape, most often being bowl, saddle, funnel and embedded. The main peculiarity of these superficial forms (especially some bowl-shaped dolines) is the fact that many of them are associated with the Meso-Cenozoic siliciclastic cover (Fig. 17.8), sometimes indicating a pre-Cretaceous karst phase or (in other cases) a cryptokarstic evolution— most likely a combination of these two processes. In the Degracias-Alvorge plateau, as well as in the western border of the Penela-Alvaiázere block, there are relatively larger karst depressions (uvala-type), partially open by an incipient superficial hydrographic network and always associated with the siliciclastic cover. Since the Sicó massif is characterized predominantly by a fluvio-karst landscape, the valleys are of particular importance. There are several suspended dry and blind valleys, some amphitheatre head valleys (named fórnias in Portuguese or reculées in France) and four deep canyons (Mouros, Buracas, Poio Novo and Poio Velho; Cunha 1990; Cunha and Dimuccio 2014, 2017), which constitute a kind of hallmark of the massif (Fig. 17.4). In the Buracas valley, a set of rock-shelters (named “Buracas“—holes) and associated cryonival deposits (Fig. 17.10a, b), together with important archaeological remains of the Upper Palaeolithic found on the valleysides, were extremely useful in framing and understanding the palaeoenvironmental evolution in the Late Quaternary (Cunha et al. 2006; Aubry et al. 2011). Moreover, the Poio Novo valley (Fig. 17.11a) is one of the most visited and studied landforms of the Sicó massif due to its dimension and scenic impact, as well as to the presence of some strong temporary exsurgences (e.g. Malhadouro karst spring) from which a surface water stream forms in the valley floor in rainy years. The presence of rock-shelters and related stratified slope deposits, such as the presence of small archaeological caves/rock-shelters with high relevance for the study of the Middle-to-Upper Palaeolithic transition, e.g. Buraca Grande and Buraca Escura caves (Fig. 17.11b, c; Aubry et al. 2011; Dimuccio et al. 2014a), also contributes to increase the interest for this specific fluvio-karst valley.

17

The Sicó Massif: Morphostructural Aspects, Hydrology …

221

Fig. 17.8 Doline associated with the Meso-Cenozoic siliciclastic cover (near the Buracas valley)

17.5

Caves and Karst Hydrology

In the Sicó massif, about three hundred caves of different types, sizes and speleogenetic features are inventoried, almost all occurring in the limestone mountains/plateaus of the north-western Condeixa-Sicó block (Fig. 17.4). A few caves of small size were also found in the dolomitic hills (Dimuccio 2014; Dimuccio and Cunha 2018). The largest and most interesting endokarst system of the whole massif is the so-called Dueça Speleological System—a set of exsurgences and ponors linked by various extended and predominantly subhorizontal caves, including the Soprador do Carvalho (or Talismã) cave, which is crossed by an active underground river along its lower level (Neves et al. 2003; Iurilli et al. 2013). Among the caves with predominantly subvertical development, the 107-m-deep “Abismo de Sicó” (Sicó abyss) stands out. A direct relationship between the location/morphology of the caves and the tectonic features, mainly the fractures with meridian and submeridian

orientations, has been shown (Cunha 1990; Dimuccio and Cunha 2015, 2018; Dimuccio et al. 2017). The Sicó massif shows an important structural control on hydrodynamics, particularly related to its monoclinal geological structure, as well to the fracturing with submeridian orientation, both generating a westward regional groundwater flow (Cunha 1990). The recharge process is purely autogenic, and the infiltration is mostly diffuse. The only exception is the Algar da Várzea sinkhole (ponor) where the temporary overland flow sinks and flows to the east in the complex endokarst of the Dueça Speleological System. The discharge occurs through a set of temporary and perennial exsurgences located on the western border of the Sicó massif (Fig. 17.4), mainly along the Anços valley, which drain * 60% of the groundwater circulation. While the north-western border of the massif shows many permanent exsurgences (Olhos de Água do Anços—Fig. 17.12, Ourão and Arrifana), on the south-eastern block even more important are temporary or seasonal karst springs (Olhos de Água do Dueça, Olhos de Água de Ansião and Olho do

222

Fig. 17.9 Karren field partially exhumed from the Meso-Cenozoic siliciclastic cover (Buracas valley, Casmilo village)

Fig. 17.10 Geomorphological features of the Buracas valley. a. Rock-shelters (the Buracas), b. Cryonival slope deposits

L. Cunha et al.

17

The Sicó Massif: Morphostructural Aspects, Hydrology …

223

Fig. 17.11 Geomorphological features of the Poio Novo valley. a. View of the valley’s cross-section, b. Buraca Escura cave, c. Buraca Grande cave

Tordo), which may dry out during summer. Furthermore, in the Rabaçal region, the eastern slope of the Degracias-Alvorge plateau shows several karst springs with

small discharge (Legaçao, Alcalamouque and Alvorge), showing up in the contact of the Middle Jurassic limestones with the Lower Jurassic marly-limestones (Fig. 17.4). In

224

L. Cunha et al.

Fig. 17.12 Permanent exsurgence of Olhos de Água do Anços

addition, the Alcabideque karst spring is the most important exsurgence related to the dolomitic hills, also exploited since Roman times for public water supply (Dimuccio and Cunha 2008; Dimuccio 2014). Recent studies carried out in the Degracias-Alvorge plateau have shown that the local recharge is mainly diffuse, flowing through the fissures in the carbonate rocks and essentially through its karst and palaeokarst surface forms (Paiva 2015). Concentrated recharge only occurs locally (into swallow holes), especially during major rainfall events, when part of the water infiltrates immediately through highly karstified limestones. This quick-flow rapidly reaches the exsurgences of the western border of the massif (less than two days from the recharge area to the Olhos de Água do Anços karst spring). The endorheic features and the altitude of the recharge area (350–550 m) explain the recharge values, higher than 50% of the annual rainfall (mean annual recharge about 650 mm estimated by the water balance method) (Paiva 2015). The discharge of the main karst spring of the whole Sicó massif (Olhos de Água do Anços) ranges from less than 0.2 m3/s in summer to 5.8 m3/s in winter, showing a regime influenced by the annual distribution of rainfall. In a daily

perspective, the hydrograph of Olhos de Água do Anços is characterized by peaks of discharge following intense rainfall days, which overlap the base-flow component, clearly emphasized during the summer flow rate (Paiva 2015). As the outflow from the karst springs carries an imprint of the behaviour of the aquifer, the duality of the Sicó karst system in terms of hydrogeological functioning is evident. First, an important component of quick-flow during intense rainfall events is shown by the increase of turbidity and the fast drop of electrical conductivity/temperature of the karst springs outflow (this strong variability evidences a clear influence of short flow paths on the discharge). Second, the predominance of the base-flow shown by the perennial character of some exsurgences during several dry months in summer and autumn demonstrates that the aquifer filters the rainfall input very well and has a very high storage capacity.

17.6

Conclusions

The whole Sicó massif is a carbonate relief where multiple phases of karstification since the Jurassic were recognized. Such phases, within a palaeoclimatic variability framework,

17

The Sicó Massif: Morphostructural Aspects, Hydrology …

result in polygenic karst/palaeokarst landforms. The polygenic nature of this karstification regards the combination of the processes that typically characterize the covered and exhumed karsts, with associated cryptokarstic evolution. A discontinuous Meso-Cenozoic siliciclastic cover, with different types and ages, not completely impermeable but one that promotes superficial runoff, was responsible for organizing a fluvial drainage network, as demonstrated by a set of suspended dry/blind valleys and canyons that cut the carbonate reliefs. These latter fluvio-karst landforms testify how the fluvial network tries to follow the progressive and spatially differentiate post-Jurassic uplift of the Sicó massif, mainly during the Pliocene-Pleistocene. The combination of karst and fluvio-karst landforms, the articulation of surface and subsurface forms and the relationship with the vegetation cover and soil arrangement processes by humans, were responsible for a sui generis karst/palaeokarst landscape of high geoheritage value and with sufficiently potential for the local development. Acknowledgements This work is a contribution to the CAVE project PTDC/CTE-GIX/117608/2010, supported by the European Fund for Economic and Regional Development (FEDER) through the Program Operational Factors of Competitiveness (COMPETE) and National FCT Funds (FCOMP-01-0124-FEDER-022634), as well as the strategic project UID/GEO/04084/2013 (POCI-01-0145-FEDER-006891). Constructive comments and English revision on an earlier version of the manuscript by the editors of this book were gratefully acknowledged.

References Almeida AC (1997) Dunas de Quiaios Gândara e Serra da Boa Viagem - Uma abordagem ecológica da paisagem. Edição Fundação Calouste Gulbenkian, Junta Nacional de Investigação Científica e Tecnológica, Lisboa Almeida AC, Soares AF, Cunha L, Marques JF (1990) Proémio ao estudo do Baixo Mondego. Biblios, Coimbra, LXVI:17–47 Aubry T, Dimuccio LA, Almeida M, Neves MJ, Angelucci D, Cunha L (2011) Palaeoenvironmental forcing during the Middle-Upper Palaeolithic transition in Central-Western Portugal. Quatern Res 75(1):66–79 Burg JP, Iglesias M, Laurent Ph, Matte Ph, Ribeiro A (1981) Variscan intracontinental deformation: the Coimbra-Córdoba Shear Zone (SW Iberian Peninsula). Tectonophysics 78:15–42 Crispim JA (1995) Dinâmica cársica e implicações ambientais nas depressões de Alvados e Minde. Tese de Doutoramento, em Geologia. Faculdade de Ciências da Universidade de Lisboa Crispim JA (1999) Seismotectonic versus man-induced morphological changes in a cave on the Arrábida chain (Portugal). Geodin Acta 12:135–142 Crispim JA (2008) Património Geológico da Serra de Montejunto. Sociedade Portuguese de Espeleologia, Lisboa Crispim JA (2010a) Panorama das Regiões Cársicas de Portugal. In: Geologia Clássica, Ciências Geológicas: Ensino, Investigação e sua História, vol V. Lisboa, pp 469–478 Crispim JA (2010b) Aspetos relevantes do património cársico da Orla Ocidental. Revista e-Terra 18(4)

225 Cunha L (1990) As Serras Calcárias de Condeixa, Sicó, Alvaiázere Estudo de Geomorfologia. Geografia Física I, Instituto Nacional de Investigação Científica, Imprensa Nacional, Casa da Moeda, Coimbra Cunha L (1993) Geomorfologia Estrutural e Cársica. O Quaternário em Portugal. Balanço e Perspectivas, Colibri, Lisboa, pp 63–74 Cunha L (1996) Les Karsts Portugais. Problèmes et Perspectives. Karstologia 28(2):41–48 Cunha L (1999) Depósitos de vertente no sector setentrional do Maciço de Sicó. In: Actas do Encontro de Geomorfologia, Coimbra, 85–94, Projecto PRAXI XXXI, 2/2.1/CTA-156/94 Cunha L (2003a) Maciço de Sicó: Valorização dos Recursos Naturais e Criação de Emprego a Nível Local. Território, do Global ao Local e Trajectórias de Desenvolvimento. Centro de Estudos Geográficos, Coimbra, pp 185–198 Cunha L (2003b) A montanha do centro português: espaço de refúgio, território marginal e recurso para o desenvolvimento local. In: Território, Ambiente e Trajectórias de Desenvolvimento, Centro de Estudos Geográficos, Coimbra, pp 175–191 Cunha L (2003c) Estudos de geomorfologia Cársica em Portugal. Um ponto de situação relativo aos maciços do sector setentrional da Orla Mesocenozóica Ocidental Portuguesa (Outil, Boa Viagem e Sicó). In: Actas do IV CNEspeleo Congress, Leiria Cunha L, Almeida M, Neves MJ, Dimuccio LA, Aubry T (2006) Contributo da sequência cultural pleistocénico/holocénico para a compreensão da génese e evolução do canhão flúviocársico do Vale das Buracas. In: Acta do 20 Congresso Nacional de Geomorfologia, vol III, pp 69–75 Cunha L, Dimuccio LA, Vieira A (2007) Património cársico do Maciço de Sicó. In: Brandão J, Calado C, Sá Couto F (eds), Património Geológico, Arqueológico e Mineiro em Regiões Cársicas, Livro de Resumos do Simpósio Ibero-Americano, 29 Junho a 1 Julho, Batalha Cunha L, Dimuccio LA (2014) Formas e processos cársicos nos Maciços calcários do centro de Portugal. O caso particular do Maciço de Sicó. Revista Brasileira de Geomorfologia 15(4): 673–68 Cunha L, Dimuccio LA (2017) O Maciço de Sicó (Portugal Central): estrutura geológica, geomorfologia e carsificação superficial. In: Gomes AA, Teixeira J, Soares L (eds) Livro de Atas do 8 Congresso Nacional de Geomorfologia. Porto, APGeom, pp 77–78 Cunha L, Dimuccio L, Aubry T (2014) Karstic heritage in Central Portugal. The case of the Sicó Massif. In: Património Geomorfológico e Geoconservação. Experiências em Portugal e no Brasil. Actas/Proceedings I Encontro Luso-Brasileiro de Património Geomorfológico e Geoconservação, Associação Portuguesa de Geomorfólogos (eds), pp 27–34 Cunha L, Dimuccio L, Paiva I (2018) Geopatrimónio cársico e desenvolvimento local no Maciço de Sicó. In: Vieira, A., Bento Gonçalves, A., Costa, F., (eds), Livro de Atas do II Encontro Luso-Afro-Americano de Geografia Física e Ambiente, Desafios para afirmar a Lusofonia na Geografia Física e Ambiente, pp 1227– 1233 Cunha L, Soares AF (1987) A carsificação no Maciço de Sicó, principais fases de evolução. Cadernos de Geografia 6, Coimbra, pp 119–137 Cunha L, Vieira A (2002/2004) Património geomorfológico, recurso para o desenvolvimento local em espaços de montanha. Exemplos no Portugal Central. Cadernos de Geografia 21/23, pp 15–28 Daveau S (1985) Les Bassins de Lousã et d’Arganil. Recherches Géomorphologiques et Sédimentologiques sur le Massif Ancien et sa coverture à l’Est de Coimbra. Memórias do Centro de Estudos Geográficos 8, vol I, II, Lisboa De Marco A, Dimuccio LA (1999) La evolucion de los materiales de acumulacion en el Altiplano carbonatado de Cantanhede (NO de Coimbra—Portugal). In: Actas of the scientific study of Karstic

226 cavities as a contribution to geological knowledge, 17–20 June, Patronato de la Cueva de Nerja, Malaga, Espanha, pp 195–205 Dias RP, Cabral J (2002) Interpretation of recent structures in an area of cryptokarst evolution. Neotectonic versus subsidence genesis. Geodinâmica Acta 15:233–248 Dimuccio LA (1998) Studio morfoevolutivo dell’Altopiano Carbonatico di Cantanhede (NW di Coimbra—Portogallo). Tesi di laurea in Geologia, Dipartimento di Geologia e Geofisica, Facoltà di Scienze Matematiche Fisiche e naturali dell’Università degli Studi di Bari, Italia & Instituto de Estudos Geograficos, Faculdade de Letras, Universidade de Coimbra Dimuccio LA (2005) Torre Vale de Todos anticline and related morphological depressions (Central Portugal). In: Abstract sixth international conference on geomorphology, Zaragoza Dimuccio LA (2014) Karstification of Coimbra Hills at South of Coimbra (western-central Portugal). Depositional facies and stratigraphic controls of the (palaeo)karst affecting the Coimbra Group (Lower Jurassic); Tese de Doutoramento em Geologia (especialidade de geodinâmica externa), Universidade de Coimbra Dimuccio LA (2017) Tempo e espaço num geossistema cársico: os “pilares” em que assenta e se sustenta a interpretação da sua evolução geológico-geomorfológica. In: Cravidão F, Cunha L, Santana AP, Santos N, (eds), Espaços e Tempos em Geografia, Homenagem a António Gama, Imprensa da Universidade de Coimbra, University Press, pp 207–238 Dimuccio LA, Cunha L. (1999) O estudo de fenómenos cársicos aplicado á reconstituição paleambientais. O caso do Planalto de Cantanhede. In: Actas do Encontro de Geomorfologia, Coimbra, Projecto PRAXI XXXI, 2/2.1/CTA-156/94, pp 85–94 Dimuccio LA, Cunha L (2008) Modelação da vulnerabilidade intrínseca do aquífero elementar, fissurado e cársico do sector setentrional das Colinas Dolomíticas a Sul de Coimbra. In: Brandão J, Calado C, Sá Couto F, (eds), Património Geológico, Arqueológico e Mineiro em Regiões Cársicas, Actas do Simpósio Ibero-Americano, 29 Junho a 1 Julho, pp 67–78 Dimuccio LA, Cunha L (2015) Os tempos da carsificação nas Colinas dolomíticas a sul de Coimbra (Portugal centro-ocidental). In: Actas do VII Congresso Nacional de Geomorfologia, APGeom, pp 19–27 Dimuccio LA, Cunha L, Aubry T (2017) Grutas do Maciço de Sicó (Portugal Central): geologia, geomorfologia e espeleogênese. In: Gomes AA, Teixeira J, Soares L, (eds), Livro de Atas do 8 Congresso Nacional de Geomorfologia, APGeom, pp 75–76 Dimuccio LA, Cunha L (2018) Síntese interpretativa do (paleo)carso na cidade de Coimbra (Portugal). In: Cunha L, Yamaki H, (orgs), P149 Paisagem e Território, Universidade Estadual de Londrina, CDU 712(81)(469): 67–82 Dimuccio LA, Dinis JL, Aubry T, Cunha L (2014a) Clastic Cave sediments and speleogenesis of the buraca escura archaeological site (Western–central Portugal). In: Rocha RB, Pais J, Kullberg JC, Finney S (eds) Strati 2013. First international congress on stratigraphy. At the cutting edge of stratigraphy, Springer Geology XLV, pp 931–935 Dimuccio LA, Duarte LV, Cunha L (2014b) Facies and stratigraphic controls of the palaeokarst affecting the lower jurassic coimbra group, Western Central Portugal. In: Rocha RB, Pais J, Kullberg JC, Finney S, (eds), Strati 2013. First international congress on stratigraphy. At the cutting edge of stratigraphy. Springer Geology, vol XLV, pp 787–791 Dimuccio LA, Duarte LV, Cunha L (2016) Definição litostratigráfica da sucessão calco-dolomítica do Jurássico Inferior da região de Coimbra-Penela (Bacia Lusitânica, Portugal). Comunicações Geológicas 103:77–95 Dinis J (2001) Definição da Formação da Figueira da Foz; Aptiano a Cenomaniano do sector central da margem oeste ibérica. Comunicações do Instituto Geológico e Mineiro, t. 88:127–160

L. Cunha et al. Duarte LV, Soares AF (2002) Litostratigrafia das séries margo-calcárias do Jurássico inferior da Bacia Lusitânica (Portugal). Comum. Inst. Geol. Mineiro 89:135–154 Fleury E (1915) Sur l’hydrologie souterraine de l’Alviela. Comunicações dos Serviços Geológicos de Portugal, t. XI, Lisboa Fleury E (1917) Notes sur l’erosion en Portugal, II: les lapiés dês calcaires ao nord du Tage. Comunicações dos Serviços Geológicos de Portugal XII, Lisboa, 127–274 Ford D, Williams P (2007) Karst Geomorphology and Hydrology. Chapman & Hall, London Guerreiro P (2015) Tufos calcários no Algarve central. Geomorfologia, sedimentologia e paleoambientes. Tese de Doutoramento em Geografia, Universidade de Coimbra, Coimbra Iurilli V, Martimucci V, Dimuccio LA, Rodi M, Bene V, Borneo V, Chirizzi G, Grassi D, Manzari M, Marzulli M, Montanaro A, Netti P, Sannicola GC, Selleri G, Sordoilette C, Sportelli D (2013) Talismã 2010. Sistematizzazione di un rilievo speleologico. In: Atti del XV Incontro Regionale di Speleologia Pugliese “Spélaion 2010”, 10–12 dicembre 2010, pp 63–84 Kullberg JC, Rocha RB, Soares AF, Rey J, Terrinha P, Azerêdo AC, Callapez P, Duarte LV, Kullberg MC, Martins L, Miranda R, Alves C, Mata J, Madeira J, Mateus O, Moreira M, Nogueira CR (2013) A Bacia Lusitaniana: Estratigrafia, Paleogeografia e Tectónica. In: Dias R, Araújo A, Terrrinha P, Kullberg JC (eds), Geologia de Portugal, vol II. Escola Editora, pp 195–347 Martins AF (1949) Maciço Calcário Estremenho. Contribuição para um estudo de Geografia Física. Tese de Doutoramento, Ciências Geográficas, Faculdade de Letras, Universidade de Coimbra. Reedição em 1999—Maciço Calcário Estremenho: 50 anos. Jornadas de Estudo, Parque Natural das Serras de Aire e Candeeiros, Maio, Bairro, pp 7–8 Mendes AG (1985) Os Tufos de Condeixa—Estudo de Geomorfologia. Cadernos de Geografia 4:53–119 Neves J, Soares M, Redinha N, Medeiros S, Cunha L (2003) O Sistema espeleológico do Dueça. In: Actas do IV CNEspeleo Congress, Leiria Paiva IM (2015) Hidrossistema cársico de Degracias-Sicó. Tese de Doutoramento em Geografia, Universidade de Coimbra, Estudo do funcionamento hidrodinâmico a partir das suas respostas naturais Palmer AN (2007) Cave Geology. Allen Press, Lawrence, Kansas Ribeiro A, Pereira E, Chaminé H, Rodrigues J (1995) Tectónica de Megadomíno de cisalhamento entre a Zona de Ossa Morena e Zona Centro Ibérica na região de Porto-Lousã. In: Atas 40 Congresso Nacional de Geologia, Porto Ribeiro A, Cabral J, Baptista R, Matias L (1996) Stress pattern in Portugal mainland and the adjacent Atlantic region. West Iberia. Tectonics 15(2):641–659 Rodrigues ML (1998) Evolução geomorfológica quaternária e dinâmica actual, aplicações ao ordenamento do território, exemplos no Maciço Calcário Estremenho. Faculdade de Letras da Universidade de Lisboa, Tese de Doutoramento em Geografia Física Rodrigues ML, Cunha L, Ramos C, Ramos Pereira A, Teles V, Dimuccio L (2007) Glossário Ilustrado de Termos Cársicos. Coordenação Maria Luisa Rodrigues, Edições Colibri, Lisboa Rodrigues ML, Fonseca A (2010) Geoheritage assessment based on large-scale geomorphological mapping: contributes from a Portuguese limestones massif example. Géomorphologie: Relief, Process, Environment 2, 189–198 Soares AF (1998/2001) Reflexões sobre os tempos de carsificação dos Maciços Calcários de Sicó, Alvaiázere e Estremenho. In: Livro de Homenagem ao Prof. Doutor Gaspar Soares de Carvalho, 103–128 Soares AF (2007/2008) Um fragmento curioso. A Serra de Sicó. Cadernos de Geografia 26/27: 19–24 Soares AF, Cunha L, Marques JF (1997) Les tufs calcaires dans la région du Baixo Mondego (Portugal) – Les tufs de Condeixa.

17

The Sicó Massif: Morphostructural Aspects, Hydrology …

Présentation générale. Études de Géographie Physique, Travaux 1997, Supll. XXVI, Aix-en-Provence: 55–58 Soares AF, Marques JF, Rocha RB (1985) Contribuição para o Conhecimento geológico de Coimbra. Memórias e Noticias, Publicação Museu Laboratório Mineralógico e Geológico da Universidade de Coimbra 100:41–71 Soares AF, Marques JF, Sequeira AJD (2007) (eds) Notícia explicativa da Folha 19-D Coimbra-Lousã. Instituto Nacional de Engenharia, Tecnologia e Inovação, Departamento de Geologia, Lisboa Terrinha P, Rocha RB Rey J, Cachão M, Moura D, Roque C, Martins L, Valadares V, Cabral J, Azevedo MR, Barbero L,

227 Clavijo E, Dias RP, Matias H, Madeira J, Silva CM, Munhá J, Rebelo L, Ribeiro C, Vicente J, Noiva J, Youbi N, Bensalah MK (2013) A Bacia Do Algarve: Estratigrafia, Paleogeografia E Tectónica. In: Dias R, Araújo A, Terrrinha P, Kullberg JC (eds) Geologia de Portugal, Escola Editora, vol II, pp 29–166 Thomas C (1985) Grottes et Algares du Portugal. Editado pelo autor, Comunicar Lda, impressão EUROGRAF, Lisboa Vieira A, Cunha L (2006) Património geomorfológico—de conceito a projecto. O maciço de Sicó. Publicações da Associação Portuguesa de Geomorfólogos 3:147–153

18

The Limestone Massif of Estremadura Maria Luísa Rodrigues

Abstract

The karst landscapes of Portugal are confined to the sedimentary basins where there are uplifted limestone rocks. The most important limestone massif is the Limestone Massif of Estremadura (LME) located in the Western Sedimentary Basin that contact by an overthrust fault with the active Tagus River sedimentary basin. Although there are other limestone massifs in Portugal, they are smaller and have less developed karst landforms. What makes the LME special is the thickness of the limestone, its high content of calcium carbonate and tectonic uplift of the entire massif in relation to the surrounding areas. No permanent river cuts across the limestone mass, and the water circulation is subterranean. For this reason, most of great karst springs are located along the LME borders, principally in the eastern side, near the tectonic contact with the impermeable sediments of the Tagus Basin. In this chapter, the main geomorphological units within the LME are characterized: three anticline mountains, two plateaus and three tectonic depressions in graben structures. Examples of the main types of karst landforms according to dimension are presented, namely: large karst landforms (poljes, big uvalas, karst canyons or amphitheatre head valleys), medium karst landforms (dolines, dry valleys, karst springs or waterfalls) and small karst landforms (karren features or swallow holes). Among this set of karst landforms, some show a particular value and should be preserved as geoheritage and geomorphosites. Two cases

are the polje of Minde and the Fórnia amphitheatre head valley that contains valuable remnants of relict slope deposits from Quaternary cold periods. Keywords






Karst landforms Geomorphological units Geoheritage Geosites Geomorphosites

18.1




Introduction

The Limestone Massif of Estremadura (LME) is located in the Lusitanian Basin (western Meso-Cenozoic inactive basin), located in Central Portugal in contact with the Tagus Cenozoic Basin. It is the most important limestone massif of Portugal, not only by its extension, but also by the diversified set of karst forms it presents. The massif, located about 90 km north of Lisbon and 20 km from the Atlantic Ocean (Fig. 18.1), shows a clear-cut geographical, geological and geomorphological individuality. Visually, the most striking features are the large and imposing uplifted limestone compartments, reaching an elevation of 677 m asl, punctuated by manifold karstic forms, as well as the absence of permanent subaerial rivers. The LME, part of the Lusitanian Basin, represents, in its overall traits, an uplifted block between two important tectonic alignments of Betic direction, both of the fold-faultoverthrust type: the Lousã–Pombal–Nazaré and the

M. L. Rodrigues (&) Centre of Geographical Studies, Institute of Geography and Spatial Planning, University of Lisbon, Lisbon, Portugal e-mail: [email protected] © Springer Nature Switzerland AG 2020 G. Vieira et al. (eds.), Landscapes and Landforms of Portugal, World Geomorphological Landscapes, https://doi.org/10.1007/978-3-319-03641-0_18

229

230

M. L. Rodrigues

Fig. 18.1 Location of the Limestone Massif of Estremadura and its main geomorphological units. A. Depression of Alvados, M. Depression of Minde, Md. Depression of Mendiga

Montejunto-Serra de Aire alignments, which in the ELM sector correspond to the overlapping of the Tagus Basin sediments by the Jurassic limestones.

18.2

Geological Framework

As regards lithology, the presence of Jurassic to Lower Cretaceous formations is to be noted, as well as the absence of more recent formations apart from different types of terra rossa (mainly argillaceous or with more or less sand and pebbles) and angular debris deposits formed by frost shattering and mass wasting in Quaternary cold periods. Drilling made for oil prospection beneath the limestone series confirmed the existence of sandy marls and sandstones lying under an important clay-evaporitic complex (the “Dagorda Marls”), from the base of the Jurassic (Triassic age). This clay-evaporitic unit plays an important role in the morphostructural individualization of the LME and is overlain by a thick package of Jurassic sediments, predominantly limestones, reaching several hundred metres thick. The diapiric materials outcrop only in narrow diapiric depressions (Fig. 18.2), due to the soft rocks’ preferential erosion when brought to the surface, linked with deep tectonic faults affecting the basement. The thick Dogger (Middle Jurassic) limestone complex reaching almost 500 m (Ruget-Perrot 1961) decisively contributes to the geomorphological characteristics of the

massif. Among the Dogger formations, the most prone to dissolution are the Bajocian and Bathonian compact or oolithic limestones, where the majority of karst landforms (surficial and underground ones) are developed. On the other hand, the Aalenian is clayey and marly in the bottom, with increasing limestone content towards the top. The Callovian shows a sparse distribution, is more argillaceous and represents the end of the sequence, and the outcrops show ancient karst forms that developed before the Upper Jurassic sedimentation (palaeokarst, fluvial incisions, etc.). The Upper Jurassic is represented by the Upper Oxfordian and Kimmeridgian which discordantly overlie the Bathonian–Callovian complex. Those formations show different facies, and while outcrops of the Oxfordian are shaped by the same processes as the Bajocian–Bathonian units (karst development, rock falls, etc.), the Kimmeridgian is developed as clays and marls and is prone to water erosion, slides and creep. The Lower Cretaceous is represented by eruptive rocks at its base, with the detrital complex being only present in the north at the Ourém basin, outside the LME. Its absence in the massif corresponds to a major sedimentary gap, although there are residual deposits of coarse sands and pebbles (quartz and quartzite), as well as “terra rossa” formations. The latter are formed mostly by clay, but in some cases show a high content of sand and pebbles, that can be correlative of erosional phases during the Tertiary, marked also by different karst episodes.

18

The Limestone Massif of Estremadura

231

Fig. 18.2 Part of the elongated diapiric depression in Bezerra. The diapiric outcrops (with colours from red to wine-lees) correspond to the agricultural fields in front of the village and are bordered by faults in

the contact with limestone rocks (base of Candeeiros Mountain, behind the houses, and a horst in first plan)

More recent are inherited deposits from cold Quaternary periods. Most of them are stratified slope deposits classified according to field criteria into three major groups (Rodrigues 1998; Rodrigues and Fonseca 2010): (i) openwork or clast-supported stratified slope deposits with different degrees of consolidation due to calcium carbonate cement (episodes C1, C2 and C3), (ii) solifluction deposits, generally matrix-rich (episodes S1, S2 and S3) and (iii) deposits included in well-developed talus screes with vertical and longitudinal sorting of clasts by size. Within the first group, the second episode (C2) has a larger spatial representation and better-preserved sedimentary characteristics. Karst landforms are clearly linked with the lithology and the tectonic stresses that affected the limestone rocks. They show spatial distribution that coincides mostly with the Bajocian–Bathonian–Oxfordian outcrops and with some

clear alignments following the main faults and fracture directions. This generalization is valid for the surficial karst forms (swallow holes, springs, dolines, uvalas, poljes and fluvio-karst landforms), as well as for the underground one.

18.3

Geomorphological Units

If the calcareous nature of the rocks controls the particular landscapes of the LME, reinforcing the grandeur of the escarpments and conditioning the development of karst morphology, the fundamental architecture of the LME is due to tectonics. Consequently, the following geomorphological units can be defined within LME (see Figs. 18.3 and 18.4): (i) three mountain ranges developed in anticline structures— the mountains of Candeeiros, Aire and Alqueidão, (ii) two

232

M. L. Rodrigues

Fig. 18.3 Limestone Massif of Estremadura (LME) Digital Elevation Model. A. Depression of Alvados, M. Depression of Minde, Md. Depression of Mendiga

plateaus—Santo António and São Mamede (including its extension to the Fátima platform), (iii) three tectonic depressions (grabens)—Minde, Alvados and Mendiga, which follow two fault alignments and (iv) one diapiric depression elongated from Rio Maior to Batalha. The Candeeiros Mountain builds over an elongated anticline cut by faults on both west and east sides. The western slope corresponds simultaneously to a fault scarp and to an ancient littoral cliff, and the eastern slope is bound by one of the faults that limit the diapiric depression. This 30-km-long mountain constitutes the western limit of the LME (Fig. 18.3), reaching an elevation of 615 m asl.

A complex system of faults and fractures, involving those elongated along the anticline axis and the perpendicular set of fractures, underpins the distribution of karst depressions, karren and old fluvio-karst erosional trenches. Morphologically, the contrast between the flat summits and the convex part of the slopes is clear (Figs. 18.3, 18.4 and 18.5). The former shows slope angles below 10°, while the latter, with long rectilinear slope sectors, shows angles above 25°, and surpassing 30° in the western slope. The Aire Mountain is also associated with an anticline which is faulted along its E and S borders. With an almost circular shape and reaching 678 m asl (LME’s highest

18

The Limestone Massif of Estremadura

233

Fig. 18.4 The Limestone Massif of Estremadura (LME) slope angles map. A. Depression of Alvados, M. Depression of Minde, Md. Depression of Mendiga

altitude), this range is located in LME’s eastern border, where the Dogger limestone contacts with the Tertiary sediments of the Tagus Basin along a major overthrust. This tectonic setting resulted in a long scarp, locally named the Arrifes, and proposed to be classified as a geosite (Leal and Cunha 2014). The flat mountain summit is carved by dissolution forms, such as dolines and different types of karren (Fig. 18.6) and the steep slopes (20°–30°) are trenched by fluvio-karst gullies related to major fractures. The Alqueidão anticline supports different morphology when compared with the Candeeiros and Aire anticlines (see Figs. 18.3 and 18.4). The latter are anticlines uplifted by

tectonics and formed by hard limestone, while the Alqueidão anticline suffered subsidence and is currently a graben in relation to a fault scarp located in its eastern side (Reguengo do Fetal fault scarp that uplifted the São Mamede Plateau), besides being formed by the Upper Jurassic softer materials. The Santo António and São Mamede plateaus are separated by the tectonic depressions (grabens) of Alvados and Minde (Figs. 18.3 and 18.4) and are the LME units that show less intense deformations. The São Mamede Plateau is the northernmost morphostructural unit of the LME and is limited westwards by the fault scarp of Reguengo do Fetal that separates it from

234

M. L. Rodrigues

Fig. 18.5 The eastern slope of the Candeeiros Mountains (in front) and Mendiga tectonic depression

the lower Alqueidão anticline (Figs. 18.3 and 18.4). In the east, it contacts with the elevated Aire Mountain, and in the south, it is uplifted in relation to the Alvados and Minde grabens. The dominant lithology is the Bathonian limestone, prone to the development of karst landforms, resulting in elongated karst depressions and corridors showing a close link with the main tectonic directions (NW–SE and NE–SW). The pattern of karst landforms of the Santo António Plateau is different from the one of São Mamede. The plateau is tectonically balanced southwards, so there are higher altitudes in the northern triangular shape where the surficial and underground karst forms are more developed (Figs. 18.3 and 18.4). This plateau extends from the overthrust with the Tagus Basin in the eastern side to the fault scarp contacting with the Mendiga tectonic depression (graben) westwards.

Together, the two plateaus (São Mamede and Santo António) show the richest set of karst landforms. The three depressions correspond to the lower altitudes inside the LME, caused by tectonic subsidence (see Figs. 18.3 and 18.4). The Minde and Alvados grabens are linked to NW–SE faults, but the movement on each side is different, forming asymmetric grabens. The highest throw typifies the NE margin of the Santo António Plateau, giving origin to impressive fault scarps (the Costa de Minde and the Costa de Alvados) with relief of around 300 m (Fig. 18.7). The floor of the Minde closed depression shows altitudes below 200 m asl near the Minde village, but the Alvados open depression shows a more irregular floor due to secondary faulting, different rock resistance and erosional processes (Fig. 18.8), varying between 220 and 250 m asl.

18

The Limestone Massif of Estremadura

235

Fig. 18.6 Covão do Milho doline in the Aire Mountain top. Note the Spitzkarren in front and the Karrentisch in the doline slope where limestone shows slightly inclined to horizontal bedding planes

The Mendiga depression is oriented NNE–SSE to N–S in relation to a set of submeridian faults linked to the Candeeiros anticline (Figs. 18.3 and 18.4) and to the orientation of the diapiric depression. Its floor is more elevated in the northern edge (330 m asl) and hanging 180 m above the Porto de Mós diapiric depression and is balanced and open southwards, where the altitudes reach 240–250 m. One of the most striking landforms in the LME is the Minde polje (Fig. 18.9). This polje occupies most part of the closed tectonic depression and is 4 km long and 1.5 km wide (Rodrigues 1988, 1991). It is a seasonal/temporary flooded polje with the duration of the flood depending on the duration of the rainy season and the level of flooding connected with the amount of winter rainfall. During the

summer, the bottom of the polje is dry, with the exception of some permanent small lakes. The discharge of the permanent karst springs located along the NW and N borders is not sufficient to keep the small rivers present inside the polje flowing. Normally in the fall, with the beginning of the rainy season, the small rivers show water flow, but it disappears in swallow holes scattered across the polje floor. As the polje floor altitude is very close to the ground water level, when it rises in response to rainfall, the swallow holes (Fig. 18.10) stop absorbing the river water and act as springs contributing to the flooding of the polje. This type of hydrological functioning can only be seen in the Minde closed depression, since neither Alvados nor Mendiga depressions are closed; Alvados is open towards

236

M. L. Rodrigues

Fig. 18.7 Fault scarp of Costa de Minde linked with the flat bottom of the Minde polje (during the dry season)

the NW (see Fig. 18.8), and Mendiga is open at both extremities (N and S).

caves and underground hydrological landscapes, but are not dealt with here.

18.4

18.4.1 Large Karst Landforms

Karst Landforms

In the LME, as in many other karst massifs, it is possible to classify the karst landforms in four main groups: large, medium and small surface karst landforms and subterranean karst. The latter include horizontal galleries, vertical shafts,

Large karst landforms are normally more spectacular and capture the attention of more visitors. These include the polje, big uvalas, karst canyons or amphitheatre head valleys. In the LME, the main examples are the emblematic

18

The Limestone Massif of Estremadura

237

Fig. 18.8 Alvados tectonic depression, with the lowest sector of the floor and in the top-left, the fault scarp of Costa de Alvados. The elevated areas that disrupt the floor regularity (such as the one in the

middle) are due to secondary faults parallel to that of Costa de Alvados. In the top-right, the opening towards northwest is visible

polje of Minde (Figs. 18.9, 18.11 and 18.12), which is well known internationally (Cunha 1996; Nicod 1995; Rodrigues 1995), the uvala located in Chão das Pias in the northern sector of Santo António Plateau (Fig. 18.13), the Alviela springs karst canyon (Fig. 18.14), the Fórnia amphitheatre head valley (Fig. 18.15) and the Fórnia river waterfall (Fig. 18.16).

the Santo António Plateau SE boundary, although the density of forms is higher in its northern extremity. Although the plateaus are more prone to dissolution processes (and so to the development of karst depressions), dolines can also be observed in the flat summits of the Aire and Candeeiros anticlines (Figs. 18.6 and 18.18). These two anticline mountains also show fluvio-karst forms, such as dry valleys (Fig. 18.19). Karst springs occur all over the LME, although the more important permanent ones are located in its limits, where the limestones contact with more impermeable materials, especially along the boundary with the Tagus Basin. The Alviela is the most important river that is formed by LME karst springs (Fig. 18.20), with the water flow sufficient to supply the city of Lisbon in the past.

18.4.2 Medium Karst Landforms Medium karst landforms include the dolines, dry valleys, karst springs and waterfalls. The examples here provided are associated with the LME geomorphological units. In Fig. 18.17, we can see a big karst depression located near

238

M. L. Rodrigues

Fig. 18.9 Tectonic depression of Minde seen from the top of the Santo António Plateau (near the Costa de Minde fault scarp) during summer. The area occupied by the Minde polje is clear (with trees and

cultivated fields) and ends in a small edge near the Minde village. The polje is surrounded by the Mira de Aire village constructions (N and NW borders)

18.4.3 Small Karst Landforms

Figs. 18.6 and 18.22a, b, and (iii) those of biochemical origin such as the solution pans, honeycomb or rainpit microforms (Fig. 18.23a–c).

Small karst landforms can actually form large groups and even shape an entire landscape, and include karren features, swallow holes, etc. The small landforms are decisive to transport water from the surface into the subsurficial and underground karst. There are different types of karren in the LME, such as (i) those due to surficial running water associated with limestone solution (Rinnenkarren or Meanderkarren) as shown in Fig. 18.21a, b, (ii) those where solution is controlled by rock fractures and bedding planes (Karrentisch, Kluftkarren and Spitzkarren), such as shown in

18.5

Examples of Geomorphosites

Some of the morphostructures and karst landforms presented in the previous sections can be classified as geosites and, particularly, as geomorphosites. A geosite is an element representing geoheritage, which is considered here as all the natural abiotic elements present in the Earth surface,

18

The Limestone Massif of Estremadura

239

Fig. 18.10 Some of the ponors spread in the Minde polje floor. Their hydrological functioning shows that they act as both as swallow holes and karst springs

Fig. 18.11 Partial flooding of the Minde polje viewed from the NW. Note the greater amount of water accumulated near the Minde village where the floor is lower

240

M. L. Rodrigues

Fig. 18.12 Record flooding in the Minde polje in February 1996, which cut off the road connecting to the Santo António Plateau

emerged or submerged, that should be preserved due to its heritage value (Rodrigues and Fonseca 2007, 2008). Hence, geoheritage includes all types of abiotic heritage, such as geological (fossils, minerals, structures, sediments, etc.), geomorphological (landforms, correlative deposits, landscapes, etc.), hydrological (sources, rivers, hydrographic basins, karst hydrology, etc.) and pedological (palaeosoils, “pedosites”, etc.). Besides the polje of Minde which was presented above (Figs. 18.6, 18.8, 18.9, 18.10 and 18.11), another excellent example of a significant geomorphosite in the LME is the

Fórnia amphitheatre head valley, located in the Alvados depression (Fig. 18.14). This site should even be considered as of international significance due to its exceptional beauty, the complexity of processes that contribute to its formation, the particular geodiversity preserved inside (with associated biodiversity) and to the value of the preserved geomorphological heritage (with an enormous variety of geosites and extensive examples of geomorphological processes, forms and deposits). Inside this spectacular landform, there are several karst springs, including one emerging from an accessible cave, a river with waterfalls and, most of all, a set

18

The Limestone Massif of Estremadura

241

Fig. 18.13 Chão das Pias uvala located in the northern extremity of the Santo António Plateau

of Quaternary deposits that contribute to the improvement of the palaeoenvironmental reconstitution, with special relevance to the Iberian Peninsula. The slope deposits enclosed in the Fórnia were described and analysed by Rodrigues (1998) and mapped and evaluated by Rodrigues and Fonseca (2010, Fig. 18.24). The scientific and protection values of each deposit were assessed according to their representativeness, rareness, integrity and vulnerability (function of the degree of consolidation and of its accessibility). These criteria revealed that the Fórnia relict deposits show a total of 8.75 points in a maximum of 10 points, despite a lower cultural value (0.25 in a maximum of 1.0).

18.6

Conclusions

The first important studies about the Limestone Massif of Estremadura were done in the 1940s and 50s (Martins 1949, 1950), but the poor geological and topographical maps available by that time limited detailed analysis. In the 1980s and 1990s, new and more accurate research in the LME, including detailed field surveys at a scale larger than 1:10,000, has been conducted (Rodrigues 1988, 1998). These allowed to refine the definition of the boundaries of the LME morphostructural units, but also allowed for identification of the types and spatial distribution of karst

242 Fig. 18.14 Karst canyon in the proximity of the Alviela River springs

M. L. Rodrigues

18

The Limestone Massif of Estremadura

243

Fig. 18.15 Fórnia amphitheatre head valley, a circular cone-shaped form due to fluvial, karst and cryonival processes

landforms, geomorphosites and relict Quaternary cryonival slope deposits. Despite the advances made in the study of the LME, there is still significant research agenda to be implemented,

including the survey of underground network of galleries, caves and flow directions, and mapping of Quaternary slope deposits still preserved in steep dry valleys, such as those present in the western slope of the Candeeiros Mountain.

244

Fig. 18.16 Fórnia waterfall

M. L. Rodrigues

18

The Limestone Massif of Estremadura

245

Fig. 18.17 Covão do Feto doline developed in the Santo António Plateau. In the central part, there are dry stone circular constructions (casinas)

Fig. 18.18 Pia d’Água asymmetric doline in the Candeeiros Mountain

246

Fig. 18.19 Dry valley incised into the eastern slope of the Candeeiros Mountain, already disorganized by dissolution

M. L. Rodrigues

18

The Limestone Massif of Estremadura

Fig. 18.20 Temporary springs of the Alviela River which only shows stream flow in extreme flood situations (overflow)

247

248

M. L. Rodrigues

a

b

Fig. 18.21 Rinnenkarren and Meanderkarren in the Limestone Massif of Estremadura. a Rinnenkarren in the Candeeiros Mountain. This type of karren develops in rock slopes cut by joints. b Meanderkarren near the Bezerra village (base of the Candeeiros eastern slope)

a

Fig. 18.22 Karrentisch and Spitzkarren in the Limestone Massif of Estremadura. a Karrentisch in Barreira da Junqueira (Santo António Plateau) developed in subhorizontal limestones, although the most impressive ones are normally located in horizontal structures.

b

b Spitzkarren in the Candeeiros Mountain. This type of karren develops in the very deformed and fractured limestone rock and in this area reaches a height of about 50 cm

18

The Limestone Massif of Estremadura

a

249

b

c

Fig. 18.23 Examples of biochemical dissolution forms. a Asymmetric solution pan, b Grubchenkarren controlled by fissures, c honeycomb microforms

Fig. 18.24 Map of the Fórnia relict cryonival deposits, according to Rodrigues and Fonseca (2010)

250 Acknowledgements I am very grateful to my colleagues Gonçalo Vieira and Piotr Migón, because their text revision was precious and provided clarity to the content and form of my contribution to this book.

References Cunha L (1996) Les karsts portugais, problèmes et perspectives. Karstologia 28(2):41–48 Leal C, Cunha L (2014) Proposta de classificação da escarpa dos Arrifes do Maciço Calcário Estremenho (Portugal central) como património geomorfológico. Inventariação e caracterização dos valores patrimoniais. Proceedings I Encontro Luso-Brasileiro de Património Geomorfológico e Geoconservação, APGeom, pp 55–61 Martins AF (1949) Maciço Calcário Estremenho. Contribuição para um estudo de Geografia Física, Coimbra Martins AF (1950) Aspectos do relevo calcário em Portugal: os poljes de Minde e de Alvados. Cadernos de Geografia 1:25–33 Nicod J (1995) Découverte des karsts du Portugal Central. Karstologia 26:59–60 Rodrigues ML (1988) As depressões de Minde e de Alvados. Depósitos e evolução quaternária das vertentes. MS Diss. in Physical and Regional Geography, Specialization in Geomorphology, FLUL, Univ. de Lisboa

M. L. Rodrigues Rodrigues ML (1991) Depósitos e evolução quaternária das vertentes nas depressões de Minde e de Alvados (Maciço Calcário Estremenho, Portugal). Finisterra XXVI(51):5–26 Rodrigues ML (1995) Évolution quaternaire des versants, dissolution et karsification dans le Massif Calcaire de l’Estremadura. Livret-Guide de l’Excursion - Massif de Sicó, Massif Calcaire de l’Estremadura, Table Ronde Franco-Portugaise “Le Karst au Portugal (Géomorphologie, Spéléologie, Etudes Environnementales)”, pp 35–54 Rodrigues ML (1998) Evolução geomorfológica quaternária e dinâmica actual. Aplicações ao ordenamento do território. Exemplos no Maciço Calcário Estremenho. PhD Diss. in Physical Geography, Univ. de Lisboa, Lisboa Rodrigues ML, Fonseca A (2007) A valorização do geopatrimónio no desenvolvimento sustentável de áreas rurais. VII Colóquio Ibérico de Estudos Rurais – Cultura, Inovação e Território, Coimbra Rodrigues ML, Fonseca A (2008) Geopatrimónio e Desenvolvimento Sustentável. Estratégias de Valorização de Áreas Rurais. Cultura, Inovação e Território: o Agroalimentar e o Rural (Coord. L Moreno, M Sánchez, O Simões), pp 143–152, SPER - Sociedade Portuguesa de Estudos Rurais, Lisboa Rodrigues ML, Fonseca A (2010) Geoheritage assessment based on large-scale geomorphological mapping. Géomorphologie: Relief, Processus, Environ (2), 189–198 Ruget-Perrot C (1961) Études stratigraphiques sur le Dogger et le Malm inférieur du Portugal au Nord du Tage. Bajocien, Bathonien, Callovien, Lusitanien. Mem. nº 7, Serv. Geol. Portugal, Lisboa

Landforms and Geology of the Serra de Sintra and Its Surroundings

19

Maria Carla Kullberg and José Carlos Kullberg

Abstract

The Serra de Sintra is a landmark on the western coast of the Iberian Peninsula, resulting from the intrusion of a complex of alkaline igneous bodies during the upper Cretaceous in a stretched continental passive margin associated with the opening of the Atlantic Ocean. It is a differential erosion mountain standing out on a coastal plateau laid over the Mesozoic sedimentary rocks of the Lusitanian Basin and where the Cenozoic materials are scarce, difficult to date and essentially of continental facies. The morphological evolution of the Serra de Sintra reflects its progressive isostatic rebound and the work of marine erosion combined with Quaternary fluvial retouching. Keywords
















Granite landforms Raised beaches Hanging valleys Raised wave-cut platforms Coastal dunes Serra de Sintra

19.1

Introduction

The Serra de Sintra is a remarkable morphological feature, located in the central part of the West Iberian coast, overlooking the Atlantic Ocean, about 25 km to the west of Lisbon. It is a small mountainous massif with a significant set of structural landforms due to differential rock resistance, M. C. Kullberg (&) Departamento Geologia, Instituto Dom Luiz (IDL), Faculdade de Ciências, Universidade de Lisboa, Lisbon, Portugal e-mail: [email protected]

built on the intrusive rocks of the Sintra Igneous Complex (SIC) and its surroundings. The igneous rocks of the complex are much more resistant to erosion than the sedimentary host rocks around, which form a set of stepped surfaces that completely encircle the mountain. The summits of Serra de Sintra rise to 528 m in altitude, forming a E–W elongated interfluve that rises about 300–350 m above the adjacent planated landscape (Fig. 19.1). The Serra de Sintra has a rich and diverse vegetation cover, sometimes exuberant, combining components of the Mediterranean and Northern floras to hundreds of exotic trees and flower species in a rare frame of gardens, parks and forests. The mountain was classified as World Heritage under the “Cultural Landscape” category on the 6 December 1995 during the 19th Session of the UNESCO World Heritage Committee in Berlin. Studies on the Serra de Sintra have been developed by diverse personalities who have made history in the Earth sciences since the late eighteenth century, such as Déodat Dolomieu (1750–1801) and Wilhelm Ludwig von Eschewege (1777–1855). However, it was Paul Choffat (1849– 1919), who in 1883 began the modern geological studies of the region (Choffat 1883–87). It is also noteworthy to mention the works of the geographer Orlando Ribeiro (1940) and the geologist Carlos Matos Alves (1964), who, respectively, made the first in-depth studies on the geomorphology and petrography of the rocks of the Serra de Sintra. More recently, a comprehensive research based on detailed mapping was performed by M. C. Kullberg related to the geometry of the massif and the host rocks, as well as the mechanism of emplacement of the magmatic core of the Serra de Sintra (Kullberg 1996; Kullberg and Kullberg 2000).

J. C. Kullberg Departamento Ciências da Terra, GeoBioTec, Faculdade Ciências e Tecnologia, Universidade NOVA de Lisboa, 2829-516 Caparica, Portugal e-mail: [email protected] © Springer Nature Switzerland AG 2020 G. Vieira et al. (eds.), Landscapes and Landforms of Portugal, World Geomorphological Landscapes, https://doi.org/10.1007/978-3-319-03641-0_19

251

252

M. C. Kullberg and J. C. Kullberg

Fig. 19.1 General setting of the Serra de Sintra, in the westernmost region of the Estremadura Spur, including main roads and localities

19.2

Geology of the Sintra Igneous Complex Ant Its Host Rocks

The Late Cretaceous Sintra Igneous Complex intruded the Mesozoic sedimentary series of the Lusitanian Basin during the post-rift, passive margin stage of the West Iberian Margin (WIM, Fig. 19.2). This is one of the Late Cretaceous intrusive complexes, along with Sines and Monchique, that all show elliptical E–W elongated outcrop areas, rooted along a NNW-SSE lineament in the onshore of the West Iberian Margin (Rock 1982; Kullberg and Kullberg 2000; Miranda et al. 2009). On the magnetic anomaly map of Portugal (Silva et al. 2000) and adjacent offshore areas, these intrusions stand out as strong anomalies that are aligned with a fourth one located on the Guadalquivir Bank, thus forming a 300 km-long lineament (Kullberg et al. 2013; Terrinha et al. 2018). Miranda et al. (2009) included these intrusive complexes in the latest of the three main magmatic cycles that affected the Iberian margin during the Mesozoic: the alkaline cycle is of Late Cretaceous age (94–72 Ma), preceded by the tholeiitic (Hettangian, 200 Ma) and the transitional cycles

(Lower Cretaceous, 145 Ma). Besides these three large magmatic bodies, there are other smaller magmatic occurrences included in the alkaline cycle, all located in the onshore of the Lisbon peninsula: the intrusive Ribamar diorite (88 Ma), the extrusive Lisbon Volcanic Complex (75–72 Ma) and the Mafra Radial Dyke Complex, by the same age (Fig. 19.2). The geometry of the SIC shows a composite intrusion consisting of a granite laccolith (*80 Ma), elongated E–W and topping vertical gabbroic plugs and a syenite plug and laccolith (*85 Ma). A complex of sills and dykes are included in the SIC, with the basic sills being precursor of the gabbro intrusives. The ring felsic dykes and radial dykes post-date the granite (Kullberg 1996; Kullberg and Kullberg 2000; Terrinha et al. 2018) (Fig. 19.3). This geometry was only slightly modified during the Palaeogene and the Late Miocene inversions that resulted in thrusting of the northern border of the intrusion over the country rocks (Kullberg and Kullberg 2000; Terrinha et al. 2018). The intrusion of the two magmatic bodies (granite and gabbro–syenite) is associated with two sequential alkaline magmatic episodes in the passive Iberian margin. The

19

Landforms and Geology of the Serra de Sintra …

253

Fig. 19.2 Geological setting and structural map of the southern part of the Lusitanian Basin: a Simplified geological framework of the region of Sintra–Lisboa–Arrábida (mod. from Ribeiro et al. 1990), with (1) locating the Ribamar dioritic intrusion and LVC the younger

extrusive Lisbon Volcanic Complex. Abbreviations for the legend: A. thrust fault, B. blind thrust fault, C. inferred thrust fault; D. anticline; E. syncline. b Location and geological context of the region represented in (a)

location of the feeding planes and pipes during both episodes was controlled by pre-existing faults of NNW–SSE, E–W and NE–SE directions, which are probably late Variscan faults that were active during the Jurassic–Early Cretaceous rifting. The onshore part of the SIC has an area of about 57 km2 depicting an elliptical, E–W elongated outcrop of granite (*10.5  5.5 km), which is the upper part of a less than 1 km thick laccolith (according to gravimetric modelling, Terrinha et al. 2018) that intrudes the Upper Jurassic rocks (Fig. 19.3). The offshore part of the SIC is estimated to be approximately equal to the onshore one (Fig. 19.2). In the middle of the granite mass, a NNW–SSE trending sub-elliptical complex of syenite, gabbro, diorite and intrusive multi-compositional breccias crop out (Alves 1964) within an area of about 20 km2. According to Alves (1964), the igneous breccias are always found either within the

gabbro–diorite–syenite body or at the contact of this intrusion with the granite. Scattered gabbro also crop out along the northern thrust of the SIC. These intrusive bodies are accompanied by sills, cone-sheets and ring-dykes of varied compositions and orientations (Fig. 19.3). The basic sills are micro-gabbro, dolerite and lamprophyre, and they are found only in the sedimentary host rocks, mostly near the eastern side of the intrusion. The cone sheets consist of dykes of varied composition, including microgranites, microsyenites, trachytes, microdiorites and rare andesites, some of these rocks with a vitreous matrix (Alves 1964). They are restricted to the central part of the southern flank of the SIC and dip towards the north and northwest, i.e. towards the gabbro–syenite intrusion. Granite facies, displaying different grain sizes, consist mainly of quartz and feldspar and lack solid state deformational structures. Gabbro, where brittle structures are

254

M. C. Kullberg and J. C. Kullberg

Fig. 19.3 Geology of the Sintra Intrusive Complex. a Simplified geological map of the Sintra Intrusive Complex and host rocks, showing the location and orientation of the cross section, b digital

terrain model with main tectonic features (faults, fractures and lineaments) and c modelled geological cross section of the SIC intrusion and its sedimentary host rocks

frequent, includes plagioclase, biotite, pyroxene and opaque minerals (mostly magnetite, also present in some specimens of granite). Syenite facies show plagioclase with porphyritic, microcrystalline texture in some cases. Geochronological data based on U–Pb zircon ages indicate that the Sintra granite is slightly younger than the gabbro body of the SIC. Miranda et al. (2009) obtained ages of 79.2 ± 0.8 Ma for the granite and Grange et al. (2010) obtained an age of 81.7 ± 0.4 Ma for the granite, 80.1 ± 1.0 Ma for the micro-syenite and a robust 83.4 ± 0.7 Ma age for the gabbro bodies. The onshore outcrop of the SIC is surrounded by sedimentary rocks of Upper Jurassic to Quaternary ages, forming two distinctive groups: (i) Mesozoic marine facies rocks from the Lusitanian Basin (Upper Oxfordian to Upper

Cenomanian) predating the SIC, thus structured by its emplacement and (ii) the post-intrusion rocks of Cenozoic age, mostly of continental facies. The post-Oxfordian Mesozoic sedimentary sequence intruded by the Sintra Igneous Complex is about 2700– 3000 m thick. The Upper Jurassic and Lower Cretaceous are mainly crystalline and compact limestones, interspersed by marly limestones and limestones of pelagic facies, rich in organic matter. In the Lusitanian Basin, this is the only region where the Jurassic–Cretaceous transition is continuous and represented by marine environment sedimentation, although at shallow depth. The first fine grained sandstone beds, which are of Valanginian age, occur interspersed in marly limestones and clay beds. They are markers of a marine regression period whose apogee was in the Upper

19

Landforms and Geology of the Serra de Sintra …

Aptian, characterized by the deposition of the formation of the Almargem sandstone (“Grés de Almargem”, Kullberg and Kullberg 2000). The Albian–Cenomanian transition points out the beginning of an important marine transgression at the Lusitanian Basin scale, which caused the deposition of marly layers with ostracods, progressively evolving to compact and crystalline limestones with rudists, already in the Upper Cenomanian. Afterwards, in this region, an important sedimentary gap lasting about 40–50 Ma followed. The oldest sedimentary units of Cenozoic age are continental facies deposits, constituting the Monte Santos Conglomerate, superimposed by a set of more recent units grouped in the Galamares Complex, of Paleogene or, possibly, of Lower Miocene age (Carvalho 1994). This older conglomerate, with its limestone and granite pebbles, shows that the erosion of the post-intrusion relief started shortly after. They are slightly deformed and overlaid by sub-horizontal marine deposits of Miocene age (Serravalian– Lower Tortonian) producing an angular discordance, also represented in the easternmost region of the Serra de Sintra domain. The residual deposits over the planation surfaces are of Pliocene age. The Vinagre Formation, similar to certain raña deposits of the Alentejo (south Portugal), was considered more recent than the mentioned marine Miocene rocks, thus being possibly of Old Quaternary age (Carvalho 1994). Most of the coastal deposits, beach sands, dunes (covering a large part of the coastal area to the south and north of the Serra de Sintra) and consolidated dunes (e.g. Oitavos Dune), slope deposits and alluvium are Quaternary in age. Due to the intrusion of the SIC, the Mesozoic sedimentary host rocks were stretched and form an asymmetric rim syncline with an overturned flank of Upper Jurassic and Lower Cretaceous sedimentary rocks overthrust by the SIC towards the north. This thrust zone extends into the offshore for an uncertain distance and eastwards up to the Tagus River where it becomes a blind thrust (Figs. 19.2 and 19.3). Altogether, it forms an ENE–WSW northwards directed, more than 50 km-long thrust zone. The thrust displacement decreases eastwards away from the SIC, both gradually and by discrete attenuation through N–S striking transfer faults. The sills located in the host rocks show also extensional structures near the contact with the granite. The host Oxfordian carbonates display thermal metamorphism, semi-ductile extensional faults, extreme flattening of blocks and pebbles from conglomerates and debris flow layers, and a pervasive set of fissures, which are perpendicular to bedding and their strike is parallel to the contact with the granite. These fissures colour the black marls in white,

255

Fig. 19.4 Characteristic zebra-like pattern of the “Xistos do Ramalhão” Formation

giving them a zebra-like pattern that results from the reaction of oxidizing fluids exhaled from the intrusion (“Xistos do Ramalhão” Formation, Fig. 19.4). Gathering all the geological and geophysical information (field observations, gravimetry, anisotropy of magnetic susceptibility-AMS), petrological and radiometric dating, the origin and structure of the Sintra Intrusive Complex can be explained as the result of the following sequence of magmatic events (Terrinha et al. 2018): (i) intrusion of the basic sills presently surrounding the SIC, predominantly on the eastern side, (ii) intrusion of the gabbro–diorite–syenite bodies, whose composition has mantle like affinities, using the previous anisotropies (forming prolate roots aligned along NNW–ESE and E–W trending main faults), (iii) intrusion of the granite magma, having crustal affinities, that formed the laccolith, caused uplift of the cover and

256

M. C. Kullberg and J. C. Kullberg

stretching of Jurassic and Cretaceous host rocks as well as the basic sills, (iv) intrusion of the cone sheets and (v) intrusion of the radial dykes.

immature forms which testify to the relative youth of the relief. Valleys running westwards to the coast become hanging above the coastal cliffs (Ribeiro 1940).

19.3

19.3.1 The Serra de Sintra

Landforms

In the Serra de Sintra region, the major landforms show clear lithological control. The igneous rocks are more resistant to weathering, so differential erosion controls the main traits of relief. On the other hand, the fluvial network and the course of valleys are almost always controlled by faults and fractures. The bordering region of the Serra de Sintra is a complex erosional surface that completely encircles the mountainous massif. To the south and the east, it is called the Cascais Platform (Figs. 19.5 and 19.6a, b) and, to the north, the São João das Lampas Platform. The latter is limited in the east by an area of hilly relief on Meso-Cenozoic formations, cut by faults and eruptive rocks, mostly belonging to the Lisbon Volcanic Complex (LVC) (Fig. 19.5). Within the mountainous area, the fluvial network is represented by locally deeply carved valleys, exhibiting

The main relief type of the Serra de Sintra is a mountainous topography that evolved by differential erosion, with the harder rocks of the SIC supporting more elevated terrain. Along with unroofing of this intrusive magmatic complex, the sedimentary country rocks atop of the granitic laccolith and the gabbro–sienitic plug and laccolith were completely eroded away. This sedimentary cover was about 3000 meters thick, corresponding to a time span of about 68 million years, between the Upper Jurassic (Oxfordian—150 Ma) and the Upper Cretaceous (Cenomanian—92 Ma). The eastern sector of the mountain range is mainly composed of multiple granite peaks, which generally correspond to in situ clusters of large boulders, standing on the crests of the hills, forming typical tors (Fig. 19.7). These granite boulders are a dominant geomorphic feature and are a result of the interplay of deep weathering, mainly along the

Fig. 19.5 Terrain model of the Sintra region, seen from the WSW to the ENE, illustrating the major landforms: the main relief built on the SIC rocks, 1 the aligned peripheral hills (to the south), 2 the surrounding plains, 3 beaches on the western border with coastal

cliffs, where the SIC rocks face the ocean, 4 raised beaches atop the western cliffs and 5 deep fluvial incision, producing hanging valleys over the coastal cliffs

19

Landforms and Geology of the Serra de Sintra …

Fig. 19.6 Panoramas from the rocky promontory of Cresmina. a (on top). View northwards to the Serra de Sintra. In the foreground, the sedimentary host rocks (Cretaceous) dipping northwards, to the SIC, corresponding to the southern flank of the rim syncline (Alcabideche syncline). In the background, the Serra de Sintra approaches the sea by

257

stepped plains forming raised beach erosional levels (see text— Sect. 19.3.3c—for explanation). b View southwards to the Cascais Erosion Platform. The Cretaceous sedimentary host rocks are dipping northwards, with decreasing dip angle to the south, further away from the SIC

Fig. 19.7 Tors in the upper areas of the eastern sector of the Serra de Sintra. On the background, the Pena Palace, built on top of the Pena peak

258

M. C. Kullberg and J. C. Kullberg

Fig. 19.8 Tors in the eastern granitic sector of the Serra de Sintra showing different phases of evolution. c is a detail from (a), and b is a detail from (d)

orthogonal decompression joint sets, sub-aerial weathering and erosion of the weathering mantle (Fig. 19.8). The variety of sizes of the boulders reflects the variability of primary fracture spacing (Migon 2006). Among the highest summits are Cruz Alta (528 m), Pena (527 m) and Pedra Amarela (406 m). The western sector of the mountain, mostly composed of syenite, exhibits a slightly different morphology, displaying rounded hill tops and almost flat surfaces, showing different reaction to weathering when compared to granites. In this sector, Monge (490 m), Peninha (487 m) and Adro Nunes (422 m) stand out as the highest summits (Fig. 19.9).

19.3.2 Southern Peripheral Hills The southern peripheral hills (about 130 m–170 m asl) follow the contact zone between the southern slope of the Serra de Sintra and the Cascais Platform (Fig. 19.5). They are the testimony of differential erosion in the metamorphosed sedimentary country rocks close to the contact with the SIC. Here, the contact or thermal metamorphism recrystallized the calcareous host rocks and enriched them with silicic components, thereby increasing their hardness (see Fig. 19.4). Conversely, near the contact, the loss of silicic constituents weakened the granite, favouring erosion and formation of a

19

Landforms and Geology of the Serra de Sintra …

259

Fig. 19.9 Peaks of the Serra de Sintra. a Tors standing on the crests along the main interfluve of the Serra de Sintra, view taken from W to E, b Tors on syenite rocks at Peninha, with the São João das Lampas

Platform in the background to the north, c Peninha from W to E, d idem, view towards SW

depression along the granite-host rocks border. This lower area highlights the alignment of peripheral rounded hills which are incised by fluvial network (Kullberg and Kullberg 2000). The southern peripheral hills and their geological and geomorphological features are very clear in the area of Malveira da Serra, in the southern part of the massif.

the boundary of the platform is difficult to identify, since a complex contact with an extensive range of fault bounded terrain elevations occurs there (Ribeiro 1940; Dias 1980). The São João das Lampas Platform is cut by drainage network of recent, deeply incised valleys, which exploit zones of structural weakness or softer lithologies. The main drainage is towards the northwest and the west, and the fluvial network is generally formed by small SE–NW trending valleys, with length not exceeding 10–15 km. These directions are parallel to the faults responsible for the uplift and emplacement of the SIC.

19.3.3 Littoral Platforms The surrounding regions of the Serra de Sintra are constituted by Upper Jurassic to Quaternary sedimentary formations which support littoral platforms. (a) The São João das Lampas Platform The São João das Lampas Platform, located in the north of the Serra da Sintra, is a set of regular, planated surfaces between 100 and 250 m asl. This erosional polygenic platform results from combined wave-cut abrasion and fluvial incision, probably of Pliocene age, and shows several erosion levels, as an effect of displacements induced by more recent NNE-SSW and N-S faulting (Figs. 19.3 and 19.5) (Cabral 1995). The platform surface is tilted westwards, where it is bounded by a generally straight, roughly NE-SW extended coastline, marked by cliffs decreasing in altitude northwards. To the east,

(b) The Cascais Platform The Cascais Platform is present in the east and south of the Serra de Sintra region and shows altitudes between 40 and 130 m asl. It is fairly flat and slopes gently to the south, towards the Cabo Raso, corresponding to an erosional wave-cut surface (Ribeiro 1940) (Fig. 19.6b). The complete razing of the geological structure is clear when observing the cliffs at the Cresmina beach, with strata dipping northwards (Fig. 19.6a), as part of the south flank of the Alcabideche syncline, the rim structure that southbounds the Sintra massif. At the same location and all along the coast southeastwards to Cascais, the littoral platform shows karstification phenomena affecting the Cretaceous limestone outcrops (Fig. 19.10).

260

M. C. Kullberg and J. C. Kullberg

Fig. 19.10 Cascais Platform seen from the south. a karstification phenomena affecting the Cretaceous limestone outcrops, b Cliff with northwards dipping strata of the Alcabideche syncline and c Sharp contrast between the Cascais Platform and the Serra de Sintra

19

Landforms and Geology of the Serra de Sintra …

261

(c) The raised beaches of the west flank of Sintra

19.3.4 Coastal Cliffs

On its west flank, the Serra de Sintra slopes approach the coastline along a series of poorly preserved levels. A raised remnant of a pediment-like surface occurs at about 250 m and another one at 190 m asl, being 800–900 m wide, so that the villages of Azóia and Ulgueira may have been established (Brum Ferreira 1984). These erosional surfaces show discontinuous accumulations of pebbles and sands with beach facies. They are the remains of ancient marine abrasion platforms and beaches, separated from each other by steep slopes and forming raised beaches. One of these platforms, at about 150 m above sea level, is well represented at Cabo da Roca, ending abruptly in the present-day marine cliffs (Fig. 19.5). These features are clearly seen from the Cresmina Fortress and Guincho beach (Fig. 19.6a).

The dominant lithology of the SIC facing the Atlantic seaboard is granite, except in a small sector at Cabo da Roca where syenite rocks outcrop. Granites are highly resistant to erosion and abrasion, and therefore, they tend to support relatively stable and steep coastal landforms even along high-energy wave coasts, such as the Atlantic seaboard of western Europe. SIC’s coastal landforms are dominated by steep cliffs, carved in densely orthogonally fractured granitoids. Stacks are frequent along the coast, associated with the overall fracture pattern and rare pocket sandy beaches occur in sheltered sections. So, despite the almost linear profile of the coast—NE–SW north of Cabo da Roca and NW–SE to the south—headlands separate small bays, where rock fall deposits and beach sands accumulate (Fig. 19.11).

Fig. 19.11 Serra de Sintra coastal cliffs. a Headlands, stacks and pocket sandy beaches in sheltered sections, south of Cabo da Roca, b Cliffs in Jurassic limestones (grey) cut by cone-sheet dykes, in the foreground and the northern flank of the rim syncline leaning the contact with the granite in the background, c The southern end of the

raised beach mentioned in Sect. 19.3.3c, near Cabo da Roca, d The northern end of the west flank raised beaches, over almost vertical beds of Cretaceous limestones and sandstones (the transition between lower and upper Cretaceous) at Praia Grande beach, north of the SIC

262

North of the SIC, the cliffs are still very steep and expose Jurassic and Cretaceous limestones, dolomites and sandstones that show a northwards sub-vertical dip (reverse in some cases) close to the SIC, which becomes gentler northwards, with the decreasing influence of the uplift of the igneous rocks. This sequence, which also includes the thrust fault that bounds the Serra de Sintra in the north, may be observed in the cliffs backing several beaches from Praia da Adraga to Praia Grande and Praia das Maçãs.

19.3.5 Coastal Dunes and Aeolianites The area south of the Serra de Sintra, along a corridor between the Guincho beach and Cabo Raso–Oitavos, shows

M. C. Kullberg and J. C. Kullberg

an active dune field, with an excellent example of a parabolic dune at Cresmina. There, a transgressive loose sand body of approximately 300 m wide by 230 m long is moving from NNW to SSE (Fig. 19.12). Due to coastal morphology and orientation, and to the prevailing wind regime from NNW, the sand enters the dune system from two beaches in the north (Guincho and Cresmina), migrates on top of a marine abrasion platform cut into Cretaceous hard rocks, and then returns to the sea again, at the south. This sedimentary dynamics resulted in a so-called headland bypass dune field (Rebelo et al. 2002). At Oitavos, also within the Cascais Platform, a consolidated dune deposit (aeolianite) represents the culminating point in the landscape, rising to an altitude of 55 m. The deposit has been dated circa 32,000 BP (Monge Soares et al.

Fig. 19.12 Guincho–Oitavos dune field. a General overview towards the north, b–e The Guincho beach and the Cresmina parabolic dune and f The Oitavos aeolianite showing the dune stratification

19

Landforms and Geology of the Serra de Sintra …

2006) and was formed at lower sea-level stands during the Late Pleistocene, when large source areas of sand occurred towards the west and northwest. An excellent exposure of dune stratification is visible in Oitavos (Fig. 19.12f), with bedding reflecting the direction of the prevailing winds during deposition. The sands are consolidated by calcareous cement associated with the presence of marine biogenic sands. Aeolianites occur in several locations along the Portuguese coast, with another interesting coastal outcrop at Magoito in the north of Sintra.

19.4

Conclusions

The progressive emplacement of the intrusive rocks of the Sintra Intrusive Complex led to the development of positive relief, whose long-term evolution was modulated by the type and intensity of exogenous and endogenous processes and by rock types. The most recent sedimentary solid rocks (marly limestones and crystalline limestones with rudists) affected by the intrusion of the SIC are of Upper Cenomanian age, about 90 Ma. An important sedimentary gap with the duration of about 40–50 Ma followed. The oldest units of Cenozoic age correspond to continental facies deposits, the Monte Santos Conglomerate (Paleogene or possibly Eocene age), superimposed by a set of more recent units grouped in the Galamares Complex, whose age is not well defined but is between the Paleogene and possibly the Lower Miocene (Carvalho 1994). This complex is covered in angular unconformity by marine deposits of Miocene age (Lower Serravalian–Tortonian), also represented in the eastern region. The Pliocene is represented by residual deposits that lay on top of the flat surfaces whose evolution began after the SIC intrusion. The Vinagre Formation, similar to certain alluvial fans (rañas) of the Alentejo, is possibly Early Quaternary (Carvalho 1994). Most of the coastal deposits, beach sands, dunes (covering much of the coastline north of the Serra de Sintra and south of Guincho beach) and consolidated dunes (Oitavos), slope deposits and alluvium, are of Quaternary age. The Cenozoic sedimentation, especially in the northern part of the mountains, in the so-called Colares Basin, witnesses much of the evolution of the Serra de Sintra, highlighting, for example, the existence, at the beginning of the Cenozoic, of a tropical semi-arid climate, with well-marked seasonality, and with predominance of dry months. Accounting for the great thickness of the succession of sedimentary layers affected by the magmatic intrusion, the original relief of the mountain must have been much larger, possibly forming an island not far from the coast. Such conditions may have occurred in the Miocene (15–6 Ma), as shown by marine deposits present around the mountains.

263

Later, in the Early Quaternary, the sea must have invaded the region once again, as suggested by the presence of raised beaches. The morphology of the Serra de Sintra reflects its progressive isostatic rebound, probably accompanied by movement on the northern thrust fault boundary of the SIC, which accelerated some 6 Ma ago. The ages of lithological formations involved are not all well constrained, but the competition between uplift and erosion seems to be still ongoing, favouring the former. On the other hand, marine erosion is probably the most impressive element of the morphogenesis of the lowland area surrounding the Serra de Sintra and emphasizing its individuality, showing also Quaternary fluvial retouching under clear structural controls. The Sintra Intrusive Complex also shows an important number of granitic landforms, such as diversity of tors and boulders, revealing the interaction between deep chemical weathering and erosion of the weathering mantle. Acknowledgements José Carlos Kullberg work was supported by the FCT/MCTES’s GeoBioTec Project ref. UIDB/04035/2020.

References Alves CAM (1964) Estudo Petrológico do Maciço de Sintra. Revista da Faculdade de Ciências de Lisboa, 2ª série, C, 12(2):123–289 Brum Ferreira A (1984) Découverte d’un Littoral à 250 metres sur le Piemont Occidental de la Serra de Sintra. Finisterra, XIX, 37, Lisboa 83–127 Cabral J (1995) Neotectónica em Portugal Continental. Mem Serv. Geol Port 31:265p Carvalho AMG (1994) O Cenozóico Continental a norte da Serra de Sintra (estudo tectono-sedimentar). Museu Nac Hist Natural Mem Geociências 1:89p Choffat P (1883–87) Age du granite de Sintra. Comun Com Trab Geol Portugal I:155–157 Dias MH (1980) A plataforma litoral a norte de Sintra, Estudo dos depósitos de cobertura. Rel. n.º 11, Linha de Acção de Geografia Física, C.E.G Grange M, Scharer U, Merle R, Girardeau J, Cornen G (2010) Plume– lithosphere interaction during migration of cretaceous alkaline magmatism in SW Portugal: evidence from U-Pb ages and Pb–Sr– Hf isotopes. J Petrol 51:1143–1170 Kullberg MC (1996) Estudos Tectónicos e Fotogeológicos nas Serras de Sintra e Arrábida. Tese de Doutoramento. Faculdade de Ciências da Universidade de Lisboa, 189p Kullberg MC, Kullberg JC (2000) Tectónica da Região de Sintra. In Tectónica das regiões de Sintra e Arrábida. Mem Geociências Univ Lisboa 2:01–34 Kullberg JC, Rocha RB, Soares AF, Rey J, Terrinha P, Azerêdo AC, Callapez P, Duarte LV, Kullberg MC, Martins L, Miranda JR, Alves C, Mata J, Madeira J, Mateus O, Moreira M, Nogueira CR (2013) A Bacia Lusitaniana: Estratigrafia, Paleogeografia e Tectónica. In: Dias R, Araújo A, Terrinha P, Kullberg, JC (eds) Geologia de Portugal no contexto da Ibéria. Escolar Editora, pp 989–1141 Migon P (2006) Granite landscapes of the world. Oxford University Press, In the Geomorphological Landscapes of the World series, 384p

264 Miranda R, Valadares V, Terrinha P, Mata J, Azevedo MR, Kullberg JC, Ribeiro C (2009) Age constraints on the Late Cretaceous alkaline magmatism on the West Iberia Margin. Cretac Res 30:575–586 Monge Soares AM, Moniz C, Cabral J (2006) The consolidated Dune of Oitavos (West of cascais–Lisbon Region)—its dating by the radiocarbon method. Com Geol 93:105–118 Rebelo LP, Brito PO, Monteiro JH (2002) Monitoring the Cresmina dune evolution (Portugal) using differential GPS. J Coast Res SI 36:591–604 Ribeiro O (1940) Remarques sur la morphologie de la région de Sintra et Cascais. Rev. Géograph Pyrénées Sud-Ouest II(3–4):203–218 Ribeiro A, Kullberg MC, Kullberg JC, Manuppella G, Phipps S (1990) Review of Alpine tectonics in Portugal. Foreland detachment in basement and cover rocks. Tectonophysics 184:357–366

M. C. Kullberg and J. C. Kullberg Rock NMS (1982) The Late Cretaceous alkaline igneous province in the Iberian Peninsula, and its tectonic significance. Lithos 15:111–131 Silva EA, Miranda JM, Luis JF, Galdeano A (2000) Correlation between the Palaeozoic structures from West Iberian and Grand Banks margins using inversion of magnetic anomalies. Tectonophysics 321:57–71 Terrinha P, Pueyo EL, Aranguren A, Kullberg JC, Kullberg MC, Casas-Sainz A, Azevedo MR (2018) Gravimetric and magnetic fabric study of the Sintra Igneous complex: laccolith-plug emplacement in the Western Iberian passive margin. Int J Earth Sci 107 (5):1807–1833

The North of Lisbon Region—A Dynamic Landscape

20

José Luís Zêzere

Abstract

20.1

The alternating lithology together with the low-to-moderate monocline south to southeast dipping in the North of Lisbon Region promoted the development of cuesta landforms that were shaped by differential erosion during the Quaternary. The fluvial erosion generated a large depression—the Loures Basin—where several deposits were formed during the Quaternary. The oldest terrace testifies a paleo-drainage towards NE, and the present-day organization of the fluvial system was marked by the stream piracy in the terminal zone of the Trancão River. In the north part of the Loures Basin, a debris flow deposit is conserved and it is probably related to the rupture zone of an old slope movement identified by Ferreira in 1984. This feature is the oldest evidence of slope instability in the region. More recently, in November 1755, the Lisbon earthquake generated rockfalls along the larger fluvial valley in the area—the Trancão River valley. The recent and present-day slope instability have been characterized by the occurrence of rainfall-triggered shallow slides and deep-seated slope movements. Shallow slides have been triggered by intense rainfall events, whereas deep-seated slope movements have been associated to long-lasting rainfall events. Keywords

North of Lisbon Landslides




Cuestas




Quaternary deposits

J. L. Zêzere (&) Centre of Geographical Studies, Institute of Geography and Spatial Planning, University of Lisbon, Lisbon, Portugal e-mail: [email protected]




Geological and Geomorphological Setting

The North of Lisbon Region is part of a geologically old basin (the Western Lusitanian Basin of Meso-Cenozoic age) and is located close to the contact between this old basin and the much younger Tagus Cenozoic Basin. The geological setting is a monocline with layers dipping from 5° to 25° towards south and south-east. These layers form the southern flank of a large anticline centred northwards in the Arruda dos Vinhos Basin. Rocks are of sedimentary and volcanic origin, dating from the Upper Jurassic to the Quaternary (Fig. 20.1). The oldest geological formation is a Lower to Middle Kimmeridgian clay and marl complex with detrital intercalation, known as the Abadia formation, which crops out in the northern part of the study area. The Abadia formation, whose thickness reaches 800 m, is overlain by coralline limestone (the Amaral formation) of Upper Kimmeridgian age. This limestone supports rocky escarpments which surround the Arruda dos Vinhos Basin developed on the Abadia formation (Ferreira 1984). In comparison with the Kimmeridgian, the transition to the Lower Tithonian was characterized by more detrital character of sediments (clay, marl and limestone with sandstone intercalations), which was accentuated during the Tithonian (sandstone with marl and limestone intercalation). The Lower Cretaceous is typically detrital (sandstone with marl intercalations), whereas the Albian–middle Cenomanian is marked by a 300 m thick complex formed by marl and clay, with marly limestone intercalations. This complex is overlain by compact limestone of Upper Cenomanian age. Sediments dated to later epochs of the Cretaceous do not exist in the region. Overlying the Cenomanian, there is the 400 m thick Volcanic Complex of Lisbon, made up of alternating basalts and clay-rich volcanic tuffs. The Volcanic Complex of Lisbon is covered by the Benfica Complex of Paleogene age, which is a 400 m thick

© Springer Nature Switzerland AG 2020 G. Vieira et al. (eds.), Landscapes and Landforms of Portugal, World Geomorphological Landscapes, https://doi.org/10.1007/978-3-319-03641-0_20

265

266

J. L. Zêzere

Fig. 20.1 Geological setting of the North of Lisbon Region

continental clastic complex consisting, in its central part, of clays and marls, whereas sandstones, conglomerates and lacustrine limestones dominate the top and the bottom of the succession. The Miocene rocks were deposited over the Paleogene complex and are 300 m thick. Formations of Miocene age are made by alternating sands, sandstones, clays and limestones, representing six sedimentary cycles dating from the Upper Chattian to the Tortonian (Ribeiro et al. 1979). During the Quaternary, most sedimentation occurred in the largest geomorphological depression of the region, the Loures Basin, which is described in the next section. The alternating lithology, together with the low-to-moderate monocline dipping, promoted the

development of cuesta landforms that were shaped by differential erosion during the Quaternary. From north to south, two cuestas are prominent landforms in the regional geomorphology: (1) the Lousa–Bucelas Cuesta, which shows a W-E direction and has developed along 12 km over Cretaceous formations (Figs. 20.2 and 20.3); (2) the Odivelas– Vialonga Cuesta, which shows a SW-NE direction and has developed along 18 km over Paleogene and Miocene formations (Figs. 20.4 and 20.5). Northwards, the steep slope of the Odivelas–Vialonga Cuesta is overlooking the Loures Basin, whose floor is a flat area with altitudes ranging typically from 1 to 20 m asl. The latter was excavated in poorly consolidated geological formations of Paleogene age—the Benfica Complex.

20

The North of Lisbon Region—A Dynamic Landscape

267

Fig. 20.2 Geological profile of the Lousa–Bucelas Cuesta. 1 alluvium (Holocene), 2 sandstone and lacustrine limestone (Paleogene), 3 Volcanic Complex of Lisbon (Upper Cretaceous), 4 limestone (Upper Cenomanian), 5 marl and marly limestone (Albian–Middle Cenomanian), 6 sandstone (Upper Barremian–Hauterivian), 7 limestone and marl (Upper Hauterivian–Lower Barremian), 8 sandstone and clay (Lower Hauterivian), 9. sandstone, marl and limestone (Tithonian); 10 marl and limestone (Upper Kimmeridgian–Lower Tithonian), 11 dike

Fig. 20.3 Panoramic view of the face slope of the Lousa–Bucelas Cuesta

The uplift of the North of Lisbon Region relative to the Tagus Basin is evidenced by the non-existence of any significant sedimentation in the region since the Late Miocene up to the recent times (Ferreira et al. 1987; Zêzere 1991, 2001b). Moreover, this tectonic framework explains the development of stepwise pattern of several erosional levels, in relation to the general lowering of the base level, as well as strong fluvial erosion that generated very steep valley slopes, despite the typically low altitude of the region.

20.2

The Loures Basin and Its Quaternary Deposits

The Loures Basin extends along 7 km in the SW-NE direction, whereas its width in NW-SE direction is less, 3 km (Fig. 20.6). The basin is partially covered by alluvium, in an area named locally ‘Várzea’ that formed during the higher sea level stands recorded in the Holocene (Zbyszewski 1964). In addition, the Loures Basin includes the most important Quaternary terrace levels of the region (Fig. 20.6): Quinta do Infantado (QI), Santo Antão do Tojal (SAT) (Fig. 20.4), São Julião do Tojal (SJT) and Quintanilho (Q). These terraces have been assigned to a

transgression prior to the last cold period of the Quaternary (Breuil and Zbyszewski 1943). Terraces of QI, SAT and SJT have similar sedimentological characteristics and stratigraphic position and should be contemporaneous. They are made by fine texture deposits constituted by clay, silt, sand and fine gravel that suffered short fluvial transport, starting mostly on the Paleogene formation that surrounds the basin. The terrace of SAT provided remains of Elephas antiquus and Equus caballus as well as several Mousterian (Middle Paleolithic) artefacts, which support the last interglacial age proposed by Breuil and Zbyszewski (1943). The Quintanilho terrace (Q) is located in the NE border of the Loures Basin and is composed of cobbles of limestone, basalt and quartz, within fine- and medium-carbonated sandy matrix. A deposit with similar characteristics was found in the eastern sector of the SJT terrace, embedded in the fine-textured terrace deposit. The coarser character of the Quintanilho terrace testifies to a more energetic fluvial system in comparison with the one that generated the fine-textured terrace deposits. It indicates reactivation of fluvial erosion in the NE margin of the Loures Basin, starting mostly on the surrounding outcrops of the Upper Cenomanian limestone and the Volcanic Complex of Lisbon.

268

J. L. Zêzere

Fig. 20.4 Geological profile of the Odivelas–Vialonga Cuesta: 1 alluvium (Holocene), 2 terrace (Pleistocene), 3 sand with Placuna miocena (Burdigalian), 4 Casal Vistoso limestone (Burdigalian), 5 Quinta do Bacalhau sand (Burdigalian), 6. Forno do Tijolo clay (Burdigalian), 7 Entre Campos limestone (Burdigalian), 8 Estefânia sand (Aquitanian), 9 sandstone and conglomerate (Paleogene), 10 marl and clay (Paleogene), 11 lacustrine limestone (Paleogene), 12 Volcanic Complex of Lisbon (Upper Cretaceous)

Fig. 20.5 Panoramic view of the Loures Basin and the face slope of the Odivelas–Vialonga Cuesta

In the SJT terrace, in addition to the fine-textured deposits and deposits with characteristics similar to the Quintanilho terrace, an older thick debris flow deposit was found beneath the fine-textured deposits. It is poorly sorted and massive, containing basalt pebbles and boulders, enveloped in an abundant clay matrix and is probably associated with the large landslide rupture zone identified by Ferreira (1984) on the Volcanic Complex of Lisbon, 1.5 km upstream (Fig. 20.6). The oldest Quaternary sediment found in the North of Lisbon Region is a terrace deposit located at Reentrante in an ancient fluvial valley floor at 40–50 m asl (Fig. 20.6). It shows a well-defined structure, with alternating fine (sand and clay) and coarse (limestone and basalt cobble) beds, that cannot be associated with the small tributary of the Tagus River that currently flows near Reentrante. In addition, the Reentrante zone is located within an erosional level located at 40–50 m asl, currently divided into three separate parts, that extends the Loures Basin towards NE without any geomorphological constraint. Therefore, the paleogeography at the time of origin of this erosional level must have been

different from present-day one. The Loures Basin opened in the NE direction, and the Reentrante terrace is a remnant of a former fluvial drainage flowing north-eastwards to the Tagus River. Assuming the old drainage towards NE, Zêzere (1988) concluded that the breach in the Odivelas–Vialonga Cuesta, where the Trancão valley is found nowadays, occurred after the formation of the erosional level located at 40–50 m asl, probably due to the headward erosion of a former river flowing southwards to the Tagus, which modified the former fluvial organization of the Loures Basin through stream piracy.

20.3

Recent and Present-Day Landslides

Due to its geological and geomorphological characteristics, the North of Lisbon Region is one of the most landslide-prone areas in Portugal (Zêzere 2001a). In particular, the Upper Jurassic marls, clays and limestones, the Albian–Middle Cenomanian marls and clays and the

20

The North of Lisbon Region—A Dynamic Landscape

269

Fig. 20.6 Geomorphological map of the Loures Basin and surrounding area. 1 elevation (m asl), 2 river, 3 face slope of cuesta, 4 structural slope (rectilinear, concave), 5 volcanic intrusion, 6 fluvial gorge, 7 valley and gully, 8 slope (rectilinear, concave), 9 scarp and path of old debris flow, 10 erosional level (100–130 m), 11 erosional level (40–

50 m), 12 old terrace, 13 old debris flow deposit, 14 sandy terrace, 15 coarse terrace, 16 alluvial plain. Fluvial terraces: QI Quinta do Infantado, SAT Santo Antão do Tojal, SJT São Julião do Tojal, Q Quintanilho and R Reentrante

Volcanic Complex of Lisbon have been recurrently affected by landslides in recent years. Landslides have been inventoried and mapped for over 30 years, and the landslide density is 5.8 per km2, with a total affected area of over 1.6 km2 (2.6% of the landscape) along the cuesta landforms (Zêzere 2001a). The most frequent slope movement types in the region are rockfalls, shallow translational slides, deep-seated translational slides, deep-seated rotational slides

and composite and complex slope movements, which were summarized by Zêzere et al. (2005). Most rockfalls in the region are ancient events that affected compact Cretaceous and Jurassic limestone on slopes over 30° (Zêzere 2001a). The density of rockfalls is highest along the Trancão River gorge (Fig. 20.7) where 192 fallen blocks were inventoried (Vaz and Zêzere 2016). These are limestone blocks and range from 1 to 125 m3. The major

270

J. L. Zêzere

Fig. 20.7 Rockfalls triggered by the 1755 Lisbon earthquake along the Trancão valley in the dip slope of the Lousa–Bucelas Cuesta

rockfalls along the valley are described in historical documents as being triggered by the 1755 Lisbon earthquake (Vaz and Zêzere 2016). Shallow translational slides are the most frequent landslides in the region. These are slope movements with planar slip surfaces with a typical depth of up to 1.5 m, and a small dimension (mean area, 550 m2; mean volume, 290 m3). In most cases, shallow landslides occur on steep valley slopes (mean slope angle = 23°) and affect colluvium covering impermeable rocks, such as volcanic tuffs, marls and clays (Fig. 20.8). Deep-seated translational slides are at least one order of magnitude larger than shallow movements (mean area, 4059 m2; mean volume, 5232 m3). These landslides are more frequent on marls and marly limestones of Jurassic and Cretaceous age. They occur on structural slopes following

Fig. 20.8 Shallow translational slide triggered by rainfall in January 1996 near Camarões village

stratification, along shear surfaces coincident with impermeable bedding planes. As a rule, the gradient of slopes affected by deep-seated translational slides (17° in average) exceeds the dip of strata. Deep-seated rotational slides show the highest average depth (5 m) and are larger than translational slides (mean area, 9407 m2; mean volume, 34,843 m3). These landslides are more common in the northern part of the region, where Upper Jurassic formations crop out (Fig. 20.9). The clays and marls of these formations are very prone to rotational sliding, which includes single, confined and multiple retrogressive sub-types. Composite and complex slope movements present at least two types of mechanism, simultaneously (composite slope movement) or in sequence (complex slope movement). In many cases, particularly for old landslides, it is impossible to

20

The North of Lisbon Region—A Dynamic Landscape

271

Fig. 20.9 Rotational slide evolving downslope into an earth flow affecting marls and clays of Upper Jurassic age, which was triggered by rainfall in January 2001 near Alrota village

distinguish between composite and complex slope movements. In the North of Lisbon Region, most composite/ complex slope movements combine rotational slides with translational slides and rotational slides with flows (Fig. 20.10), and affect mostly marls, clays and marly limestones dated from Jurassic and Cretaceous. This landslide group has the largest average area (27,011 m2) and volume (42,998 m3).

Fig. 20.10 Complex slope movement (translational slide flow) triggered by rainfall in December 1989, affecting the face slope of the Odivelas–Vialonga Cuesta

20.4

Temporal Occurrence of Rainfall-Triggered Landslides

Landslide events that occurred in the North of Lisbon Region in the last decades were triggered by rainfall, as extensively addressed in the literature (Ferreira et al. 1987; Zêzere 1988, 2001a; Zêzere and Trigo 2011; Zêzere et al. 2015). Rainfall

272

J. L. Zêzere 900 800

y = 6.9x + 121.9 R2 = 0.936

Rainfall (mm)

700 600 500 400 300 200 100 0

0

20

40

60

80

100

consecutive days

no landslides

Shallow landslides

Deep landslides

Fig. 20.11 Cumulative rainfall—rainfall duration threshold for landslide occurrence in the North of Lisbon Region (rainfall data from São Julião do Tojal, 1956–2010)

triggered 25 landslide events in the area from 1956 to 2010. From these, the events generating shallow translational slides have been associated to short periods (1–15 days) of intense rainfall, while deep-seated rotational and translational slides as well as composite/complex slope movements relate to longer periods (4–12 weeks) of less intense rain. The rainfall conditions associated with shallow and deep-seated landslides are in accordance with the hydrological processes acting on the affected slopes (Zêzere and Trigo 2011). The shallow translational slides occur at the contact of the shallow soil with the underlying more impermeable bedrock, or within the soil material in response to the prompt growth of pore water pressure and the decrease of soil’s apparent cohesion, following intense rainfall events. In contrast, deep-seated landslides occur due to the reduction of shear strength of soils and soft rocks, resulting from the steady rise of the groundwater table and the development of positive pore water pressures in the affected material, as a consequence of long-lasting rainfall episodes. Despite the different relationships between rainfall conditions and the triggering of shallow and deep-seated landslides, a single linear trend (R = 6.9 D + 121.9) relates cumulative rainfall (R) and the rainfall duration in days (D) for the total set of landslide events that occurred in the Lisbon region from 1956 to 2010 (Fig. 20.11).

20.5

Conclusions

The cuesta landforms are major geomorphological features in the North of Lisbon Region that result from the interactions between tectonic uplift and differential erosion exploring lithological differences since the end of the Miocene. Fluvial erosion was responsible for the Loures Basin, where several

deposits formed during the Quaternary. The oldest terrace testifies a paleo-drainage towards NE, and the present-day organization of the fluvial system was marked by stream piracy in the terminal zone of the Trancão River. Fluvial erosion was essential to the development of cuestas and generated very steep slopes along the cuesta fronts and along the cataclinal valleys. Such slopes are typified by the occurrence of different types of landslides, including rockfalls and shallow and deep-seated slides. The most important rockfalls were triggered by the Lisbon earthquake in 1755, whereas slides have been triggered by rainfall, which includes intense rainfall events and long-lasting rainfall events, the former generating shallow slides and the latter being causally linked with deep-seated slides.

References Breuil A, Zbyszewski G (1943) Le quaternaire de Santo Antão do Tojal. Com Serv Geol Port XXIV, Lisboa 43–70 Ferreira AB (1984) Movements de terrain dans la region au Nord de Lisbonne. Conditions morphostructurales et climatiques. Mouvements de Terrain, Colloque de Caen, Documents du BRGM, 83, Paris, pp 485–494 Ferreira AB, Zêzere JL, Rodrigues ML (1987) Instabilité des versants dans la région au Nord de Lisbonne. Essai de cartographie géomorphologique, Finisterra 22(43):227–246 Ribeiro A, Antunes MT, Ferreira MP, Rocha RB, Soares A F, Zbyszewski G, Almeida FM, Carvalho D, Monteiro JH (1979) Introduction à la géologie générale du Portugal. Serv Geol Portugal, Lisboa Vaz T, Zêzere JL (2016) Landslides and other geomorphologic and hydrologic effects induced by earthquakes in Portugal. Nat Hazards 81:71–98 Zbyszewski G (1964) Notícia explicativa da Folha 2 Loures (Carta Geológica dos Arredores de Lisboa). Serv Geol Portugal, Lisboa Zêzere JL (1988) As costeiras a Norte de Lisboa. Dinâmica de vertentes e cartografia geomorfológica. Dissertação Mestrado Geografia Física e Regional, Universidade de Lisboa Zêzere JL (1991) As costeiras do Norte de Lisboa: evolução quaternária e dinâmica actual das vertentes. Finisterra 26(51):27–56 Zêzere JL (2001a) Distribuição e ritmo dos movimentos de vertente na região a Norte de Lisboa. Centro de Estudos Geográficos, Lisboa Zêzere JL (2001b) Evolução geomorfológica da Bacia de Loures no decurso do Quaternário. In Câmara Municipal de Loures (ed) Redescobrir a Várzea de Loures. Ambiente, Geologia e Préhistória Antiga na Várzea. Loures, pp 33–40 Zêzere JL, Trigo R (2011) Impacts of the North Atlantic oscillation on landslides. In: Vicente-Serrano S, Trigo R (eds) Hydrological, socioeconomic and ecological impacts of the North Atlantic Oscillation in the Mediterranean Region, Advances in Global Change Research, Vol 46. Springer, Berlin, pp 199–212 Zêzere JL, Trigo R, Trigo I (2005) Shallow and deep landslides induced by rainfall in the Lisbon region (Portugal): assessment of relationships with the North Atlantic Oscillation. Nat Hazards Earth Syst Sci 5:331–344 Zêzere JL, Vaz T, Pereira S, Oliveira SC, Marques R, Garcia R (2015) Rainfall thresholds for landslide activity in Portugal: a state of the art. Environ Earth Sci 73(6):2917–2936

The Arrábida Chain: The Alpine Orogeny in the Vicinity of the Atlantic Ocean

21

André F. Fonseca, José Luís Zêzere, and Mário Neves

Abstract

The Arrábida Chain is one of the finest structural examples of the Alpine orogeny in Portugal. Placed along the south-western coast of the Setubal Peninsula, it presents one of the most spectacular coastal geomorphological settings in Portugal, with vertical sea cliffs with over 150 m plunging into the Atlantic Ocean. Due to its geographical position, post-Miocene landscape evolution was essentially a response to base-level change imposed by Neogene sea-level fluctuations, tectonic uplift of the Arrábida Chain and subsidence of the lower Tagus basin. Strong contrasts in bedrock erodibility played a crucial role in landscape evolution by imposing limits to drainage network incision, leaving competent rock bodies in clear association to the highest sector of the chain. Keywords








Tectonic geomorphology Lusitanian basin orogeny Arrábida chain Portugal

21.1




Alpine

Introduction

The geomorphic expression of the Alpine orogeny in mainland Portugal is recorded in the morphostructural units of the Hesperian Massif and in the Lusitanian Basins, through the uplift and folding of fault-bounded tectonic compartments, including reactivation of Palaeozoic A. F. Fonseca (&)
J. L. Zêzere
M. Neves Centre of Geographical Studies, Institute of Geography and Spatial Planning, University of Lisbon, Lisbon, Portugal e-mail: [email protected] J. L. Zêzere e-mail: [email protected] M. Neves e-mail: [email protected]

basement faults. The Arrábida Chain forms one of the finest structural examples of the Alpine orogeny, resulting from the tectonic inversion of the Western Lusitanian Basin through the reactivation of ENE–WSW to NE–SW trending faults. Placed along the Portuguese central-west coast, the Arrábida Chain presents one of the most spectacular coastal geomorphological settings in Portugal, exhibiting vertical sea cliffs over 150 m high, plunging into the Atlantic Ocean. Marine terraces and erosion surfaces positioned at different altitudes above the present-day sea level, bear evidence to post-Miocene to Quaternary sea-level fluctuations and to neotectonic activity within the southern sector of the Setúbal Peninsula. The name Arrábida is thought to originate from the Castellan “Rábida”, which derives from the Arabic word “al-ribat”, meaning “place of prayer”. In fact, due to its natural beauty and secluded position, the Arrábida Chain was home to Franciscan monks living as hermits in the Convent of Nossa Senhora da Arrábida during the sixteenth century. The recognition of the scenic and environmental value of the Arrábida Chain led to its classification as a Natural Park in 1976 (excluding the Cape Espichel area), attracting visitors from Setúbal and Lisbon in search of its numerous trails and pristine beaches.

21.2

Geographical Setting

The Arrábida Chain is located in central-west Portugal, about 40 km south of Lisbon, at the south-western end of the Setúbal peninsula. Reaching 501 m asl, it stretches from WSW to ENE along 30 km, from the Cape Espichel to Mount São Luís (Fig. 21.1). While the southern flank plunges into the Atlantic Ocean through vertical sea cliffs, the northern flank is connected to the paleo-Tagus River alluvial plain. To the west, between Cape Espichel and

© Springer Nature Switzerland AG 2020 G. Vieira et al. (eds.), Landscapes and Landforms of Portugal, World Geomorphological Landscapes, https://doi.org/10.1007/978-3-319-03641-0_21

273

274

Mount Formosinho, lies a gentle, nearly flat topography at 190–220 m asl, commonly known as Plataforma do Cabo. To the east, the mounts of Formosinho (501 m), São Luís (392 m), Pincaro (320 m) and São Francisco (250 m) dominate over the valleys of Ajuda, Coina, Alambre and Pateira (Fig. 21.1). Along the southern flank, a triangular-shaped depression open to the ocean interrupts the sea cliff continuity, sheltering the fishing village of Sesimbra (Fig. 21.1). Characterised by a temperate Mediterranean climate, the Arrábida Chain shows a mean annual precipitation between 500 and 600 mm, mainly concentrated between mid-October and April. Mean maximum temperatures range between 29 ° C in July and 15 °C in January. Spatial variations in daily temperatures are strongly conditioned by topography and distance to the ocean. Owing to its close proximity to the ocean, both the Cape Espichel and southern flanks are characterised by low daily thermal amplitudes (Mora 1998). The northern flank, while sheltered from marine influences by the Mount Formosinho, presents high daily thermal amplitudes, with the valleys of Ajuda, Coina, Alambre and Pateira showing the lowest minima, as a consequence of cold

Fig. 21.1 Structure and simplified geology of the Arrábida Chain

A. F. Fonseca et al.

air accumulation in response to katabatic air flow from the nearby mounts (Mora 1998). The native vegetation is typically Mediterranean forming a dense maquis covering the southern flank of the Formosinho. These shrub habitats are mainly composed by cork oak (Quercus suber), olive (Olea europea), holm oak (Quercus ilex), kermes oak (Quercus coccifera) and strawberry tree (Arbutus unedo), along with a great variety of aromatic herbs (i.e. Rosmarinus officinalis, Thymbra capitata).

21.3

Structure and Bedrock Geology

The Arrábida Chain is a small WSW–ENE trending Alpine orogenic belt, formed by south-verging ENE–WSW folds and thrust planes, connected to left-lateral NNE–SSW and N–S strike-slip faults (Kullberg et al. 2000). Although fairly small, with 35 km in length and 7 km in width, the Arrábida Chain exposes an almost complete sedimentary sequence from the lower Jurassic to the Pliocene. From a structural point of view, the chain is limited in the west and east by

21

The Arrábida Chain: The Alpine Orogeny in the Vicinity …

275

Fig. 21.2 Southern flank of the Arrábida Chain and beach of Portinho da Arrábida. Notice the lower to middle Jurassic limestone strata forming the axis of the Arrábida anticline and thrust. Photograph

credits Duarte Fernandes Pinto, A Terceira Dimensão, http:// portugalfotografiaaerea.blogspot.com

strike-slip structures, to the south by the Arrábida thrust and to the north by the Lagoa de Albufeira syncline (Fig. 21.1). The tectonic deformation and main uplift phase of the Arrábida Chain occurred during the Middle to Late Miocene in response to the convergence between Africa and Eurasia. Two stages of deformation are identified: (1) Burdigalian (17–16 Ma)—uplift and formation of the south-verging Formosinho anticline (Fig. 21.2) in response to N–S compression (Antunes et al. 1995); and (2) upper Tortonian (8– 7 Ma)—change in the shortening direction from N–S to NW–SE, causing uplift in the eastern part of the Chain and the formation of the São Luís anticline (Choffat 1908). The Meso-Cenozoic sedimentation reflects the complex tectonic and eustatic history that affected this sector of the Portuguese margin for the last 250 million years. The lower Jurassic is formed by an evaporitic sequence (i.e. marls and clay) followed by compact, oolitic and coral limestone of middle to upper Jurassic age (Fig. 21.1). The upper Jurassic and Cretaceous deposits present strong lateral facies variations, related to differences in the depositional environments between the western (marine) and the eastern (fluviomarine) zones of the Chain. While to the west bedrock lithology is mostly composed by limestone with fine pelitic intercalations, surface geology in the east is characterised by poorly consolidated sandstone and sandy limestone (Fig. 21.1). Cropping out in the eastern sector of the chain, the Paleogene and Miocene strata are characterised by

coarse-grained conglomeratic deposits and by shallow marine sequences (i.e. marls and coral limestone). The Pliocene (Fonte da Telha Formation) and lower Quaternary (Belverde Formation) sedimentation in the Setúbal peninsula were related to the paleo-drainage system of the Tagus River. Before its establishment along the Tagus gorge (northbounding the Setúbal Peninsula), the Tagus River reached the Atlantic Ocean in the vicinity of the Arrábida Chain. During this period, sediment accumulation to the north of the Chain was controlled by tectonic subsidence in the Tagus plain. Pliocene sedimentation (i.e. Fonte da Telha formation) is characterised by a thick (over 150 m) fluvial sequence, containing yellow coloured, fine to coarse-grained sand with occasional pebble beds and sandy–clay intercalations (Azevedo 1982). The Belverde formation comprises a poorly consolidated conglomeratic deposit, containing quartz and quartzite rounded pebbles in a sandy matrix (Azevedo 1982). Pebble fabric within the Belverde formation indicates fluvial deposition in association to the E–W flow of the Tagus River, followed by later pebble reorganization in response to marine transgression (Azevedo 1982). Following the northward migration of the Tagus River, torrential flows covered the piedmont area to the north and south-east of the chain. These deposits are known as the Marco Furado Formation (middle Pleistocene), being characterised by a 30–40 m weakly consolidated and poorly

276

A. F. Fonseca et al.

sorted deposit, containing angular clasts of quartz, quartzite, jasper, flint and schist, within a sandy–clay matrix (Azevedo 1982).

21.4

Landforms

21.4.1 Structural Landforms The structural control on the morphology of the Arrábida Chain is strongly evidenced in the Formosinho and São Luís anticlines, where both lithology, fold and fault geometry control the present-day topography. Formed by lower to middle Jurassic compact limestone and dolomitic units, these structures survived the action of erosional processes acting since the earliest stages of uplift. The progressive exposure of the anticline core led to the present-day topographic setting, with the asymmetry of both the Formosinho and São Luís explained by the southerly vergence of the anticline folds and associated thrusts. Along the northern flank of the Formosinho, the erosion of upper Jurassic units led to the formation of typical hogback and chevron landforms supported by compact limestone and dolomitic layers. These rocky outcrops were the source of relict scree deposits that extend to the base of the slopes, presently fed by occasional rockfalls and rockslides. To the north of Mount Formosinho and São Luís, the upper Jurassic to Miocene layers strike approximately ENE– WSW and dip to the north. The dip is higher in the vicinity of the anticline folds and diminishes to the north (75–50°). Differences in bedrock erodibility played a crucial role in the evolution of this sector of the chain by imposing limits to drainage network incision. While the less competent units of the upper Jurassic, Cretaceous and Miocene (i.e. sand, conglomerates and clay) gave place to strike valleys formed by prolonged drainage incision, the competent limestone and sandy limestone belonging to Cretaceous, Paleogene and Miocene beds were left untouched forming parallel sets of homoclinal ridges (Fonseca et al. 2014, 2015). Along the southern flank of the Arrábida Chain a triangular-shaped depression opened to the Atlantic Ocean harbours the village of Sesimbra. While limited by a set of NE–SW and NW–SE trending faults, the morphology of this sector of the chain is owed to the erosion of the lower Jurassic evaporitic sequence, leaving competent rock bodies of Jurassic limestone along its flanks. The core of the depression was progressively lowered through the combined action of fluvial and marine processes in response to base-level lowering.

21.4.2 Karst Features Karst landforms are limited to the south-central and western sectors of the chain and associated with outcrops of lower to middle Jurassic limestone and dolomite. The largest features are observed within the surface of Plataforma do Cabo, forming large to medium-sized depressions predominantly oriented along fractures and bedding planes. Some of these landforms are opened along its lowest flank and integrated in the upper sectors of the present-day drainage network. The largest of these depressions occur between Mount Formosinho and Píncaro forming an E–W-oriented fluvio-karstic depression (Terras do Risco and Fojo), filled with fine sandy–clayey sediments (Daveau and Azevedo 1980–1981; Fonseca et al. 2015). The endokarst in the Arrábida Chain is mostly developed within the lower Jurassic limestone and dolomitic units. Due to its proximity to the ocean, the endokarst system is commonly connected to paleo-marine caves positioned along the southern flank of the chain. Over the last decades, a large number of caves (i.e. Gruta da Cave, with at least 40 explored galleries and over 300 m in length) and potholes have been discovered by local speleology teams (i.e. SPE— Sociedade Portuguesa de Espeleologia; NECA—Núcleo de Espeleologia da Costa Azul), which have been responsible for most of the work regarding cave inventory and mapping.

21.4.3 Erosion Surfaces Following the paroxysmal phase of tectonic deformation in the Late Miocene, vertical movements persisted in the Setúbal Peninsula during the Plio–Quaternary through the uplift of the Arrábida Chain and subsidence in the Tagus basin. Large-scale geomorphic evidence of surface uplift is provided by four erosion surfaces (L1—190 to 220 m; L2— 140 to 170 m; L3—70 to 110 m; L4—30 to 50 m) perched above the present-day drainage network (Fonseca et al. 2014, 2015). The preservation of these geomorphic markers is strongly associated with differences in bedrock resistance to erosion, particularly in the case of the uppermost level (L1). While to the west, the compact units of Jurassic limestone and dolomite allowed its preservation, to the east, the upper Jurassic sandstones and poorly consolidated conglomerates favoured drainage network incision, limiting geomorphic evidence of L1 to the lower flank of Mount Formosinho and São Luís. The uppermost level (L1—Plataforma do Cabo, Fig. 21.3) extends from Cape Espichel to the base of the São Luís Mount at c. 190–220 m asl. The fact that it has

21

The Arrábida Chain: The Alpine Orogeny in the Vicinity …

277

Fig. 21.3 Cape Espichel. Notice the upper Jurassic limestone strata dipping to the north. The erosion surface along the top corresponds to the L1 phase, commonly known as the level of the Plataforma do Cabo.

Photograph credits Duarte Fernandes Pinto, A Terceira Dimensão, http://portugalfotografiaaerea.blogspot.com

developed within the compact limestone and dolomitic unit of lower to middle Jurassic age, forming a nearly flat surface, has led geomorphologists to classify it as a paleo-marine level (Ribeiro 1968; Daveau and Azevedo 1980–1981; Pereira 1988; Cabral 1993). Besides the occasional quartz pebble, the lack of stratigraphic references hampers the definition of a clear time frame for this erosional phase. Nevertheless, given that the L1 cuts the northern flank of the St. Luís anticline, a post-Tortonian age and possible association with the high sea-level stands of upper Miocene and/or Pliocene (Fonseca et al. 2015) are suggested. The intermediate surface (L2) descends from the northern edge of the upper level (L1) and towards the top of the homoclinal ridges, suggesting a degradation phase of L1, connected with a northerly-directed flow of surface waters during the Late Pliocene and Early Pleistocene time (Daveau and Azevedo 1980–1981; Fonseca et al. 2014, 2015). The external level (L3) cuts the Pliocene terrain and the Belverde Formation along the northern flank of the Arrábida Chain and is fossilised by the torrential deposits of the Marco Furado formation. The lack of absolute ages for the Belverde (lower Pleistocene) and Marco Furado (middle Pleistocene) formations hinders the definition of a specific timeframe for the elaboration of L3 (Fonseca et al. 2014). The lowest level (L4) represents a degradation of L3 in

response to Pleistocene sea-level lowering, leading to the formation of the Lagoa de Albufeira during the Holocene.

21.4.4 Marine Landforms The beauty and singularity of the Arrábida Chain is much owed to its southern flank where it plunges into the Atlantic Ocean through 100–300 m vertical sea cliffs, a scenery only interrupted by the diapiric depression of Sesimbra and by the narrow stretches of sand north of the Portinho da Arrábida (Fig. 21.2). While facing way from the predominant wave direction along the western coast of Portugal (NW), the southern flank suffers limited wave impact and the present-day cliff evolution is mostly controlled by gravitational processes triggered by intense rainfall (i.e. rockfalls, debris flows). The morphology of the southern flank has been associated to the tectonic control imposed by the Arrábida thrust (Manuppella et al. 1999). The presence of paleo-marine levels positioned at different altitudes along the WSW–ENE extension of the cliff bears evidence of Quaternary sea-level fluctuations. Tectonic deformation within critical stretches of the southern flank hinders a clear correlation between the highest levels, presently positioned at 150–170 m asl. Only for the lower and more recent levels did the study of

278

A. F. Fonseca et al.

marine/aeolian deposits and archaeological findings allowed a successful comparison between marine abrasion landforms (Antunes 1991; Pereira and Regnauld 1994; Pereira et al. 2007).

21.5

Conclusions

The morphological features presently observed in the Arrábida Chain result from the complex interaction of tectonic and erosional processes acting since the Late Miocene. Landscape evolution was a response to base-level change imposed by Neogene sea-level fluctuations and tectonic uplift of the Arrábida Chain along with subsidence of the lower Tagus basin. Geomorphic evidence of surface uplift is preserved in the form of high vertical cliffs with a geometry similar to the Arrábida thrust, as well as in erosional surfaces perched above the present-day drainage network. Differences in the resistance of bedrock to erosion played a crucial role in landscape evolution by imposing limits to drainage network incision. While the Formosinho and São Luís anticlines and the homoclinal ridges along the northern flank are associated with outcrops of compact Jurassic, Cretaceous and Paleogene/Miocene limestone, the low areas in-between are developed within the Jurassic evaporites (i.e. diapiric depression of Sesimbra) and upper Jurassic and Cretaceous poorly consolidated continental sequences (i.e. Ajuda, Coina, Alambre and Pateira).

References Antunes MT (1991) O homem da gruta da Figueira Brava (ca. 30.000 BP), context geológico, alimentação, canibalismo. Memórias da Academia das Ciências de Lisboa, Classe de Ciências 31:487–536

Antunes MT, Elderfield H, Legoinha P, Pais J (1995) Datações isotópicas com Sr do Miocénico do flanco sul da Serra da Arrábida. Comunicações Instituto Geológico e Mineiro 81:73–78 Azevedo TM (1982) O Sinclinal de Albufeira. Evolução Pós-Miocénica e Reconstituição Paleogeográfica. Dissertação de doutoramento, Centro de Geologia, Fac. de Ciências de Lisboa, p 302 Cabral J (1993) Neotectónica de Portugal Continental. Dissertação de doutoramento, Departamento de Geologia, Faculdade de Ciências da Universidade de Lisboa, p 435 Choffat P (1908) Essai sur la téctonique de la Chaine de l’Arrabida. Memórias dos Serviços Geológicos Portugueses, p 89 Daveau S, Azevedo T (1980–81) Aspectos e evolução do relevo da extremidade sudoeste da Arrábida (Portugal). Bol. Soc. Geol. Port., volume de homenagem aos Professor Carlos Teixeira, Lisboa, pp 163–180 Fonseca AF, Zêzere JL, Neves M (2014) Geomorphology of the Arrábida Chain. J Maps 10(1):103–108 Fonseca AF, Zêzere JL, Neves M (2015) Contribution to the knowledge of the geomorphology of the Arrábida Chain (Portugal): Geomorphological mapping and geomorphometry. Rev Bras Geomorfol 16 (1):137–163 Kullberg MC, Kullberg J, Terrinha P (2000) Tectónica da Cadeia da Arrábida. In Tectónica das regiões de Sintra e Arrábida, Memórias Geociências. Museu Nac Hist Nat Univ Lisboa 2:35–84 Manuppella G, Antunes MT, Pais, Ramalho MM, Rey J (1999) Carta geológica de portugal na escala 1:50000. Notícia explicativa da folha 38-B Setúbal. Instituto Geológico e Mineiro, p 143 Mora C (1998) Aspectos do clima local da Arrábida. Dissertação de Mestrado em Geografia Física e Ambiente apresentada à F.L.U.L, p 156 Pereira AR (1988) Aspectos do relevo de Portugal. Litorais ocidental e meridionais da Península de Setúbal. Finisterra 23(46):335–349 Pereira AR, Regnauld H (1994) Litorais quaternários (emersos e submersos) na extremidade sudoeste da Arrábida (Portugal). Contribuições para a Geomorfologia e Dinâmicas Litorais em Portugal, Linha de Acção de Geografia Física, Relatório 35, Centro de Estudos Geográficos, Lisboa, pp 55–69 Pereira AR, Borges B, Soares Monge A, Santos AP, Neves M (2007) Coastal Palaeoenvironments: a balance between sea level fluctuations and neotectonics. Examples on Portuguese Estremadura. In: Gómez-Pujol L, Fornós JJ (eds) Investigaciones recientes (2005– 2007) en Geomorfología Litoral, pp 175–177

Part IV Urban Areas

Geomorphology in a World Cultural Heritage Site: The City of Porto

22

Laura Soares and Carlos Bateira

Abstract

22.1

Located in the northwest of Portugal, along the Douro River estuary and facing the Atlantic on the west side, Porto is the second largest city of the Portuguese territory. Retaining in its urban structure, several characteristics that reflect the economic, social and cultural evolution over several epochs, the historical center of Porto is a World Heritage Site since 1996. Holding a complex structural framework, given its location in a contact strip between the Central Iberian and the Ossa-Morena zones of the Variscan Iberian Massif, the city is carved in granites associated with a narrow belt of metasedimentary rocks and different types of gneisses and amphibolites. Some continental, fluvial and marine deposits overlap these outcrops, reflecting a (neo)tectonic and paleoclimatic evolution that marks the geomorphological context of Porto. The steep slopes of the Douro valley, leading to slope movements, major river floods or the erosion problems linked to ocean dynamics, are stored in the memory of the inhabitants of Porto and are reflected in several features of contemporary land management practices.

The city of Porto, whose historic center was declared UNESCO World Heritage Site in December 1996, holds a unique scenic value, awarded by the harmonious and creative articulation between an urban structure, where it is possible to identify different stages of historical evolution, and the rugged morphology of a territory essentially carved in granite and heavily conditioned by the deep incision of the Douro River and the coastal dynamics dictated by Atlantic Ocean (Fig. 22.1). These characteristics, which implicitly recall a (neo)tectonic and paleoclimatic evolution, gave rise to a geocultural landscape where currently 237,584 people live, and which has become one of the most important European tourist destinations. Reflecting economic, social and cultural conditions of several historic periods, Porto is a city where the memories of an urban expansion that had to deal with the Douro floods, the instability of its slopes and problems related to ocean storms and coastal erosion, still remain. This geomorphological context is the subject of this chapter.

Keywords

22.2

Urban geomorphology Porto




Natural hazards




Heritage

L. Soares (&)
C. Bateira (&) Centre of Studies on Geography and Spatial Planning (CEGOT), University of Porto, Porto, Portugal e-mail: [email protected] C. Bateira e-mail: [email protected]




Introduction

Geographical and Historical Setting

Located in the northwest of Portugal, in a strategic point between the river and the sea, the city of Porto is situated on the littoral platform (Fig. 22.2), an erosional surface next to the shoreline below 125 m asl, covered with fluvial and marine formations usually of Plio-Pleistocene age (Araújo 2000). The littoral platform is bordered inland by a rectilinear escarpment zone (the so-called marginal relief) interpreted by several authors as a fault scarp, showing a NNW-SSE direction and crossed by transverse faults, introducing a compartmentalized and unleveled appearance (Ferreira 1991; Araújo 1991, 1997). The origins of the city date back to the late Bronze Age, finding its embryo nucleus in Alto da Pena Ventosa or

© Springer Nature Switzerland AG 2020 G. Vieira et al. (eds.), Landscapes and Landforms of Portugal, World Geomorphological Landscapes, https://doi.org/10.1007/978-3-319-03641-0_22

281

282

L. Soares and C. Bateira

Fig. 22.1 Porto’s urban landscape. a Overview of the historic center. b Alto da Pena Ventosa. c Night view over Dom Luis I bridge and the Serra do Pilar Monastery

Morro da Sé, although the earliest archaeological remains are Paleolithic (Silva 2000). But like a complex stratigraphic profile with several layers, Porto also preserves evidence from its proto-history and memories and influences dictated by the Roman, Suevi, Visigoth and Muslim peoples, who left their marks until the time of the ‘Reconquista,’ when its development is established as a burgh linked to Portugal’s history (Barroca 1990–1991). Illustrating the natural constraints that influenced the origin of many settlements, the initial deployment of the city reveals defensive strategies that explain its primary location in a high place. This position probably justifies the toponym Cale, which Silva (2000, p. 90) considers as meaning ‘stone’, ‘rock’, ‘hard’, an interpretation that fits “(…)the characteristics of the granitic hill of Pena Ventosa, where the original settlement took place”. Following the Roman invasions and recognizing the value of the proximity of fluvial and maritime resources, important terrestrial routes and suitable soils for agriculture, there was an expansion to a lower position, in connection with the Douro River, giving

rise to a second core site: the Portus (Port, harbor) of Cale, from which the name of Portugal derives. After this initial phase, the city grew steadily and overcome its older limits, defined by a succession of walls, which allows reconstructing Porto’s expansion until the fourteenth century, when it started extending mainly along the Douro waterfront, due to the intensification of commercial and maritime activities (Fig. 22.3). From the ‘Cerca Velha’ (old fence) or Romanesque Wall, constructed in the third century and covering approximately 3 ha—enclosing the Pena Ventosa hill—there remains only a small section. Around it, the ‘Cerca Nova’ (new fence) or Gothic Wall (also known as ‘Fernandina’) was built near 1370, comprising an area of 44.5 ha (Silva 2010–2011). But if Porto keeps the memories of these earliest times, it also shows a set of monuments and buildings in different architectural styles, proving the prosperous period of the Portuguese Discoveries (fifteenth and sixteenth centuries), the favorable economy linked to Port Wine trade and exportation since the middle of eighteenth century, and the great engineering works of the nineteenth

22

Geomorphology in a World Cultural Heritage Site …

283

Fig. 22.2 Location of Porto. The lower left map shows the geomorphological units of northwest Portugal. The right map shows the relief and main faults in the vicinity of the city

century—the iron bridges, the new customs building, the railway stations, as well as the start of the construction of the Leixões Seaport (Alves and Dias 2001). This historic evolution results on a visual and aesthetic landscape harmonious diversity.

22.3

Geological Setting

The geology of Porto is part of a complex structural framework, given its location in a contact strip between the Central Iberian (CIZ) and the Ossa-Morena (OMZ) zones of the Variscan Iberian Massif, defined by the PortoTomar-Ferreira do Alentejo shear zone (PTFASZ). Forming a NNW-SSE deep crustal structure, the PTFASZ (of interplate nature and presenting a transform fault geometry), dates from the middle-upper Proterozoic (Dias and Ribeiro

1993) and integrates the southwest branch of the IberoArmorican Arc, forming a suture zone which passes through the Foz do Douro-Nevogilde area, extending then southwards (Dias and Ribeiro 1995; Afonso et al. 2004; Romão et al. 2008). Porto’s coastline is sub-parallel to this structure and its lithology reflects a history that allows the reconstruction of the geotectonic evolution since pre-Variscan times (Fig. 22.4). From the São Francisco Xavier Fort (also known as the ‘Cheese Castle’) and approximately to the River Douro mouth, a belt of Precambrian metasedimentary rocks (mica schists and quartz-tectonites) occurs. These are associated with different types of gneisses and amphibolites, the former sometimes exceeding 600 Ma in age and the latter being 1.05 Ga old, forming the Metamorphic Complex of Foz do Douro (Fig. 22.5a, b). This one is intruded by syn- and post-tectonic granites, showing a parallel alignment to the

284

L. Soares and C. Bateira

Fig. 22.3 Distribution of the archaeological and architectural heritage of Porto, and a zoom over the Historic Center with the reconstitution of the Romanesque (red) and Gothic Walls (black)

PTFASZ, which in association with other tectonic zones has conditioned their emplacement (Noronha and Leterrier 1995, 2000). These granites form the outcrop on which the ‘Cheese Castle’ is built (some believe that its name derives from the rounded shape of the outcrop), a post-tectonic biotitic medium to coarse-grained granite (Fig. 22.5c), but with the predominance of the medium-grained (two mica sin-D3 facies), the city’s dominant substrate (Fig. 22.5d). This fact led to its designation as the ‘Porto Granite,’ genetically associated, near Arrábida bridge area, to a fine-grained facies, with which it contacts through a N130° E fault (Oliveira et al. 2010). The early series of biotitic porphyritic granites that cuts the Schist-Graywacke Complex (Douro Group), essentially formed by mica schists and metagraywackes, is to be found in the eastern limit of the city. This lithological diversity culminates with a set of Plio-Quaternary, predominantly fluvial and marine deposits, sometimes covered by a sandy-silty formation that probably dates from the Last Glacial Period (Araújo 1984).

22.4

Geomorphology

22.4.1 Plio-Quaternary Evolution: Climate and Sea-Level Change and Correlative Deposits The city of Porto integrates an erosional surface of sub-aerial origin—the littoral platform—which usually stands below 100–125 m asl. A more detailed analysis reveals a succession of stepped levels (Fig. 22.6), whose origin is associated with Plio-Quaternary dynamics, combining sea level variations with probable recent movements of the PTFASZ, evidenced by a series of fluvial and marine deposits located at different altitudes (Figs. 22.6 and 22.7), and by the strong incision of the Douro valley near its mouth. Continental deposits are located between 50 and 130 m asl, while marine formations are below 40 m, being divided into three evolutionary phases.

22

Geomorphology in a World Cultural Heritage Site …

285

Fig. 22.4 Geological and structural framework of the region of Porto

The oldest deposits (phase I) locally exceed 130 m asl and present a structure with three distinct layers (Fig. 22.7— IA, B and C): the lower one contains boulders of weathered granite or quartz, sometimes reaching about 1 m diameter; above lies a greenish-gray layer with micaceous elements, resulting from a low energy depositional environment; the upper unit, coarser than the previous and formed by gravel and small pebbles, presents cross-stratification and sometimes iron crusts (Araújo 2000). On both sides of the marginal relief, some of the phase I deposits are tilted, which supports the (neo)tectonic character of this relief, uplifted, at least in part, later than phase I deposits were laid down (Araújo et al. 2003). The strong weathering affecting bedrock under these deposits suggests a wet tropical climate, while the presence of iron crusts on the upper layer reflects a climate change toward dryness (Araújo 1997). Deposits of phase II are coarser and poorly calibrated (sometimes with fanglomeratic facies) and occur close to the Douro valley, always above 50 m asl, in the west side of marginal relief. They are correlative of a torrential dynamics and comprise materials of the previous phase in the lower

levels (light-colored sandstone blocks), and probably correspond to alluvial fans formed in association with the uplift of the marginal relief, as shown in trenches affected by reverse faulting. These deposits have been assigned by Araújo (2004) to a Pliocene-Quaternary transition phase (Gelasian?) and present characteristics seemingly correlative with the raña deposits found elsewhere in Portugal. The marine formations, associated with interglacials are spread over three altitudinal (30–40, 18–15 and less than 10 m) and sedimentological levels, showing deformations that denounce neotectonics. OSL dating indicates an age of 180 ± 25 ka to the intermediate deposit (Fig. 22.8), which according to Ribeiro et al. (2010) corresponds to a brief warming pulse at the end of MIS 7. Its top level, that resembles the sandy-silty cover formation, appears to derive from solifluction denouncing a periglacial environment considering, among other features, its poor sorting and the vertical position of the major axis of lower-level pebbles. That statement agrees with the fourteenth-century dating, correlated with a wet phase of the Würm (Araújo 1995; Ribeiro et al. 2010). Illustrating climatic changes that characterize the Quaternary period, these formations, which extend north and

286

L. Soares and C. Bateira

Fig. 22.5 Lithological aspects of Porto. a and b Metamorphic Complex of Foz do Douro (gneisses and amphibolites), classified as Municipal Natural Heritage since 2001, c granitic outcrop of São

Francisco Xavier (‘Cheese Castle’), d Guindais scarp sculpted in the Porto Granite, above which still remains some sections of the fourteenth-century wall

south along the coastline, allow, jointly with neotectonics and anthropogenic interventions, to draw the evolutionary framework of the littoral zone and the Douro valley in the more recent past and in the present.

the Quaternary, in association with sea-level fluctuations, with the Douro paleovalley floor in São Paio Bay being at 50 m below sea level (Gomes and Chaminé, 2010). The uplift of the Douro compartment helps to explain strong incision of the river so close to its mouth, as well as a probable epigenetic phenomenon—the origin of an antecedent stream (Cabral 1995, Fig. 22.9). The connection between the sea and the Douro River has always been one of the most important aspects of Porto’s socio-economic and cultural development, imposing several changes in the urban landscape, particularly in riverside areas and in the coastal zone. In fact, it was the functionality between the river and the sea that led to the development of several projects that substantially modified the fluvio-marine dynamics and the life of the population in Foz do Douro and along the shore. The measures undertaken, namely some engineering works, such as the construction of harbors and dams, coastal defenses, dredging of waterways for navigation purposes, the sand/gravel exploitation, in addition to a secular trend of sea-level rise, caused a reduction of the

22.4.2 Fluvio-Marine Dynamics: The Douro Estuary and Coastal Erosion The Douro estuary, located between the cities of Porto and Vila Nova de Gaia and extending 21 km upstream to the Crestuma–Lever Dam, represents the terminal section of the largest drainage basin of the Iberian Peninsula (97,682 km2), of which only 19% are in Portuguese territory. The São Paio Bay and the Cabedelo sand spit, which belong to the Local Natural Reserve of Douro Estuary, are the main morphological elements in the estuary, which shows its maximum width (1310 m) precisely in this area, while the minimum (130 m) stands between the Dom Luís I and Dona Maria bridges. Its topography was shaped during

22

Geomorphology in a World Cultural Heritage Site …

287

Fig. 22.6 A. Simplified geomorphological map of Porto and cross-section. B. Geological cross-section shows several stepped surfaces derived from the interplay of neotectonics and climate change. This is reflected by the presence of continental and marine deposits at

different elevations, some affected by reverse faults, and by the deep incision of the Douro River, which near the Dona Maria Bridge (Fontaínhas escarpment) ascends to 80 m and in the Arrábida area still exceeds 70 m

sedimentary load that nourishes the coastline (Dias et al. 2000). In this context stands out the Leixões harbor, the largest in northern Portugal, as well as the latest interventions in the Douro inlet (2004–2008), including the construction of the north jetty, the south breakwater, the strengthening works of the Cabedelo and the reconfiguration of the estuary access channel (Fig. 22.10). These structures are obstacles to sediment transport by the longshore drift, which shows a dominant north-south direction along the Portuguese northwestern coast. Although the Douro breakwaters seem to have stabilized the estuary banks through the consolidation and enlargement of the sand spit, which showed a recent inland migration, they resulted in an increase of ocean overtopping. They also improved the navigability of the Douro and the protection of riverside areas such as Cantareira, Passeio Alegre and Afurada, frequently affected by floods following storm surges (IPTM 2004). A recent study focused on the Cabedelo dynamics before and after the construction of those infrastructures (Bastos et al. 2012)

supports these observations, although the authors stress that the spit is now more affected by fluvial and sea dynamics on its eastern inland margin, and especially in southeast section. On the other hand, the breakwaters led to a greater accumulation of sediments in the São Paio Bay, modifying the ecology of this wetland area. In the long-term, it is expected that this increase will have a positive impact over the nourishment of the beaches toward the south, which suffer from severe erosion since the mid-twentieth century (Bastos et al. 2012). However, it is still too early to evaluate the results of these interventions, mainly because it also implies a study of sediment retention by dams and the effects of aggregate extraction, as well as a decrease of flooding, which play an important role in the transport of sediments and in the morphology of the Douro estuary. These factors contribute to a sand deficit in littoral supply of over 80% (Dias 1993; Portela 2008). Oliveira et al. (1982) estimated a significant decrease of sediment transport from the Douro, from an average of 1.8  106 m3/year before the 1950s to

288

L. Soares and C. Bateira

Fig. 22.7 Fluvial and marine deposits of Porto’s littoral platform. Chronological and paleoclimatic interpretation based on Araújo (1991, 2000, 2004), Araújo et al. (2003). Photos by M. A. Araújo

Fig. 22.8 Lavadores marine deposit (15–18 m asl). Dating techniques allow to associate the upper sandy-pelitic cover to the Würm, while the lower layers reflect a sea-level transgression (interglacial period)

0.25  106 m3/year after the construction of Crestuma– Lever Dam. Since the Douro River is the principal sediment source in the area, the main consequence is an increase of coastal erosion, especially in the south beaches, a situation that has prevailed for several years, leading to the

transformation of the coast into a ‘groin field’ (Fig. 22.10). The result is a transgressive trend of the coastline, with a rate of 1.7 mm/year since 1920, having implied, between 1980 and 1989, a shoreline retreat in Espinho and Cortegaça, reaching a maximum value greater than 12 m/year (Ferreira

22

Geomorphology in a World Cultural Heritage Site …

289

Fig. 22.9 Douro River and the city of Porto. a Aerial view between D. Luis I bridge and Foz do Douro (view in https://www.youtube.com/ watch?v=77B6Uh4cH1A). b Pensil bridge (prior to its demolition in 1887), illustrating the sector where the river presents its minimum width (in https://ncultura.pt/porto-a-ponte-pensil-d-maria-ii/). c The

Arrábida bridge, near the river mouth, showing the Douro strong incision immediately before its enlargement in São Paio Bay. d Foz do Douro: Cabedelo sand spit and new breakwaters (in the foreground) (Google Earth view 2017). e Cabedelo detail

and Dias 1991). Several authors consider that sea-level rise only explains a small part of this retreat, assigning the major responsibility to the sedimentary deficit (Dias 1993; Oliveira and Araújo 2009).

22.5.1 The Douro Floods and Their Impact in the Cities of Porto and Vila Nova de Gaia

22.5

Hydrogeomorphological Hazards

Floods and landslides are natural events that involve most personal injury in northern Portugal. The results of the project Disaster—GIS database on hydro-geomorphologic disasters in Portugal: a tool for environmental management and emergency planning, emphasize a concentration of occurrences involving personal injury in the cities of Porto and Vila Nova de Gaia. The development of hydrogeomorphological hazards is largely related to inadequate spatial planning and management, which often tend to increase the vulnerability of exposed elements. This situation becomes even more evident in areas of high density of population and infrastructure.

The Douro floods clearly marked the life of Porto and Vila Nova de Gaia riverside population. The Disaster database, gathering information for 1865–2010, shows records of 100 progressive flood occurrences and 43 urban flooding, involving 16 deaths, 28 injuries, 610 evacuations and 3701 displacements, which were usually associated with long-lasting rainfall episodes affecting vast areas (Soares et al. 2012). With a length of about 938 km, of which 200 km are in Portugal, the Douro River in a typical year presents an annual average flow around 450–470 m3/s but can exceed 10,000 m3/s during exceptional floods (INAG 2001; Rodrigues et al. 2003). Oliveira (1973) considers extraordinary floods as those exceeding the height of +6.00 m measured in the Douro right bank, near the Dom Luis I bridge. This value involves the flooding of the Ribeira quayside, since it is

290

L. Soares and C. Bateira

Fig. 22.10 Porto’s coastline southwards to Esmoriz. a Overview of the littoral between Porto, Foz do Douro and Esmoriz. b Douro River mouth and coastal zone between Lavadores and Madalena. São Paio Bay and Cabedelo sand spit are the main morphological elements in this image. c Espinho-Esmoriz littoral. To the south of Foz do Douro, the coast presents a clear inland throwback trend that the building of groins does not solve

situated at +5.9 m, but when this happens, Miragaia (+4.19 m) is already flooded (Aires et al. 2000). Combining historical data with the most recent records, the Management Plan of the Douro Hydrographic Region (PGRHD 2012) states that in every decade there is at least one extraordinary flood (with a peak flow of 10,510 m3/s in the Crestuma–Lever Dam), whereas an extraordinary flood with discharge of 15,517 m3/s has a return period of 50 years, a number that is sufficient to destroy the Cabedelo sand spit, as happened in 1909 (Gomes and Chaminé 2010). In fact, this flood was the largest during the twentieth century, followed by those occurred in 1962 (Fig. 22.11). However, peak flows seem to be decreasing, with the last flood exceeding 10,000 m3/s having occurred in 1979. This decrease can be partly attributed to flow regularization provided by dams, whereas some authors suggest it is also associated with the larger storage capacity of Spanish dams

(Rodrigues et al. 2003). Nevertheless, the Porto and Vila Nova de Gaia riverside will always be a susceptible area to flooding: implanted in a floodplain, progressively sealed by the infrastructures of a growing population, this area has learned to live, for centuries, with a river “(…) willing to be the winner in the race, galloping fast trough hills and valleys, without choosing paths; climbed cliffs; crashed in canyons; surrounded or broking mountains, to arrive before to the great sea” (Correia 2013, n.p.).

22.5.2 Mass Movements in the Douro Valley Slopes The strong incision of the Douro valley between Porto and Vila Nova de Gaia led to the formation of steep rocky slopes, which in association with a dense fracture network

22

Geomorphology in a World Cultural Heritage Site …

291

Fig. 22.11 Douro River floods in Porto. a Douro flood records: flows and heights. b, c, d 1909, 1962 and 2006 floods in Ribeira quayside. In recent years, there has been a decrease of exceptional floods

and differential weathering, promotes the development of mass movements. The importance of these processes has been assessed by surveying newspapers back to the nineteenth century, although more consistent information is only available since 1940s. In January 1879, the periodicals reported the ‘Guindais horrible catastrophe,’ where several persons died. The occurrences increased throughout the twentieth century and became less frequent since 2001 after the beginning of slope stabilization measures, with containment works and demolition of deeply degraded residential structures mainly along the Guindais/Fontaínhas and Serra do Pilar escarpments (Bateira and Soares 1997a, b; Bateira and Soares 2010; Borges and Correia 2003). The Disaster database comprises 31 slope movements in both municipalities, among which 51.6% are earth falls and 29% are rock falls. These events resulted in 21 deaths, 52 injuries, 102 evacuations and 451 displaced people, corresponding to a damage corporal index (ratio between the number of deaths/injuries and the total of cases for each

dangerous event) significantly higher than the flooding: 0.3 and 2.4, respectively. In this context, the areas with highest geomorphological susceptibility are located between the Dom Luis I and Dona Maria Bridges, where the most important slope stabilization interventions took place, and also in some sectors of the Afurada and the Arrábida bridge (Fig. 22.12). One of the most important conditioning factors of slope instability is the bedrock fracture network. The Douro River presents an E–W general direction, but in detail, it is adapted to the orientation of the principal fractures: NNE–SSW dipping 86° SE, NW–SE dipping 60° SW at the Afurada and Serra do Pilar outcrops, and a secondary N–S family, tilting to 82° N (Chaminé et al. 2010). These directions generate a nearly orthogonal fracture network, often in accordance with slope gradient, enhancing block falls. These fractures promote deep weathering, leaving fresh or slightly weathered rock cores. Such conditions facilitate the occurrence of earth falls, sometimes due to poorly planned interventions.

292

L. Soares and C. Bateira

Fig. 22.12 Susceptibility to slope movements in Porto. Note the high values in the Douro margins, essentially near the historic center. The Guindais (photos on top) and Serra do Pilar escarpments have revealed a high incidence of instability processes, which entailed several interventions

22.6

Conclusions

The city of Porto presents a morphostructural context and high urban pressure requiring careful risk management practices. In the last few years, several interventions have been made in terms of fluvial, marine and slope dynamics, which aim to ensuring population and infrastructure safety. But the frequency of human action over the conditioning factors induces a systematic change on these natural dynamics, requiring a permanent monitoring e evaluation. The historic center of Porto, UNESCO World Heritage Site since 1996, is recognized as a masterpiece of human creative mind, and simultaneously a very susceptible area to dangerous events. Ensuring their preservation involves all actors, in an effort essential to the local beauty and identity. As Sack (1997, p. 35) mentions “(…) place and its landscape become part of one’s identity and one’s memory. Its features are often used as mnemonic devices… For all of us the landscape is replete with markers of the past (…) that help us remember and give meaning to our lives”.

References Afonso MJ, Chaminé H, Gomes A, Teixeira J, Araújo MA, Fonseca P, Carvalho J, Silva M, Rocha F (2004) Cartografia geológica e geomorfológica estrutural da área metropolitana do Porto: implicações na gestão dos recursos hídricos subterrâneos. Xeográfica: Revista de Xeografía. Territorio e Medio Ambiente 4:101–105

Aires C, Pereira D, Azevedo T (2000) Inundações do rio Douro: dados históricos e hidrológicos. I Jornadas do Quaternário da APEQ, Porto Alves J, Dias E (2001) O fio de água—o Porto e as obras portuárias (Douro-Leixões). Revista da Faculdade de Letras-História III Série 2:93–106 Araújo MA (1984) A formação areno-pelítica de cobertura. Biblos, LX, pp 71–89 Araújo MA (1991) Evolução geomorfológica da plataforma litoral da região do Porto. Tese de Doutoramento, Faculdade de Letras da Universidade do Porto, p 534 Araújo MA (1995) Os facies dos depósitos wurmianos e holocénicos e as variações climáticas correlativas na plataforma litoral da região do Porto. Actas do VI Colóquio Ibérico de Geografia, Publicações da Universidade do Porto, pp 783–793 Araújo MA (1997) A plataforma litoral da região do Porto: dados adquiridos e perplexidades. Lisboa, Estudos do Quaternário 1:3–12 Araújo (2000) Depósitos continentais e marinhos na plataforma litoral da região do Porto. Importância da tectónica na sua organização espacial. Ciências da Terra 14: 113–124. Lisboa (UNL) Araújo MA (2004) O final do Cenozóico na plataforma litoral da região do Porto. In: Araújo e Gomes (ed) Geomorfologia do NW da Península Ibérica. Porto, GEDES, pp 117–137 Araújo MA, Gomes A, Chaminé H, Fonseca P, Pereira L, Jesus A (2003) Geomorfologia e geologia regional do sector de Porto-Espinho (W de Portugal): implicações morfoestruturais na cobertura sedimentar cenozóica. Cuadernos Laboratorio Xeológico de Laxe 28:79–105 Bateira C, Soares L (1997a) Movimentos em massa no norte de Portugal. Factores da sua ocorrência. Territorium 4:63–77 Bateira C, Soares L (1997b) A importância da definição de áreas de risco natural e/ou antrópico dos planos de protecção civil. Estudo de caso: a escarpa de Guindais. Comunicações das Jornadas de Protecção Civil. Câmara Municapal de V. N. Gaia, p 36 Bateira C, Soares L (2010) Escarpa dos Guindais/Escarpa da Serra do Pilar. Georriscos e Protecção Civil em contexto urbano. In: Guia de campo do V Congresso Nacional de Geomorfologia, APGeom, pp 61–69

22

Geomorphology in a World Cultural Heritage Site …

Barroca M (1990–91) Do Castelo da Reconquista ao Castelo Românico (Séc. IX a XII). Portvgalia, Nova Série XI–XII: 89–136 Bastos L, Bioa A, Pinho J, Granja H, Jorge da Silva A (2012) Dynamics of the Douro estuary sand spit before and after breakwater construction. Estuar Coast Shelf Sci 109:53–69 Borges L, Correia A (2003) Escorregamentos de terra e queda de blocos —o exemplo do passeio das Fontaínhas (Porto). Seminário Riscos Geológicos, APG, pp 35–36 Cabral J (1995) Neotectónica em Portugal Continental. Lisboa Memórias do Inst Geol E Mineiro 31:265 Chaminé H, Afonso MJ, Silva R, Monteiro R, Teixeira J, Moreira P, Meixedo JP, Trigo JF (2010) Da teoria à prática em geotecnia urbana de maciços rochosos: o exemplo da zona ribeirinha de Gaia. Tecnologia e Vida 6:39–45 Correia A (2013) Tejo, Douro e Guadiana. In: Contos, fábulas, facécias e exemplos da tradição popular portuguesa. Recolhidos e narrados por Ana de Castro Osório. Faculdade de Letras da Universidade de Lisboa (2008) Dias JMA (1993) Causas da erosão costeira. In: Estudo de Avaliação da Situação Ambiental e Proposta de Medidas de Salvaguarda para a Faixa Costeira Portuguesa (Geologia Costeira), pp 13–38 Dias J, Boski T, Rodrigues A, Magalhães F (2000) Coast line evolution in Portugal since the last glacial maximum until present—a synthesis. Mar Geol 170:177–186 Dias R, Ribeiro A (1993) Porto-Tomar shear zone, a major structure since the beginning of the Variscan orogeny. Comun Inst Geol Mineiro Lisboa 79:31–40 Dias R, Ribeiro A (1995) The Ibero-Armorican arc: a collision effect against an irregular continent. Tectonophysics 246:113–128 Ferreira AB (1991) Neotectonics in Northern Portugal. A geomorphological approach. Z Geomorph NF 82:73–85 Ferreira J, Dias O (1991) Evolução recente de alguns troços do litoral entre Espinho e o Cabo Mondego. Actas do 2° Simposio sobre a Protecção e Revalorização da Faixa Costeira do Minho ao Liz, Porto, pp 85–95 Gomes A, Chaminé H (2010) Zona ribeirinha do Porto e Gaia: dinâmicas geomorfológicas. Enquadramento regional. In: Guia de campo do V Congresso Nacional de Geomorfologia, APGeom, pp 11–25 INAG (2001) Plano da Bacia Hidrográfica do Rio Douro. Relatório final, p 583 IPTM—Instituto Portuário e dos Transportes Marítimos (2004) Relatório de conformidade ambiental do projecto de execução (RECAPE) das obras de melhoria da Barra do Douro

293 Noronha F, Leterrier J (1995) Complexo Metamórfico da Foz do Douro. Geoquímica e geocronologia. Resultados preliminares. In: Borges FS, Marques MM (eds) IV Congresso Nacional de Geologia, Mem Mus Labor Miner Geol Fac Ciênc Univ. Porto 4:769–774 Noronha F, Leterrier J (2000) Complexo metamórfico da Foz do Douro (Porto). Geoquímica e geocronologia. Santiago de Compostela. Rev Real Academia Galega Ciencias 19:21–42 Oliveira (1973) O espaço urbano do Porto: condições naturais e desenvolvimento. Tese de doutoramento. Universidade de Coimbra Oliveira C, Araújo A (2009) As praias entre a Foz do Douro e a Granja: algumas reflexões sobre a erosão costeira. Cadernos Curso de Doutoramento em Geografia, Flup, pp 213–228 Oliveira I, Valle A, Miranda F (1982) Littoral problems in the Portuguese West Coast. Coast Eng 3:1950–1969 Oliveira M, Noronha F, Lima A (2010) Cartografia geológica à escala 1:10.000 da região SW da Folha Geológica 9C—Porto. e-Terra 22 (16) PGRHD (2012) Plano de Gestão da Região Hidrográfica do Douro. Relatório de Base, Parte 2:2432 Portela L (2008) Sediment transport and morphodynamics of the Douro River estuary. Geo-Mar Lett 28:77–86 Ribeiro H, Pinto de Jesus A, Mosquera D, Abreu I, Vidal Romani J, Noronha F (2010) Estudo de um terraço de Lavadores. Contribuição para a dedução das condições paleoclimáticas no Plistocénico médio. e-Terra 2(1): 4 Rodrigues R, Brandão C, Costa J (2003) As cheias no Douro ontem, hoje e amanhã. INAG, Direcção dos Serviços dos Recursos Hídricos, p 2 Romão J, Ribeiro A, Pereira E, Fonseca P, Rodrigues J, Mateus A, Noronha F, Dias R (2008) Desligamentos interplaca e intraplaca em cadeias deformadas: exemplos no bordo SW dos Variscides Ibéricos Sack R (1997) Homo Geographicus: a framework for action, awareness, and moral concern. Johns Hopkins University Press, Baltimore, p 292 Silva A (2000) As origens do Porto. In: Oliveira Ramos L (ed) História do Porto. Porto Editora, pp 46–117 Silva A (2010–11) As muralhas romanas do porto: um balanço arqueológico. Portvgalia Nova Série 31–32: 43–64 Soares L, Santos M, Hermenegildo C, Bateira C, Martins L, Matos F, Gomes A, Peixoto A, Couceiro S, Gonçalves S, Lourenço S (2012) Reconstruction of the 1909 hydro-geomorphologic events in North of Portugal: the importance of GIS databases. Actas de la XII Reunión Nacional de Geomorfología, Santander, pp 147–150

The Urban Geomorphological Landscape of Lisbon

23

Teresa Vaz and José Luís Zêzere

Abstract

The geological and geomorphological characteristics of Lisbon are presented and linked with city settlement and development. The population and infrastructure concentration make Lisbon more vulnerable to geomorphological hazards. Important geomorphological disasters affected the city in the past and were responsible for significant transformations in land use giving rise to new landforms. The 1755 earthquake and the São Jorge Castle and the Santa Catarina earthquake-induced landslides are presented as major disasters. Keywords

Lisbon

23.1




Geomorphology




Earthquake




Landslides

Introduction

The location of downtown Lisbon, stretched between hills and valleys in the north bank of the Tagus River (Fig. 23.1), early became the setting for the occupation of different peoples and cultures, such as the Romans (second century BC to fifth century) and the Arabs that followed (eighth to twelfth century). Geomorphology played a key role in the choice of the settlement site and in the further development of the city. Lisbon is known as the ‘city of seven hills’, which are São Vicente, Santo André, São Jorge Castle, Santana, São Roque, Chagas and Santa Catarina. Although the designation ‘city of multiple elevations’ should be more appropriate (Gaspar 1994), the former expression reveals the T. Vaz (&)
J. L. Zêzere Centre of Geographical Studies, Institute of Geography and Spatial Planning, University of Lisbon, Lisbon, Portugal e-mail: [email protected] J. L. Zêzere e-mail: [email protected]

importance of geomorphology as a major character of the city. The adaptation to the terrain gives to Lisbon’s neighbourhoods a unique physiognomy. On the other hand, as in other cities, the needs of construction and planning have changed the landscape itself (Ahnert 1996 in Bathrellos 2007). Today, as the capital of Portugal, more than 540 thousand people live inside Lisbon municipality (INE 2011) and during weekdays, 425 thousand additional people commute from the surrounding municipalities to work or study. The concentration of people and of critical infrastructures makes the city particularly vulnerable to geomorphological hazards. In this chapter, the geological and geomorphological characteristics of the city of Lisbon are presented. Afterwards, major geomorphological disasters that affected the city in the past, such as the 1755 earthquake and the São Jorge Castle and the Santa Catarina earthquake-induced landslides, are discussed. These urban landslides were first addressed by Zêzere et al. (2001) and Ferreira et al. (2002) and were further analysed in detail by Vaz and Zêzere (2016).

23.2

Geographical Setting

Lisbon is located in the southern Portuguese Estremadura and limited in the south by the Tagus River (Fig. 23.2). The municipality covers an area of approximately 85 km2 (INE 2011) and is bound to the north by the Loures and Odivelas municipalities and to the west by Amadora and Oeiras. The mid-latitude location at 38º N and the proximity to the Atlantic Ocean induce a thermal amenity to the climate, which is nevertheless typically the Mediterranean (Alcoforado et al. 2009), with normally hot and dry summers (Oliveira et al. 2011). The mean monthly temperature ranges from 8.3 °C (in December) to 23.5 °C (in August). The mean annual rainfall in Lisbon is 774 mm at the Lisboa– Geofísico rain gauge (1981–2010). However, the rainfall

© Springer Nature Switzerland AG 2020 G. Vieira et al. (eds.), Landscapes and Landforms of Portugal, World Geomorphological Landscapes, https://doi.org/10.1007/978-3-319-03641-0_23

295

296

T. Vaz and J. L. Zêzere

Fig. 23.1 Lisbon viewed from the southwest, with the Tagus River and the 25 April Bridge in the foreground. Photo credits Duarte Fernandes Pinto, A Terceira Dimensão, http:// portugalfotografiaaerea.blogspot. com

Fig. 23.2 Location of Lisbon and neighbouring municipalities

regime is irregular with wide year-to-year variability. Most rainfall concentrates in the period from October to February (70% of annual rainfall).

23.3

Geology and Geomorphology

23.3.1 Geology Geologically, Lisbon is located within the Lusitanian Basin and the Lower Tagus Basin (Lopes 2001). The first is a

complex subsidence structure formed along a NNE–SSW direction (Ribeiro et al. 1979). It evolved during the part of the Mesozoic and was generated by lithospheric extension associated with the fragmentation of Pangaea, more precisely with the opening phases of the North Atlantic (Kullberg et al. 2006). Its evolution was influenced by several rifting episodes alternating with regional subsidence and uplift periods (Pais et al. 2006). In the Late Jurassic—Early Cretaceous (Tithonian–Barremian), the tectonic distension ceased after a rifting episode (Pais et al. 2006). During the Albian, a marine transgression episode occurred again,

23

The Urban Geomorphological Landscape of Lisbon

creating conditions for sedimentation of limestones and marls (Upper Albian to Middle Cenomanian) and compact limestone (Upper Cenomanian) (Pais et al. 2006) (Fig. 23.3). These limestones were formed in shallow seas, of warm and clear waters, by a slow accumulation of shells and polyps (Ribeiro 1994) and can be found in the southwest part of the city. In the initial period of the Alpine tectonics (Late Cretaceous) in the Iberian Peninsula, the emplacement of alkaline igneous rocks of the Volcanic Complex of Lisbon took place (Pais et al. 2006). This was both an intrusive and extrusive extensive event that covered the Lisbon region by basaltic lavas and pyroclastic deposits (Pinto et al. 2011). After the volcanic activity ceased, the landforms were eroded, and a fluvial detrital complex was deposited during the Paleogene over both the Mesozoic igneous and the sedimentary substrates (Pais et al. 2006). The sediments are composed of poorly sorted pebbly deposits with alluvial fan facies (Pais et al. 2006). This type of sedimentation highlights relief rejuvenation associated with tectonic activity (Pais et al. 2006). This formation, called the Benfica Complex, outcrops in the northwest and the north sectors of the

Fig. 23.3 Geological units of the municipality of Lisbon

297

municipality, along the contact with the Volcanic Complex of Lisbon. During the Paleogene, the individualization of the Lower Tagus Basin was initiated along a tectonic depression with NW–SW direction, which suffered subsidence during the Miocene, and consequently, a marine transgression (Pais et al. 2006). Within this period, the Miocene Formations, consisting of alternating sands, clays and limestones, rich in fossils, animals and plants were deposited (Lopes 2001). The Miocene formations currently show a monocline dipping to E-SE and dominate in the eastern and northern parts of the city. After the Miocene series, a sedimentary gap exists (Lopes 2001). The Quaternary evolution was characterized by discontinuous marine regression events, with multiple fluctuations of the sea level (Lopes 2001). The Holocene formations present in Lisbon are mainly alluvium and landfills (Pais et al. 2006). The alluvium occurs along the main fluvial valleys within the city (Pais et al. 2006). The landfills are heterogeneous deposits, constituted mainly by clay and sand. These deposits have been built during centuries along the right bank of the Tagus River to

298

enlarge the city, mainly for harbour extension purposes. Landfills have been also associated with natural disasters, as the material resulting from earthquakes and landslides was used as a landfill to rebuild the city (Almeida 1991).

23.3.2 Geomorphology The altitude in Lisbon ranges from 2 to 3 m near the Tagus River, to 227 m in the Monsanto hill (Fig. 23.4). Two major geomorphological units can be distinguished in the city

Fig. 23.4 Topography of the municipality of Lisbon

T. Vaz and J. L. Zêzere

(Almeida 1991) divided by the Alcântara Valley, which is the largest natural barrier inside the municipality (Ribeiro 1994). The first geomorphological unit corresponds to the southwest part of the city and has developed over the Cenomanian limestone and the Lisbon Volcanic Complex. This unit has the most rugged landscape, including the Monsanto and the Ajuda anticline structures. The Monsanto hill is a dome associated with Cenomanian limestone (Ribeiro 1994), with steep slopes. The drainage network in this unit is dendritic over the limestone and ill-defined over basalts (Almeida 1991).

23

The Urban Geomorphological Landscape of Lisbon

The second geomorphological unit is developed over the Paleogene and Miocene sedimentary series in the eastern part of the city (Fig. 23.4). It is dominated by a low gradient plateau with a gentle slope towards ESE, in the same direction as the dip of the geological layers (Almeida 1991; Ribeiro 1994). To the north and northwest, the plateau border dominates the elongated depression of Odivelas–Vialonga that is part of a cuesta structural landform (Ribeiro 1994). To the south and southeast, the plateau is cut by fluvial valleys with a prevailing north–south direction towards the Tagus River.

23.3.3 Urban Geomorphology The potential of the place and position of Lisbon made it an attractive area for human settlement and explains the diverse conquering and reconquering events that occurred throughout its history. The primitive city was built on the top and the flanks of São Jorge hill (Ribeiro 1994). When incorporated into the Roman Empire, in the second half of the second century BC and until the fifth century, Lisbon was named Olisipo and becomes a strategic defensive place, considering its topography and natural protection at the entrance of the Tagus Estuary. Under the Muslim dominion, from the eighth to the twelfth century, the city spread over the São Jorge hill, surrounded by a defensive wall (so-called old or Moorish wall). However, Lisbon became the political and economic capital of the kingdom only in the thirteenth century (Salgueiro 1996). The importance of the city as a fluvial and maritime port grew during the fifteenth century, as a strategic hub for the Mediterranean and Atlantic trade networks and as the starting point for the Portuguese discoveries (Gaspar 1994). In addition, the river with its broad estuary, and excellent conditions for the installation of the port of Lisbon, was the key element to the development of the city (Ribeiro 1994). The different geomorphological elements within the city’s landscape are historically associated with different land uses. The hills, separated by fluvial valleys, gave protection and were firstly occupied by convents and churches (Ribeiro 1994), while the flat-floored valleys and plateaus with fertile land were traditionally used for agriculture (Ribeiro 1994). Geomorphology also conditioned the urban landscape. For example, the geometrical plan of the new avenues designed at the end of the nineteenth century was developed on the flat surface of the plateaus of the Avenidas Novas (Ribeiro 1994). On the other hand, the stairways, elevators and small trams, characteristic of Lisbon, are clear adaptations to the landscape constraints. In addition, the geological composition has been extensively exploited for economic activities. As an example, limestone was combined with basalt to build the Portuguese stone pavements that characterize most cities in Portugal (Ribeiro 1994).

299

23.4

Hazards in Lisbon

23.4.1 Earthquakes The 1755 earthquake, also named the Lisbon earthquake, is probably the best-known historical earthquake worldwide. However, other earthquakes caused damage to the city, namely in 1344, 1512, 1531, 1858, 1909 and 1969, with little information being available for earthquakes occurring prior to the sixteenth century. That is the case of the 1344 earthquake, whose records only scarcely mention the destruction of buildings and fatalities in Lisbon (Moreira 1984). In 28 January 1512, another important earthquake caused great damage and fatalities in Lisbon (Resende 1973) and triggered a landslide in the São Jorge Castle Hill (Zêzere et al. 2001; Ferreira et al. 2002; Vaz and Zêzere 2016). The 26 January 1531 earthquake was the first, the consequences of which were described with some detail in Portugal (Moreira 1979) and have been associated with the Lower Tagus Fault zone, with an estimated Richter magnitude of 7.1 (Martins and Mendes-Victor 2001). The shock caused approximately 1000 fatalities and generated severe damage in the city, destroying about 1/3 of the building stock (1500 houses) (Miranda et al. 2012). On 1 November 1755, the ‘Lisbon earthquake’ occurred, with an estimated Richter magnitude of 8.5 (Martins and Mendes-Victor 2001). At the time, Lisbon was characterized by labyrinthic streets (Oliveira 2005) and many houses collapsed with an estimated 10–30 thousand casualties, mainly in churches that were full for the All Saints Day mass (Moreira 1991; Pereira de Sousa 1919–1932). The effects in the city were more damaging in its eastern and central part, which is explained by the old age of the buildings in the eastern area and the less stable ground in the central area, with construction over a range of landfills (Moreira 1993). The earthquake was followed by a tsunami and a fire that lasted from five to six days, increasing the destruction (Moreira 1993; Oliveira 2005). Lisbon’s reconstruction was carried out following modern urban planning regulations (Fig. 23.5) and implementing anti-seismic measures in the building architecture to resist new seismic events. Despite the time elapsed since the 1755 earthquake, the source of the earthquake is still discussed. Traditionally, the earthquake was considered to have occurred along the Gorringe Bank— Horseshoe Abyssal Plain region (e.g. Johnston 1996). But, a more complex generation mechanism was proposed (Cabral 1996) based on the rupture of more than one active seismic fault, such as the Marquês de Pombal Fault and the Horseshoe Fault (Terrinha et al. 2003) or the Marquês de Pombal Fault and Guadalquivir Bank (Baptista et al. 2003). Vilanova et al. (2003) maintained that the main seismic event could have induced a local rupture along the Tagus Valley,

300

T. Vaz and J. L. Zêzere

Fig. 23.5 Downtown Lisbon showing the sector that was completely rebuilt after the 1755 earthquake (the ‘Baixa Pombalina’) following an orthogonal plan. Photo credits: Duarte Fernandes Pinto, A Terceira Dimensão, http://portugalfotografiaaerea. blogspot.com

a hypothesis that has been contested by other researchers (Matias et al. 2005). Recently, Duarte et al. (2013) suggested a new subduction zone initiating at the southwest Iberia margin that could explain large energetic seismic events like the 1755 earthquake. On 11 November 1858, an earthquake with magnitude 7.2 (Martins and Mendes-Victor 2001) affected several villages in the southwest of Portugal. In Lisbon, the earthquake damaged buildings, generating cracks in the walls and the collapse of chimneys (Moreira 1991). On 23 April 1909, Lisbon experienced another earthquake (Mw 6), with the epicentre in the Lower Tagus Valley (Teves-Costa et al. 1999). However, the damage was limited to several villages close to the epicentre area (Choffat and Bensaúde 1912). The 28 February 1969 earthquake (M  7.9), with the epicentre in the Horseshoes Abyssal Plain (Baptista and Miranda 2005), was the last important earthquake that affected Lisbon, causing partial power failure (Mendes 1970) and only small damage to old buildings (Moreira 1969).

23.4.2 Landslides Induced by Earthquakes The seismic activity often induces landslides, which amplify the consequences of earthquakes. In Lisbon, eight landslides induced by earthquakes were recently identified by Vaz and Zêzere (2016). The time elapsed and the land use changes since the landslides occurred hamper their field recognition. However, four landslides that occurred in the São Jorge Castle Hill and the Santa Catarina Hill, dating from 1512 to 1620, will be presented, considering the substantial morphological change generated and the precision and detail of historical descriptions. The first landslide (ID1) was triggered by the 28 January 1512 earthquake (Richter magnitude of 6.3). This landslide

affected the north slope of São Jorge Castle Hill (Figs. 23.6 and 23.7) and is confirmed by historical and archaeological data. The landslide was an earth flow that mobilized sand, sandy clay, silt and sandstone blocks, of Burdigalian age (Lower Miocene). Considering the occurrence of several deaths, the velocity must have been moderate to rapid (following the Cruden and Varnes 1996 classification). On 26 January 1531, another earthquake induced a landslide (ID2) on the NW slope of the São Jorge Castle Hill. The affected material and landslide type (earth flow) were similar to ID1, with the mass movement partially destroying the Rose Monastery. The evidence of the landslide depletion zone can be still seen in the present-day topography. An earthquake (Richter magnitude of 5.7) that occurred on 22 July 1597 induced a landslide that affected the Bica neighbourhood (ID3) on the Santa Catarina Hill (Fig. 23.7). This landslide generated important geomorphological changes in the area. Before the landslide, the Santa Catarina Hill was contiguous to the Chagas Hill (Chagas, 1880 in Barata et al. 1989; Castilho 1893). The contour line inflexion in the landslide depletion area is still identifiable, despite the current dense urbanization. The slope is steeper in its lower part (up to 25º), whereas in the intermediate and upper sectors it shows no more than 14º. The geological structure of the area is a monocline, and the layers dip 8º to SE. The landslide was a coherent soil slump that affected sands and clays of Miocene age. The analysis of the topography in the Digital Elevation Model allowed the identification of two scars, one belonging to the original landslide and the other, located eastwards, probably originated from its reactivation in a retrogressive style. On 13 April 1620, another earthquakeinduced landslide affected the Santa Catarina Hill (ID4), however in its western sector (Fig. 23.7). The landslide affected the Casas Caídas (fallen houses) neighbourhood, whose name was given to remember the landslide. Despite the affected material being the same as in landslide ID 3, the

23

The Urban Geomorphological Landscape of Lisbon

301

Fig. 23.6 Densely built west slope of the São Jorge Castle Hill where several historical landslides took place

Fig. 23.7 Location of historical earthquake-triggered landslides in the city of Lisbon

movement type was probably different (disrupted earth slide?) as a result of the higher slope gradient (25–34º).

23.5

Conclusions

Geomorphology played an important role since initial Lisbon’s urban settlement and conditioned to some extent the urban development throughout the centuries. In addition, the occurrence of natural hazards was also responsible for the generation of new morphologies. In fact, natural hazards

generated significant changes in Lisbon concerning the urban structure and its evolution. The most important changes in urbanization took place after the occurrence of strong earthquakes, mainly following the 1755 ‘Lisbon Earthquake’. The earthquake-induced landslides that occurred along the São Jorge Castle Hill and Santa Catarina Hill were locally constrained but also created changes in the landscape. This shows that the knowledge of urban geomorphology, including the historical natural hazards, needs to be properly addressed to ensure sustainable urban development.

302

References Alcoforado MJ, Andrade H, Lopes A, Vasconcelos J (2009) Application of climatic guidelines to urban planning: the example of Lisbon (Portugal). Landsc Urban Plan 90(1–2):56–65 Almeida IM (1991) Características geotécnicas dos solos de Lisboa. PhD dissertation, University of Lisbon Baptista MA, Miranda JM, Chierici F, Zitellini N (2003) New study of the 1755 earthquake source based on multi-channel seismic survey data and tsunami modeling. Nat Hazards Earth Syst Sci 3:333–340 Baptista MA, Miranda JM (2005) Tsunamis em Portugal. In: Baptista MA, Teves-Costa P, Matias L, Miranda JM, Cabral J, Terrinha P (eds) Terramotos e tsunamis. Livro Aberto, Lisboa, pp 27–54 Barata MR, Braga ML, Wagner M, Guerra B, Alves J, Neto J (1989) Sismicidade de Portugal—Estudo da Documentação dos Séculos XVII e XVIII, Vol II, Ministério do Planeamento e da Administração do Território, Secretaria de Estado do Ambiente e dos Recursos Naturais, Gabinete de Protecção e Segurança Nuclear Bathrellos GD (2007) An overview in urban geology and urban geomorphology. Bull Geol Soc Greece 40:1354–1364 Cabral J (1996) Sismotectónica de Portugal. Colóquio/Ciências: Revista de Cultura Científica. Fundação Calouste Gulbenkian 18:39–58 Castilho J (1893) A Ribeira de Lisboa. Descripção histórica da Margem do Tejo. Desde a Madre-De-Deus até Santos-O-Velho. Imprensa Nacional, Lisboa, p 750 Choffat P, Bensaúde A (1912) Estudos sobre o sismo do Ribatejo de 23 de Abril de 1909. Imprensa Nacional, Lisboa, p 146 Cruden DM, Varnes DJ (1996) Landslide types and processes. In: Turner AK, Schuster RL (eds) Landslides investigation and mitigation. Transportation research board, US National Research Council. Special Report 247, Washington, pp 36–75 Duarte JC, Rosas F, Terrinha P, Schellart WP, Boutelier D, Gutscher M-A, Ribeiro A (2013) Are subduction zones invading the Atlantic? Evidence from the southwest Iberia margin. Geology 41:839–842 Ferreira AB, Zêzere JL, Rodrigues ML (2002) Historical seismicity and landslides in Portugal. Examples from the 16th century. In: Delahaye D, Maquaire O (Eds) Geomorphology: from expert opinion to modelling. A tribute to Professor Jean-Claude Flageollet. CERG, Rouen, pp 105–114 Gaspar J (1994) O desenvolvimento do sítio de Lisboa: de finisterra e charneira. In: Moita I (coord) O Livro de Lisboa. Livros Horizonte, pp 11–24 INE (2011) Censos 2011. Resultados Definitivos – Região Lisboa. Instituto Nacional de Estatística, Madrid Johnston AC (1996) Seismic moment assessment of earthquakes in stable continental regions -III. New Madrid 1811–1812, Charleston 1886 and Lisbon 1755. Geophys J Int 126:314–344 Kullberg JC, Rocha RB, Soares AF, Rey J, Terrinha P, Callapez P, Martins L (2006) A Bacia Lusitaniana: Estratigrafia, Paleogeografia e Tectónica. In: Dias R, Araújo A, Terrinha P, Kullberg JC (eds) Geologia de Portugal no contexto da Ibéria. Universidade de Évora, pp 317–368 Lopes IMF (2001) Avaliação das condições geológicas e geotécnicas para a caracterização do risco sísmico. Aplicação à colina do Castelo de S. Jorge. Msc Dissertation. University of Lisbon Martins I, Mendes-Victor LA (2001) Contribuição para o Estudo da Sismicidade da região oeste da península ibérica. Publicação nº 25, Instituto Geofísico Infante D. Luís, Universidade de Lisboa, p 67

T. Vaz and J. L. Zêzere Matias L, Ribeiro A, Baptista MA, Zitellini N, Cabral J, Terrinha P, Teves-Costa P, Miranda JM (2005) Comment on “Lisbon 1755: a case of triggered onshore rupture?” by Susana P. Vilanova, Catarina F. Nunes; Joao F. B. D. Fonseca. Bull Seismol Soc Am 95(6):2534–2538 Mendes AS (1970) Considerações sobre o sismo de 28 de Fevereiro de 1969. Lisboa, Serviço Meteorológico Nacional, p 18 Miranda J, Batlló J, Ferreira H, Matias LM (2012) The 1531 Lisbon earthquake and tsunami. 15th World Conferences on Earthquake Engineering, Lisbon Moreira VS (1969) Inquérito feito na cidade de Lisboa para avaliar os efeitos produzidos pelo sismo de 28 de Fevereiro de 1969. Serviço Meteorológico Nacional, Lisboa Moreira VS (1979) Contribuição para o conhecimento da sismicidade histórica de Portugal continental. Revista do Instituto Nacional de Meteorologia e Geofísica 2:121–136 Moreira VS (1984) Sismicidade histórica de Portugal Continental. Separata Revista do Instituto Nacional de Meteorologia e Geofísica, Lisboa, p 79 Moreira VS (1991) Sismicidade histórica de Portugal Continental. Separata Revista do Instituto Nacional de Meteorologia e Geofísica, Lisboa, p 29 Moreira VS (1993) Alterações topográficas provocadas por grandes sismos e maremotos em Portugal Continental. Revista Instituto Geográfico e Cadastral, pp 67–43 Oliveira CS (2005) Descrição do Terramoto de 1755, sua extensão, causas e efeitos. O sismo. O tsunami. O incêndio. In: O Grande Terramoto de Lisboa, vol. I. Descrições. FLAD e Público, pp 23–86 Oliveira S, Andrade H, Vaz T (2011) The cooling effect of green spaces as a contribution to the mitigation of urban heat: a case study in Lisbon. Build Environ 46(11):2186–2194 Pais J, Moniz C, Cabral J, Cardoso J, Legoinha P, Machado S, Morais M, Lourenço C, Ribeiro M, Henriques P, Falé P (2006) Notícia explicativa da Folha 34-D Lisboa. Tecnologia e Inovação, Instituto Nacional de Engenharia, p 74 Pereira de Sousa FL (1919–1932) O terramoto do 1 de Novembro de 1755 em Portugal: um estudo demográfico. I - Distritos de Faro, Beja e Évora; II - Distritos de Santarém e Portalegre; III - Distrito de Lisboa; IV Distritos de Leiria, Castelo Branco, Coimbra, Guarda, Aveiro e Viseu. Tipografia do Comércio. Serviços Geológicos, Lisboa Pinto C, Vicente J, Pinto MM, Espírito Santo G, Muñoz M, Moitinho I (2011) Inventory, dissemination and preservation of the geological heritage in urban areas—Lisbon city case study. Geo J Tourism Geosites 8(2):263–271 Resende G (1973) Crónica de Dom João II e miscelânea. New edition according to the 1798 edition, Imprensa Nacional-Casa da Moeda, Lisboa, p 382 Ribeiro A, Antunes MT, Ferreira MP, Rocha RB, Soares AF, Zbyszewski G, Moitinho de Almeida F, Carvalho D, Monteiro JH (1979) Introduction à la géologie générale du Portugal. Lisboa, Serviços Geológicos de Portugal, p 114 Ribeiro O (1994) Opúsculos geográficos. 5º Volume Temas Urbanos. Fundação Calouste Gulbenkian, Lisboa, p 557 Salgueiro TB (1996) The urban development of Lisbon. In: Ferreira AB, Vieira GT (eds) Mediterranean and urban areas European. Fifth European intensive course on applied geomorphology. University of Lisbon, Erasmus, Lisbon, pp 45–52 Terrinha P, Pinheiro LM, Henriet J-P, Matias L, Ivanov MK, Monteiro JH, Akhmetzhanov A, Volkonskaya A, Cunha T, Shaskin P, Rovere M (2003) Tsunamigenic–seismogenic structures, neotec-

23

The Urban Geomorphological Landscape of Lisbon

tonics, sedimentary process and slope instability on the southwest Portuguese margin. Mar Geol 195:55–73 Teves-Costa P, Borges JF, Rio I, Ribeiro R, Marreiros C (1999) Source parameters of old earthquakes: semi-automatic digitization of analog records and seismic moment assessment. Nat Hazards 19:205–220 Vaz T, Zêzere JL (2016) Landslides and other geomorphologic and hydrologic effects induced by earthquakes in Portugal. Nat Hazards 81:71–98

303 Vilanova SP, Nunes ACF, Fonseca JFBD (2003) Lisbon 1755: a case of triggered intraplate rupture? Bull Seism Soc Am 93(5):2056– 2068 Zêzere JL, Ferreira AB, Rodrigues ML (2001) Actividade sísmica e instabilidade de vertentes na cidade de Lisboa, Volumen III. V Simposio Nacional sobre Taludes y Laderas Inestables, Madrid, pp 1253–1264

Part V The UNESCO Global Geoparks of Mainland Portugal

Geoconservation in Portugal with Emphasis on the Geomorphological Heritage

24

José Brilha and Paulo Pereira

Abstract

Geoconservation in Portugal has been gaining importance, particularly during the last decade. The inventory of geosites with international and national scientific relevance is now complete, and the national legislation concerning nature conservation includes the management of geoheritage. Forty-three per cent of the inventoried geosites are geomorphosites, showing the importance of this type of geological heritage in the Portuguese natural heritage. The geoscientific community is slowly recognizing geoconservation as an emergent component of the geosciences. The existence of four UNESCO Global Geoparks in Portugal is also an example of the country’s involvement in the international geoconservation scene. Keywords








Geoconservation Geoheritage heritage Inventory Portugal

24.1




Geomorphological

Introduction

It is getting more and more evident that the increase of human population and the consequent demand for natural resources, the growth of big cities with the arrival of people coming from the countryside, and the land occupation with the multiplication of infrastructures are pressing nature to an extent without parallel in history. The impacts on nature are still being assessed as more research is being produced all over the world, but typically, societies are more aware of the J. Brilha (&)
P. Pereira Institute of Earth Sciences, Pole of the University of Minho, Braga, Portugal e-mail: [email protected] P. Pereira e-mail: [email protected]

impacts on biodiversity and consequently, in most of countries protected areas were implemented in order to preserve sensitive ecosystems. Only recently, geoscientists began to alert also about the impacts on geodiversity, but people are still not very convinced that rocks, fossils, and landforms need to be preserved! Threats to geodiversity are poorly known by a society that ignores the role of geodiversity and how its values are highly relevant for humans (Gray 2013; Brilha et al. 2018). Obviously, we cannot protect all geodiversity as we need to consume huge amounts of geological resources to maintain our living standards. This assumption constitutes the main reason why we need to identify and select localities with exceptional geodiversity values, the preservation of which guarantees a sustainable scientific, educational, and touristic use of these natural elements. The exceptional elements of geodiversity with scientific value can occur in situ, as geosites, or can be stored ex situ in museum collections, as geoheritage elements (Brilha 2016). When geomorphological aspects are the main justification to select a geosite, it can be also named geomorphosite, following the adoption of the International Association of Geomorphologists. The collection of geosites that occur in a particular area (a park, a municipality, a country, etc.) constitutes the geological heritage of that area. Geological heritage should be understood as a general reference to all geosites that include all types of geodiversity elements, such as landforms, fossils, minerals, rocks or soils, among others. The term “geomorphological heritage” refers to geosites with geomorphological significance (geomorphosites). Recently, Brilha (2016) has proposed that sites which have no scientific relevance but present educational, aesthetic, or cultural value should be named as geodiversity sites. Geoconservation is an emergent branch of the geosciences aiming at the conservation of any type of geological feature that has a particular value (scientific, educational, cultural, aesthetic, etc.). Henriques et al. (2011) discussed

© Springer Nature Switzerland AG 2020 G. Vieira et al. (eds.), Landscapes and Landforms of Portugal, World Geomorphological Landscapes, https://doi.org/10.1007/978-3-319-03641-0_24

307

308

J. Brilha and P. Pereira

the theoretical bases to consider geoconservation as a part of geoscience with three scopes: basic, applied, and technical applications of geoconservation. Geoconservation aims at the proper management of sites, including all stages, starting with an inventory and assessment of sites, followed by their protection and definition of conditions to guarantee a sustainable use, and finally, periodic monitoring of its preservation. Considering public policies, geoconservation is closely related to nature conservation and land-use planning. Geoheritage corresponds to the abiotic sector of the natural heritage, despite the major conservation actions still being focused on the preservation of biodiversity. For over 60 years of activity, the International Union of Conservation of Nature (IUCN) has been promoting almost exclusively biodiversity. It was only recently that IUCN showed a slow change in this perspective, recognizing the importance of geoheritage in nature conservation. In 2008, 2012, and 2016, the IUCN has approved resolutions stressing the importance of geodiversity and the need to protect geoheritage. A new handbook about protected areas and management published under the auspices of the IUCN includes, for the first time, a chapter dedicated to geoconservation (Crofts et al. 2015). This chapter is one of the first outcomes of the Geoheritage Specialist Group, created in 2013 under the IUCN World Commission on Protected Areas. This evolution in the IUCN perspective is significant and can bring changes in nature conservation policies at the international and national levels. The existence of geosites and geodiversity sites must be considered in land-use planning and in environmental impact assessment procedures (Reynard and Brilha 2018). The need to conserve these places and the consequent set-up of management procedures may imply restrictions in the normal use of the territory. For instance, the protection of a site may justify changes in the initial plans for new infrastructure such as roads, dams, and buildings. During the environmental impact assessment of a certain project, the occurrence of sites in the area and the possible effects on them should also be considered in the final evaluation.

24.2

Legal Setting and Geosites Management in Portugal

The protection of geoheritage in Portugal is supported by national legislation related to nature conservation (Brilha 2010). The Decree 142/2008 defined, for the first time in the national legislation, the concept of geosite and geological heritage. Protected areas can be created and managed taking into account the geological heritage and penalties that can be

applied to anyone who damages geosites located inside protected areas. Although not focused on geodiversity, there is other legislation that might contribute indirectly to geoconservation: the law for the Protection of Cultural Heritage (which includes the palaeontological record as cultural heritage), the European Landscape Convention, the Natura 2000 Network, and the National Ecological Reserve. The “Institute of Conservation of Nature and Forests” (ICNF) is the official body responsible for the management of protected areas. The national system of protected areas is composed of 44 areas belonging to different categories (national and natural parks, natural reserves, natural monuments, and protected landscapes). The Azores and Madeira archipelagos have another set of protected areas in accordance with the regional legislation of these two autonomous regions. There are geosites of national significance located inside many protected areas, and there are even some protected areas that were established based on the occurrence of a particular geosite. In mainland Portugal, all natural monuments gained statutory protection due to the need to protect geological features. These are dinosaur footprints of the Ourém, Carenque, Lagosteiros, Pedra da Mua, and Pedreira do Avelino Natural Monuments, the Jurassic sedimentary record of worldwide significance for the Cabo Mondego Natural Monument, and the quartzite ridges of the Portas de Ródão Natural Monument. The latter was designated in 2009 mainly due to its geomorphological assets. The Protected Landscape of the Fossil Cliff of Costa da Caparica was created in 1984 taking into account the protection of geomorphological features, like some other local protected areas. In the Azores, the majority of geosites is inside 123 protected areas scattered across the nine islands of the archipelago and managed by the regional natural conservation body. In Madeira, the limited number of protected areas (6) does not cover the majority of geosites of the archipelago. Like in many other countries, geoparks are being implemented in Portugal and promote geoconservation, in spite of the informal character of this type of territorial management. In Portugal, presently there are four UNESCO Global Geoparks: the Naturtejo Geopark (since 2006) enclosing the municipalities of Castelo Branco, Idanha-a-Nova, Nisa, Penamacor, Proença-a-Nova, Oleiros, and Vila Velha de Ródão; the Arouca Geopark (since 2009) corresponding to the area of this municipality; the Azores Geopark (since 2013), which integrates the nine islands of the archipelago; and the Terras de Cavaleiros Geopark (since 2014), corresponding to the area of Macedo de Cavaleiros municipality. The geomorphological heritage of these geoparks is a major asset responsible to attract geotourists and to promote local development.

24

Geoconservation in Portugal with Emphasis …

24.3

The National Inventory of Geoheritage

The initiatives in Portugal towards the protection of geoheritage started at the beginning of the twentieth century, but these were mainly local actions and limited in time (Brilha 2005; 2012; Brilha and Galopim de Carvalho 2010). It was only in the end of the 1980s that more comprehensive actions were implemented, which helped to raise awareness for the need to execute an effective geoconservation. Concerning the national inventory of geoheritage, it was only in 2012 that a systematic and truly nationwide endeavour was concluded. For five years, the University of Minho coordinated a research project with other Portuguese partner universities (Aveiro, Açores, Algarve, Coimbra, Évora, Lisboa, Madeira, Nova de Lisboa, Porto, and Trás-os-Montes e Alto Douro), in order to define a national geoconservation strategy (Brilha et al. 2008). This project has produced several outputs, namely i. An inventory of geosites of scientific value with national and international relevance, ii. An online database of the national geoheritage inventory (available at http://geossitios.progeo.pt), iii. Legislative proposals about geoconservation, iv. A selection of the most important Portuguese geosites and submission to national authorities, requesting their official designation and integration in the national network of protected areas, v. Scientific cooperation between Portuguese and Spanish geoconservationists for the identification of geosites with Iberian relevance, vi. An outreach book addressed to the general public (Brilha and Pereira 2012).

Table 24.1 Geological frameworks defined in Portugal to integrate the inventory of geosites with scientific value

309

The national geosite inventory followed the method proposed by The European Association for the Conservation of the Geological Heritage (ProGEO) and applied in several European countries (Wimbledon 1996; Wimbledon et al. 1999). Twenty-seven geological frameworks were defined (Table 24.1), and 325 representative geosites were selected and assessed for their scientific value, representing a national endeavour carried out voluntarily by 70 geoscientists (Brilha et al. 2010). Geosites were selected using the following criteria: representativeness, rareness, diversity of geodiversity elements, integrity, and scientific knowledge. The final list of geosites is now included in the national database of natural heritage, under ICNF responsibility. The risk of degradation of all geosites was quantitatively evaluated using the following criteria: natural fragility of geodiversity elements, proximity to potential threatening activities, present protection status, accessibility, and population density. Despite being the most complete inventory made in Portugal so far, it is obvious that such an inventory is never closed. New geosites may be included in the future as scientific knowledge develops.

24.4

Geomorphological Heritage

The national inventory of geoheritage includes 140 geomorphosites, occurring in seven of the 27 frameworks (Fig. 24.1 and Table 24.2) (Pereira et al. 2013, 2015). Figure 24.2 shows selected examples of Portuguese geomorphosites in different settings. The inventoried geomorphosites are heterogeneous in scale, varying from isolated landforms with a few square

• Neoproterozoic-Cambrian Metasediments in Central Iberian Zone • Palaeozoic Marbles of the Ossa-Morena Zone • Ordovician of Central Iberian Zone • Palaeozoic succession of the Barrancos region • Exotic Terranes of NE Portugal • Geotraverse of the Portuguese Variscan Fold Belt • Geology and metallogenesis of Iberian Pyrite Belt • Marine Carboniferous of the South Portuguese Zone • Continental Carboniferous • Pre-Mesozoic granitoids • The Iberian W-Sn Metallogenic Province • Gold mineralization in Northern Portugal • Meso-Cenozoic tectonic evolution of the western Iberian Margin

• • • • • • • • • • • • • •

Late Triassic of SW Iberia Jurassic record in the Lusitanian Basin Cretaceous rocks of the Lusitanian Basin Dinosaur footprints of western Iberia Meso-Cenozoic tectono-stratigraphy of the Algarve Cenozoic basins of the western Iberian Margin Landforms and river network of the Portuguese Iberian Massif Karst systems of Portugal Active and fossil coastal cliffs Low coasts Neotectonics in mainland Portugal Vestiges of Pleistocene glaciations Volcanism of The Azores Archipelago Volcanism of The Madeira Archipelago

Geoscientists have identified representative geosites for each framework in a total of 325 geosites

310

J. Brilha and P. Pereira

Fig. 24.1 Distribution of the 140 geomorphosites in Portugal, grouped by seven of the 27 geological frameworks. The numbers are the same for Table 24.2

metres in area to large-scale landforms occupying several hundred square kilometres. Large-scale geosites constitute serious management challenges. The definition of the perimeter, a fundamental step for the management of any geosite, needs to be established with parsimony and objective criteria in order to avoid huge areas and consequent difficulties to guarantee proper management. In spite of many geomorphosites being included in protected areas, their conservation and management are not

automatically assured. A geoconservation action plan must be designed and implemented for all geosites with high scientific value, a task under the responsibility of park managers, according to the Portuguese legislation. Usually, geomorphological heritage shows high potential to be used as tourist attractions due to aesthetic reasons. Many geosites listed in Table 24.2 are already traditional touristic destinations in Portugal, but the general public is not aware that it is visiting a geomorphosite. Hence, geosite

24

Geoconservation in Portugal with Emphasis …

311

Table 24.2 List of the 140 geomorphosites grouped in seven geological frameworks. The numbers are the same for Fig. 24.1

Table 24.2 (continued) 041. Santo Adrião caves

Landforms and river network of the Portuguese Iberian Massif

042. Condeixa tufa deposits

001. Cortes terrace

043. Buracas do Casmilo

002. Campo terraces

044. Anços springs and Poios valleys

003. Penameda bornhardt

045. Ateanha-Dueça transverse

004. Rocalva bornhardt

046. Lapedo valley

005. Gerês tectonic valley

047. Grota valley and Lis springs

006. Cheira da Noiva granite landforms

048. Vale do Mogo springs and caves

007. Vilar de Nantes deposits

049. Candeeiros fossil sea cliff

008. Minhéu viewpoint

050. Fonte da Bica–Porto de Mós diapiric valley

009. Fisgas do Ermelo waterfall

051. Mendiga and S. Bento karst landscape

010. S.João das Arribas viewpoint

052. Alvados–Minde transpressive lane

011. Atenor deposits

053. Almonda cave

012. Fraga do Puio viewpoint

054. Arrife fault scarp

013. Faia da Água Alta waterfall

055. Olhos de Água do Alviela springs

014. Bornes pop-up mountain

056. Óbidos–Caldas da Rainha diapiric valley

015. Vilariça tectonic basin

057. Maceira diapiric valley

016. Senhora do Salto crest

058. Ota canyon

017. Poiares sincline

059. Granja dos Serrões and Negrais karrenfelds

018. Barca d’Alva terraces

060. Adraga and Pedra d’Alvidrar caves

019. Longroiva tectonic basin

061. Karren and caves of Raso cape

020. Frecha da Mizarela waterfall

062. Creiro crevice caves

021. Marofa crest

063. St. Margarida and Figueira Brava caves

022. Nave de Haver deposits

064. Frade cave

023. S. Pedro Dias crest

065. Forte da Baralha wave-cut platform

024. Alva meanders

066. Escoural cave

025. Picadouro deposits

067. Cova da Moura cave

026. Sra. da Candosa valley

068. Fossil karren and karst caves of Preguiça mines

027. Lousã tectonic basin

069. Estombar springs and Ibne Ammar cave

028. Sacões hill

070. Rocha da Pena mesa hill

029. Penedos de Góis crest

071. Nave do Barão and Nave dos Cordeiros depressions

030. Sta. Luzia crest

072. Varejota and Barrocal da Tôr karrenfelds

031. Zêzere meanders

073. Fonte Benémola spring and Solustreiras caves

032. Monsanto Inselberg

074. Cerro da Cabeça karrenfeld

033. Penha Garcia crest

Active and fossil coastal cliffs

034. Ponsul Fault scarp

075. Carvoeiro cape cliffs

035. Medronheira valley

076. Costa da Caparica fossil cliff

036. Portas de Ródão crest

077. Serra do Risco cliff

037. Rodão terraces

078. S. Vicente–Sagres coastal platform

038. Marvão crest

079. Ponta da Piedade cliffs

039. Pulo do Lobo waterfall

Low coasts

Karst systems

080. Aveiro Ria

040. Lorga de Dine cave

081. Mira–Quiaios dunes (continued)

(continued)

312

J. Brilha and P. Pereira Table 24.2 (continued)

Table 24.2 (continued) 082. S. Martinho do Porto bay

123. Pico das Camarinhas and Ponta da Ferraria

083. Tejo estuary

124. Carvão volcanic cave

084. Sado estuary and Troia spit

125. Fogo volcano

085. Ria Formosa

126. Vila Franca islet

Vestiges of Pleistocene glaciations

127. Congro and Nenúfares maar

086. Alto Vez valley

128. Furnas volcano

087. Gorbelas–Junqueira

129. Barreiro da Malbusca

088. Homem valley

130. Ponta do Castelo

089. Compadre valley

Volcanism of the Madeira Archipelago

090. Couce plateau

131. Pico da Selada deposits

091. Toco–Soutinho

132. Pedras

092. Lagoacho–Covão do Urso

133. Girão cape

093. Nave Travessa

134. Arco de São Jorge

094. Lagoa Comprida plateau

135. Ribeira do Faial mouth

095. Covões de Loriga

136. Caldeirão do Inferno

096. Salgadeiras

137. Eira do Serrado

097. Zêzere valley

138. São Lourenço cape

098. Lagoa Seca

139. Ana Ferreira peak

099. Covão Cimeiro-Cântaro Magro

140. Porto Santo beach

100. Nave de Santo António 101. Pedrice

managers should consider the implementation of good interpretation resources as a priority, not only to foster the geomorphological literacy, but also to better promote geosites as touristic attractions.

Volcanism of the Azores Archipelago 102. Caldeirão 103. Fajã Grande and Fajãzinha 104. Rocha dos Bordões and volcanic necks 105. Pico da Sé and volcanic necks 106. Funda, Comprida, Seca and Branca maars

24.5

Conclusion

107. Funda and Rasa maars 108. Capelinhos volcano

Geoconservation in Portugal has developed significantly during the last decade, particularly with the development of the national inventory of geosites, the change in legislation supporting nature conservation policies, and the implementation of geoparks. However, the efforts to pursue a geoconservation strategy must continue, mainly focusing on management issues of the most important geosites at the national and international levels.

109. Faial Caldera 110. Pedro Miguel graben 111. Lajidos de Santa Luzia 112. Torres volcanic cave 113. Pico Mountain 114. Axial volcanic ridge 115. Fajãs dos Cubres and Caldeira de Santo Cristo 116. Graciosa Caldera and Furna do Enxofre 117. Santa Bárbara Volcano and Mistérios Negros 118. Pico Alto, Biscoito da Ferraria and Biscoito Rachado 119. Algar do Carvão 120. Monte Brasil 121. D. João de Castro bank 122. Sete Cidades volcano (continued)

Acknowledgements A national inventory of geosites is only possible with the participation of geoscientists who are experts in different geoscience domains. All colleagues that participated in the inventory are acknowledged for this truly national effort. This work was co-funded by the European Union through the European Regional Development Fund, based on COMPETE 2020 (Programa Operacional da Competitividade e Internacionalização), project ICT (UID/GEO/04683/2013) with reference POCI-01-0145-FEDER-007690, and national funds provided by Fundação para a Ciência e Tecnologia.

24

Geoconservation in Portugal with Emphasis …

313

(A)

(B)

(C)

(D)

(E)

(F)

Fig. 24.2 Examples of geomorphosites in Portugal. A. Ria Formosa barrier islands geosite in Ria Formosa Natural Park, south-eastern Portugal. Geological framework: low coasts. Geomorphosite Nr. 85 in Fig. 24.1, B. Coastal cliffs of Ponta da Piedade geosite in south-western Portugal. Geological framework: Active and fossil coastal cliffs. Geomorphosite Nr. 79 in Fig. 24.1, C. Pulo do Lobo waterfall geosite in Vale do Guadiana Natural Park, south-eastern Portugal. Geological framework: landforms and river network of the Portuguese Iberian Massif. Geomorphosite Nr. 39 in Fig. 24.1, D. Lateral moraine at

Compadre valley geosite in Peneda-Gerês National Park, north-western Portugal. Geological framework: vestiges of Pleistocene glaciations. Geomorphosite Nr. 89 in Fig. 24.1, E. Furnas volcano caldera geosite in São Miguel Island, Azores. Geological framework: volcanism of the Azores archipelago. Geomorphosite Nr. 128 in Fig. 24.1, F. Coastal landforms in São Lourenço cape geosite in Madeira island. Geological framework: volcanism of Madeira archipelago. Geomorphosite Nr. 138 in Fig. 24.1

314

References Brilha J (2005) Património Geológico e Geoconservação: a Conservação da Natureza na sua Vertente Geológica. Palimage Editores, Viseu, p 190 Brilha J (2010) Enquadramento legal de suporte à protecção do património geológico em Portugal. In: Cotelo Neiva JM, Ribeiro A, Mendes Victor L, Noronha F, Magalhães Ramalho M (eds) Ciências Geológicas: Ensino, Investigação e sua História. Associação Portuguesa de Geólogos, Volume II, pp 443–450 Brilha J (2012) Portugal. In: Wimbledon WAP, Smith-Meyer S (eds) Geoheritage in Europe and its conservation. ProGEO, Oslo, pp 264–273 Brilha J (2016) Inventory and quantitative assessment of geosites and geodiversity sites: a review. Geoheritage 8(2):119–134 Brilha J, Galopim de Carvalho AM (2010) Geoconservação em Portugal: uma introdução. In: Cotelo Neiva JM, Ribeiro A, Mendes Victor L, Noronha F, Magalhães Ramalho M (eds) Ciências Geológicas: Ensino, Investigação e sua História. Associação Portuguesa de Geólogos, Volume II, pp 435–441 Brilha J, Pereira P (eds) (2012) Património geológico: geossítios a visitar em Portugal/geological heritage: geosites to visit in Portugal. Porto Editora, Porto, p 137 Brilha J, Barriga F, Cachão M, Couto MH, Dias R, Henriques MH, Kullberg JC, Medina J, Moura D, Nunes JC, Pereira DI, Pereira P, Prada S, Sá A (2008) Geological heritage inventory in Portugal: implementing geological frameworks. In: Proceedings of 5th International Symposium ProGEO on the Conservation of the Geological Heritage, Rab, Croatia, pp 93–94 Brilha J, Alcala L, Almeida A, Araújo A, Azeredo A, Azevedo MR, Barriga F, Brum da Silveira A, Cabral J, Cachão M, Caetano P, Cobos A, Coke C, Couto H, Crispim J, Cunha PP, Dias R, Duarte LV, Dória A, Falé P, Ferreira N, Ferreira Soares A, Fonseca P, Galopim de Carvalho A, Gonçalves R, Granja H, Henriques MH, Kullberg JC, Kullberg MC, Legoinha P, Lima A, Lima E, Lopes L, Madeira J, Marques JF, Martins A, Martins R, Matos J, Medina J, Miranda R, Monteiro C, Moreira M, Moura D, Neto Carvalho C, Noronha F, Nunes JC, Oliveira JT, Pais J, Pena

J. Brilha and P. Pereira dos Reis R, Pereira D, Pereira P, Pereira Z, Piçarra J, Pimentel N, Pinto de Jesus A, Prada S, Prego A, Ramalho L, Ramalho M, Ramalho R, Relvas J, Ribeiro A, Ribeiro MA, Rocha R, Sá A, Santos V, Sant’ovaia H, Sequeira A, Sousa M, Terrinha P, Valle Aguado B, Vaz N (2010) The national inventory of geosites in Portugal. Abstracts Book of the International Conference on Geoevents, Geological Heritage and the Role of IGCP (First Meeting of ProGEO Regional Working Group SW Europe), Ayuntamiento de Caravaca de la Cruz, Spain, pp 18–24 Brilha J, Gray M, Pereira D, Pereira P (2018) Geodiversity: an integrative review as a contribution to the sustainable management of the whole of nature. Environ Sci Policy 86:19–28 Crofts R, Gordon J, Santucci V (2015) Geoconservation in protected areas. In: Worboys GL, Lockwood M, Kothari A, Feary S, Pulsford I (eds) Protected area governance and management. ANU Press, Canberra, pp 531–568 Gray M (2013) Geodiversity: valuing and conserving abiotic nature, 2nd edn. Wiley, Chichester, p 512 Henriques MH, Pena dos Reis R, Brilha J, Mota TS (2011) Geoconservation as an emerging geoscience. Geoheritage 3 (2):117–128 Pereira P, Pereira D, Crispim J, Nunes JC, Brum da Silveira A (2013) Geomorphosites within the inventory of geosites with national and international relevance in Portugal. In: 8th International Conference on Geomorphology Abstracts Volume, Paris, p 554 Pereira D, Pereira P, Brilha J, Cunha P (2015) The Iberian Massif Landscape and Fluvial Network in Portugal: a geoheritage inventory based on the scientific value. Proc Geol Assoc 126(2):252–265 Reynard E, Brilha J (eds) (2018) Geoheritage: assessment, protection and management. Elsevier, Amsterdam, p 450 Wimbledon WAP (1996) Geosites—a new conservation initiative. Episodes 19(3):87–88 Wimbledon WAP, Andersen S, Cleal CJ, Cowie JW, Erikstad L, Gonggrijp GP, Johansson CE, Karis LO, Suominen V (1999) Geological World Heritage: GEOSITES—a global comparative site inventory to enable prioritisation for conservation. Memorie Descrittive della Carta Geologica d’Italia, vol LIV, pp 45–60

Terras de Cavaleiros Geopark: A UNESCO Global Geopark

25

Diamantino Insua Pereira and Paulo Pereira

Abstract

The Terras de Cavaleiros Geopark (TCG), a UNESCO Global Geopark, is located in Northern Portugal and is established on rare and unique geological, scenic, ecological and cultural values. The most significant geological value is related to the most complete sequence of Pre-Mesozoic allochthonous geological units in NW Iberia. The Vilariça fault is an important geomorphological feature in the TCG related to the evolution of landforms such as push-up blocks and strike-slip basins. Forty-two geosites were selected in the TCG, 16 of them being of geomorphological interest. A set of programs, including cultural heritage, biodiversity and leisure, has been prepared for scientific, educational and touristic use. Keywords




Geopark Allochthonous complex Geotourism

25.1




Fault




Geosite




long tradition in research and scientific visits. The Geopark territory is also nationally recognized for having a significant range of traditional quality products with national certification (olive oil, sausage, ham, cheese, potatoes, olives, chestnuts, honey and veal and lamb meat, among others). In addition, there are several reference sites for tourism, as the Azibo Reservoir, with a beach ranked as the best lake beach of Portugal, or the Sabor Valley, where visitors can enjoy landscape diversity with floristic richness and unique fauna. The Terras de Cavaleiros Global Geopark project is ongoing since 2010, promoting geological and environmental conservation, social justice and sustained economic development for the territory and its inhabitants. The tourism is based on scenic, geological, ecological, cultural, historical and local identity values, pointing out what is authentic and unique (Pereira et al. 2013). Within the Geopark, a detailed inventory and assessment of 42 geosites were accomplished. Seven of them are already listed in the national geosites inventory, which justifies their higher national and/or international significance (Pereira et al. 2012). Sixteen geosites were selected based on the geomorphological and tectonic features.

Introduction

The Terras de Cavaleiros Geopark (TCG) or The Land of Knights Geopark covers an area of 699 km2 corresponding to the administrative limits of the Macedo de Cavaleiros municipality in northern Portugal (Fig. 25.1). The TCG was established in recognition of rare and unique geological, scenic, ecological and cultural values. The local geology and geomorphology have a well-documented scientific value and D. I. Pereira (&) Terras de Cavaleiros UNESCO Global Geopark, Macedo de Cavaleiros, Portugal e-mail: [email protected] D. I. Pereira
P. Pereira Institute of Earth Sciences, Pole of the University of Minho, Braga, Portugal e-mail: [email protected]

25.2

Geological Setting

The TCG is located in the Iberian Massif, the largest morphotectonic unit of the Iberian Peninsula, which is composed of pre-Mesozoic units consolidated during the Variscan orogeny. In many cases, the bedrock includes relics that have allowed the definition of the geological aspects preceding that cycle (Ribeiro 2013). The Iberian Massif is the westernmost segment of the European Variscan orogen (560–245 Ma), with which it was connected before the opening of the Bay of Biscay, between 110 and 75 Ma. The territory of TCG has a rich and complex geology (Fig. 25.2), mainly expressed in the following geological units (Pereira 2006a; Pereira et al. 2012):

© Springer Nature Switzerland AG 2020 G. Vieira et al. (eds.), Landscapes and Landforms of Portugal, World Geomorphological Landscapes, https://doi.org/10.1007/978-3-319-03641-0_25

315

316

D. I. Pereira and P. Pereira

Fig. 25.2 Location of the Terras de Cavaleiros UNESCO Global Geopark in the framework of the Allochthonous Complexes of NW Iberia [adapted from Ribeiro et al. (1990), Pereira et al. (2012)]

Fig. 25.1 Location of Terras de Cavaleiros Global Geopark in Northern Portugal

– Pre-Mesozoic allochthonous geological units, – Variscan granitoids, – Cenozoic sediments.

25.2.1 Pre-Mesozoic Allochthonous Geological Units The Pre-Mesozoic allochthonous geological units are composed by the: – Parautochthonous Complex, a unit that moved a few miles and shows paleogeographic affinities with the Central Iberian Zone, with schists, greywackes and quartzites as the most representative lithologies. – Allochthonous Basal Complex, a unit that moved more than 100 km over the Parautochthonous Complex and is

representative of the Gondwana continent, showing metavolcanic rocks, schists and quartzites. – Allochthonous Ophiolitic Complex, a complete sequence of the oceanic crust constituted by several types of mafic and ultramafic rocks. This ophiolite sequence results from the obduction of oceanic lithosphere over the Allochthonous Basal Complex. The ocean corresponded to the south branch of the Rheic Ocean, known as the Galiza/ Trás-os-Montes—Central Massif Ocean. The complete Ordovician to Devonian oceanic crust sequence comprises, from top to bottom, amphibolites, complexes of dykes, flaser gabbros, gabbros, mafic cumulates and ultramafic rocks with the generic designation of peridotites. – Allochthonous Upper Complex, representing a whole sequence of continental crust from an ancient continent located far away from the autochthonous domain. This complex is represented by metasediments, orthogneisses and mafic and ultramafic rocks. It represents a complete sequence of continental crust derived from a distant margin, relatively to the autochthonous domain. Presumably, this complete fragment of continental crust had its origin at the Armorica microplate, a continental

25

Terras de Cavaleiros Geopark: A UNESCO …

fragment independent from the north of Gondwana (Ribeiro et al. 2007). Thus, one of the most complete and continuous sections of the Variscan chain in the Iberian Peninsula is represented in the TCG. The Allochthonous Ophiolitic Complex and the Allochthonous Upper Complex, as well as the thrust faults that mark the contacts between the units, are particularly well represented at the core of the TCG, known as the Morais Massif.

25.2.2 Variscan Granitoids Some igneous rocks occur in the TCG, cutting the metasedimentary and metavolcanic units mentioned above. Beyond the veins, mostly of quartz, different granitoid facies may be distinguished, such as two-mica granites, muscovite granite and granodiorites. These granitoids are contemporary of the Variscan Orogeny and show a clear relation with the third orogenic phase, ranging between the so-called syn-D3 and post-D3 (Noronha et al. 2006).

25.2.3 Cenozoic Sediments The sedimentary units that fill strike-slip basins and paleovalleys in the western border of the Cenozoic Douro Basin are well represented in the TCG. Up to the 1990s, these sediments had been systematically included in the so-called Iberian Raña facies, a gravelly deposit with significant coverage in the Douro Basin and also in the Iberian Massif. Raña refers to an alluvial fan model, chronologically placed near the Plio-Pleistocene limit, an episode related to the transition from the endorheic drainage of the Cenozoic Iberian basins to the present Atlantic drainage. More detailed investigations on these sediments (Pereira 1997, 1998, 1999, 2006a; Pereira et al. 2000) have revealed a fluvial network in the proximal sector of the Douro Basin and diverse tectonosedimentary units as described below (Pais et al. 2012). The Bragança Formation (Upper Miocene to Lower Pliocene) is defined in north-eastern Portugal as a lithostratigraphic unit recording a proximal fluvial paleodrainage to the Cenozoic Douro Basin in Spain (Pereira 1997, 1998, 1999; Pereira et al. 2000). The fluvial sediments fill incised paleovalleys in response to two tectonic episodes and the consequent orogenic uplift. These paleovalleys remain well preserved in TCG (Vale da Porca, Salselas and Castro Roupal outcrops), where they are oriented E–W, and to the east, near Vimioso (Vimioso outcrop) and Miranda do Douro (Silva, Sendim and Atenor outcrops), where they are oriented NW–SE and N–S, respectively. Given the context

317

of the major Vilariça fault, the fluvial system was strongly influenced by the development of strike-slip basins (De Vicente et al. 2011; Pais et al. 2012), especially in the TCG. The Bragança Formation comprises two members with similar composition and depositional architecture. An unconformity based on the recognition of a regional erosion surface and a well-developed paleosoil occurs. Deep channel gravel deposits and gravelly bars are the most characteristic lithofacies of the Bragança Formation. The sediments are immature and contain moderately weathered feldspars in the sand fraction and a predominance of smectite and kaolinite in the clay fraction. The gravel units are mostly red in colour with lutite being brown, grey or green. Geomorphological features suggest that prior to the deposition of the Bragança Formation river valleys incised in the bedrock developed as an erosional response to mountain uplift occurring since the Eocene (Pereira et al. 2000; De Vicente et al. 2008, 2011). Subsequently, the activity of this major tectonic episode, which corresponds to the Betic compression at about 9.5 Ma (Calvo et al. 1993), caused a staircase organization of large fault blocks in northern Portugal and the development of strike-slip basins associated with the Vilariça fault detachment (Ferreira 1991; Cabral 1995). The Aveleda Formation (Upper Pliocene to Lower Pleistocene) is located in two different geomorphological settings: i. occurrences surrounding the TCG lie over the North Iberian Plateau, which marks a discontinuity with the older units, and have its source on the resistant reliefs; ii. occasionally, the unit lies within tectonic depressions associated with the Vilariça fault (Pereira 1997), especially in the TCG. The Aveleda Formation consists of reddish deposits mainly of muddy matrix-supported gravel. Clasts of several metasedimentary rocks and quartz are subangular. Kaolinite and illite dominate the clay fraction. The lithofacies and architecture of the Aveleda Formation indicate nearby sources and debris flows deposited as alluvial fan bodies. The unit establishes the transition between the previous endorheic drainage network and the Atlantic fluvial network (Pereira 2006b).

25.3

Geomorphology

The TCG area consists mostly of small plateaus, with altitudes between 700 and 800 m asl, and the Bornes and Nogueira mountains reaching 1200 and 1300 m asl. These push-up compressive structures are related to a major faultoriented NNE-SSW and showing neotectonic activity—the Vilariça fault. Associated with it, several small strike-slip basins filled with Cenozoic sediments occur (Pereira and Pereira 2019). The deeply carved Sabor River defines the eastern limit of the TCG. West of the fault, the drainage is

318

D. I. Pereira and P. Pereira

Fig. 25.3 Simplified geomorphological map of the Terras de Cavaleiros UNESCO Global Geopark

towards the Tua River (Fig. 25.3). The Sabor and Tua sub-catchments are part of the Douro River catchment, one of the largest Iberian rivers, which has its mouth in Oporto. The regional significance of the Vilariça fault is widely recognized in studies of the landscape of northern Portugal (e.g. Cabral 1995; De Vicente et al. 2008, 2011; Pais et al. 2012). This strike-slip fault has great morphological expression in the TCG, through several strike-slip basins such as the Santa Combinha, Macedo de Cavaleiros and Vilariça

basin to the south, as well as uplifted compressive structures in a push-up model, like the Bornes and Nogueira mountains (Cabral 1995; Pereira 1997, 2006). In the NW sector of the TCG, the south flank of the Nogueira Mountain stands out, reaching an altitude of 1231 m in the Pombares Massif granites. This NNE-SSW tectonic block is located to the west of the main branch of the Vilariça fault. In the south, the Bornes Mountain (1,200 m asl) stands out as a tectonic relief, oriented NNE-SSW, parallel to the Vilariça fault

25

Terras de Cavaleiros Geopark: A UNESCO …

319

Fig. 25.4 Bornes Mountain, limited by the Vilariça fault, view from the Senhora do Campo geosite

(Figs. 25.3 and 25.4). In the southern limit of the TCG, the N-S fault scarp extends to the Vilariça depression. Regionally, the Vilariça fault constitutes also the limit between the eastern sector, where the fundamental surface of the North Iberian Plateau (Meseta) is more regular, and the western sector where the fundamental surface is extensively dissected by the Douro fluvial network (Fig. 25.3). The regular flattish surface of the Morais Massif occurs to the north of the Morais fault, about 750 m asl and is representative of the North Iberian Plateau, also known as North Iberian Meseta. This surface, well preserved in the Morais Massif, represents a reference to the interpretation of all other regional surfaces. Portions of the same surface are also preserved to the north and east. North of the Morais Massif, the Vale da Porca-Talhinhas depression is oriented E-W and 150 m below the fundamental surface. This depression is one of the paleovalleys that preserve sediments of the Bragança Formation, associated with a previous fluvial system flowing eastwards towards the Douro Cenozoic Basin, mentioned above (Fig. 25.5). The NE-SW depression of Macedo de Cavaleiros is limited between faults of the Vilariça tectonic zone and preserves alluvial fan sediments of the Aveleda Formation. The fact that the Macedo de Cavaleiros tectonic depression is drained towards the Tuela River by the Macedo and the

Carvalhais tributaries is a noteworthy peculiarity that shows the tectonic control of the drainage system. The remaining territory lies within the Sabor Basin. The Sabor River, bordering the Geopark in the east, shows steep slopes and is incised about 400 m in the plateau (Fig. 25.6). The tributary streams also show deep valleys, except when crossing tectonic depressions. In the western sector of the TCG, some planation surfaces are slightly lowered relative to the regular level of the plateau, which is due to differential uplift and subsidence. These surfaces are tectonic steps connecting to the Mirandela depression (Fig. 25.3).

25.4

Geosites

The selection of geosites in Terras de Cavaleiros Geopark was primarily focused on their scientific value. After the first identification of potential geosites, 42 were selected as effective geosites, based on a qualitative assessment. The selected geosites represent mineralogical, petrological, structural, geomorphological and hydrogeological themes. Sixteen geosites are specifically related to geomorphological and tectonic features (Table 25.1, Fig. 25.3). For geotouristic and general touristic support, the TCG promoted the selection of geosites after an assessment of

320

D. I. Pereira and P. Pereira

Fig. 25.5 Sediments of the Bragança Formation filling the Vale da Porca-Talhinhas paleovalley (Castro Roupal geosite)

touristic interest. These geosites, which always show scientific value, also stand out for their cultural, economic and/or scenic values. In addition to the geoconservation and management issues, its valuation includes outreach with simplified explanations. Some of the TCG most representative geosites are described below.

Bornes mountains, which are tectonic landforms associated with the Vilariça fault, (iii) the Mogadouro Mountain, on the horizon, an excellent example of residual landform standing out from the plateau and (iv) the Azibo River valley carved in the plateau. (b) Cabeço Berrão geosite

25.4.1 Geomorphosites

(a) Senhora do Campo geosite The Senhora do Campo geosite is an exceptional place to observe and understand the most significant features of the regional landscape, in particular (Fig. 25.7): (i) the surface of the Morais Massif, representing an isolated portion of the North Iberian Plateau, a planation surface, well-known and also recognized in other regions, (ii) the Nogueira and the

Cabeço Berrão geosite is a panoramic viewpoint to the deep incision of the Sabor River in the North Iberian Plateau (Fig. 25.6). In addition to the geomorphological value, the site presents cultural interest due to the presence of ruins of a fortification attributed to the Iron Age, in which local rocks were used, namely amphibolites, schists and gabbros. (c) Bornes South geosite The Bornes South geosite is a panoramic viewpoint located on the southwest slope of the Bornes Mountain, from where landforms connected to the Vilariça fault can be observed.

25

Terras de Cavaleiros Geopark: A UNESCO …

321

Fig. 25.6 Sabor River deeply carved in the North Iberian Plateau, view from Cabeço Berrão geosite

The fault produces well-defined scarps and controls the Burga River course in a straight-lined valley (Fig. 25.8). Further to the south, the Vilariça strike-slip basin (Pereira and Pereira 2019) can also be seen from here. (d) Vilariça fault gouge at Podence geosite The Podence geosite is the best place to perceive the Vilariça fault at an outcrop-scale (Fig. 25.9). The vertical fault gouge, about 10 m wide, places metavolcanic rocks of the ancient bedrock (Silurian) in contact with Cenozoic sediments (Gelasian), testifying the recent movement of the fault.

25.4.2 Other Geosites

processes associated with the Variscan orogeny can be interpreted. The geosite includes the tectonic contact between the Earth’s upper continental crust (represented by the Lagoa gneiss), the lower continental crust (represented by the granulite), and the mantle (represented by the peridotite). The geosite location offers a panoramic view to the thrusted geological units differentially eroded in the opposite slope of the Sabor River valley (Fig. 25.10). (b) Foz do Azibo thrust fault geosite At the Foz do Azibo geosite, the tectonic stacking of the main geological units involved in the Variscan orogeny can be seen. It is possible to interpret the Armorica continent (represented by the Lagoa gneiss) overlapping the remains of the Paleozoic Rheic Ocean (represented by the amphibolite) (Fig. 25.11). (c) Poço dos Paus geosite

(a) Conrad and Moho discontinuities geosite The Conrad and Moho discontinuities geosite is an important spot in TCG, where ophiolite and allochthonous

The Poço dos Paus geosite combines scientific and scenic values of the Azibo valley, with the visitor being encouraged to observe rocks typical of the ocean floor (Fig. 25.12). The

322

D. I. Pereira and P. Pereira

Table 25.1 Main features of the 16 geosites with geomorphological interest (geomorphosites) in the TCG territory Reference

Geosites

Main geological features

G1

Tuela valley

300 m deep canyon in the Tuela River

G2

Torre de Dona Chama granite

Granite boulders and other typical granite landforms

G4

Macedo river meanders

Meanders of the river Macedo canyon controlled by N-S faults

G6

Alto da Serra granite

Typical granite landforms like tor and castle kopje

G7

Vilariça fault gouge at Podence

Vilariça fault with a significant 10 m wide fault gauge

G9

Senhora do Campo panorama

A panoramic site to observe the major Bragança–Vilariça–Manteigas fault alignment, the Azibo Reservoir, the Morais Massif and the North Iberian Plateau

G10

Cubo panorama

A 360º panorama of the TCAG showing the main landforms

G14

Vale da Porca Cenozoic sediments

Cenozoic sediments affected by small faults as evidence of neotectonic events

G15

Salselas tectonic basin

Small basin filled with sediments is an example of a geomorphological feature with tectonic control

G18

Castro Roupal palaeovalley

Cenozoic sediments representing an ancient drainage system with cross-bedded stratification

G30

Cabeço Berrão panorama

Panorama over the Sabor River canyon

G35

Morais fault

ENE-WSW fault with neotectonic activity

G37

Vilariça fault at Vale Bemfeito

Breccia of the Vilariça fault with fragments of granites, quartz and boulders of the cenozoic sediments

G38

Bornes North panorama

Panorama over the general geomorphology of the Geopark area

G39

Vilariça fault scarp at Burga

Panoramic site to observe the geomorphological expression of the Vilariça fault scarp

G41

Bornes South panorama

Panorama over the Vilariça strike-slip basin

Fig. 25.7 Main landforms observed in the Senhora do Campo geosite

site shows mafic dikes in bands of dark colour, that broke through gabbro, showing light and dark minerals of larger dimensions. A simplified explanation of when and how the rocks were formed and on their exotic condition is presented on-site.

hundreds of kilometres away and the doubt about the exact age of this occurrence. The outcropping also preserves very clear kinematic criteria that constitute a precious element for the geodynamic reconstitution of the Variscan orogeny in Iberia.

(d) Lagoa Gneiss geosite

(e) Murçós Mine geosite

Lagoa Gneiss geosite has high scientific and scenic values. The approach is based on the beauty of the gneiss in the outcrop (Fig. 25.13), its exotic nature attending to its origin

The Murçós mine geosite is dedicated to several outcrops of an open-air mine and to the ruins of support buildings separation of the ore took place between 1940 and 1980. This

25

Terras de Cavaleiros Geopark: A UNESCO …

Fig. 25.8 Panoramic view to the south at the Bornes South geosite, where the Burga River valley is controlled by the Vilariça fault

Fig. 25.9 Vilariça fault gouge at the Podence geosite

323

324

D. I. Pereira and P. Pereira

Fig. 25.10 Panoramic view from the Conrad and Moho discontinuities geosite, to the thrusted geological units in the opposite slope of the Sabor River valley, where differential erosion occurs

Fig. 25.11 Foz do Azibo thrust fault geosite

25

Terras de Cavaleiros Geopark: A UNESCO …

325

Fig. 25.12 Poço dos Paus geosite has high scientific value attending to the large amount of mafic dikes cropping out at the riversides of the Azibo River (detail in the upper right corner). The scenic value is also considered for geotouristic purposes

Fig. 25.13 Lagoa Gneiss geosite (photograph Pedro Peixoto)

326

D. I. Pereira and P. Pereira

Fig. 25.14 Azibo’s Reservoir, a protected area dedicated to biodiversity conservation

mine has served for the exploitation of tungsten and tin, which occur in quartz veins that can still be observed. The visit focuses on the observation of quartz veins with tungsten, on its industrial applications, strong relationship with the World War II and on an outlook to the future. (f) Limestone of Salselas geosite The geosite shows limestones, rare rocks in northern Portugal, that were exploited here in the past. Actually, this is an example of the utilization of a rare geological feature in the region, which constitutes the raw material of lime, produced in furnaces that still persist in the region.

25.5

abandoned talc mine geosite, or the Asbestos geosite, emphasizing the importance of the geological resources to society, ii. the trail “Geological faults and earthquakes in the TCG” links geosites related to active faults and tectonic landforms and iii. the “Morais Ocean” trail covers the theme of the ophiolite sequence, with the geosites presented as exotic occurrences of rocks and seismic discontinuities typical for ocean floor and the Earth’s interior settings that rarely can be seen at the surface. Within the TCG, the Azibo’s Reservoir is a protected area dedicated to biodiversity conservation (Fig. 25.14). This area offers a network of pedestrian paths especially dedicated to biodiversity, namely the observation of different types of insects. In addition to other activities and leisure sites, the area was elected the best lake beach in Portugal.

Thematic Trails

The Terras de Cavaleiros Global Geopark offers thematic trails that link several geosites. Three trails are dedicated to the relation between geology, geomorphology and society, natural hazards and Earth’s history: i. the trail “Geological resources in the TCG” links several geosites like the Murçós Mine geosite, the Limestone of Salselas geosite, the

25.6

Conclusions

The particularities of the Terras de Cavaleiros Geopark geology and geomorphology support its early recognition as a UNESCO Global Geopark. Besides the geoheritage and the geoconservation issues, the development of the Geopark

25

Terras de Cavaleiros Geopark: A UNESCO …

is also supported by the commitment of the municipality, the excellent accessibility, the engagement of the partners, the broad scientific support, as well as by the biodiversity and unique cultural heritage. In the TCG, several infrastructures support scientific research, school visits, recreation and nature sports. Acknowledgements This work is co-funded by the European Union through the European Regional Development Fund, based on COMPETE 2020 (Programa Operacional da Competitividade e Internacionalização), project ICT (UID/GEO/04683/2013) with reference POCI-01-0145-FEDER-007690 and national funds provided by Fundação para a Ciência e Tecnologia.

References Cabral J (1995) Neotectónica em Portugal Continental. Memórias do Instituto Geológico e Mineiro 31:265 Calvo J, Daams R, Morales J, Lopez-Martínez N, Agusti J, Anadon P, Armenteros I, Cabrera L, Civis J, Corrochano A, Diaz-Molina M, Elizaga E, Hoyos M, Martin-Suarez E, Martínez J, Moissenet E, Muñoz A, Pérez-Garcia A, Pérez-Gonzalez A, Portero J, Robles F, Santisteban C, Torres T, Van der Meulen AJ, Vera J, Mein P (1993) Up-to-date Spanish continental Neogene synthesis and paleoclimatic interpretation. Rev Soc Geol Espana 6(3–4):29–40 De Vicente G, Cloetingh S, Muñoz-Martín A, Olaiz A, Stich D, Vegas R, Galindo-Zaldivar J, Fernández-Lozano J (2008) Inversion of moment tensor focal mechanisms for active stresses around microcontinent Iberia: tectonic implications. Tectonics 27:1–22 De Vicente G, Cloetingh S, Van Wees JD, Cunha PP (2011) Tectonic classification of Cenozoic Iberian foreland basins. Tectonophysics 502(1–2):38–61 Ferreira AB (1991) Neotectonics in Northern Portugal. A geomorphological approach. 2. Geomorph N F sup.-Bd 82:73–85 Noronha F, Ferreira N, Marques de Sá C (2006) Rochas granitóides: Caracterização Petrológica e Geoquímica. In: Pereira E (coord) Notícia Explicativa da folha 2 da Carta Geológica de Portugal à

327 escala 1/200000. Instituto Nacional de Engenharia, Tecnologia e Inovação, Lisboa, p 119 Pais J, Cunha P, Pereira DI, Legoinha P, Dias R, Moura D, Silveira AB, Kullberg JC, González-Delgado JA (2012) The Paleogene and Neogene of Western Iberia (Portugal): a Cenozoic record in the European Atlantic Domain. Springer Briefs in Earth Sciences, p 158 Pereira DI (1997) Sedimentologia e estratigrafia do Cenozóico de Trás-os-Montes oriental (NE Portugal). Ph.D., Univ. Minho, p 341 Pereira DI (1998) Enquadramento estratigráfico do Cenozóico de Trás-os-Montes oriental. Comunicações do IGM 84(1):A126–A129 Pereira DI (1999) Terciário de Trás-os-Montes oriental: evolução geomorfológica e sedimentar. Comunicações do IGM 86:213–226 Pereira DI (2006a) Depósitos Cenozóicos. In Pereira E (coord), Notícia Explicativa da Folha 2 da Carta Geológica de Portugal na escala 1:200000, Inst. Geol. Mineiro, pp 43–48 Pereira E (coord) (2006b) Carta Geológica de Portugal à escala 1/200000. Notícia explicativa da Folha 2. Instituto Nacional de Engenharia, Tecnologia e Inovação, Lisboa Pereira DI, Pereira P (2019) The geomorphological landscape of Trás-os-Montes and Alto Douro. In Vieira G, Zêzere JL, Mora C (eds) Landforms and landscapes of Portugal. World Geomorphological Landscapes series. Springer, Berlin (in this volume) Pereira DI, Alves MI, Araújo MA, Cunha PP (2000) Estratigrafia e interpretação paleogeográfica do Cenozóico continental do norte de Portugal. Ciências da Terra 14:73–82 Pereira E, Rodrigues J, Castro P (2012) O Maciço de Morais: Terras de Cavaleiros Geopark report Pereira DI, Pinto B, Marcos S (2013) Terras de Cavaleiros Aspiring Geopark: An outreach strategy based on the typology of visitors. 12th European Geopark Conference extended proceedings Ribeiro A (2013) A evolução Geodinâmica de Portugal: os ciclos ante-mesozóicos. Geologia de Portugal, Escolar Editora I:11–54 Ribeiro A, Munhá J, Dias R, Mateus A, Pereira E, Ribeiro ML, Fonseca P, Araújo A, Oliveira JT, Romão J, Chaminé H, Coke C, Pedro JC (2007) Geodynamic Evolution of the SW Europe Variscides. Tectonics, 26, Art. No TC6009 Ribeiro A, Pereira E, Dias R (1990) Structure in the NW of the Iberia Peninsula (Alloctonous sequences). In: Dallmeyer RD, Martinez Garcia E (eds) Pre-Mesozoic Geology of Iberia, Springer, Berlin,, pp 220–236

Arouca UNESCO Global Geopark: Geomorphological Diversity Fosters Local Development

26

Artur Abreu Sá and Daniela Rocha

Abstract

26.1

The Arouca UNESCO Global Geopark is recognized for its outstanding and diverse geological heritage represented by 41 geosites, twenty-four of these are of geomorphological interest. Major landforms including planation surfaces, bowl-shaped valleys and narrow river valleys dominate this territory. The landforms in the Arouca Geopark have been recognized in recent years as representative of the most important features in the regional landscape, with educational and geotouristic significance. Integrated in a regional strategy for sustainable development, promoted by Arouca Geopark Association, these geosites allow visitors and the local inhabitants to learn about and understand the processes that gave rise to the territories geomorphology and landscape, and how this contributes to the Geopark’s economic development. Visits to these geosites during educational programs, guided tours or tourism events provide visitors with close contact with the region and its people, promoting the revitalization of the communities and the development of the sense of place. Keywords




Landforms Geoheritage Sustainable development Geopark Portugal








Geomorphological geosites Arouca UNESCO Global

A. A. Sá Departamento de Geologia, Escola de Ciências da Vida e do Ambiente, Universidade de Trás-os-Montes e Alto Douro, Vila Real, Portugal A. A. Sá (&)
D. Rocha Centro de Geociências, Universidade de Coimbra, Coimbra, Portugal e-mail: [email protected] D. Rocha e-mail: [email protected]




Introduction

The Arouca UNESCO Global Geopark is contained within the borders of the Arouca Municipality (Aveiro District, North Portugal). This territory has been recognized as a member of the Global Geoparks Network under the auspices of UNESCO since April 2009, due to its iconic geological heritage and the existence of a strategy for territorial development. This strategy involves the protection and promotion of geological and geomorphological heritage together with archaeological, historical and cultural heritage, both tangible and intangible. The strategy entails a holistic approach based on the implementation and delivery of educational, scientific, cultural and/or geotouristic activities. Local communities are involved in these activities and in working together to achieve sustainable economic development. The Arouca Global Geopark territory is recognized for the diversity of its landscapes, both natural and cultural. Among the 41 inventoried geosites, characterized, protected and advertised, 24 are of geomorphological interest (Rocha 2008; Sá et al. 2008), 18 being integrated in the “Geosites Route of the Arouca Geopark” and five in the “Paiva Walkways” (Fig. 26.1). Some of these geosites are viewpoints located on the Montemuro and Freita Mountains that provide overviews, leading to an understanding of the major geomorphological features of the landscape. These panoramas reveal the Portuguese mainland, from the Atlantic Ocean to the Marofa crest (Figueira de Castelo Rodrigo), along the border with Spain, or from the Gerês Mountain, in the far north of Portugal, to the Estrela and Caramulo Mountains in the centre of the country. In addition, the geological diversity of the Arouca Geopark, consisting primarily of Neoproterozoic and Paleozoic metasedimentary rocks and Variscan granites, together with the products of tectonic processes, is the main determining factor in the geomorphological diversity of this region, both in terms of its large-scale and minor landforms.

D. Rocha Associação Geoparque Arouca, Arouca, Portugal © Springer Nature Switzerland AG 2020 G. Vieira et al. (eds.), Landscapes and Landforms of Portugal, World Geomorphological Landscapes, https://doi.org/10.1007/978-3-319-03641-0_26

329

330

A. A. Sá and D. Rocha

Fig. 26.1 Geology of the Arouca UNESCO Global Geopark with location of geosites with geomorphological interest: 1–7. Viewpoints (1. Detrelo da Malhada, 2. Costa da Castanheira, 3. Senhora da Mó, 4. Sobreiros, 5. Pedra Posta, 6. Mira Paiva, 7. “Hells door” and “the claw”), 8–14. Fluvial landforms (8. Caima River potholes, 9. Frecha da Mizarela Waterfall, 10. Paiva River gorge, 11. Vau fluvial beach, 12. Gola do Salto step, 13. Paiva River meanders and alluvial deposits, 14.

26.2

Geographical Setting

The Arouca UNESCO Global Geopark, which covers an area of 328 km2 and is located about 70 km southeast of Oporto, is integrated in the sub-region of Entre Douro e Vouga (North Portugal). This territory is a mountainous area dissected by narrow valleys, where the altitude varies mainly between 200 and 600 m, but exceeding 1000 m in the Freita (1100 m) and Montemuro mountains (1222 m). Structurally, the territory is situated in the western Iberian Massif, between two important geological structures: the major NNE-SSW trending late Variscan fault of Verín-Penacova in the east and the NNW-SSE-oriented Porto–Tomar shear zone to the west. Morphologically this area is located in the north-central sector of the mountainous region known as Western Mountains of Central and Northern Portugal (Montemuro Mountain and Gralheira Massif). These mountains are included primarily in the Douro basin

Aguieiras Waterfall), 15–19. Granitic landforms (15. S. Pedro Velho bornhardt, 16. “Cornbread” rocks of Junqueiro, 17. Serlei gnammas, 18. Espinho corestones, 19. Viveiros da Granja boulders), 20–24. Residual landforms and asymmetric slopes (20. Côto do Boi, 21. “Library” of the Paiva River, 22. Galinheiros quartzitic ridge, 23. Gralheira d’Água quartzitic ridge, 24. “Pedra Má” hornfels)

(drainage basins of rivers Arda and Paiva and their tributaries) and, on the southern slope of the Freita Mountain, in the Vouga basin (Caima River). The Arouca UNESCO Global Geopark shows a temperate Mediterranean climate with an Atlantic influence characterized by rainy winters (average annual precipitation of 1212 mm) and dry short warm summers (average annual temperature of 14 °C). However, on the crests of the Freita and Montemuro mountains the annual precipitation exceeds 1500 mm and snow is common during the (Moura 2001).

26.3

Landforms

26.3.1 Planation Surfaces The geomorphology of the Arouca UNESCO Global Geopark is strongly influenced by Variscan tectonics, which

26

Arouca UNESCO Global Geopark: Geomorphological …

is responsible for the general NW-SE direction of the relief and for the NE-SW to NNE-SSW trending major fault system that controls, for example, the drainage pattern. These faults were reactivated during the Alpine tectonic cycle. The Variscan heritage is also responsible for the Appalachian-type relief and the granitic landforms (Pereira et al. 1980, 2007; Cordeiro 1988, 2004; Oliveira 1997). The prominent features of the Arouca UNESCO Global Geopark include Montemuro Mountain and the Gralheira massif composed by the Arestal and Freita mountains (Ferreira 1978, 2005). The Gralheira massif (Girão 1922; Ribeiro et al. 1943) is the first significant mountain to the east of the Portuguese coastline and is located in the southern part of the municipality of Arouca. The Gralheira massif includes fundamentally asymmetric reliefs. Its western area is characterized by a staircase-like series of erosion levels, and the much dissected north-eastern zone is drained by the Paiva River and its tributary the Paivó River (Ferreira 1978). The Freita Mountain is the most iconic area of the Arouca UNESCO Global Geopark and contains the majority of

331

geosites. This mountain was described by Ribeiro et al. (1943) as an approximately hexagonal block, whose mountainsides reflect the strong influence of Variscan tectonics. The eastern slope is dominated by the late Variscan Verín-Penacova Fault responsible for the altitude difference between the mountain summit (900–950 m) and the “Upper Surface of Viseu”, with elevations ranging between 600 and 700 m (Cordeiro 2004). In contrast, the western slope is cut by two faults with perpendicular directions: in the northwest, the NE-SW Vale de Cambra fault and in the southwest, the Felgueira-Preguinho fault, defining two fault blocks that is responsible for the differences in altitude between the planation surfaces that crown the Freita and Arestal mountains (Fig. 26.2, Ferreira 1978; Cordeiro 2004; Pereira et al. 2007). The NW-SE-oriented Variscan folds are responsible for the Appalachian-type relief of the north-east slope of Freita Mountain. River valleys carved in shale layers can reach depths of several hundred metres, while the narrow interfluves consist of elongated quartzite ridges (Cordeiro 2004). The north-eastern most area of the Arouca UNESCO Global Geopark is the Montemuro Mountain, forming an

Fig. 26.2 Northeastern slope of the Freita Mountain with the planation surface and a landform, locally known as “the claw”, where small streams appear to carve the fingers of a giant claw (yellow arrows)

332

asymmetrical massif with steep slopes and a roughly triangular shape. The massif contains three homogeneous morphostructural units: the Western unit, the Perneval—São Pedro do Campo unit and the Montemuro unit (Vieira 2002, 2008). The area of the Geopark is part of the Perneval—São Pedro do Campo unit, which is constrained to the south by the Paiva River. The lower part of this unit occupies a topographically depressed area, with altitudes between 350 and 550 m, coinciding with a predominance of Proterozoic and Paleozoic metasediments. Moreover, the Alvarenga granite which crops out in this area behaves like a softer rock relative to metasediments (Pereira et al. 1980; Vieira 2008).

A. A. Sá and D. Rocha

between Rossas and Várzea parishes, the contact metamorphism resulting from the intersection of the batholith with the Pre-Ordovician metasediments produced a hard pelitic hornfels, popularly known as “bad stone”, which is resistant to weathering. The differential weathering of the softer quartz diorite and the harder hornfels resulted in the formation of the bowl-shaped valley. The valley floor shows an ellipsoidal shape at an altitude of 300–350 m asl. and is considered by Ferreira (1978) as one of the “lower levels of the Western Mountains“. The main settlements in the Geopark occur within the bowl-shaped valleys, where the conditions are favourable to agriculture and cattle and sheep farming have, for centuries, been the mainstay of the economy.

26.3.2 Granitic Bowl-Shaped Valleys The granitic bowl-shaped valleys are major landforms representing open basins with kilometric to hectometric dimensions, which narrow downstream and show a weathering mantle with varying thickness. Granitic bowl-shaped valleys occur in Arouca, Moldes, Mansores, Vér and Fermedo (Cordeiro 1995; 2004). The complex bowl-shaped Arouca basin is the most important basin (Fig. 26.3). It occupies a large area of the quartz diorite batholith, which is intersected by lines of tectonic weakness with a predominantly E-W direction. The K feldspar—biotite main composition of this rock makes it sensitive to weathering. Downstream, in the border

Fig. 26.3 Bowl-shaped valley of Arouca from Detrelo da Malhada

26.3.3 River Valleys The Arouca UNESCO Global Geopark area is integrated in the Douro and Vouga watersheds. The Douro watershed drains the east, north and western areas of the territory, while the Vouga watershed drains the southern part of Freita Mountain (Fig. 26.1). Major tributaries, the Arda and Paiva rivers (Douro watershed) and the Caima River (Vouga watershed), also contribute to the present geomorphology, excavating deep valleys and producing fluvial deposits. The permanent flow of these rivers is due, in part, to the significant rainfall and in a small amount to snowmelt in the

26

Arouca UNESCO Global Geopark: Geomorphological …

mountains. The analysis of the drainage patterns reveals the occurrence of subsequent streams with flow directions determined by the rectangular pattern of regional tectonics and schistosity. There are, however, many streams without any structural control that are responsible for the dominance of the dendritic drainage pattern in the hydrographic network (Medeiros et al. 1964; Pereira et al. 1980, 2007).

26.4

Geomorphological Geosites of the Arouca UNESCO Global Geopark

The Arouca UNESCO Global Geopark has 41 geosites of geomorphological, mineralogical, petrological, sedimentological, tectonic, stratigraphic, paleontological and paleogeographic significance. Twenty-four of these geosites are predominantly of geomorphological significance. Several of these geosites are visited in educational and geotourism activities, attracting more than 300,000 visitors per year. Their popularity contributes to the involvement and sense of ownership by the inhabitants of the area and contributes to the consolidation of the territorial development strategy defined and implemented by the Arouca Geopark Association (AGA). The following text provides a brief description of the geomorphological geosites identified and characterized in Arouca Geopark.

333

(b) Costa da Castanheira (Castanheira, 1046 m asl) Costa da Castanheira is the best-known viewpoint of the southern area of the Freita Mountain, providing a view of the geomorphological features in the landscape of Portugal mainland between the Freita and the Estrela and Caramulo mountains. From there, it is possible to see the Felgueira-Preguinho fault that subdivides the Gralheira Massif, and the Aveiro Lagoon in the Atlantic coast. This geosite it is equipped with the panoramic belvedere (50 m high) of the Meteorological Radar of Arouca. (c) Senhora da Mó (Arouca, 680 m asl) Senhora da Mó is the best-known viewpoint of the Geopark, located in a position overlooking Arouca; it provides an excellent site to view the general geomorphological pattern of the region within a 360º panorama. The landscape is characterized by the occurrence of igneous, metamorphic and sedimentary rocks with differential resistance to weathering. The Arda Valley, with its fertile soil, is a symbol of the main economic activity developed in the region for centuries. (d) Sobreiros (S. Miguel do Mato, 470 m asl) From Sobreiros, it is possible to view the Douro valley towards the north and the Variscan syncline corresponding to the Valongo-Tamames domain. The old coal mines of Pejão (Castelo de Paiva municipality) can also be seen in the distance.

26.4.1 Viewpoints (e) Pedra Posta (Alvarenga, 1222 m asl) (a) Detrelo da Malhada (Moldes, 1099 m asl) The Detrelo da Malhada is a viewpoint over the Arouca Geopark and offers a platform of observation and an interpretive panel about the landscape and its main geomorphological features (Fig. 26.3). The geological contact between the Arouca quartz diorite and the Pre-Ordovician greywackes and schists, defining the Arouca bowl-shaped valley, is evident in the landscape due to differences in topography and vegetation. The structuring of the Arouca UNESCO Geopark Global landscape during the upper Miocene, due to the movements of large lithospheric blocks, exhumed andalusite-rich schists, forming the typical residual relief in the surrounding area of the viewpoint, which includes rocky crags and boulder scatters.

The Pedra Posta is the most elevated geosite in the Arouca UNESCO Global Geopark. The site affords a magnificent view of a fantastic landscape and especially of the Montemuro Mountain and the Alvarenga and Nespereira valleys. The surrounding area contains many examples of small granitic landforms related to the surface exposure of the Montemuro granite. (f) Mira Paiva (Alvarenga, 165 m asl) From the viewpoint, one can observe the Paradinha Village, classified as the “Village of Portugal”. The village, which is characterized by its typical architecture, is underlain by schists and is associated with a river beach, the mouth of the

334

A. A. Sá and D. Rocha

Fig. 26.4 Portal do Inferno (“Hell’s door”) with the deeply incised valleys

Paivó River and fluvial deposits whose nature is closely related to the dynamics of streamflow. The nature of the clasts reveals the upstream geology, and the deposit occurs on the convex bank, where it forms a small beach often used as a base for canoeing and rafting activities. (g) “Hell’s door” and “the claw” (Covêlo de Paivó, 940 m asl) Located on a unique viewpoint, this geosite is surrounded by two deeply incised valleys, which explain the origin of the name “Hell’s door” (Fig. 26.4). From this site, it is also possible to observe a curious landform locally known as “the claw” (Fig. 26.2). The “Hell’s door” is located in the Gralheira Massif, about 1000 m asl, over Pre-Ordovician metasedimentary rocks. It rises between two creeks, a tributary of the Covas do Monte stream, at the east, and a tributary of Palhais stream, to the west. This narrow passage between hills has always been referred to as a place that frightened all those passing by. It is a place with high scenic interest, especially for the “claw”, which is a landform carved by several streams, with a shape similar to the claw of a bird of prey.

26.4.2 Fluvial Landforms (a) Caima River potholes (Albergaria da Serra, 895 m asl) The site is located in front of the Mizarela waterfall, where several potholes of different size and depth occur on the margins and in the bed of the Caima River. The formation of these potholes is related to the turbulent flow of the river during winter. (b) Frecha da Mizarela waterfall (Albergaria da Serra, 900 m asl) The highest waterfall in mainland Portugal, with about 70 m height, is located at the contact between the Pre-Ordovician metasediments and the Serra da Freita granite (Fig. 26.5). The differential erosion and the local tectonics (Freita Mountain shear zone) are responsible for the occurrence of this waterfall. Recently, an urbanistic arrangement was performed in the viewpoint, which includes an interpretive panel to explain the geosite.

26

Arouca UNESCO Global Geopark: Geomorphological …

335

outcropping quartzites and conglomerates (Fig. 26.7). The existence of this “leap” is directly related to the combination of two geological faults, one with N-S direction, responsible for the rectilinear alignment of the river in this area, and another one NE-SW, which determines the extension of the step. This site is much appreciated by rafting practitioners and is classified as white water grade 5. (f) Paiva River meanders and alluvial deposits (Janarde village, 200 m asl) Tectonics and lithological differences are responsible for the formation of these meanders. There are two levels of alluvial terraces on the margins of the Paiva River. One terrace is located 10–15 m above the river and is composed mainly by clasts of quartzite, quartz sandstone and greywacke. The second terrace is located 30–40 m above the river and consists of consolidated fluvial sediments. The Romans extracted gold from these alluvial deposits (Fig. 26.8). (g) Aguieiras Waterfall (Alvarenga, 458 m asl).

Fig. 26.5 Frecha da Mizarela, the highest waterfall in mainland Portugal, with about 70 m height

The Aguieiras stream, which drains the Alvarenga valley, creates a waterfall on the granitic scarps of the Paiva River. The “Alto do Pereiro” viewpoint is the best site to admire this waterfall, clearly defined by the orthogonal fracture pattern of the granitic massif of Alvarenga. It is currently one of the key points of attraction for the visitors of the Paiva Walkways.

(c) Paiva River gorge (Alvarenga village, 180 m asl) This geosite is located close to the Alvarenga bridge, built in 1701 using an old Roman structure from 110 AD (Fig. 26.6). The gorge crosses the hornfels and granites that crop out in the area and was excavated by the river which exploited the dense system of joints with a dominant NW-SE direction. (d) Vau fluvial beach (Canelas, 150 m asl) The Vau River beach is a sandbar on the left bank of the river, from which typical erosional features of fluvial origin can be viewed. Near this site, the small Fontão stream enters the Paiva River via a beautiful waterfall. (e) Gola do Salto step (Canelas, 90 m asl) The dense fracturing and tectonic features at this site, located in the bed of the Paiva River create a 4 m high step in the

26.4.3 Granitic Landforms (a) São Pedro Velho bornhardt (Albergaria da Serra, 1077 m asl). This site is a bornhardt landform, a type of inselberg, developed on the Freita Mountain granite together with diverse granitic boulders with weathering pits (Fig. 26.9). From the top of this landform, there is a 360º view over the Freita Mountain allowing to observe almost half of the Portuguese mainland: the Estrela Mountain (south), the Gerês Mountain (north), the Marofa Mountain (east) and the Atlantic Ocean (west). This geosite is equipped with a 360º observation deck and four interpretive panels directed to the four main cardinal points. (b) “Cornbread” rocks of Junqueiro (Albergaria da Serra, 975 m asl).

336

A. A. Sá and D. Rocha

Fig. 26.6 Paiva River gorge excavated by the river in the dense system of joints of the Alvarenga granite

This site shows two granitic boulders with polygonal cracking, known locally as “cornbread” rocks. In the vicinity of the site, it is possible to observe boulders with exfoliation along sheeted joints. The geosite is equipped with a platform for access and observation and an interpretive panel.

(e) Viveiros da Granja boulders (Moldes, 880 m asl). Numerous large rounded boulders resulting from the orthogonal jointing pattern and weathering of the Arouca quartz diorite massif.

(c) Serlei gnammas (Albergaria da Serra, 1044 m asl). This area presents several granitic boulders with numerous weathering pits (Fig. 26.10). These are flat bottomed depressions with essentially circular and elliptical shapes, with irregular borders and sometimes coalescent, are typical features of granite weathering. (d) Espinho corestones (Espinho, 772 m asl). The orthogonal jointing of the Arouca quartz diorite massif, exploited by subsurface weathering, creates outstanding examples of corestones with onion skin weathering.

26.4.4 Residual Landforms and Asymmetric Slopes (a) Côto do Boi (Moldes, 1001 m asl). The asymmetry of this slope is due to the fact that the surface of the southern slope is consistent with the foliation pattern, while the northern slope, which is steep and rugged, cuts across the foliation (Fig. 26.11). The slope break, which gave rise to the local name “tailless ox”, is accentuated by the proximity to the contact with the Arouca quartz diorite pluton, by the medium-grade to high-grade regional metamorphism and also

26

Arouca UNESCO Global Geopark: Geomorphological …

Fig. 26.7 Gola do Salto, a 4 m step in the Paiva River very appreciated by canoeing and rafting practitioners

Fig. 26.8 Meanders in the village of Janarde, where the Romans extracted gold in the inner convex bank river deposits

337

338

A. A. Sá and D. Rocha

Fig. 26.9 São Pedro Velho bornhardt, one of the most emblematic geomorphological geosites of the Arouca Geopark Association Educational Programmes

Fig. 26.10 Granitic boulder with surface covered by gnammas in Serlei area on the top of the Freita Mountain

26

Arouca UNESCO Global Geopark: Geomorphological …

339

Fig. 26.11 Coto do Boi geosite

by the streams of Roças to the west and Moldes to the east. The countless crystals of andalusite in these rocks validate the exhumation process of large crustal blocks associated with the Porto-Viseu metamorphic band. From this site, it is also possible to observe the Moldes bowl-shaped valley and the neighbouring area. (b) “Library” of the Paiva River (Janarde, 200 m asl). The vertical quartzite layers near the Mourinha stream in the Paiva River valley are locally referred as the “library”, due to their resemblance to books stacked regularly on bookshelves. Due to its high quartz content, quartzite outcrops stand out in the landscape as a result of differential erosion relatively to the surrounding rocks, occurring during the Cenozoic. (c) Galinheiros quartzite ridge (Canelas, 603 m asl). This residual relief is formed by Hirnantian (Upper Ordovician) quartzites of the Sobrido Formation corresponding to sands deposited during the early deglaciation phase following the Late Ordovician Glaciation. (d) Gralheira d’Água quartzite ridge (Canelas, 629 m asl). This area is a residual relief constituted by Arenigian (Lower Ordovician) quartzite with abundant ichnofossils.

Furthermore, the site contains remains of Roman gold mining and provides a viewpoint over the famous “Canelas quarry”, where the fossils of the largest trilobites in the world were found, and also towards most of the Arouca UNESCO Global Geopark. (e) “Pedra Má” hornfels (Várzea, 250 m asl). This geosite corresponds to a hornfels outcrop locally known as “Pedra Má” (bad rock), due to its extreme hardness, which is a result of contact metamorphism associated with the intrusion of the Arouca quartz diorite pluton. The presence of this rock type is closely connected with the formation of the Arouca bowl-shaped valley, as explained above in the description of the viewpoints Detrelo da Malhada and Senhora da Mó. There are also archaeological remains, which may correspond to the “old castle of Arauka”, the origin for the present-day name of Arouca.

26.5

Final Remarks

The significance of the contribution of the geological diversity to the development of the geomorphology and landscape of the Arouca Global Geopark is increasingly recognized. The recognition of this relationship contributed significantly to the territorial development strategy, defined and implemented by

340

the Arouca Geopark Association. This includes educational programs and geotourism itineraries involving geosites of geomorphological significance, such as the “Geosites Route of the Arouca Geopark” and the “Paiva Walkways”. These sites now attract an increasing number of students and teachers (about 50,000 since 2008) to the Arouca Geopark, which is increasingly used as a destination for didactic fieldwork. On the other hand, the increasing number of tourists and the provision of information associated with trails and geosites has raised awareness in the general public about the meaning and importance of geosites. In addition, visitors come into direct contact with the local population, with their knowledge and traditions, and this involvement has resulted in the promotion of the local identity. This growing development has allowed the inhabitants of the Arouca UNESCO Global Geopark to become increasingly involved in issues related to environmental integrity, social justice and sustainable economic development. Acknowledgements We thank Prof Tony Ramsay, School of Earth and Ocean Sciences, Cardiff University and Fforest Fawr Geopark (UK), Prof Diamantino Pereira, Department of Earth Sciences, University of Minho (Portugal) and Prof Gonçalo Vieira, Institute of Geography and Spatial Planning, University of Lisbon (Portugal) for the careful reading, detailed corrections and constructive criticism of the final version of the manuscript. We also thank Pedro Bastos, Ivo Brandão and Joaquim Gonçalves for the pictures that illustrate this work.

References Cordeiro AMR (1988) A Evolução das Vertentes da Serra da Freita no Quaternário Recente. Cadernos de Geografia 7:87–133 Cordeiro AMR (1995) Alvéolos graníticos do Centro-Norte de Portugal. Génese e tipologia. Actas do VI Colóquio Ibérico de Geografia, 1992, Porto, pp 689–697

A. A. Sá and D. Rocha Cordeiro AMR (2004) Dinâmica de Vertentes em Montanhas Ocidentais do Portugal Central. Dissertação de Doutoramento. Faculdade de Letras. Universidade de Coimbra, p 566 Ferreira AB (1978) Planaltos e Montanhas do Norte da Beira – Estudo de Geomorfologia. Memórias do Centro de Estudos Geográficos 4:1–374 Ferreira AB (Coord.) (2005) Geografia de Portugal: Volume 1—O Ambiente Físico. Círculo de Leitores, Lisboa Girão AA (1922) Bacia do Vouga. Estudo Geográfico. Imprensa da Universidade, Coimbra, p 190 Medeiros AC, Pilar L, Fernandes AP (1964) Carta e notícia explicativa da folha 13 – B (Castelo de Paiva) da Carta Geológica de Portugal à escala 1:50 000. D.G.G.M. Serviços Geológicos de Portugal, p 58 Moura AR (2001) Serra da Freita. Associação de Defesa do Património Arouquense & Universidade de Aveiro, p 12 Oliveira JMS (1997) A Reserva Ecológica Nacional: a contribuição da geografia para a eficácia deste instrumento no planeamento e ordenamento do território. Dissertação de Mestrado n. publ., Faculdade de Letras da Universidade do Porto, Porto, p 174 Pereira E, Gonçalves LS, Moreira A (1980) Carta e notícia explicativa da folha 13 – D (Oliveira de Azeméis) da Carta Geológica de Portugal à escala 1:50 000. D.G.G.M. Serviços Geológicos de Portugal, p 68 Pereira E, Rodrigues J, Gonçalves LSM, Moreira A, Silva AF (2007) Carta e Notícia explicativa da folha 13-D (Oliveira de Azeméis) da Carta Geológica de Portugal à escala 1:50 000. Lisbon, Departamento de Geologia, INETI, p 55 Ribeiro O, Almeida JP, Patrício A (1943) Nota preliminar sobre a morfologia do maciço da Gralheira. Boletim da Sociedade Geológica de Portugal 3(1/2):81–85 Rocha DMT (2008) Inventariação, Caracterização e Avaliação do Património Geológico do concelho de Arouca. Dissertação Mestrado n. publ., Departamento de Ciências da Terra, Universidade do Minho, Braga, p 159 Sá AA, Brilha J, Rocha D, Couto H, Rábano I, Medina J, Gutiérrez-Marco JC, Cachão M, Valério M (2008) Geoparque arouca: Geologia e Património Geológico. Câmara Municipal de Arouca (ed), Arouca, p 127 Vieira ABV (2002) A Serra de Montemuro. Contributo da Geomorfologia para a análise da paisagem enquanto recurso turístico. Cadernos de Geografia 21/23:211–212 Vieira ABV (2008) Serra de Montemuro: dinâmicas geomorfológicas, evolução da paisagem e património natural. Tese de Doutoramento n. publ. Universidade de Coimbra, Coimbra, p 689

27

The Estrela Geopark—From Planation Surfaces to Glacial Erosion Gonçalo Vieira, Emanuel de Castro, Hugo Gomes, Fábio Loureiro, Magda Fernandes, Filipe Patrocínio, Gisela Firmino, and João Forte

Abstract

The Estrela Geopark rises to 1993 m asl and occupies an area over 2000 km2 in the western sector of the Iberian Central System, the mountain range that extends from Guadarrama in Spain to Montejunto in the north-west of Lisbon. The Estrela is located in the Central Iberian Zone showing various types of granites and the turbiditic metasediments of the Beiras Group as the main lithologies. After the planation of the Variscan orogen, the Alpine compression uplifted the Iberian Central System and rejuvenated the landscape, elevating the planation surfaces in a pop-up structure and accelerating fluvial erosion along the main Late Variscan faults. The elevation of the Serra da Estrela, the plateau character of the summit and its position as the first barrier to the moist Atlantic air masses entering Iberia, generated the ideal conditions for fast glacial inception during the cold phases of the Pleistocene. The last glacial showed the

formation of an extensive plateau ice field and several valley glaciers, which deeply sculpted the landscape, leaving an excellent imprint of glacial processes in the mountain. The interplay of glacial erosion, granite weathering, tectonics and fluvial erosion generated a landscape of very high scenic, scientific and educational value. These, together with a rich biodiversity and long history of human presence with strong cultural and economic links to the mountain, are the main reasons for the labelling of the Estrela as a UNESCO Global Geopark. Keywords




Glacial Periglacial UNESCO

27.1 G. Vieira (&)
J. Forte Centre of Geographical Studies, Institute of Geography and Spatial Planning, University of Lisbon, Lisbon, Portugal e-mail: [email protected] J. Forte e-mail: [email protected] G. Vieira
E. de Castro
H. Gomes
F. Loureiro
M. Fernandes
F. Patrocínio
G. Firmino Associação Geopark Estrela, Guarda, Portugal e-mail: [email protected] H. Gomes e-mail: [email protected] F. Loureiro e-mail: [email protected] M. Fernandes e-mail: [email protected] F. Patrocínio e-mail: fi[email protected] G. Firmino e-mail: giselafi[email protected]




Geology




Geoconservation




Introduction

The Estrela UNESCO Global Geopark (in short: Estrela Geopark) brings together the landscapes and landforms of the Serra da Estrela, the ecosystems that have developed under their control, as well as the local peoples—the Serranos, their traditions and socio-economic activities, which have laid an important imprint on the present-day landscape. The territory presents a rich geoheritage, with remarkable geomorphological features which are the roots of its recognition by UNESCO, and encompasses the highest part of Iberian Central System in Portugal. However, the Geopark is not limited to the highest parts of the mountain, but extends well into the marginal lowlands, allowing for a full understanding of its geomorphological history, but also providing vital links with its peoples, their history, culture and local economy. With an excellent road network allowing for a facilitated visit to most geosites, the area has been a traditional national winter tourism destination, with peak occupation in a short number of days, mostly around the summit

© Springer Nature Switzerland AG 2020 G. Vieira et al. (eds.), Landscapes and Landforms of Portugal, World Geomorphological Landscapes, https://doi.org/10.1007/978-3-319-03641-0_27

341

342

area and the ski resort at Torre. However, most visitors have not yet discovered the much broader spectrum of sites of scenic, cultural, pedagogical or scientific relevance, which exist in the territory. Furthermore, the area also offers numerous other tourist attractions, such as diverse historical sites (e.g. megaliths, Roman structures, medieval castles and settlements, traditional villages), museums and interpretation centres, rich regional gastronomy and valuable endogenous products, as well as numerous high-quality fluvial beaches and thermal spas. Despite this rich potential, the region, as well as most interior Portugal, has been strongly affected by rural exodus and strong population ageing since the late 1960s, leading to the abandonment of traditional agriculture and grazing practices, as well as to low population density. These socio-economical changes contributed to modifications in the mountainous landscapes, impoverishing the complex agro-ecological mosaics responsible for the high biodiversity of the region and its ecosystems (Jansen et al. 2013). The Serra da Estrela is one of the regions in Portugal with longest tradition of geological and geomorphological research. The glacial imprint was first identified by Vasconcelos Pereira Cabral in 1882 (Cabral 1882) and has, since then, become one of the main highlights for the visitor. In 1976, the Serra da Estrela Natural Park (PNSE) was established in order to preserve its ecological and geomorphological values, but also to support the traditional mountain economy-based population. The PNSE is a central partner of the Estrela Geopark and occupies about 41% of its area, providing legal protection to 102 geosites. It was also through the PNSE that the Serra da Estrela became one of the first areas in Portugal to promote geoheritage with the publication of the “Geological and geomorphological guide of the Serra da Estrela” in 1999 (Ferreira and Vieira 1999), with two maps and 16 interpretation panels installed in the late 1990s. The tradition continued with the publication of the “Geobotanical guide of the Serra da Estrela” (Jansen, 2002), which is a key reference linking geology and biodiversity. Geomorphological research has been supported for several years by the PNSE, which provided logistical support to research. Making use of the existing knowledge on the geoheritage of the Serra da Estrela, and as an approach to tackle the challenges of territorial development in the light of the United Nations Sustainable Development Goals, together with objectives for promoting geoconservation, the Associação Geopark Estrela (AGE) started to prepare the application of the Estrela to become a UNESCO Global Geopark in 2015. The submission took place in 2017, with its entering into force, after a positive evaluation, foreseen for April 2020. The AGE is formed by nine municipalities

G. Vieira et al.

(Belmonte, Celorico da Beira, Covilhã, Fornos de Algodres, Gouveia, Guarda, Manteigas, Oliveira do Hospital and Seia), and two higher education institutions (Instituto Politécnico da Guarda and Beira Interior University), with the cooperation from IGOT—University of Lisbon and other regional organizations, such as the Natural Park of the Serra da Estrela and Turismo do Centro. The Estrela Geopark is framed by a solid strategy for regional development, with an emphasis on promoting geotourism, local economy, science and education, as well as geoconservation, all in close connection with the municipalities.

27.2

Geographical Setting

The Estrela Geopark is located in Central Portugal, occupying an area of c. 2216 km2, from close to the town of Guarda in the north-east, to Oliveira do Hospital in the south-west, following the SW-NE direction of the Portuguese Central System (Fig. 27.1). The core of the Geopark is the Estrela (star), a predominantly plateau-type mountain terrain, elongated in SW-NE direction and bounded by two major fault-generated escarpments that separate it from the piedmont planation surfaces of Mondego (NW) and Cova da Beira (SE) (Fig. 27.2). Most of the Estrela is granitic, with metasedimentary formations—mainly shales and greywackes—outcropping in the south-western part and in its centre (Fig. 27.3). These two areas show deep and sinuous valleys and long ridge-like interfluves, with a dense drainage network. Granitic terrains, on the other hand, show well-preserved plateaus and linear, tectonically controlled valleys. The contrast between the gentle plateau surfaces and the steep slopes and deep valleys is striking. The northern and north-eastern limits of the park, in the areas of Fornos de Algodres and Guarda, are the transition zones to the plateaus of north-central Portugal and the Iberian Meseta, bearing a close genetical link to the main mountainous relief. The elevation rises slowly and in several steps from Guarda, in the north-east, at c. 1100 m, to the Alto da Torre, at 1993 m, in the south-west, just before plunging to about 1300 m in the ridges that bridge to the Serra do Açor (Fig. 27.2). The territory is drained by two main rivers that flow north-eastwards while inside the mountain massif. They leave it by turning to the south and then south-west—the Zêzere, an important tributary of the Tagus and the source of drinking water to Lisbon, or by turning first to north-west and then to south-west—the Mondego, the longest river flowing entirely in the Portuguese mainland. Considering the regional morphology, the Estrela Geopark may be divided into the following units, with close relation with lithology and tectonic history (Fig. 27.3):

27

The Estrela Geopark—From Planation Surfaces to Glacial Erosion

343

Fig. 27.1 Relief of the Estrela Geopark and main localities mentioned in the text (topography from NASA ASTER GDEM v2, roads from OpenStreetMaps)

Plateaus

Valleys

Piedmont surfaces Scarps and transition slopes

Summit granite plateaus (SGP) Cabeça Alta—Cerro do Gato plateaus (CAP) South rim of the Portuguese Central Plateau (SRP) Transitional zone to the Meseta surface (TZMS) South-west metasedimentary valleys (SMV) Intramontane valleys (IV) South-east piedmont (SEP) NW piedmont (NWP) South-east scarps and transition slopes (SESS) NW scarps and transition slopes (NWSS)

27.3

Geological Evolution and Landform Development

In the tectonic and stratigraphic zoning of the Iberian Peninsula, the Estrela Geopark (EG) is located in the Central Iberian Zone (CIZ). This is the axial zone of the Variscan orogen, which resulted from the continental collision following the opening and subsequent closing of the Rheic and Palaeothethys oceans (Ribeiro 2013). In the area of the EG, the CIZ consists of the Schist-Greywacke Complex Domain, which is currently named in Portugal the Douro-Beiras Supergroup, with the Beiras Group being present in the Geopark area. The latter shows a turbiditic lithofacies and is traditionally considered a monotonous non-carbonated Neoproterozoic deeper facies sequence, when compared to

344

G. Vieira et al.

Fig. 27.2 Relief of the Estrela Geopark and main morphostructural and morphological units. SGP—Summit granite plateaus, CAP— Cabeça Alta—Cerro do Gato plateaus, SRP—South rim of the Portuguese Central Plateau, TZMS—Transitional zone to the Meseta

surface, SMV—South-west metasedimentary valleys, IV—Intramontane valleys, SEP—South-east piedmont, NWP—NW piedmont (topography from NASA ASTER GDEM v2)

the Douro Group (Meireles et al. 2014). The Beiras Group are the older rocks in EG and are present approximately south of the Covilhã—Oliveira do Hospital latitude, as well as in the upper Mondego River basin, mostly north of Manteigas (Fig. 27.3). However, most of the area of the EG is granitic, with a genesis closely associated with the evolution of the Variscan orogen, which was active in Iberia from the Early Devonian to the end of the Carboniferous. The compression resulted in three main phases of deformation (D1, D2 and D3), with crustal thickening having generated metamorphism and synorogenic magmatism, with formation of granitic rocks (Azevedo and Valle Aguado 2006). The CIZ is the section of the European Variscan Chain where granitic rocks are more diverse and occupy a larger area (Azevedo and Valle Aguado 2006), a fact that marks the EG geology and also its subsequent evolution. The late- and post-tectonic magmatism was widespread from 310 to 290 Ma, being associated with the compressive phase D3, which is the last ductile deformation stage. Considering the relation with D3, the Variscan granites are classified in pre-D3, sin-D3, late-D3 and post-D3 (Ferreira et al. 1987). Small intrusions of pre-Variscan granites are also present in the EG, dating from the Upper Proterozoic to the Lower

Palaeozoic (Neiva et al. 2009). Table 1 synthesizes the EG granite diversity, which as shown by Migon and Vieira (2014) has a significant impact on landforms across different spatial scales. In the contact zones between the Beiras Group metasediments and the batholith, contact metamorphism occurred, with the development of hornfels, which also contributes to striking rock-controlled differences in landform evolution. At the end of the Variscan orogenesis, the Iberian Massif was affected by brittle tectonics, resulting in two prevailing directions of lateral strike-slip faults: NNE-SSW to ENE-WSW (sinistral) and NNW-SSE (dextral) (Pais et al. 2012). The former had significant impacts on the evolution of landforms of the Estrela and corresponds to large valley lineaments that cut the mountains today, such as the Unhais da Serra (Alforfa)—Zêzere, or the upper Mondego valleys. These are part of the Bragança-Vilariça-Manteigas fault that is over 250 km long and still shows remarkable tectonic activity. The Variscan orogeny finished in the Late Permian with the planation of the mountain belt, forming the pre-Cretaceous planation surface that developed under a warm and wet climate, generating thick regoliths (Martin-Serrano 1988; Ferreira 2005). This planation surface

27

The Estrela Geopark—From Planation Surfaces to Glacial Erosion

345

Fig. 27.3 Geology of the Estrela Geopark (according to the Geological Map of Portugal 1:500,000 Oliveira et al. 1992)

is not present anymore in the EG area, and the planated summits that are visible in the Estrela and other Portuguese uplands are more recent and are remnants of the Palaeogene planation surfaces that were uplifted at the onset of the Alpine orogeny, possibly in the Middle to Late Miocene (Martín-González 2009). At this time, the Iberian Central System (the Portuguese Cordilheira Central) was uplifted as a horst in a pop-structure controlled by thrusts that were reactivated as inverse faults (Ribeiro et al. 1990, Pais et al. 2012). The NW slope of the Estrela is a fault-generated escarpment associated with the Seia-Lousã fault, while the SE slope is also a fault-generated escarpment, roughly parallel to the former (Fig. 27.4). The platforms in the west (Mondego) and east (Cova da Beira and Castelo Branco) are also remnants of the Palaeogene planation surface, maintaining flat interfluves which preserve the pre-uplift topography, mainly in the granite outcrops (Fig. 27.5). In the planation surfaces, excellent examples of residual relief occur, such as the Belmonte inselberg in the EG (Fig. 27.6), or the Monsanto Inselberg in the Naturtejo Geopark further south.

The uplift of the Serra da Estrela continued during the Quaternary with rates of about 0.2 mm/yr, especially in the highest parts of the mountains (Cabral 1995, 2012). The presence of Late Hercynian faults affecting the bedrock generated a major control facilitating fast incision of the drainage network. One of the main geomorphological differences at the landscape scale in the EG is due to the contrast between granites and slates, schists and greywackes (Ribeiro 1954, Daveau 1969). In the granite terrains, the resulting valleys are linear and follow the faults, forming long lineaments, while the interfluves are generally flat, preserving the planation surfaces. In metasedimentary terrains, the valleys show incised meanders and the interfluves are narrow and long, forming ridges that reflect the significance of mass-wasting and water erosion on less permeable slopes (Fig. 27.2). During the Pleistocene cold periods and mainly during the Last Glacial, local glaciation developed in the Serra da Estrela, with a plateau ice field covering the upper plateau from the Alto da Torre to Fraga das Penas (Fig. 27.7). Five main valley glaciers radiated from the ice field, with the

346

G. Vieira et al.

Fig. 27.4 Geological cross-sections in the Estrela Geopark illustrating the impact of tectonics on the elevation of the planation surfaces, as well the different geological control on landforms

Fig. 27.5 Castelo Branco Platform from Varanda dos Carqueijais in the SE slope of the Serra da Estrela, in the road from Covilhã to Penhas da Saúde

27

The Estrela Geopark—From Planation Surfaces to Glacial Erosion

347

Fig. 27.6 Belmonte Inselberg

longest one being the Zêzere glacier (Lautensach 1929), about 11 km in extent (Vieira 2004, 2008). The total glaciated area at the last maximum ice extent, dated at about 30 ka BP, was close to 66 km2. The glacial landforms and deposits in the Estrela are striking, especially when considering the low altitude of the mountain and its geographical setting in western Iberia. The Torre plateau is characterized by widespread bare granite outcrops, completely stripped by glacial erosion. As the slope angle increases at the main valley heads, with increasing ice flow, small lakes associated with glacial overdeepenings start to show, as well as numerous areas with roches moutonnées and polished rock surfaces (Fig. 27.8). This type of landscape prevails in the upper Loriga valley and close to Lagoa Comprida. At the headwalls of the main valleys, magnificent deeply carved glacial cirques occur, with the ones incised into the eastern margin of the plateau deserving special reference: the Covão Cimeiro (Zêzere valley) and the Covão do Ferro (Alforfa valley) (Fig. 27.9). Both are clearly visible from the main road that links to the summit. The Estrela also shows several well-developed glacial troughs with a perfect

U-shape, with the Zêzere valley providing the best example, but with other noteworthy examples, such as the Caniça and Loriga valleys (Fig. 27.10). Below 1650 m, the landscape starts to change from one dominated by glacial erosion features, to the domain of moraines and paraglacial deposits, such as debris cones and talus slopes. The moraines at Nave de Santo António, Lagoa Seca and Covão do Urso, among others, are excellent examples. The distribution of glacial erosion features of the Estrela led Daveau (1971) to infer on the climatic asymmetry of the mountains during the Last Glaciation. Glacial landforms are more developed, also with longer glaciers, in the east and north of the Torre—Penhas Douradas plateau, showing a strong W-E and S-N gradient. The former reflects snow redistribution by the western winds, while the latter highlights the contrasts in solar radiation between the north and south of the mountains. The glacial landforms and deposits are at the core of the scientific value of the Estrela Geopark and were essential for its recognition by UNESCO. A more detailed description of them may be found at Vieira and Nieuwendam (2020—this volume). Periglacial deposits and their relationship with

348

G. Vieira et al.

Fig. 27.7 Model of the Estrela plateau ice field and tributary glaciers at the maximum ice extent of the last glacial. Small glaciers, such as the cirque glacier at Covais or the one at Covão do Teixo, are not represented. View from the south-east

glacial features are also very relevant to the geoheritage of the Estrela Geopark, with key sites at the Pedrice blockslope, the talus slopes of Souto do Concelho and São Sebastião, close to Manteigas, as well as at several localities of stratified slope deposits. The rich diversity of the Estrela granites occurring in a relatively small area, and the interplay between the pre-Quaternary deep weathering, active tectonics and erosion, makes the EG unique for the study of rock control on landforms at various scales (Migon and Vieira 2014). For example, when exposed to Pleistocene cold climate conditions, fine-grained granite variants generated blockfields and blockslopes with decimetre to metric rock fragments. On the other hand, neighbouring coarse-grained granite variants,

when exposed to similar conditions, were more prone to granular disaggregation resulting in gravels and coarse sands, which fed the stratified slope deposits within the valleys. A similar type of rock control has been found for the tor-type landforms, which are widespread outside the glaciated area, both in the mountains, as in the lowlands (Migon and Vieira 2014). Rounded tors and boulders are associated with coarse-grained granites, while more angular tors relate to fine-grained variants. Excellent granite weathering landscapes with tors, but also other landforms such as nubbins, bornhardts and castle koppies, as well as small-scale weathering features, are present in the Penhas Douradas, Covão do Teixo, but also in the lowlands, such as in the Vila Verde area (Fig. 27.11).

27

The Estrela Geopark—From Planation Surfaces to Glacial Erosion

349

Fig. 27.8 Erosion landscape in the margins of the Torre plateau and upper valleys. a Polished granite surfaces in the Loriga valley. b Small glacial grooves in the Candieira valley. c The Fragão do Poio dos Cães erosion area. d The Peixão pond in the Candieira valley

Fig. 27.9 Glacial cirques of Covão Cimeiro (a) and Covão do Ferro (b)

350

G. Vieira et al.

Fig. 27.10 Two of the best examples of glacial troughs in the Estrela Geopark. a The Loriga valley. b The Zêzere valley

27.4

Geosites

The geological sites of special interest in the Estrela Geopark have been classified into 124 Geosites, accompanied by an evaluation of their scientific, educational, scenic, ecological, cultural and touristic values. Each geosite has been characterized for its accessibility, infrastructure and vulnerability, with specific management plans being under development for the most vulnerable ones. Due to the large area of the Geopark, scattering of geosites and the large number of stakeholders involved in the application of law-abiding measures (e.g. municipalities, the Natural Park of the Serra da Estrela, SEPNA-GNR and the CCDR), 19 Integrated Management Areas (IMA) have been identified to facilitate management and geoconservation. These are well-defined spatial units, geologically or geomorphologically homogeneous, that include several neighbouring geosites and aim at promoting common management measures. Each IMA will have a management plan, which include a 4-year consolidation and development plan. The geosites have been classified according to eight types: (i) glacial and fluvioglacial (28%), (ii) bedrock geology (17%), (iii) Panorama Observation Points (15%), (iv) granite weathering landforms (14%), (v) periglacial and slope dynamics (9%), (vi) fluvial geomorphology (8%), (vii) hydrogeological (5%) and (viii) mining (4%).

27.4.1 Glacial and Fluvioglacial Geosites Glacial and fluvioglacial geosites are present mainly in the central area of the Geopark and were at the scientific core for the recognition by UNESCO. Three of these have been selected as scientifically relevant at the international level:

the granite columns of the Covão do Boi, the Lagoa Seca col moraine field and the Zêzere Glacial Valley. The granite columns of the Covão do Boi are located at 1840 m asl, at the eastern margin of the Torre Plateau (Fig. 27.12). The site shows a large set of natural, tor-like granite columns, about 2–5 m wide and 4–8 m high, whose shape is controlled by a dense orthogonal fracture network. Besides the scenic character of granite weathering features and its rarity, it is remarkable that they are located inside the glaciation limits and close to the headwalls of the Covão do Ferro cirque and of the Zêzere valley, where glacial erosion was very strong. Similar elevation of the top of the columns reflects the razing by the glacier flow in this difluence area and shows that the columns surfaced after deglaciation, probably after the removal of the saprolite by mass-wasting and water erosion. The geosite is next to the road, and access is very easy. The Lagoa Seca col moraine field is located at 1420 m asl, at the headwaters of the Beijames valley in the contact with the right (eastern) slope of the Zêzere valley. It shows a sequence of four moraine ridges testifying the diffluence of the Zêzere glacier over the col and several events close to the maximum ice extent (Fig. 27.13). Preliminary unpublished dating using cosmogenic nuclides indicates that the external moraine ridge has an age of 135 ka BP (MIS 6), while the inner moraines and TL-ages from silts from an infilled intramoraine basin show ages of about 30 ka BP, which would correspond to the timing of the last maximum ice extent (Vieira et al. 2017). The geosite also includes a sedimentary sequence showing a good example of lodgement and flow till (Vieira 2004). The Zêzere glacial valley is probably the main highlight of the Estrela Geopark, with its classic textbook U-shape cross-section and a large number of easily accessible and clear examples of glacial and periglacial landforms and

27

The Estrela Geopark—From Planation Surfaces to Glacial Erosion

351

Fig. 27.11 Granite weathering landforms are widespread in the non-glaciated areas of the Estrela Geopark. a Granite platforms and boulders in Penhas Douradas. b Fraga das Penas castle koppie close to

Penhas Douradas. c Fraga da Pena tor, close to Fornos de Algodres. d The Aguilhão castle koppie at the Beijames valley. e The Penedo Cogumelo and f the Penedo do Sino, two pedestal rocks

deposits (Fig. 27.10b). From the main road, or along several walking paths, it is possible to observe hanging valley, glacial cirques, glacial overdeepenings, riegels, roches moutonnées, small kame terraces and also evidence of paraglacial and periglacial activity, such as talus slopes, debris cones, rock falls, head-type and stratified slope deposits.

27.4.2 Periglacial and Slope Dynamics This class includes both relict Pleistocene periglacial deposits, which consist mainly of blockslopes, blockfields, screes and stratified slope deposits (see Vieira and Nieuwendam 2020), and deposits associated with paraglacial dynamics, such as taluses and debris cones, which have been

352

G. Vieira et al.

Fig. 27.12 Granite columns of Covão do Boi Geosite

Fig. 27.13 Lagoa Seca geosite with its main geomorphological features (orthomosaic over high resolution digital surface model). View towards the north-east

27

The Estrela Geopark—From Planation Surfaces to Glacial Erosion

353

Fig. 27.14 Incised meanders in the upper Mondego Valley, one of the fluvial geomorphology geosites

active during the Holocene. Some of the latter also show present-day activity, mainly following wildfire events and heavy rainfall, with the remobilization of either deeply weathered bedrock from the upper parts of the slopes or moraine deposits from the last glaciation. This situation occurs mainly along the Zêzere and Alforfa valleys, with sections showing high exposure to hazardous phenomena such as debris flows. These examples are used pedagogically for both visitors and locals, to emphasize the importance of mountain geohazards and the link between present-day phenomena and geomorphic inheritance, such as the presence of unstable moraine deposits in the upper parts of slopes.

However, geosites of this type are relatively scarce, which is due to the moderate scientific significance of most fluvial valleys, but also because some of them need further research. Competition with other geological highlights is also high, and hence, only the best examples have been selected for classification and promotion. Most geosites in this class have scenic, cultural (mainly local tradition) and also pedagogical values. They include various examples of waterfalls (Candieira, Caniça and Caldeirão), potholes and kettle holes (Vila Soeiro, Caniça and Mondego), meanders, both incised (Alto Mondego) and abandoned (Vale de Amoreira), and alluvial plains (Zêzere) (Fig. 27.14).

27.4.4 Granite Weathering Landforms 27.4.3 Fluvial Geomorphology Fluvial erosion has been the main responsible factor for the sculpting of the Estrela Geopark landscape, a fact that is evident in the deep valleys that incise the mountains.

Although not exclusive to the Estrela and also present in many other areas within the Central Iberian Zone in Portugal, granite weathering landforms are spectacular in the geopark and deserve special consideration in geosite

354

typology. The main value of these landforms is scenic, although some also have high scientific value for the understanding of long-term landscape evolution and denudation. Other than scarce descriptive studies, very little is known about the age of most granite landforms and on their genesis. Furthermore, numerous tors and boulders bear very high cultural relevance, especially those which show zoomorphic or anthropomorphic resemblances, such as the Cabeça da Velha (old-lady head) and Cabeça do Velho (old-man head). Most of granite weathering geosites are torlike landforms, as indicated in Sect. 27.3, but cases of inselbergs (Belmonte), mushroom boulders, pedestal rocks (Penedo do Sino) and balancing rocks are also present (Fig. 27.11). Several geosites are historical landmarks and show important archaeological heritage. For example, the Penedo do Sino, close to Celorico da Beira, shows traces of occupation since at least the fifth century BC, but more intensive in the Roman (first–fourth centuries) and High Medieval (ninth century to tenth century) periods, with the remnants of a Roman villa and also an interesting Christian necropolis with several graves dug in the monzonitic granite. Another example is the Castro de Santiago tor in the north of the Geopark, in the municipality of Fornos de Algodres. The tor in its prominent position was the ideal setting for a “castro”—a settlement of the chalcolithic period (Valera 1997), with an age of 3–2.8 thousand years BC. Besides the archaeological remnants, numerous examples of granite weathering are observable, such as boulders, weathering pits and grooves.

G. Vieira et al.

Lagoa Seca col, an area with a moraine cover over deeply weathered granite, which filters the rainwater promoting its outflow further downslope. Other significant geosites are the Manteigas and the Unhais da Serra thermal springs, with warm waters associated with the deep Bragança–Vilariça– Manteigas fault.

27.4.6 Bedrock Geology This wide category includes geosites of stratigraphic, petrographic and tectonic relevance, and aims at providing an overview of bedrock geology of the Estrela Geopark, with the focus on the educational and scientific values of the geosites. Some of these geosites are also relevant geomorphologically, as examples of rock control on landform development. The Folgosinho quartz dyke geosite is remarkable for the massive character of the dyke and for the resulting resistance relief, forming a small hill protruding above the village, that led to the installation of an exotic castle in the early twentieth century (Fig. 27.15). Quartz usage is widespread in pavements of the village, with the dyke having been subject to wolfram and tin mining in the 1940s and 1950s. Another example is the Poço do Inferno, showing a small gorge and pothole, carved in the contact metamorphism zone between the metasediments (hornfels) and granites at the Leandres valley, close to Manteigas.

27.4.7 Other Geosite Types 27.4.5 Hydrogeological Geosites The Serra da Estrela is the first orographic barrier that faces the moist Atlantic air masses that enter the Iberian Peninsula. As a consequence, it records very high annual precipitation values, surpassing 2500 mm and is seen as the “water tower” of Central Portugal, due to its contribution to large Portuguese rivers such as the Mondego and the Zêzere—Tagus. The interplay between meteoric waters, deep weathering and tectonics gave origin to several hydrogeological geosites, many of which have high economical value. The selected geosites are springs, both related to drinking mineral waters and to thermal waters, with associated spas. The Paulo Luís Martins spring in the upper Zêzere valley is a good example of a site with high economical, educational and cultural value, with its waters that flow at a constant 6 °C, bottled in the village of Manteigas. The geosite is located below the

The Estrela Geopark has a long history of mining activities, which are deeply embedded in the culture, tradition and socio-economics of the region. Although not geosites sensu stricto, several sites of mineral exploitation, both active and inactive, have been identified and are used and valued to emphasize the significance of georesources and problems associated with their exploitation. Finally, the Panorama Observation Points (POP) are selected locations offering good panoramic viewpoints allowing to analyse and interpret regional geomorphology and landscape organization, linking natural processes and human occupation of the territory. A total of 19 POPs have been identified in the EG, being located mostly at easily walkable distance from the roadside, and several of them have landscape interpretation panels. Excellent POPs are those located at Varanda dos Carqueijais (Fig. 27.4),

27

The Estrela Geopark—From Planation Surfaces to Glacial Erosion

355

Fig. 27.15 Folgosinho quartz dyke geosite

Varanda dos Pastores, Varandas de Avô, Linhares da Beira Castle, Cabeço de Santo Estevão, Mocho Real, Fraga Negra and Piornos (Fig. 27.16).

27.5

Conclusions

The Estrela Geopark is one of the largest Portuguese Geoparks, occupying a complex mountainous terrain, rich in geoheritage and in human history, and shared among nine municipalities. As such, the challenges for bringing all its assets and stakeholders together were large, but were surpassed with the work of the Association Geopark Estrela.

The Estrela benefits now of an international framework supported by a strong strategical implementation plan that provides a new set of instruments to promote sustainable development based on geodiversity, geoconservation and tourism. The region has thus the chance to move towards a more sustainable development strategy and to diversify its offer for visitors. This strategy will benefit both the municipalities at the core of the mountain, as well as those more peripheral, because the designed Geopark concept is truly holistic and links all the Estrela areas through strong ties based on landscape and geoconservation values, which had not been subject to a formal development framework before.

356

G. Vieira et al.

Fig. 27.16 Piornos Panorama Observation Point at a tor, with a view over the Nave de Santo António and towards the Alto da Torre. By the roadside, on the left, the lateral moraine of the Alforfa glaciers is clear.

Further upvalley, the Covão do Ferro cirque shows up. The Poio do Judeu moraine is visible on the right side, with the large boulder that names it

References

Ferreira N, Iglésias M, Noronha F, Pereira E, Ribeiro A, Ribeiro ML (1987) Granitóides da Zona Centro Ibérica e seu enquadramento geodinâmico. In: Bea F, Carnicero A, Gonzalo J, Lopez Plaza M, Rodriguez Alonso M (eds) Geologia de los Granitóides y Rocas asociadas del Macizo Hespérico. Editorial Rueda, Madrid, pp 37–51 Ferreira N, Vieira G (1999) Guia geológico e geomorfológico do Parque Natural da Serra da Estrela. Parque Natural da Serra da Estrela. ICN, Ministério da Economia, Inst. Geológico e Mineiro, p 111 Jansen J (2002) Geobotanical Guide of the Serra da Estrela. ICNF, Lisboa, p 276 Jansen J, Castro P, Costa L (2013) Economic-ecologic interactions in the Serra da Estrela, Portugal. Chapter 4, p. 66–90. In: Diemont WH, Heijman WJM, Siepel H, Webb NR (eds) Economy and ecology of heathlands. KNNV Publishing, Zeist, p 462 Lautensach H (1929) Eiszeitstudien in der Serra da Estrela (Portugal). Zeitschrift für Gletcherkunde 17:324–369 Martín-González F (2009) Cenozoic tectonic activity in a Variscan basement: evidence from geomorphological markers and structural mapping (NW Iberian Massif). Geomorphology 107:210–225

Azevedo MR, Valle Aguado B (2006) Origem e Instalação de Granitóides Variscos na Zona Centro-Ibérica. In: Dias R, Araújo A, Terrinha P, Kullberg JC (Coord) Geologia de Portugal no Contexto da Ibéria, pp 107–122 Cabral FAVP (1884) Vestígios glaciários na Serra da Estrela. Revista de Obras Públicas e Minas, Lisboa, pp 435–459 Cabral J (1995) Neotectónica em Portugal Continental. Mem Inst Geol Min 31:265 Cabral J (2012) Neotectonics of mainland Portugal: state of the art and future perspectives. J Iberian Geol 38(1):71–84 Daveau S (1969) Structure et relief de la Serra da Estrela. Finisterra 4 (7):33–197 Daveau S (1971) La glaciation de la Serra da Estrela. Finisterra— Revista Portuguesa de Geografia 6(11):5–40 Ferreira AB (2005) O Ambiente Físico. Vol. I de Geografia de Portugal, dirigida por Carlos Alberto Medeiros. Lisboa, Círculo de Leitores, p 495

27

The Estrela Geopark—From Planation Surfaces to Glacial Erosion

Martin-Serrano A (1988) El relieve de la region ocidental zamorana. La evolucion morfológica de um borde del macizo hespérico. Inst. de Estudios Zamoranos Florien de Ocampo, Zamora, p 311 Meireles C, Castro P, Ferreira N (2014) On the presence of Cadomian angular unconformity in Beiras Group (Central Portugal): cartographic, lithostratigraphic and structural evidences. Comunicações Geológicas 101(I): 495–498 Migoń P, Vieira G (2014) Granite geomorphology and its geological controls, Serra da Estrela, Portugal. Geomorphology 226:1–14 Neiva AMR, Williams IS, Ramos JMF, Gomes MEP, Silva MMVG, Antunes IMHR (2009) Geochemical and isotopic constraints on the petrogenesis of Early Ordovician granodiorite and Variscan two-mica granites from the Gouveia area, central Portugal. Lithos 11:186–202 Oliveira JT, Pereira E, Ramalho M, Antunes MT, Monteiro JH (1992) Noticia Explicativa da Carta Geológica de Portugal, escala 1/500000, Serviços Geológicos de Portugal Pais J, Cunha PP, Pereira D, Legoinha P, Dias R, Moura D, Silveira AB, Kullberg JC, González-Delgado JA (2012) The Paleogene and Neogene of Western Iberia (Portugal). A Cenozoic record in the European Atlantic domain. Springer, Heidelberg, p 156 Ribeiro A (2013) A Evolução Geodinâmica de Portugal; os ciclos ante-mesozóicos. In: Dias R, Araújo A, Terrinha P, Kullberg JC (eds) Geologia de Portugal no contexto da Ibéria. Univ, Évora, pp 15–57

357 Ribeiro A, Kullberg MC, Kullberg JC, Manuppella G, Phipps S (1990) A review of Alpine tectonics in Portugal: foreland detachment in basement and cover rocks. Tectonophysics 184:357–366 Ribeiro O (1954) Estrutura e Relevo da Serra da Estrela. Bol Real Soc Esp Hist Nat (homenaje E. Hernández-Pacheco) 549–566 Valera AC (1997) O Castro de Santiago (Fornos de Algodres, Guarda): aspectos da calcolitização da bacia do Alto Mondego. Edições Colibri, Lisboa, p 192 Vieira G (2004) Geomorfologia dos planaltos e altos vales da Serra da Estrela. Ambientes frios do Plistocénico Superior e dinâmica actual. Dissertação de Doutoramento em Geografia. Universidade de Lisboa, p 724 Vieira G (2008) Combined numerical and geomorphological reconstruction of the Serra da Estrela plateau icefield, Portugal. Geomorphology 97:190–207 Vieira G, Nieuwendam A (2020) Glacial and periglacial landscapes of the Serra da Estrela. In: Vieira Z, Mora (eds) Landforms and landscapes of Portugal. Springer, Berlin Vieira G, Palacios D, Mora C, Andrés N, Vasquez Selem L, Castro E (2017) Lagoa Seca: a key geosite in the Estrela Aspiring Geopark. International Conference Managing Mediterranean Geoheritage. Manteigas, 6–7 May 2017, AGE

28

Naturtejo UNESCO Global Geopark: The Culture of Landscape Carlos Neto de Carvalho and Joana Rodrigues

Abstract

Keywords

The Meridional Meseta Naturtejo Geopark was the doorway for the development of several geoparks in Portugal seeking to become part of a formal UNESCO initiative under the Global Geoparks Network. The outstanding geological heritage summing 176 geosites is part of an ancient etchplain-type landscape where residual reliefs and deeply incised rivers, including the Tejo (Tagus), coexist with Variscan and Alpine orogeniesrelated tectonic landforms, between the Southern Plateau and the Iberian Central Mountain Belt. Local identity is strongly bonded to geological landscapes, a relation that is being used to promote the territory as a new and different nature tourism destination in the domestic and foreign markets, and to foster projects for local sustainable development. The approach of the Naturtejo Global Geopark is to promote networking within the territory in both public and private sectors and with other geological-related institutions and geoparks in subjects such as heritage protection and use, formal and non-formal education and sustainable economy based on local resources.

Geopark UNESCO Geological landscapes Geocultural heritage Territorial marketing Geotourism

C. Neto de Carvalho (&)
J. Rodrigues Serviço de Geologia, Centro Cultural Raiano, Câmara Municipal de Idanha-a-Nova., Portugal e-mail: [email protected] J. Rodrigues e-mail: [email protected] C. Neto de Carvalho Instituto D. Luiz, Faculdade de Ciências da Universidade de Lisboa, Lisbon, Portugal J. Rodrigues Naturtejo, EIM, Castelo Branco, Portugal Centro de Geologia da Universidade do Porto e Centro de Ciências da Terra, Universidade do Minho, Castelo Branco, Portugal




28.1









Introduction

A geopark is a clearly defined territory focused on protection and promotion of geological heritage which represents a significant, internationally recognized piece of Earth history, with a management structure provided with the territorial management instruments able to foster local communitybased sustainable development (McKeever and Zouros 2005). The Naturtejo Global Geopark is included in the European and Global Geoparks Network since 2006 and the National System of Classified Areas since 2008, and since 2015 in the new International Geoscience and Geoparks Programme of UNESCO. The area, with more than 5000 km2, shows a unique inclusive heritage linking geology, geomorphology, biology and human activities (Fig. 28.1). The Naturtejo is located between the Alto Alentejo and the Beira Baixa regions bearing an ancient and mostly flat landscape, the Meridional Meseta, a vast peneplain that widens across the Portuguese border eastwards towards the interior of Iberia. The Alpine orogeny shaped the Naturtejo Geopark territory as a staircase that starts from the Tagus fluvial terraces near Portas de Ródão Natural Monument, finds major steps in Ponsul and Sobreira Formosa-Grade fault scarps and reaches beyond Alvelos and Gardunha Mountains, with the summit at 1227 m asl (Fig. 28.2). Quartzite ridges, Cenozoic sedimentary buttes and granite inselbergs rising 350 m above the planation surface, pinpoint its flatness from afar. The Tagus Tejo river system carves the plateau, crossing the Naturtejo Geopark along a 65 km section, flowing between 130 m asl, at the confluence of the Erges/Erjas River in the East, and 44 m asl, at the

© Springer Nature Switzerland AG 2020 G. Vieira et al. (eds.), Landscapes and Landforms of Portugal, World Geomorphological Landscapes, https://doi.org/10.1007/978-3-319-03641-0_28

359

360

C. Neto de Carvalho and J. Rodrigues

Fig. 28.1 Geomorphological map of the Naturtejo UNESCO Global Geopark territory (adapted from Ferreira 1980)

confluence of the Ocreza River towards Southwest. There, the fauna and flora flourish near vertical valley cliffs, up to 150 m high. The International Tagus Tejo Natural Park, a UNESCO Biosphere Reserve since 2016, protects these major habitats for conservation of biodiversity. Also, along the Tagus Tejo valley, the Portas de Ródão shows up as a national natural monument to the geological evolution of the landscape. The geopark area shows the sedimentary record of three major global icehouse periods: the first one in Neoproterozoic that burst the dawn of metazoan life (e.g. Fedonkin et al. 2007); the second one in the Late Ordovician, responsible for one of the most devastating mass extinctions that Earth has ever faced (e.g. Finnegan et al. 2011); and the last one in the Late Pleistocene, resulting in the extinction of large mammals in Europe, reflected in some of the last evidences of the Neanderthals and of the straight-tusked elephant collected at Foz do Enxarrique (e.g. Kolbert 2014). But outstanding evidence is also found on the Ordovician major biodiversification event and opening of the Rheic Ocean (e.g. Nance et al. 2010), present at palaeontological sites such as the Ichnological Park of Penha Garcia, and Talhadas and Muradal geosites, including a magmatic event registered

by Salvaterra do Extremo, Zebreira and Idanha-Oledo granitoids (Shaw et al. 2012), of the major stages of the Variscan Orogeny (e.g. Ribeiro et al. 2007) at the Muradal and Talhadas Mountains, and concomitant granitization, such as at Castelo Branco, Monsanto–Penamacor and Nisa (Antunes et al. 2008; Solá et al. 2010), and the fault scarps reactivated during later stages the Alpine orogeny, controlling the development of sedimentary basins such as Sarzedas or Ródão-Moraleja (Cunha and Martins 2004). There are evidences of human settlement for exploitation of natural resources since the Lower Paleolithic (Cunha et al. 2016). Gold opencast Roman mining is particularly evident with significant changes in the riverside landscapes, such as in Conhal do Arneiro-Charneca, Ponsul, Termas de Monfortinho, and Presa-Covão do Urso. But other civilizations and cultures also left important legacy which includes the vestiges of the megalithic culture and tomb builders of Neolithic to Calcolithic ages, the upper Palaeolithic to Iron Age rock art of the Tejo valley, the Roman and Visigoth city of Idanha-aVelha, the Templar and Hospitaller castles in once changing borders, the Jewish quarters of Castelo Branco, Penamacor and Medelim, the Historical (Idanha-a-Velha and Monsanto) and Schist (Álvaro, Figueira, Martim Branco and Sarzedas)

28

Naturtejo UNESCO Global Geopark: The Culture of Landscape

361

Fig. 28.2 The two main geomorphological features of the UNESCO Naturtejo UNESCO Global Geopark: the southern or meridional Meseta and the Central Iberian Mountain Belt: a The Castelo Branco Platform (or Lardosa applanation) on the tardi-Variscan granites of Castelo Branco plutonite, the same that constitute the summit of the geopark in the Gardunha Mountain (closer view); b The impressive Monsanto granite inselberg rise over 350 m the Meridional Meseta;

c Central Iberian Mountain Belt at Malcata–Sierra de Gata Mountain (photograph: Ana Ramos). The altitude difference to the Meridional Meseta is of over 700 m; d The deep dendritic pattern of stream incision on the schist mountains composing the Central Iberian Mountain Belt, at Corgas Mountain, is only oriented when it is controlled by Variscan faults

villages, as well as the Muradal-Talhadas Defensive Line built in the eighteenth century for the Fantastic Wars. Living the landscape, following the harvest and shepherding rhythms, left an important record in local culture. Examples are present in popular religion customs, particularly during Easter and especially in Idanha-a-Nova, as well as the Christmas Madeiro priviledged in Penamacor, and in sacred natural places such as Monsanto and Our Lady of Almortão, as well as in music diversity, with local instruments such as the Adufe, the Zamburra or the Beiroa guitar, or even handcrafting, like the ‘Pedrado de Nisa’ pottery and the Marafona dolls. Together with the municipalities that constitute the territory, i.e. Castelo Branco, Idanha-a-Nova, Nisa, Oleiros, Penamacor, Proença-a-Nova and Vila Velha de Ródão, the Naturtejo Geopark adds to previous local culture-related projects of rural development on understanding and enjoyment of a vast and highly significant geomorphological landscape that conditioned human settlement, land use and

traditions. The added value of geological time to the three-dimensional landscape is bringing new perspectives for tourism development, territorial marketing, nature and historical heritage conservation and use, and outdoor education.

28.2

Geology and Geomorphology

The Naturtejo Geopark is located in Central Portugal along the border with Spain (Extremadura). Castelo Branco is the only city of a territory with a population of 90,831 inhabitants (2011), situated 250 km from Lisbon and 450 km from Madrid. The geopark is cross-cut by the Tagus Tejo River, between the Beira Baixa and north-eastern Alentejo, mostly included in the Iberian Massif in the Central Iberian Zone, but reaching the Tomar-Córdoba Shear Zone and even the Ossa-Morena Zone in the southernmost part at Alpalhão (Neto de Carvalho and Rodrigues 2012a).

362

C. Neto de Carvalho and J. Rodrigues

Fig. 28.3 Examples of the widely distributed Appalachian-type quartzite ridges across the territory of Naturtejo Geopark: a Griffon vulture´s view of the Ródão syncline at Portas de Ródão, between the tectonic depressions of Vila Velha de Ródão, controlled by the development of the Ponsul fault towards NE, and the graben of Vilas

Ruivas-Arneiro, between the Ponsul fault at Serrinha (to west) and the Variscan thrust fault of Vinagra-Portas de Ródão (to east); b Penha Garcia-Cañaveral syncline; c Muradal monocline with a NNW–SSE direction parallel to Castelo Branco-Unhais-o-Velho alignment (behind)

The general geomorphological evolution of the Iberian Meseta is well known since the pioneering work of Orlando Ribeiro in the 1930s and 1940s (see below), with the comprehensive updates of Cabral (1995), which included comparisons with Spanish contributions, Feio and Daveau (2004), and the studies developed in the frame of a wider tectonostratigraphic and paleoclimate model for the Iberian Massif by Cunha and Martins (2004), Cunha et al. (2005, 2008, 2019) and Cunha (2019). The area corresponds to a wide etchplain with Appalachian-type quartzite ridges (Fig. 28.3), sparsely distributed and up to 350 m high, and granite inselbergs (Fig. 28.2b). After the Betic stage of the Alpine orogeny (latest 10 Ma) this ancient etchplain was divided into three main tilted areas: The Alto Alentejo

surface (200–320 m), the Castelo Branco Platform (350– 450 m; Fig. 28.2a, c) and the southern parts of the Central Cordillera (900–1000 m, but reaching here up to 1227 m; Fig. 28.2b, c), by reactivation of late Variscan thrust faults in a pop-up tectonic regime (Cabral 1995). The main NW–SE direction and distribution of the quartzite ridges is directly related with the Variscan direction and intensity of progressive deformation in the southern part of the Central Iberian Zone after 400 Ma ago. Quartzite ridges are commonly divided into misaligned mountain segments due to strike-slip movements of Variscan faults, as in the Monforte da Beira-Unhais-o-Velho or Talhadas (Fig. 28.5c) mountain structures. Some of the ridges reach over 1000 m of displacement, as in the highly educative case of Pedras

28

Naturtejo UNESCO Global Geopark: The Culture of Landscape

Brancas-Venda kinematic marker at Sobreira FormosaGrade fault (Fig. 28.5c), or São Martinho-Monforte (Fig. 28.5b) and Fonte Longa-Piçarra Vermelha displacements at the Ponsul fault. The Variscan orogeny is also responsible for the fault control of quartzite fold limbs, with thrusts and backthrusts from early Variscan stages doubling the thickness of quartzite sequences or developing mechanical contacts with shales (fault gauge) where hydrothermal fluids circulated and precipitated as quartz veins (cm-thick, occasionally reaching some tens of metres thick and developing 12 km long, almost uninterrupted quartz crests as near Meimão), fostering the regional metamorphism of the Armorican Quartzite Formation and making the siliciclastic sequence much more resistant to weathering. During the Mesozoic, deep weathering of the Iberian Massif prevailed in sub-to-equatorial paleolatitudes. The leveling of quartzite summits shows the development of the Initial Surface of the Meseta during the Late Jurassic (Cabral 1995; Martin-Serrano 2000; Fig. 28.3a), particularly clear in Ródao and Penha Garcia synclines (Fig. 28.3b). Also, in Penha Garcia, the Alagoas plateau is found (Sequeira and Serejo Proença 2004), a 650 m-high remnant of the applanation decoupling sometime between the Late Jurassic and Late Cretaceous. After the Late Cretaceous, the deep weathering mantle was removed by erosion leading to the Meseta Fundamental Surface (Cabral 1995; Martin-Serrano 2000), dated as of pre-middle Eocene age (Cunha and Martins 2004). This polygenetic peneplain cuts metasedimentary sequences and thin-to-very coarse-grained granitoids in such a perfect way as in Nisa, Amieira do Tejo, Alagoa or Castelo Branco (Fig. 28.2a), OledoIdanha-a-Nova and Zebreira plutonites, but left residual landforms in different types of granitoids, such as São Gens Lower Ordovician granodiorites, Gardete or the impressive Monsanto inselbergs in tardivariscan monzonite granites, the later of which rising to 350 m above the plain (Fig. 28.2b). The asymmetric shape of the Monsanto inselberg, made of alternating benches and ramps, may show the evolution of the landform in direct relation with the weathering-erosional tectono-climatic cycles involved in the evolution of the Meseta Fundamental Surface (Rodrigues et al. 2009). After the Eocene and particularly after the Tortonian (Miocene), the Central Cordillera Mountain Belt popped-up and became divided into several horsts as a result of Alpine orogenic mechanisms with a NE-SW trend. Allostratigraphic, alluvial fan to braided river sequences were deposited in semiarid or seasonal (dry–wet) climate between the Eocene and Pliocene, partially fossilizing the Appalachian type of relief. The discontinuity bounded sequences may have been an applanation expression between major tectonic paroxysms (Cunha and Martins 2004). RódãoMoraleja and Sarzedas Basins (Fig. 28.4) were formed in strong relation with the vertical reactivation of Variscan

363

faults, such as Ponsul, Sobreira Formosa-Grade and Rapoula faults. The Estreito plateau shows the net slip of more than 400 m along the Sobreira Formosa fault displacing the Meseta Fundamental Surface (Fig. 28.4b). Even larger vertical displacements up to 600–700 m can be found in the Gardunha and Malcata Mountains (Fig. 28.2). However, the Ponsul fault scarp is the largest tectonic landform, 120 km long and with a displacement of up to 150 m in some sectors, such as the Idanha-a-Nova granitic scarp (Dias and Cabral 1989; Fig. 28.5). Along the fault zone, at Rosa Cometa and Rochão, it is possible to find polygenetic reactivation creating two different fault scarps in the fault zone and showing the spectacular displacement of the Idanha-a-Nova Lower Ordovician granodiorite over the Cenozoic arkoses at Devesa (Fig. 28.5a). In Rochão, the Ponsul River is controlled by a younger fault plane and runs for 8 km in a 150 m-deep valley. The Ponsul’s hanging wall has a general tilt trend towards the fault scarp, and the arkoses from Eocene–Oligocene age can be found up to 400 m high at Marota-Ovelheiros-Cabeço Alto (Rosmaninhal). Climate changes after the Late Pliocene are responsible for the last imprint in the landscape made by the incision of the main river systems responding to the evolution of the endorheic pre-Tagus towards the Atlantic. The Portas de Ródão area is highly significant to understand the Tejo incision in response to tectonoclimate changes (Cunha et al. 2005, 2008). Several mesa-like hills in the Falagueira Formation (Montalvão, Fratel, Cabeço de Boi: up to 325 m high) represent the alluvial plain of the pre-Tejo just before the incision and capture in Portas de Ródão (Cunha and Martins 2004). The Tagus flows generally from NE to SW, but in the Ródão area follows the quartzite crest to the NW along a fault that is crossed by the ENE–WSW Senhora da Alagada fault, allowing the river to cross Talhadas and Perdigão Mountains at Portas de Ródão in a major fault intersection (Fig. 28.3a). Six terraces representing erosional–aggradational events were developed in the Vila Velha de Ródão-Charneca area below 180 m asl and are dated for the last million years (Cunha et al. 2008). Asymmetries of the terraces in both sides of the Tejo are good indicators of neotectonic activity in the area. At least four terraces are developed along the Ponsul River at the Malpica bridge at 181–189, 159–176, 141–146 and 133–136 m asl. At the confluence with the Vidigal stream, the Ponsul valley is more than 1000 m wide, the riverbed is flat and the valley slopes are cut almost vertical in the Eocene carbonates reminding an oued landform typical for semiarid climates (Fig. 28.6c). Most of the river incision would be also controlled by reactivation of previous existing faults, such as along the Ponsul River, Medelim, Godinha, Fonte Santa and Almaceda streams or several sections of the Tejo (Fig. 28.5).

364

C. Neto de Carvalho and J. Rodrigues

Fig. 28.4 Central Iberian rise between the Eocene and the Pliocene led to deposition of alluvial–fluvial sediments covering the Meseta Surface: a The Ponsul gorge at Penha Garcia syncline’s south-western limb and the residual landforms of Murracha, Murrachinha and Pedras Ninhas (Murracha Group, post-Tortonian) sealing the Ponsul fault (in the

horizon; photo: Jesus Salazar); b The Magarefe butte in the footwall of the Sobreira Formosa-Grande fault also showing the southern termination of the Muradal monocline which was the source for the coarser-up sediments that constitute the butte; c Sarzedas flat-top mesa marking the applanation at the Lower Pliocene

The Mesão Frio fault-line valley shows a NNW–SSE direction for 8 km, and the Valdedra at Malcata Mountain, with a N–S direction, over 12 km (Fig. 28.5d).

River incision reaches up to 150 m at the Tejo valley along the Spanish border (International Tejo) and more than 260 m at Portas de Ródão. The epigenic gorges were formed

28

Naturtejo UNESCO Global Geopark: The Culture of Landscape

365

Fig. 28.5 Tectonic landforms: a Ponsul fault scarp at Idanha-a-Nova. The latest vertical scarp affecting the granitoids contrasts with the former one (in closer plan) almost destroyed by erosion; b The Ponsul fault at Castelo Branco responsible for the dextral displacement of S. Martinho quartzite hill (in the hangingwall) from the Monforte Mountain (in the footwall); c The intersection of Variscan faults with

the Tallhadas Mountain is responsible for the development of serial dextral-displaced quartzite ridges; d Valdedra fault-line valley; e Nisa River section controlled by fault; f Intersection of faults at Tejo valley, where the main E–W fault controlling the river incision was responsible for the dextral displacement of a NE–SW fault plane (photos b, d, f: Jesus Salazar)

in different lithotypes, their position controlled by the main fracture directions and fault intersections, such as the Erges gorges in granitoids or Almourão and Penha Garcia gorges

in quartzites, up to 300 m deep (Fig. 28.7). The Central Iberian Belt summits are affected by the upstream erosion and pop-up tectonics. The middle Zêzere valley is developed

366

C. Neto de Carvalho and J. Rodrigues

Fig. 28.6 River valleys in the Naturtejo Geopark: a Zêzere River trenched meanders; b Nisa River meanders incising the Beiras Group (photograph: Jesus Salazar); c Ponsul River section showing ‘oued’

configuration; d The wide valley of Meimoa filled with sediments from the pre-Bazágueda

Fig. 28.7 Examples of epigenic gorges showing inadaptation of the present drainage system to a previous existing geotectonic condition: a Portas de Almourão quartzite gorge deeply affected by D1 and

tardi-Variscan fault intersections; b Erges gorge on the Salvaterra do Extremo-Cabeza de Araya granites (photograph: Jesus Salazar)

into a suite of entrenched, kilometre-size meanders controlled by the main fracturing direction between the Vermelha Mountain horst (Mosteiro-Valhelhas fault) and the Cebola fault (Fig. 28.6a). The Isna River is controlled by the

Sertã-Proença-a-Nova fault-line valley in the area of Maljoga-Aldeia Ruiva. Valleys are usually deeply incised and narrow between smooth linear mountain ridges in shales (Lourenço 1996;

28

Naturtejo UNESCO Global Geopark: The Culture of Landscape

367

Fig. 28.8 Pedestal rocks in granites of Nisa (a and b) and Castelo Branco (c and d): a Lameirancha pedestal rock with a very large cap and narrow base; b Tapada do Bião pedestal rock, the largest record in the Naturtejo Geopark; c Tapada dos Carvalhos pedestal rock with the

evidence of at least 20 weathering-denudation cycles marked in the narrower base; d Barrocal Park’s most unusual pedestal rock showing strong asymmetry of the cap following the slope direction, as well as weathering-denudation cycles marked in the narrower base

Fig. 28.6b). But there are exceptions worth to mention. That is the case of the Meimoa valley, with an E–W direction (Fig. 28.6d). This valley, more than 1 km wide, shows the bottom covered with Pleistocene sediments and represents the former valley of the Bazágueda River as tributary of the Zêzere River and before being captured by the Erges River. In the granite massifs of Castelo Branco, Nisa and Penamacor–Monsanto, a wide range of textbook-quality granite landforms are present (Neto de Carvalho 2004; Silva 2005; Rodrigues and Neto de Carvalho 2012; Figs. 28.8 and 28.9). At Gardunha Mountain, some small plateaus at the ‘brandas’ (former seasonal settlements) of AndorinhaBarrocas do Mercado and Cavaco, 850 m asl high on average, may be remnants of the Fundamental Surface controlled by reverse faulting. In the Castelo Branco Platform, most of the Cenozoic Formations were eroded towards the lower areas, with the exception of Sarzedas, Magarefe and Cantareira buttes at Sarzedas Basin, and Murracha, Murrachinha and Pedras Ninhas at Ródão-Moraleja Basin

(Fig. 28.4). The Meseta Fundamental Surface was generally slightly retouched by the incision of the drainage system, as it is shown by the general exposure of the bedrock in granite areas, except for the Lardosa regolith, and the development of pedestal rocks both in Castelo Branco and Nisa granites, reaching up to 6 m high, being asymmetric according to the gentle slope orientation and evidencing more than 20 weathering-erosion cycles marked in the narrower base (Rodrigues and Neto de Carvalho 2013; Fig. 28.8). Geomorphological landscapes are considered a geological heritage in Naturtejo Geopark since the pioneering works of Carvalho (1999) and Cunha and Martins (2000). The National Inventory of Geosites of international or national scientific relevance under ProGEO guidelines included 13 geosites in the area of Naturtejo Geopark, 7 of them being geomorphosites (Pereira et al. 2013). This shows the high scientific significance of the geopark’s landscape that can and is being valued for the benefit of local communities.

368

Fig. 28.9 Minor granite landforms in Naturtejo Geopark recognized by their relevance: a Polygonal weathering in a boulder protected under law by the municipality of Castelo Branco (Gardunha); b Boulder with tafoni showing honeycomb weathering is the central piece of the land art route at the village of Alpalhão (Nisa); c Development of polygonal weathering associated with joints and surfaces modified by hydrothermal activity during the cooling of the granite. These landforms and granite landscapes where the main reason for the protection of

C. Neto de Carvalho and J. Rodrigues

Gardunha Mountain as Regional Protected Landscape; d Large giant’s kettles in the bottom of the Salvaterra do Extremo gorge is a very important habitat for fish species during summer in International Tejo Nature Park; e ‘Thirteen Bowls’ at the centre of the old medieval village of S. Miguel of Monsanto has been ‘explained’ by legends but the human print in their natural form still cannot be discarded; f Examples of weather pits in a tilted boulder, with an organization similar to the ‘Thirteen Bowls’ (Gardunha)

28

Naturtejo UNESCO Global Geopark: The Culture of Landscape

28.3

The Naturtejo Geopark: ‘Stones Made of People’

The landscape architecture in the Naturtejo Global Geopark reveals more than 340,000 years (Cunha et al. 2012) of direct intimacy, and almost symbiotic relationship between technological, social, economic, demographic and cultural evolution, and the geological resources (Fig. 28.10a), many times elevated to the intangible: ‘We, the Monsanto people, already love that stone (…), the one from Monsanto. All of them at Monsanto.’, are the famous words of Cesaltina Gilo, a local. Monsanto inselberg is the best example of how a landmark populated since at least the Neolithic times, and later in the Iron Age transformed into a formidable stronghold, has reached a sacred dimension for the local inhabitants, keeping celebrations to the mountain that survived to cultural and religion acculturations since Roman times (Divine Holy Cross), and is now destination for the new pilgrimages of the global tourism (Fig. 28.10b). The heritage

Fig. 28.10 Human activities’ impact in the landscape of Naturtejo Geopark: a Quartzite lithic tools dated from Lower Paleolithic very common in the terraces of the Tagus Tejo River valley (Fonte Santa, Rosmaninhal); b Monsanto inselberg a landmark in the landscape of the

369

value of cultural landscapes from Naturtejo Global Geopark can be also measured by the diversity of assimilation modes of the builders and players of cultural environments: from the shepherds and peasants, poets and writers to the scientists of the landscape (Neto de Carvalho et al. 2010). The abundance of rock art from the Paleolithic to the present days across the region, from the summits of the Alvelos Mountains to the valleys of the Ocreza and Tagus Tejo Rivers, in the Tagus Tejo Valley Prehistoric Art Complex, and the plains of Rosmaninhal, take us to the shepherd’s imaginary in the understanding of landscape diversity, their values and practical uses. In the written expression of the subject, Fernando Namora, a famous Portuguese writer from the twentieth century suggested for Nobel Prize in 1981, was unique among writers in first-hand description of the landscapes’ humanism of this territory, in his ‘neo-realistic’ novels, Casa da Malta (1945), Minas de S. Francisco (1946), Retalhos da Vida de um Médico (1949 and 1963), A Noite e a Madrugada (1950) or A Nave de

Meseta (photo: Jesus Salazar); c Conhal do Arneiro Roman gold mine in Tagus Tejo River; d The impact on the landscape (and biodiversity) of the areas prepared for eucalyptus

370

Pedra (1975). But no other comprehended the natural and cultural dimensions of these landscapes, with a holistic approach, better than the geographer Orlando Ribeiro. As it is demonstrated by more than 300 papers and books published since 1937, and for more than 50 years, as well as several thousand photos of this region, Orlando Ribeiro became the great Master of the scientific knowledge of the landscapes, and this territory was his atelier (e.g. Ribeiro 1939a, b, 1942, 1943a, b, 1949a, b, 1968). Like in the past, people nowadays look for their modus vivendi closer to the landscapes, basing their traditions and life styles in the landforms, the microclimates, the crops provided by soil labour, as well as in the thermal waters (Termas de Monfortinho, Nisa, Águas) and mineral wealth of the substrate. During the Roman Empire period, river landscapes were subjected to profound changes for gold mining by the washing of millions of cubic metres of terrace deposits, hundreds of hectares of tailing piles still persisting in the present along the valleys of Tejo, Erges and Ocreza Rivers that are very important geoarcheological heritage (Fig. 28.10c). The meagre soils of the large schist areas were responsible for the major transformations of the landscape in the last five decades with the replacement of the Mediterranean forest and goat pastures by the introduction of the eucalyptus to supply the expanding paper industry (Fig. 28.10d). For these reasons, it is important to elevate the landscape condition to the dimension of patrimony (Neto de Carvalho et al., 2006) resulting in a sustainable ecological use and in the right to the socio-cultural integrity of the landscape. Naturtejo Global Geopark was constituted in this fundamental basis (Neto de Carvalho and Rodrigues 2010). The great success achieved by geoparks in this short period of existence is their capacity of social organization to defend local interests, as well as the management of natural and cultural resources (e.g. McKeever and Zouros 2005; Ramsay et al. 2010). A geopark is a strategy of development by local authorities, whose decision-making represents the interests and demands of local communities concerning social–environmental issues. This strategy of development is formed by innovative projects put into practice and generating social, cultural, environmental and/or economic revenues in benefit of local populations (Fig. 28.11b). The Naturtejo Geopark management reunites and organizes the positive feedback of scientific knowledge and the timeless know-how of local culture, their daily application by technicians and pedagogical communication by teachers, the liability claims and actions of NGOs and the demands and ideas of the entrepreneurs for the building of a collaborative development plan. A territorial marketing plan relied upon the umbrella brand UNESCO GEOPARK fosters local education for a more interventional citizenship, reinforces the mechanisms of participative environmental protection,

C. Neto de Carvalho and J. Rodrigues

motivates self-esteem and cultural proud, stimulates new business opportunities and, not less important, establishes new destinations where humans can be closer to Nature (Neto de Carvalho et al. 2011). A geopark may bring a mainly rural region in to wider, global recognition. However, its recognition as brand of environmental high-quality and sustainability is still officially missing in Portugal. An active participation in a geopark project is guaranteed by cooperation networks, from local community to supranational levels, such as the Global Geoparks Network Association and EU funding programmes and may contribute for an inclusive approach to local sustainability, economic and life quality growth, as well as for a stronger conservation and qualification of local culture and environment (Neto de Carvalho et al. 2009a). In the Portuguese-spoken countries, there are presently four UNESCO geoparks in Portugal (Naturtejo, Arouca, Azores and Terras de Cavaleiros Geoparks) and one in Brazil (Araripe Geopark), which are key-witnesses of Earth History. As one of the pioneer Portuguese-spoken geopark projects (together with Araripe), Naturtejo Global Geopark is managed by Naturtejo, E.I.M., a public–private partnership constituted in 2004 by the Association of Municipalities ‘Natureza e Tejo’, which includes 7 municipalities forming the geoparks’ territory and 24 private companies from the region. Naturtejo intervention areas are the consultancy to the protection of the geological heritage and the integrated value with the remaining natural heritage, together with the historic-cultural legacy, the development of education programmes for schools and the organization of local tourism sector under the strategic regional umbrella of Nature Tourism (Neto de Carvalho and Rodrigues 2010). Naturtejo Geopark is a Tourist Brand of the Center of Portugal Tourism Body, being included in the National Strategic Plan for Tourism as a first priority for development of Nature Tourism-related investment projects (THR 2006). The Naturtejo Global Geopark includes 176 geosites inventoried during the Project of Geological and Geomining Assessment that began in 2004 (Neto de Carvalho et al. 2009b; Neto de Carvalho and Rodrigues 2012a, b, c) and covering more than 6% of the country’s total area. In this geodiversity with some singular characteristics, 17 so-called geomonuments (sensu Carvalho 1999) were selected according to their landscape complexity, scientific singularity or representativeness, pedagogical applicability, cultural relevance, scenic imposing and high aesthetics, in inverse measure of their vulnerability, to explore their educational and geotourist potentialities. These 17 geomonuments altogether tell the geological history of Naturtejo Global Geopark in the last 600 million years and represent the milestones for the approval of the territory in the European and Global Geoparks Network under UNESCO (Neto

28

Naturtejo UNESCO Global Geopark: The Culture of Landscape

371

Fig. 28.11 Protected geodiversity-related habitats for biodiversity of the Naturtejo Geopark: a The rock walls of Tejo Internacional Nature Park are essential nesting habitats for a high diverse avifauna including the black stork and different species of vultures; b Murracha hillside debris is the privileged habitat for ‘Rosa-Albardeira’ Paeonia broteroi, an endangered species of Peony that is being valued for tourism

development by the village of Toulões, ‘The Peony Village of Portugal’; c The Regional Protected Landscape of Gardunha Mountain aims to protect and promote the granite landscapes and habitats, including traditional land use and sustainable activities of this area between Castelo Branco and Fundão municipalities

de Carvalho 2005). Part of them were already protected under the national laws for nature conservation and culture heritage (International Tejo Natural Park and since 2016 UNESCO Biosphere Reserve, Gardunha Regional Protected Landscape, Natura 2000—sites Malcata, Gardunha, Nisa/Laje de Prata and S. Mamede, Monsanto National Monument; Fig. 28.11), some others are being protected mainly for their geological heritage (Portas de Ródão Nature Monument, Vale do Ponsul–Penha Garcia Municipal Site, Gardunha Landforms Municipal Sites, and the projects Almourão Regional Nature Park or the Barrocal Park in the

city of Castelo Branco) and through integration in the territorial management plans (Nisa, Oleiros, Proença-a-Nova, Vila Velha de Ródão, Penamacor and Gardunha Protected Landscape). The work for protection and value of the geological heritage in the Naturtejo Geopark territory was awarded, both in 2004 and 2007, with the Geoconservation Prize attributed annually by ProGEO-Portugal and National Geographic Portugal, as well as honourable mentions of the Environment National Award, attributed in 2009 and 2010 by the Portuguese Confederation of Associations for the Protection of the Environment.

372

Fig. 28.12 Activities developed in the UNESCO Naturtejo Global Geopark: a River activities in Portas de Ródão Natural Monument such as boat trips or geo-kayaking; b Interpretative panels in the geomonuments; c Educational activities organized by the geopark bring students from kindergarten to universities to understand and contact Nature; d Geotour guides such as Casa do Forno, a family project managed by the geologists João Geraldes and Rita Ferreira, provide

C. Neto de Carvalho and J. Rodrigues

since 2008 geological-oriented, hiking or off-road visits to the geopark; e Promoting geodiversity at the municipality of Penamacor; f The development of geoproducts such as the Geo-Restaurant Petiscos & Granitos at Monsanto are examples of innovation based on identity, long-established know-how and high-quality local products, that help to promote the sustainable goals of the geopark

28

Naturtejo UNESCO Global Geopark: The Culture of Landscape

28.4

Geotourism and the Future of Naturtejo

373

Geotourism as a recent concept and segment of sustainable tourism with exponential growth during the last decade is in a broader view as ancient as sacralization of the landscapes, rocks, caves, minerals, or fossils, being included in the pilgrimage myths. Leaving behind the ambiguous definition of the National Geographic Traveller (proposed by Tourtellot

2000) and getting closer to what is intended to be the main value in geoparks, which is integration of geodiversity and geological heritage, geotourism may be defined as the sustainable management of tourist resources, their protection, conservation and value, and the inclusive organization of the offer of services and facilities, divulgation and promotion (communication) of the destination, which are established for one or more (geotouring) assets of the geological heritage (Neto de Carvalho et al. 2011). Shortly, geotourism is

Fig. 28.13 Different activities for sustainable tourism development in Naturtejo Geopark: a Geotechnical study performed with the Faculty of Sciences of the University of Lisbon and the Instituto Superior Técnico, under the coordination of the Prof. Isabel Fernandes, for mapping hazard probability in the urban slopes with large granite boulders of the historical village of Monsanto; b Thematic guided visits and contact

with Nature at Gardunha Mountain; c Development of interpreted paths such as the Boulders Trail at Monsanto; d Successful opening of the Grand Trail Muradal/Pangea, the first Portuguese sector of the International Appalachian Trail, with the presence of its president, Paul Wylezol, the IAT Chapter for Spain, Ruth Hernández and the Consul of Canada in Portugal

374

travelling for the geological heritage, more in accordance with the original definition of Hose (2000), supported by Dowling and Newsome (2006). As a nature-based tourism segment fostering benefits for the destination and their inhabitants, with direct and indirect relations with cultural tourism (landscape touring, mining parks, museums, and interpretative centres), and active tourism (trails and footpaths, caving, …) and even health and well-being tourism (thermal spas), geotourism is developing with an increasing visibility together with the fast expansion of the geoparks worldwide, starting from last decade (Farsani et al. 2011). Nevertheless, the Naturtejo Geopark fosters tourism activities in a wider range of tourism segments, taking into account the following convergence principles: – ‘Value of destination highlights’, through the conservation of natural habitats, heritage sites and local culture; – ‘Resource sustainability’,soils where companies and local institutions contribute to minimize the overexploitation of natural resources, pollution of water, soils and air, production of solid waste, consumption of energy and water and the use of chemicals, …; – ‘Multimedia interactive interpretation’, by fostering populations to learn and communicate about their natural and cultural heritage. This holistic approach not only rises the quality but also diversifies the touristic offer, improving it for the wider public, in a unique combination of experiences and emotions that makes geoparks in general (Farsani et al. 2011), and Naturtejo Global Geopark in particular, different from other tourism destinations, in Portugal and in the international tourism trade. The Portuguese ethnographer and archaeologist José Leite de Vasconcelos, in the beginning of the twentieth century, wrote that travelling is the best way of learning. The tours in Naturtejo UNESCO Global Geopark propose to (re) discover the geocultural landscapes with unique features in Portugal, through the work carried on in the last years by Naturtejo, the municipalities, NGOs, entrepreneurs and communities (Figs. 28.12 and 28.13). The educational activities offered to students and general public take examples from the regional geological heritage for some of the main stages of the geodynamic evolution of the country’s territory, understanding the Cadomian, Variscan and Alpine cycles, and resulting landforms. Above all, experiencing geotourism in the geopark is breathing slower than in ordinary days, feeling the warmth and light of the sun and the intense aroma of the seasons, letting the eyes slowly catch the vast horizons and landforms, relaxing and tasting local flavours…it is learning and sharing know-how, edutainment at its best.

C. Neto de Carvalho and J. Rodrigues

References Antunes IMHR, Neiva MR, Silva MVG, Corfu F (2008) Geochemical and isotopic data on the granite-granodiorite, concentrically zoned Castelo Branco pluton (central Portugal). Lithos 103(3/4):445–465 Carvalho AM (1999) Geomonumentos – uma reflexão sobre a sua caracterização e enquadramento num projecto nacional de defesa e valorização do Património Natural. Lisboa, Liga dos Amigos de Conímbriga, p 30 Cabral J (1995) Neotectónica em Portugal Continental. Memórias do Instituto Geológico e Mineiro, vol 31, p 265 Cunha PP (2019) Cenozoic Basins of Western Iberia: Mondego, Lower Tejo and Alvalade Basins. In: Quesada C, Oliveira JT, editors. The Geology of Iberia: A Geodynamic Approach. Springer Regional Geology Reviews, pp 105–30 Cunha PP, Almeida NAC, Aubry T, Martins AA, Murray AS, Buylaert J-P, Sohbati R, Raposo RL (2012) Records of human occupation from Pleistocene river terrace and aeolian sediments in the Arneiro depression (Lower Tejo River, central eastern Portugal). Geomorphology 165–166:78–90 Cunha PP, de Vicente G, Martín-González F (2019) Cenozoic sedimentation along the piedmonts of Thrust related basement ranges and strike-slip deformation belts of the Iberian Variscan Massif. In: Quesada C, Oliveira, JT, editors. The Geology of Iberia: A Geodynamic Approach. Springer Regional Geology Reviews, pp 131–166 Cunha PP, Martins AA (2000) Património geológico e geomorfológico da área de Vila Velha de Ródão. Estudos do Quaternário 3:91–104 Cunha PP, Martins AA (2004) Principais aspectos geomorfológicos de Portugal Central, sua relação com o registo sedimentar e a importância do controlo tectónico. In: Araújo MA, Gomes A (eds) Geomorfologia do NW da Península Ibérica. FLUP, pp 155– 182 Cunha PP, Martins AA, Daveau S, Friend PF (2005) Tectonic control of the Tejo River fluvial incision during the late Cenozoic in Ródão —Central Portugal (Atlantic Iberian border). Geomorphology 64:271–298 Cunha PP, Martins AA, Gouveia MP (2016) As escadarias de terraços do Ródão à Chamusca (Baixo Tejo) – caracterização e interpretação de dados sedimentares, tectónicos, climáticos e do Paleolítico. Estudos do Quaternário 14:1–24 Cunha PP, Martins AA, Huot S, Murray A, Raposo L (2008) Dating the Tejo River lower terraces in the Ródão area (Portugal) to assess the role of tectonics and uplift. Geomorphology 102:43–54 Dias RP, Cabral J (1989) Neogene and Quaternary reactivations of the Ponsul fault in Portugal. Comunicações dos Serviços Geológicos de Portugal 75:3–28 Dowling R, Newsome D (eds.) (2006) Geotourism, sustainability, impacts and management. Elsevier, Oxford, p 260 Farsani NT, Coelho C, Costa C, Neto de Carvalho C (eds.) (2011) Geoparks & Geotourism—new approaches to sustainability for the 21st Century. Brown Walker Press, Florida, USA, p 208 Fedonkin MA, Gehling JG, Grey V-R (2007) The rise of animals evolution and diversification of the kingdom animalia. The Johns Hopkins University Press, Baltimore, p 295 Feio M, Daveau S (eds) (2004) O Relevo de Portugal – Grandes Unidades Regionais. Publicações da Associação Portuguesa de Geomorfólogos, vol 2, p 151 Ferreira DB (1980) Carta Geomorfológica de Portugal à escala de 1:500000. Instituto Geográfico e Cadastral, Lisboa Finnegan S, Bergmann K, Eiler JM, Jones DS, Fike DA, Eisenmman I, Hughes NC, Tripati AK, Fischer WW (2011) The magnitude and duration of the Late Ordovician-Early Silurian Glaciation. Science 331(6019):903–906

28

Naturtejo UNESCO Global Geopark: The Culture of Landscape

Hose TA (2000) European ‘Geotourism’—geological interpretation and geoconservation promotion for tourists. In: Barettino D, Wimbledon WA P, Gallego E (eds) Geological Heritage: its conservation and management. Instituto Tecnológico Geominero de España, pp 127–146 Kolbert E (2014) The Sixth Extinction: an unnatural history. Bloombury Publishing Lourenço L (1996) Serras de Xisto do Centro de Portugal. Contribuição para o conhecimento geomorfológico e geoecológico. Universidade de Coimbra, p 757 Martin-Serrano A (2000) El paisaje del área fuente cenozóica, evolución e implicaciones, correlación con el registro sedimentar de las cuencas. Ciências da Terra 14:25–28 Mckeever PJ, Zouros N (2005) GEOPARKS: celebrating Earth Heritage, sustaining local communities. Episodes 28(4):274–278 Nance RD, Gutiérrez-Alonso G, Keppie JD, Linnermann U, Murphy JB, Quesada C, Strachan RA, Woodcock NH (2010) Evolution of the Rheic Ocean. Gondwana Res 17:194–222 Neto de Carvalho C (2004) O “Parque Geomorfológico de Monsanto” através do seu percurso pedrestre As Pedras para Além do Sagrado. Geonovas 18:67–75 Neto de Carvalho C (2005) Geomonuments and tourism development in the Naturtejo area: the next big thing. In: IV international symposium ProGEO on the conservation of the geological heritage, Braga, p 9 Neto de Carvalho C, Rodrigues JC (2010) Building a Geopark for fostering socio-economic development and to burst cultural pride: the Naturtejo European Geopark (Portugal). In: Florido P, Rábano I (eds) Una visión multidisciplinar del património geológico y minero. Cuadernos del Museo Geominero, vol 12, pp 467–479 Neto de Carvalho C, Rodrigues JC (2012a) Património Geológico e Geomineiro de Nisa: caracterização do território e sua integração no Geopark Naturtejo. Açafa Online 5:91–168 Neto de Carvalho C, Rodrigues JC (2012b) Património Geológico de Proença-a-Nova: caracterização e gestão no âmbito do Geopark Naturtejo. Açafa Online 5:178–230 Neto de Carvalho C, Rodrigues JC (2012c) Geopark Naturtejo: a evolução da paisagem. In: Andrade PS, Quinta Ferreira M, Lopes FC (eds) I Congresso Internacional “Geociências na CPLP”, 240 Anos de Geociências na CPLP, Excursões Científicas, vol 2. Universidade de Coimbra, pp 109–129 Neto de Carvalho C, Anastácio ML, Viegas P (2006) Geomonumentos classificados como Património Cultural. In: Mirão J, Balbino A (eds) VII Congresso Nacional de Geologia, Livro de Resumos, Évora, v. III, pp 937–941 Neto de Carvalho C, Rodrigues, JC, Chambino E (2010) Património geocultural do Geopark Naturtejo da Meseta Meridional. e-Terra 18 (10):1–4 Neto de Carvalho C, Rodrigues JC, Jacinto A (eds) (2009a) Geotourism & Local Development. Câmara Municipal de Idanha-a-Nova, pp 309 Neto de Carvalho C, Rodrigues JC, Metodiev D (2009b) Inventário do património geológico do concelho de Vila Velha de Ródão: contributo para a caracterização do Geopark Naturtejo da Meseta Meridional. Açafa Online 2:1–53 Neto de Carvalho C, Rodrigues JC, Canilho S, Amado S (2011) Geopark Naturtejo, bajo los auspicios de la UNESCO: la construcción participativa de un destino geoturístico em Portugal. Tierra y Tecnología 40:52–56

375 Pereira P, Pereira D, Crispim J, Nunes J, Brum Da Silveira A (2013) Geomorphosites within the inventory of geosites with national and international relevance in Portugal. In: 8th international conference on geomorphology, Paris, p 554 Ramsay T, Weber J, Kollman ZN (2010) Regional development in European Geoparks. European Geoparks Magazine 5:18–21 Ribeiro A, Munhá J, Dias R, Mateus A, Pereira E, Ribeiro L, Fonseca P, Araújo A, Oliveira T, Romão J, Chaminé H, Coke C, Pedro J (2007) Geodynamic evolution of the SW Europe Variscides. Tectonics 26(6) Ribeiro O (1939a) Sur la morphologie de la Basse-Beira. Bulletin de l’Association de Géographes Français 122:113–122 Ribeiro O (1939b) “Observations” geologiques et morphologiques dans les environs de Vila Velha de Ródão. Revue de Géographie Phisique et de Geologie Dynamique XII-4 Ribeiro O (1942) Notas sobre a evolução morfológica da orla meridional da Cordilheira Central entre Sobreira Formosa e a fronteira. Boletim da Sociedade Geológica de Portugal, I(III): 123-144 Ribeiro O (1943a) Novas observações geológicas e morfológicas nos arredores de Vila Velha de Ródão. Publicações do Museu e Laboratório Mineralógico e Geológico da Faculdade de Ciências do Porto XXXII(2ª série):5–23 Ribeiro O (1943b) Evolução da falha do Ponsul. Comunicações dos Serviços Geológicos de Portugal XXIV:109–123 Ribeiro O (1949a) O fosso do médio Zêzere. Comunicações dos Serviços Geológicos de Portugal XXX:79–85 Ribeiro O (1949b) Le Portugal Central (Livret-Guide de l’Excursion C). In: XVI Congrés International de Géographie, Lisbonne, p 180 Ribeiro O (1968) Excursão a Estremadura e Portugal Central. Finisterra 6:274–299 Rodrigues JC, Neto de Carvalho C (2012) Património geomorfológico da vertente meridional da Serra da Gardunha (Castelo Branco): potencialidades e ameaças. Geomorfologia 2010. Publicações da Associação Portuguesa de Geomorfólogos, 7, APGEOM, Porto:61– 70 Rodrigues JC, Neto de Carvalho C (2013) Geoformas graníticas do Geopark Naturtejo: blocos pedunculados. In: Atas do VI Congresso Nacional de Geomorfologia, Coimbra, pp 223–227 Rodrigues JC, Neto de Carvalho C, Oliveira T (2009) Património Geomorfológico de Monsanto. In: Geomorfologia 2008, Associação Portuguesa de Geomorfólogos, Braga, vol 6, pp 243–248 Sequeira AJD, Serejo Proença JM (2004) O Património Geológico Geomorfológico do concelho de Idanha-a-Nova. Contributo para a sua classificação como Geoparque. Geonovas 18:77–92 Shaw J, Johnston ST, Gutiérrez-Alonso G, Weil AB (2012) Oroclines of the Variscan orogen of Iberia: paleocurrent analysis and paleogeographic implications. Earth Planet Sci Lett 329–330:60–70 Silva RM (2005) Geomorfologia granítica da Serra da Gardunha (Fundão). Geonovas 19:89–114 Solá AR, Neiva AMR, Ribeiro ML (2010) Geocronologia, petrologia e geoquímica dos granitoides do NE Alentejano (transição ZCI/ZOM): significado geodinâmico. Ciências Geológicas I:281– 290 THR (2006) Turismo de Natureza. IP, Turismo de Portugal, p 59 Tourtellot JB (2000) Geotourism for your community. National Geographic drafts, Washington DC, p 2

Index

A Abadia formation, 265 Abandoned incised meanders, 208 Abismo de Sicó, 221 Ablation, 188 Acheulean artefacts, 168 Açor mountain, 6, 16, 34, 309, 342 Adro Nunes, 258 Aeolianite, 111–113, 262, 263 African plate, 9, 10, 25, 26, 29, 109 Afurada, 287, 291 Águeda River, 141, 164 Aguieira, 178, 180, 335 Aguieira-Fronhas-Coimbra dams, 175 Aguieiras Waterfall, 330, 335 Aguilhão castle koppie, 351 Aire mountain, 34, 234, 235 Aivados-Bugalheira Formation, 110–113 Ajuda valley, 274, 278, 298 Alagoas plateau, 363 Alambre, 274, 278 Albufeira flexures, 22 Alcabideche syncline, 257, 259, 260 Alcalamouque, 223 Alcântara valley, 298 Alentejo, 4, 7, 12, 17–20, 24, 34, 36, 38, 43, 56, 109, 255, 263, 283, 359, 361, 362 Alforfa, 53, 188–190, 192–194, 344, 347, 353 Alforfa glacier, 194, 356 Algar da Várzea sinkhole, 221 Algar do Caçador, 217 Algarve, 4, 6–8, 10, 12, 13, 19, 20, 22, 24, 25, 36, 48, 54–56, 109, 113, 117, 118, 121–123, 211–213, 309 Algarve coast, 47, 48, 212 Algarve Sedimentary Basin, 7, 18, 20, 22, 109, 113, 114 Aligned saddle-like depressions, 143 Alignment Carregoussal - São Teotónio, 110 Alijó, 156 Aljezur Fault, 113 Alkaline cycle, 252 Alkaline igneous bodies, 251 Allochthonous complex, 316 Alluvial fan, 8, 91, 110, 112, 170, 199, 201, 263, 285, 297, 317, 319 Alluvial fan deposits, 90, 91, 110, 111 Alluvial plains, 22, 23, 172, 202, 203, 217, 269, 353, 363 Alpine compression, 10, 187, 341 Alpine horn, 188 Alpine orogeny, 10, 154, 273, 345, 359, 360, 362

Alqueidão anticline, 234 Alqueidão mountain, 232 Alto da Pedrice, 135, 193, 194, 197 Alto da Pedrice – Curral da Nave plateau, 188 Alto da Pena Ventosa, 281, 282 Alto da Torre, 186–190, 193, 194, 342, 345, 356 Alto Douro, 139–141, 146, 151 Alto Douro Wine Region, 151, 153, 156, 159, 160 Alva, 152, 153, 164, 173, 183, 188, 192, 311 Alvados depression, 232–235, 237, 241 Alvaiázere, 6, 21, 213 Alvaiázere mountain, 6, 21 Alvalade Sedimentary Basin, 4, 10, 17–19 Alvão mountain, 6, 13 Alvarenga granite, 332, 336 Alva River, 178, 180 Álvaro, 360 Alvelos, 6, 16, 359, 369 Alvelos mountain, 6, 16, 359, 369 Alviela River springs, 242 Alvoco, 188, 192 Alvor estuary, 56, 117, 122 Alvorge, 223 Amadora, 295 Amaral formation, 66, 68, 265 Amarela mountain, 6, 13, 127, 135 Ameal-Santo Varão deposits, 183 American plate, 8, 26, 86 Amieira do Tejo, 363 Amphitheatre head valleys, 217, 220, 229, 237, 238, 241 Ancares, 133 Anços valley, 221 Ante-Hercynian remains, 4 Anthrosols, 151, 158, 160 Anticline structures, 219, 232, 298 Anticline syncline, 253 Aplite-pegmatites, 128 Appalachian, 29, 86, 139, 202, 331, 362, 363, 373 Arabs, 295 Arada mountain, 6, 13 Arade estuary, 117, 121–123 Arades Stream, 203 Arado, 131 Archaeological heritage, 354 Archaeology, 99, 102, 104, 107 Arches, 121, 122 Arcos de Valdevez, 63 Arctic Oscillation, 43

© Springer Nature Switzerland AG 2020 G. Vieira et al. (eds.), Landscapes and Landforms of Portugal, World Geomorphological Landscapes, https://doi.org/10.1007/978-3-319-03641-0

377

378 Aric anthrosols, 158 Ariques, 219 Arkoses, 163, 164, 167, 170, 206, 363 Armação de Pêra Bay, 122 Armazéns Deposits, 183 Armorican micro-plate, 153 Armorican quartzite crests, 141 Armorican Quartzite Formation, 141, 153, 363 Arneiro, 203, 205, 360, 369 Arouca Geopark, 308, 329, 333, 338, 340 Arrábida bridge, 91, 289, 291 Arrábida Chain, 273–278 Arrábida mountain, 6, 21, 213, 253 Arregaça, 183 Arribas do Douro, 145 Arrifana, 109, 110, 113, 114, 221 Arrife fault, 22, 311 Arrife-Montejunto fault, 11, 22 Arrifes, 12, 19, 21, 234 Arruda dos Vinhos, 65, 66, 265 Atenor, 311, 317 Atlantic Ocean, 4, 8–11, 13, 15, 26, 29, 33, 34, 99, 100, 117, 118, 152, 163–165, 175, 179, 181, 213, 229, 251, 273, 275–277, 281, 295, 296, 329, 335, 363 Ave, 83, 90, 163 Aveiro graben, 24 Ave-Leça interfluve, 89 Aveleda Formation, 317, 319 Aveleira, 135, 136 Ave River, 86, 94 Azibo River, 320, 325 Azimbres, 192 Azores, 3–5, 7, 10–13, 26–29, 33–38, 41, 308, 309, 312, 313, 370 Azores Geopark, 308 Azores-Gibraltar boundary, 10 Azores-Gibraltar Fracture Zone, 9, 26 Azores-Gibraltar plate border, 48 Azores Triple Junction, 49

B Bajocian-Bathonian units, 230 Baleeira beach, 118, 119 Barca de Alva, 152, 153, 173 Bare granite outcrops, 188, 347 Bare-rock landscape, 133 Bare slopes, 151, 158 Barlavento, 117 Barra do Sado channel, 99, 100, 102 Barreira da Junqueira, 248 Barrier islands, 77, 99, 102, 104–106, 313 Barroca das Lameiras, 188 Barroca de Água, 194, 195, 198 Barrocal, 22, 212, 311, 367, 371 Barroso mountain, 6, 13 Base level, 155, 267, 273, 276, 278 Basic rocks, 128, 153, 186 Basin morphology landscape, 189 Basins, 4–13, 15, 20–22, 28, 29, 38, 44, 54, 63–66, 68–70, 77, 110, 123, 130, 139, 140, 143–146, 152–154, 157, 163–165, 167, 168, 170–173, 175, 176, 178, 179, 183, 192, 199–203, 211, 212, 215, 217, 229, 241, 265, 267, 286, 315, 317–319, 322, 330, 332, 344, 350, 360, 363, 367 Batalha, 232 Bateiras Formation, 153 Batholith, 65, 142, 186, 187, 332, 344

Index Bay of Biscay, 130, 142, 315 Bazágueda River, 367 Beach, 8, 24, 47, 54–56, 77, 83, 86, 89–95, 97, 99, 101, 102, 109–111, 114, 115, 117–123, 179, 255, 256, 259, 261–263, 273, 275, 287, 288, 312, 315, 326, 333–335, 342 Bedding, 121, 122, 182, 183, 235, 240, 255, 263, 270, 276 Beheaded streams, 143 Beijames valley, 350, 351 Beira Baixa, 199–201, 203, 207, 208, 359, 361 Beiras Group, 201, 341, 343, 344, 366 Belmonte, 342, 345, 347, 354 Belverde Formation, 275, 277 Benfica Complex, 265, 266, 297 Berlengas Islands, 6 Betic compression, 317 Betic direction, 229 Betula woodlands, 43 Bezerra village, 248 Biduiça Valley, 134 Biochemical, 240, 249 Biodiversity, 127, 213, 241, 307, 308, 315, 326, 327, 341, 342, 360, 369, 371 Biosphere Reserve, 360, 371 Bird communities, 122 Blind thrust fault, 253 Blind valleys, 217, 220, 225 Blockfield, 135, 193, 348, 351 Blockslope, 135, 193, 348, 351 Blockstream, 194 Boa Viagem mountain, 6, 21 Boavista, 183 Boca do Rio, 117, 120, 121 Bølling, 42 Bornes half-horst, 16 Bornes mountain, 6, 16, 145, 311, 317–320 Bornes push-up, 143, 145, 317, 318 Bornhardt, 127, 130–132, 311, 330, 335, 338, 348 Borrageiros, 131 Bowl-shaped dolines, 220 Bowl-shaped valleys, 329, 332, 333, 339 Bragança, 16, 36, 41, 143, 173 Bragança Formation, 317, 319, 320 Bragança-Manteigas fault, 7, 15, 16, 156, 157 Bragança-Vilariça-Manteigas fault, 142, 163, 167, 322, 344, 354 Bragança-Vilariça-Manteigas strike-slip fault, 163, 187, 190 Branda da Junqueira, 135, 136 Bridge of São Miguel, 133 Buçaco quartzite ridge, 180 Buraca Escura, 220, 223 Buraca Grande, 220, 223 Buracas, 220, 222, 311 Buracas valley, 220–222 Burga, 321–323 Burgau beach, 120, 121

C Cabeça da Velha, 354 Cabeça do Velho, 354 Cabeço de Santo Estevão, 355 Cabeço do Infante, 201 Cabedelo sand spit, 286, 289, 290 Cabo da Roca, 36, 49, 261 Cabo Mondego Natural Monument, 308 Cabreira mountain, 6, 13 Cabril River valley, 134

Index Cachão da Valeira, 171, 173 Cadomian Orogeny, 153 Cagarouço, 133 Caima River, 330, 332, 334 Calcareous tufa/travertine, 182, 211–215, 217, 220 Calcium carbonate cement, 231 Caldeirão mountain, 6, 18, 19, 22, 36, 123, 312, 353 Calhandriz landslide, 63, 64, 67, 69 Cambisols, 158 Cambrian metamorphic rocks, 151 Cambrian schists and greywackes, 141, 146, 201 Campanhó/Ferradosa Formation, 153 Campanian, 139 Campo, 12, 16, 181, 217, 311, 319, 320, 322 Campo-Camporez, 217 Campo depression, 217 Campo do Bolão, 181 Camporez, 217 Camporez depression, 217 Campos do Mondego, 181 Canary mantle plume, 25 Candeeiros Mountain, 6, 21, 213, 231, 232, 234, 236, 238, 244–246, 248 Candieira, 42, 43, 353 Candieira valley, 189, 349 Caniça, 188, 190, 192, 197, 353 Caniça valley, 347 Cantabrian Mountains, 10, 42, 93, 130, 141, 142 Cantabrian-Pyrenean Mountain chain, 10 Cantabrian Range, 141 Cantareira, 203, 287, 367 Cântaro Magro, 190, 195, 312 Cântaro Raso, 188, 190, 195 Canyon, 139, 145, 146, 154, 203, 206, 220, 225, 290, 311, 322 Canyon of the Águeda River, 141 Cape Carvoeiro, 101, 122, 311 Cape Espichel, 102, 273, 274, 276, 277 Cape Silleiro, 83, 85, 86, 96 Cape St. Vicent, 117–120, 122 Capture, 15, 16, 139, 170, 200, 202, 203, 208, 237, 363 Caramulo Mountain, 6, 13, 14, 329, 333 Carboniferous, 5, 7, 8, 63, 86, 153, 309, 344 Carboniferous granite bedrock, 63 Carqueija, 182 Carqueija-Salabardos torrential deposits, 182, 183 Carris granite, 129 Cascais erosion platform, 257 Castelo Branco, 12, 17–19, 187, 188, 199, 202, 203, 205–207, 308, 345, 346, 360–363, 365, 367, 368, 371 Castelo Branco plateau, 202, 208 Castelo do Sobral, 219 Castilla, 15, 172, 173 Castilla la Vieja Plateau, 15 Castle-koppie, 348, 351 Castro Laboreiro, 129, 130, 135 Castro Roupal, 317, 320, 322 Caves, 22, 121, 211, 217, 220, 221, 223, 237, 241, 244, 276, 311, 312, 373 Cávado, 14, 163 Cávado River, 14, 86, 130 Ceira, 183 Celorico da Beira, 179, 180, 342, 354 Celorico da Beira Basin, 179 Cenozoic, 4, 7, 10, 12, 13, 15, 17–19, 22, 24, 29, 86, 91, 96, 130, 135, 140–143, 145, 148, 154, 166, 167, 170, 175, 180, 199–203, 208,

379 215, 219, 220, 251, 254, 255, 263, 309, 316, 317, 321, 322, 339, 359, 363, 367 Cenozoic deposit, 17, 83, 89, 153, 155, 165, 200–203 Cenozoic Douro Basin, 317 Cenozoic Sado Basin, 52 Cenozoic sedimentary rocks, 6 Cenozoic Tagus basin, 52 Central Iberian graben, 153 Central Iberian Zone, 4–7, 86, 283, 309, 316, 341, 343, 344, 353 Central Plateau, 157, 163, 169, 343, 344 Central Portugal, 23, 34, 36, 39, 42, 55, 56, 106, 133, 139, 175, 185, 186, 196, 211, 213, 229, 342, 354, 361 Cercal mountain, 6, 18–20 Cerealia pollens, 43 Cernache, 220 Cesareda plateau, 211, 212 Chagas, 10, 295, 300 Chão das Pias, 237, 241 Channel-shaped features, 132 Charco da Candieira lake, 42, 43 Cheese Castle, 283, 284, 286 Cheira da Noiva, 142, 143, 311 Cirques, 127, 132–134, 190–193, 348, 350, 356 Civil Protection, 73–75 Civil protection stakeholders, 56 Cliffs, 54, 56, 77, 78, 86, 88, 90, 97, 102, 111–114, 117, 118, 120–123, 233, 256, 259–262, 277, 278, 290, 311, 360 Climate, 8, 10–14, 28, 29, 33–36, 38, 39, 41–44, 92, 93, 106, 107, 110, 113, 114, 123, 139, 146, 151, 152, 154, 171, 175, 179, 185, 188, 201, 211, 263, 284, 285, 295, 344, 348, 363 Climate Change, 10, 12, 29, 41, 42, 54, 73–75, 110, 146, 154, 285, 287, 363 Climate evolution, 39, 41, 44 Côa, 15, 34, 145, 155, 157, 159 Coal mines, 333 Côa River, 15, 157, 159 Coastal cliffs, 47, 54–56, 102, 109, 121, 256, 261, 309, 311, 313 Coastal drift, 114, 123 Coastal dunes, 101, 103, 105, 262 Coastal erosion, 47, 54, 56, 57, 74, 75, 78, 91, 286, 288 Coastal plateau, 24, 251 Coastal systems, 56, 109 Coastal Zone Program, 75 Côa Valley Archaeological Park, 145 Cocões de Concelinho cirque, 134 Coimbra, 47, 56, 175–179, 181–183, 213, 218, 309 Coimbra and S. Miguel Formation, 213, 217 Coimbra-Penela, 217 Coina valley, 274, 278 Cold air drainage, 37 Cold-air pools, 37 Cold Land of Trás-os-Montes, 171 Compadre, 134, 312, 313 Conímbriga, 220 Condeixa, 213, 220, 311 Condeixa-Sicó, 215 Condeixa-Sicó block, 219, 221 Conhal do Arneiro-Charneca, 360 Conrad discontinuities, 321, 324 Continental crust, 128, 153, 316, 321 Continental facies, 251, 254, 255, 263 Continentality, 34, 36, 37, 152 Continental passive margin, 12, 251 Cordilheira Central, 169, 345 Corestones, 330, 336

380 Corgo das Mós, 175 Corgo River, 153, 157 Cornbread rocks, 330, 335, 336 Cornos de Candela, 134 Costa da Castanheira, 330, 333 Costa da Galé, 106 Couce valley, 134 Courel, 133 Cova da Beira, 187, 342, 345 Covais, 190, 192, 348 Covão Cimeiro, 37, 189, 190, 192, 193, 312, 347, 349 Covão do Boi, 190, 196, 350, 352 Covão do Curral, 189 Covão do Ferro, 189–192, 347, 349, 350, 356 Covão do Feto, 245 Covão do Teixo, 348 Covão do Urso, 188, 191, 197, 312, 347, 360 Covão Grande, 188, 189, 192 Covas do Douro, 156 Covões da Clareza/Salgadeiras, 189 Cresmina, 257, 259, 261, 262 Crest of Marofa, 141, 329 Crestuma-Lever dam, 286, 288, 290 Cretaceous, 9–11, 14, 54, 56, 86, 117, 120, 121, 130, 142, 175, 183, 212, 215, 219, 220, 252–254, 256, 257, 259–262, 265, 266, 269–271, 275, 276, 278, 296, 297, 309, 344, 363 Cruz Alta, 258 Cryonival deposits, 220 Cryonival processes, 243 Cryoplanation, 193 Cryptokarstic, 211, 220, 225 Cuestas, 21, 22, 266, 272 Culminant Fluvial Surface, 201 Cultural landscape, 146, 147, 151, 251, 281, 369, 374 Cultural Landscape of Alto Douro Wine Region, 145, 147, 151 Curral do Vento, 193, 194

D Dagorda Marls, 8, 230 Dansgaard-Oeschger cycles, 41 Dão, 180 Dead-ice valley glacier, 195 Debris, 64, 230, 371 Debris cones, 347, 351 Debris flow, 11, 26, 53, 63, 64, 66, 195, 255, 265, 268, 269, 277, 317, 353 Deep fluvial incision, 145, 256 Deep-seated, 69, 272 Deep-seated landslides, 63, 64, 272 Deep-seated rotational slides, 66, 269, 270, 272 Deep-seated slope movements, 265 Deep-seated translational slides, 269, 270, 272 Deep valley, 27, 130, 155, 161, 180, 217, 319, 332, 342, 353, 363 Deformation till, 191 Degracias, 213 Degracias-Alvorge plateau, 217, 219, 220, 223, 224 Depression of Alvados, 230, 232–235, 237, 241 Depression of Mendiga, 230, 232–237 Depression of Minde, 230, 232, 233, 238 Desejosa Formation, 153, 158 Desertas islands, 5, 25, 33 Detrelo da Malhada, 330, 332, 333, 339 Devesa, 363

Index Diamicton, 193 Diapiric depression, 230–233, 236 Diapiric depression of Caldas da Rainha, 21 Diapiric depression of Sesimbra, 277, 278 Diapiric materials, 230 Diapiric phenomenon, 215 Differential erosion, 14, 22, 66, 120, 156, 180, 211, 251, 256, 258, 265, 266, 272, 324, 334, 339 DISASTER database, 47, 48, 52, 56, 289, 291 Dissolution processes, 238 Dissolution shafts, 217, 218 Dogger limestone, 234 Doline, 217, 220, 221, 229, 231, 234, 235, 238, 245 Dolomitic hills, 211–213, 217, 218, 220, 221, 224 Dome blocks, 148 Dom Luís I bridge, 91, 286, 291 Dona Maria bridge, 286, 287, 291 Douro, 7, 15, 16, 38, 44, 54, 56, 86, 90, 91, 93, 139, 141, 146, 151–159, 164, 167, 170, 172, 173, 179, 183, 282, 286, 287, 289, 292, 317, 319, 330, 332 Douro-Beiras Supergroup, 187, 343 Douro Cenozoic basin, 141, 143, 145, 146, 164, 319 Douro floods, 170, 281, 289, 291 Douro Group, 141, 153, 156, 158, 284, 344 Douro Hydrographic Region, 290 Douro River, 11, 13–16, 36, 91, 93, 139, 141, 143–146, 152–154, 156, 157, 164, 165, 169–173, 281, 282, 286–291, 318 Douro River canyon, 141, 147, 148 Douro Valley, 15, 47, 54, 56, 139, 141, 145, 146, 151, 152, 154–157, 160, 161, 163, 164, 168–171, 173, 281, 284–286, 290, 333 Drainage network, 27, 114, 123, 163, 164, 201, 225, 259, 273, 276, 278, 298, 317, 342, 345 Drainage system, 11, 143, 155, 159, 160, 179, 201, 275, 319, 322, 366, 367 Dry valleys, 217, 220, 229, 238, 244, 246 Dueça, 311 Dueça River, 183, 217 Dueça Speleological System, 221 Dykes, 8, 68, 69, 123, 128, 190, 252, 253, 261, 316, 354, 355 Dystric cambisols, 158

E Earthquake, 13, 47–51, 56, 74, 107, 143, 265, 270, 272, 295, 298–301, 326 Earthquake-triggered landslides, 52, 301 East Azores Fracture Zone, 26 Eira Pedrinha, 220 Elephas antiquus, 111, 267 Emergency management, 73, 74, 79 Endokarst, 217, 221, 276 Endorheic, 15, 16, 146, 164, 170, 179, 183, 201, 224, 317, 363 Endorheic basin, 145 Entre-Penedos, 180 Envendos, 202 Enxarrique, 360 Eocene, 10, 130, 141, 142, 263, 317, 363, 364 Epigenetic, 220, 286 Epigenetic valleys, 199, 203, 208 Epigenic gorges, 364, 366 Epikarst, 220 Equus caballus, 267 Erges River, 203, 367

Index Erosion, 7, 10, 12, 19, 20, 22, 24, 26, 29, 47, 54–56, 74, 75, 93, 97, 101, 102, 104, 109, 114, 117, 118, 121, 123, 131, 135, 141, 146, 155, 156, 158, 159, 161, 175, 178, 188–191, 201, 202, 206, 208, 217, 220, 230, 251, 255, 258, 259, 261, 263, 265, 267, 268, 272, 273, 276–278, 281, 287, 317, 331, 341, 345, 348–350, 353, 363, 365, 367 Erosional knob, 189 Erosional landforms, 136, 190, 211 Erosional landscape, 185 Erratic boulders, 136, 189 Ervedosa do Douro Formation, 153, 158 Ervidinho-Vila Verde Deposits, 183 Espiche estuary, 122 Espinho, 54, 83, 85, 86, 89–94, 96, 288, 290, 330, 336 Estrela, 38, 42, 185–188, 190, 192, 329, 341, 342, 344, 345, 347, 348, 353, 355 Estrela Geopark, 191, 341–348, 350, 351, 353–355 Estrela mountain, 6, 17, 34, 53, 185, 335 Estrela plateau, 39, 185, 187–189, 348 Estremadura Limestone Massif, 22, 211–213 Estuary, 54, 99–101, 103–105, 107, 120–123, 175, 179, 183, 281, 286, 287, 299, 312 Etchplain-type landscape, 359 Eurasian plate, 8–10, 47 Eurasia-Nubia plate boundary, 12, 48 European Directive, 73, 77 European Landscape Convention, 308 Eustatic, 24, 92, 96, 219, 275 Eutric cambisols, 158 Eutric leptosols, 158 Evaporitic Complex, 21, 22, 54, 215, 230 Exorheic, 146, 179, 183 Exorheic basin, 11 Exsurgence, 211, 217, 221, 224 External moraine ridge, 188, 350

F Fafião river, 134 Faial island, 5, 26–28, 312 Falagueira, 203 Falagueira Formation, 201, 363 Fão “Horses”, 86 Fatalities, 38, 47, 48, 56, 299 Fátima platform, 232 Fault, 6, 8–12, 15–19, 21, 22, 26, 48, 49, 87, 91, 92, 96, 109–112, 118, 123, 130, 139, 142, 143, 145, 148, 153, 154, 163, 164, 166–169, 172, 180, 187, 190, 199–203, 213–215, 217, 219, 229–233, 235–237, 253–256, 259, 263, 273, 276, 283, 284, 287, 299, 317, 319, 321, 322, 326, 331, 335, 342, 345, 361–363, 365, 366 Fault scarp, 20, 109, 143–145, 157, 164, 168, 187, 199, 200, 203, 205, 208, 217, 232, 234–238, 281, 311, 319, 322, 359, 360, 363, 365 Fault valleys, 199, 203, 208 Felgueira-Preguinho, 331, 333 Felgueira-Preguinho fault, 331, 333 Fervidas, 65 Figueira, 117, 118, 120, 311, 360 Figueira Beach, 117, 118 Figueira da Foz, 175, 179, 181, 182 Figueira da Foz Formation, 219 Fill strike-slip basins, 317 Flandrian transgression, 181 Flash floods, 26, 38, 39, 56, 59, 74, 75, 77, 123 Flat-floored depressions, 164 Flat landscape, 22, 359

381 Flood, 22, 38, 39, 47, 56, 58, 59, 74, 77, 79, 103, 121–123, 145, 170, 175, 176, 178, 179, 236, 247, 281, 287, 289–291 Floodplain, 158, 168, 172, 175, 181, 183, 290 Flow till, 350 Fluvial, 8, 9, 12, 15, 20, 24, 26, 89, 91, 111, 113, 117, 121, 136, 146, 154, 170, 173, 175, 181–183, 202, 204, 211, 217, 220, 225, 243, 256, 259, 265, 267–269, 272, 275, 276, 281, 282, 284, 287, 288, 292, 297, 299, 317, 319, 332, 334, 335, 341, 342, 353 Fluvial captures, 11, 201 Fluvial dynamics, 179, 180 Fluvial geomorphology, 350, 353 Fluvial incision, 19, 146, 164, 201, 230, 259 Fluvial landforms, 141, 199, 202, 203, 208, 330, 334 Fluvial landscape, 145 Fluvial sediments, 110, 123, 130, 140, 141, 181, 317, 335, 364 Fluvial terraces, 12, 163, 170, 181–183, 200, 202, 203, 269 Fluvioglacial, 185, 350 Fluvioglacial deposits, 133, 134, 192 Fluvioglacial silts, 188 Fluvioglacial terraces, 192 Fluviokarst, 22, 238 Fluvio-torrential, 175 Fluvisols, 158 Flysch Group, 7, 18 Folds, 19, 21, 22, 86, 141, 153, 156, 180, 274, 276, 309, 331, 363 Folgosinho, 354, 355 Fonte da Telha Formation, 275 Formosa lagoon, 103–105 Formosinho anticline, 275 Fórnias, 220 Fornos de Algodres, 342, 351, 354 Fortification of Alqueidão, 65 Foz do Azibo, 321, 324 Foz do Enxarrique, 360 Fractures, 12, 14, 15, 53, 83, 87, 88, 92, 120, 122, 129–131, 155, 156, 217, 219, 221, 231, 233, 234, 254, 256, 258, 261, 276, 290, 291, 335, 350, 365 Frades landslide, 63, 65, 69 Fraga das Penas, 191, 345, 351 Fraga Negra, 355 Fragão do Poio dos Cães, 349 Fratel, 203, 363 Frecha da Mizarela waterfall, 311, 330, 334, 335 Freita, 334 Freita Mountain, 6, 13, 329–335, 338 Freixo de Espada à Cinta, 141, 142, 173 Fronhas, 178 Frontal moraines, 192, 350 Fundamental Surface, 14, 15, 141, 154, 319, 363, 367

G Gabbro intrusives, 252 Galamares Complex, 255, 263 Galicia, 42, 83, 86, 88, 131, 133 Gamoneda, 142 Gardunha, 203, 368, 371 Gardunha mountain, 6, 16, 359, 361, 363, 367, 368, 371, 373 Gavieira, 131, 135 Gavieira river, 135 Gelasian, 11, 90, 91, 141, 145, 201, 285, 321 Gelivation, 193 Geoconservation, 307–310, 312, 320, 326, 342, 350, 355, 371 Geoheritage, 141, 142, 206, 211, 225, 229, 240, 241, 307–309, 326, 341, 342, 348, 355 Geological landscapes, 359–361

382 Geomorphological geosites, 333, 338 Geomorphological hazards, 47, 56, 60, 73, 74, 79, 295 Geomorphological heritage, 200, 241, 307–310, 329 Geomorphological units, 3, 4, 10, 12, 13, 16, 19, 21, 22, 29, 47, 52, 141, 199, 201, 208, 229, 231, 238, 283, 298, 299 Geomorphology, 3, 4, 57, 99, 102, 107, 118, 141, 163, 170, 179, 186, 196, 213, 251, 266, 284, 295, 296, 298, 299, 301, 315, 317, 322, 326, 329, 330, 332, 339, 354, 359, 361 Geopark, 206, 307, 308, 312, 315, 316, 318, 319, 322, 326, 329–333, 339, 341, 342, 350, 353–355, 359–361, 367, 370, 372–374 Geosite, 136, 141–143, 191, 234, 240, 241, 307–310, 312, 313, 315, 319–326, 329–331, 333–336, 339–342, 350, 352–355, 359, 360, 367, 370 Geotourism, 333, 340, 342, 373, 374 Gerês and Peneda mountains, 17, 34, 38, 42, 127–129, 133, 135, 185 Gerês granite, 127, 129, 131, 132, 135 Gerês mountain, 6, 13, 17, 34, 38, 42, 86, 127–130, 133, 329, 335 Glacial, 12, 29, 33, 42, 91, 92, 111, 132–136, 185, 186, 188–192, 194–196, 284, 341, 342, 345, 347, 348, 350 Glacial cirques, 37, 135, 136, 189, 192, 193, 347, 349, 351 Glacial cycle, 41, 42, 135 Glacial deposits, 17 Glacial erosion, 134, 188, 189, 191, 341, 347, 350 Glacial erratics, 135 Glacial geomorphology, 135 Glacial lakes, 134 Glacial landforms, 127, 128, 132–134, 136, 185, 193, 347 Glacial overdeepenings, 347, 351 Glacial retreat, 135 Glacial system, 185 Glaciation, 17, 41, 42, 103–105, 107, 118, 132–135, 185, 186, 188, 191, 193–195, 339, 345, 347, 350, 353 Gloria transform fault, 12 Glory Fault, 48, 49 Gnammas, 131, 135, 142, 143, 330, 336, 338 Gola do Salto step, 330, 335, 337 Gorringe Bank, 11, 25, 299 Gorringe Bank Fault, 49 Gothic walls, 282, 284 Grândola fault, 19, 22 Grândola mountain, 6, 18, 19, 22 Graben, 8, 9, 13, 16, 22, 24, 27, 83, 110, 113, 157, 167, 181, 229, 232, 234, 235, 312 Graben of Vilas Ruivas-Arneiro, 362 Graciosa Island, 5, 26–28, 312 Gralheira Massif, 330, 331, 333, 334 Grande da Pipa River, 63–66, 68–70 Granite laccolith, 252 Granite landforms, 14, 135, 139, 142, 143, 203, 311, 322, 354, 367, 368 Granite weathering, 53, 142, 336, 341, 348, 350, 351, 353, 354 Granitic landforms, 263, 330, 331, 333, 335 Gravitational processes, 277 Gravity block falls, 121 Grimaldian dunes, 99, 105 Guadalquivir Bank, 252, 299 Guadarrama, 341 Guadiana River, 17, 36, 56 Guarda, 36, 187, 342 Gulf Stream, 34, 43

H Hanging valley, 256, 351 Hazardscapes, 63, 64, 68 Head-type slope deposits, 351

Index Heathlands, 43 Heinrich Stadials, 42 Hercynian Massif, 4, 5, 13, 17, 52–54, 212, 215, 217 Heritage, 22, 99, 109, 115, 128, 136, 143, 145, 148, 161, 163, 200, 240, 241, 251, 281, 284, 286, 307–310, 315, 327, 329, 331, 354, 359, 361, 367, 369–371, 373, 374 Hesperian Massif, 167, 175, 180, 273 Hesperic Massif, 4 History, 17, 39, 99, 104, 107, 158, 163, 165, 171, 173, 175, 183, 188, 251, 275, 282, 283, 299, 307, 326, 341, 342, 354, 355, 359, 370 Holocene, 22, 42, 43, 83, 86, 91, 99, 102–107, 122, 181, 201, 267, 268, 277, 297, 353 Honeycomb, 240, 249, 368 Horseshoe Abyssal Plain, 299, 300 Horseshoe Fault, 11, 13, 49, 299 Hotspot, 25, 26, 29 Hydrogeological, 54, 213, 224, 319, 350, 354

I Iberian Central System, 16, 142, 185, 341, 345 Iberian Massif, 4, 6–10, 12, 13, 19–22, 24, 25, 29, 86, 109, 111, 114, 136, 139–143, 201, 202, 281, 283, 309, 311, 313, 315, 317, 330, 344, 361–363 Iberian microplate, 9, 10, 109 Iceberg, 42 Icefield, 189, 345 Ichnological Park of Penha Garcia, 360 Idanha-a-Nova, 201, 207, 308, 361, 363, 365 Idanha-a-Velha, 206, 360 Idanha-Oledo, 360, 363 Incised meanders, 143, 154, 199, 206, 208, 345, 353 Incised valleys, 148, 152, 181, 217, 259, 334 Inferred thrust fault, 253 Ingote Red Sands, 182, 183 Injuries, 39, 47, 73, 160, 289, 291 Inselberg, 12, 18, 29, 199, 202, 207, 335, 345, 347, 354, 359, 361, 362 Institute of Conservation of Nature and Forests, 308, 309 Interfluve, 12, 14, 15, 22, 43, 89, 130, 133, 135, 156, 189, 251, 259, 331, 342, 345 Intermoraine basin, 188 International Disasters Database, 47 International Tagus Tejo Natural Park, 360 International Tejo, 364 Intrusion, 5, 10, 68, 153, 251–256, 263, 269, 339, 344 Intrusive dome, 142 Irregular thalwegs, 156 Isna River, 366 Isostatic rebound, 251, 263

J Jet stream, 33 Jewish quarters, 360 Junqueiro, 330, 335 Jurassic, 9, 21, 22, 54, 56, 86, 113, 117, 118, 122, 211–213, 217, 219, 223–225, 230, 254, 256, 261, 262, 269–271, 274–278, 308, 309, 363 Jurassic-Early Cretaceous rifting, 253

K Kame terrace, 195, 351 Karren, 211, 217, 220, 222, 229, 233, 234, 240, 248, 311 Karren fields, 220, 311 Karrentisch, 235, 240, 248

Index Karst canyons, 217, 220, 229, 237, 238, 242 Karstic, 121, 123, 211, 213, 229 Karstic landscapes, 121 Karstic processes, 211, 213 Karstification, 123, 211–213, 217, 219, 224, 225, 259, 260 Karst landscapes, 213, 219, 229, 311 Karst spring, 220, 221, 223, 224, 229, 236, 238, 239 Karst springs waterfalls, 229, 238, 241 Kettle holes, 353 Kettles, 368 Kimmeridgian, 214, 215, 230, 265, 267 Kluftkarren, 240 Knickpoint, 179, 180

L Lageosa do Mondego, 183 Lagoa Comprida, 39, 188, 189, 191, 192, 312, 347 Lagoa dos Salgados, 122 Lagoa Seca, 188, 191, 192, 195, 197, 312, 347, 350, 352, 354 Lagos, 22, 24, 109, 117, 121, 123 Lagos-Portimão Formation, 121–123 Lakes, 27, 28, 42, 43, 132, 135, 236, 315, 326, 347 Lamego, 161 Land embankments, 151, 159, 160 Landslides, 26, 39, 47–49, 52–54, 56, 63–70, 74, 75, 160, 268–272, 289, 295, 298–301 Land use planning, 74 Land use regulation, 73, 79 Lardosa, 199, 206, 361, 367 Lares, 181 Larouco, 6, 13, 130 Larouco mountain, 6, 13, 130 Last Glacial Maximum, 17, 42, 189, 348 Late Miocene, 10, 11, 123, 140, 187, 201, 252, 267, 275, 276, 278, 345 Lateral moraine, 134, 191, 194, 195, 197, 313, 356 Latero-frontal moraines, 192 Late-tectonic granitic massifs, 154 Late Variscan faults, 14, 17, 86, 154, 157, 253, 330, 331, 341, 362 Lavadores, 86, 90, 92, 288, 290 Law of the land use planning, 74 Leandres valley, 354 Leça River, 83, 89, 92 Leeward, 117 Left-lateral stream deflections, 143 Legação, 223 Leixões, 92, 93, 283, 287 Lemede, 213 Leptosols, 158 Leporidae, 111 Lima, 79 Lima river, 14, 79, 129, 163 Limestone, 6, 8–10, 18, 21, 22, 53, 54, 56, 64–66, 68, 69, 109, 113, 117, 118, 120, 121, 153, 175, 181, 211–215, 220, 223, 224, 229–231, 234, 235, 238, 240, 248, 254, 255, 259–263, 265–271, 275–278, 297–299, 326 Limestone Massif of Estremadura, 22, 34, 211–213, 229, 230, 232, 233, 243, 248 Limestone mountains, 21, 211, 213, 217, 219, 221 Lindoso and Várzea granite, 132 Linear valleys, 143 Linhares da Beira Castle, 355 Liquefaction, 111, 113

383 Lisbon, 10, 21, 34, 36, 38, 41, 47, 48, 50, 51, 54, 56, 64, 76, 77, 109, 121, 238, 251, 252, 265, 267–270, 272, 273, 295–301, 340, 342, 361, 373 Lisbon earthquake, 13, 265, 270, 272, 299, 301 Lisbon Volcanic Complex, 252, 253, 256, 298 Lithic leptosols, 158 Lithologic units, 52–54 Lithology, 6, 16, 29, 54, 66, 114, 117, 156, 201, 211, 230, 231, 234, 259, 265, 266, 275, 276, 283, 316, 341, 342 Little Ice Age, 43, 44 Littoral platform, 12, 13, 18–25, 83, 87–89, 91, 92, 96, 109–114, 163, 164, 217, 259, 281, 284, 288 Livraria do Mondego, 180, 181 Lodgement till, 133–135, 350 Longitudinal profile, 145, 156, 164, 167, 170, 179, 180, 200 Longitudinal staircase–like profiles, 155, 156 Longroiva, 16, 143, 145, 146, 163–171, 173, 311 Longroiva depression, 166 Longroiva strike-slip basin, 143 Loriga, 17, 188–190, 192, 312, 347, 349, 350 Loures basin, 265–269, 272 Louriça, 127 Lousa-Bucelas Cuesta, 266, 267, 270 Lousã mountain, 6, 16, 34, 38 Lousã-Pastor-Torre Vale de Todos, 215 Lovios-Gerês, 129 Low altitude glaciation, 127, 133 Lower Cretaceous, 8, 25, 120, 214, 215, 230, 252, 254, 255, 265 Lower Devonian, 153 Lower Mondego, 175, 176, 178, 179, 181–183 Lower Tagus Basin, 6, 10, 11, 22, 273, 278, 296, 297 Lower Tagus Fault Zone, 49, 299 Lower Tagus Valley Fault Zone, 10, 47, 48 Lower Tejo Cenozoic Basin, 199–201, 203, 208 Lower terraces, 169 Low sediment supply, 54 Lusitanian Basin, 6–9, 11–13, 19, 21–24, 86, 91, 92, 211, 212, 215, 229, 251–255, 273, 296, 309 Lusitanian endemic species, 99 Luz, 109, 120 Luz beach, 120, 121

M Macaronesia biogeographic Region, 35 Macedo de Cavaleiros, 16, 170, 308, 315, 318, 319 Madeira, 3–5, 10, 11, 13, 25, 29, 33, 34, 36, 37, 308, 309, 313 Madeira island, 5, 25–27, 29, 35, 313 Madeira-Tore submarine, 10, 25 Madorno, 133 Mafra Radial Dyke Complex, 252 Magarefa, 203, 205 Magoito, 263 Malcata Mountain, 361, 363, 364, 371 Malhadouro, 220 Malhão, 111, 112, 114 Malpica, 203, 363 Manteigas, 354 Manteigas thermal Spring, 354 Manteigas- Vilariça-Bragança Fault, 48, 49 Mantle, 25, 63, 145, 153, 255, 321 Maquis, 274 Marão, 6, 13, 152 Marão mountain, 6, 13, 152

384 Marco Furado Formation, 275, 277 Mareta beach, 118, 119 Marginal Massif of Coimbra, 179, 180, 182 Marginal moraine complexes, 192 Marine caves, 121, 276 Marine erosion, 12, 86, 87, 89, 251, 263 Marine terraces, 273 Marine transgression, 10, 12, 220, 255, 275, 296, 297 Marinho glacial lake, 134 Marly-limestone depressions, 211, 213, 217, 218 Marquês de Pombal Fault, 11, 13, 49, 299 Martim Branco, 360 Maunder Minimum, 43 Meander, 164, 170, 179, 181, 183, 311, 322, 330, 335, 337, 353, 366 Meanderkarren, 240, 248 Medas, 127, 131 Medieval castles, 342 Medieval Climate Anomaly, 43 Medieval settlements, 342 Mediterranean climate, 21, 33, 34, 37, 38, 40, 41, 44, 175 Megalithic, 360 Megaliths, 342 Meia Praia beach, 122 Mendiga depression, 230, 232–237 Meridional Meseta, 206, 359, 361 Meseta, 12, 13, 15–19, 22, 139, 141, 143–146, 148, 154, 156, 157, 163–165, 169, 201, 319, 342–344, 362–364, 367, 369 Meso-Cenozoic sedimentary borderlands, 4 Meso-Cenozoic western borderland, 175, 181 Mesomediterranean formations, 43 Mesomediterranean stage, 43 Mesozoic, 4, 7–9, 16, 21, 29, 86, 139, 154, 201, 202, 252, 254, 296, 297, 309, 315, 316, 363 Mesozoic igneous rocks, 6 Mesozoic sedimentary rocks, 6, 7, 251, 252, 254, 255 Messejana Fault, 7, 8, 22, 49, 110 Metagreywackes, 7, 128, 153, 156, 158, 199, 201, 206, 208, 215 Metamorphic rocks, 4, 86, 87, 92, 95, 128, 139, 151, 153, 155, 156, 158, 161, 283, 333 Microkarstification features, 217 Middle Devonian, 5, 7, 86, 153 Minde polje, 229, 236–240 Minho, 8, 36, 38, 163, 309, 340 Minho River, 14, 83, 84, 86, 93 Mining, 128, 339, 350, 354, 360, 370, 374 Miocene, 9–11, 16, 17, 19, 44, 54, 113, 117, 122, 123, 146, 157, 163, 164, 169, 170, 206, 212, 215, 255, 263, 266, 272, 273, 275–278, 297, 299, 300, 317, 333, 363 Miranda do Douro, 141, 147, 156, 170, 317 Miranda Plateau, 141 Mirandela, 15, 143, 170, 319 Mirandela basin, 143, 170 Mirandela depression, 15, 319 Mira River, 18, 109, 111, 114 Missing and homeless people, 47, 56 Mocho Real, 355 Mogadouro, 141, 173 Mogadouro Hills, 141 Mogadouro Mountain, 320 Moho discontinuities, 321, 324 Molybdenum, 128 Monchique Massif, 10, 122 Monchique mountain, 6, 18, 19, 21, 22, 36, 123, 252 Mondego Platform, 15, 179, 180, 187, 188 Mondego River, 21, 56, 175, 176, 178, 180–182, 217, 344 Monforte da Beira, 202, 203, 362

Index Monfortinho, 199, 200, 202, 203 Monge, 258 Monocline, 21, 22, 113, 265, 266, 297, 300 Monsanto, 203, 207, 298, 360, 361, 368, 369, 372, 373 Monsanto hill, 298 Monsanto inselberg, 19, 203, 207, 311, 345, 361, 363, 369 Monte de Vez, 215 Monte Figueira Formation, 111 Montejunto, 12, 19, 341 Montejunto massif, 211, 212 Montejunto mountain, 6, 21, 22, 34 Montemor-o-Velho, 181 Montemuro, 14, 333 Montemuro mountain, 6, 13, 152, 329–331, 333 Montemuro unit, 332 Monte Santos Conglomerate, 255, 263 Montesinho, 142 Moorish wall, 299 Moradal, 202, 205 Moradal mountains, 16 Moraine boulders, 188, 190 Moraines, 127, 132–136, 190–192, 197, 347, 350, 353, 354 Morais Massif, 141, 317, 319, 320, 322 Moraleja, 203 Moreirinha, 203, 207 Moreirinha inselberg, 19, 207 Morro da Sé, 282 Mountain massif of Monte Figo, 6, 22 Mountains, 4, 7, 10, 11, 13, 17–19, 21, 22, 24, 37, 39, 43, 44, 123, 127, 133–135, 141, 142, 179, 180, 185–188, 190, 196, 201, 232–234, 251, 256, 258, 263, 331, 335, 341, 342, 344, 347, 353, 355, 359, 361–363, 365, 366, 369 Mountain uplift, 110, 130, 135, 141, 142, 317 Mount Formosinho, 274, 276 Mount São Luís, 273, 274, 276 Mourela, 130 Mouros, 220 Mouros River, 217 Mousterian artifacts, 267 Municipal Emergency Plan, 74 Muradal monocline, 362, 364 Murracha, 203, 207, 364, 367, 371 Murrachinha, 203, 207, 364, 367 Mushroom boulders, 354 Muslim, 282, 299

N Narrow valley, 156, 203, 329, 330, 366 Nateiro, 171 National Ecological Reserve, 74, 75, 77, 308 National Park, 127–130, 132, 313 National Program on the Territorial Planning Policy, 73 National Strategy for Integrated Coastal Zone Management, 75 Natura 2000, 99, 103, 105, 106, 213, 308, 371 Natural hazards, 44, 73, 74, 79, 301, 326 Natural Monument, 308, 360 Natural Park, 99, 109, 127, 145, 206, 213, 273, 308, 313, 342, 350, 360, 371 Natural Park of Aire and Candeeiros Mountains, 213 Natural Park of Arrábida Mountain, 99, 213 Natural Reserve of Douro Estuary, 286 Natural Reserve of the Sado Estuary, 99 Naturtejo Geopark, 206, 308, 345, 359–362, 366–374 Nave de Santo António, 190–192, 195, 197, 312, 347, 356 Nave Travessa, 192, 312

Index Nazaré Canyon, 47, 48 Nazaré fault, 9, 11, 19, 21, 215 Neanderthals, 360 Neoproterozoic, 86, 93, 153, 186, 201, 215, 309, 329, 343, 360 Neotectonic activity, 47, 273, 317, 322, 363 Neotectonics, 12, 154, 182, 278, 285–287, 309, 322 Nerineia algarbiensis, 121 Nisa, 17, 199, 207, 208, 308, 360, 361, 363, 365–368, 370, 371 NisaGardunha, 371 Nogueira half-horsts, 16 Nogueira mountain, 6, 317, 318, 320 Normative instruments, 73 Nortada, 36 North Atlantic Oscillation Index, 38 Northeast Portugal, 139, 141, 142, 148, 152, 163, 173 Northerly winds, 36 Northern Beira, 157, 166 Northern Hemisphere Temperate zone, 33 Northern Meseta, 12, 13, 15–17, 93, 141, 163 North Iberian Plateau, 317, 319–322 North of Lisbon, 21, 49, 54, 59, 63–66, 229, 265–268, 271, 272 Northwest Portugal, 24, 34, 44, 79, 83, 92, 127, 281, 283 Nubbins, 348

O Ocean floor, 25, 47, 48, 321, 326 Ocean storms, 281 Ocreza River, 205, 360, 369, 370 Odelouca River, 123 Odivelas-Vialonga, 299 Odivelas-Vialonga Cuesta, 266, 268, 271 Oeiras, 295 Oitavos Dune, 255, 262, 263 Oleiros, 207, 308, 361, 371 Olho do Tordo, 223 Olhos de Água Beach, 56, 117, 118, 121 Olhos de Água de Ansião, 221 Olhos de Água do Anços, 221, 224 Olhos de Água do Dueça, 221 Olisipo, 299 Oliveira do Hospital, 342, 344 Oolithic limestones, 230 Oporto, 47, 54, 56, 83, 86, 89, 91, 96, 152, 173, 281–292, 318, 330 Ordovician Armorican Quartzite Formation, 201 Ordovician rocks, 5–7, 86, 141, 153, 156, 186, 201, 215, 309, 316, 332–334, 360 Ormonde peak, 25 Orographic barrier, 34, 127, 354 Oromediterranean bioclimatic stage, 43 Orthoclinal valley, 217 Ossa Morena Zone, 4–7, 283 Ourém basin, 230, 308 Outil-Cantanhede plateau, 211–213 Overdeepenings, 133, 190

P Paiva River gorge, 330, 335, 336 Paiva Walkways, 329, 335, 340 Palaeodune, 118, 119 Palaeokarst, 211, 218, 220, 224, 225, 230 Palaeovalleys, 122, 140, 322 Palaeozoic, 110, 123, 128, 139, 140, 212, 214, 273, 309, 344 Paleocene sediments, 154

385 Paleogene, 10, 11, 130, 141, 145, 146, 163, 164, 169, 170, 187, 201, 206, 252, 255, 263, 265–268, 275, 276, 278, 297, 299, 345 Paleogeographic evolution, 3, 4, 7, 10, 83 Paleo-Tagus River alluvial plain, 273 Paleothethys ocean, 343 Paleovalleys, 286, 317, 319, 320 Paleozoic metasedimentary rocks, 329 Paleozoic metasediments, 6, 14, 332 Paleozoic volcanic rocks, 6 Palynology, 99, 102, 107 Pangaea, 296 Paraglacial, 347, 351 Parautochthonous Complex, 316 Pardelhas Formation, 153 Pateira, 274, 278 Paufito granite, 129 Paulo Luís Martins Spring, 354 Peat-rich structures, 103 Peaty mountain soils, 135 Pedestal, 142, 143, 351, 354, 367 Pedra Amarela, 258 Pedrada, 127, 135, 136 Pedrada and Ermida granite, 129, 132, 135 Pedrada massif, 135 Pedras Brancas, 362 Pedras Ninhas, 203, 207, 364, 367 Pedrice blockslope, 194, 348 Peixão pond, 349 Pejão, 333 Pena, 258 Penacova, 179–181 Penacova-Régua-Verin fault, 48, 49 Pena de Numão, 132 Penamacor, 207, 308, 360, 361, 371, 372 Penameda, 132, 311 Peneda-Gerês National Park, 127–136, 313 Peneda mountain, 6, 13, 17, 34, 38, 42, 127–129, 132, 133, 135, 136, 185 Penedo do Castro, 180 Penedo do Sino, 351, 354 Penedo Durão scarp, 141 Penela-Alvaiázare, 215 Penela-Alvaiázere block, 219, 220 Penha Garcia, 19, 202, 207, 311, 363–365, 371 Penha Garcia-Cañaveral syncline, 362 Penhas da Saúde, 39, 193, 346 Penhas Douradas, 39, 348, 351 Peninha, 258, 259 Periglacial, 29, 42, 43, 93, 135, 136, 185, 186, 193, 194, 196, 211, 285, 347, 350, 351 Periglacial slope deposits, 133, 351 Permafrost, 185, 186, 194, 195 Perneval - São Pedro do Campo unit, 332 Peso da Régua, 152, 153, 157 Phytogeography, 99, 105, 107 Piacenzian, 11, 12, 89, 90, 146 Pia d’Água, 245 Pico da Nevosa, 127 Pico do Areeiro, 26 Pico do Facho, 26 Pico island, 5, 26–28, 35 Pico Mountain, 28, 312 Pico Ruivo, 26, 35 Piedmont, 113, 188, 199, 201, 206, 207, 275, 342–344 Pincães River Waterfall, 131

386 Píncaro, 276 Pinhão, 153, 157, 158 Pinhão Formation, 153 Pinus pinaster, 43 Pinus sylvestris, 43 Piornos, 355, 356 Planalto (plateau) Mirandês, 154 Planation, 10, 14, 17, 18, 156, 201, 202, 341, 344 Planation levels, 14, 130, 141, 156 Planation surface, 12, 14–20, 24, 29, 113, 130, 139, 142, 154, 161, 163, 167, 180, 187, 188, 199–203, 208, 217, 255, 319, 320, 329–331, 341, 344–346, 359 Planation surfaces of Cova da Beira, 187, 342, 345 Planation surfaces of Mondego, 15, 180, 187, 188, 342 Plataforma do Cabo, 274, 276, 277 Plateau, 19, 26, 42, 109, 118, 130, 135, 139, 141, 145, 157, 163, 164, 166, 167, 171, 172, 185–194, 202, 203, 211–213, 217, 220, 221, 229, 232, 235, 238, 299, 312, 317, 319, 320, 341, 342, 345, 347, 359, 363, 367 Plateau ice-field, 42, 133, 188–190, 341, 345, 348 Plateaus of Southern Portugal, 199, 208 Pleistocene, 10–12, 22, 42, 86, 106, 109, 111, 133, 135, 182, 185, 188, 196, 214, 217, 225, 263, 268, 275, 277, 281, 317, 341, 345, 348, 351, 360, 367 Pleistocene glaciation, 127, 136, 309, 312, 313 Pliocene, 10, 11, 19, 26, 89, 91, 109, 110, 113, 141, 142, 154, 155, 163, 164, 167, 179, 180, 182, 201, 214, 217, 220, 225, 255, 259, 263, 274, 275, 277, 285, 317, 363, 364 Plunging cliffs, 118, 121 Pluton, 128, 336, 339 Plutonic, 6, 139 Pocinho, 157, 168, 170–172 Poço do Inferno, 354 Poço dos Paus, 321, 325 Podzolization processes, 104, 105 Poiares syncline, 141, 142, 311 Poio Novo, 220 Poio Novo valley, 220, 223 Poio Velho, 220 Polar Front, 33, 34, 38, 42, 96 Polished surfaces, 135, 188, 347, 349 Polje, 217, 220, 229, 231, 236–238 Polje of Minde, 229, 236–241 Polygonal weathering, 368 Pombal, 54, 213 Pombares Massif granites, 318 Ponor, 217, 220, 221, 239 Ponsul and Sobreira Formosa faults, 199, 208, 359 Ponsul Fault, 48, 49, 200–207, 311, 362–365 Ponsul River, 203, 206, 363, 366 Ponta do Adoxe, 101 Ponte de Tábua, 176 Pop-up structure, 11, 187, 188, 341 Pop-up type mountains, 139, 140, 311 Portas de Ródão, 204, 206, 207, 311, 360, 362–364 Portas de Ródão Natural Monument, 308, 359, 371, 372 Portas do Almourão, 205, 206 Portela, 181 Portinho da Arrábida, 275, 277 Porto, 36, 41, 83, 91, 139, 309 Porto Covo, 109 Porto de Mós beach, 117, 120, 121 Porto Santo Island, 5, 25, 26, 33, 35 Porto-Tomar Fault, 8, 13, 21, 83–86, 96 Porto–Tomar shear zone, 330 Portuguese Central System, 142, 342

Index Portuguese discoveries, 282, 299 Portuguese Municipal Master Plans, 73 Port wine, 145, 151, 158, 160, 161, 173, 282 Postglacial fluvial incision, 192 Post-glacial runoff, 191 Póvoa da Lomba, 213 Praia da Adraga, 262 Praia da Murtinheira marine deposits, 183 Praia da Rocha beach, 122 Praia das Maçãs, 262 Praia Grande, 122, 261, 262 Presa, 360 Proença-a-Nova, 207, 308, 361, 366, 371 Protalus lobes, 194 Protected Landscape Area, 109 Protected Landscape Area of Montejunto massif, 213 Protected Landscape of the Fossil Cliff of Costa da Caparica, 308, 311 Proterozoic, 139, 153, 214, 215, 332, 344 Proto-Mondego, 179 Pseudobedding, 131, 132, 135, 142, 143 Push-up, 139, 140, 143, 148, 315 Pyrenean Orogeny, 142

Q Quartz, 7, 11, 128, 153, 182, 183, 231, 253, 267, 275–277, 283, 285, 317, 322, 326, 332, 335, 336, 339, 354, 355, 363 Quartzite, 7, 11, 16, 18, 24, 53, 86, 109, 128, 139, 141, 153, 156, 175, 180, 182, 183, 200–204, 206, 208, 215, 231, 275, 276, 316, 335, 339, 363, 365, 366, 369 Quartzite ridges, 12, 16, 18, 19, 106, 141, 142, 154, 181, 199, 202, 204, 205, 308, 331, 339, 359, 362, 365 Quartzite ridges of the Portas de Ródão, 204, 308 Quartzitic-Phyllite Formation, 153 Quaternary, 10, 12–15, 17, 22, 25, 26, 29, 83, 86, 90, 93, 96, 107, 110, 113, 140, 142, 148, 157, 163, 164, 167, 169, 175, 180, 181, 183, 211, 214, 215, 217, 220, 229–231, 243, 244, 254, 255, 259, 263, 265–268, 272, 273, 275, 277, 285, 286, 297, 345 Quaternary deposits, 86, 93, 163, 181, 241, 267 Quaternary fluvial retouching, 251, 263 Quebradas/hummocky morphology, 65 Queixa-Invernadoiro, 133 Quercus forests, 42 Quiaios and Cantanhede marine sands, 183 Quinta da Quada, 183 Quinta da Ventosa Formation, 153 Quinta do Infantado, 267, 269 Quinta do Vale Meão, 169 Quintanilho, 267–269 Quintãs Formation, 169

R Rabaçal, 217, 223 Rabaçal depression, 217, 218 Radial dykes, 252, 256 Rainfall, 14, 19, 26, 28, 29, 38, 39, 41, 44, 47, 49, 52, 56, 63–65, 68, 93, 110, 123, 127, 153, 178, 185, 224, 236, 237, 265, 270–272, 277, 289, 295, 296, 332, 353 Rainfall triggered, 265, 272 Rainfall-triggered landslide, 52, 63, 64, 271 Rainpit microforms, 240 Raised beaches, 12, 256, 257, 261, 263 Raiva, 178, 180 Ramisquedo cirque, 135 Raña, 12, 110, 200, 255, 263, 285, 317

Index Rapid debris flow, 54, 64 Rapids, 34, 41, 42, 103, 123, 145, 156, 300 Rapoula fault, 201, 363 Rasa, 24, 89, 312 Rebofa, 170, 171 Reboredo, 141 Reboredo hills, 141 Recessional moraines, 135 Reconquista, 282 Rectilinear structure-controlled valleys, 164 Regional and Municipal Master Plans, 74 Regressive erosion levels, 155, 156 Régua, 157 Reguengo do Fetal fault scarp, 234 Regulation of Safety and Actions for Building and Bridge Structures, 74 Relative sea level change, 109 Relict cryonival deposits, 211, 220, 229, 243, 249 Residual crests, 148 Residual hills, 18, 130, 131, 135 Residual ridges, 139, 141, 148 Residual sedimentary relief, 199, 200, 202, 203, 208 Rheic Ocean, 7, 316, 321, 343, 360 Ria, 181, 311–313 Ria de Alvor, 122 Rias of Galicia, 83 Ribamar diorite, 252 Ribeira das Negras valley, 134 Ribeira da Vila, 164 Ribeira de Mortágua, 183 Ridge mountain settings, 188 Riegel, 133, 351 Rifting episode, 296 Rills, 131, 132 Ring felsic dykes, 252 Rinnenkarren, 240, 248 Rio Maior, 232 River Arda, 330, 332 River captures, 207 River Douro, 11, 13–16, 36, 91, 93, 139, 141, 143–146, 152–154, 156, 157, 164, 165, 169–173, 281–283, 286–291, 318 River network incision, 141 River Paiva, 330–332, 335, 337, 339 River terraces, 143 River valleys dominate, 329 Rocalva, 132, 311 Rocalva valley, 134 Roches Moutonnées, 188, 189, 347, 351 Rock falls, 26, 230, 261, 291, 351 Rock fractures, 240 Rock glacier, 194 Rock-shelters, 211, 220, 222 Rocky Coast, 54, 83, 117, 118, 121 Rodão, 203, 311, 360, 363 Ródão - Idanha a Nova – Moraleja, 201 Ródão syncline, 362 Roman, 105, 111, 151, 171, 220, 224, 282, 295, 299, 335, 339, 342, 354, 360, 369, 370 Romanesque, 282, 284 Rosmaninhal, 363, 369 Rotational slide, 54, 64, 69, 77, 271 Rouças, 135 Rounded boulders, 133, 156, 192, 336 Rounded karren, 220 Rugged relief, 127, 130, 131, 135 Runoff, 11, 43, 67, 159, 160, 225

387 S Sabor, 15, 155, 318, 319 Sabor River, 164, 165, 171, 173, 317, 319–322, 324 Sabor Valley, 315 Sado estuary lagoon, 99–107, 312 Sado River, 10, 22, 99 Sagres, 24, 49, 109, 113, 118, 119, 311 Sagres-Algoz flexure, 22 Sagres unit, 110, 113, 114 Salabardos, 182 Salavessa, 203 Salema, 109 Salema beach, 121 Salgueiro do Campo, 202 Salselas, 317, 322, 326 Salt marsh ecosystems, 99 Salvaterra do Extremo, 360, 366, 368 Sanabria Lake moraine complex, 135 Sand spit, 99–102, 107, 122, 287 Sandstones, 6, 8, 10, 54, 56, 65, 66, 68, 78, 102, 113, 120, 121, 169, 175, 201 sandstones, 214, 215, 230, 254, 255, 261, 262, 265–268, 275, 276, 285, 300, 335 Santa Catarina, 295, 300, 301 Santa Catarina earthquake, 295 Santa Clara a Velha Monastery, 176, 177 Santa Comba Hill, 141 Santa Combinha, 318 Santa Cruz, 171 Santa Maria Island, 5, 26–28, 35 Santana, 295 Santiago do Cacém, 212 Santo André, 295 Santo António, 135, 232, 234, 235 Santo António bridge, 193 Santo António plateau, 235, 237, 238, 240, 241, 245, 248 São Domingos Formation, 153, 158 São Félix the quartzite ridge, 86 São Francisco, 274 São Francisco Xavier Fort, 283, 286 São Gião, 213 São João, 132, 147, 256, 259, 311 São João das Arribas, 147, 311 São João das Júnias, 132 São João das Lampas platform, 256, 259 São Jorge Castle, 295, 299–301 São Jorge hill, 299 São Jorge island, 5, 26–28 São Julião do Tojal, 267–269, 272 São Luís anticline, 275, 276, 278 São Mamede mountain, 13, 18, 38 São Mamede plateau, 232, 234, 235 São Marcos-Quarteira depression, 19 São Miguel island, 5, 26–28, 313 São Paio bay, 286, 287, 289, 290 São Pedro Velho, 335, 338 São Roque, 295 São Sebastião, 194, 348 São Vicente, 117, 295 Sarzedas, 201, 203, 205, 360, 363, 364, 367 Schist-Greywacke Complex, 5, 179, 187, 284, 343 Schistosity, 156, 333 Schists, 4, 15, 29, 53, 86, 128, 135, 136, 141, 146, 153, 156–160, 175, 180, 182, 183, 215, 276, 283, 284, 316, 333, 345, 360, 361, 370 Scree slopes, 194 Sea cliffs, 273, 274, 277, 311

388 Sea level fluctuations, 111, 115, 273, 277, 278, 286, 297 Sea level rise, 54, 75, 93, 99, 101, 103, 104, 106, 181, 286, 289 Seasonal frost, 195 Sea surface temperature, 42 Sediments, 5, 7, 10, 22, 24, 42, 43, 54, 56, 86, 90, 93, 99, 101–105, 109–111, 114, 118, 121, 122, 134, 135, 141–143, 145, 148, 153, 157, 163, 164, 170, 173, 175, 178, 179, 181, 187, 201, 229, 230, 241, 265, 268, 275, 276, 287, 288, 297, 316, 317, 319–322, 364, 366, 367 Segundera-Cabrera, 133 Seia-Lousã fault, 15, 16, 48, 49, 345 Seismic waves, 26 Selvagens islands, 5, 25, 33 Semi-horst of Serra do Cercal, 111 Sendim, 317 Sendim tectonic palaeo-valley, 141 Senhora da Estrela, 213 Senhora da Mó, 330, 333, 339 Senhora da Peneda, 129, 131 Serlei, 330, 336, 338 Serra Amarela, 127, 129, 131, 133, 135 Serra da Arrábida, 211, 212 Serra da Boa Viagem, 183, 211–213 Serra da Estrela, 16, 17, 36, 37, 39, 42, 43, 133, 135, 175, 179, 180, 183, 185–197, 341, 342, 345, 346, 350, 354 Serra da Nogueira, 143 Serra da Ota, 212 Serra da Peneda, 127, 129–133, 135 Serra das Janeanes, 220 Serra da Villa erosive palaeosurface, 217 Serra de Alvaiázere, 219, 220 Serra de Ariques, 220 Serra de Bornes, 143 Serra de Montesinho, 139, 141–143 Serra de Mouro, 219 Serra de Sicó, 219, 220 Serra de Sintra, 24, 251, 252, 255–263 Serra do Bouro, 212 Serra do Caramulo, 180 Serra do Cercal, 110, 112 Serra do Circo, 219, 220 Serra do Gerês, 127, 130–135, 163 Serra do Marão, 152, 153, 156, 163 Serra do Pilar, 282, 291, 292 Serra do Rabaçal, 217, 219, 220 Serranos, 341 Serras da Aveleira and Roxo, 180 Serras de São Bento and Moinhos, 183 Serra Serrada, 142, 143 Serrinha, 362 Sesimbra, 274, 276 Setúbal Peninsula, 10, 99, 102, 273, 275, 276 Shallow slides, 66, 265, 272 Shallow slips, 66 Shallow soils, 160, 272 Shallow translational slides, 54, 269, 270, 272 Shore platforms, 91, 120, 121 Sicó massif, 211–215, 217–221, 224, 225 Sicó mountain, 6, 21 Sierra de Guadarrama, 185 Siliciclastic cover, 211, 213, 219–222, 225 Sills, 128, 252, 253, 255, 256 Siltation, 175, 176, 178, 181 Silurian, 5, 7, 128, 129, 153, 321 Silurian quartzite ridges, 141 Silurian schists, 142

Index Silva, 12, 48, 102, 252, 282, 317, 367 Silveirinha dos Figos, 201 Silves, 8, 20, 22 Silves Sandstones, 8, 20, 22 Sines, 10, 24, 47, 48, 102, 109, 252 Sinkholes, 123, 217, 220 Sintra Intrusive Complex, 254, 255, 263 Sítio das Pessoltas, 194 Slope dynamics, 186, 292, 350, 351 Slope movements, 49, 54, 265, 269–272, 281, 291, 292 Small granite landforms, 202, 203 Soajo, 129, 132 Sobreira Formosa, 199, 200 Sobreira Formosa Fault, 12, 199, 201, 203, 208, 363 Sobreira Formosa-Grade Fault, 16, 359, 363, 364 Socalcos, 146 Social damage, 47 Soil, 22, 29, 44, 53, 64–66, 68, 151, 158–161, 225, 272, 282, 300, 307, 333, 370, 374 Soil erosion, 43, 44, 74, 151, 157–160 Solifluction deposits, 91–94, 231 Solifluction lobes, 193 Soprador do Carvalho (or Talismã) cave, 221 Sotavento, 117 Southern Europe, 43, 107, 127, 133 Southern Meso-Cenozoic Borderlands, 52, 54, 211 South Portugal Planation Surface, 199, 201 South Portuguese Zone, 5–7, 309 Souto do Concelho, 187, 194, 348 S. Paio beach, 88, 90, 91, 94 Sparse moraine covers, 192 Speleology, 276 Spitzkarren, 235, 240, 248 Stacks, 26, 77, 121, 122, 261 Steep cliffs, 145, 261 Steep slopes, 14, 54, 63, 130, 131, 133, 146, 151, 156–161, 234, 261, 266, 272, 281, 298, 319, 332, 342 Step-like architecture, 187 Stepped surfaces, 14, 15, 141, 251, 287 Straight-tusked elephant surface, 360 Straight valleys, 129 Strath terraces, 172, 199, 206, 208 Stratified slope deposits, 194, 220, 231, 348, 351 Striated rock, 133, 135 Striations, 189 Strike-slip fault, 7, 11, 19, 48, 109, 110, 129, 139, 142, 143, 154, 157, 163, 167, 187, 274, 318, 344 Strike-slip fault of Bragança-Manteigas, 7, 14–16, 156, 157 Strike-slip faults of Verín-Penacova, 7, 14, 15, 157 Strike-slip Porto-Coimbra-Tomar fault zone, 215 Strike-slip tectonic basins, 143 Subduction zone, 13, 48, 300 Subglacial melt-out till, 134, 135 Subglacial till, 133, 136 Submarine mountains, 4, 13 Subtropical anticyclonic belt, 33 Suevi, 282 Superimposition, 206 Supraglacial till, 134, 135 Supramediterranean stage, 43 Sustainable development, 75, 301, 329, 340, 355, 359 Swallow holes, 224, 229, 231, 236, 237, 239, 240 Syncline, 18, 180, 207, 253, 255, 257, 261, 275, 333, 363, 364 Syn-tectonic Variscan granites, 154

Index T Tafoni, 132, 368 Tagus basin, 10, 229, 230, 234, 235, 238, 267, 276 Tagus Cenozoic basin, 229, 265 Tagus fluvial terraces, 359 Tagus River, 13, 17, 21, 36, 106, 217, 229, 255, 268, 275, 295–299 Tagus River alluvial plain, 22, 23, 65 Tagus Tejo River, 359, 361, 369 Tagus Valley Prehistoric Art Complex, 369 Tahiti, 131 Talhadas Mountains, 360–363 Talus screes, 231 Talus slopes, 347, 348, 351 Tectonic basins, 140, 143, 163, 166, 167, 173, 311, 322 Tectonic inversion, 10, 11, 29, 273 Tectonic landforms, 17, 139–141, 199, 202, 203, 208, 320, 326, 359, 363, 365 Tectonic rim, 24 Tectonics, 3, 4, 7–16, 18, 19, 21, 22, 24–27, 29, 44, 47, 49, 65, 74, 83, 85, 88, 90–92, 96, 109–112, 115, 123, 130, 135, 139–143, 145, 148, 151, 153–157, 163–167, 169, 170, 179–181, 187, 188, 199–201, 205, 207, 211, 213, 215, 217, 219, 221, 229–232, 234–238, 254, 267, 273, 275–278, 281, 284, 285, 296, 297, 309, 311, 315, 317–319, 321, 322, 329–335, 341–344, 346, 348, 354, 362, 363, 365 Tectonic subsidence, 235, 275 Tectonic uplift, 11, 12, 182, 219, 229, 272, 273, 278 Tejo, 199–202, 204–207, 312, 359, 371 Tejo River, 200, 201, 203 Teleférico moraine, 192 Temperate Mediterranean climate, 274, 330 Temporary exsurgences, 217, 220 Tentúgal-Gabrielos Deposits, 183 Terceira Island, 5, 26–28 Terceira Ridge, 49 Terceira Ridge Leaky Transform, 12, 48, 49 Terceira Rift, 26 Termas de Monfortinho, 360, 370 Terminal moraines, 134, 197 Terraced slopes, 151, 158, 160, 161 Terraces, 159, 168, 171, 172, 175, 192, 193, 201, 204, 205, 265, 267–269, 272, 311, 335, 370 Terrace staircases, 201, 205, 207 Terraces with schist stone walls, 151 Terra Fria trasmontana, 171 Terra Quente (Hot Land), 171 Terra rossa, 230, 231 Terras de Cavaleiros Geopark, 308, 315, 317–322, 326, 327, 370 Tertiary sediments, 234 Tethys, 4, 7–10, 29 Thermal belt, 37 Thermal expansion, 54 Thermal metamorphism, 255, 258 Thermomediterranean character, 43 Tholeiitic cycle, 252 Thrust fault, 13, 219, 253, 262, 317, 324 Till deposits, 133, 136 Tin, 128, 326, 354 Tomar-Córdoba Shear Zone, 361 Tor, 131, 142, 189, 191, 193, 256–259, 263, 322, 348, 350, 351, 354, 356 Torre de Moncorvo, 141, 157, 172, 173 Torre—Penhas Douradas plateau, 188, 347 Torre Plateau, 16, 189, 190, 347, 349, 350 Torre Vale de Todos, 215, 217 Tortonian, 130, 142, 145, 187, 201, 255, 263, 266, 275, 277, 363, 364

389 Toulões, 203, 371 Tourém, 129, 130 Trás-os-Montes, 34, 36, 38, 106, 139–141, 163, 167, 168, 173, 179, 309, 316 Tróia Peninsula, 99–107 Tróia Roman archaeological site, 101 Tróia-Sines coastal arc, 99, 102 Trancão River, 265, 269, 272 Transgressive, 262, 288 Transitional cycle, 252 Translational flow, 64, 271 Translational rotational flow, 64 Travessa lagoon, 103–105 Trevinca massif, 135 Triangular facets, 143 Tsunami, 47–49, 51, 56, 74, 76, 107, 121, 299 Tua, 155, 157, 318 Tua River, 156, 318 Tungsten, 128, 326 Turbidites, 5, 18, 24, 109, 114, 153

U Umbric leptosols, 158 UNESCO, 123, 151, 158, 206, 251, 281, 292, 307, 308, 315, 316, 318, 326, 329–333, 339–342, 347, 350, 359–361, 370–372 UNESCO Naturtejo Geopark, 374 Unhais da Serra, 187, 192, 344 Unhais da Serra thermal springs, 354 Uplifted blocks, 130, 229 Upper Cretaceous, 18, 21, 54, 214, 215, 251, 256, 261, 267, 268 Upper Douro, 15, 16, 152, 153 Upper Jurassic, 9, 54, 64, 65, 118, 212, 219, 230, 234, 253–256, 259, 265, 268, 270, 271, 275–278 Upper Ordovician quartzites, 141 Upper Oxfordian, 230, 254 Urban geomorphology, 299, 301 Urban landscape, 91, 282, 286, 299 Urbión mountain, 152 U-shape, 133, 190, 347, 350 U-shaped valleys, 127, 132–136 Uvala, 220, 229, 231, 237, 241

V Vale da Porca, 317, 320, 322 Vale da Porca-Talhinhas depression, 319 Vale das Fontes, 213 Vale da Vila, 164, 169 Vale de Baixo, 171 Vale de Cambra fault, 331 Vale do Conde, 192 Vale do Conde moraine, 192 Vale Meão, 143 Valley glaciers, 17, 42, 185, 188, 189, 192, 341, 345 Valleys abandoned after capture, 208 Valongo anticline, 86 Valverde- Senhor das Chagas horst, 10 Varanda dos Carqueijais, 346, 354 Varanda dos Pastores, 355 Varandas de Avô, 355 Variscan granites, 329, 344, 361 Variscan Massif, 153 Variscan orogen, 5, 86, 315, 341, 343, 344 Variscan orogeny, 86, 128, 130, 153, 157, 187, 315, 317, 321, 322, 344, 360, 363

390 Variscan thrust fault, 362 Vau fluvial beach, 330, 335 Várzea, 217, 267, 332, 339 Várzea da Granja depression, 215 Várzea da Póvoa, 217 Várzea do Crasto, 187, 194 Velha de Rodão gorge, 203 Verín, 157 Verín-Penacova, 7, 14, 15, 86, 157, 330 Verín-Penacova fault, 13, 157, 180, 331 Verride anticline, 211, 212 Vez river, 135, 136 Viana do Castelo, 88 Vicentine Coast Natural Park, 109 Vidigueira fault, 17 Vidigueira-Moura Fault, 48, 49 Vigia mountain, 6, 18 Vila Nova de Foz Côa, 145 Vila Nova de Gaia, 286, 289, 290 Vila Nova de Milfontes, 20, 109–112, 114 Vilariça, 16, 86, 139, 142–145, 163–165, 167–173, 311, 318, 319 Vilariça Creek, 164, 171 Vilariça fault, 140–146, 148, 157, 315, 317–323 Vilariça Formation, 145, 146, 167, 169 Vilariça graben, 157 Vilariça scarp, 143 Vilariça strike-slip basin, 143, 321, 322 Vilas Ruivas- Arneiro graben, 362 Vila Velha de Ródão, 200, 202, 204, 205, 207, 308, 361–363, 371 Vila Velha de Ródão - Nisa plateau, 202, 208 Vimioso, 317 Vinagre Formation, 255, 263 Vinagra-Portas de Ródão fault, 362 Vineyards, 145–147, 151–153, 157–161, 171 Visigoth, 282, 360 Volcanic activity, 7, 25, 26, 43, 297 Volcanic tuffs, 265, 270 Vouga, 47, 56, 163, 330, 332 Vouga basin, 330

Index W Waterfalls, 130, 131, 145, 146, 229, 238, 241, 244, 311, 313, 334, 335, 353 Weathering, 14, 29, 63, 118, 120, 132, 140, 154, 156, 158, 175, 190, 193, 201, 203, 256, 258, 263, 285, 291, 332, 333, 336, 348, 353, 354, 363, 367, 368 Weathering mantle, 53, 63, 189, 191, 258, 263, 332, 363 Weathering pits, 131, 142, 335, 336, 354 Western Iberian System, 169 Western Meso-Cenozoic Borderlands, 52, 54 Western Mountains, 133, 152, 157, 163, 167, 330, 332 Western or Lusitanian Basin, 4, 265, 273 Western unit, 332 Wilson cycle, 4, 7, 28 World Heritage, 145, 147, 151, 251, 281, 292

X Xistos do Ramalhão, 255

Y Younger Dryas, 42, 43

Z Zambujeira do Mar, 109 Zanclean, 123, 146, 169, 201 Zebreira, 207, 360, 363 Zêzere, 39, 47–49, 52–54, 56–58, 63–65, 73, 188, 189, 267–272, 295, 299, 300, 311, 342, 344, 353, 354 Zêzere glacial valley, 17, 190, 350 Zêzere glacier, 195, 347, 350 Zêzere River, 16, 217, 366, 367 Zêzere Valley, 37, 185, 188–191, 193, 194, 312, 347, 350, 353, 354, 365 Zonal circulation, 33, 34