Electrical Phenomena During Freezing of Water and Soils 9780784415085, 9780784409473, 9780784409893, 9780784475485, 9780784401927, 9780784484487, 9780784484494

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Electrical Phenomena During Freezing of Water and Soils PROBE INSTALLED IN PINGO 9

PINGO 9

PROBE INSTALLED IN PINGO 9

LOCATION MAP OF PINGO 9

V. R. (Sivan) Parameswaran, Ph.D., P.Eng. PINGO 9

Sponsored by the Frozen Ground Committee

Electrical Phenomena During Freezing of Water and Soils

Other Titles of Interest Frost Action in Soils: Fundamentals and Mitigation in a Changing Climate, edited by Sally A. Shoop (ASCE/Cold Regions 2020). This report reviews and updates the state of knowledge on frost-action fundamentals, the impact of climate change, and mitigation of frost action on pavements and other structures. (ISBN 978-0-7844-1508-5) Permafrost Foundations: State of the Practice, edited by Edwin S. Clarke (ASCE/Cold Regions 2007). This TCCRE Monograph presents the most current techniques available for the design and construction of foundations on permafrost. (ISBN 978-0-7844-0947-3) Frozen in Time: Permafrost and Engineering Problems, by Siemon W. Muller; edited by Hugh French and Frederick Nelson (ASCE/Cold Regions 2007). This book, a previously unpublished revision of Siemon W. Muller’s classic work on engineering and permafrost, offers an advanced and unusually comprehensive treatment of permafrost science and associated engineering problems. (ISBN 978-0-7844-0989-3) Thermal Analysis, Construction, and Monitoring Methods for Frozen Ground, edited by David C. Esch (ASCE/Cold Regions 2004). This TCCRE Monograph contains 13 papers presenting the latest in design theory and engineering practice for analyzing, constructing, and monitoring foundation soils affected by permafrost. (ISBN 978-0-7844-7548-5) Cold Regions Utilities Monograph, Third Edition, edited by Daniel W. Smith. (ASCE/Cold Regions 1996). This volume introduces the basic principles of cold region environmental engineering as they relate to the delivery of water, the removal of liquid and solid wastes, and the provision of power. (ISBN 978-0-7844-0192-7)

Electrical Phenomena During Freezing of Water and Soils Sponsored by the Frozen Ground Committee of the Cold Regions Engineering Division of the American Society of Civil Engineers

V. R. (Sivan) Parameswaran, Ph.D., P.Eng.

Published by American Society of Civil Engineers

Published by American Society of Civil Engineers 1801 Alexander Bell Drive Reston, Virginia 20191-4382 www.asce.org/bookstore | ascelibrary.org Any statements expressed in these materials are those of the individual authors and do not necessarily represent the views of ASCE, which takes no responsibility for any statement made herein. No reference made in this publication to any specific method, product, process, or service constitutes or implies an endorsement, recommendation, or warranty thereof by ASCE. The materials are for general information only and do not represent a standard of ASCE, nor are they intended as a reference in purchase specifications, contracts, regulations, statutes, or any other legal document. ASCE makes no representation or warranty of any kind, whether express or implied, concerning the accuracy, completeness, suitability, or utility of any information, apparatus, product, or process discussed in this publication, and assumes no liability therefor. The information contained in these materials should not be used without first securing competent advice with respect to its suitability for any general or specific application. Anyone utilizing such information assumes all liability arising from such use, including but not limited to infringement of any patent or patents. ASCE and American Society of Civil Engineers—Registered in US Patent and Trademark Office. Photocopies and permissions. Permission to photocopy or reproduce material from ASCE publications can be requested by sending an email to [email protected] or by locating a title in the ASCE Library (https://ascelibrary.org) and using the “Permissions” link. Errata: Errata, if any, can be found at https://doi.org/10.1061/9780784484487. Copyright © 2023 by the American Society of Civil Engineers. All Rights Reserved. ISBN 978-0-7844-8448-7 (PDF) ISBN 978-0-7844-8449-4 (ePub) Manufactured in the United States of America. 27 26 25 24 23    1 2 3 4 5

Contents Preface...........................................................................................................................................ix About the Historic Images.....................................................................................................xi Acknowledgments................................................................................................................. xiii Chapter 1  Introduction................................................................................ 1 Chapter 2  Early Observations of Electrical Phenomena in Nature.......... 3 2.1 Definition of the Phenomenon..........................................................................3 2.2 How the Problem Was Initiated in the Early 1950s......................................3 2.2.1 Historical Background..............................................................................3 2.2.2 Charge Separation Mechanisms in Clouds......................................4 2.2.3 Electrical Charges Associated with Clouds......................................4 References............................................................................................................................5 Chapter 3  Early Observations..................................................................... 7 3.1 How Do These Values Relate to the Potentials That Developed?..........7 References......................................................................................................................... 10 Chapter 4  Early Measurements................................................................. 13 References......................................................................................................................... 14 Chapter 5 Early Laboratory Measurements in Water and Dilute Solutions���������������������������������������������������������������������������������� 17 References......................................................................................................................... 24 Chapter 6  Measurements in Pure Water.................................................. 27 References......................................................................................................................... 30 Chapter 7  Freezing Potentials in Aqueous Solutions............................. 31 References......................................................................................................................... 35 Chapter 8  Freezing Potential Measurements in Soils............................. 37 References......................................................................................................................... 47 Chapter 9  Scope of the Studies of Electrical Potentials during Freezing/Thawing..................................................................................49 References......................................................................................................................... 54 Chapter 10 Description of the Work Done in the National Research Council Canada, Ottawa�������������������������������������������������������� 55 Appendix A: Experimental Setup in NRCC Laboratories.................................. 56 v

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Contents

Appendix B: Laboratory Experiments in Moist Soils.......................................... 65 Appendix C: Explanation of the Reversal of Potentials While Freezing...... 67 References......................................................................................................................... 67 Chapter 11 Freeze–Thaw Studies at Carleton University, Department of Geography and Environmental Sciences����� 69 References......................................................................................................................... 75 Chapter 12  Field Studies............................................................................77 12.1 Illisarvik Site............................................................................................................ 77 12.2 Inuvik Site................................................................................................................ 80 References......................................................................................................................... 85 Chapter 13  Results and Discussions of Field Studies.............................. 87 13.1 Illisarvik Site............................................................................................................ 87 13.2 Inuvik Site................................................................................................................ 87 References......................................................................................................................... 90 Chapter 14  Field Studies of EFP in Freezing Lakes in Inuvik.................. 91 References......................................................................................................................... 95 Chapter 15  Results from Lake Studies in Inuvik: Upland and Delta Lakes.............................................................................................. 97 Reference........................................................................................................................... 99 Chapter 16  Concluding Remarks............................................................ 101 How It Works...................................................................................................................102 Scientific Use...................................................................................................................102 Justification for Continuing Investigations on Electrical Potentials and Other Electro-Kinetic Phenomena Occurring during Freezing of Soils and Solutions.....................................................................103 Reference.........................................................................................................................103 Appendix A: Background: Basic Information of Potential Measurements����������������������������������������������������������������������105 Ground..............................................................................................................................105 Coulomb’s Law...............................................................................................................105 Electric Flux and Gauss’s Law....................................................................................107 Charge Transport and Electric Current..................................................................107 Reference.........................................................................................................................107 Appendix B: Calculations of Charge Concentration at a Metal/ Dielectric Interface and Force of Adhesion������������������������109 References....................................................................................................................... 113 Appendix C: G  eophysical Methods Used in Permafrost Investigations����������������������������������������������������������������������� 115 Electrical Methods........................................................................................................ 115 C.1 Electrical Resistivity............................................................................................117

Contents

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C.2 Galvanic Resistivity Data.................................................................................. 120 C.3 Surface Geophysical Methods....................................................................... 120 C.4 Time-Domain Reflectometry in Permafrost............................................. 121 C.4A Principles of Time-Domain Reflectometry Measurements.......................................................................................122 C.4B Ground-Penetrating Radar............................................................... 124 References....................................................................................................................... 124 Bibliography................................................................................................ 129 Index............................................................................................................. 139

Preface This book reviews the early observations of the generation of charges and electrical potentials that developed during freezing of water and dilute aqueous solution and in moist soils. Atmospheric electricity associated with lightning and thunder has been studied from very early days by scientists and engineers who were curious to understand the mechanism of the phenomenon and to measure the magnitude of the electricity generated and their possible effects on our daily lives. As Basil John Mason speculated in his 1957 book, The Physics of Clouds, lightning and thunder could generate up to about 3.6 million volts! This review describes some of the early observations and studies of the natural phenomena—lightning and thunderstorms. Beginning from these very early observations of the electricity generated during freezing, early laboratory measurements in solutions and soils are described. The significance of these electrical potentials that developed across a freezing interface in permafrost areas is brought out and some field measurements are described. Possible improvements in measurement techniques and combining with other geophysical methods currently used in the field are also discussed. The book contains extensive data on the measurements of the electrical freezing potentials (EFP) carried out in the laboratory and in the field, with accompanying references.

ix

About the Historic Images In this book are images that are rare and in many cases one of a kind. They have been gathered by the author for the purpose of preserving the past when discussing electric phenomena. We ask the reader to understand that the quality is secondary to the importance of having a historic record in the form of this book.

xi

Acknowledgments The author is grateful to many of his past associations—institutions and colleagues with whom he worked closely on this problem. The Division of Building Research (DBR) of the National Research Council Canada (NRCC), Ottawa, where the author was a research officer for 12 years in the late 1970s and 1980s, encouraged and provided cold room facilities and other equipment for this work. The author appreciates the permission granted by Edward Penner, the Head of the Geotechnical Section in DBR at that time to pursue this work that arose out of serendipity, aside from his regular research program on foundations in permafrost. Harry Baker, his colleague, pointed out the merit of researching on the topic of electric potentials at the freezing interface, as he himself was trying to use the TDR technique to study frozen soils. Several technical officers, Gary Mould, Colin Hubbs, and others, helped with the setting up of the equipment, and the workshop at DBR did an excellent job in making the probes. A cold fluid circulating bath was provided by the Department of Energy Mines and Resources, Canada, from its laboratories on Booth Street, Ottawa. The author is thankful to Dr. Stephen Jones, the Head of the Ice Research Team at the Department in the 1970’s for this. In fact, the author was invited to come to Canada to work on the mechanical properties of ice by Dr. Jones and the author is grateful to him for this. The author is also grateful to the late G. H. (Hank) Johnston, research officer at DBR/NRCC, for introducing him to the Northern Terrain (in Inuvik) and helping him in installing the probes in the hummocks there. Professor Ross Mackay and his students in the Geography Department, University of British Columbia, helped in this installation. Professor Mackay also encouraged the author to construct the long probe for installation in Pingo 9 (shown on the cover page of this book) in the Tuktoyaktuk Peninsula and arranged flights (by helicopter) to transport the probe and helped to install the same in the pingo. Professor Christopher Burn of the Department of Geography and Environmental Sciences invited the author to be an adjunct professor in the department and provided facilities for designing the equipment to study EFP in freezing aqueous solutions in the laboratory, and later, to make the probes installed in the Inuvik Lakes. Larry Kutny, in-charge of the work-shop of Carleton University Geography Department, helped in fabricating the probes that were installed in the Inuvik sites and Quang Ngo of the same work-shop helped with making the equipment for laboratory studies conducted in Carleton University. Chris Burn and the author are grateful to the staff of Inuvik Research Laboratories (now known as Western Arctic Research Centre), in particular to Larry Boyle, for help in field measurements.

xiii

xiv

Acknowledgments

The author is thankful to Professor Zhaohui (Joey) Yang, Professor of Civil Engineering, University of Alaska, Anchorage and chair of the Frozen Ground Subcommittee of CRED/ASCE during 2020–2022, for his encouragement to publish this book through ASCE, and to Jay Snyder, Manager of Technical Advancement at ASCE in Reston Virginia, for facilitating this publication. Finally, the author is grateful to the Editorial Staff of ASCE and to Michie Gluck, senior manager, Book Production, for their excellent work in pointing out several corrections needed in the references, and for providing the Index, Preface, and the list of Other Titles of Interest to this volume.

CHAPTER 1

Introduction

Permafrost is widespread in the Northern Hemisphere, in the Arctic regions such as Greenland, the US state of Alaska, northern Canada such as Northwest Territories—Yukon and Nunavut—China, and Eastern Europe. Permafrost is present in 85% of Alaska, 55% of Russia, and Canada. In the Southern Hemisphere, probably all of Antarctica may be underlain by permafrost. Permafrost can be found on land as well as below the ocean floor. It is found in areas where temperatures rarely rise above the freezing point. With construction activities increasing in the northern regions underlain by permafrost, for excavations of minerals, oil, and gas and building new communities and improving the existing facilities for the people who have been living there for the last several centuries, it is important to study the behavior of frozen ground and how it will be affected by these construction activities. A considerable number of studies are being undertaken for this purpose and to develop techniques to monitor the extent and behavior of frozen ground. Geotechnical methods used in the investigation of frozen ground in permafrost areas include several electrical methods, some of the commonly used being the direct-current electrical resistivity measurements, self-potential measurements, and induced-polarization methods, including spectral-induced polarization, electrical resistivity measurements, and to some extent measurement of electrical potentials generated across a freezing interface. Some of these methods are described briefly in this book with relevant references. The main emphasis, however, is on the measurement of the electrical freezing potential (EFP). This book specifically deals with the development of electrical potentials observed during freezing and thawing of water, dilute aqueous solutions, and moist soils in the laboratory and in the field in cold regions. In permafrost areas where the ground goes through yearly freezing and thawing cycles, electrical potentials of small magnitudes, ranging from a few millivolts to several volts, have been observed and measured across the freeze–thaw interface. Note: A millivolt is a unit of potential equal to one-thousandth of a volt, which is a measure of the potential energy of a unit charge at a given point in a circuit relative to a reference point, the ground. These have been measured using suitable probes installed in the ground, in freezing lakes, and inside a freezing Pingo. Pingos, also called Hydrolaccoliths or 1

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Electrical Phenomena During Freezing of Water and Soils

Bulgunniakhs, are mounds of earth-covered ice mainly found in the Arctic and Subarctic regions that can reach up to 70 m (230 ft) in height. EFP measurements have been made by several scientists and engineers in water and dilute aqueous solutions, beginning in the 1950s. This book traces the origin of the studies of electrical freezing potentials and how the research progressed with time and looks into the future possibilities of such studies. The book is divided into a few chapters devoted to the studies in the laboratory in the early stages (1950s), field studies in freezing and thawing ground in permafrost areas, some considerations on the mechanism and theory of EFPs, possibility of future studies using more sophisticated techniques and equipment, considerations of the possibility of using such potentials for any practical purposes, and looking into the possibility of using EFP measurements as a geophysical method to detect the freezing/thawing interface in permafrost areas. These chapters cover the following. 1. What is EFP? Why should one know about it? How did the studies start? 2. Early work: Background and history—EFP in water and dilute solutions: while freezing and thawing; and EFP in soils: laboratory studies and in freezing and thawing ground. 3. Recent measurements and observations: Laboratory and field studies: ○

Theoretical studies,

○

Future work needed using more sophisticated measurement techniques,

○

Combining with other measurement techniques such as TDR,

○

Considerations for practical use of such electrical potentials, and

○

Conclusions.

In Appendix A, some definitions of the basic terminology used in electrostatics, such as charge, electric field, flux, charge transport, electric current, and others, are given. In Appendix B, a brief calculation of charge concentration at the metal/dielectric interface and the force of adhesion are given. In Appendix C, the general geophysical methods used in the field in the study of permafrost are briefly reviewed. This book discusses the possibilities of EFP measurements and their usefulness in future developments: (1) If freezing produces an electrical potential, will the application of a reverse potential prevent ice accumulation around pipelines and other structures? (2) Can one use the potentials that developed during freezing by collecting the charges into suitable capacitors for use of other purposes (lighting lamps or in heaters)? Some of the effects that need to be studied in EFP measurements and utilization include the • Effect of the grain size of the soils; • Effect of unfrozen water content, governed by the grain size and temperature; and • Effect of the rate of cooling.

CHAPTER 2

Early Observations of Electrical Phenomena in Nature

2.1  DEFINITION OF THE PHENOMENON Electrical freezing potentials (EFPs) develop when water and dilute solutions freeze. Water, being a polar molecule, has a charge separation occur, with the positive charges frozen into the freezing side and negative charges rejected into the solution side, thereby causing an electrical potential that can be measured between the frozen (+ve) and the unfrozen (−ve) side. In the case of pure water (H2O), this is mostly the case. However, in some ionic solutions, such as those containing (NH4)+ ions, a reverse polarity has also been observed, with the unfrozen solutions gaining a positive charge with respect to the negative frozen side.

2.2  HOW THE PROBLEM WAS INITIATED IN THE EARLY 1950s 2.2.1  Historical Background As early as the beginning of 1800s, some curious scientifically oriented minds were interested in finding a scientific explanation of thunderstorm production in nature and resulting lightning, producing sparks. Generation of the electric charge by the splashing of water drops has been known for a long time. In his pioneering papers more than a century ago, Lenard (1892, 1915) discussed the negative charging of air near waterfalls. Some experiments were carried out to measure the charges produced, if any, when water splashed off an ice surface. Faraday (1845) observed that when water droplets impacted on ice, ice attained a positive charge, and the water was charged negatively. Charges of considerable magnitude were noticed from the contact potentials between water and ice, but as with most meteorological experiments in those early days, the results were 3

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Electrical Phenomena During Freezing of Water and Soils

inconclusive and inconsistent as to the magnitude and polarity of the potentials. This could have been mostly on account of the lack of precision and reliable equipment used for such measurements. Atmospheric lightning and thunderstorm electricity fascinated early observers, which led to scientific investigations to understand the phenomena, as it was speculated that these could cause static charging of aircraft flying through clouds containing supercooled water in the upper atmosphere. [Cirrus clouds are thin and wispy white clouds formed at altitudes of 6,000 to 12,000 m (6,562 to 13,124 yds) and are composed of ice crystals that originate from the freezing of supercooled water droplets.] Brillouin (1897) invoked the concept of photoelectric effect on ice crystals to explain the positive charges on ice crystals found in cirrus clouds and the negative charges in the air at high altitudes. The earliest reports on these observations were from Wilson (1929), Byers (1940), and Edwards and Brock (1945).

2.2.2  Charge Separation Mechanisms in Clouds The generally accepted concept for the development of the thunderstorm charge is the physical separation of oppositely charged particles (dipoles) within the cloud. Larger cloud particles fall under gravity, whereas smaller particles are transported in the updraught. Saunders (2008) presents and discusses the mechanisms of thunderstorm electrification. After these initial observations, many researchers studied the phenomenon of EFP in pure water as well as various solutions. These led to the interest in studying the development of such freezing potentials in freezing soils and ground, as construction in cold regions started for mining and excavations and for pipeline and road construction in permafrost areas. During freezing of the ground, water in the soil migrates to the freezing front and form huge ice bodies at the interface, which could endanger pipelines and structures buried in the ground in permafrost areas. Electrical potentials could be established between the freezing front, such as a pipeline, and this could also cause stress and corrosion problems. The amount of electricity present in thunderstorms, its magnitude, capture, storage, usefulness, and the cost of saving it, is discussed in the next section.

2.2.3  Electrical Charges Associated with Clouds Each lightning strike has on average only 5 billion joules, which is equivalent to only around 1,400 kW·h of energy if one assumes zero loss in transfer and storage. Lightning strikes over a year are around 1.4 billion, and of these, only about 25% are actually ground strikes, because most (75%) are intra-cloud and cloud-cloud and cannot be harnessed. This leaves only 350 million lightning strikes that could possibly be harnessed. Also, assuming 100% harnessing of all lightning strikes, there is no loss in capture, transfer, and storage, that is 490,000,000,000 (490 trillion) kW·h/year. In 2009, the world used around 20,279,640,000,000 (about 20,280 trillion) kW·h—more than 40 times the electrical energy that

Early Observations of Electrical Phenomena in Nature

5

can hypothetically be harnessed from all the land strikes. So, basically, all the lightning one can capture will give the world enough electricity for only 9 days! (Quora, n.d.) However, there is more, if one wants to see how much it would cost to do that. To capture each and every lightning strike (land strikes only), one would most likely have to put extremely tall towers (probably as tall as the Eiffel Tower) around 1 mi (1.6 km) apart in a grid formation, covering the entire globe. That is one tower for each of the almost 150 million mi2 of the Earth’s surface (Quora, n.d.). Earth’s surface area: 510 million km2 Land area: 150 million km2 Area of water: 360 million km2

(about 197 million mi2) (about 57 million mi2) (about 140 million mi2)

To cover the entire land surface by tall towers to capture every possible lightning strike, one would need (150 million km2) 60 million towers! Imagine the cost of building them all around the world!

References Brillouin, M. 1897. “L’electricite atmospherique.” Ecl. Electro. 13 (17): 577–599. Byers, H. 1940. Terrestrial magnetism and atmospheric electricity, Vol. 45, 345–350. Edwards, R. C., and G. W. Brock. 1945. “Meterological aspects of precipitation static.” J. Meteorol. 2 (4): 205–213. Faraday, Hr. M. 1845. “Ueber die Liquefaction und Solidification der Gase.” Ann Phys. Lpz. 342. First published: 1845. https://doi.org/10.1002/andp.18451400312 Quora. n.d. “Can we produce electricity by thunderstorm?” Accessed October 7, 2022. https://www.quora.com/Can-we-produce-electricity-by-thunderstorm. Saunders, C. P. R. 2008. “Charge separation mechanisms in clouds.” Space Sci. Rev. 137 (1): 335–353. Wilson, C. T. R. 1929. J. Franklin Institute 208 (1243-1, July): 1–12.

CHAPTER 3

Early Observations

According to Drake (1968) of Imperial College, London, the first observation of electrical charges produced during melting of ice was reported by Dinger and Gunn (1946). They measured the charges carried by a flowing air stream over melting ice in a dish. Charges up to 2 esu were measured per gram of pure ice melted and mentioned that the charge decreases with contamination by CO2. The magnitude depended on the rate of melting and rate of freezing. Dinger (1965) conducted experiments with extreme care in uncontaminated water and reported measuring charges up to 6.6 esu per gram of ice melted.

3.1 HOW DO THESE VALUES RELATE TO THE POTENTIALS THAT DEVELOPED? On the units, Wilson (1929) mentions the following: The induced charge on each half of a spherical drop is proportional to the area of cross section and to the field. For a drop of 1 mm radius in a field of 10,000 volts per centimetre is about 0.25 esu. (0.1 esu of electrical potential is equivalent to 29.97925 V.) If the drop acquires a negative charge of 1/10 of this amount (increasing the upper negative charge by 1/20 and diminishing the lower positive charge by an equal amount, the net charge will be about 6 esu per cc of water. A drop of 1/10 mm only require to gain a negative charge equal to 1/20 of the induced charge in order that its net charge per cc may reach the amount (about 30 esu) required for it weight to supported by a field of 10,000 volt per cm. Many early observations of thunderstorms in cold regions indicated the presence of positive charges in regions below the 0 °C (32 °F) isotherm. Mason (1957) suggested the presence of positive charges of 4 C distributed in a sphere of diameter 1 km (7,456 mi). [What does this mean in voltages? How many volts are in a coulomb? Joules equals a measure of energy. Voltage is the amount of energy (J) per unit charge (C). 1 V is exactly 1 J of energy done by 1 C of charge (1 J/C).] 7

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Electrical Phenomena During Freezing of Water and Soils

Here is a simple calculation using the equation relating the voltage and charge (Nave 2017):

V = Q /4π∈ o R

(3-1)

where V is in volts, Q is in coulombs, and R is in meters, with Q = 4 C; ∈o is the dielectric constant of the medium, in this case, air, with a value of 8.854 × 10−12 and R = 1,000 m (1,094 yds), the value of V comes to about 3.6 million volts. This is why one sees so much of power in thunderstorm electricity, with the lightning and the loud thunderclap. The charge separation effect during freezing and thawing of water attracted the attention of Blanchard (1963) and Day (1964), who interprets them as arising from an electric double layer at the freezing interface. MacCready and Proudfit (1964) observes strong negative charges in cumulus clouds (see the following) in Flagstaff, Arizona, during the melting of ice in the clouds, in their hydrometeor (see the following) measurements, using research aircraft. Clouds are made up of very light water droplets or ice crystals. … The different types of clouds are cumulus, cirrus, stratus and nimbus. Cumulus clouds are puffy clouds that sometimes look like pieces of floating cotton. The base of each cloud is often flat and may be only 1,000 me (3,300 ft) above the ground. The top of the cloud has rounded towers. Hydrometeors are any water or ice particles that have formed in the atmosphere or at the Earth’s surface as a result of condensation or sublimation. Some well-known hydrometeors are clouds, fog, rain, snow, hail, dew, rime, glaze, blowing snow, and blowing spray. To study this phenomenon of charge separation, MacCready and Proudfit conducted measurements under simulated conditions in the laboratory and observed that appreciable charges can develop during melting of ice. There was uncertainty in the sign and magnitude of the charging and concluded that further systematic experiments needed to be carried out in flight and in the laboratory, as this phenomenon plays a significant role in thunderstorm electricity. As early as 1929, C. T. R. Wilson, a distinguished professor at the University of Cambridge, United Kingdom, and a Franklin medalist, reported on his study and several years of observations of the electrical fields in thunderclouds. Note: The Franklin Institute was founded in honor of America’s first scientist Benjamin Franklin and is one of America’s oldest and premier centers of science. Benjamin Franklin had one of the greatest scientific minds of his time and was a scientist and inventor, one of the most versatile and talented men in America. His inventions included the Franklin stove and the lightning rod. He demonstrated that lightning and electricity are identical with his famous kite experiment. With his very early experiments, Franklin had studied thunderstorms and concluded that the surface of the Earth below a thundercloud was, in general,

Early Observations

9

positively charged, which was proven by later investigators. The potential gradients below thunderclouds [reaching values up to 10,000 V/m (10,000 N/C) are more often negative than positive, with discharge currents flowing upward. More quantitative measurements by Wormell in England (1930, 1939) and Schonland in South Africa (1982b) showed that the upward currents from points of discharge lead to an interchange of electricity between the Earth and the atmosphere. Simpson and other observers confirmed by experimental measurements that rain carries positive electricity downward, leaving negative charges at the bottom of the thunderclouds. A cloud of positive polarity will produce a negative potential gradient at the ground and could produce point discharges and an upward current of positive ions. Wilson (1929) emphasizes that rain showers and thunderstorms are the main agents producing the negative charges on the Earth, moving positive electricity from the Earth to the upper conducting atmosphere, which could attain a potential of nearly one million volts. The energy of a lightning flash is estimated to be 1.7 × 1010 J (Wilson), and if 100 lightning flashes occur per second, the energy amounts to 1.7 × 1012 W or more than 1 billion kW (ergs) per second. Huge amounts of energy are thus imparted to electrons in thunderclouds on a scale that cannot be achieved by any artificially created means. In general, power is defined as energy over time. Watts are defined as 1 W = 1 J/s (1 W = 1 J/s), which means that 1 kW = 1,000 J/s. 1 W · h is equal to 3,600 J (3.6 kJ). Simpson, in a lecture delivered to the Royal Meteorological Society on January 28, 1942, described the electricity of clouds and rain. Although electricity plays no part in the process of condensation that causes clouds, rain, and snow, they are highly charged with electricity. A cloud should be thought of as a mass of nonconducting air in which are suspended various particulates, spheres of water droplets, and ice crystals that carry the electrical charges. The first observations of these charges carried by the atmospheric precipitation were made around 1887 by Schottky (1918). They captured the precipitation during thunderclouds in an insulated vessel connected to an electrometer and measured the charges. Simpson made some elaborate equipment to capture the charges from rain fall. In 1906, he went to India and developed an equipment for this while working in the India Meterological Department in Simla (or Shimla, the capital of British India in the late 1800s and early 1900s). The daily rainfall there in the monsoon season provided ideal conditions for studying the electricity of rains. His equipment and experimental methods are described in Simpson (1909). He measured the amount of rain falling every 2 min, the charge carried by it, and the potential gradient. The number of lightning flashes was measured by using a radio receiver. Several other measurements carried out by various experimenters in different locations [Potsdam, in the Berlin/Brandenburg region of Germany, Puy-en veley in South-Central France near the river Loire, Freioburg (also called Freiburg) in Switzerland; Dublin, Ireland; Kew Observatory near London, England, and others] are also mentioned. The conclusions from these experiments were as follows: Rain brings down more positive electricity in general

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Electrical Phenomena During Freezing of Water and Soils

Figure 3-1.  Change of electricity with the change in the character of rain. Source: Simpson (1942).

than negative. However, this changes with the rate of rainfall, as observed in the readings taken in Kew Observatory (located in Richmond upon Thames, Greater London, England) (Figure 3-1). In Shimla, the amount of charges measured under normal rainfall was generally less than 6 esu per cc of water (about 1,800 V), but in exceptionally high volumes of rains under storms, negative charges up to 19 esu per cc were measured. Gschwend (1922), in his measurements of charges in individual raindrops and snow fakes, recorded charges of −206, +122, and +130 esu per cc. Such high charges could produce electric fields as high as 10,000 V/cm (10,000 N/C). The main point is, in quiet, steady rains, charges carried by the raindrops are predominantly positive.

References Blanchard, D. Cg. 1963. Vol. 1 of Progress in oceanography. Oxford: Pergamon. Day, J. A. 1964. “Production of droplets and salt nuclei by the bursting of air-bubble films.” Q. J. R. Meteorol. Soc. 90 (383): 72–78. Dinger, J. E. 1965. “Electrification associated with the melting of snow and ice.” J. Atmos. Sci. 22 (2): 162–175. Dinger, J. E., and R. Gunn. 1946. “Electrical effects associated with a change of state of water.” Terr. Magn. Atmos. Electr. 51: 677. Drake, J. C. 1968. “Electrification accompanying the melting of ice particles.” Q. J. R. Meteorol. Soc. 94 (400): 176–191. Gschwend, P. P. 1922. “Beilage zum Jahresbericht der kantonalen.” Lehernstalt in sarnen Pro, 1921/1922, pp. 1–55. Quoted by Chalmers in his book: “Atmospheric Electricity” Pergamon Press, NY. 1957. 515 pages. MacCready, P. B., and A. Proudfit. 1964. Self-charging of melting ice. Altadena, CA: Atmospheric Research Group. (This research was done under the Atmospheric Research Programme of the National Science Foundation, Ref: 551.574.14: 551.594.25: 536.421).

Early Observations

11

Mason, B. J. 1957. The physics of clouds. Oxford, UK: Clarendon Press. Nave, C. R. 2017. “Potential: Charged conducting sphere.” HyperPhysics. Accessed October 7, 2022. http://hyperphysics.phy-astr.gsu.edu/hbase/electric/potsph.html. Schottky, W. 1918. “Uber spontane stromschwankungen in verschiedenen electrizitatslitern.” Annalen der Physik v 362, No. 23, pp. 541–567. Simpson, G. C. 1909. “On the electricity of rain and its origin in thunderstorms.” Philos. Trans. R. Soc. A 200: 379–413. Simpson, G. C. 1942. “The electricity of cloud and rain.” Q. J. R. Meteorol. Soc. 68 (293): 1–34. Wilson, C. T. R. 1929. “Some thundercloud problems.” J. Franklin Inst. 208 (1): 1–12.

CHAPTER 4

Early Measurements

Simpson (1919) first suggested that the impact of ice crystals on one another could cause charge separation and could result in the high potential gradients observed in blizzards. Observations of charge development when snow was poured over ice or when ice pieces were rubbed together were also reported. Findeisen (1940) in Germany reported that water drops on impact on ice gave a positive charge to ice and the negative charges were carried away by the droplets splashing away from the ice surface. Meinhold (1951) for the first time reported observing strong negative charge to be produced on the surface of an aircraft flying through supercooled cloud with glazing taking place. Glazing is the process in which supercooled water striking a surface forms a water layer, which in turn forms an amorphous glassy (or glazy) ice. Glace is the French term for ice. Riming is the process in which supercooled water striking a cold surface is instantaneously converted to crystalline rime ice. Reynolds (1954) suggested that under natural conditions in the clouds, riming occurs for temperatures below −15 °C (5 °F) and glazing occurs above that. Supercooled water and ice can coexist down to −41 °C (−41.8 °F), below which supercooled water abruptly crystallizes. Herrman (1964) found that a space charge of up to 5 × 10−10 C could accumulate in blowing snow. He measured charges up to 1 × 10−15 C per particle, 100 to 1,000 times larger than a falling snow particle. (As to how he measured this, one has to perhaps go to the reference cited.) Because electronic charge is 1.6 × 10−19 C, falling snow particles could have a charge equivalent of 10 to 100 electrons. These early investigations were reviewed by Chalmers (1957). The Signals Corps of the US Army funded the study of these phenomena in the 1940s during the Second World War years. With funding from the old National Advisory Committee for Aeronautics (NACA), detailed investigation of the atmospheric electrification was authorized in the R&D division of the New Mexico School of Mines in Socorro, New Mexico. [NACA was a US federal agency founded on March 3, 1915, to undertake, promote, and institutionalize aeronautical research. NACA was dissolved on October 1, 1958, and its assets and personnel transferred to the newly created National Aeronautics and Space Administration (NASA)]. 13

14

Electrical Phenomena During Freezing of Water and Soils

Equipment to measure such electrical potentials in freezing dilute solutions was developed, and some of the earliest reports on the research carried out there were reported by Workman et al. (1942), Workman and Reynolds (1949). In their first laboratory work supported by the US Army Signal Corps, Workman and Reynolds (1946) dropped supercooled water through cold air on to a cold metal plate and measured potential differences up to 50 V between the cold plate and the unfrozen water splashing away. In their subsequent work (1950), they measured freezing potentials of up to 230 V (ice-positive) in dilute solutions containing small amounts (10−7 to 10−2 mole/L) of ionic impurities such as NaCl, NH4OH, and others. Thus, one can see that a lot of uncertainty exists in the charges (signs and amounts) carried by rain and snow coming down to earth. Simpson himself concluded in his keynote paper of 1942 that more than 40 years of investigations in several countries have not produced conclusive results on atmospheric electricity. Perhaps future systematic experiments using more sophisticated equipment and methods available now could resolve this. The only conclusion is that the three physical processes giving electrical charges during precipitation are • Contact between ice particles, • Breaking of rain drops, and • Absorption of ions under the influence of an electrical field. The first of these processes occurs in the upper regions of clouds where temperature drops below the freezing point, and the other two processes occur in the lower regions of the clouds where the temperatures are above 0 °C (30 °F). It is this process of the development of electrical charges during freezing that the authors are interested in their study of freezing water, dilute solutions, and freezing ground containing moisture.

References Chalmers, J. A. 1957. Atmospheric electricity. New York: Pergamon Press. Findeisen, W. 1940. “Uber die entstehung ser gewitterelectrizitat.” In German. Meteorol. Z. 57 (6): 16–30. Herrman, J. R. 1964. “On the electrical properties of blowing snow.” Ann. Geophys. 20 (3): 235–241. Meinhold, H. 1951. “Die elektrische ladung eines flugzeuges bei vereisung in quellwolken.” In German. Geofis. Pura Appl. 19 (3–4): 176–178. Reynolds, S. E. 1954. Compendium of thunderstorm electricity. US Signal Corps Research Rep. Soccoro, NM: New Mexico Institute Mining and Technology. Simpson, G. C. 1919. “British Antarctic expedition 1910–13.” Meteorology (Calcutta) 1: 302–312. Workman, E. J., R. E. Holzer, and G. T. Pelsor. 1942. “The electrical structure of thunderstorms.” Washington, DC: NACA Tech. Note No. 864.

Early Measurements

15

Workman E. J., and S. E. Reynolds. 1949. “Electrical activity as related to thunderstorm cell growth.” Bull. Am. Meterological Soc. 30 (4): 142–144. Workman, E. J., and S. E. Reynolds, 1950. “Electrical phenomena occurring during the freezing of dilute aqueous solutions and their possible relationship to thunderstorm electricity.” Phys. Rev. 78 (1): 254–259.

CHAPTER 5

Early Laboratory Measurements in Water and Dilute Solutions

Some early measurements of electrical freezing potential (EFP) developed during freezing of water and solutions are now described. Gill and Alfry (1952) of the Clarendon Laboratory of the Department of Physics in Oxford University, England, immersed a copper block cooled to liquid air temperatures (−193 °C) into liquid water and measured freezing potentials (ice-positive) up to 50 V between the copper block and a wire electrode in water. They found higher potentials with faster rates of cooling or freezing. After these initial experiments, several investigators studied the development of electrical potentials during the freezing of pure water (Arabadzhi 1948, Gill 1953, Bayadina 1960, Murphy 1970) and in dilute aqueous solutions containing different ions (Na+, K+, NH4 +, Cs+, Li+, Cl−, F−, Br−, I−, OH−, etc.) (Gross 1967; Pruppacher et al. 1968; Cobb and Gross 1969; Murphy 1970, Korkina 1975). The earlier work on the Workman–Reynolds effect was reviewed by Drost-Hansen (1967), Gross (1965), and Cobb and Gross (1969). These early works indicated that the magnitude and sign of EFP depended on factors such as (1) the type of ions in solution, (2) concentration of the electrolyte solution, and (3) rate of cooling. Table 5-1 shows the results in pure water, and Table 5-2 summarizes the EFP values measured in different solutions. Most of these investigators have explained EFP in terms of a potential barrier at the ice/liquid interface and the probabilities for different ions to be incorporated into the solid or liquid phase. Workman and Reynolds suggest the orientation of the dipole water molecules at the interface and incorporate opposite charges in the solid and liquid phases. The double layer so formed is of thickness of a few nanometers. Owing to the low conductivity of ice (four orders of magnitude lower than that of the liquid water), the incorporated charges accumulate and distribute through the ice phase as frozen-in space-charges, and very high fields of up to 400 V/mm can be built up (Gelin and Stubbs 1965), which, along with the surface charges of opposite sign in the ice–solution interface layer (a few nanometers thick), give rise to high EFPs. Some values of these potentials are given in Table-I, p. 109. 17

18

Electrical Phenomena During Freezing of Water and Soils

Table 5-1.  Freezing Potentials Observed in Water.

Source

Water used

Temperature of cold side

Workman and Reynolds (1950)

Double-distilled −5 to −30 °C water Double-distilled −5 to −30 °C water (free of ammonia)

Gill and Alfry (1952)

Distilled water

Korkina (1975) Bayadina (1960) Arabadzhi (1948) Murphy (1970)

DD water — — DD water, CO2 free Deaerated Distilled, deaerated water

Parameswaran

−193 °C (liquid air) −30 °C — —

Maximum freezing voltage observed (ice-positive) 60 V A few volts, sign changes as freezing progressed 50 V

12 V 5 to 100 V 170 ± 25 mV −79 °C (dry ice) 50–120 V −30 °C

2.3 V

−45 °C −196 °C (liquid Nitrogen)

2.78 V 12 V

Dilute solutions (2.5 × 10−4  M) of potassium fluoride, cesium fluoride, and lithium iodide were frozen at rates from approximately 1 to 20 µ/s. During freezing, ionic transfer takes place at the ice–solution interface. Anions are incorporated in greater numbers than the cations, regardless of the relative ionic sizes. [This could be attributed to the greater mobility of the negative anions (−) in the solution side and the lower mobility of the positive ions incorporated into the frozen side, the ice phase.]. The difference between incorporated halogen anions and incorporated alkali cations is made up of hydrogen ions, supplied either from the freezing base (shunt case) or from the liquid (open-circuit case) or from both. The relationship between the rates of freezing and ionic transfer determines the extent of this replacement. Trace impurities, growth rate, and phase-boundary conditions during growth are the determining factors of the electrical bulk properties of ice. The highest values of EFP measured by Cobb and Gross (1969) and Gross (1965, 1967) were in dilute solutions (10 to 15 µM) of ammonium salts (chloride, carbonate, acetate). Note: A micromolar aqueous solution contains 10−6 times the molecular weight in grams of the substance in 1 L of water.

Early Laboratory Measurements in Water and Dilute Solutions

19

Table 5-2.  Freezing Potentials Observed in Dilute Solutions.

Source

Solution/ concentration 10−6 M*

Workman and NaCl Reynolds (1950) CaCl2 KCl NH4Cl Nh4OH NH4NO3 Pb-acetate (NH4)2 CO3 NH4 Br Korkina (1975) NH4Cl NH4OH NH4OH NH4OH NH4OH NaCl

Maximum freezing voltage (V) observed with reference to ice 100 — 200 70 30 3 — — — 70 100 50 30 15 3,000

30,000 100

−30 −14 −14 +105 +232 +185 +100 +109 +84 +13 +0.15 +0.33 +23 +12 −9.2 at −20 °C −12.5 at −30 °C −4.6 at −20 °C −3.0 at −30 °C −0.43 at −20 °C +8

Ice-negative Ice-negative Ice-negative Ice-positive Ice-positive Ice-positive Ice-positive Ice-positive Ice-positive Ice-positive Ice-positive Ice-positive Ice-positive Ice-positive Ice negative Ice negative Ice negative Ice negative Ice negative Ice-positive

100 100

+4 +4

Ice-positive Ice-positive

100 100

+4 +3

Ice-positive Ice negative

15 5 5 11 20 250 20 250

+214 +151 +92 +102 −40 −37 −44 −43

Ice-positive Ice-positive Ice-positive Ice-positive Ice negative Ice negative Ice negative Ice negative

16,500

Pruppacher et al. (1968)

Cobb and Gross (1969)

LiF, NaF, KF CsF, LiCl, LiBr, NaCl, NaBr, KCl, KBr, CsCl, CsBr NH4F NH4OH, (NH4)2 CO3 (NH4)2 CO3 Am. acetate NH4Cl Lead acetate KF KCl NaF NaCl

(Continued)

20

Electrical Phenomena During Freezing of Water and Soils

Table 5-2.  Freezing Potentials Observed in Dilute Solutions. (Continued)

Source Murphy (1970)

Solution/ concentration 10−6 M* NH4Cl LiCl KCl

Maximum freezing voltage (V) observed with reference to ice 0.1 0.1 0.1

+100 +50 +40

Ice-positive Ice-positive Ice-positive

* 10−6 M = One micromolecular weight of the solute in 1 L of liquid.

Ice-positive potentials of 84 to 214 V were measured. Lead acetate and lead nitrate solutions yielded potentials of 102 and 68 V, respectively. Sulfates of sodium and potassium (20 µM) and of lithium (100 µM) showed potentials of 8–22 V. Solutions of chloride, bromide, and fluoride of Na, K, and Li (20 to 200 µM), however, showed ice-negative potentials of 30 to 50 V. Freezing

Figure 5-1.  Experimental arrangement used for studying electric charge separation. Source: Cobb and Gross (1969). © The Electrochemical Society. Reproduced by permission of IOP Publishing. All rights reserved.

Early Laboratory Measurements in Water and Dilute Solutions

21

potentials were a function of the freezing rate. These researchers suggested that charge separation during freezing can occur only if ionic impurities are present in the water. The equipment and the experimental arrangement used by these researchers are shown in Figures 5-1 to 5-2. Korkina (1975) describes the measurement of EFP in freezing dilute solutions containing ions of Fe, Ca, Na, and ammonia [CRREL translation No. 490 (1975)] and suggested that EFP measured depended on (1) the type and concentration of the solutes, (2) type and distance between the electrodes, and (3) the temperature of the cold side, which controls the rate of cooling in pure double-distilled water. The question mark within parentheses is to suggest that even the purest water is bound to pick up minute amounts of CO2 from the atmosphere during measurements. Korkina also quotes the work of Bayadina (1960), who observed maximum EFP values of 5 to 100 V between the ice and the unfrozen water, across the freezing front. However, she reported observing an EFP of +12 V. Her measurements in dilute NaCl (3 millinormal) solution showed an EFP of +12.5 V, and in 03 millinormal NH4OH solution, −3 V. Figures 5-3 to 5-6 give Korkina’s measurements in different solutions under various conditions.

Figure 5-2.  Experimental arrangement. Source: Gross (1965). Note: A = experimental arrangement for measuring freezing current; B = electric analog of the interface; Rb = interface barrier resistance; Re = external shunt resistance; Ri = ice resistance; Rl = liquid resistance.

22

Electrical Phenomena During Freezing of Water and Soils

Figure 5-3.  Korkina’s measurement of EFP in freezing dilute solutions containing ions of Fe, Ca, Na, and ammonia. Source: Korkina (1975), CRREL Translation No. 490.

Figure 5-4.  Variation of the voltage measured with distance between measuring electrodes. Source: Korkina (1975). Note: a = vertical axis (V); b = horizontal axis (h). Curves: (1) 30 mm; (2) 20 mm; (3) 10 mm. Temperature = −30 °C.

Early Laboratory Measurements in Water and Dilute Solutions

23

Figure 5-5.  Voltage change in NH4OH solution, with concentration, cooling rate, and distance between electrodes (h). T = −30 °C; h = 28 mm. (1). 3 × 10−5 normal solution; (2) 1.5 × 10−5 normal solution; (3) 1 × 10−5 normal solution; (4) 5 × 10−5 normal solution; (5) 10 × 10−5 normal solution. (a) vertical axis (V), (b) vertical axis (h). Source: Korkina (1975).

24

Electrical Phenomena During Freezing of Water and Soils

Figure 5-6.  Voltage that developed in NaCl solutions with concentration. (a) 1: 3 × 10−3 N; 2: 9.8 × 10−3 N; 3: 16.5 × 10−3 N; (b) 3 × 10−4 N. A – vertical axis (V); B – horizontal axis (h). Source: Korkina (1975).

References Arabadzhi, V. I. 1948. “The contact potential difference between water and ice.” Reports of the Academy of Sciences, USSR In Russian. Doklady Akademii Nauk SSR 60 (5): 811–812. US Army SIPRE Translation No. 1, translated by William Mandel, 1950. Washington, DC: US Corps of Engineers. Bayadina, F. I. 1960. “Voltage difference originating between the solid and liquid phases of water.” USSR Academy of Sciences, News, Geophysical Series No. 2. Cobb, A. E., and G. W. Gross. 1969. “Interfacial electrical effects observed during the freezing of dilute electrolytes in water.” J. Electrochem. Soc. 116 (6): 796–804. Gelin, H., and R. Stubbs. 1965. “Ice electrets.” J. Chem. Phys. 42 (3): 967–971. Gill, E. W. B. 1953. “Electrification by freezing.” Br. J. Appl. Phys. 4 (Suppl. 2): 516–519. Gill, E. W. B., and G. F. Alfry. 1952. “Production of electrical charges on water drops.” Nature 169 (4290): 103–104. Gross, G. W. 1965. “The Workman–Reynolds effect and ionic transfer processes at the ice-solution interface.” J. Geophys. Res. 70 (10): 2291–2300. Gross, G. W. 1967. “Ion distribution and phase boundary potentials during the freezing of very dilute ionic solutions at uniform rates.” J. Colloid Interf. Sci. 25 (2): 270–279.

Early Laboratory Measurements in Water and Dilute Solutions

25

Korkina, R. I. 1975. Electrical potentials in freezing solutions and effect on migration. US Army CRREL Draft Translation No. 490. Washington, DC: US Army Cold Regions Research and Engineering Laboratory. Murphy, E. J. 1970. “The generation of electromotive forces during the freezing of water.” J. Colloid Interf. Sci. 32 (1): 1–11. Pruppacher, H. R., E. H. Steinberger, and T. L. Wang. 1968. “On the electrical effects that accompany the spontaneous growth of ice in supercooled aqueous solutions.” J. Geophys. Res. 73 (2): 571–584. Workman, E. J., and S. E. Reynolds. 1950. “Electrical phenomena occurring during the freezing of dilute aqueous solutions and their possible relationship to thunderstorm electricity.” Phys. Rev. 78 (1): 254–259.

CHAPTER 6

Measurements in Pure Water

Korkina’s (1975) measurements in pure double-distilled water (?) (as described in Chapter 5) are given a maximum potential of +12 V. An early SIPRE (Snow, Ice, and Permafrost Research Establishment, the predecessor of CRREL) translation (No. 1, 1950) of an article by Arabadzhi (of USSR) reported that collision of water drops with ice crystals in clouds causes the electricity in lightning, and laboratory measurements of contact potentials of 150 to 200 mV between water and ice were measured during freezing. As early as 1948, Arabadzhi studied the “contact potential difference between water and ice.” As suggested by Frumkin (1924), Arabadzhi and his group conducted a simple laboratory experiment to measure such contact potentials. A schematic diagram of their equipment is shown in Figure 6-1. The value of the contact potential measured was about 0.17 V, and Arabadzhi’s group concluded that such contact potentials are the cause of electricity in lightning. More recently, Murphy (1970) meticulously measured the potentials generated during freezing of double-distilled water in a special cell from which air was pumped out, to avoid CO2 absorption by water. Ice-positive potentials of 50 to 120 V were measured, which Murphy attributed to the capture of positive charges by the ice at the interface and by the formation of long-chain molecules (trees), the relaxation of which produces the freezing potentials. In a polar molecule such as water, the centers of (+) and (−) charges are separated by a distance d and the molecule has a permanent dipole moment p = qd, where q is the charge. A nonpolar molecule does not possess an inherent dipole moment in the absence of an external field. Charge separation and accumulation in the two different phases at the interface can influence electrical phenomena such as electrocatalysis, corrosion, crystal growth, adhesion, flow behavior of colloidal suspensions, and clays, among others. The equipment used by Murphy is shown in Figure 6-2. As explained in the figure itself, air could be pumped out of the central tube to avoid CO2 pick up from air. Murphy, however, found that the presence of CO2 or air did not change the potential much. Murphy attributed electrical freezing potential (EFP) to the rate of capture of the ions by ice rather than their equilibrium distribution in ice. Note: Murphy’s figure (Figure 6-2) does not clearly 27

28

Electrical Phenomena During Freezing of Water and Soils

Figure 6-1.  Experimental setup to study the “contact potential difference between water and ice.” Source: Arabadzhi (1948).

Figure 6-2.  Murphy’s apparatus to measure potentials generated during the freezing of double-distilled water. Source: Murphy (1970). Note: E1 and E2 are electrodes sealed into the glass. Freezing is done by applying dry ice to the tube F. Air is pumped out of the water through tube P.

Measurements in Pure Water

29

Figure 6-3.  Freezing potentials as a function of concentrations. Source: Murphy (1970). Note: Positive potentials indicate ice-positive, water-negative.

indicate how he measured the potentials between the ice and the water, as no electrode is shown in the frozen ice, with both electrodes being in the unfrozen water itself. Values of EFP measured by Murphy in various solutions are shown in Figure 6-3. In general, Murphy found that in pure water and most dilute solutions (NH4Cl, Na Cl, K Cl, LiCl, NaI, CaCl2, MgCl 2, KMnO4, K-dichromate, HCl, HNO3, NaOH, ethyl alcohol, Na-barbiturate, and phenol-phthalein) that in high concentrations (exceeding 1 µM), most of these solutions showed ice-negative or zero potentials (Figure 6-3). Table 6-1 shows the freezing potentials observed in pure water by various researchers.

30

Electrical Phenomena During Freezing of Water and Soils

Table 6-1.  Freezing Potentials Observed in Water.

Source

Water used

Temperature of cold side

Workman and Double-distilled −5 °C to −30 °C Reynolds (1950) water (23 °F to −22 °F) Double−5° C to −30 °C distilled (23 °F to −22 °F) water (free of ammonia) Gill and Alfry Distilled water −193 °C (liquid air) (1952) (−315.4 °F) Korkina (1975) DD water −30 °C (−22 °F) Bayadina (1960) — — Arabadzhi (1948) — — Murphy (1970) DD water, CO2 −79 °C free −110.2 °F) Deaerated (dry ice) Parameswaran Distilled, −30 °C deaerated (−22 °F) water 2.78 V −45 °C −196 °C (liquid 12 V nitrogen) (−328.8 °C)

Maximum freezing voltage observed (ice-positive) 60 V A few volts, sign changes as freezing progresses 50 V 12 V 5 to 100 V 170 ± 25 mV 50–120 V 2.3 V

References Arabadzhi, V. I. 1948. “The contact potential difference between water and ice.” Reports of the Academy of Sciences, USSR. In Russian. Doklady Akademii Nauk SSR 60 (5): 811–812. US Army SIPRE Translation No. 1, translated by William Mandel, 1950. Washington, DC: US Corps of Engineers. Frumkin, A. 1924. “Electrical properties of thin films.” Nature 114: 158–159. Gill, E. W. B., and G. F. Alfry. 1952. “Production of electrical charges on water drops.” Nature 169: 103–104. Hayadina, F. I. 1960. “Voltage difference originating between the solid and liquid phases of water.” USSR Academy of Sciences, News, Geophysical Series No. 2. Korkina, R. I. 1975. “Electrical potentials in freezing solutions and effect on migration.” Hanover, NH: US Army CRREL Draft Translation 490: 15. Murphy, E. J. 1970. “The generation of electromotive forces during the freezing of water.” J. Colloid Interf. Sci. 32 (1): 1–11. Workman, E. J., and S. E. Reynolds. 1950. “Electrical phenomena occurring during the freezing of dilute aqueous solutions and their possible relationship to thunderstorm electricity.” Phys. Rev. 78 (1): 254–259.

CHAPTER 7

Freezing Potentials in Aqueous Solutions

Early observations of thunderstorm electrification in the atmosphere were attributed to the large electrical potentials developing between the frozen and the unfrozen regions of water and aqueous solutions subjected to freezing temperatures. The charges that developed by such electrification could affect aircraft flying through clouds containing supercooled water mixed with ice particles. The metallic fuselage or body of the aircraft could acquire these charges, which could affect the electrical control systems in the airplane. The US Signal Corps funded studies on this phenomenon in the early 1940s (Second World War years). Workman and Reynolds (1950) made a detailed investigation of the phenomenon in the R&D division of the New Mexico School of Mines in Socorro, New Mexico, in 1946. Careful studies on the electrical properties of thunderstorm indicated that electrical charge separation in the cloud is related to the formation of glaze ice, or hail. Supercooled water drops falling through cold air caused the build of layers of glaze ice on a cold insulated metallic plate. The potential difference measured between the plate and the water drops splashing away from the surface was huge, up to 50 V. They developed an equipment to measure such potentials using a copper block cooled to −5 °C (23 °F) to −30 °C (−22 °F). In dilute ammonia solutions, potentials up to 230 V were observed during freezing (Table 7-1). They did not observe a reverse potential during thawing. They were also not definite about the effect of the rate of freezing on the magnitude of the potentials that developed. Note: As given subsequently, our own investigations at the National Research Council Canada and later in Carleton University, Ottawa, showed the development of reverse potentials during thawing, as well as a significant effect of the rate of freezing on the magnitude of the freezing potentials developed, which were higher potentials for a faster rate of cooling. Under slow cooling rates, the ice crystals formed oriented with the C-axis perpendicular to the cooling surface, but under rapid cooling, the orientation was random. The sign and the magnitude of the potentials that developed during freezing of dilute solutions depended on the type of the dissolved ions and the concentration (Table 7-1). 31

32

Electrical Phenomena During Freezing of Water and Soils

Table 7-1.  Freezing Potentials Observed in Dilute Solutions.

Source Workman and Reynolds (1950)

Korkina (1975)

Pruppacher et al. (1968)

Cobb and Gross (1969)

Solution/ concentration 10−6 M*

Maximum Freezing Voltage (V) observed with reference to ice

NaCl CaCl2 KCl NH4Cl Nh4OH NH4NO3 Pb-acetate (NH4)2 CO3 NH4 Br NH4Cl NH4OH NH4OH NH4OH NH4OH NaCl

100 — 200 70 30 3 — — — 70 100 50 30 15 3,000

LiF, NaF, KF CsF, LiCl, LiBr, NaCl, NaBr, KCl, KBr, CsCl, CsBr NH4F NH4OH, (NH4)2 CO3 (NH4)2 CO3 Am. acetate NH4Cl

−30 −14 −14 +105 +232 +185 +100 +109 + 84 +13 +0.15 +0.33 +23 +12 −9.2 at −20 °C (−4 °F) −12.5 at −30 °C (−22 °F) 16,500 −4.6 at −20 °C (−4 °F) −3.0 at −30 °C (−22 °F) 30,000 −0.43 at −20 °C (−4 °F) 100 +8

Ice-negative Ice-negative Ice-negative Ice-positive Ice-positive Ice-positive Ice-positive Ice-positive Ice-positive Ice-positive Ice-positive Ice-positive Ice-positive Ice-positive Ice-negative

100 100

+4 +4

Ice-positive Ice-positive

100 100

+4 +3

Ice-positive Ice-negative

15 5 5

+214 +151 +92

Ice-positive Ice-positive Ice-positive

Ice-negative Ice-negative Ice-negative Ice-negative Ice-positive

(Continued)

Freezing Potentials in Aqueous Solutions

33

Table 7-1.  Freezing Potentials Observed in Dilute Solutions. (Continued)

Source

Murphy (1970)

Solution/ concentration 10−6 M*

Maximum Freezing Voltage (V) observed with reference to ice

Lead acetate KF KCl NaF NaCl NH4Cl LiCl KCl

11 20 250 20 250 0.1 0.1 0.1

+102 −40 −37 −44 −43 +100 +50 +40

Ice-positive Ice-negative Ice-negative Ice-negative Ice-negative Ice-positive Ice-positive Ice-positive

* 10−6 M = one micromolecular weight of the solute in 1 L of liquid.

Following these first observations of Workman and Reynolds, Gill and Alfry (1952), in the Cavendish Laboratories in Oxford, England, measured the freezing potentials that developed in distilled water by immersing a copper block cooled in liquid air [−194.35 °C (−317.83 °F), liquid nitrogen is below −196 °C (−320.8 °F)] and measured freezing potentials up to 50 V, with ice attaining a positive charge and the adjacent liquid accumulating the negative ions. These researchers did observe that the potentials that developed were dependent on the rate of cooling, and they also observed a reverse potential during melting of the accumulated ice. Gill (1953) observed very high potentials (of the order of 100 V) that developed during freezing of dilute solutions. The high potentials of the order of 100 V that developed when ice was formed from dilute solutions were investigated to discover the mechanism. Contact potentials between solids and liquids are usually of the order of 1 V, and hence, some further fact must operate to achieve 100 V. The theory suggested is that, whereas in the usual case, the charges producing the potentials are adjacent to the boundary, in the case of freezing ice, the charges extend to a small distance from this boundary. During freezing, positive charges are accumulated in successive layers in the ice and negative charges accumulate in the solution, both across the freezing boundary, which leads to a space-charge buildup. Gross (1954) put forward a theory of thermo-dielectric effect explaining the high potential differences observed across the freezing interface (or boundary) as caused by charge separation and distribution in the two phases and the development of an electric field owing to the frozen-in space charges. The system behaves like a capacitor with opposite charges across the freezing boundary. In the early measurements of EFP, several uncertainties were present—such as the nature of charge separation (whether ice is positive and the water negative— or in some dilute solutions, ice accumulates the negative charges, with the positive

34

Electrical Phenomena During Freezing of Water and Soils

charges collecting in the solution). The magnitude of the potentials that developed depended on the type of ions and rate of freezing. The method of measurement also had an influence, whether the potential was measured with respect to a ground or with respect to an electrode within the system. To bring out the uncertainties in the measurements by various authors, Kelsh and Taylor (1988) investigated the freezing potential phenomenon in a short study conducted in CRREL in 1988. Although they acknowledged the existence of the phenomenon, they were quite critical about the techniques of measurements and uncertainties and the difficulty in using electrical freezing potential (EFP) as a measurement technique for studying corrosion and water migration in freezing moist soils (Kelsh and Taylor 1988). An equipment they used to study EFP in soils is shown in Figure 7-1.

Figure 7-1.  Experimental cell used to study freezing potentials. Source: Kelsh and Taylor (1988).

Freezing Potentials in Aqueous Solutions

35

References Cobb, A. E., and G. W. Gross. 1969. “Interfacial electrical effects observed during the freezing of dilute electrolytes in water.” J. Electrochem. Soc. 116 (6): 796–804. Gill, E. W. B. 1953. “Electrification by freezing.” Br. J. Appl. Phys. 4 (Suppl. 2): 516–519. Gill, E. W. B., and G. F. Alfry. 1952. “Production of electrical charges on water drops.” Nature 169 (4290): 103–104. Gross, G. W. 1954. “Theory of thermodielectric effect.” Phys. Rev. 94: 1545. Kelsh, D., and S. Taylor. 1988. “Measurement and interpretation of electrical freezing potential of soils,” CRREL Report 88-10. Hanover, NH: US Army Corps of Engineers, CRREL Korkina, R. I. 1975. “Electrical potentials in freezing solutions and effect on migration.” Hanover, NH: US Army CRREL Draft Translation 490: 15. Murphy, E. J. 1970. “The generation of electromotive forces during the freezing of water.” J. Colloid Interf. Sci. 32 (1): 1–11. Pruppacher, H. R., E. H. Steinberger, and T. L. Wang. 1968. “On the electrical effects that accompany the spontaneous growth of ice in supercooled aqueous solutions.” J. Geophys. Res. 73 (2): 571–584. Workman, E. J., and S. E. Reynolds. 1950. “Electrical phenomena occurring during the freezing of dilute aqueous solutions and their possible relationship to thunderstorm electricity.” Phys. Rev. 78 (1): 254–259.

CHAPTER 8

Freezing Potential Measurements in Soils

Reports on the observations of freezing potentials in soils and rocks were meager and inconclusive. As early as 1958, Jumikis had reported measurements of freezing potentials of 40 to 120 mV in Dunellen Clay (a glacial till) and suggested enhanced moisture transport under such potentials. Korkina (1975) studied the freezing potentials in clay suspensions containing micro-particles, saturated with ions such as Fe3+, Ca 2+, Na+, and NH4+. The magnitude and polarity of the induced voltage depended on the density of the suspension, type of particles, and type of ions. Korkina’s results showed that at low concentrations, the potentials were ice-positive (as observed in pure water). At higher densities, the potentials were reversed, with ice attaining −ve charges. All the early results are given in Table 8-1. Verschinin et al. (1949), as well as Hoekstra and Chamberlain of CRREL (1964), reported the possibility of water movement under the influence of an electrical gradient, leading to huge ice bodies around the cathode. Borovitskii (1976) measured electrical freezing potentials (EFPs) in argillaceous rocks in the laboratory and measured values of 150 to 200 mV, although the polarity was not specified. Yarkin (1974, 1978) measured EFPs in sand and kaolin, with different moisture contents. His work was reported in the Proceedings of Permafrost: Second International Conference, 1973. Maximum potentials up to 325 mV were measured in powdered sand containing 22.7% moisture, whereas in granular sand containing 22% moisture, the maximum potential was only 75 mV, showing that particles with a larger specific surface area (area-to-volume ratio) give larger EFPs. The potentials were also higher for the larger separation of electrodes. Bentonite with 155% moisture showed −80 mV, whereas with 100% moisture, peak voltage was only −30 mV. Yarkin found that the peak potential that developed in kaolin increased with a decreasing rate of freezing—from −35 mV at 06 mm/h to −20 mV at 4 mm/h. In pure water and dilute solutions, the general observations were, an increase in EFP with higher rates of cooling.

37

Hanley and Rao (1980) in Regina clay with 50% moisture (untreated as well as treated with ions: K+, Ca2+, Fe3+) Korkina (1975) Clay Gumbrine Gumbrine Gumbrine Gumbrine Gumbrine Gumbrine Gumbrine Gumbrine Gumbrine

Dunellen silt (a glacial till) Argillaceous rock (laboratory measurements) Field measure in Permafrost in USSR Powdered sand with 22.7% moisture Granular sand with 20% moisture Bentonite clay with 150% moisture Bentonite clay with 150% moisture Kaolin, frozen at 0.6 mm/h (0.02 in.) Kaolin, frozen at 4 mm/h (0.16 in.)

Jumikis (1958) Borovitskii (1976)

Yarkin (1974, 1978)

Material

Source

Table 8-1.  Freezing Potentials Observed in Soils.

Na+ Na+ NH4+ NH4+ Fe2+ Fe3+ Ca2+

Density 1.424 0.208 1.54 0.208 1.04 0.208 0.82 0.208 0.54

50 mV 325 mV 75 mV −80 mV −30 mV −45 mV −20 mV 10–15 mV

Ice positive Ice positive Ice positive Ice negative Ice negative Ice negative Ice negative Ice positive Ions present (natural) (natural)

40–120 mV 150–200 mV

Ice positive Ice positive

Max. Fr. voltage observed

−6.2 V +0.7 V −30 mV +65 mV −200 mV +0.15 V −35 mV +95 mV −0.95 V

38 Electrical Phenomena During Freezing of Water and Soils

Granular sand with 14% moisture Granular sand with 14% moisture Granular sand with 20% moisture Silty sand with 20% moisture Silty sand with 20% moisture—long term Clay with 30% moisture—long term

Parameswaran (1982a)

Parameswaran (1982a)

Parameswaran (1982a)

Parameswaran (1982a)

Parameswaran (1982a)

Parameswaran (1982a)

Parameswaran (1982a)

Na+ Na+ NH4+ NH4+ Ca2+ Fe2+

Ca2+ (Natural) (Natural)

Gumbrine Kaolin Kaolin Kaolin Kaolin Kaolin Kaolin Kaolin Kaolin Granular sand with 14% moisture −30 °C (−22 °F) −196 °C (−320.8 °C) −2.2 °C (28 °F) −196 °C (−320.8 °C) −30 °C (−22 °F) −2.2 °C (28 °F) −2.2 °C (28 °F)

0.208 1.204 0.208 1.38 0.208 1.1 0.208 0.52 0.04

+320 mV

+220 mV

−160 mV

−220 mV

+200 mV

−200 mV

+0.15 V −1.7 V +0.19 V +0.20 V +0.47 V +2.3 V +0.43 V −6.4 V +0.18 −80 mV

Freezing Potential Measurements in Soils

39

40

Electrical Phenomena During Freezing of Water and Soils

Yarkin proposed different mechanisms operating in sandy soils and clays: In sandy soils where a redistribution of moisture is not noticeable, EFP arises by a redistribution of ions at the phase boundary, creating a zone of excess +ve charges that prevent migration of moisture to the freezing front. In clays, excess −ve charges create a “potential well” that promotes moisture movement to the freezing front. Yarkin’s observations are given in Figures 8-1 to 8-6. Figure 8-1 shows the effect of the surface area of the grains, and Figure 8-2 shows the higher potential for a larger electrode separation. Tom Hanley and Ramachandra Rao (of Campion College, Regina, Saskatchewan, 1980 to 1982) studied the effects of ions (such as K+, Ca 2+, and Fe3+) on EFPs observed in Regina clay containing 50% moisture (Figure 8-7). Under slow freezing rates, with the freezing interface advancing at the rate of 2.8 × 10−4 cm/s, they observed ice-negative potentials of −30, −43, and −35 mV, respectively. They proposed that EFP and moisture migration are associated phenomena and each influences the other. The equipment used in the laboratory and the results are shown in Figure 8-8.

Figure 8-1.  Variation of potential difference during freezing of samples of sandy soils. Note: 1 = Sand with 20% moisture content; 2 and 3 = sand powder with a moisture content of 19.8% and 22.7%.

Freezing Potential Measurements in Soils

41

Figure 8-2.  Variation of PD with spacing between electrodes. Note: 1 = 20 mm; 2 = 10 mm, 3 = 5 mm, 4 = 2.5 mm.

Figure 8-3.  Variation of potential difference (Curve 1) and potential gradient (Curve 2), with change in the spacing between electrodes.

42

Electrical Phenomena During Freezing of Water and Soils

Figure 8-4.  Electric charge distribution along the profile of the sample of freezing. Note: 1, 2, and 3 = areas of potential jump; “H” and “h” are the heights of the potential barrier in the frozen and thawed zones. The dashed line is the freezing boundary.

The potentials and currents measured by them during the freezing of clays are shown in Figures 8-9 and 8-10. In addition to the freezing potentials that developed by charge separation at the freezing boundary, the charges inherent in the clay particles could also influence the potentials that developed. Also, the finer the particles, the larger the specific surface area and the higher the measured potentials.

Figure 8-5.  Change in freezing potential in freezing bentonite samples with different moisture. contents. Note: 1, 2, 3, and 4 = 76.3%, 100%, 127.8%, and 155.8% moisture, respectively. 5 = Bentonite of small grain size [5,000

100 130 125 120

130 135 300 200

>1,700

Table 11-1 gives the maximum values of the freezing potentials and shorting potentials observed in each solution in this series of experiments. In general, the freezing potentials are higher with a faster rate of cooling when using a colder circulating bath. Ionic impurities increase the magnitude of the potentials.

References Lathan, J., and B. J. Mason. 1961. “Electric charge transfer associated with temperature gradients in ice.” In Proc. R. Soc. London, Ser. A 260 (1303): 523–536. Parameswaran, V. R., C. R. Burn, A. Profir, and Q. Ngo. 2005. “A note on electrical freezing and shorting potentials.” Cold Reg. Sci. Technol. 41 (2): 83–89. Workman, E. J., and S. E. Reynolds. 1950. “Electrical phenomena occurring during the freezing of dilute aqueous solutions and their possible relationship to thunderstorm electricity.” Phys. Rev. 78 (1): 254–259.

CHAPTER 12

Field Studies

Very few measurements of electrical freezing potentials (EFPs) in the field under natural conditions have been published. Borovitskii (1976) measured the inherent electric fields that developed in the active layer in USSR. The measured values did not exceed 50 mV but varied with depth in the ground because of differences in the moisture migration. This led to the installation of field electrode probes to measure the EFPs in the Canadian Arctic (Parameswaran and Mackay 1983).

12.1  ILLISARVIK SITE One area chosen was in the middle of an artificially drained lake (Illisarvik, meaning a place of learning in Inuvialuktun) in Richards Island, NWT, where the permafrost was aggrading from top downward (Mackay 1979a, b; 1981; 1983a, b). The other area was in Inuvik, NWT, where the active layer in a mud hummock was monitored. The area is shown in the maps in Figures 12-1 to 12-3. The location of the pingo, called Pingo 9, in Tuktoyaktuk and a schematic diagram of the cross section of the pingo are shown in Figure 12-3. An electrode probe, about 10 m (0.39 in.) long, consisting of five plexiglas tubes connected together, was installed in the center of the drained lake in June 1981. The probe had 22 copper electrodes set 150 mm (5.9 in.) apart, in the bottom 3 m (0.11 in.) length, to monitor the downward movement of the active layer or the freezing front in the lake freezing downward. A parallel cable containing thermistors was also installed to measure the temperature at each electrode location. Details of the hardware and connections and instruments for reading the voltages that developed at each electrode are given in Parameswaran and Mackay (1983). Figure 12-4 shows a schematic diagram of the installation at Illisarvik.

77

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Electrical Phenomena During Freezing of Water and Soils

Figure 12-1.  Illisarvik Lake site in Richards Island. Source: Mackay and Burn (2002).

Figure 12-2.  Location of the pingo, called Pingo 9, in Tuktoyaktuk. Source: Mackay and Burn (2002). Note: Location map of Richards Island and the Tuktoyaktuk Peninsula area, in NWT. Numbers 1–7 refer to the sites of recently drained lakes of which Illisarvik is Site 6.

Field Studies

79

Figure 12-3.  Location of the pingo, called Pingo 9 in Tuktoyaktuk and a schematic diagram of the cross section of the pingo are shown subsequently. Source: Parameswaran and Mackay (1996).

The depth of permafrost at the time of installation of these probes in June 1981 was 5.65 m, the uppermost electrode was at a depth of 6.11 m (9.8 ft), and the bottom electrode was at a depth of 9.31 m (30.5 ft) below the ground level. The material in the ground was a saturated sand of medium-to-fine grain size.

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Electrical Phenomena During Freezing of Water and Soils

Figure 12-4.  Location of electrodes and thermistors after installation in the Illisarvik site. Source: Parameswaran and Mackay (1996).

Figure 12-5 shows the relative positions of the electrodes and thermistors after installation in Pingo 9.

12.2  INUVIK SITE This site is about 3 km (1.9 mi) north of the town of Inuvik in an area of colluvium that has developed a pattern of mud hummocks. The electrode probe consisted of a PVC tubing, 21 mm (0.83 in.) diameter, 3 m (9,8 ft) long, with 12 copper band

Field Studies

81

Figure 12-5.  Relative positions of the electrodes and thermistors after installation in Pingo 9. Source: Parameswaran and Mackay (1996).

electrodes, each 12.5 mm (0.5 in.) wide, installed in grooves, 150 mm (5.9 in.) apart. Coaxial cables were soldered to the copper electrodes and the wires taken out through the inner diameter of the tube and connected to a meter through a rotary switch. Parallel to the tube was a cable with thermistors to measure the temperature at each electrode location. The probe and thermistor cable were installed in August 1981, in the center of a mud hummocks, each about 2 m (6.5 in.) in diameter. Figures (12-6 to 12-8) show the schematic diagram of this installation. Schematic diagrams of the Inuvik installation are shown in Figures 12-7 to 12-9. A picture of the Inuvik site after the installation of the probes and recorders is shown in Figure 12-10.

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Electrical Phenomena During Freezing of Water and Soils

Figure 12-6.  Electrical potential probe and the switch box (not to scale). Source: Parameswaran and Mackay (1996).

Field Studies

Figure 12-7.  Probe locations 1, 2, and 3, in a hummock. Source: Kinosita and Fukuda (1985).

Figure 12-8.  Probe locations 3 and 4 in a hummock. Source: Kinosita and Fukuda (1985).

83

84

Electrical Phenomena During Freezing of Water and Soils

Figure 12-9.  Location of electrodes and thermistors after installation at the Inuvik site. Source: Kinosita and Fukuda (1985).

Field Studies

85

Figure 12-10.  Inuvik site after the installation of the probes and recorders. Source: Kinosita and Fukuda (1985).

References Borovitskii, V. P. 1976. “The development of inherent electrical fields during the freezing of rocks in the active layer and their role in the migration of trace elements.” J. Geochem. Explor. 5(1): 65–70. Kinosita, S., and M. Fukuda, eds. 1985. In Proc., 4th Int. Symp. on Ground Freezing. Rotterdam: Balkema. Mackay, J. R. 1979a. “An equilibrium model for hummocks (non-sorted circles), Garry Island, Northwest Territories.” In Current research, Part A, Paper 79–1A, 165–167. Ottawa: Geological Survey of Canada. Mackay, J. R. 1979b. “Pingos of the Tuktoyaktuk Peninsula area, Northwest Territories.” Géographie physique et Quaternaire, 23: 3–61. Mackay, J. R. 1981. “An experiment in lake drainage, western Arctic coast.” In Current research, Part A, Paper 81–1A, 63–68. Ottawa: Geological Survey of Canada. Mackay, J. R. 1983a. “Downward water movement into frozen ground, western Arctic coast. Canada.” Can. J. Earth Sci. 20: 120–34. Mackay, J. R. 1983b. “Oxygen isotope variations in permafrost, Tuktoyaktuk Peninsula area, Northwest Territories.” In Current research, Part B, Paper 83–1B, 67–74. Ottawa: Geological Survey of Canada. Mackay J. R., and C. R. Burn. 2002. “The first 20 years (1978–1979 to 1998–1999) of activelayer development, Illisarvik experimental drained lake site, western Arctic coast, Canada.” Can. J. Earth Sci. 39 (11): 1657–1674. Parameswaran, V. R. and J. R. Mackay. 1983. “Field measurements of electrical freezing potentials in permafrost areas.” In Proc., 4th Canadian Conf. on Permafrost. Ottawa: National Research Council of Canada, 962–967. Parameswaran, V. R., and J. R. Mackay. 1996. “Electrical freezing potentials measured in a pingo growing in the western Canadian Arctic.” Cold Reg. Sci. Technol. 24(2): 191–203.

CHAPTER 13

Results and Discussions of Field Studies

13.1  ILLISARVIK SITE As the Illisarvik site was not accessible easily, frequent readings could not be taken at regular intervals. The first readings obtained were those taken on March 23, 1982; June 8, 1982; and August 12, 1982. The temperature profiles are shown in Figure 13-1a to c. None of these figures show a sudden change in gradient in the temperature profile at 0 °C (30 °F), revealing that the freezing front is actually below that. A deflection in temperature profile can, however, be noticed around −0.1 °C (31.8 °F). This is consistent with the freezing point depression usually observed in freezing soils. Because the subpermafrost pore water has an increased salinity from ion rejection during permafrost aggradation, the freezing point will be lower than pure water. The specific conductance of the pore water just below the permafrost, measured in 1982 when the probe was installed, was about 300 µ Ω−1 cm−1 (compared to about 0.05 µ Ω−1 cm−1 for pure water), showing the salinity. The peak potentials reached are also shown by the solid lines in Figure 13-2a to  c. The highest freezing potentials observed at the electrodes located at the freezing front were between 1.08 and 1.35 V. The results, however, demonstrate the need for improving the measurement techniques using more precision instruments.

13.2  INUVIK SITE The soil at this site was a silty clay with particle size, 50% finer than 0.002 mm (7.87402e-5), with a specific surface area of about 120 m2/g. The amount of unfrozen pore water in such clayey matter, calculated using the method of Anderson et al. (1973), was estimated at about 9.5% at −5 °C (23 °F) and about 7% at −10 °C (14 °F). Voltage and temperature readings were taken every 2 weeks by the staff of the Inuvik Scientific Resource Centre (later to be known as Aurora

87

88

Electrical Phenomena During Freezing of Water and Soils

Figure 13-1.  Data of voltage and temperatures from three sets of readings. Source: Parameswaran and Mackay (1983).

Research Institute, Western Arctic Research Centre of the Research Division of Aurora College). Figure 13-2a to e show the variations of temperature and electrical freezing voltages measured at various depths below the ground surface, as the ground froze and thawed in the 1981 to 1982 season. At depths of 0.05 and 0.2 m (0.16 and 0.52 ft), respectively, a freezing potential as high as 650 mV developed as the temperature dropped through the freezing

Results and Discussions of Field Studies

89

Figure 13-2.  (a–e) Variations of temperature and freezing voltages measured at various depths below the ground surface as the ground froze and thawed in the 1981–1982 season. Source: Parameswaran and Mackay (1983).

point in the month of October 1981. As the temperature dropped through winter, the potentials also dropped. In the spring of May 1982, as the ground started to thaw and the temperature rose above 0 °C (30 °F), a thawing potential up to 700 mV was observed. This could be attributed to the melt water from the thawing active layer reaching the still frozen part of the lower active layer and for ice (Cheng 1982, Mackay 1983 (a, b, c), Parmuzina 1978, Wright 1980). This was not prominent at lower levels of the active layer.

90

Electrical Phenomena During Freezing of Water and Soils

At the levels of 0.51 and 0.96 m (1.67 and 1.96 ft), the measured EFP remained at 600 to 700 mV, after the first rise of EFP, even after the temperature dropped below 0 °C (30 °F). This is attributed to the upward migration of unfrozen water from the freezing front into the frozen active layer (Mackay 1979a) and causing further electrical freezing potentials (EFPs). All these measurements suggest that EFPs do develop at the freezing front in soils as ground freezes. Also, electrical probes to measure these potentials could be developed to detect the advance/retreat of the freezing front and the technique could be refined to form a geophysical method to study in permafrost.

References Anderson, D. M., A. R. Tice, and H. L. Hakim. 1973. “The unfrozen water and apparent specific heat capacity for frozen soils.” In Proc., 2nd Int. Conf. on Permafrost, North American Contribution, 289–295. Washington, DC: National Academy of Sciences. Cheng, G. 1982. “The forming process of thick layered ground ice.” Sci. Sin. Ser. B 25 (7): 777–788. Mackay, J. R. 1979a. “An equilibrium model for hummocks (non-sorted circles), Garry Island, Northwest Territories.” In Current research, Part A, Paper 79-1A, 165–167. Ottawa: Geological Survey of Canada. Mackay, J. R. 1979a. “An equilibrium model for hummocks (non-sorted circles), Garry Island, Northwest Territories.” In Current research, Part A, Paper 79–1A, 165–167. Ottawa: Geological Survey of Canada. Mackay, J. R. 1979b. “Pingos of the Tuktoyaktuk Peninsula area, Northwest Territories.” Géographie physique et Quaternaire 23:3–61. Mackay, J. R. 1981. “An experiment in lake drainage, western Arctic coast.” In Current research, Part A, Paper 81–1A, 63–68. Ottawa: Geological Survey of Canada. Mackay, J. R. 1983a. “Downward water movement into frozen ground, western Arctic coast. Canada.” Can. J. Earth Sci. 20:120–34. Mackay, J. R. 1983b. “Oxygen isotope variations in permafrost, Tuktoyaktuk Peninsula area, Northwest Territories.” In Current research, Part B, Paper 83–1B, 67–74. Ottawa: Geological Survey of Canada. Mackay, J. R. 1983c. Pingo growth and subpingo water lenses, western Arctic coast, Canada. In Proc., 4th Int. Conf. on Permafrost, Vol. 1. July 17–22. 762–66. Washington, DC: National Academy Press. Parameswaran, V. R., and J. R. Mackay. 1983. “Field measurements of electrical freezing potentials in permafrost areas.” In Proc., 4th Int. Conf. on Permafrost, 962–967. Washington, DC: National Academy Press. Parmuzina, O. Y. 1978. “Cryogenic texture and some characteristics of ice formation in the active layer.” [In Russian] Problemy kriolitologii 7: 141–164. Translated in Polar Geogr. Geol. 1980: 131–152. Wright, R. F. 1980. The water balance in a lichen tundra underlain by permafrost. McGill Subarctic Research Paper No. 33, Climatological Research Series No. 11. Montreal: McGill University.

CHAPTER 14

Field Studies of EFP in Freezing Lakes in Inuvik

In the winter of 1996 to 1997, the author, in collaboration with the Department of Geography and Environmental Sciences of Carleton University, Ottawa, designed equipment to study the development of electrical potentials that developed during the freezing of large bodies of water—lakes—in a natural environment in permafrost areas. No data have been recorded on this aspect to date. Two lakes in Inuvik (NWT) area were chosen that had contrasting hydrologic regimes and were within 10 km of each other. Inuvik is on the east side of Mackenzie Delta, about 40 km south of the tree line and in the continuous permafrost zone (Mackay 1963, Heginbottom 1995), with a mean monthly air temperature below 0°C through October to May (Environment Canada 1993). The area and the location of the lakes are shown in Figure 14-1. Upland Lake is an inland lake with no discharge or influx of water from outside, except from precipitation. The second lake called the Delta Lake, located in the Mackenzie Delta, 3 km (about 2 mi) west of Inuvik (Lake 15b in Figure 3 of Burn 1995), is connected to the Mackenzie discharge throughout the year and has higher concentrations of dissolved ions than in the Upland Lake (Figures 14-2 and 14-3). General environmental conditions such as snow depth and air temperature are similar in the middle of the lakes, but the water chemistry is distinctly different, because of the fact that the Upland Lake is an inland lake with no discharge or influx of water from outside, except from precipitation. The ionic concentrations (ppm) in the lakes are shown as follows: Ionic impurities (ppm)

Upland Lake

Delta Lake

Mg Ca K Na

5.1 16 0.9 3.5

8 30 10 11

91

92

Electrical Phenomena During Freezing of Water and Soils

Figure 14-1.  Mackenzie Delta area, Northwest Territory, indicating the locations of gauging stations. Source: Burn (1995).

Field Studies of EFP in Freezing Lakes in Inuvik

93

Figure 14-2.  Aerial view of the frozen Mackenzie Delta, north of Inuvik, Northwest Territory. Source: Burn (1995).

Figure 14-3.  Lakes in the Mackenzie Delta area, Northwest Territory. Source: Burn (1995).

94

Electrical Phenomena During Freezing of Water and Soils

Ice begins to form on the surface of the lake bodies in late September and remains until early June. The maximum ice thickness reached is about 1 m (3.5 ft). Details of the lake and their infill can be found in Burn (1995). Figure 14-4a shows a schematic diagram of the probe (dimensions, not to scale) used to measure the freezing potentials in the lakes. Each probe has 10 copper electrodes, numbered 1 through 10, with a thermistor attached behind each electrode. Figure 14-4a shows a schematic diagram of the probe installed in the Upland Lake. Figure 14-4b shows the assembled probe ready to be installed in the Upland Lake. The design details are the same as those described in Parameswaran and Mackay (1983, 1996). The bottom of the probes, installed vertically, goes down to one meter below the surface. The electrical potential differences between the bottom electrode (1) and each of the others above were measured using a multimeter of high impedance. Measurements were done every week from mid-November 1996, when freezing starts from the top downward, until early March 1997, when thawing begins from the surface.

Figure 14-4.  (a) Probe installed in the Upland Lake site (not drawn to scale), (b) Assembled probe, ready to be installed in the Upland Lake site. Source: Burn et al. (1998).

Field Studies of EFP in Freezing Lakes in Inuvik

95

References Burn, C. R. 1955. “The hydrologic regime of Mackenzie River and connection of ‘no-closure’ lakes to distributary channels in the Mackenzie Delta, Northwest Territories.” Can. J. Earth Sci. 32 (7): 926–937. Burn, C. R., V. R. Parameswaran, L. Kutny, and L. Boyle. 1998. “Electrical potentials measured during growth of lake ice, Mackenzie Delta area, N. W. T., Canada.” In Proc., 7th Int. Conf. on Permafrost, Yellowknife, Yukon. Collection Nordicana 55: 101–106. Environment Canada. 1993. Canadian climate normals, 1961­–1990: Yukon and Northwest territories. Whitehorse, YT: Environment Canada, Canadian Climate Program. Heginbottom, J. A. 1995. Permafrost, Atlas of Canada, 5th Ed. Plate 2.1. Ottawa: Natural Resources Canada. Mackay, J. R. 1963. The Mackenzie delta area. Geographical branch memoirs. Ottawa: Dept. of Mines and Technical Survey. Parameswaran, V. R., and J. R. Mackay. 1983. “Field measurements of electrical freezing potentials in permafrost areas.” In Proc., 4th Canadian Conf. on Permafrost. Ottawa: National Research Council of Canada, 962–967. Parameswaran, V. R., and J. R. Mackay. 1996. “Electrical freezing potentials measured in a pingo growing in the western Canadian Arctic.” Cold Reg. Sci. Technol. 24 (2): 191–203.

CHAPTER 15

Results from Lake Studies in Inuvik: Upland and Delta Lakes

Figure 15-1 shows the increase of thickness of ice cover. Figure 15-2 shows the electrical potentials measured at different depths. The electrical freezing potentials observed at the Delta Lake are larger than those at the Upland Lake, probably because of the large ionic concentrations in the former. Figure 15-3 shows the freezing potentials measured at the water–ice interface.

Figure 15-1.  Estimated ice thickness in the Upland and Delta Lakes. Source: Burn et al. (1998). Note: Thickness of the ice cover in the lakes, November 1996 to March 3, 1997, interpreted from temperatures.

97

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Electrical Phenomena During Freezing of Water and Soils

Figure 15-2.  Freezing potentials measured in the lakes in December 1996. Source: Burn et al. (1998). Note: Electrical potentials measured in the two lakes, on December 26, 1996, on different electrodes at different depths.

Figure 15-3.  Potential drops across the ice–water interface in the lakes, November 23, 1996, to March 3, 1997. Source: Burn et al. (1998).

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The readings showed larger fluctuations at the Delta Lake than in the Upland Lake, again probably because of larger ion concentrations and influx from the Mackenzie River. The magnitude of the freezing potentials was 300 to 500 mV in general and went as high as 700 mV, the potentials being ice-negative. As mentioned in the previous parts of this book, and as shown in Chapter 7, Table 7-1, the sign of the potentials depends on the ionic impurities present in the water. The conclusions from these measurements of electrical freezing potentials in natural lakes during the development of ice cover show a definite charge separation and potential difference at the freeze–thaw interface.

Reference Burn, C. R., V. R. Parameswaran, L. Kutny, and L. Boyle. 1998. “Electrical potentials measured during growth of lake ice, Mackenzie Delta area, N. W. T., Canada.” In Proc., 7th Int. Conf. on Permafrost, Yellowknife, Yukon. Collection Nordicana 55: 101–106.

CHAPTER 16

Concluding Remarks

Electrical potentials develop during freezing of water, aqueous solutions, and moist soils because of the polar nature of the water molecule and the separation and accumulation of charges of opposite signs into the liquid and solid phases of water at the freezing interface. The experiments described in this manual show that this phenomenon can be used as another geophysical method to locate the freezing boundary in freezing ground. The method, however, requires the installation of suitable probes containing electrodes connected to suitable equipment for the detection and measurement of the small voltages produced at the interface (freezing boundary). With the availability of advanced electronic sensors and data transmission equipment, one may be able to monitor the advancement of the freezing front in permafrost areas, without having to monitor them by the physical presence of scientists in the remote areas, especially in severe weather conditions. Some uncertainty exists with regard to the sign and magnitude of the potentials that develop, and further investigations need to be carried out in a systematic way to study some of the effects that govern electrical freezing potential (EFP) measurements, such as the effect of various ions on the sign of the potentials in solutions, effect of grain size of the soils, effect of unfrozen water content, governed by the grain size and temperature, and the effect of the rate of cooling. Systematic studies can be undertaken with new equipment with more precision than the ones used in the beginning of these studies and by developing new and improved measurement techniques. In remote areas under harsh weather conditions, it may be difficult to directly monitor and measure the small potentials that develop during freezing. There are new techniques of transmission of the measured potentials measured remotely, via meteor burst communications (Cumberland et  al. 2004). Meteor burst communications (MBC), also referred to as meteor scatter communications, is a radio propagation mode that exploits the ionized trails of meteors during atmospheric entry to establish brief communication paths between radio stations up to 2,250 km (1,400 mi) apart. SNOTEL is an automated system of snowpack and related climate sensors operated by the Natural Resources Conservation Service (NRCS) of the United States Department of Agriculture in the western United States. Figure 16-1 shows a schematic representation of how the system works. 101

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Electrical Phenomena During Freezing of Water and Soils

Figure 16-1.  Meteor scatter propagation as used by SNOTEL. Source: National Water and Climate Center.

HOW IT WORKS As the Earth moves along its orbital path, millions of particles known as meteors enter the Earth’s atmosphere every day, a small fraction of which has properties useful for point-to-point communication. When these meteors begin to burn up, they create a trail of ionized particles in the E layer of the atmosphere that can persist for up to several seconds. The ionization trails can be very dense and thus used to reflect radio waves. The frequencies that can be reflected by any particular ion trail are determined by the intensity of the ionization created by the meteor, often a function of the initial size of the particle and are generally between 30 and 50 MHz. The distance over which communications can be established is determined by the altitude at which the ionization is created, the location over the surface of the Earth where the meteor is falling, the angle of entry into the atmosphere, and the relative locations of the stations attempting to establish communications. Because these ionization trails exist only for fractions of a second to as long as a few seconds in duration, they create only brief windows of opportunity for communications.

SCIENTIFIC USE The US Department of Agriculture (USDA) uses meteor scatter extensively in its SNOTEL system. More than 800 snow water content gauging stations in the

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western United States are equipped with radio transmitters that rely on meteor scatter communications to send measurements to a data center. The snow depth data collected by this system can be obtained from USDA. In Alaska, a similar system is used in the Alaskan Meteor Burst Communications System (AMBCS), collecting data for the National Weather Service from automated weather stations, as well as occasional data from other US government agencies. In 1986 to 1987, the technology (Meteor Burst Communications) was tested in the NRCC Laboratories to access the data of EFP obtained from the Inuvik installation. Signals could be received and plotted, but the quality of the signals was very poor, and owing to a lack of availability of a good data acquisition system and in the absence of trained personnel, the project could not be pursued further. This is an area that could be investigated further. In the long term, one could look into the possibility of utilizing the small voltages and currents for any practical use in the field. For this, more field installations and studies need to be carried out. Although the capital investment for equipment for this venture may not be large, it could involve larger costs for labor and time of scientists and engineers. But the costs will be worth it from the scientific and engineering point of view, considering the effects of the electrical freezing potentials in construction, such as in pipelines in permafrost areas.

J USTIFICATION FOR CONTINUING INVESTIGATIONS ON ELECTRICAL POTENTIALS AND OTHER ELECTRO-KINETIC PHENOMENA OCCURRING DURING FREEZING OF SOILS AND SOLUTIONS It has been established and definitely confirmed that electrical potentials do develop during freezing of solutions and soils. The magnitude, sign, effects of cooling rates, and so on, need to be studied further to make any use of the potentials. Establishing a network of electrodes to capture any currents that can develop through such static electrical potentials could be considered, although it is only a nascent scientific curiosity now, similar to the analogy of establishing towers to capture thunderstorm electricity.

Reference Cumberland, B. C., J. S. Valacich, and L. M. Jessup. 2004. “Understanding meteor burst communications technologies.” Communications of the ACM 47 (1): 89–92.

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Phan, C. L., and J. L. Laforte. 1968. “The influence of electro-freezing on ice formation on high-voltage DC transmission lines.” Cold Reg. Sci. Technol. 4 (1): 15–25. Pruppacher, H. R., E. H. Steinberger, and T. L. Wang. 1968. “On the electrical effects that accompany the sponataneous growth ice in supercooled aqueous solutions.” J. Geophys. Res. 73: 571–584. Quora. n.d. “Can we produce electricity by thunderstorm?” Accessed October 7, 2022. https://www.quora.com/Can-we-produce-electricity-by-thunderstorm. Reynolds, S. E. 1954. Compendium of thunderstorm electricity. Research report, Soccoro, NM: US Signal Corps. Ross, N., P. J. Brabham, C. Harris, and H. H. Christiansen. 2007. “Internal structure of open system pingos, Adventdalen, Svalbard: The use of resistivity tomography to assess ground-ice conditions.” J Environ. Eng. Geophys. 12: 113–126. Sanger, E. D., and P. J. Hyde, eds. 1978. Permafrost: 2nd Int. Conf., July 13–28, 1973: USSR contribution. Washington, DC: National Academy of Sciences. Sartorelli, A. N., and R. B. French. 1982. “Electro-magnetic induction methods for mapping permafrost along northern pipeline corridors.” In Proc., 4th Canadian Conf. on Permafrost. Ottawa: National Research Council of Canada, 283–295. Saunders, C. P. R. 2008. “Charge separation mechanisms in clouds.” Space Sci. Rev. 137 (1): 335–353. Schonland, B. F. J. 1953. Atmospheric electricity by J. Alan Chalmers. 2nd ed. London: Pergamon Press. Schonland, B. F. J. 1956. “The lightning discharge.” In Vol. 22, Hnadbuch der Physik, edited by S. Flügge. Berlin: Springer. Schonland, B. F. J. 1982a. “The polarity of thunderclouds.” In Proc., Royal Society of London, Series A, 118: 233–251. Schonland, B. F. J. 1982b. “The interchange of electricity between thundercloud and earth.” In Proc., Royal Society of London, Series A. 118: 252–2262. Schonland, B. F. J., and J. Craib. 1927. “The electric field of South African thunderstorms.” In Proc., Royal Society of London, Series A. 114: 229–243. Schonland, B. F. J., and J. P. T. Viljoen. 1933. “On a penetrating radiation from thunderclouds.” In Proc., Royal Society of London, Series A. 140: 314–333. Scott, W. J., and J. A. Hunter. 1977. “Applications of geophysical techniques in permafrost regions.” Can. J. Earth Sci. 14: 117–127. Scott, W. J., P. V. Sellmann, and J. A. Hunter. 1978. “Geophysics in the study of permafrost.” In Proc., 3rd Int. Conf. on Permafrost, Edmonton. 2: 93–116. Scott W. J., P. V. Sellmann, and J. A. Hunter. 1990. “Geophysics in the study of permafrost.” In Geotechnical and Environmental Geophysics, edited by W. J. Ward. Tulsa, OK: Society of Exploration Geophysicists, 355–384. Simpson, G. C. 1909. “On the electricity of rain and its origin in thunderstorms”. Philos. Trans. Royal Soc. A. 200: 379–413. Simpson, G. C. 1919. British (Terra Nova) Antarctic expedition 1910 to 1913, Vol. 1. Calcutta: Thacker, Spink, and Co., 302–312. Simpson, G. C. 1942. “The electricity of cloud and rain.” Q. J. R. Met. Soc. 68 (293): 1–34. Sladen, W. E., L. Dyke, and S. L. Smith. 2009. Permafrost at York Factory National Historic Site of Canada, Manitoba, Canada. Current Research 2009-4. Ottawa: Geological Survey of Canada. Slater, L. D., and D. Lesmes. 2002. “IP interpretation in environmental investigations.” Geophysics 67: 77–88. Saunders, C. 2008. “Charge separation mechanisms in clouds.” Space Sci. Rev. 137 (1): 335–353. 

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Supper, R., D. Ottowitz, B. Jochum, A. Römer, et al. 2014. “Geoelectrical monitoring of frozen ground and permafrost in alpine areas: field studies and considerations towards an improved measuring technology.” Near Surf. Geophys. 93–115. Verschinin, P. V., B. V. Deriagin, and N. V. Kirilenko. 1949. The nonfreezing water in soil. US Army CRREL Translation No. 30. Waltham, MA: Arctic Construction and Frost Effects Laboratory, US Army Engineer Division. Wilson, C. T. R. 1929. “Some thouderclous problems.” J. Franklin Inst. 208 (1): 1–12. Wolfe, S. A., C. W. Stevens, A. J. Gaanderse, and G. A. Oldenborger. 2014. “Lithalsa distribution, morphology and landscape associations in the Great Slave Lowland, Northwest Territories, Canada.” Geomorphology 204, 302–313. Workman, E. J., R. E. Holzer, and G. T. Pelsor. 1942b. “The electrical structure of thunderstorms.” NACA Tech. Note No. 864. Washington, DC: Work of the US Government. Workman E. J., and S. E. Reynolds. 1949. “Electrical activity as related to thunderstorm cell growth.” Bull. Am. Meterological Soc. 30 (4): 142–144. Workman, E. J., and S. E. Reynolds, 1950. Electrical phenomena occurring during the freezing of dilute aqueous solutions and their possible relationship to thunderstorm electricity. Phys. Rev. 78 (1): 254–259. Workman, E. J., and S. E. Reynolds. 1953. “Structure and electrification.” In Thunderstorm electricity, edited by H. R. Byers, 139–149. Chicago: University of Chicago Press. Wormell, T. W. 1927. “Currents carried by point charges beneath thunderclouds and showers.” In Proc. Royal Society of London, Series A. 115: 443–455. Wormell, T. W. 1930. “Vertical electric currents below thunderstorm and showers.” In Proc. Royal Society of London, Series A. 127: 567–590. Wormell, T. W. 1939. “The effects of thunderstorms and lightning discharges on earth’s electric field.” Philos. Trans. Roy. Soc. London, Series A. 238: 249–303. Wormell, T. W. 1953. “Atmospheric electricity: some recent trends and problems.” Q. J. R. Met. Soc. 79 (339): 3–38. Wormell, T. W. 1955. “Theories of thunderstorm electrification—Some general conclusions.” In Proc., Conf. on Atmospheric Electricity, Portsmouth, New Hampshire. Hanscom AFB, MA: Air Force Cambridge Research Center, 157–161. Wu, Y., S. Nakagawa, T. J. Kneafsey, B. Dafflon, and S. Hubbard. 2017a. “Electrical and seismic response of saline permafrost soil during freeze–thaw transition.” J. Appl. Geophys. 146: 16–26. Wu, Y., S. Nakagawa, T. J. Kneafsey, B. Dafflon, and S. Hubbard. 2017b. “Electrical and seismic response of saline permafrost soil during freeze–thaw transition: Supporting data.” Oak Ridge, TN: Oak Ridge National Laboratory, Next Generation Ecosystem Experiments Arctic Data Collection, Carbon Dioxide Information Analysis Center. Yarkin, I. G. 1974. “The nature of natural electrical potentials occurring when soils freeze.” In Physico-chemical process in freezing soils and ways of controlling them. Collected papers No. 64, N. NM. Moscow: Gersevanov Foundation and Underground Structure Research Institute, Stroiizdat, 59–81. Yarkin, I. G. 1978. “Effect of natural electrical potentials on water migration in freezing soils.” In Proc., Permafrost: 2nd Int. Conf., USSR Contribution, edited by F. J. Sanger and P. J. Hyde. Washington, DC: National Academy of Sciences, 351–361. You Y., Q. Yu, X. Pan, and L. Guo. 2013. “Application of electrical resistivity tomography in investigating depth of permafrost base and permafrost structure in Tibetan Plateau.” Cold Reg. Sci. Technol. 87 (3): 19–26.

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Yuxin, W., S. Nakagawa, T. J. Kneafsey, B. Dafflon, et al. 2017. “Electrical and seismic response of saline permafrost soil during freeze–thaw transition.” J. Appl. Geophys. 146: 6–26. Zhou, X., J. Zhou, W. Kinzelbach, and F. Stauffer. 2014. “Simultaneous measurement of unfrozen water content and ice content in frozen soil using gamma ray attenuation and TDR.” Water Resour. Res. 50 (12): 9630–9655.

APPENDIX A

Background: Basic Information of Potential Measurements

Basic Electricity and Magnetism Tutorial (Oxford University Press 1998)

GROUND Every electrical circuit has a point of reference to which all circuit voltages are compared, known as Ground (SweetHaven Publishing Services 2002), with respect to which the measured voltages can be (+) or (−). The difference of the potential between a point in the circuit and the ground is measured by using a voltmeter. Ground is usually referred to earth itself and is represented as a point of zero potential or zero volts. Without this zero point, voltages cannot be expressed as (+) or (−). Charge Fundamental property of elementary particles; Electron Charge: 1.6 × 10−19 C; mass: 9.1 × 10−31 kg (∼10−25 mg); Proton Charge: +1.6 × 10−19 C; mass: 1.67 × 10−27 kg (∼1.7 × 10−21 mg); Neutron Charge: 0; mass: 1.66 × 10−27 kg (∼1.7 × 10−21 mg); and Ion A moving charged particle (+) or (−) consists of an atom, molecule, or a cluster of molecules.

COULOMB’S LAW Force exerted on one particle by another is proportional to the product of the charge of each particle and inversely proportional to the square of the distance between them, directed along the line between them: • Force F21 = (1/4πε) (q1q2ér2), where (1/4πε) is the proportionality constant, for free space = 10−7c2, where c is the speed of light. 105

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• Electric field, E = F21/q1, is the force experienced by Charge 1 placed at a distance, r, from q2. E at a radius r from the point charge q1 is E = (1/4πε) (q/r2). • Unit for an electric field is Newton per Coulomb, which is equivalent to volt per meter. The polarity of an electric field is the direction in which a positive charge will move under a constant force F. • Electric field of a charge is radial—spherically symmetric. • Force on a test charge q in an electric field caused by another charge is F = q1 E. Field lines radiate outward from a (+) charge and radiate inward to a (−) charge. • Force on a charge q owing to an electric field E from the charge is F = qE, which should be applied externally to keep the charge in location (ÉÉÉ). • Work is the force acting over a distance. Applied force works against a resisting electric force that tends to move the charge q1. • Energy is the work done by an electric field. Change in energy dW = −F · dL = q · E · dL. • Unit of energy is joule (J). • Energy change per unit charge is electrostatic or electric potential: dW/q′ = dϕ = E · dL, in J/C (J C−1), equivalent to a volt (V). • Difference in electric potential at two points A and B is ϕB − ϕA = ∫E · dL. This potential difference depends only on the location of points A and B and NOT on the path taken by charge q′ to go from A to B.

ϕB − ϕA = (q /4πε) (1/rB ) − (1/rA )

(A-1)

If point A is moved to infinity, φA becomes zero, and rA = 0 ϕ = ϕB = q/4πεr, where r = rB. • Potential is a scalar quantity and not direction. Many authors writing about atmospheric electricity use the terms field or electric field to express the potential gradient (i.e., ∇ϕ). An electric field is given by the maximum rate of change of the potential. The gradient of the potential (usually called the potential gradient, given previously) provides the direction and magnitude of the maximum rate of change of ϕ. This means, “the electric field is the negative of the potential gradient”, E = −∇ϕ. The symbol V is often used for potential in place of ϕ, with a unit of volt. The potential difference between two points is often referred to as the voltage between two points. In this document, V is used as the symbol for potential difference the voltage between two points rather.

Background: Basic Information of Potential Measurements

107

• Dipole is a pair of opposite charges, closely spaced, separated by a distance d, caused by an electric field E, exerting opposite forces on the (+) and (−) charges (protons and electrons). Dipole formation can also occur on the molecular level. • Dipole moment, p = qd (q is the charge). • Potential produced at a given point r, by a vertical dipole centered at the origin is expressed as follows: ϕ( XYZ ) = (1/4πεr 2 ) ⋅ p ⋅ r



(A-2)

• Electric field of the dipole can be calculated from the potential.

ELECTRIC FLUX AND GAUSS’S LAW Gauss’s Law is a different form of Coulomb’s Law. In free space, electric field rearranges charges on a molecular level inside the substance and causes an electric flux. Electric flux is a scalar and its value through a surface is obtained by integrating it over the entire surface. Flux provides an easy means of determining E. By definition, 1C of a charge causes an electric flux of 1C through a surface normal to the charge. Flux is linked to the concept of electric field lines.

CHARGE TRANSPORT AND ELECTRIC CURRENT Movement of charges under the influence of an electric field causes an electric current, I, through a surface, and defined as the net charge passing through that surface per second. Current is measured in amperes (A), equivalent to coulombs per second. Current density, J, through a unit area of the surface, has both magnitude and direction, measured in amperes per m2. Many materials (including metals) obey Ohm’s Law, written in terms of current J and field intensity E and conductivity of the material, σ, as J = σE.  (In atmospheric electricity, λ is often used for conductivity.) For electronic circuits, Ohm’s Law is expressed either as V = IR, where V is the voltage, I is the current, and R is the resistance, or as I = V/R, which could be large for metals, as R is very low for metals).

Reference SweetHaven Publishing Services. 2002. Definition of “ground.” Columbus, OH: Sweethaven Publishing Services.

APPENDIX B

Calculations of Charge Concentration at a Metal/ Dielectric Interface and Force of Adhesion

As mentioned in the main text, the development of electrical potentials because of charge separation during freezing of water, aqueous solutions, and moist soils could have some effect on the adhesion of water and soils to structures. In this section, the calculation of charge separation in the electrical double layer at the freezing interface is presented using classical theories. The force of adhesion of ice (treated as a dielectric) to a metallic substrate can be calculated from the charge density at the interface, which can be compared to the values of adhesive force (strength) measured in the laboratory. Consider the possibility of electrons flowing from the metal electrode into the conduction band of a dielectric or insulator. Electron flow can occur only if an appreciable fraction of electrons have energies more than (Φ − χ) above the Fermi level Φ of the metal (Figure 9 of DBR 84). When (Φ − χ) is less than the work function of the metal or when (Φ − χ) is not too large compared to kT, electrons may be emitted by the metal into the insulator even at relatively low temperatures. A vapor of electrons will form in the dielectric, with the electrons having energies lying in the conduction band. An equal positive charge will be formed on the surface of the metal. This gives rise to a toral field in the insulator or dielectric that will raise the conduction levels as the distance increases from the metal/ dielectric interface (Figure 9). The field and the electron density in the dielectric can be calculated in a way similar to the calculation of the density of electron gas around a thermionic emitter (Mott and Gurney 1940, Deryagin et al. 1978). If F is the field within the dielectric (ice in this case),

(dF /dx ) = (4πNE /κ)

(B-1)

where N = Number of electrons per unit volume at a distance x from the metal/ dielectric interface, 109

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Electrical Phenomena During Freezing of Water and Soils

e = Electronic charge, and κ = Dielectric constant. If υ and D are the mobility and diffusion coefficients of the electrons at the equilibrium state when no current flows, NeυF − De(Dn /dx ) = 0



(B-2)

Integration of this equation gives Log(N /N o ) = (υ /D)o ∫ x Fdx



(B-3)

where No is the density of electrons in the dielectric at the interface with the metal. If the number of particles (per unit volume) N(x) is in equilibrium in a field of F, of which the potential is Φ, assuming F varies only in the x-direction, F = ∂Φ/∂x



(B-4)

According to Boltzmann’s Law, N (x ) = (a constant)× exp(−eΦ /kT )



(B-5)



Equation (B-2), after substituting for F, can also be integrated to obtain N: N = (A constant)× exp(−υΦ /D)



(B-6)



A comparison of Equations (B-5) and (B-6) gives the Einstein relation υ/D = e /kT



(B-7)

The potential energy V(x) = e Φ of an electron, from Equation (B-4), is V (x ) = −eo ∫ x Fdx



(B-8)

From Equation (B-5), N (x ) = (A constant)× exp[−V (x )/kT ]

or

N /N o = exp(−V /kT )



(B-9)

From Equations (B-1), (B-8), and (B-9), d 2 y /dx 2 = (−4πN oe 2 ) ⋅ exp(−V /kT )



(B-10)

To solve Equation (B-10), the following boundary conditions are imposed: V(0) = 0 and V (∞) = Vc = the contact potential difference or the difference in the work functions of the metal and the dielectric. Integration of Equation (B-10) leads to

1

2

(dV /dX )2 = [4πN 0 E 2kT /κκ] exp(−V /kT )

dV /dX = 2 [2πN 0 E 2kT /κ]0.5 exp(−V /kT )

111

Calculations of Charge Concentration at a Metal/Dielectric Interface



exp(V /kT )dV = 2[2πN 0 E 2kT /κ]0.5 dX



2kT exp(V /kT )dV = 2[2πN 0 E 2kT /κ]0.5 dX + a constant A



exp(V /kT ) = [2πN 0 E 2kT /κ]0.5 X + A/2kT When X = 0, V = 0, and exp (V/kT) = 1, V = 2kT log(1 + X /X0 )



(B-11)

where X0 = [2πN 0 E 2 /κkT ]−0.5

Hence,

N /N 0 = exp(−VkT ) = [ X0 /( X + X0 )]2



(B-12)

The density of electrons, N0, in the dielectric at the metal/dielectric boundary will be determined by using the same Fermi distribution function as for electrons in the metal. Hence,

N 0 =o ∫ ∞ N (E )dE /Exp{[E − (Φ − X )]/kT } + 1

(B-13)

where N(E) is the density of states in the dielectric. This may be taken as equal to (4π/3)(2mE ⋅ h2 )3/2



where m = Electronic mass, h = Planck’s constant, and E = energy. As (Φ – X) is much larger than kT, integration of Equation (B-13) gives

N 0 = 2[2πmkT /h2 ]3/2 exp[ − (Φ − X )/kT ]

(B-14)

N 0 = 1019 exp[−(Φ − X )/kT ]

(B-15)

which reduces to

which further reduces to

N o = 1019 exp[ − (Φ −χ ) / kT ]

(B-16)

If the static dielectric constant κ of ordinary ice at −10 °C (263 °K) is assumed to be equal to 100 (Auty and Cole 1952, Johari and Whalley 1973), the values of Xo and No obtained for various values of (Φ − χ) can be calculated, and these values are given in Table B-1. Equation (B-11) shows that if the density of electrons at the boundary layer is large, V, the potential energy of the electron rises rapidly by a few multiples of kT.

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Table B-1.  Values of No and Xo for Various Values of (Φ - χ). (Φ − χ)ev No (cm−3) Xo (cm)

0.1 1.2 × 1017 4.5 × 10−6

0.5 2.6 × 109 3.1 × 10−2

1.0 0.7 1.9 × 103

Knowing the charge density No of electrons at the metal/dielectric interface [given in Equation (B-14)], we can calculate the force of adhesion of the dielectric to the metallic substrate. If the electrical double layer is considered a parallel plate capacitor, the force of interaction F of two unlike bodies will be the same as the force of attraction per unit area of the capacitor plates; this can be calculated according to the formula F = (A constant)×(e / r 2 )Σ i , j Ez ( XiY j )



(B-17)

where Xi Yj are the coordinates of the charge in one of the planes (e.g., the positive plate), and Ez (Xi Yj) is the field created by all charges of the other plane at the point at which the charge is located, and r is the distance between the plates. Taking Σi,j = Noe in this case, where No is the total surface charge density, F = No e2/r2 = (1/r2) No (4,805 × 10−10)2; F = 23 × 10−4 (No/r2) dynes/cm2, with r expressed in Angstroms (Å = 10−8 cm); and F = 23 × 10−11 (No/r2) in MPa. Using the values of No given in Table B-1, the values of the adhesive force between a metal and a dielectric (in this case, ice) for the values of “r” can be calculated. Some typical values are given in Table B-2. Although the calculation of the adhesive force was relatively simple enough using the analogy of planar lattice charges in electrostatics, the real situation in adhesion is more complex, and therefore, an exact solution cannot be provided. Inhomogeneity in the chemical properties of the surface of the adherend plays a major role in the coupling of real materials. Surfaces are never ideally smooth. The aforementioned calculations, however, can be used to obtain an estimate of the force of adhesion. Table B-2.  Force of Adhesion F Expressed in MPa as a Function of the Charge Concentration No in the Electrical Double Layer and its Thickness “r.” Values of F in units of MPa. N (cm2) 1017 1015 1010 105

r = 3 Å

r = 5 Å

r = 10 Å

r = 100 Å

2.55 × 106 2.55 × 104 2.55 × 10−1 2.55 × 10−6

0.9 × 10 6 0.9 × 104 0.9 × 10−1 0.9 × 10−6

2.3 × 105 2.3 × 103 2.3 × 10−2 2.3 × 10−7

2.3 × 103 2.3 2.3 × 10−5 2.3 × 10−10

Calculations of Charge Concentration at a Metal/Dielectric Interface

113

It is worthwhile comparing the results obtained from the measurements of adfreezing force of piles to ice in the laboratory, with the values given in Table B-2. Cobb and Gross (1969) found that the maximum charge transferred per m3 of ice frozen could be up to 3 × 1023 elementary charges in dilute solutions. This is equivalent to 3 × 109 elementary charges per cm2 area per Å thickness. For a double layer of thickness of 3 Å, the total number of charges per cm2 could be ∼1010 per cm2. From Table B-2, the value closest to this range is 2.55 × 10−1, corresponding to a surface charge density of electrons of 1010 per cm2 and a double layer thickness of 3 Å. This indicates that in a real situation, the thickness of the double layer formed between a metallic pile and an adhering material—ice or frozen soil—is indeed very small, on the order of a few Angstroms (about a tenth of a nanometer)!

References Auty, R. P., and R. H. Cole. 1952. “Dielectric properties of ice and solid D2O.” J. Chem. Phys. 20 (8): 1309–1314. Deryagin, B. V., N. A. Krotova, and V. P. Smilga. 1978. Studies in soviet sciences: Adhesion of solids, translated by R. K. Johnston. New York: Consultants Bureau. Cobb, A. E., and G. W. Gross. 1969. “Interfacial electrical effects observed during the freezing of dilute electrolytes in water.” J. Electrochem. Soc. Electrochem. Sci. 116 (6): 796–804. Johari, G. P., and E. Whalley. 1973. “Orientational order in ice, I, V, VI and VII.” In Physics and chemistry of ice, edited by E. Whalley, S. J. Jones and L. W. Gold, 278–282. Ottawa: Royal Society of Canada. Mott, N. F., and R. W. Gurney. 1940. Electronic processes in ionic crystals. Oxford: Clarendon Press.

APPENDIX C

Geophysical Methods Used in Permafrost Investigations

With electrical freezing potential (EFP) measurements being one of the geophysical methods that could be used in permafrost areas, some of the other geophysical methods commonly used to study the extent and properties of frozen ground are described in this section. Several geophysical methods have been used to examine the subsurface properties of frozen ground to delineate horizontally and vertically, the active layer, permafrost, and taliks. A talik is a layer of unfrozen ground in continuous permafrost areas, usually under shallow thermokarst lakes and rivers, where deep water does not freeze in winter, and hence, the ground underneath remains unfrozen. Thermokarst lakes are formed by subsidence as ground ice below the surface layers decays. Burn and Smith (1990) concludes that local land disturbances are more of a factor in determining where a thermokarst feature will exist rather than climate alone. Several thermokarst landforms have been identified based on their topographical characteristics, including beaded streams formed by the melting of ice wedges, collapsed pingos, and thermokarst fens forming as a result of rapid thaw of lowland deposits from groundwater springs.

ELECTRICAL METHODS Kneisel and Hauck (2008) describe the commonly used electrical methods in applied geophysics: • Direct-current (DC) electrical measurements; • Self-potential measurements (SP); and • Induced-polarization (IP) methods, including spectral-induced polarization (SIP). Direct current resistivity methods utilize distinct changes in the electrical resistivity within the subsurface and constitute one of the traditional geophysical methods that have been applied in permafrost research. Because a marked 115

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Electrical Phenomena During Freezing of Water and Soils

increase in the electrical resistivity occurs at the freezing point, these methods are expected to be the most suitable to detect, localize, and characterize structures containing frozen material. The SP method is based on passive measurements of natural electrical potential differences in the ground, which are often negligible in periglacial areas as electrically conductive materials or water flow have to be present to generate distinct SP patterns. A cryospheric example measuring subglacial drainage conditions with SP is given by Kulessa et al. (2003). The IP and SIP methods are based on actively induced polarization effects in the subsurface, which require polarizable material to be present. Again, these effects are usually small in frozen environments, which is why all three methods have seldom been used in periglacial research to date. A review concerning SP and IP methods is included in the review paper pertaining to the application of geophysical methods in permafrost areas by Scott et al. (1990). Further details on these techniques are given in Weller and Börner (1996) and Slater and Lesmes (2002). Two excellent reviews containing several references on geophysical methods used in permafrost investigations are available (Briggs et al. 2014, 2016). The direct current resistivity method depends on the changes in the electrical resistivity within the subsurface and is a traditional geophysical method used in permafrost research. A marked increase in the electrical resistivity occurs at the freezing point and these methods are the most suitable to detect, localize, and characterize frozen ground. The SP method is based on the measurements of natural electrical potential differences in the ground, but electrically conductive materials or water flow have to be present to generate distinct SP patterns. A cryospheric example measuring subglacial drainage conditions with SP is given by Kulessa et al. (2003). The IP and SIP methods are based on actively induced polarization effects in the subsurface containing water or aqueous solutions. These effects are usually small in frozen environments, and hence, seldom used in periglacial research. A review of SP and IP methods is included in the paper by Scott et al. (1990). Further details on these techniques are given in Weller and Börner (1996) and Slater and Lesmes (2002). The unique electrical properties of frozen ground make electrical and electromagnetic geophysics a potential tool for the characterization of permafrost terrain (Scott and Hunter 1977, Hoekstra 1978, Sartorelli and French 1982, Scott et al. 1990, Hauck et al. 2001, Ross et al. 2007, Fortier et al. 2008, Sladen et al. 2009, Oldenborger et al. 2012, Hauck 2013, You et al., 2013, Supper et al. 2014, Wolfe et al. 2014). These electromagnetic techniques include • Frequency-domain EM systems (FDEMs), • Time-domain electromagnetic systems (TDEMs), • Systems using very low frequencies (VLFs), and • Radio-magneto-telluric (RMT) method.

Geophysical Methods Used in Permafrost Investigations

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Geophysical techniques have been used to study the extent, depth, and distribution of permafrost in the arctic and subarctic regions in different parts of the world. Spatial and temporal changes in subsurface geophysical properties caused by permafrost cooling, warming, aggradation, or degradation can be assessed through geophysical monitoring. A review of many geophysical methods used in studying permafrost distribution is given by Scott et al. (1978). An excellent review of many such methods (with 68 references) can be found in a recent article by Kneisel et al. (2008). Some of these techniques are described in the following paragraphs.

C.1  ELECTRICAL RESISTIVITY Electrical resistivity (the inverse of electrical conductivity) is the primary property governing the low-frequency electrical and electromagnetic geophysical response of earth materials, such as rocks and sediments, and this response depends on the amount of pore fluid, its connectivity, and the availability and mobility of chargecarrying ions (McNeil 1980a, Klein and Santamarina 2003). Low temperatures reduce the mobility of charge-carrying ions and the freezing of water greatly reduces the availability and connectivity of pore fluid for electrolytic conduction, and hence, electrical resistivity increases gradually down to the freezing point, below which it increases dramatically (King et al. 1988). Electrical resistivity (ER) (as used in geophysics) is the measurement of ground variations gathered by applying a small and highly controlled electric current across an array of electrodes. Electrical resistivity imaging (ERI)—also known as electrical resistivity tomography (ERT)—is a geophysical technique used to create an image of a specific portion of the Earth’s subsurface, through the use of automated geophysical instruments that gather thousands of resistivity measurements via an electrode cable and multiple electrodes (Markus 2016). This article explores what electrical resistivity surveys are used for and the important facts about electrical resistivity. Significant contrasts in electrical resistivity and elastic properties between frozen and unfrozen soil are the basis for these methods. Typical electrical resistivity values for unfrozen soils vary from a few to hundreds of ohm-meters depending on pore water salinity, saturation, soil type, and texture, whereas typical resistivity for frozen soils ranges from tens to hundreds of kilo-ohm-meters. Thus, the electrical resistivity of moist soils increases more than thousandfold after freezing. Murrmann (1973) of Cold Regions Research Engineering Laboratory (CRREL) describes the use of electrical resistivity measurements to estimate the unfrozen water content. Wu et  al. (2017) studied the electrical and seismic response of saline permafrost soil during freeze–thaw transition to measure the unfrozen water content in the soils. In freshwater permafrost soils, most of the unfrozen water

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exists as surface-bound water and thin water films in the vicinity of soil grains. In saline permafrost, unfrozen water could also occupy the bulk pore space (Hivon and Sego 1996), can fluctuate significantly during freeze–thaw transitions and is the dominant factor controlling its mechanical and hydrological properties. Electrical and seismic signals show characteristic changes during freeze–thaw cycles and different hysteresis behavior. The changes in resistivity may reflect the changes of the distribution pattern of the unfrozen water (or ice) in the soil during repeated freeze–thaw processes. However, there is uncertainty and challenge in the estimation of unfrozen water by these geophysical methods. A geoelectrical model based on electrical resistivity, tomography, and ground-penetrating radar data was compared to geological observations from the permafrost region of the Samoylov island coastline in Russia in the Lena River Delta by Olenchenko et al. (2018) of the Trofimuk Institute of Petroleum Geology and Geophysics, Sobolev Institute of Geology and Mineralogy and Novosibirsk State University, in Novosibirsk, Russia. Their study of different types of frozen deposits, influence of river water on permafrost, ice wedges of different thickness, and others is very useful in permafrost research in other areas also. They quoted 52 references in their article in Hydrogeology Journal (2016). Henry (1997) of CRREL, Hanover, New Hampshire, studied the problem of electrical grounding in cold regions. The electrical resistivity of frozen soil can be several orders of magnitude higher than that of unfrozen soil. The contact resistance between the grounding electrodes and the soil becomes significantly large if a layer of ice forms on the electrode. Low-frequency and DC current may flow through earth materials by the movement of ions in the water present in the pore spaces between particles or attached to particle surfaces. The conductivity of most earth materials is a function of the concentration and mobility of ions, and hence, the amount of water in a soil strongly influences conductivity. Electrical conductivity generally increases with decreasing grain size because finer-grained soil has more surface area per unit volume and therefore holds more-adsorbed water than coarse-grained soil. Very fine soils may also contain clay minerals holding diffuse layers of ions that are free to migrate under the influence of an electric field, providing an additional electrical path. The resistivity of frozen soil depends on temperature, ice volume, and soil type (grain size effects). Small, portable units are commercially available to measure near-surface electrical resistivity of soils, and these have been used for mapping the distribution of shallow permafrost (Hoekstra et al. 1975, Arcone et al. 1979). These may be difficult to use in the winter because of high contact resistance at the electrodes. More research is required to determine the actual effects of unfrozen water content and temperatures on resistance-to-ground values and recommended grounding procedures in areas of seasonally frozen ground and permafrost. The gradual thawing of permafrost regions owing to global warming can lead to natural hazards, such as rock slope failure, and a rapid increase in greenhouse gas emissions. The thermo-hydro-mechanical (THM) processes occurring in permafrost areas have been studied by the ERT method in subarctic and highmountain permafrost areas. This relies on calibrated resistivity–temperature

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relationships. Also, resistivity is not directly sensitive to water flow occurring in thawing permafrost systems. Because of these limitations, data from different geophysical methods, such as resistivity and seismic data, are combined to improve the resolution and to explore the potential of complementary geoelectrical methods for permafrost characterization and monitoring. Induced polarization (IP) and the self-potential (SP) methods hold promise. The SIP response of frozen soils and rocks is strongly affected by the characteristic electrical polarization response of ice and could help in improved imaging and quantification of ice content in permafrost regions. The SP method offers direct sensitivity to meltwater flow in thawing permafrost systems. These geoelectrical methods have been successfully used for characterizing and monitoring permafrost systems in a noninvasive manner, with a relatively high spatial and temporal resolution. The information so obtained has helped in understanding the processes in cryospheric environments under the impact of global warming. Kenna (2019) of the University of Bonn, Institute of Geosciences and Meteorology, Geophysics Section, Germany, discusses the imaging of the frozen subsurface from geoelectrical signatures of thawing permafrost systems. In a study of electrical resistivity tomography in Qinhai-Tibet Plateau in southwest China, Gao et al. (2019) found that the method was useful for delineating permafrost hydrogeology in the headwater area of Yellow River on Qinghai-Tibet Plateau, SW China, March 2019. They quoted 52 references in their article (Gao et al. 2019). An ERT study can help delineate the frozen and thawed zones and can be applied in permafrost hydrogeology by measuring the differences in the subsurface electrical potential. A combined approach of ERT and borehole measurements was implemented to map the flow paths of the supra-permafrost and subpermafrost waters. The results showed the presence of permafrost at depths up to 15 m, in which electrical resistivity is >250 Ω m. Below the permafrost (at a depth of 15 to 80 m), electrical resistivity is generally