Glacial Environments
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GLACIAL ENVIRONMENTS Michael Hambrey Summary of the geological time scale, based on International Union of Geological Sceinces Global Stratigraphic Chart (IUGS 1989), together with the main phases of glaciation in Earth’s history. Names in italics are based on those regions where the evidence is best displayed. Frontispiece: vertical air photograph of glaciers at the head of Engelskbukta (“English Bay”) in nw Spitsbergen. This demonstrates the complexities of the glacial environment. Small cirque glaciers with aretes between, and moraines near their snouts occur at the .top of the picture. Two large valley glaciers (Uversbreen; mid-right, and Comfortlessbreen, lower right) approach the bay from the right, both having contorted medial moraines and complexes of push moraines close to, and beyond, the ice limits. Large areas of braided outwash, both active and abandoned, are evident in the middle of the picture, the main channel complex producing a prominent sediment plume as the glacial meltwaters enter the sea. Comfortlessbreen ends partially in tidewater as a prominent calving ice cliff and, in front of it, beach ridges or spits of sand and gravel enclose muddy lagoonal areas. The field of view is approximately 8km from top to bottom (photograph courtesy of Norsk Polarinstitutt, RClO, dated 7 August 1977). Glacial Environments Michael J. Hambrey . rkr'oool John Moores University A UCL © Michael Hambrey 1994 This book is copyright under the Berne Convention. No reproduction without permission. All rights reserved. First published in 1994 by UCL Press UCL Press Limited University College London Gower Street London WC1E6BT The name of University College London (UCL) is a registered trade mark used by UCL Press with the consent of the owner. British Library Cataloguing-in-Publication Data A c ip catalogue record for this book is available from the British Library. ISB N s: 1-85728-005-9 HB 1-85728-004-0 PB Typeset in Times New Roman. Printed and bound by Butler & Tanner Limited, Frame, England. Contents vii 4rt-~:v. eagements viii 1 Introduction 1 - storical background 1 '1 "-r'-'iinology and classification of glacigenic sediments 8 *3 -acies analysis of glacigenic sediments 14 - O trer methods of analysis of glacigenic sediments 19 ' 5 E. cience of glaciation in the geological record 27 1-6 E\:entof glacier ice today 31 * 7 Geological timescale 31 1 Glacier dynamics 32 1 ‘ "roduction 32 Formation and properties of glacier ice 32 1 3 Wxphology of glaciers 37 . - Сэ d and warm glaciers 42 . : С acier hydrology 43 1 : С acier fluctuations in response to climate 51 2 ~ С acier flow 54 1 : 5:'-cture of glaciers and ice sheets 61 . - С acier surges 69 1 ‘ Г Z-eoris in transport 73 3 Glacial erosional processes and landforms 81 3 ' "'oduction 81 ; 1 3-ocesses of glacial erosion 81 3 3 -a-dforms resulting from erosion by glaciers 83 - r'- a u ra l geological controls on glacial erosion 108 : Reservation potential of erosional forms 109 Environments of terrestrial glacial deposition 110 4.1 Introduction 110 - 1 ='ocesses of terrestrial glacial deposition 110 -t 3 ~r"estrial glacigenic facies and facies associations 119 - - 5~'.5ical, chemical and mineralogical characteristics 121 4_3 _.-c*orms in terrestrial glacial depositional environments 129 - : I iciotectonic landforms 147 - ~ : ---'.ation potential of terrestrial glacigenic sediments 150 v CONTENTS 5 Glaciofluvial processes and landforms 151 5.1 Introduction 151 5.2 Glaciofluvial processes 151 5.3 Glaciofluvial landforms 154 5.4 Glaciofluvial fades and fades associations "168 5.5 Preservation potential of glaciofluvial sediments 172 6 Glaciolacustrine processes and sediments 173 6.1 Introduction 173 6.2 Pleistocene-early Holocene glacial lakes 175 6.3 Physical character of glacial lakes 176 6.4 Glaciolacustrine sedimentary processes 177 6.5 Landforms resulting from glaciolacustrine deposition 178 6.6 Glaciolacustrine facies 182 6.7 Glaciolacustrine facies associations 185 7 Glaciomarine processes and sediments 188 Parti Fjords 188 7.1 Introduction to the glaciomarine environment 188 7.2 Fjord environments with active glaciers 190 7.3 Processes controlling fjord sedimentation 191 7.4 Patterns and rates of sedimentation in fjords 198 7.5 Textural characteristics of fjord sediments 200 7.6 Facies analysis of fjord sediments 201 7.7 Depositional and soft-sediment erosional features in fjords 205 7.8 Stratigraphic architecture in fjords 216 8 Glaciomarine processes and sediments 220 Part 2 Continental shelf and deep sea environments 220 8.1 Introduction 220 8.2 Transport of glacigenic sediment out of the ice-sheet-system 221 8.3 Sedimentation on glacier-influenced continental shelves 224 8.4 Physical, chemical and mineralogical characteristics 235 8.5 Erosional features on the continental shelf and slope 242 8.6 Depositional features on the continental shelf and slope 246 8.7 Sediment distribution patterns 251 8.8 Sedimentation rates 254 8.9 Sedimentary facies in glaciomarine environments 254 8.10 Stratigraphic architecture and depositional models of glacially influenced continental shelves 264 8.11 Preservation potential of glaciomarine sediments 269 Glossary 271 Bibliography 281 Index 293 VI Preface Glacial environments are scenically and scientifically among the most exciting and complex on Earth. Apart from phenomena associated directly with moving or stagnating glaciers, fluvial, aeolian, lacustrine ^r.d marine processes frequently interact with ice and its deposits. Glacial environments therefore pos- -ris a wide variety of landforms and sediment associations. Some 10% of the Earth’s land surface today is covered by ice, a figure that exceeded 30% during '.e Quaternary glaciations of the past two million years. In earlier geological history, the Earth under- ' snt glaciations of continent-wide extent on several occasions, some of them even more intense than :r. ?se of the Quaternary period. Yet these earlier glaciations have received little attention compared with :ther global climatic events. Furthermore, the study of ancient glacial sequences has, until recently, >een relatively simplistic, and frequently revealed an unawareness of the complexities of glacial proc esses. The principal aims of this book are as follows: (a) to examine the processes associated with contem- -• ran- ice masses, especially those that can be observed or monitored in the field; (b) to emphasize the 'inge and character of erosional and depositional landforms present at contemporary glacier margins, iad those left by the Pleistocene ice sheets; (c) to draw examples from both Quaternary and ancient ^.icial periods, thereby providing a link between what we see at the surface and the rock record; and J to give equal emphasis to the glaciomarine environment which has been neglected in most textbooks. The book deliberately avoids the use of most mathematical formulae since the emphasis here is on hat can be seen and interpreted on the ground, or otherwise sampled. There are other excellent works, ^';ed throughout the text, which provide rigorous mathematical treatment for those who desire it, but леге the subject matter has been chosen to be accessible to those without advanced mathematical train- r.g. It is anticipated that the book will be of value to undergraduates studying physical geography, ge- \ogy, environmental science and countryside management, as well as to secondary/high school teach ers and those who wish to understand better the processes that have shaped our lands. No previous knowl- rdge of the subject is assumed, other than an elementary knowledge of geological concepts. By historical accident, Quaternary studies and glacial processes have been largely neglected in the traditional British geology departments. Rather, they commonly have formed a core element in physi cal geography courses, but here there has been a tendency to avoid rigorous application of sedimentological principles. In contrast, in North America, there has always been a much closer affinity between ;eomorphology and geology. The strategy adopted in this book is to integrate the approaches of the two disciplines as far as possible. With the “greening” of earth sciences, and the development of employment opportunities in such areas as waste disposal, water management and the extraction of aggregates, earth scientists need to know more about the superficial glacial deposits that cover so much of the populated areas of the Northern Hemisphere. Ancient glacial deposits are also of economic importance since, in some regions, they provide petroleum plays, as in the Permo-Carboniferous and late Precambrian of the Middle East and South America. Furthermore, recent research, especially deep drilling on the continental shelves, has demonstrated the volumetric importance of glacial sediments. In a relatively small book such as this, it has not been possible to reference relevant literature thor oughly. Instead, I have cited key references together with those that provide particularly good exam- PREFACE pies of the phenomena under review. Nor has it been possible to describe all components of the glacier system as one might wish; for example, glaciofluvial and glaciolacustrine environments are treated only lightly to allow for more thorough treatment of less-readily obtainable information on the glaciomarine environment. However, if the diversity and fascination of glacial environments becomes apparent through reading this book, it will have served its purpose. M ic h a e l J. H a m b r e y Liverpool, 1994 “O ye ice and snow, bless ye the Lord, praise him and magnify him forever.” Benedicite Omnia Opera Book of Common Prayer Acknowledgements This book would not have been possible without the efforts of many colleagues throughout the world in promoting the subject. Foremost among them are W. H. Theakstone who was my mentor when 1 first began working in glacial environments; A. G. Milnes who convinced me of the strong linkage between glaciology and structural geology; and W. B. Harland who led me into investigations of ancient glacial sediments in areas where modern ones were being formed. I am indebted to leaders of various expeditions for opportunities to work in glacial environments: P.