Rocks and Landforms

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TITLES OF RELATED INTEREST

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in engineering rock mechanics E.T. Brown (ed.) Applied geomorphology R.G. Craig & J.L. Craft (eds) Catastrophic flooding L. Mayer & D. Nash (eds) Environmental change and tropical

geomorphology I. Douglas & T. Spencer (eds) Experiments in physical sedimentology J.R.L. Allen The face of the Earth G.H.Dury Geology for civil engineers A.C. McLean & C.D. Gribble Geomorphological field manual V. Gardiner & R. Dackombe Geomorphological hazards in Los

Angeles R.U. Cooke Geomorphological techniques A.S. Goudie (ed.) Geomorphology: pure and applied M.G. Hart Geomorphology and engineering D.R. Coates (ed.) Geomorphology and soils K.S. Richards et al. (eds) Geomorphology in arid regions D.O. Doehring (ed.) Glacial geomorphology D.R. Coates (ed.)

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rock mechanics S.D. Priest Hillslope processes A.D. Abrahams (ed.) Image interpretation in geology S. Drury Introducing groundwater M. Price Models in geomorphology M. Woldenberg (ed.) The outcrop quiz J.B. Wright A practical approach to sedimentology R. Lindholm Principles of physical sedimentology J.R.L. Allen Rock glaciers J.R. Giardino et al. (eds) Rock mechanics B.H.G. Brady & E.T. Brown Sedimentology : process and product M.R. Leeder Soils and landforms J. Gerrard Space and time in geomorphology C.E. Thorn (ed.) Tectonic geomorphology J.T. Hack & M. Morisawa (eds) Theoretical geomorphology C.E. Thorn Theories of landform development W.N. Melhorn & R.C. Flemal (eds)

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Rocks and Landfurms

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AJ.GERRARD Department of Geography, University of Birmingham

London UNWIN HYMAN

-Boston Sydney Wellington

© J. Gerrard, 1988

This book is copyright under the Berne Convention. No reproduction without permission. All rights reserved.

Published by the Academic Division of Unwin Hyman Ltd

15/17 Broadwick Street, London WI V IFP

Allen & Unwin Inc., 8 Winchester Place, Winchester, Mass. 01890, USA

Allen & Unwin (Australia) Ltd, 8 Napier Street, North Sydney, NSW 2060, Australia

Allen & Unwin (New Zealand) Ltd in association with the Port Nicholson Press Ltd,

60 Cambridge Terrace, Wellington, New Zealand

First published in 1988

British Library Cataloguing in PubHcation Data

Gerrard, John Rocks and landforms.

1. Geomorphology I. Title 551.4 GB401.5

Library of Congress Cataloging-in-Publication Data

Gerrard, John, 1944-Rocks and landforms/John Gerrard.

p.cm. Bibliography: p. Includes index. ISBN-13: 978-94-011-5985-2 e-ISBN-13: 978-94-011-5983-8 DOl: 1 0.1 007/978-94-0 11-5983-8

1. Geomorphology. I. Title. GB401.5.G48 1987 551.4-dcI9

Typeset in 10 on 12 point Times by Columns Ltd., Reading, Berks.

Preface

Geomorphology can be defined simply as the study of landforms. Landforms are the result of the interaction between what Ritter (1978) has called the driving and resisting forces. The driving forces or processes are the methods by which energy is exerted on earth materials and include both surface, geomorphological or exogenous processes and subsurface, geological or endogenous processes. The resisting forces are the surface materials with their inherent resistances determined by a complex combination of rock properties. Stated in these simple terms it would be expected that both sides of the equation be given equal weight in syntheses of landform evolution. However, this has not been the case. Until about the 1950s, geomorphology was mainly descriptive and concerned with producing time-dependent models of landscape evolution. Although the form of the land was the main focus, there was little detailed mention of process and scant attention to the properties of surface materials.

There were, of course, exceptions. In the late 19th century G.K. Gilbert was stressing the equilibrium between landforms and processes. Many hydrologists were examining the detailed workings of river 'systems and drainage basins, culminating in the classic paper of Horton (1945). These developments were the precursors of great changes that took place in the Earth sciences in the 1960s and 1970s. There were several reasons for these changes. There ·was a general dissatisfaction with the 'traditional' time-dependent approach to landform evolution and a concern to elevate knowledge of processes above the purely descriptive plane. The traditional time-dependent approach was challenged by alternative time-independent paradigms and the development of systems analysis. The quantitative revolution of the 1960s, with the availability of increasingly sophisticated statistical and computing techniques, enabled vast quantities of field data to be analysed. Much of this stimulus was provided by Strahler (1952) in an extremely important paper which is widely regarded as the manifesto of dynamic geomorphology. Strahler envisaged a system of geomorphology grounded in basic principles of mechanics and fluid dynamics that enables geomorphic processes to be treated as manifestations of various types of shear stresses (1952, p. 923). Strahler (1950, 1958) also emphasized the need for more quantitative descriptions of landforms.

In the 30 or so years since Strahler made this plea there have been great advances in our understanding of the operation of geomorpho-

vi PREFACE

logical processes. Unfortunately, in order to investigate the operation of such processes attention has been focused on smaller and smaller parts of the landscape and the wider perspective has been lost. Also, detailed description of landforms has not always been as easy and fruitful as expected. At the same time there has been a comparative neglect of the 'geological' or surface materials part of geomorphology. A number of syntheses have been produced by, for example, Sparks (1971), Tricart (1974), Twidale (1971) and Yatsu (1966), but compared with other aspects of geomorphology, there has been a relative neglect.

The latest phase in the development of geomorphology has been the need to assess the significance of the results obtained in the last 30 years or so. Enough may have been learned about the operation of processes to make possible a synthesis more firmly based on a sound appreciation of these processes (Higgins 1980). Higgins argues that the urge to make broad generalizations, after several decades of detailed statistical analyses, may have become irresistible. However, realistic generalizations are only possible if the advances in the understanding of geomorphic processes, the driving forces, are matched by advances in knowledge of rock properties and behaviour, the resisting forces. Fortunately, as King (1976) has remarked, the science of geomorphology has developed alongside geology and other Earth sciences and has grown in ever­widening circles, resulting in expanding contacts with other disciplines. One of these cognate disciplines is engineering geology, which has expanded considerably in the last decade or so, and it is this field that has provided a great deal of information of use to geomorphologists.

Journals such as Engineering Geology and Quarterly Journal of Engineering Geology have fostered this interaction between geologists, geomorphologists, engineers and other Earth scientists. The trade in information has not been one-sided. Although geomorphology has gained considerably from this interaction, it has also been able to contribute something special itself and there appears to be a distinct subdiscipline, engineering geomorphology, developing. Coates (1976) was one of the first to link geomorphology and engineering and a conference on the theme of the engineering implications of Earth surface processes was held in England at Birmingham in 1982. Some of the papers presented at this conference have been published in the Quarterly Journal of Engineering Geology 16 (4), 1983 and reviewed by Derbyshire (1983). The trend has been continued in Engineering geomorphology by Fookes and Vaughan (1986). Developments such as these are important if the increasing number of applied environmental problems are to be tackled efficiently.

It is the aim of this book to examine recent developments on the theme of rock control and to try to balance the rock material-geomorphic process equation. It has not been the intention of the book to cover every geomorphological situation but it is hoped that the important topics have

PREFACE vii

been covered. It is further hoped that it will provide a stimulus for continued interaction between the various subdisciplines of the Earth sciences.

John Gerrard

Acknowledgements

We are grateful to the following individuals and organizations who have given permission for the reproduction of copyright material (figure numbers in parentheses): Figure 1.1 reproduced from Structural geomorphology by J. Tricart by permission of Longman; Geobooks (1.2, 6.10, 7.3, 7.10); Ginn (1.3); Tuebner (1.4); Australian University Press (2.2, 2.3); Dowden Hutchinson & Ross (2.4, 2.5, 2.6); Gebruder Borntraeger (3.1, 3.2, 3.4, 3.5, 3.6, 3.8, 8.1, 8.2); Figure 3.3 reproduced from G. Aronsson, Earth Surface Processes and Landforms 7, by permission of J. Wiley; Institute of British Geographers (3.9, 8.6); McGraw-Hill (3.10); Figure 3.11 reproduced from G. H. Ashley in Geological Society of America Bulletin 46, pp. 1395-436 by permission of the Geological Society of America; Figure 3.12 reproduced by permission from the American Journal of Science 32; Figure 3.13 reproduced from H. D. Thompson in Geological Society of America Bulletin 50, pp. 1323-55 by permission of the Geological Society of America; Unwin Hyman (4.1, 5.1, 7.6, 9.6); Figure 4.4 reproduced by permission from W. R. Wawersik & C. Fairhurst in International Journal of Rock Mechanics and Mining Science 7, Copyright 1970, Pergamon Journals Ltd.; Figure 4.5 reproduced from P. G. Fookes & A. B. Poole in Quarterly Journal of Engineering Geology 14, 1986, by permission of the Geological Society; Figure 5.3 reproduced from H. F. Shaw, Quarterly Journal of Engineering Geology 14, 1986, by permission of the Geological Society; Elsevier (5.4); Figures 6.1,6.7 reproduced from B. P. Ruxton & L. Berry in Geological Society of America Bulletin 68, pp. 1263-92, by permission of the Geological Society of America; American Society of Civil Engineers (6.1, 6.2, 6.3, 6.9); Figure 6.4 reproduced from Tropical geomorphology by M. F. Thomas by permission of Macmillan; Figure 6.5 reproduced from Geology of clays by G. Millot by permission of Springer-Verlag; Figure 6.6 reproduced from R. P. Moss in Journal of Soil Science 16, by permission of Blackwell Scientific Publications; Figure 6.8 reproduced from P. G. Fookes et al. in Quarterly Journal of Engineering Geology 4, 1971, by permission of the Geological Society; Figure 7.1 reproduced from D. M. Ross-Brown in Quarterly Journal of Engineering Geology 6, 1980, by permission of the Geological Society; Figure 7.2 reproduced from Slopes by A. Young by permission of Oliver & Boyd; Thomas Telford (7.3, 9.2, 9.4, 9.7, 9.8); Figure 7.4 reproduced from Engineering Geology by permission of Blackwell Scientific Publica­tions; The Almqvist and Periodical Company (7.8, 10.1, 10.2); South

x ACKNOWLEDGEMENTS

African Geographical Journal (7.9, 7.10, 7.11, 8.2); Figure 8.3 reproduced from M. J. Selby, Earth Surface Processes and Landforms 7, Copyright 1982, by permission of J. Wiley and Sons; Figure 8.4 reproduced from D. L. Linton, in Geographical Journal 121, by permission of the Royal Geographical Society; Yorkshire Geological Society (8.5); US Army Engineers Nuclear Cratering Group (9.1); Figure 9.3 rep:-oduced from J. C. Cripps & R. K. Taylor in Quarterly Journal of Engineering Geology 14, 1981, by permission of the Geological Society; Figure 9.9 reproduced from E. N. Bromhead in Quarterly Journal of Engineering Geology 12, 1979, by permission of the Geological Society; Figure 9.10 reproduced from J. N. Hutchinson in Earth Surface Processes and Landforms 8, Copyright 1983, by permission of J. Wiley and Sons; Figures 10.3, 10.4, 10.5 reproduced from Hills/ope form and process by M. A. Carson & M. J. Kirkby by permission of Cambridge University Press.

Contents

Preface page v

Acknowledgements ix

List of tables xv

1 General background 1

Introduction 1 Spatial scale 8 Rock resistance 10 Mechanisms of rock control 12 Conclusions 13

2 Rock type and landform assemblages 15 Igneous rocks 15 Metamorphic rocks 24 Sedimentary rocks 26 Assessment of landform assemblages 33 Spatial distribution of rock types 42 Other rock classifications 49 Conclusions 54

3 Landscape evolution and rock properties 55 Slope angle, form and processes 55 Denudation rates 60 Slope development on horizontally bedded rocks 65 Drainage basin properties 70 Bedrock meanders 72 Drainage patterns 74 Conclusions 84

4 Rock strength and resistance 85

Hardness and toughness 85 Porosity, permeability and water absorption 88 Strength and rock deformation 91 Appraisal 100

xii CONTENTS

5 Resistance to weathering 107

Chemical weathering 113 Chemical weathering of minerals 114 Chemical weathering of rocks 120 Physical weathering 122 Conclusions 136

6 Weathering profiles and landform development 138

Weathering front 138 Weathering profile differentiation 139 Weathering grades 148 Weathering depths 151 Weathering and the water table 154 Spatial patterns of weathering profiles 154 Duricrusts 156 Weathering profiles and slope form 159 Weathering and rock strength 161 Weathering and slope instability 163 Threshold slopes 167

7 Instability in jointed and fissured rock 170

Characteristics of jointed rock 171 Unloading joints and rebound phenomena 182 Models of jointed rock behaviour 184 Rock mass strength classifications 190 Strength equilibrium slopes 192 Modes of rock failure 200

8 Landforms on granitic rocks 208

Inselbergs 209 Domed inselbergs (bornhardts) 212 Tors (boulder inselbergs) 221 Landscape types 227 Conclusions 230

9 Properties and landforms of mudrocks 231

Terminology of mudrocks 231 Composition of mudrocks 231 Consolidation and unloading of mudrocks 233

Consistency limits Microstructure Macrostructure Shear strength Weathering effects Swelling and shrinkage

CONTENTS

Landslides and slope development Mudslides Sensitive clays Conclusions

10 A rock-landform synthesis

Landforms of glacial erosion Marine cliffs and shore platforms Rocks, landforms and climate Conclusions

Bibliography

Index

xiii

234 237 239 239 243 244 244 249 255 258

259

261 267 269 274

275

313

List of tables

1.1 Morphogenetic systems and landscape characteristics 1.2 Suggested scheme for the investigation of rock-landform

relationships 1.3 Altitudes of rock types around the Phoenic Dome, near

Baltimore, Maryland (percentage of area underlain by rock type within specific elevation ranges)

. 2.1 Rock type identification criteria on aerial photography for arid regions

2.2 Predicted versus actual rock type 2.3 Predicted metamorphic rocks in New York State and

Vermont 2.4 Evaluation of published criteria for identifying metamor-

phic rocks 2.5 Revised criteria for identifying metamorphic rocks 2.6 Rock classification based on texture 2.7 Classification of rock materials by Duncan 2.8 Rock type classification by the Geological Society

Engineering Group working party 3.1 Rates of solution 3.2 Ground lowering by solution alone 3.3 Rates of slope retreat 3.4 Rates of retreat of cliffs (free faces) 3.5 Rates of marine cliff retreat 3.6 Rates of denudation 3.7 Drainage densities of the Dartmoor area 3.8 Rock type and characteristics, Kumaun, Himalaya, India 4.1 Primary and secondary rock permeabilities 4.2 A summary of experimental results of water absorption 4.3 Some typical rock strengths 4.4 Some physical properties of igneous and metamorphic

rocks 4.5 Some physical properties of sandstones 4.6 Some physical properties of carbonate rocks 4.7 Some physical properties of argillaceous rocks 4.8 Tests for assessing rock durability characteristics in a

marine environment 5.1 A classification of weathering relationships 5.2 Weathering sequence for common rock-forming minerals

LIST OF TABLES

5.3 Relative resistance of rocks to frost action 5.4 Properties of rock used in freeze-thaw experiments 5.5 Properties of 10 Hellenic marbles 5.6 Integrated behaviour of Hellenic marbles 5.7 Rock resistance to weathering 6.1 Comparisons of classifications of weathering profiles 6.2 Weathering scheme for Keuper Marl 6.3 Classification of weathered mudrocks 6.4 Weathering grade of Hingston Down Granite, Cornwall,

based on micropetrographic indices 6.5 Stages of weathering of granite in terms of microscopical

properties 6.6 Geomorphological effects of duricrusts 7.1 Critical angles for jointed and bedded rocks 7.2 Strength classification for joint orientations 7.3 Suggested classification for joint spacing 7.4 Mechanical classification of discontinuities 7.5 Description of joints on a horizontal granite surface in

Brittany 7.6 Friction angle data for joints in weathered granite 7.7 Rock quality designation values 7.8 Geomorphic rock mass strength classification and ratings 7.9 Characteristics of major rockslides in the Rocky

Mountains of Canada 8.1 Numerical indices for domed inselbergs 8.2 Relationship between jointing, tor type, tor height and

topography 9.1 Consistency limits of some British clays 9.2 Activity values of various types of clays 9.3 Slope history and residual factors for a variety of clays 9.4 Stability analyses on the Jurassic escarpment near

Rockingham, Northamptonshire 9.5 Examples of mudslides and the materials involved in the

movement