ese * I t-h eaggy Gem-r g g, CII.Cr~rd'Sc .htz Lesotho T,,/ Geology, Geomorphology, Soils G. Schmitz F. Rooyani National University of Lesotho 1987 The Authors: Gerard Schmitz, Ph.D. Professor of Geography. Applied Environmental Sciences Programme Department of Geography. National University of Lesotho Firouz Rooyani. Ph.D. Team Leader, Education Component of Lesotho Agricultural Production and Institutional Support Project Adjunct Assistant Professor, Department of Soil and Water Science, University of Arizona Honorary Lecturer. National University of Lesotho © 1987 G. Schmitz Funded by: The Netherlands University Foundation for International Cooperation The United States Agency for International Development The National University of Lesotho Distributed by: The National University of Lesotho Printed by Morija Printing Works - Lesotho Cover picture by Dirk Schwager Acknowledgements We wish to thank all those who gave permission for us to reproduce copyright material in this book. Information regarding sources is given in the captions. We greatly appreciate the assistance given to us in the preparation of this book by the fol­ lowing persons: Martinus Vranken, Utrecht University, for making the drawings for Sections One, Two and Three. Tom Lynn, National University of Lesotho, for editing the text. Mrs. C. Russell, USAID Mission in Lesotho, for typing the manuscript, Dr. C. Mabbs - Zeno, for taking and developing photographs of rock samples, Dr. B. Badamchian, Ministry of Agriculture and Marketing, for her comments on Section Four of this text. Preface This publication has been written for all those interested in the characteristics and dynamics of Lesotho's natural environment, especially for teachers, fieldworkers, and for students at the National University of Lesotho and at the Lesotho Agricultural College. A glossary has been added to facilitate the reading of the text, as well as a summary of the U.S. soil classification system, as the Lesotho Government has adopted it for the classification of its soils. The reader will discover that relatively little is known about the geomorphology of Lesotho, as not much research into this topic has so far been undertaken in the country. More is known about the geology of Lesotho. In 1947, G.M. Stockley published the first comprehensive study on "the geology of Basutoland". Since then, the Government's Department of Mines and Geology has undertaken to map the country and has published a good number of geological reports and maps of different scales. Much information has been obtained from studies of areas with a similar geology in the immediate surroundings of Lesotho. Soil analysis, soil mapping and soil classification have been undertaken quite exten­ sively in Lesotho, and a comprehensive general picture of the soils of Lesotho isarising. As agriculture is amajor economic activity in Lesotho, and as soils are being eroded in a drastic way, a chapter on recent processes and forms of accelerated erosion and de­ position has been included. The authors have undertaken an extensive literature survey, and to a large extent this publication is based on studies undertaken by other researchers. We hope to have given due acknowledgement to the many authors quoted, and apologise if some references have been erroneously omitted. We invite comments and criticisms of this publication, so that we may improve on our understanding of the natural environment of Lesotho. G. Schmitz Roma F. Rooyani Maseru 1987 Contents SECTION ONE: GEOLOGICAL EVOLUTION Chapter One The GeneralFramework ........................................... 3 1.1 Cratonisation .................................... 3 1.2 Gondwanaland.................................. 4 1.3 The Karoo Basin and Basin Floor Characteristics .......... 6 1.4 I..ieBoundary between the Kaapvaal Craton and the Namaqualand-Natal Circum-Cratonic Belt ................... 10 ChapterTwo Basin Sedimentation ............................... 12 2.1 Karoo Sedimentary History and Basin Floor Characteristics 12 2.2 D wyka Form ation ................................................... 12 2.3 Ecca Group .......................................................... 14 2.4 Beaufort G roup .......,W ........................................... 16 2.5 Storm berg G roup ................................................... 20 ChapterThree Magmaticand Tectonic Episodes ................................ 35 3.1 The Karoo Volcanic Episode .................................... 35 3.2 Intrusions aiid Structural Deformations ....................... 42 3.3 Kimberlite :Emplacements ........................................ 45 3.4 Seismicity ............................................................. 48 SECTION TWO: GEOLOGICAL RESOURCES ChapterFour GroundwaterResources ............................................ 59 4.1 Groundwater Occurrences ........................................ 59 4.2 Springs ................................................................. 61 4.3 Groundwater Estimates .......................................... 63 ChapterFive Mineral Resources .................................................. 64 5.1 Diamonds ............................................................. 64 5.2 Uranium ............................................................... 64 5.3 Mercury ............................................................... 66 5.4 Building Stones ...................................................... 66 5.5 Clay Deposits ....................................................... 66 SECTION THREE: GEOMORPHOLOGY Chapter Six Geomorphological Units ........................................... 69 6.1 Definition and Description ..................................... 69 6.2 Geomorphological Units and Associated Soils .............. 76 6.3 Geomorphology and Land Suitability Classification .......78 Chapter Seven Geomorphological Evolution ..................................... 85 7.1 The Formation of Planation Surfaces ......................... 85 7.2 Reorientation from Interior to Coastal Drainage ........... 91 7.3 Nivation/Glaciation Hollows ..................................... 95 Chapter Eight Accelerated Erosion and Sedimentation ........................ 98 8.1 Introduction ......................................................... 98 8.2 Erosion Processes and Forms .................................... 98 S.3 Sediment Transport and Deposition ........................... 103 8.4 Climatic Factors ..................................................... 104 8.5 Soil Factors ........................................................... 106 8.6 Terrain Factors ...................................................... 108 8.7 Human Factors ...................................................... 108 8.8 Estimation of Soil Loss and the Universal Soil Loss Equation .................................................. 111 SECTION FOUR: SOILS Chapter Nine Soil Materials ......................................................... 123 9.1 Organic Component ................................................ 123 9.2 Mineral Component ................................................ 126 Chapter Ten Soil Formation ....................................................... 130 10.1 Weathering and Formation of New Material ................. 130 10.2 Erosion and Deposition Processes .............................. 132 10.3 Eluviation and Illuviation ......................................... 134 Chapter Eleven Soil Forming Factors ............................................... 138 11.1 Climate ..... ................ ..................... 138 11.2 Vegetation ............................................................ 140 11.3 Parent Material ...................................................... 141 11.4 Topography ........................................................... 142 11.5 Genesis and Classification ......................................... 144 -A, t ChapterTwelve ImportantSoil Groupsof Lesotho: I. Mollisols ............. 147 12.1 Mollisols with an Aquic Moisture Regime .................... 148 12.2 Mollisols with a Cryic Temperature Regime ................. 150 12.3 Mollisols with a Ustic Moisture Regime ....................... 150 12.4 Mollisols with a Udic Moisture Regime ....................... 153 ChapterThirteen ImportantSoil Groups of Lesotho: I1. Alfisols .............. 157 13.1 Alfisols with an Aquic Moisture Regime ...................... 159 13.2 Alfisols with a Udic Moisture Regime Bordering on Aquic 160 13.3 Alfisols with a Udic Moisture Regime ............................ 162 13.4 Alfisols with a Ustic Moisture Regime ......................... 163 ChapterFourteen ImportantSoil GroupsofLesotho: III. Entisols, Inceptisols, Vertisols ................................................ 166 14.1 Entisols ................................................................ 166 14.2 Inceptisols ............................................................. 169 14.3 Vertisols ............................................................... 172 APPENDIX ............................................................................. 175 GLOSSARY ............................................................................. 183 REFERENCES ............................................................................. 192 IN D EX ............................................................................. 202 Section One Geological Evolution Lesotho: Geology, Geomorphology, Soils 3 Chapter One The General Framework 1.1 Cratonisation The structural development of the African continent has been marked by several