Physiography and Soils of the Llanos Orientäles, Colombia

PHYSIOGRAPHY AND SOILS OF THE LLANOS ORIENTÄLES, COLOMBIA Ir. D. Goosen SOL OFFSETDRUK, AMSTERDAM Promotor: PROF. Dr. P. D. JUNGERIUS Co-promotor: PROF. Dr. Ir. A. P. A. VINK Dit proefschrift verschijnt tevens als: Publicaties van het Fysisch-Geografisch en Bodemkundig Laboratorium van de Universiteit van Amsterdam, nr. 20 (1971) en Publications of the International Institute for Aerial Survey and Earth Sciences (ITC) - Enschede - The Netherlands, Series B, number 64,1971 PHYSIOGRAPHY AND SOILS OF THE LLANOS ORIENTALES, COLOMBIA ACADEMISCH PROEFSCHRIFT TER VERKRIJGING VAN DE GRAAD VAN DOCTOR IN DE WISKUNDE EN NATUURWETENSCHAPPEN AAN DE UNIVERSITEIT VAN AMSTERDAM OP GEZAG VAN DE RECTOR MAGNIFICUS IN HET OPENBAAR TE VERDEDIGEN IN DE AULA DER UNIVERSITEIT (TIJ DELIJK IN DE LUTHERSE KERK, INGANG SINGEL 411, HOEK SPUI) OP WOENSDAG 1 DECEMBER 1971 DES NAMIDDAGS TE 15.00 UUR PRECIES. door DOEKO GOOSEN geboren te Wildervank 1971 Scanned from original by ISRIC - World Soil Information, as ICSU World Data Centre for Soils. The purpose is to make a safe depository for endangered documents and to make the accrued information available for consultation, following Fair Use Guidelines. Every effort is taken to respect Copyright of the materials within the archives where the identification of the Copyright holder is clear and, where feasible, to contact the originators. For questions please contact [email protected] indicating the item reference number concerned. £B}o CONTENTS Acknowledge jments 7 Summary 9 Resumen 12 Samenvatting 16 Chapter 1 INTRODUCTION 19 Chapter 2 DESCRIPTION OF THE AREA 22 2.1 General 22 2.2 Climate 24 2.3 Geology 27 2. 3.1 Geology of the Eastern Andes Cordillera 27 2. 3. 2 Geology of the Llanos Orientales 30 2.4 Hydrology 33 2.5 Vegetation and land use 34 2. 5.1 Vegetation 34 2. 5.2 Land use 37 Chapter 3 PHYSIOGRAPHY 39 3.1 Introduction 39 3.2 Description of the physiographic units 43 3. 2.1 Piedmont (M, P) 43 3.2.2 Terraces (T) 46 3.2.3 Alluvial Overflow Plain (D) 48 3.2.4 Aeolian Plain (E) 53 3.2.5 Alluvium (V) 57 3.2.6 High Plains (A) 58 Chapter 4 SOILS 64 4.1 Introduction 64 4.2 Soils of the Alluvial Overflow Plain 70 4. 2.1 Soil Associations 70 4. 2. 2 Aspects of Soil Formation and Classification 71 4.2.3 Soil Profile Data 72 4.3 Soils of the Aeolian Plain 74 4. 3.1 Soil Associations 74 4. 3.2 Aspects of Soil Formation and Classification 79 4.4 Soils of the High Plains 83 4.4.1 Soil Associations 83 4.4.2 Aspects of Soil Formation and Classification 89 4.4. 3 Chemical, Physical and Mineralogical Considerations 93 Chapter 5 RELATIONSHIPS BETWEEN SOIL PROPERTIES, 112 EROSION AND MASS MOVEMENT Introduction 112 Processes of landscape development 112 5.2.1 Landforms resulting from Degradation 113 and Sedimentation 5.2.2 Soil Properties influencing 114 Degradation 5.3 Sheet erosion 122 5. 3.1 General 122 5. 3.2 Sheet Erosion in the Llanos 123 5. 3. 3 Soil Properties related to Sheet 126 Erosion 5.4 Gully Erosion 129 5.4.1 General 129 5.4.2 Reticular Gully Erosion in the Llanos 130 5.4.3 Soil Properties related to Reticular 132 Gully Erosion 5.4.4 Comparison of Reticular Gully Erosion 135 with Similar Phenomena 5.5 Solifluction 139 5. 5.1 General 139 5.5.2 'Escarceos' in the Llanos 142 5. 5. 3 Factors inducive to the Formation 148 óf the Escarceos 5. 5.4 Formation of the Esteros by Solifluction 152 5. 5. 5 Comparison of Escarceos with Similar 154 Phenomena 5.6 Interaction of sheet erosion, reticular gully 159 erosion, and solifluction Chapter 6 AGRICULTURAL EVALUATION 161 6.1 General 161 6.2 Soil management in the Alluvial Overflow 161 Plain 6. 3 Soil management in the level, well drained 163 High Plains 6.4 Soil management in the level, poorly drained 164 areas of the Aeolian Plain and of the High Plains 6.5 Final remarks 166 Appendix I METHODS 167 1.1 Soil survey methods 1.2 Laboratory methods 167 Appendix n 170 SOIL PROFILE DESCRIPTIONS 171 References 186 ACKNOWLEDGEMENTS Many of the conclusions incorporated in this study were arrived at in discussions during the period 1960-1964 when the soil survey of the Llanos Orientales was executed. Grateful acknowledgement is made here of the contribution in constructive ideas of the project manager, Dr. Armand van Wambeke, who also provided the organizational stimulus together with the co-directors Mr. Alfonso Garcia and Mr. Miguel Varona. Mr. Richard S. Merritt, assisted by Mr. Jaime Villegas and Mr. Humberto Toquica, laid the foundation for the soil classification; Mr. Ricardo Bernal, Mr. Marco F. Cano and Mr. Elvers Marfn contributed to the soil mapping. Aspects of vegetation were discussed with Dr. John Blydenstein and his team of vegetation experts, Mr. German Clavijo and Mr. Jaime Rivera. The chemical investigations were carried out under the guidance of Mr. Francisco Silva by Dr. Carlos Luna, Mr. Leónidas Mejia, Mr. Josué Quintero and Mr. Eduardo Palacio. Several drawings were devised by Mr. Hernando Daza. The Government of Colombia through the Departamento Adminis trative de Planeación Nacional and the Instituto Geografico 'Agustfn Codazzi', and the Food and Agriculture Organization of the United Nations kindly permitted the use of personnel, time and material indispensable for gathering the data for this study. Similar support has been provided by the International Institute for Aerial Survey and Earth Sciences (ITC), Enschede. The author is indebted to Prof. Dr. Ir. J. Bennema and to Dr. Ir. J. van Schuylenborgh for several valuable discussions concerning the soil classification. Dr. van Schuylenborgh also provided additional laboratory analyses of many soil samples, and has been very helpful with the inter pretation of the results. Some aspects of soil mechanics were discussed with Prof. Dr. C. Voute and with Dr. A. Langejan, and on the topic of erosion and mass movement valuable suggestions were received from Drs. F. J. P.M. Kwaad. Thanks are due to Mr. Maurice Eggeling for improving the grammar and to Mr. C.J. Snabilié for assistance in printing. The completion of this study was made possible through the active cooperation of Prof. Dr. P. D. Jungerius and Prof. Dr. Ir. A. P. A. Vink, of the Laboratory for Physical Geography and Soil Science, University of Amsterdam. The author is greatly indebted to them for the interest they have shown in the subject, and for their stimulating advice on the content and presentation of this study. 7 SUMMARY This study deals with the relationships between physiography and soils in the Llanos Orientales, the eastern tropical savanna plains of Colombia. Extensive use has been made of the results of the soil sur vey, carried out in 1960-1964 (FAO report, 1965). Chapter 1 describes the background of this study, and its relations to the soil survey. Chapter 2 describes the general features of the area, including the geology of the Eastern Andes Mountains. The physiography of the Llanos is discussed in chapter 3. Chapter 4 deals with the prin cipal soil associations and soil series of three landscapes: the Alluvial Overflow Plain, the Aeolian Plain and the High Plains. Chapter 5 treats degradational processes occurring in these three landscapes, and cer tain Correlations between soil properties and degradational processes. Chapter 6 describes the significance of the results discussed in chapters 4 and 5, for the physical soil management in future agricultural devel opment schemes. The most important conclusions can be summarized as follows. The majority of the surface sediments in the Llanos date from Late Pleistocene to Early Holocene. The alluvial sediments extend from the Eastern Andes Mountains far to the East. Near the mountains large Alluvial Fans were built up, which at about 50 km East of the moun tains gradually change into a vast Alluvial Overflow Plain, character ized by numerous natural levees, with many splays branching out from the levees. The intermediate areas in the Alluvial Overflow Plain are slackwater areas, at present heavily inundated by rain water during the wet season. Towards the East this Alluvial Overflow Plain is covered by an aeolian sediment, called Llanos loess. This area has been called Aeolian Plain. Apart from the level, poorly drained Llanos loess several strips of longitudinal rivers dunes are found within the Aeolian Plain. Farther East, starting at the right-hand bank of the river Meta, the so-called High Plains occur. The geogenesis of the High Plains is similar to that of the Aeolian Plain, viz. the substratum consists of Pleistocene alluvial sediments, which has been covered by the deposit of Llanos loess to a depth of several meters. The reason to separate the High Plains from the Aeolian Plain lies in the fact that the bound- 9 ary between them is a fault line, along which the river Meta runs. The High Plains are now situated several tens of meters higher than the Aeolian Plain and are therefore much better drained, except for the most level parts which occur principally in the northeastern part of the High Plains. It is possible that the alluvial substratum and the aeolian cover of the High Plains are somewhat older than the surface sediments of resp. the Alluvial Overflow Plain and of the Aeolian Plain. The relative position of the described landscapes is sketched in fig. 5. From it can be seen, that the zone between the Andes and the river Meta is a zone of tectonic subsidence. This subsidence is still going on, as evidenced by the occurrence of faults across recent al luvial sediments near the mountains.

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