Geomorphology of the Cape Peninsula

GEO MORPHOLOGY Of THE CAPE PENINSULA by W. 8. KING University of Cape Town Submitted to the University of Cap e Town in part fulfilment of the requirements for the degree of Master of Arts in Geography October 1983 The University of Cape Town has be n given the right to rePfoduce this thesl In whole or 1n part. Copyright I held by the author. The copyright of this thesis vests in the author. No quotation from it or information derived from it is to be published without full acknowledgement of the source. The thesis is to be used for private study or non- commercial research purposes only. Published by the University of Cape Town (UCT) in terms of the non-exclusive license granted to UCT by the author. University of Cape Town The Cape Peninsula as seen from Bokbaai on the west coast north of Cape Town. (Frontispiece) (ii) "The flight of time is measured by the weaving of composite rhythms day and night, calm and storm, summer and winter, birth and death such as these are sensed in the brief life of man. But the career of the earth recedes into a remoteness against which these lesser cycles are as unavailing for the measurement of that abyss of time as would be for human history the beating of an insect's wing." BARRELL, J. 1 1917 (iii) PREF ACE This study originated as a result of a number of Geography field courses which were conducted by the writer around the Cape Peninsula with matric students at first, and subsequently with students at Training College level. Whilst preparing for these field courses many questions arose and these, together with those posed by the students both in the classroom and in the field prompted this attempt at formu lating answers to some of them. This study makes no claims to being a definitive work. If' in the process of attempting to answer some questions new ones are raised, then some useful purpose would have been served by this attempt. It gives the writer great pleasure to make the following acknowledgements . The writer wishes to express his sincere tha~ks to Professor R. Davies for making f acilities available to him within the Geography Department. The writer is also deeply grateful to Or. L.L.H. Impey who sypervised the work, for his constructive ideas, criticism, guidance, meticulous approach to scholarship, his insistence upon finding the matte juste, and long hours spent in discussion. It is apparent that the sections of this study which entailed fiel dwork could not have been carried out unaided. for this reason the writer wishes to record his sincere thanks and appreciation to two of his ex-students, now colleagues in the teaching profession. firstly, the writer wishes to thank Mitchell Clark who literally coverod kilometres upon kilometres carrying the zero end of the steel measuring tape, together with the staff for use with the Abney Level. The writer is also greatly indebted to (iv) Sternray Lesch who accompanied him on nume rous occasions, and who was responsible for taking the photographs. The writer also wishes to express his heartfelt thanks to his long-suffering family, and in particular to his wife Lilian for her unflagging interest, constant encouragement and support • • • • • • • • This study is gratefully dedicated to the memo ry of my parents. ( v) CONTENTS Chapter Page Preface (iii) Contents (v) Figures (vii) Tables (ix) Plates (ix) INTRODUCTION 1 l GENESIS OF THE AREAL MATRIX Early beginnings 4 Late Pre-Cape Times 5 Malmesbury Period 5 Deposition of the T. M. s. 12 Table Mountain Basin reconstructed 14 Oro genesis 21 Conclusion 28 11 GLYPTOGENESIS AND THE · EMERGENT LANDSCAPE 35 The Ocean Level 38 Denudation and changes during the Cainozoic 41 Rising of the coastal zone 43 Planation surfaces 46 The Pre-Peninsular l andscape 47 Denudational levels 51 Eustasy 57 Raised Beaches 63 111 STRUCTURE ANO THE PHYSICAL LANDSCAPE Introduction 73 The Malmesbury Series 75 Granite 78 The Tabla Mountain Series HO (vi) Tho Rola of water 85 The Peninsular Co asts 88 lV CLIMATIC DEVELOP ME NT ANO CHANGES IN VEGETATION Approach to be utilised 95 Present climatic conditions 96 Present vegetation of the Cape Peninsula 102 Climate and Vegetation during Late Cretaceous and Tertiary Eras 105 Climate of the Quaternary Age 113 Vegetation during Glacial and Interglacial Periods 117 Geomorphological implications of the different climatic regimes 119 V DRAINAGE Of THE CAPE PENINSULA 135 Drainage development 136 Classification of Streams 138 Early development of the Dlsa River 145 Pattern of Drainage Lines · 149 Vl AN EXAMPLE OF RIVER CAPTURE ON TABLE MOUNTAIN The Problem stated 161 Approach to the problem 165 Initial survey and Observations 170 factors contributing to the Capture 172 Results of the Capture 186 Two examples of Incipient Capture 191 Vll CONCLUSION 194 (vii) LIST OF FIGURES Figure Page Location Map l 1.1 Tectonic framework of the Damara eugeosynclinal complex 6 1.2 Reconstruction of conditions prevailing during the earlier part of the Cape Period 9 2.1 Phanerozoic sea-level changes 37 2.2 The Pratt and Airy Theories of Isostasy 44 2.3 Palaeogeography and suggested ages applicable to the Flandrian transgression 61 3.1. The Cape Peninsula: structural and directional control 86 4.1 Location of s. W. Cape borehole zones 107 4.2 Palaeo temperature Curve of the Southern Ocean 110 4.3 Re construction of conditions during a hypothermal minimum 116 4.4 Climatic boundaries and Regions 121 5.1 Geology of the Cape Peninsula 140 5.2 Geological outcrop-map 142 5.3 Directional control of Drainage lines 144 The Disa River: hypothetical erosion history 146 5.5 Development of the Disa River 148 5.6 The Disa River: Hydrographic boundaries 150 5.7 The Cape Peninsula: structural control 152 5.a Table Mountain -- Drainage 154 5.9 (a) Semi-dendritic pattern the Good Hope stream 156 (b) Semi-dendritic pattern Blinkwater stream and tributaries 158 s.10 Radial Drainage pattern 159 6.1 The Valley No. 4 Slangolie Capture Area 164 (v' i i) 6.2 {a) Valley characteristics No. 1 166 6.2 (b) Valley ch ar acteristics No. 2 169 6.3 Geological s ection along line A A 171 6.4 Table Mountain looking N. N. [. 173 6.5 Valley characteristics No. 4 175 6.6 Slangolie Ravine . Long profile 177 6.7 Old Accordant surface 180 6.8 Gradient prior to uplift: the Disa Valley 182 6.9 Fault-lines: position and alignment 187 (ix) LIST OF TABLES Table Page 1.1 Succession of the T. M. S. 12 1.2 Estimated Age of the Table Mountain Group 20 4.1 Rainfall Normals ( 1921 - 1950 ) 97 4.2 Stations reflecting Average Rainfall 98 4.3 Maximum and minimum mean sunshine duration 101 4.4 Pollen zones of late Cainozoic deposits 109 4.5 Stratigraphy of pollen profile of the s. w. Cape 118 6.1 Stations reflecting Average rainfall 178 LIST OF PLATES Plate facing Page 1 51 2 53 3 54 4 55 5 62 6 66 7 76 8 78 9 127 Plates 10 34 197 - 222 ~- BA Y/ ~e Town SALT RIV[Ro OOSE RVATORYo ROSE BANK• RONOEBOSCHo NEWLMlOSo CLAREMONT 0 C APE KENILWORTHo 0 oo' s LLANOUDNO WYNBERG• FLATS PLUMSTEAD• DUIKERPUNT DIEP RIVERo HEAT Hf I ELD• RETREAT• LAKESIDE• CHAPMAN'S BAY F A L S E I B A Y 20 18° 301 E Locat1on Hop of the Cape Peninsula APE ·--------------.L.P-Ol_~t INTRODUCTION The Cape Peninsula is distinctive in man y ways. Apart from being •••• "a most stately thing, and the fairest Cape in the whole circumference of the earth," and stretching like a curved finger into the Atlantic Ocean, it also possesses characteristic physical features such as the plateau and-scarp topography plus a magnificient coastline. The areal matrix stretches from 33° 54 ' s. to 34° 22' s. and from Duikerpunt, 18° 18' in the west to where the sands of the Cape Flats begin in the east. The study area encompasses amongst others, suburbs such as Woodstock , Observatory, Rondebosch, Newlands, Kenilworth and Diep River through to Muizenberg. The eastern section of the Peninsula is bounded by Tabla Bay in the north and False Bay in the south. The western margin is circum- scribed by the Atlantic Ocean. It is axiomatic that we live in a world characterized by op posites. We are thus aware of day and night, winter and summer , uplift and subsidence, lithosphere and hydrosphere, upland and lowland areas, past and present the list is endless. This · dichotomy or ambivalence is present in this study as well. On the one hand it attempts to trace the genesis and geornorphic history of · the areal matrix, and on the other it looks at the contemporary landscape and the changes wrought through time. The writer is of the opinion that the past cannot be ignored, since the present physical landscape can be explained only in the context of geomorphic evolution. This is generally accept able since today is tho child of yesterday and the father of tomorrow. Other aspects which are examined include evidence of changes wrought in the past in tho form of denudation or erosion surfaces, the r elationship between the under- lying geological structure and prosent landforms, to£ether with the strong structural and directional control which is manifested within the study area. Present drainage patterns are examined, whilst the role played by running water and the sea in creating and changing the physical landscape is a theme which runs through the greater part of this dissertation.

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