Block and debris deposits in the high drakensberg, lesotho, southern africa: implications for high altitude slope processes

Abstract

Past evaluation of high altitude slope development in Lesotho, southern Africa, is largely based on hypothetical or macro‐scale geomorphic approaches. Consequently, the information pertaining to high altitude southern African Quaternary slope environments has remained rather rudimentary. The present study describes the morphology and discusses the likely palaeogeomorphic processes of blockstreams and debris deposits on the Popple Peak and Njesuthi‐Mafadi south‐facing‐slopes in the Drakensberg. The geomorphic evidence provides much needed information to help improve the understanding of south‐facing slope processes during past colder periods. A model for high altitude Drakensberg south facing slopes is presented and used to challenge and expand on recent models and ideas on southern African valley asymmetry. It is found that solifluction and debris flows/avalanches were operative on south‐facing slopes during past cold periods and thereby contributed to past slope development at some high altitude sites in Lesotho. However, the geomorphological observations do not support the valley asymmetry hypothesis and it is suggested that greater caution be exercised in valley‐form interpretations, particularly where geomorphological ground‐truthing has been absent.