On the geomorphic evidence for a late quaternary periglaciation of the main escarpment region of eastern southern Africa

Abstract

Conflicting reports from geomorphic studies appear in the literature describing the environment of the southern African Main Escarpment region adjacent to the Lesotho Highlands during the cold phases of the Late Quaternary. Evidence cites limited glaciation and/or periglacial conditions with or without permafrost. The thesis emphasises debates and presents arguments for alternative interpretation of landforms previously described in the literature as indicative of specific cold environments. Field investigations into the distribution and characteristics of openwork accumulations in southern Africa show that blocky accumulations are found within a range of climatic conditions, including arid and semi-arid environments. Mode of emplacement is highlighted as the critical factor in association with a periglacial environment. Relict openwork block accumulations in the Lesotho highlands area around Thabana Ntlenyana, the highest summit in the escarpment range, supports the contention for a relatively arid periglacial environment during the Late Pleistocene. Findings militate against either deep snow cover or localised glaciation of insolation-protected south-facing slopes. The evidence for periglacial conditions is supported by the presence of relict sorted patterns that indicate deep seasonal freeze. Contemporary soil temperature monitoring indicates a near-surface current seasonal freeze of two and a half months which would have been prolonged and deepened under depressed temperature. No specific evidence for periglacial conditions is found for the escarpment region in the Amatola mountains.