The present-day frost action environment and its geomorphological significance in the Western Cape Mountains, South Africa

Abstract

Studies on periglacial features in the Western Cape mountains provide a fragmented picture on the existence of both active and relict frost action in the region. As anywhere else in the country quantitative analysis and identification of active frost action processes and landforms are noticably lacking . In response, this study aims to analyze and identify the cryogenic landforms and processes that result in the region and establish the environmental controls that govern them. The study thus provides a modern datum for the evaluation of past periglacial activity. Results from the climatic record show the summit areas of the Mediterranean mountains of the Western Cape to experience surficial, diurnal frost cycles only from May to September. No evidence in favour of frost-induced soil processes was found over most of the summit regions due to several environmental controls. First, irrespective of climatic controls, sandstone-derived sediments were found to be too coarse to allow for effective soil frost over most of the Western Cape mountains. Second, the frequency of effective soil frost days is extremely small due to insulation effects by cover and vegetation, the effectiveness of the zero-curtain effect and the high albedo values of sandy soils. Soil moisture forms no limiting factor to effective soil frost activity in the region. A wide spectrum of weathering features were observed. Solution weathering features dominate in the field, while fires are considered the most important agent for mechanical fracturing at present.