The distribution and characteristics of deep-seated palaeo-mass movements in the northern and central Drakensberg, South Africa

Abstract

Evidence for large deep-seated palaeo-mass movements are found within the Drakensberg. However, the distribution and origin of these movements are not fully documented or understood. By studying the distribution and geomorphic characteristics of palaeo-mass movements in the Northern and Central Drakensberg, this study set out to understand the formation of these large deep-seated palaeo-mass movements. The method was divided into three phases; detection, verification and mapping. Thirty-three possible mass movements were located through the use of a criteria-based searching method of satellite imagery, topographic maps and geological maps. The criteria consists of geomorphic features associated with known international and national palaeo-mass movements. Confirmation consisted of infield verification of the features identified in the criteria and thirteen sites were verified. In the third phase, confirmed sites were mapped, a morphological analysis was conducted and a relative age was estimated. Three important facts were confirmed. Due to the distribution of mass movements within the sandstone formations and close relation to dolerite sills, the geological characteristics, such as weaknesses in the sandstone formations, are considered major predisposing factors. The geomorphic characteristics of the mass movements have a large variety in appearance, size, age and types. This indicates that one single trigger event is an unlikely cause to the movements in this area. This study proposes that the main cause for large deep-seated mass movements in the Drakensberg was the Neogene uplift, which caused deeply incised valleys that led to the ideal conditions for the occurrence of these movements.