Rock Mass Strength and Scarp Forms in Southern Africa

Abstract

The influence of rock mass strength on slope gradients on the seaward facing scarps surrounding the interior plateaux of southern Africa is analysed. From a study of scarp slopes on a variety of lithologies (basalt, shales, sandstones and granites) it is possible to demonstrate that gradients of bedrock slopes are in equilibrium with the mass strength of the rock. The idea that parallel retreat is the cause of free face development is contested, and it is contended that the widespread occurrence of strength equilibrium slopes is evidence of the continuing adjustment of slope form to rock mass strength, and that parallel retreat will occur only when rock mass strength is uniform into the slope.