Geomorphometric indices over the Drakensberg basalts: Implications for landscape evolution of the Great Escarpment

Abstract

The application of geomorphometric indices to assess landscape evolution of active or neo-tectonic regions is well-known. However, using these indices to study landscape evolution of passive margins is often overlooked. This study utilises several established geomorphometric indices to test the applicability of these indices in a passive landscape context. The study also provides insights into landscape evolution of the Drakensberg Escarpment and Lesotho Highlands which represent a large igneous province composed of basalt. The following geomorphometric indices were obtained using a moving window over a 30m pixel digital elevation model (DEM): hypsometric integral, surface roughness, relief anomaly, and the surface index. Based on the results, highly elevated but low relief regions were identified and mapped together with areas characterised by high rates of erosion or deposition. The indices indicate that, with support from low denudation rates, that it is the undercutting and retreat of basalts that determined the morphometric shape of the Drakensberg Escarpment.