Late Quaternary Landforms and Environmental Change in Northwest Botswana: The Evidence of Lake Ngami and the Mababe Depression

Abstract

Lake Ngami and the Mababe Depression contain series of concentric shoreline features controlled by volume: area thresholds in the Okavango Delta region. Of particular interest are the 945 m (Lake Palaeo-Makgadikgadi) and the 936 m shorelines, the latter representing the amalgamation of the two lakes along the Thamakalane axis. Lower shorelines and fluvial landforms permit reconstruction of the final desiccation of the two lakes. Preliminary dating suggests the 936 m level was attained from 17 000-12 000 BP and c. 2000 BP, whilst lower levels prevailed c. 25 000 BP and 8000-6000 BP. Consideration of the palaeohydrologic budget attributes the 936 m level to increased precipitation and possibly increased inflow, whilst tectonism must have played a part in the 945 m level. The present erratic regime of the Okavango is a result of the interplay of factors such as variations in inflows and local precipitation, and hydrological changes due to minor tectonic events, siltation and vegetation blockage.