Drainage development, neotectonics and base-level change in the Kalahari Desert, southern Africa

The Kalahari Desert contains extensive networks of ephemeral and fossil drainage which are potential indicators of past and present neotectonic activity and climatedriven environmental change. An absence of topographic data has hindered our understanding of their development. We present long-profile information for twentynine valley networks derived from Shuttle Radar Topographic Mission (SRTM) digital elevation data. In total, 8354 km of valley talweg was measured for x, y and z information. Most valleys exhibit concave-up profiles. Fifty-five previously unknown knickpoints were identified. The majority coincide with lithological boundaries or fractures, but many developed in response to Neogene uplift and/or downwarping or occur where valleys cross palaeolake shorelines. The headwaters of four valleys cross the Kalahari–Limpopo drainage divide and predate the presumed Miocene uplift of the Kalahari–Zimbabwe axis, suggesting that they are of considerable antiquity.