The shape of glacial valleys and implications for southern African glaciation

Abstract

The classic U-shaped valley is a typical expression of glacial erosion, but situations can occur where the glacier effects little to no change in the landscape. Such an occurrence would be where the glacier is cold-based and remains so during its demise – never entering into a warm-based (erosional) phase. Here two present-day examples are provided where glaciers exist but valley form has remained unaltered despite multiple glacial events. The key to such a situation is suggested to be the altitudinal/latitudinal spatial location such that the ice has completely disappeared before, during the move towards an interglacial, there is the time for it to transform into warm-based ice. The argument is then made that perhaps the same is the situation for the reconstructed, small glaciers in the Lesotho-Drakensberg area. The ice was cold-based due to a combination of its thinness and the cooling effect of shading. Cold-based ice would explain the lack of striated clasts found in the moraines, the absence of any change to valley form, and the preservation of breaks in slope observed in the area of the former glacier.