GEOMORPHIC EVOLUTION OF DEBRIS FANS IN THE DU TOIT'S KLOOF, WESTERN CAPE MOUNTAINS

ABSTRACT

Two debris fans in Du Toit's Kloof are investigated by means of geomorphological mapping and relative-age dating (Schmidt hammer, lichen cover and weathering rinds) of their deposits. Both fans mostly consist of debris flow deposits, with minor indications of flooding. Volume estimation and relative-age dating show four phases of debris flow activity, with a progressive decrease in magnitude of flow events. Relative-age dating techniques, however, are restricted in the maximum ages that can be determined. A high proportion of very large events (>10⁴m) is associated with late Pleistocene periglacial conditions, but requires direct evidence by reliable dating. Fan stabilisation and incision occurred in response to reduced sediment storage in the catchment and increased slope stability during the Holocene. The data provide important new insights into footslope dynamics of the Western Cape Mountains for the Late Quaternary.