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The evidence for cirque glaciation in Lesotho
Author(s) -
Marker Margaret E
Publication year - 1991
Publication title -
permafrost and periglacial processes
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.867
H-Index - 76
eISSN - 1099-1530
pISSN - 1045-6740
DOI - 10.1002/ppp.3430020106
Subject(s) - cirque , geology , glacial period , escarpment , pleistocene , moraine , geomorphology , landform , plateau (mathematics) , paleontology , physical geography , glacier , geography , mathematical analysis , mathematics
The cirque‐like hollows of the Lesotho high Plateau and its South African extension are a class of erosional landform attributed to processes active during Pleistocene cold phases. The hypothesis that these hollows are the product of glaciation is examined by a morphological analysis based on 12 parameters from a population of 628 hollows. Eight parameters were derived from map analysis. The survey extends over 156000 km 2 between latitudes 28º30′ S and 30º00′ S. The data were considered by latitudinal belts subdivided into the Escarpment region and the Interior. Most hollows are 800‐1000 m wide, almost circular and relatively shallow. Hollow distribution is related to plateau residuals on Drakensberg Formation basalt. Hollow frequency and density are greatest adjacent to the Great Escarpment between latitudes 29º S and 30º S and diminish westwards towards the Interior. Indices of Flatness, as a means of differentiation between cirques of glacial and nival origin, were computed. Only 27% fall unequivocally into the glacial size class; a further 29% are intermediate in depth. The correlation of hollow frequency, density and morphological variability with areas of high present‐day precipitation and high altitudes support the hypothesis. The strong northern orientation and strong preference for hollows on the leeside of ridges aligned NW‐SE and E‐W is attributed to snow‐bearing southerly and southwesterly winds. This also supports the hypothesis. The conclusion is reached that weak cirque glaciation occurred on the high plateau at least once during the Pleistocene.