The Formation of Shear Moraines: an Example from South Victoria Land, Antarctica

Abstract

An analysis of the margin of the ice sheet in the upper Ferrar Glacier area of south Victoria Land, Antarctica, shows that the shear hypothesis and the theory of Weertman are both of value if an attempt is made to explain the formation of the morainic deposits of this area.Three types of debris layer have been observed within the glacier:i.Silty and sandy layers, with a slight dip towards the interior of the glacier, are separated from one another by white bubbly ice and blue dense ice at the edge of the glacier. They have resulted from a freezing-in process due to the formation of segregation ice and upwarping near the margin of the ice sheet.ii.Fault planes in the glacier, filled with slabs and gravel, are the result of shearing which has occurred along and transformed thermal-contraction fissures. The debris has been scraped from the glacier bed, carried into the ice and ultimately transported along these planes.iii.Three coarse debris layers of different ages associated with major shear zones at the boundary between stagnant and active ice.Due to favourable circumstances, the debris layers of Weertman have been observed to be faulted by shear planes of the second type.