Sean J. Fitzsimons
Department of Geography, University of Otago, PO Box 56, Dunedin New Zealand
Several dry-based alpine glaciers in the Dry Valleys of south Victoria Land, Antarctica, have prominent end moraines. Examination of their morphology, structure and sedimentology shows they consists of blocks of sand, gravel and organic silt within which sedimentary structures unrelated to entrainment and transportation by ice are well preserved. the anture and preservation of sedimentary structures, together with the presence of algae mats in the sediment, suggest formation by proglacial entrainment, transportation and depostion of frozen blocks of lacustrine sediment. Previous explanations of the formation of thrust-block moraines, including those that stress the importance of elevated pore-water pressure and Weertman's ice-debris accretion hypothesis, depend on the presence of subglacial meltwater or the 0°C isotherm being situated close to the glacier bed. These models appear inappropriate for cold, dry-based glaciers because their basal temperatures are well below freezing point and they rest on deep permafrost. Three alternative models for the formation of thrust-block moraines at the margins of dry-based glaciers are examined in this paper: block entrainment of sediment associated with frozen-bed deformation; entrainment by overriding and accretion of marginal-ice and debris aprons; and transient wet-based conditions associated with glaciers flowing into ice-marginal lakes.
Fitzsimons, S. J. 1996. Formation of thrust-block moraines at the margins of dry-based glaciers, south Victoria Land, Antarctica. Annals of Glaciology, 22, 68-74. [PDF 506kb]
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