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Late Cainozoic glaciation and mountain geomorphology in the Central Highlands of Tasmania

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Kiernan, K (1985) Late Cainozoic glaciation and mountain geomorphology in the Central Highlands of Tasmania. PhD thesis, University of Tasmania.

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Abstract

The broad topographic framework and erosion surface
morphology of west central Tasmania predates the early
Pleistocene. The valley systems, however, have been
emphasised by glacial erosion which has played a major role
in shaping the detailed geomorphology of the mountains.
Part of an extensive ice cap that developed in the Tasmanian
Central Highlands during the late Cainozoic discharged
southwards via a major outlet glacier that occupied the
valley of the Derwent River.
The heart of the Central Tasmanian ice cap probably lay west
of the Du Cane Range. When the ice cover was most extensive
the Derwent Glacier was up to 500 metres thick. It may have
extended to as low as 230 metres above sea level, 70
kilometres downstream from its source in the cirques of the
Du Cane Range. Two diffluent lobes of this glacier spread
eastwards to merge with other glaciers in the Nive Valley.
Other diffluent lobes extended southwards into the upper
Gordon Valley, and westwards into the upper Franklin and
Alma valleys. At the maximum phase the Franklin and Alma
glaciers were confluent around Mt. Alma, near the present
junction of the Collingwood and Franklin rivers.
The more westerly glaciers displayed the highest rates of
mass throughput hence glacial landforms are more abundant
and better developed in the west. Analysis of the post-depositional modification of the
glacial landforms and sediments suggests that at least three
glaciations took place. The first glaciation was probably
early Pleistocene or late Pliocene in age while the most
recent and smallest occurred during the late Last Glacial
Stage.
Glaciation would have demanded colder temperatures and an
increased solid precipitation budget, but no major shift in
the direction of snow bearing winds is neccessitated. At no
stage was the mean annual air temperature likely to have
been more than 9° C less than present.
The glaciations were probably broadly contemporaneous with
those at similar southern latitudes in Andean Patagonia and
South Island New Zealand. Like the glaciers of those areas
the ice masses of west central Tasmania were mainly of
temperate maritime character.
The glaciations were accompanied by periglacial activity
beyond the limits of the ice. The development of rock
glaciers suggests that localised areas of permafrost existed
during the Last Glaciation.
The glacial oversteepening has greatly facilitated slope
retreat in areas of high structural anisotropy, particularly
under periglacial conditions. Interglacial weathering and
erosion was comparatively innocuous, although the presence
of a substantial vegetation cover seems to have been
critical to the maintenance of slope stabilty, particularly in steeper and more elevated terrain. The geomorphic
evidence does not demand any climate deterioration during
the Holocene, The most active geomorphological agent of the
Holocene interglacial is humankind.

Item Type: Thesis (PhD)
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Date Deposited: 18 Jul 2011 02:04
Last Modified: 11 Mar 2016 05:56
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