Contribution of deep-seated bedrock landslides to denudation of a glaciated basin in southern Alaska Public Deposited

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  • The role of bedrock landslides in the denudation of fluvial catchments has received considerable attention, whereas the relative contribution of deep-seated bedrock landslides to the erosion of glaciated basins is less well known. A glaciated basin in the Chugach-St. Elias Range of southern Alaska was chosen to investigate the contribution of bedrock landslides because the debris from four major landslides on the surface of a glacier is easily distinguished from moraines and other supraglacial material. The sediment in the landslides was derived entirely from the hillslopes, as evidenced by large scars visible on the basin walls. A series of aerial and satellite photos from 1978 to 2000 and field observations in 2001 and 2002 indicate that three of the four landslides have fallen onto the surface of the glacier since -1978. The landslides originated from the steeply dipping (60-70°) bedrock walls and were deposited onto the glacier in the ablation zone. Landslide material is currently being transported downstream supraglacially. Valley walls are composed of high-grade metamorphic rock, have a steep north-dipping foliation, are fractured by numerous large joints, and have an average relief of -400 meters. A total landslide volume of - 2.3 x 105 m3 was determined by combining surface profiles, area, and thickness from high-resolution survey data. This volume indicates that deep-seated landslides resulted in a basin-scale erosion rate of 0.4 mm yr 1.Other investigations that have attempted to quantify the sediment contribution from supraglacial sources, report that sediment derived from the basin walls could represent 24-60% of the overall erosion. If correct, the total landslide volume can be used to infer an overall, basin-scale erosion rate of 0.7 to 1.7 mm yrt.
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