CGRG Bibliography of Canadian Geomorphology
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Author : Evans, S.G.
Date : 2004.
Title : The 1975 Devastation Glacier rockslide-debris avalanche, Mount Meager volcanic complex, southwestern British Columbia, Canada.
Publication : European Geosciences Union. 1st General Assembly. Nice, France, 25 - 30 April 2004.
Issue : EGU04-A-05903.
Page(s) :
Abstract
On July 22, 1975 a complex series of landslide events took place at Devastation Glacier near Pemberton, British Columbia when approximately 13 x 106m3 of altered Quaternary volcanic rock and glacier ice was lost from the west flank of Pylon Peak in the Mount Meager volcanic complex. The events were initiated by a catastrophic rockslide, involving altered Quaternary pyroclastic rocks, which continued down Devastation Creek valley as a high velocity debris avalanche. The debris avalanche ricocheted back and forth between the valley walls rising up to 100 m above the valley floor at the outside of bends in the valley before coming to rest at Meager Creek. Four people were killed by the landslide. The overall length of the slide path was 7 km and the vertical height of the path was 1220 m yielding a fahrboschung of 10. The debris avalanche was followed by a major debris flow formed from the talus deposits of ice and soft rock which had collected in a portion of the debris avalanche scar. Both slides travelled roughly the same distance. The debris avalanche also triggered a major secondary slide on the western flank of the Devastator. Other large landslides occurred in Devastation Creek valley in 1931 and 1947. The 1975 debris avalanche is thought to be very similar to the 1931 slide, although the 1931 slide is believed to have travelled approximately 1.5 km farther. Stability analysis of the initial failure suggests that the 1975 rockslide is the result of a complex history of glacial erosion, loading and unloading of the toe of the slide mass caused by the Little Ice Age advance and subsequent retreat of Devastation Glacier. The shearing resistance along the base of the rockslide mass was reduced prior to 1975 by substantial previous slope displacements. Some of this displacement is likely to have occurred as subglacial slope deformation since ice fall and crevasse patterns suggest the presence of slide like shearing displacements below the base of adjacent glacier ice. Increased fluid pressures acting along the base of the slide and on internal shear planes, which no doubt accompanied ice melting during a period of warm weather, probably reduced the overall shearing resistance sufficiently to trigger the slide.
Bibliography of Canadian Geomorphology