ABSTRACT: Application of digital cartographic techniques in the characterization and analysis of catastrophic landslides; the case of the 1997 Mount Munday rock avalanche, British Columbia.

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Abstract

The availability of digital cartographic techniques has revolutionized the extent that catastrophic landslides may be characterized for description and analysis. Such techniques include the interpretation of optical satellite imagery, the generation and analysis of high-resolution digital elevation models, and the use of image analysis software. These techniques are especially useful when the event takes place in a remote location where extensive field operations are not feasible due to weather, safety, and/or financial considerations. We investigate the 1997 Mount Munday rock avalanche which occurred near Mount Waddington in a remote part of the Coast Mountains of British Columbia and illustrate four applications of digital cartographic techniques. First, the time of occurrence of the rock avalanche was not known. Using successive SPOT and LANDSAT satellite imagery, however, we established that the landslide occurred in a 19 day window between July 18 and August 6, 1997. Second, large scale aerial photographs were taken on August 30, 1997. These provided the basis for a high-resolution digital elevation model of the landslide. Together with the comparison to pre-slide topography enabled us to study change detection in the source and depositional area of the rock avalanche which resulted in accurate estimates of source and deposit volumes. The digital terrain data also provided the basis for a simulation of the movement using the model DAN. Thirdly, the large-scale aerial photographs also enabled us to conduct image analysis of the debris with the objective of defining its fragmentation characteristics. Total number of objects, major axis (m) and volume (m3) of each boulder above a threshold major axis length of 1.6 m, equivalent to a 2-pixel resolution, were tabulated. Lastly, the post-depositional movement of the rock avalanche debris on the glacier surface has been tracked using successive SPOT and LANDSAT imagery, obtained since August 1997. Using these georeferenced images the velocity of glacier-transport of surface debris has been obtained. The rock avalanche involved a total slide volume of 4.76x10^6 m3. The rock avalanche traveled for 4.5 km over the surface of Ice Valley Glacier with a mean velocity of about 10 m/s and expended a total energy of 4.96x10^13 J. Debris covered a total area of 2.5x106 m2 with a mean thickness of 2 m.

Bibliography of Canadian Geomorphology