Rock Avalanches in High Mountains - A Sedimentological Investigation
by
Stuart Dunning
Centre for Environmental Change, University of Luton, UK
Coauthors: Paul Cole (Centre for Environmental Change, University of Luton, UK)

Catastrophic rock avalanches (sturzstrom) have been identified as major landforms and geomorphic hazards in many high mountain regions. In the 20th century it is estimated that 50000 people have been killed by massive rock slope failures. This hazard is ever increasing due to recreational and resource development in mountainous areas. As yet, little is known of the failure mechanisms, frequency, and importantly, the transport mechanisms that allow rock avalanches to have excessive run-out distances relative to their source area.

These deposits, with a lower bounding volume of 1x106m3, exhibit characteristic morphologies that are topographically controlled and include; unconstrained lobate form, lateral ridges and raised distal rims, a valley bound elongate morphology, and super-elevation effects on opposing slopes and valley sides. Distinctive sedimentological properties include 3D jigsaw fabric, crude inverse grading and preservation of source stratigraphy, both surface and sub-surface.

Seven samples taken from the Falling Mountain rock avalanche (57x106m3) and 20 taken from the Acheron rock avalanche (6x106m3), New Zealand show an interior consisting of highly fragmented, very poorly sorted, finely skewed, gravels, sandy gravels, and muddy sandy gravels. To investigate mechanisms of fragmentation further a detailed grain size study of the Flims rock avalanche (10x1010m3), Switzerland was undertaken. Initial results from 27 of the samples taken from two localities 6-7 km from the source region show different distributions to the New Zealand deposits. Samples are mainly highly fragmented, very poorly sorted, very finely skewed, muddy sandy gravels. The results show coarsening up of the deposit at outcrop scale and differences in grain size distribution produced by fragmentation of different preserved lithological bands. It is hoped that the completed data set can be tested against current models of rock avalanche motion, particularly the hypotheses of 'fragmentation spreading' to solve the problem of excessive run-out distances for this mountain hazard.

Date received: April 30, 2002

Copyright © 2002 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # caji-19.