CLIFF COLLAPSE AND ROCK AVALANCHES (STURZSTROMS) IN THE MACKENZIE MOUNTAINS, NORTHWESTERN CANADA

Cliff collapse and resulting rock avalanches or sturzstroms have occurred widely in carbonate formations of the Mackenzie Mountains. Some of the rock slides are close to a Holocene fault scarp and may be due to past earthquake activity. The Mackenzies are located within an intraplate seismic zone; presently monitored seismic activity may not indicate the maximum level of ground motion that caused failure of large rock slopes during the last 10 000 years. The mechanical analysis of dry sturzstroms has to consider two stages: failure and streaming. Failure can occur by either 'sliding' (static friction of about tan 30 degree ) or 'roller bearing' and internal collapse (kinetic friction as low as tan 13 degree ). Streaming is initiated by momentum transfer from the back of a collapsing cliff to its frontal disintegrating portion and facilitated by dispersion of large blocks in finer interstitial material. Prediction of reach or excessive travel distance of dry sturzstroms is not a simple matter and one has to consider the effect of slide mass, fall height, topographic constraints, and lithology. The best method of predicting reach in a potential sturzstrom situation is comparison with documented sturzstroms in similar geologic, climatic, and topographic settings. Refs.