Snow cover properties for skier triggering of avalanches

Snowpack characteristics for skier-triggered avalanches are described in order to better understand skier triggering, to improve snow profile observation and interpretation, to make suggestions for route selection and to provide a basis for further research. Our analysis is based on avalanche and snow profile data from skier-triggered avalanche sites in the Columbia Mountains of Canada and the Swiss Alps. Although these two mountain ranges have different climates, the characteristics for skier triggering are very similar. Whereas the snow cover in the profiles from the Columbia Mountains is more than twice as deep than in the ones from the Swiss Alps, the typical fracture depth (or slab thickness) is about the same (45 cm). Failure layer properties are very similar indicating favourable conditions for skier triggering and slab release. In both ranges, the failure layers are predominantly persistent, that is, they consist of crystals of surface hoar, facets and depth hoar, which are slow to metamorphose. The analysis has focussed on slab properties and weak layer properties, and in particular, their interaction. The findings support the simple model of skier loading in which skiers directly initiate failures in buried weak layers or interfaces. (C) 2001 Elsevier Science B.V. All rights reserved.