Item: Slab avalanches and "new" snow
Title: Slab avalanches and "new" snow
Proceedings: Proceedings of the 1998 International Snow Science Workshop, Sunriver, Oregon
Authors: Alain Duclos
Abstract: A three-year study based on observations carried out both on the field and inside the laboratory has enabled us to describe accurately 22 slab avalanches triggered by passing skiers or pedestrians, within a limited area. Simultaneously, some systematic measurements have also permitted to describe the real evolution of snow conditions upon a slope much exposed to avalanches, and the weather conditions as well. A relational database has been developed and used to secure and operate various images and alphanumeric data as well. Thanks to that new tool, the study of slabs themselves on the one hand and of the weak layers on the other, has shown that quite varied situations are likely to produce slab avalanches (whether from the point of view of grain types or from physical properties of the snow itself). Nonetheless, some major elements have emerged : they concern the important amount of fresh snow along slabs (up to 70 % of precipitation particles and partly decomposed precipitation particles), the peculiar capacity of layer of depth hoar crystals to release both thick slabs and slabs of various texture, and the capacity of fresh snow to build up weak layers. That set of observations has led us to consider that, on the field, much significant information is derived from an investigation both into the" age" of the last snow-fall (or snow-drift), and also into ascertaining its precise location. This will probably reach priority in a precise analysis of the snowpack, in order to establish a diagnostic of its stability.
Keywords: avalanche forecasting, snow cover stability, snow stratigraphy
Digital Abstract Not Available