Item: Towards a Better Understanding of Glide-Snow Avalanche Formation
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Title: Towards a Better Understanding of Glide-Snow Avalanche Formation
Proceedings: Proceedings, 2012 International Snow Science Workshop, Anchorage, Alaska
Authors:
- Christoph Mitterer [ WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland ]
- Jürg Schweizer [ WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland ]
Date: 2012
Abstract: Full-depth avalanches (i.e. glide-snow avalanches) often release due to either a failure in the basal layer (e.g. depth hoar) or a failure at the snow-soil interface. The latter one typically occurs when the snow-soil interface is moist or wet so that the basal friction is reduced. In that case, snow gliding and the formation of a glide crack precedes avalanche release. Furthermore, observations indicate that the soil surface has little roughness and the slope angle exceeds 15°. The occurrence, however, of glide cracks and their evolution to glide-snow avalanches are still poorly understood. As a consequence, glides are difficult to predict as (i) not all cracks terminate in an avalanche event, and (ii) for those who do, the timing between crack opening and avalanche event might vary from hours to weeks or even months. It seems that the processes producing liquid water at the bottom of the snowpack can be divided into a warm temperature and cold temperature event: Cold temperature events include warm and dry autumns followed by heavy snowfalls favoring the storage of heat in the ground. The stored energy might be sufficient to melt snow at the bottom of the snowpack that consequently will reduce the friction. With a simple simulation we demonstrate that if a dry snowpack overlies a wet porous medium, resulting large hydraulic pressure gradients will lead to an upward flux of soil water content. Apart from the snow-soil interface the entire snowpack is dry and cold, and the formation of glide cracks and avalanches seems poorly correlated to air temperature. Warm temperature events are characterized by rain-on-snow events or high radiation combined with warm air temperature producing melt water which then is percolating through the entire snowpack. Ponding of that water on the snow-soil interface will reduce friction and strength of the snowpack.
Object ID: issw-2012-610-616.pdf
Language of Article: English
Presenter(s): unknown
Keywords: glide avalanche, full depth avalanche, avalanche simulation, temperature gradients, rain on snow
Page Number(s): 610-616
Subjects: full-depth avalanches glide crack activity avalanche forecasting
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