Item: Slab avalanche formation, new measurements and results
Title: Slab avalanche formation, new measurements and results
Proceedings: Proceedings of the 1992 International Snow Science Workshop, Breckenridge, Colorado, USA
Abstract: Three types of experiments have been started or continued during the last two years to improve our knowledge on the formation of slab avalanches: (a) Interception. of snow by spruce and conditions for triggering snow fall from tree branches. (b) Modelling of energy and mass flux in a seasonal snow cover including a detailed investigation on short wave absorption in snow. (c) Field measurements of the strain rate dependent stress-strain relationship for potentially weak layers under shear stress. Experiment (a) helps to reveal the timing of snow dumping by spruce branches during periods of strong precipitation in sub alpine forests. Avalanching of snow from trees may distort existing continuous weak layers, adding support to the new-snow slab by local compaction but may also trigger loose snow avalanches in steep terrain. Experiment (b) enables us to refine modelling and understanding recrysta1lisation processes taking place within short periods of time close to the snow surface. These fast recrysta1lisation processes may eventually produce weak layers whose existence is a necessary condition for slab avalanche formation. Experiment (c) for the first time allows direct measurements of the constitutive relationships for thin weak layers under shear stress. The computer controlled shear apparatus has a contact area of .25m2 and allows measurements at constant strain rate (10-7 to 1O-l s-1) or constant stress (0 to 5000Pa). The stresses may be applied in-situ on weak layers.
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Keywords: weak layer, triggering, slab avalanche
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