Item: Creep instability of the weak layer and natural slab avalanche triggerings
Title: Creep instability of the weak layer and natural slab avalanche triggerings
Proceedings: Proceedings of the 2000 International Snow Science Workshop, October 1-6, Big Sky, Montana
Authors: Francois Louchet, LTPCM • UMR CNRS 5614/INP de Grenoble - Universite Joseph Fourier, St Martin d'Heres (France)
Abstract: The weak layer connecting the snow slab with the older snow substrate is modeled as an open cell ice foam made of an array of ice bonds. The comparison of bond rupture and rewelding rates under load show that the weak layer experiences stable flow for a wide range of loads of bond brittleness and of bond rewelding rates. However, a critical point may be reached, corresponding to a finite shear rate of the weak layer, beyond which the shear rate increases catastrophically, leading to a natural avalanche release. This critical situation is equivalent to a ductile to brine transition, whose activation energy is onehalf of that of self diffusion in ice. A measurement of the exponent in the shear strain vs stress relation may give a hint on the inminence of the avalanche release. A similar calculation performed at the tip of a preexisting basal crack gives a simple criterion for crack stability and an analytical expression for snow fracture toughness.
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Keywords: brittle ductile transition,creep, ice, snow, avalanche, toughness
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