Overcoming the stauchwall: Viscoelastic stress redistribution and the start of full‐depth gliding snow avalanches

Abstract

[1] When a full-depth tensile crack opens in the mountain snowcover, internal forces are transferred from the fracture crown to the stauchwall. The stauchwall is located at the lower limit of a gliding zone and must carry the weight of the snowcover. The stauchwall can fail, leading to full-depth snow avalanches, or, it can withstand the stress redistribution. The snowcover often finds a new static equilibrium, despite the initial crack. We present a model describing how the snowcover reacts to the sudden transfer of the forces from the crown to the stauchwall. Our goal is to find the conditions for failure and the start of full-depth avalanches. The model balances the inertial forces of the gliding snowcover with the viscoelastic response of the stauchwall. We compute stresses, strain-rates and deformations during the stress redistribution and show that a new equilibrium state is not found directly, but depends on the viscoelastic properties of the snow, which are density and temperature dependent. During the stress redistribution the stauchwall encounters stresses and strain-rates that can be much higher than at the final equilibrium state. Because of the excess strain-rates, the stauchwall can fail in brittle compression before reaching the new equilibrium. Snow viscosity and the length of the gliding snow region are the two critical parameters governing the transition from stable snowpack gliding to avalanche flow. The model reveals why the formation of gliding snow avalanches is height invariant and how technical measures to prevent snowpack glide can be optimized to improve avalanche mitigation. Citation: Bartelt, P., T. Feistl, Y. Bühler, and O. Buser (2012), Overcoming the stauchwall: Viscoelastic stress redistribution and the start of full-depth gliding snow avalanches,

Quantification of basal friction for technical and silvicultural glide-snow avalanche mitigation measures

“…Equations (2) and (3) are a system of two coupled ordinary differential equations that can be solved numerically. Numerical solutions are presented in Bartelt et al (2012). The model predicts the strain rate˙ = u/2l s in the stauchwall.…”

“…To predict glide-snow avalanche release, we apply the twodimensional visco-elastic continuum model of Bartelt et al (2012). The model divides the snow cover into two regions: the sliding zone and the stauchwall (Fig.…”

“…Ground friction dictates the force redistribution and therefore the loading on the stauchwall (In der Gand and Zupančič, 1966;McClung, 1975;Höller, 2004;Bartelt et al, 2012). Vegetation can increase the ground roughness significantly (de Quervain, 1979;Fiebiger, 1978;Newesely et al, 2000;Höller, 2001;Leitinger et al, 2008;Schneebeli and Bebi, 2004;Weir, 2002).…”

“…This causes an additional redistribution of stress within the snow cover, and leads to a fragile stability governed by the strength of the compressive zone. This zone is termed the stauchwall (Lackinger, 1987;Bartelt et al, 2012). The stauchwall is fixed to the ground, either because the basal surface is rough, or because the slope is flatter, leading to large compressive stresses.…”

“…The mechanics of glide-snow avalanches involve two principle components: the compressive strength of the stauchwall and the frictional properties of the ground (In der Gand and Zupančič, 1966;Häfeli, 1967;McClung, 1975;Bartelt et al, 2012). Glide-snow avalanches typically occur when water accumulates on the snow-soil interface, either by melting (because of a warm soil surface) or by meltwater penetration through the snow cover (In der Gand and Zupančič, 1966;Mitterer et al, 2011).…”