Abstract
Abstract. A long-standing problem in avalanche engineering is to design defense structures and manage forest stands such that they can withstand the forces of the natural snow cover. In this way, glide-snow avalanches can be prevented. Ground friction plays a crucial role in this process. To verify existing guidelines, we collected data on the vegetation cover and terrain characteristics of 101 glide-snow release areas in Davos, Switzerland. We quantified the Coulomb friction parameter μm by applying a physical model that accounts for the dynamic forces of the moving snow in the stauch zone. We investigated the role of glide length, slope steepness and friction in avalanche release. Our calculations revealed that the slope angle and slab length for smooth slopes correspond to the technical guidelines for defense structure distances in Switzerland. Artificial defense structures, built in accordance with guidelines, prevent glide-snow avalanche releases, even when the terrain is smooth. Slopes over 40 m in length and 45° in steepness require a ground friction of μm = 0.7 corresponding to stumps or tree regeneration to ensure protection. Forest management guidelines that define maximum forest gap sizes to prevent glide-snow avalanche release neglect the role of surface roughness and therefore underestimate the danger on smooth slopes.
Highlights
Full-depth, glide-snow avalanches are common events on the steep, smooth slopes of the European Alps (In der Gand and Zupancic, 1966; Höller, 2014)
Our calculations revealed that the slope angle and slab length for smooth slopes correspond to the technical guidelines for defense structure distances in Switzerland
The snow cover, the heights decreased to hv < 1 cm for long grass, hv = 3 cm and hv = 4 cm for short grass and low dwarf shrubs, and 10 cm < hv < 20 cm for strong lignified shrubs
Summary
Full-depth, glide-snow avalanches are common events on the steep, smooth slopes of the European Alps (In der Gand and Zupancic, 1966; Höller, 2014). The snow cover breaks first in the tensile zone, and a glide crack (a so-called Fischmaul) opens 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. 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
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