Failure of a layer of buried surface hoar

Abstract

[1] In order to study the formation of the initial failure leading to dry-snow slab avalanche release, we performed loading experiments in a cold laboratory with natural samples including a layer of buried surface hoar. The experimental setup was such that the layered snow samples were loaded continuously for various tilt (slope) angles; loading rates varied between 1 and 20 Pa s −1 . The stress at fracture decreased with increasing loading rate and increasing slope angle, i.e., increasing shear component of the load. The latter result means that the layer was stronger in compression than in shear which is attributed to the particularly anisotropic nature of layers of buried surface hoar. Particle image velocimetry revealed that almost 90% of the sample's global deformation was concentrated in the weak layer. For avalanche release our results imply that the shear component of deformation is of particular importance for failure initiation.

A new index combining weak layer and slab properties for snow instability prediction

“…2) would not decrease strongly with depth as the snow column is uniformly loaded at the top. Furthermore, we neglected the weight of the overlying slab (which is e.g., considered in the skier stability index introduced by Föhn, 1987) because we suppose that the dynamic load (rather than the static load) is essential for initiating a failure due to the well-known deformation rate dependence of snow strength (e.g., Reiweger and Schweizer, 2010). Finally, we did not consider the effect of slope angle on either stress or strength as its effect is largely unknown in the case of a CT.…”

Snow and avalanche research: A journey across scales

“…Microstructures resulting from temperature gradient metamorphism exhibited a minimum cut density larger in the vertical direction than in the horizontal plane. The anisotropy has obvious consequences on strength as has been shown by Reiweger and Schweizer (2010).…”

Stress Concentrations in Weak Snowpack Layers and Conditions for Slab Avalanche Release

“…When this criterion is met, the crack size corresponds to the so‐called critical crack length a c . The shear strength of persistent weak snow layers (natural and artificially grown faceted crystals, depth hoar, and surface hoar) was measured in laboratory experiments for different loading angles and rates (Reiweger & Schweizer, ; Reiweger et al, ). It was shown in particular that for realistic values of the normal stress σ , τ p increased with increasing values of σ (Figure , inset).…”

“…A dry-snow slab avalanche originates due to the initiation of a failure in a weak snow layer buried below a cohesive slab, followed by the onset of rapid crack propagation within the weak layer (McClung, 1979;Schweizer et al, 2003;Schweizer, Reuter, van Herwijnen, Richter, & Gaume, 2016). Our understanding of failure initiation has greatly improved over the last decade, in particular, thanks to laboratory and field experiments on snow failure (Chandel et al, 2015;Reiweger & Schweizer, 2010). Recently, Reiweger et al (2015) characterized the failure envelope of different types of weak layers under mixed-mode loading.…”