Glide-snow avalanche initiation: The influence of liquid water on snow-surface friction

Glide-snow avalanches occur when the entire snowpack slowly slides along the ground. Although liquid water at the snow–soil interface is known to play a role in glide-snowavalanche initiation, the mechanical behaviour at this interface remains poorly understood (Ancey & Bain, 2015) (Fees et al., 2024). These full-depth avalanches pose a significant risk to alpine infrastructure, as they are difficult to forecast and often involve large volumes.

This study investigates the influence of liquid water content, normal stress, and surface roughness on the shear strength of the snow–soil interface using controlled cold- laboratory experiments. Artificially produced snow is compacted and cut into cylindrical samples with a diameter of 8 cm, which are then sheared on two non-porous surfaces: a geotextile and a slate. Liquid water content at the interface is systematically increased through controlled heating of the basal surface, while shear force and displacement during the experiment are continuously measured, and interfacial liquid water content is quantified immediately after each test.

The experiments exhibited strain-softening behaviour under all conditions. Under dry conditions, peak shear strength increased with both idle time (the duration of surface contact before shearing) and applied normal load, while the Mohr–Coulomb friction angle remained constant for each surface. Increasing idle time resulted in a parallel upward shift of the yield surface toward higher shear strengths. Under wet conditions, the peak shear strength remains roughly stable with increasing interfacial liquid water content; shear behaviour was primarily governed by surface type and normal load.

Our findings indicate that, in addition to liquid water content, interface mechanics and surface properties play an important role in glide-snow avalanche release. The results provide new experimental insight into basal friction processes and contribute to an improved conceptual understanding of glide-snow avalanche initiation.

References

Ancey, C., & Bain, V. (2015). Dynamics of glide avalanches and snow gliding. Reviews of Geophysics.

Fees, A., Lombardo, M., van Herwijnen, A., & Schweizer, J. (2024). Glide-snow avalanches: insights from spatio-temporal soil and snow monitoring.