Snow-soil friction: the role of liquid water in the formation of glide-snow avalanches

Glide-snow avalanches occur when the entire snow cover slowly slides downslope until it suddenly and catastrophically releases and forms an avalanche. They can involve wet, moist, or dry snow and typically appear on slopes steeper than about 15°, where the ground surface is relatively smooth (e.g., bare rock or grass). Although the presence of liquid water at the snow-soil interface is known to be critical for avalanche release, the exact role of the liquid water and the mechanical properties of snow on gliding behavior remain largely unknown. This knowledge gap restricts our ability to predict the size and timing of glide avalanches. To better understand the lubrication at the snow-soil interface, we conducted interface shear tests to investigate the effect of liquid water at the snow-soil interface on friction. Snow samples were tested on a temperature-controlled substrate in a cold laboratory under various surface roughness conditions and snow liquid water contents. We tested two different snow types (fragmented precipitation particles and rounded grains) on four different surfaces: glass, low-friction geotextiles, and two types of sandpaper. Test results allowed us to evaluate stress-displacement behavior and investigate how interfacial liquid water and different shearing rates influence static and kinetic friction angles. On a dry, rough surface (i.e., no interfacial liquid water), the failure was within the snow sample without any sliding at the interface. In contrast, under dry conditions on a smooth surface, or lubricated conditions on a rough surface, the failure occurred at the interface. Before failure, up to the adhesive strength, we observed strain-softening behavior. For the tests where the adhesive strength was exceeded, the friction angle, both static and kinetic, showed no dependence on the liquid water content. These surprising, exploratory results call for further comprehensive studies on the role of liquid water in the fundamental processes of glide-snow avalanche release. Moving forward, we plan to refine and expand the experimental setup to investigate the role of snow compaction and assess how various snowpack properties influence glide-snow avalanche release processes.