The role of capillary forces in the formation of interfacial water layers in “cold” glide-snow avalanches

Glide-snow avalanches are generally thought to come in two flavors: “cold” and “warm”. The main difference between them is the mechanism by which liquid water is generated and reaches the basal snowpack. For warm avalanches, the water comes from the snow surface via rain or surface melt. For cold avalanches, the water is thought to be generated by capillary suction or geothermal melting. Here, we focus on cold avalanches and address the role of capillary forces at the soil-snow interface. To do so, we combine theoretical considerations, snowpack simulations, and field data. Calculations based on basic principles show that the conditions necessary for capillary suction are unlikely for the representative soil types, because high soil saturation is required. Field data from the “Dorfberg” field site above Davos (eastern Swiss Alps) confirms that these saturated conditions rarely occur. Simulations of two “cold” glide-snow avalanches at the field site further confirm (i) the absence of capillary suction and (ii) the presence of geothermal melting. Thus, we suggest that in the absence of a distinct water source (e.g. spring), geothermal melting is likely responsible for the formation of liquid water in cold avalanches, while the capillary forces are responsible for the retention of this water within the basal snowpack layers.