The source, quantity, and spatial distribution of interfacial water during glide-snow avalanche release: experimental evidence from field monitoring

Abstract. Glide-snow avalanches release at the soil-snow interface due to a loss friction which is suspected to be linked to interfacial water. To date, the formation and distribution of the interfacial water are not well understood, and glide-snow avalanches are considered unpredictable. We investigated the source, quantity, and spatial distribution of interfacial water before and during avalanche release through spatio-temporal field monitoring. The measurement setup consists of a sensor grid covering a slope with frequent glide-snow avalanche activity. The 24 grid sensors measured the soil temperature and liquid water content (LWC) throughout the seasons 2021/22 to 2023/24. Snow/interfacial temperature and LWC were monitored locally with a vertical sensor profile ranging from the soil into the snow. Seven glide-snow avalanches released on the sensor grid and their investigation showed: (i) interfacial water originated from geothermal heat, rain, and meltwater percolation, (ii) the quantity of snow LWC was lower for glide-snow avalanches that released in early winter than in spring, (iii) soil temperatures below the release area were higher than in the remaining slope if interfacial water originated from geothermal heat (iv) if interfacial water originated from rain/melt we observed (locally) higher soil LWC below the release area and (v) for four avalanches the spatial variability of soil LWC across the slope reached a local minimum at the time of avalanche release. In the future, with continued monitoring, the spatio-temporal investigation of the soil will help to quantify the drivers for glide-snow avalanche release at the slope scale. This will contribute to improved glide-snow avalanche forecasting and mitigation.