Glide-snow avalanche formation: First insights from soil and snow monitoring

Glide-snow avalanches release due to a loss of friction at the interface between the snowpack and the ground. As a result, these avalanches can involve large snow volumes and can have a high damage potential. It is hypothesized that glide-snow avalanche release is linked to the presence of liquid water at the snow-soil interface, but the driving physical processes are poorly understood. We therefore monitored soil and snow properties at our Dorfberg field site above Davos, Switzerland. The field site is a south-east facing slope with frequent snow gliding and glide-snow avalanches. Our soil monitoring setup consisted of two parts. First, we installed a grid of 22 combined, water content and temperature sensors just below the soil surface. The grid covered the entire field site to increase the likelihood of avalanche release above a sensor. Second, we installed two vertical sensor profiles in the soil, each measuring matric potential, water content, and temperature at three depths down to -20 cm. These profiles were continued in the snow with water content and temperature sensors at three heights up to 20 cm. This allowed us to detect gradients and the direction of water flow across the snow-soil interface. Initial results from glide-snow avalanche events showed an increase in water content with increasing snow depth in the days preceding the event. In addition, the soil was close to saturation (high matric potential) and the soil temperature across the entire slope was constant and above 0 °C before release. Although more data are required to confirm our findings, these initial data provide a valuable step towards identifying the driving physical processes at the snow-soil interface. This will help to better understand the source of interfacial water and to improve glide-snow avalanche forecasting.