The influence of topographic parameters on avalanche release dimension and frequency

Avalanche hazard zones in Switzerland are defined by the frequency and the impact pressure of a potential avalanche event. Therefore, it is necessary to accurately estimate the release frequency and, related to the frequency, the release area for a specific avalanche track. In order to improve this hazard mapping procedure, a statistical analysis of avalanche releases on well-documented avalanche paths was performed. In the region of Davos, an almost complete database of avalanche events over the last 50 years exists. Using Geographic Information System (GIS) technologies in combination with Digital Elevation Models (DEMs), the recorded avalanche release areas were analysed with respect to topographic characteristics. Topographic parameters like “slope”, “confinement”, “aspect” and “distance to the next ridge” are derived from the DEM. The statistical analysis results in general rules and probability distributions for release extents as a function of the frequency and the topographic parameters. The general rules are a valuable aid for avalanche experts in cases where information about historical avalanche is lacking for a particular track. Furthermore, the probability distributions can be directly used as input for uncertainty modelling of avalanche run-out distances using Monte Carlo methods. This preliminary analysis indicates that mean slope, curvature and distance to the ridge are the most important parameters influencing the avalanche release area frequency; higher average slope angles lead to the frequent release of small avalanches.