Relative influence of mechanical and meteorological factors on avalanche release depth distributions: an application to French Alps
Influence relative des facteurs mécaniques et météorologiques sur les distributions d'épaisseur de départ d'avalanches : application aux Alpes françaises.
Résumé
The evaluation of avalanche release depth distributions represents a major challenge for hazard management. This paper presents a rigorous formalism in which these distributions are expressed through a coupling of mechanical and meteorological factors. Considering that an avalanche can occur only if the snowfall depth exceeds a critical value corresponding to a stability criterion, release depth distributions obtained from a slab–weak layer mechanical model are coupled with the distribution of 3-day extreme snowfalls. We show that this coupled model is able to reproduce field data from 369 natural slab avalanches in La Plagne (France). Not only the power-law tail of the distribution, corresponding to large slab depths, but also the core of the distribution for shallow slab depths, are well represented. Small to mediumsized avalanches appear to be controlled mainly by mechanics, whereas large avalanches and the associated power-law exponent, are influenced by a strong mechanicalmeteorological coupling. Finally, we demonstrate that the obtained distribution is strongly space-dependent, and, using a consistent interpolation formalism, our model is used to obtain release depth maps for given return periods.