Modeling mass‐dependent flow regime transitions to predict the stopping and depositional behavior of snow avalanches

Abstract

How terrain, snow cover properties, and release conditions combine to determine avalanche speed and runout remains the central problem in avalanche science. Here we report on efforts to understand how surface roughness, snow properties, and internal mass fluxes control the generation of granular fluctuation energy within the basal shear layers of dense flowing snow avalanches, and the subsequent influence on avalanche speed and deposition patterns. For this purpose we augment the depth‐averaged equations of motion to account for the generation of the kinetic energy associated with the particle fluctuations, and dissipation of this energy by collisional and frictional material interactions. Using high‐resolution laser scans of the preevent snow cover and postevent deposits from two avalanches released at the Swiss Vallée de la Sionne observation station, we compare measured and calculated deposition heights. The model captures flow velocities and deposition heights without ad hoc adjustments of the constitutive parameters according to avalanche size. The model parameters are separated into a terrain and other pure material (snow) parameters. The investigations reveal how release conditions and snow entrainment influence the internal mass distribution, and control flow regime transitions between the fluidized regime (head) and plug regime (tail). The comparison between the measured and calculated velocities and deposition heights demonstrates why standard Voellmy‐type submodels are suitable for many practical mitigation problems, but also why they are limited to cases where the calibrated parameters, already accounting for terrain, snow cover properties, avalanche size, and mass intake, are known.