Estimating bulk rheological properties of flowing snow avalanches from field data

[1] Knowing the path profile and the avalanche velocity variations with downstream distance makes it possible to deduce the bulk frictional force experienced by an avalanche during its course. This derivation was applied to 15 documented events reported in the literature. Three types of rheological behavior were identified: ( 1) the inertial regime, where the frictional force drops to zero; ( 2) the Coulombic frictional force, where the force is fairly independent of the avalanche velocity; and ( 3) the velocity-dependent regime, where the force exhibits a complicated (nonlinear and hysteretic) dependence on velocity. During its course an avalanche can experience one or several regimes. Interestingly, the Coulomb model can provide predictions of the velocity and run-out distance in good agreement with field data for most events, even though for some path sections the bulk frictional force departs from the Coulomb model. This result is of primary importance in zoning applications since it makes it possible to deduce avalanche velocities from a knowledge of the run-out distance. Its physical meaning is, however, not clearly demonstrated in this paper due to the lack of suitable data.