A random kinetic energy model for rock avalanches: Eight case studies

[1] We apply a numerical avalanche dynamics model to predict runout, velocity, and spatial distribution of deposit thickness of eight rock avalanches. The model solves depth-averaged mass and momentum conservation equations for avalanche flow in general three-dimensional terrain using a second-order finite-volume method. In this paper, these standard mass and momentum equations are supplemented with an additional relation describing the production and decay of the kinetic energy associated with the random motion of rock fragments within the avalanche flow. Using results from full-scale experiments with granular snow avalanches, we show that the random energy cannot perform mechanical work. Therefore, fundamental thermodynamic constraints exist between frictional shearing and the production of random energy that explain the reduction of flow friction as a function of the random kinetic energy fluxes. We utilize this result to extend the Voellmy avalanche rheology and simulate the eight case studies using one parameter set to avoid site-specific parameter tuning. This procedure allows us to evaluate and compare simulation results of the case studies and gauge model performance. Our results support the hypothesis that the production of random kinetic energy within the flow is of relevance in the runout of rock avalanches. Although this random kinetic energy description is capable of reproducing a wide range of avalanche behavior, including extreme runout, more work is required to relate material properties of different rock types to the coefficients governing the production and decay processes. Furthermore, the fragmentation process itself must be included in the model to limit production rates.