HR: 17:45h
AN: H44A-08    [Abstracts]
TI: Energy and dissipated work in snow avalanches
AU: * Bartelt, P
EM: bartelt@slf.ch
AF: Swiss Federal Institute for Snow and Avalanche Research, Flelastrasse 11, Davos, CH-7260 Switzerland
AU: Buser, O
EM: buser@slf.ch
AF: Swiss Federal Institute for Snow and Avalanche Research, Flelastrasse 11, Davos, CH-7260 Switzerland
AB: Using the results of large scale avalanche experiments at the Swiss Vall‚e de la Sionne test site, the energy balance of several snow avalanches is determined. Avalanches convert approximately one-seventh of their potential energy into kinetic energy. The total potential energy depends strongly on the entrained snowcover, indicating that entrainment processes cannot be ignored when predicting terminal velocities and runout distances. We find energy dissipation rates on the order of 1 GW. Fluidization of the fracture slab can be identified in the experiments as an increase in dissipation rate, thereby explaining the initial and rapid acceleration of avalanches after release. Interestingly, the dissipation rates appear to be constant along the track, although large fluctuations in internal velocity exist. Thus, we can demonstrate within the context of non-equilibrium thermodynamics that -- in space -- granular snow avalanches are irreversible, dissipative systems that minimize entropy production because they appear to reach a steady-state non-equilibrium. A thermodynamic analysis reveals that fluctuations in velocity depend on the roughness of the flow surface and viscosity of the granular system. We speculate that this property explains the transition from flowing avalanches to powder avalanches.
DE: 1815 Erosion and sedimentation
DE: 1863 Snow and ice (1827)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting