Item: Snow entrainment: Avalanche interaction with an erodible substrate
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Title: Snow entrainment: Avalanche interaction with an erodible substrate
Proceedings: International Snow Science Workshop Proceedings 2018, Innsbruck, Austria
Authors:
- Perry Bartelt [ WSL Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland ]
- Marc Christen [ WSL Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland ]
- Yves Bühler [ WSL Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland ]
- Andrin Caviezel [ WSL Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland ]
- Othmar Buser [ Im Meierhof, Davos Dorf, Swzitzerland ]
Date: 2018-10-07
Abstract: In this paper we physically describe how snow entrainment enhances the formation of fluidized flow states in the avalanche core, leading to low dissipative and long runout avalanches. The theory is based on two physical-mechanical descriptions. The first is to describe the avalanche interaction with the snow cover as an elastic-plastic collision. The collisional description implies that there must be a jump condition between the initial, pre-collisional and final, post-collisional avalanche flow velocity. These velocities can be determined by the application of both momentum and energy balances. The second mechanical description is to treat the avalanche core as a particle ensemble capable of assuming different statistical mechanical configurations. The configurations model different avalanche flow regimes and change according to energy fluxes produced during the entrainment process. There is therefore a direct link between the energy fluxes induced by the collisional interaction with the snow cover and flow regime transitions, particularly the formation of powder snow avalanches. Flow configurations can be amplified (fluidization) or damped (densification), according to the thermomechanical properties of the snow cover. Avalanche interaction with the snow cover therefore produces strong streamwise variations in velocity fluctuations and structure of the avalanche core. The description indicates that the avalanche interaction with the snow cover is a mechanically non-smooth process producing sudden changes in avalanche velocity. The velocity changes are both directional (blow-outs, frontal splashing) and non-directional (random particle fluctuations, turbulence). The magnitude of the energy fluxes associated with the directional and non-directional velocities we parameterize as a function of snow quality including snow temperature, water content and microstructure.
Object ID: ISSW2018_O08.6.pdf
Language of Article: English
Presenter(s):
Keywords: avalanche, snowcover, entrainment, splashing, ploughing, flow regime
Page Number(s): 716-720
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