Vera Valero, C., Feistl, T., Steinkogler, W., Buser, O., & Bartelt, P. (2012). Thermal temperature in avalanche flow. In ISSW proceedings. International snow science workshop proceedings 2012 (pp. 32-37).
The thermal temperature of snow greatly influences the flow behaviour of avalanches. It is even common to implicitly characterize avalanche flow with respect to the thermal regime: “wet” snow avalanches contain warm, moist snow whereas “dry” flowing or powder avalanches consist of colder snow, below the melting point of ice. Despite its importance, thermal effects are largely neglected in avalanche dynamics calculations. In this contribution we explicitly calculate the avalanche flow temperature by considering two irreversible thermodynamic processes: (1) the shear work operating on the mean kinetic energy of the avalanche and (2) the dissipation of fluctuation energy due to random granular interactions. These energy fluxes regulate the configurational energy of the avalanche and therefore the flow form. However, a third, and perhaps more important source of thermal energy, is from snow entrainment. We model the temperature evolution of an avalanche by extending the basic set of differential equations used to simulate avalanches with snow energy entrainment in real terrain. Using an avalanche event at the Vallée de la Sionne test site, we show that the temperature of the snow in the starting zone in relation to the temperature of the snowcover encountered by the avalanche at lower elevations determines the thermal flow regime and therefore the behaviour of the avalanche in the runout zone. The inclusion of snow granule properties in flow models is essential to understand how temperature influences avalanche behaviour. Higher temperatures increase the dissipation of fluctuation energy of the random granular interactions – but decrease the shear work because of lubrication. This competition between the two primary irreversible processes in avalanches results in a wide range of flow behaviour, flow forms and depositional structures.