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Melting in Ice Avalanches

Dr Barbara Turnbull
Fluid & Particle Processes Group, Faculty of Engineering, University of Nottingham

Avalanches are a fascinating natural phenomenon that pose an evolving risk as increasing numbers of people take on the challenges of winter climbing and ski-touring. The hazard is also changing as climate patterns shift, bringing into question the use of historical records in assessing risk. There is a strong need for a physics-based approach to understanding the key processes that influence the dynamics of these flows, so that potential run out distances and impact pressures can be determined.

This talk will focus upon the hazard posed by avalanches of rock & ice. These can arise from collapsing glacier séracs, rock-faces previously stabilised by permafrost or the activity of an ice-capped volcano. The extraordinary mobility of the extreme event at Karmadon, Russian Caucasus, in September 2002 brought such ice-bearing flows into sharp focus. Here, we explore the hypothesis that localised melting within such ice-bearing flows may significantly alter the dynamic characteristics compared to a classical dry granular shear flow. Building sandcastles on the beach as children, we relied on the mechanical strength of moisture coating the sand grains to hold our structures together. Furthermore, when we ice skate it is in fact a microscopic ‘pre-melted’ water film between blade and ice that allows us to glide over the surface. So, when considering the granular mechanics of ice, can we expect these two phenomena to interact? The dynamical effects of melting processes that lead to wetted particle surfaces are here investigated in a laboratory experiment.