Seismic and Impact–Pressure Monitoring of Flowing Avalanches

Abstract

Abstract Continuous records have been made during the passage of dry–snow avalanches of both seismic signals, which allows the avalanche speed to be estimated, and impact pressures on load cells with surface areas of 645 and 6 450 mm2. The impact pressure recordings show an initial peak followed by a base pressure. The observed initial and base pressures vary strongly within avalanches and from one avalanche to another, but, on average, they can be correlated with the frontal speed and the density of the deposited avalanche snow. It is concluded that well–developed dry–snow avalanches have an unsteady wave motion similar to the slug flow observed in ultra–rapid flow of water, and that they consist of three stratified components: dense flowing snow at the bottom, light flowing snow, and powder snow.