Measurement and Analysis of the Motion of Dense Flow Avalanches

Abstract

Continuous avalanche flow speed measurements from start to stop of dense flow avalanches, and localized flow depth and slope perpendicular flow speed profiles, have been measured using X-band radar equipment- Maximum flow speeds of up io 65 m/s have been measured in large avalanches. Comparison of measured flow speeds with Voellmy-type model calculations shows that traditionally chosen sets of parameters, evaluated from runout measurements, cannot model the measured high speeds in the track. To get an improved quantitative understanding of flowing avalanches, it is proposed that from the start to the stop different flow regimes with different mechanical characteristics are passed through. This is based on theoretical studies of the movement of granular materials, where in adddition to the flow velocity a mean random fluctuation velocity of grains is introduced. A partly or fully fluidized state may be taken according to whether the ratio of frictional to collisional energy loss is smaller or larger than unity. In a third regime the snow is non-fluidized, ie pure gliding of the rigid snow. A good agreement of measurements with the proposed mechanisms is shown.