Insights Into the Dynamics of Rock-Ice Avalanches From Small-Scale Experiments With Erodible Beds

Abstract

Rock-ice avalanches are a destructive natural disaster in mountainous regions. Along their propagation, they erode bed materials such as snow and rock. However, the mechanisms behind these processes remain unclear. Here, we have experimentally investigated the flow characteristics, erosion, deposition and impact of gravel-ice mixtures with different ice contents and bed materials. First, the flow characteristics of rock-ice avalanches have been analyzed and associated with erosion. It is found that the flow velocity and depth increase with ice content. The erosion rate is positively correlated with the flow velocity, the flow depth, and the ratio of particle collision stress to total stress, indicating that the driving mechanism of the erosion is the particle collision stress, instead of quasi-static shear. The bed material determines dominant erosion patterns and influences subsequent deposition. Then, the deposition characteristics were quantified. The deposited masses with erodible snow and ice are similar, as the higher flow mobility on snow gives more released mass reaching the deposition zone, and the smaller snow density leads to a lower eroded mass in the deposition zone. Deposition length and width keep increasing with ice content or slope angle, while deposition height first increases and then decreases. Finally, the avalanche impact force is investigated. The ice content has positive and negative effects on the impact force at different stages due to the combined effect of enhanced velocity and decreased density. The outcomes of this study offer new insights into the dynamics of rock-ice avalanches, and provide important implications for their risk assessment.