High mobility of rock-ice avalanches: Insights from small flume tests of gravel-ice mixtures

Abstract Rock-ice avalanches in cold high-mountain regions have extremely high mobility and enormous destructive potential. As a special material component, ice is supposed to play a crucial role in enhancing the mobility of rock-ice avalanches. A series of small flume tests was performed to quantify the influence of the ice content, initial arrangement, and released mass on the behavior and mobility of gravel-ice mixtures, and to provide insights into the propagation mechanisms of rock-ice avalanches in their initial phase. Test results show that the run-out distance and abrupt-stopping distance increased significantly when the ice content reached 30%. This implies that a certain amount of ice was helpful in enhancing the mobility of rock-ice avalanches. With an ice content higher than 80%, the run-out distances decreased slightly. The run-out distance in the well-mixed case was greater than that in the layered-arrangement cases. Segregation, the phenomenon of ice cubes to tend toward the surface and front of the deposit, was vital for the mobility of gravel-ice mixtures. Segmentation was much more evident with an increase in ice content, which indicates that the deposit was highly dispersed and spreading. This was a key difference in the deposition morphology between cases of gravel-ice mixture and cases of pure gravel or pure ice. Although little meltwater was generated in this study, the development of intergranular water film and suction-induced cohesion caused the particles to pack more closely together and to act as clusters rather than individual particles. This study provides insights into the propagation mechanisms and deposition characteristics of rock-ice avalanches.