Effects of fluid ice content and bed wetness on entrainment of debris flows induced by ice avalanches

Debris flows induced by ice avalanches (DFIs) are unique glacial debris flows formed by ice melt during the movement of a rock-ice avalanche. DFIs consist of ice, water, and soil. DFIs occur frequently in alpine regions worldwide. Soil bed erosion is perhaps the most important momentum exchange process controlling the destructive potential of debris flows. To mitigate DFI hazards, erosion characteristics must be studied in depth. However, the effect of ice in fluids on the erosion process has yet to be elucidated. Bed sediments in nature are rarely saturated or fully dry, especially considering that DFIs occur during rainfall and the infiltration of ice melt water. The existing erosion theories have adopted saturated soil mechanics to describe the failure of bed soil. This study investigated the influence of ice in fluids and the water content of bed soil on entrainment by a DFI on the basis of flume tests. The results showed that the flow charge after erosion was greater than that before erosion, with an increase ranging from 34.48% to 84.21%. This demonstrated that the mobility of the DFI was significantly enhanced after erosion. The erosion depth showed fluctuating variations. Ame increased and then decreased with increasing ice content. There was no significant linear correlation with the water content of the bed soil. The maximum pore pressure in unsaturated bed soil showed positive feedback with erosion. Based on the analysis of the contribution of collisional stresses to erosion, an erosion model for DFIs was eventually proposed.