The role of friction difference between ice and rock on mobility of ice-rock avalanches based on ring shear tests

Ice-rock avalanches are extremely destructive cryospheric hazards with unexpectedly high mobility, so that traditional models fail to fully capture their behavior. This discrepancy arises from the complex interaction between low-friction ice particles and high-friction rock fragments. However, this phenomenon is still not quantitatively understood due to experimental limitations, such as insufficient shear displacement and low-stress conditions. To address this issue, a series of ring shear experiments was conducted using two types of glass beads with distinct friction coefficients to represent the ice and rock particles simulating geological stress environments and capturing the large-shear displacement behaviors. The tests systematically arranged rough particle content and shear rates to elucidate the role of surface friction heterogeneity on the flow behavior. The findings revealed that increasing rough particle content significantly enhances both peak and residual shear strength, volumetric dilatancy, and apparent viscosity. A large proportion of rough particles was associated with more pronounced dilatancy and greater flow instability at higher shear rates, while ice-rich mixtures exhibited shear contraction and facilitated basal lubrication. Furthermore, the effective friction coefficient increased with both normal stress and rough particle content, revealing a nonlinear dependence contrary to simple superposition predictions. These findings establish critical insights into the mechanical segregation and pressure-dependent fluidization of ice-rock avalanches. This study isolates pure frictional effects, without thermal phase changes, providing a refined mechanistic framework essential for modelling hypermobile ice-rock avalanches and improving hazard mitigation strategies in a warming climate.