| Summary: | The swift melting of glaciers and thawing of permafrost in mountainous regions has increased the danger of rock-ice avalanches, which poses a severe threat due to their potential transition into water-saturated debris flows. The devastating event in Chamoli, India, on February 7th, 2021, exemplifies the catastrophic consequences of such cascades of processes. Developing a model capable of predicting the dynamics and extent of these events is imperative for natural hazard science and disaster mitigation. In response, we propose a depth-averaged rock-ice avalanche model encompassing four distinct materials: rock, ice, snow, and water. The model integrates crucial physical processes, including frictional heating, phase changes, ground material entrainment, and air-blast hazards. Through a system of mass and momentum balance equations extended with grain flow and internal energy equations, the model captures heat exchanges and resulting phase changes as the fragmented material flows. Focusing on identifying the primary water source in the flow and testing the model on the Chamoli event, we quantify water’s influence on flow dynamics and regime transitions. However, uncertainties persist in heat transfer physics and quantifying the hydro-meteorological state of the flow path. Our thermo-mechanical model enables the simulation of complex avalanches and identifies key flow transitions: powder cloud formation, potential debris flow transformation. The study underscores the pivotal role of water in avalanche dynamics and the challenge of accurately quantifying water content within the flow, necessitating comprehensive ground assessments for effective disaster management.
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