Warming-driven weakening of basal ice layer as a critical cause of ice avalanche activation

Increasingly, researchers are beginning to focus on the correlation between climate warming and frequent ice avalanche (IA) events. Previous studies have revealed that mixtures of ice and rock debris (IRM) are commonly distributed in contact zones between alpine glaciers and bedrock. However, the changing mode of mechanical characteristics of basal ice-rock mixed layer in warming conditions and its contribution to ice avalanche has not been fully appreciated. Using the temperature-controlled triaxial test and numerical modeling, we investigated the mechanical behavior of the basal ice layer under changing temperature conditions and its contribution to IA events. Our research indicates that the IRM deformation mode changed significantly from freezing to thawing environment (−8 °C to 2 °C), accompanied by decreased IRM brittleness and residual strength. Furthermore, the cohesion and friction angle of IRM drop off rapidly during around −2 °C to 0.5 °C, with rates of 72.2 kPa/°C and 3.1°/°C respectively, noticeably faster than their decay rate in a frozen environment. We suggest that warming-induced reductions in IRM strength disrupt the force balance in the IA source zone, as the basal ice layer is deprived of the resistance to glacial sliding that it provides in a frozen condition. Furthermore, our numerical investigation reveals the stress evolution process and damage pattern of the basal ice layer during IA initiation. These analyses contribute to a better understanding of the role played by the weakening of the basal ice layer in IA activation in the context of climate warming.