A mechanics-based initiation criterion for ice avalanches: Linking fracture parameters to glacier-scale instability

Glacier velocity is a critical indicator for the prevention and mitigation of glacial hazards, yet its intrinsic link to ice avalanches (IAs) remains insufficiently understood. To elucidate the physical mechanisms connecting glacier velocity and IA, this study analysed pre-failure glacier motion in the Sedongpu Valley using Sentinel-2B remote-sensing imagery. Accordingly, we propose a mechanical pathway in which glacier acceleration increases the deformation rate of ice, reduces its fracture toughness, and thereby promotes IA initiation. Low-temperature four-point bending (4 PB) experiments quantified how ice fracture toughness and crack-tip yield strength (CTYS) decline progressively with increasing strain rate and temperature. The unsupported ice mass was idealized as a cantilever beam containing a single crevasse. Geometric sensitivity analysis indicates that overhang length and crack length are the primary controls on tensile stress concentration, forming the basis for a tensile-failure criterion for IA initiation in hanging glaciers. These results reveal a mechanical pathway whereby glacier acceleration reduces ice crack-growth resistance, thereby promoting IA initiation. Validation against the Eiger hanging-glacier event further shows that glacier acceleration can serve as an external signature of increasing strain rate, fracture-toughness degradation, and progressive damage accumulation. This study provides a new perspective for elucidating the initiation mechanism of tensile-type IAs in hanging glaciers.