Failure of Marmolada Glacier (Dolomites, Italy) in 2022: data-based back analysis of possible collapse mechanisms

A small, isolated portion of Marmolada Glacier broke off on 3 July 2022. The detached ice mass had an estimated volume of 70 400 m3 and slid down the slope, killing 11 mountaineers after having traveled for approximately 2.3 km along the northern slope. This event is considered among the deadliest ice avalanches historically recorded in the Alps.The unusually high air temperatures in late spring and early summer of that year led to an excess of meltwater, which, since mid-June, had overpressurized the englacial discharge network, partly blocked due to frozen conditions at its base. Ice temperature, subglacial permafrost and heat exchange from meltwater were among the primary factors controlling the thermal state of the sliding surface.The cause of the collapse was investigated by exploiting a conceptual model that was further corroborated through simplified numerical simulations using the limit equilibrium method. Pre- and post-failure satellite and aerial images, laser mapping, and geophysics and morpho-climatic data were gathered in a comprehensive database and analyzed to better understand the role and interaction of the predisposing and triggering factors as well as their mutual interaction. Particular attention was given to reconstructing the varying conditions of the failure surface, which developed partly along ice foliations near the glacieret's base and partly right at the ice-bedrock interface. An earthquake triggering the failure was excluded based on the processing of the available seismological observations.It transpired that none of the three forces considered in the numerical analysis - namely, hydrostatic pressure in crevasses, hydraulic jacking and basal friction reduction - individually caused the condition of instability. To reach this condition, it was necessary to invoke a combination of these actions, for which it was finally possible to estimate their relative weights.