Failure of Marmolada Glacier (Dolomites, Italy) in 2022: Data-based back analysis of possible collapse mechanisms as related to recent morpho-climatic evolution and possible trigger factors

Abstract. A small, isolated portion of the Marmolada glacier partially broke off on July 3, 2022. The detached ice mass had an estimated volume of 70,400 m³ and slid down the slope killing 11 mountaineers after having travelled for approximately 2.3 km along the northern slope. This event is considered among the deadliest ice avalanches historically recorded in the Alps. The cause of the collapse is most likely to be closely related to anomalously high air temperatures in late spring and early summer of that year and also to progressive warming of basal ice layers and subglacial permafrost. Increased melting resulted in significant amounts of water that could not be discharged but remained trapped in crevasses of the isolated, cold ice body. The usually high permeability of karst systems in limestone are likely to have been blocked by subglacial and surrounding permafrost rocks, thereby increasing basal water pressure. Morpho-climatic data, satellite and aerial images and geophysics were analysed to better understand role and interaction of the controlling factors. This enabled the implementation of a conceptual model that was further investigated through numerical simulations using the Limit Equilibrium Method. The outcome from the back-analysis indicates that a combination of driving forces was required to finally trigger the collapse. The seasonal alternation of prolonged heating and refreezing meltwater of subglacial permafrost (i.e. the active layer) could have caused the plasticization of the basal ice resulting in the presence of a “weak bottom layer” where the available shear strength progressively dropped, finally triggering the failure.