Large glacier failures in the Italian Alps over the last 90 years.

Ice failures are among the least known and least studied mass movements, both because large events are quite rare, and because they usually develop in remote and little-frequented areas. However, the unprecedented transformation of glaciers due to climate change, on the one hand, and the growing human pressure on high-elevation environments, on the other, nowadays require a more careful and in-depth consideration of these hazardous processes, such as tragically highlighted by the collapse of the Marmolada Glacier (Italy) on July 3, 2022. In this context, a review of existing documentation on past glacier failures is essential to learn about their spatio-temporal distribution, the characteristics of the glaciers where the failures occurred and flow properties. In turn, these findings are fundamental to inform the assessment of current and future hazards. The present work contributes to the topic by documenting, cataloguing, and analysing the glacier failures larger than 10,000 m3 that occurred in the Italian Alps in the period 1930-2022. Sixty-eight glacier failures are documented, which affected 29 glaciers distributed throughout the Italian Alps. The volumes of glacier failures are mostly between 10,000 and 50,000 m3 (1.1 × 106 m3 in one case). The events occurred mainly in summer, with a frequency peak in August. The H/L ratio, i.e. the ratio between the vertical (H) and horizontal (L) distances covered by the process, indicator of the mobility of the detached mass, is between 0.33 and 0.80. Although glacier failures can occur during both glacial advance and retreat, we found a sharp increase in the number of documented cases since the 1990s. We are aware that, due to the difficulty of finding information, the dataset provided in this work is only partially representative of the glacier failures that occurred in the Italian Alps in the period considered: nevertheless, it is a useful starting point for studies aimed at assessing hazards related to glacier failure, and for risk mitigation. Given the speed and intensity with which glaciers and their surrounding environments are evolving in response to climate change, their continuous observation is essential, as is the systematic documentation of glacier failure events. Remote sensing data and tools can nowadays facilitate glacier monitoring and the documentation of ice failures: however, field data such as those collected during the annual glaciological surveys of the Italian Glaciological Committee (CGI) remain fundamental for the validation of remote sensing data and numerical models.