Global Warming as a Predisposing Factor for Landslides in Glacial and Periglacial Areas: An Example from Western Alps (Aosta Valley, Italy)

Signals of global climate change are increasingly evident in the Alps where, in recent years, a growing number of landslides occurred in glacial and periglacial areas. In order to document such a case, a landslide is described and analysed, which affected the SE side of a rocky ridge and the Trajo Glacier below in the Gran Paradiso Massif (NW Italy) during the warm summer of 2017. It was a multiple rockfall of about ½ million m2, with vertical drop of ≈300 m, a runout distance of ≈900 m, and 17° of travel angle. Prompt field surveys, interpretation of Sentinel-2 satellite images, and an analysis of data from several weather stations, are used to reconstruct the phenomenon and its causes. This study highlights the geological structure of the area (which reflects the morphology and geo-mechanical characteristics of the slope) and the meteorological conditions during the months before the main failure. Moreover it reveals that the landslide was not a single event but developed over time through at least five failures. According to available information, several predisposing factors seem to have played an important such as the degradation of permafrost (probably affecting rock masses at depth), the alternation of freeze-thaw cycles, and the availability of a considerable amount of water from rainfall and snowmelt, infiltrating the rock mass.