## 2 Materials and Methods  
### Study Area  
The study area was the Valle d'Aosta territory, an alpine region located in the extreme north-western sector of Italy.  
From a geological point of view, this region belongs to the Alpine chain, and it is delimited by two important geological lines: the Periadratic fault system to the south and the Penninic front to the north. The geological units outcropping in Valle d'Aosta have been reclassified into 16 litho-technical groups, which are shown in Figure 1.  
Regarding the geomorphology of the area, the region is a mainly mountainous zone characterised by a very variable altitude, with values from 300 m a.s.l. to more than 4000 m a.s.l. with the main peaks of the Alpine orogen [28]. The area corresponds to the mountain section of the Dora Baltea River basin, a glacial valley with an east-west orientation that is the main evidence of Quaternary glaciations [28] (Figure 2). The main phenomena that shape a mountain territory are mass movements and glaciers. In fact, the Valle d'Aostaterritory was mainly influenced by the Pleistocene glacial phases that shaped the main valley and the tributary valleys; in the region, there is evidence of glacial modelling as both erosional and depositional forms. The subsequent fluvial action changed the landscape through the deepening of the glacial valley floors, the erosion of glacial deposits, and the formation of alluvial deposits [29].  
In addition to glacial phenomena, gravitational movements play an important role in the modelling of the region. Indeed, the geological history and the morphology of the territory cause the presence of numerous mass movements of different types and sizes. In this regard, the data of the _Inventario dei Fenomeni Franosi in Italia_ (IFFI, landslide inventory in Italy compiled by ISPRA [30; 31]) Project show a 17.8% landslide index; this means that almost 18% of the regional area consists of landslides [29]. The IFFI inventory is the only homogeneous landslide inventory at a national level, and it is a fundamental instrument for landslide risk assessment and management. The IFFI Project does not include phenomena related to torrential processes, e.g., debris flows, because they are considered extraneous to a landslide inventory. Specifically regarding the Valle d'Aosta region, due to the morphology of the territory, which is characterised by high steepness, the most common landslides are the rapid ones, such as shallow landslides and rockfalls. In fact, the IFFI inventory includes 612 polygons of rockfalls/topplings and 728 polygons of shallow landslides out of a total of 2145 landslides mapped. The climate also plays an important role; the marginal mountainous areas are characterised by an alpine climate with high rainfall/snowfall up to 1100 mm/year [32], and slope steepness and rainfall are among the main triggers of mass movements. A further factor that causes slope instability conditions in Alpine regions is snowmelt. Therefore, global climate change leading to more intense rainfall and the  
Figure 1: Litho-technical map of the Valle d’Aosta Region, Italy, distributed by regional authorities.  
growing anthropogenic impact are the main causes of the continuous increase in mass movements. There are several geological and geomorphological studies [33; 34; 35; 36] dealing with the relation of slope instability in glacial valleys with freeze-thaw cycles, and in particular with the pressure release following glacier retreat.