Statistic/cartographic approach to the geomorphological analysis of slope instabilities in the periglacial environments of the Aosta valley (Western Alps, NW-Italy)

Geomorphological studies have been performed at a regional scale in the Aosta Valley Region (a small alpine region located in NW Italy) to better understand landslide spatial and temporal frequency and to investigate the main controlling factors of instability in high mountain areas of possible permafrost degradation. A comparison between the high mountain areas and the rest of the territory has been also performed. A great amount of data collected and analysed into a GIS system: different landslides inventories (IFFI Project Database, “Catasto Dissesti”), permafrost distribution maps and several geothematic maps produced within the research for the analysis of environmental controlling factors of instability (i.e. slope and aspect maps derived from the Digital Elevation Model for topographic factors and geological maps for litho-structural ones). Then, spatial analysis and statistical studies have been applied to 255 identified landslides within the areas with permafrost: mainly rock falls, corresponding to a landslide density equal to 0.48 events/km2 and a landslide index of 11%. Data considerably lower than the analogous values calculated for the whole region (respectively 1.18 events/km2 and 19%). Furthermore, in these areas it has been observed that, in terms of landslides mean areal extent, the obtained values are higher than those of the rest of the region for almost all types of movement (i.e. rock falls increase in the mean areal extent is more than 40%). Only in the case of Deep-seated Gravitational Slope Deformations the values are considerably inferior, because of their lower evolution degree in high mountain areas. The landslide index calculated for all the classes of the controlling factors considered within the research highlighted how, almost in all cases, areas with permafrost show lower values than the rest of the territory.