Geological, geomorphological and hydrogeological study of Liro and Livo catchment basins (central Alps).

Landslides involve many different geological materials around the world. The mechanics and processes controlling mass movements in mountain environment are object of studies and analyses. Landslides occur when the shear strength of a layer in a slope becomes smaller than the shear stress. Various kind of factors can induce this strength variation for example: fluvial action, changes in groundwater level, earthquakes, human activity and also vegetation effects, fault influence, rock and soil properties. This thesis gives an analysis of slope processes to understand how geological, structural, climatic and geomorphological factors are responsibles for instabilities. Liro and Livo catchment basins are the object of this study. They are located in the north-western side of Como Lake, in Lepontine Alps. Several landslides occur in this area. Their study is fundamental to understand the landscape evolution and their impact on the territory. Geological and structural setting of this area is very complex: its relationship with the Insubric Line (and in particular with its brittle branch, the Tonale Line) and the influence on rocks strength are important data to know the triggering area of debris flows and debris avalanches. In particular the Geological Strength Index (GSI) analysis has demonstrated how rock mass behaviour is influenced by presence of structural lineaments more or less conjugated with the Tonale Fault and how this method could be utilized as an indicator of natural failure. The rainfall data show that this area is one of the most rainy zones of the Lombardia Region: the pluviometric analysis involving the calculation of height of rainfall and time of concentration (Tc), have underlined that this regime could induce mobilization of incoherent quaternary cover and trigger landslides. The slope vegetation recovery is an other important indicator for the landslide monitoring because it can give information about the age of the erosive processes. A detailed analysis of three series of aerial photos (1954, 1983 and 1998) have allowed the calculation of extinction and occurrence rates for the analysis of Liro and Livo catchment basins. This aerial analysis and interpretation, in addition to field survey, has shown a high number of landslides classified as debris flows and debris avalanches. A statistical analysis of the Liro and Livo areas and volumes has given the respective limites to understand the potential risk of the area and to estimate the general instability. In fact the volumes mobilized are approximately 450.000 m3 for an area of 300.000 m2