Landslide dams in Italy: analysis of main predisposing factors and damming susceptibility mapping

Landslide dams result from the complex interaction, not yet totally understood, between river and slope dynamics. The study of past landslide dams and their consequences has acquired a significant relevance for forecasting and preventing their induced hydraulic risk on lives and property. The main aim of this thesis was the study of the landslide dam phenomenon and design a useful and easy tools to assess the damming risk with spatial planning purpose. The research started from the geomorphologic investigation of the Italian landslide dams and setting up an archive, updating previous studies on the same topic in smaller areas (Pirocchi, 1991; Ermini, 2000; Pacino, 2002), and integrating it through a careful literature review and cartographic and aerial photos interpretation. The collected data represents the wider example of systematic inventory in Italy, with almost three hundreds of cases selected from the Alps to the Southern Apennines, in Sicily. The research includes landslide dams occurred along the Cordillera Blanca mountain range, in Peru, to study the same phenomenon in a very different geographical, climatic and tectonic settings. A morphological analysis of the collected data was performed to identify morphometric parameters that best define the formation process of a blockage. This analysis confirmed the validity of schematizations already developed by previous authors and new morphometric indexes, useful for forecasting and planning purposes, were proposed. In particular, encouraging result came from the formulation of the Morphological Obstruction Index (MOI) that allowed to perform a reliable analysis of dam formation and provided a good estimator to forecast a landslide blocking a river, from a geomorphic analysis. In order to prevent part of the damages and suffer lower consequences related to landslide dam occurrence, an useful and practical tool was proposed, to predict which areas have a higher damming susceptibility and where preventive measures should be focused. Therefore a simple GIS methodology, useful as a forecasting and planning tool, was developed. This easy methodology, used on the Arno River basin, was able to assess with few data the damming predisposition, connected to existing landslides, and the probability of obstruction, by new landslides along a river network.