Applicazione dei GIS nello studio dei fenomeni di debris flows dell'Appennino umbro-marchigiano (Regione Marche, Italia)

The present research regard a first geomorphologic and statistical approach to the knowledge and definition of the genesis of the mechanism and the main characteristics of debris flow phenomena that affected the calcareous areas of the Sibillini chain. The study is carried out with the GIS technology through the creation of a database that contain geometric and morphological parameters of debris flow phenomena. The study area is represented by the Adriatic slope of the Sibillini chain belonging the 325 sheet of the Regional Technical Chart (C.T.R.) of the Marche Region: it deal of an area characterized by presence of mainly calcareous lithology, frequently covered by quaternary continental deposits, and the slopes with high energy of relief and transversal valleys strong deepening and influenced by Plio-Quaternay tectonic. In the study area we are evidenced two main objectives: - the first to provide a survey about the genesis and dynamic of debris flow processes, through their localization, cataloguing, sampling and restitution in georeferentied data base, subsequently represented by the census forms; - the second, that have request the statistical elaboration of acquired data to give a case histories of debris flow events in the study area, with the possibility to extrapolate the evaluative informations (dynamic evolution of debris flows, time of recurrence, removal volume of materials, formulation of dynamic evolution of debris flow processes, to the environmental planning, etc.) applied to the territories that have the same geo-lithological and morpho-climatic characteristics of the studied areas. The debris flows in the study area, well distributed in the whole apenninic chain and apart from lithological domain, occurre prevalently during the summer connected with stormy rainfalls, short and severe, and in minor measure, during the autumn or spring, connected with plentiful rainfalls increasing of snow melting. Most of debris flow phenomena are produced along the slope very steep characterized by the top with a considerable quantity of detritus, stratified or not, easy remobilized, where the bedrock is very intensely fractured or stratified. The debris flow phenomena are produced inside the channels or the valleys that characterized the bedrock, building at the bottom of valleys very large alluvial fans or producing aggradation until some kilometres. Nevertheless in some cases it is possible to verified that these processes utilize the old avalanche channels characterized by the presence of melted detritus, easily removed. In fact the strong contribution of the trigger of debris flow processes is conditioned by the presence of snow during the some part of the winter. During the warm periods the snow melted facilitate the saturation of the debris body that slip at the bottom of the valleys.