Assessments on debris flow distribution, triggering and evolution in the Dolomites area (North-Eastern Italy).

Debris flows are considered among the most dangerous and destructive processes that affect mountainous areas all over the world. In Italy debris flows are very common in all the Alps, and in particular in the Dolomites (North-Eastern Italy). This paper concerns the study of debris flows distribution, triggering and evolution in the Cortina d'Ampezzo area, located in the Eastern Dolomites, sample study area over about 30 years in the context of National and European research projects. The morphology of the area is characterised by sub-vertical dolomitic cliffs and a thick talus developing from their base to the valley bottom. Through the analysis of aerial photographs, 325 debris flows, both channelized and hillslope type, have been detected. They all originate at the rock cliff base and develop towards the valley floor. The morphometric and hydrologic parameters of the rock headwater catchment and of the transport and deposition zones have been measured for each debris flow, as well as the recording of the rainfall responsible for the triggering process. The debris flows have been divided according to their type (hill-slope or channelized) and rock headwater catchments which do not give rise to debris flow have been considered separately. All the collected data have been statistically analysed getting some general conclusions especially regarding the headwaters that do not originate debris flows. The mean channel lengths increase over the years, and this would seem in connection with an increasing trend of total annual rainfall and frequency of maximum intensity since the late 1980s.