Failure mechanisms and runout behaviour of three rock avalanches in thye North-Eastern Italian Alps

The nature of the physical processes that trigger rockslope insatbility is, today, understood even if with some difficulties and simplifying hypothesis, but the striking mobility of the flow of these rock masses remains in a large part inexplicable. Three major rock avalanches in the Italian alps have been studied focusing in particular on aspects relating to the fragmentation and deposition processes. Studies have focused on grain size distribution of samples taken at different distances and elevation and on the morphology of the ground surface of the deposits. Image analysis technique was useful to complete the cumulative grain size curves to include larger particles. In none of the three cases the significant parameters of the grain size distribution and of the particles moprphology have shown any relationships with the distance from the center of the failed mass and with the height of the taken sample on the base of the deposits. The roundness of particles is practically the same within the whole deposit and even between different depositsfor which travel distances and thicknesses are different. The morphology of the three deposits gave some information on the dynamics of the phenomenon and, in particular, on the progressive thinning of the moving debris.