In the studied area the rainfalls ofautum 1973 and 1989 led to the development of gravity flows of mud and/or debris flow type and their characteristic sediments. The analysis of rain fall conditions, processes and deposits reveals that the genesis of sediment by gravity in these areas had a catastrophic and sporadic nature, and is controlled by the intensity and/or duration of rainfalls, the nature and thickness of the regolith in the slopes, the steepeness of these and development of the vegetal cover