RAINFALL AS A TRIGGERING FACTOR OF MASS MOVEMENTS

A. PASUTO (CNR-IRPI Padua, Corso Stati Uniti 4, 35100, Italy)
S. SILVANO (CNR-IRPI Padua, Corso Stati Uniti 4, 35100, Italy)

The paper deals with the correlation between rainfall and mass movements. The research has been carried out in the Cordevole River Basin (more than 800 sq. km) in the Dolomites (NE Italy). Through a wide collection of files available at public institutions it has been possible to obtain a large amount of data concerning landslides and debris flows which involved the area since the last century. Events which took place after 1920 have been correlated with the relevant pluviometric events known from the 12 rain gauge stations installed in the area. In spite of the difficulty of having good data during heavy and confined rainfall and of defining exactly snow melting influence, the data processing has enabled us to define mass movements which are usually connected with meteorological events occurring in the previous 15 days. Moreover it resulted that a pronunciated rainfall peak in the tail position of the cumulative rainfall curve is required to trigger landslides. Threshold values of respectively 250 mm for the 15 days cumulative rainfall and 70 mm for the peak have been defined. Nevertheless similar values of cumulative and/or peak rainfalls not always determine similar morphological changes.