Landslides triggered by the intense rainstorm of June 19, 1996 in southern Apuan Alps (Tuscany, Italy)

On June 19, 1996 an exceptionally heavy rainstorm (max. rain intensity 157.6 mm/h, total amount 477.6 mm/24 h) triggered hundreds of landslides in the southern Apuan Alps, particularly in the Cardoso Torrent basin. Here, the results of a preliminary study on the landslides triggered by the rainstorm are presented. Most of the landslides were probably first time landslides and mainly involved the regolith cover of the slopes. Very rapid or extremely rapid, debris slide-debris flow was the most frequent type of movement. Because of their high fluidity, sliding masses and debris flows often did not accumulate at slope toes, but flowed into the riverbeds together with the runoff. Thus, some villages in the valley floors were nearly destroyed and there were many fatalities. Landslides were probably responsible for most damage and victims: they abnormally overloaded streams with sediments and uprooted trees, which increased their destructive capacity. The aggradation of riverbeds reduced the supportable discharge of streams and favoured their flooding. The clogging of bridge spans caused local flooding and the collapse of landslide or sediment dams produced flood waves. The catastrophe demonstrated the extreme vulnerability of the area and the need for risk scenarios and prevention measures, which are dealt with in conclusion.