LANDSLIDE HAZARD AND RISK MAPPING: A CASE STUDY IN ALCANTARA RIVER BASIN (NE SICILY - ITALY)

A. Amantia (amantia@mboxict.it), V. Ferrara (vferrara@mbox.unict.it), G. Pappalardo (pappalar@mbox.unict.it) Istituto di Geologia Geofisica Corso Italia 55, 95100 Catania, Italy

At the end of March an extensive mass movement occurred in the northen side of Alcantara river valley, cutting off national road 116 that links up the small towns of Randazzo and S. Domenica Vittoria and damaging cultivated terrains and country houses. Besides the landslide has reached the Alcantara river and a barrage lake conteining over than 375.000 m3 of water has been formed. During paroxystic phase, for a period of more than one month, landslide has covered 2,2 km, dragging 20 milion of cubic meter of material make up partially by old landslides. Afterwards landslide had a complex evolution, with retrogressive movements of head scarp and new bodies development, one of those has reached the barrage lake. Studies has allowed to recognize the causes of phenomenon and to explain the evolutive mechanism in this geological and geomorphological complex system, however common in northen Sicily. To value the risk levels for buildings and infrastructures have been elaborated a specific risk map using a mesh subdivision of the slope with a 100x100m cell. For each one has been calculated hazard referring to the real mass movement and vulnerability of risk subjects. Specific risk levels have been valued for different sector of the studied area, referring to established conditions of tolerable risk. A range of priority for proper measures has been defined to reducing the vulnerability through suitable field works.