Failure Mechanisms of the Mount Catiello Rock Avalanche in the Sorrento-Amalfi Peninsula (Southern Italy)

A complex landslide, which mobilized a calcareous rock mass of about 60,000 m3, occurred on January 3, 2002, along the southwestern slope of Mt. Catiello, above Positano (province of Salerno, Italy). According to established classification schemes, such a landslide can be classified as a rock avalanche or as a complex, dry, extremely rapid rock fall—dry, extremely rapid debris flow. Landslides of this type and dimensions are quite rare in the southern Apennines, and even rarer in the Sorrento-Amalfi Peninsula. Therefore this one represents a singular case for assessing both the mechanisms leading to such a type of sudden, often hazardous mass movements, and the residual hazard still existing on Mt. Catiello. Due to the inaccessibility of the near-vertical rock slopes, the characterization of the instability mechanisms of the landslide was based on analyses of terrestrial stereoscopic photographs, taken from lateral and frontal positions with respect to the 2002 depletion zone, and on measurements/validations of structural settings carried out in accessible sectors of the mountain. Currently, the southwestern slope of Mt. Catiello, which corresponds to the depletion zone of the 2002 landslide, cannot be considered more unstable than the adjacent northern slope, where a smaller rock mass tower, with a volume of 20,000 m3 and clear signs of a propagating deformation-fracturing process at the base, was identified. Considering this remaining unstable rock tower as a part of the mass movement, the distribution of activity of the landslide can be considered as widening, and its state of activity as suspended.