Susceptibility to Sea Cliff Failures at Cala Rossa Bay in Favignana Island (Italy)

Since the Roman Age and until the last century, an intense quarry activity took place at Favignana Island (Sicily, Italy) that significantly changed the morphology of the eastern part of the Island that is characterized by sea cliffs. This mining activity produced an extensive network of open air quarries, underground quarries and tunnels, locally named “Pirrere”, that are hosted into Pleistocene calcarenites. The sea cliffs of the eastern coast of Favignana Island were also influenced by the past mining activity and they are currently affected by diffused instabilities as proved by the wide block-size talus distributed all along the coast. A more detailed slope stability analysis was performed on a sea cliff located in the western sector of Cala Rossa Bay. To constrain such an analysis, engineering-geological field and remote surveys were carried out to reconstruct the geological setting as well as to characterize the mechanical properties of the rock mass. Finally a 3D model of the joints net was obtained. Based on geometrical and geomechanical joints features, a kinematic-compatibility analysis for rock landslide mechanisms (i.e. planar sliding, wedge sliding and toppling) allowed to identify 78 rock blocks particularly prone to failure. Considering hydrostatic pressure related to joints saturation condition as well as pseudostatic forces due to earthquake, 12 hazard scenarios were considered as reliable for the sea cliff area. The obtained results demonstrate that: (i) planar and wedge sliding are more suitable landslide mechanisms respect to toppling; (ii) the SE part shows higher susceptibility to failures; (iii) water pressures within joints play a more destabilizing action respect to earthquakes. Such an analysis represents a preliminary contribution to manage protection strategies for reducing the landslide risk in the touristic site of Cala Rossa bay and to preserve the unique heritage of the “Pirrere” quarries.