Assessment of landslide risk of the coastal cliffs of Capo Caccia and Punta Giglio -northwestern Sardinia, Italy

The coast between Punta Giglio e Capo Caccia promontories in northwestern Sardinia is made up of high cliffs more than 37 km long. Here the cliff is only interrupted by the Mugoni - Porto Conte beach and by small rocky coves. The whole cliff is based mainly on Mesozoic calcareous rocks which generally give rise to high coasts with different contexts of evolution and risk. Only a short stretch in the northernmost portion is based on Triassic marly-clayly rocks, which form a highly unstable cliff due to the presence of gypseous intercalation which cause high-instability phenomena. This coast originates from the recent submersion of the Porto Conte bay when the bay was a wide karstic valley. The continental landscape of the whole area was dominated, under those particular conditions, by karstic landforms and a dense subterranean hydrographical network. The most known karstic cavities are located in the continental portion but, recently, submerged caves have become an interesting resource. Finally, it appears evident that the whole wave-cut cliff of Capo Caccia and Punta Giglio has undergone rapid evolution, favored by intense fracturing of limestone and deep and dense karstification of the rock both along the fractures and along the joints. This rapid cliff evolution is also demonstrated by the numerous landslides along the coast and the absence of fossil notches. In order to identify the risk areas of this suggestive coast, that also correspond to a Marine Protected Area and partially to a Regional Park, a GIS-based map of geomorphological risk related to the instability of the cliff was made. Such map indicates four hazard classes determined by the detection of fractures recognized exclusively along the face of the cliff and by the landslides occurred along it.