Assessment of cover-collapse sinkholes in southwest Sardinia (Italy)

The southwestern part of Sardinia has been afflicted, in recent years, by several cover collapse sinkholes mostly occurring in scarcely dense populated areas. The study area, that lies in the Iglesiente-Sulcis region, is characterised by the outcropping of the Palaeozoic basement related to the South European Hercynian chain, covered with Tertiary-Quaternary sediments. The main outcropping rock types are Palaeozoic metasandstones, metadolostones, metalimestones, shales and metaconglomerates, and Tertiary-Quaternary fluvial-lacustrine continental sediments. The combined application of several geophysical techniques integrated with boreholes and geotechnical as well as hydrogeological measurements, proved to be very useful and promising in defining in detail the geological context in which each sinkhole has formed, and the gravity method, even used alone, proved to be very effective for detecting the regional geological structures to which sinkholes are related. Eventually, the historical analysis of phenomena, the geological knowledge of the Iglesiente-Sulcis area and the results of properly designed geophysical surveys, can allow to determine the most probable areas where cover-collapse sinkholes can occur in the future. Thus, in order to prevent human losses and material damage, construction and settlement could be avoided, or at least controlled by proper rules, not only in the areas that already have been interested by collapsing phenomena, but also where hazard conditions have been recognized.