Typology, origin and distribution of anthropogenic sinkholes in Italy

Italy is among the countries in the world hosting the highest number of cultural and historical heritage sites, both at the surface and underground. The widespread presence of artificial cavities, excavated by man all over the country in different time periods and for a variety of purposes, is a primary reason for the large number of subterranean sites. It is not a case that in Italy the studies and research about artificial cavities have played a prominent role on the international scene, leading in 2012 the UIS (International Union of Speleology) Commission on Artificial Cavities to adopt the classification originally established in Italy. Growing urban expansion in Italy, which began after World War II and had a boom during the 1960s and 1970s, has resulted, in the later decades up to today, in loss of memory of many of the cavities located below the urban areas. This is one of the factors at the origin of the high number of sinkholes which have characterized and controlled the development of many important cities such as Rome, Naples and Palermo. These cities, however, are only the tip of an iceberg, since anthropogenic sinkholes are present in practically all Italian regions, and repeatedly have caused severe damage to society, and locally casualties. In this contribution, starting from the analysis of a chronological database of sinkholes in the Italian territory, we present our considerations about the different types of artificial cavities more prone to instabilities and sinkholes, the main factors controlling the underground failures, and their distribution in the different Italian regions. The most significant case studies will be used to illustrate the above features, and to present the sinkhole hazard within the general framework of geological hazards in Italy.