A huge cultural and historical heritage at risk: the underground settlements of southern Italy

The artificial cavities, excavated by man in different epochs and for many different purposes and functions in southern Italy, are increasingly suffering from problems of instabilities, which upward propagation may reach the ground surface and cause sinkholes. In addition to the main towns, as Naples and Palermo, where thousands of cavities of different sizes mark the urban and peri-urban territories, all the historical parts of towns and villages, and large rural sectors as well, are filled with man-made caves, that often pose nowadays serious risk to the built-up environment. As shown in many recent works, underground quarries are the type of artificial cavity that has caused the most severe problems in the last decades. In this paper, on the other hand, the hypogean civilian dwellings are taken into account: these are complexes of tens or hundreds of caves, that as a whole represented old villages, with civil dwellings, religious sites, and hydraulic works to guarantee the availability of the water resource to inhabitants, even during the hot dry season. In southern Italy, and in particular in the eastern regions (Basilicata, Apulia), such settlements were realized along the rock cliffs of gravine, the term used to designate the typical valleys of fluvio-karst origin, excavated in the Pliocene-Pleistocene calcarenites. With time, abandonment of these cavities, combined to degradation of the sites (often used as unauthorized landfills) and to water infiltrations, resulted in frequent collapses, that locally may threaten the nearby infrastructures and buildings. The issue of collapses linked to artificial cavities has therefore become important even for civil protection, and has to be carefully evaluated, in order to guarantee the safety of people and structures. In this paper, through description of some recent case studies, this topic is dealt with, aimed at pointing out the need to avoid degradation of this precious heritage, for preserving its remarkable cultural importance, and for mitigating the risk to society related to likely collapses and failures as well.