Karst geosites at risk of collapse: the sinkholes at Nociglia (Apulia, SE Italy)

This paper focuses on the impacts of contemporary geomorphological processes on fruition activities in a karst area of Salento (Apulia, southeastern Italy). The work illustrates the results of studies in a sinkhole field at Nociglia, in the Lecce province, recently recognized as a geosite and where shallow phreatic speleogenesis operates close to the water table level with the formation of karst caves, successive roof collapse, formation of wide caverns, and sinkhole development at the surface. All these features threaten the nearby infrastructures including a province road. Salento has a great number of active sinkholes related to natural and anthropogenic cavities. Their presence is at the origin of several problems in the built-up environment, due to increasing population growth and development pressures. In such a context, the detection of cavities, and the assessment of sinkhole hazards present numerous difficulties. To assess the potential danger from sinkholes, it is important to identify and monitor the main factors contributing to the formation process. A multi-disciplinary approach, comprising geological, geomorphological, and geophysical analyses, is necessary to obtain a comprehensive knowledge of these complex phenomena in karst areas. Geophysical methods can be of great help to monitor the processes and for identifying and mapping features related to the underground voids, by detecting contrasts in physical properties, such as density and electrical resistivity, with the surrounding sediments. At the same time, recognition of the presence of sinkholes by geophysical methods has to adapt to the local geological conditions and take advantage of the integration of the several methodologies available. The territory of Nociglia demonstrates that monitoring is essential for the safe exploitation of these type of geomorphosites.