Cover collapse sinkhole over a deep buried carbonate bedrock: The case study of Fossa San Vito (Sarno - Southern Italy)

Abstract

Sinkholes are widely found in Italy in both carbonate slopes and alluvial plain settings. Since they may occur catastrophically, without showing premonitory signs and resulting in severe economic losses and casualties, they constitute a significant risk in many areas, and even pose a threat to human life. In this paper, we carried out a detailed multidisciplinary study of the Fossa San Vito sinkhole (southern Italy) that is a particular type of cover collapse sinkhole. The latter is a sub-circular, closed depression, with a diameter of ~200 m and with inner walls up to 25 m high, located in the piedmont area placed along the inner border of the Sarno River alluvial plain. The study entailed morphological and stratigraphic analysis by means of field surveys, including nine trenches, four boreholes, and the reinterpretation of stratigraphical data from the literature. In addition, hydrogeological and soil gas analysis were carried out to investigate the possible role of deep-water uprising. The study attempted to identify the genetic mechanism and include the reconstruction of a detailed subsurface stratigraphic model, showing that the infilling of the depression is about 45 m thick and consists of well-laminated, silty-clay lacustrine sediments interbedded with tephra layers. 14C dating of fossil wood found at the base of the lacustrine deposits constrains the age of the collapse at 5483 cal. years B.P. The collapse of the topographic surface involved a volume of about 400,000 cubic metres and originated at depth >80 m.