Sinkhole development at the freshwater-saltwater interface in Apulia (southern Italy)

Sinkhole phenomena widely characterize coastal environments, especially along low-topography and flat coastlines. The freshwater-saltwater interface is a transition zone where, due to mixing of waters with different chemistries, the resulting brackish mixture is highly aggressive against soluble rocks, thus causing an intense and faster development of karst processes, including sinkhole development. This is the case of the Apulia Region (SE Italy) with more than 850 km of coastline, mostly consisting of soluble rock. In the Apulian coastal areas, karst processes act as the main morphogenetic factors to produce a variety of karst landforms, among which sinkholes are definitely the most common. In the coastal Apulian karst, this effect combines with severe problems of inland seawater advancement, due to climate change, further enhanced by anthropogenic actions, such as overexploitation of the freshwater resources for agricultural, industrial and drinking purposes and heavy tourism water demand during the summer season. In this contribution we present the main cases of sinkhole development along the Apulian coastlines, occurring both in high-rock cliffs and in low beaches, on the Adriatic as well as on the Ionian side of the region. After cataloguing the cases of identified sinkholes according to the internationally accepted classification, we present an attempt to define conceptual models for the development of the different typologies of sinkholes along the Apulian coastline, and on how they control the formation of bays and inlets