Sinkhole evolution in coastal settings: some examples from Southern Italy.

The southernmost sector of Apulia Region can be described as a karst peninsula surrounded by the Adriatic and the Ionian Seas. The process of seawater intrusion, together with groundwater outflow, mainly coming out at the coastline, produces a water mixing that enhances the solution of soluble carbonate rocks. The effect of these processes can be observed along the coastline, characterized by several areas interested by sinkhole development and evolution. In some cases, they have become famous touristic attraction as at Grotta della Poesia, visited every summer by thousands of tourists; in other cases they represent spectacular sites of high ecological values, since they host peculiar ecosystems, with many fauna and flora species. At several sites along the Apulian coasts, sinkhole evolution form elongated bays, completely protected from sea waves, as in the sector between Fasano and Brindisi. Along this coastal stretch, field surveys revealed different sinkholes stages that can be described as successive phases in the development of bays: from opening of individual collapse sinkholes, typically at distance lower than 20 m from the coastline, to evolution in elongated sinkholes deriving from coalescence of nearby features, eventually leading to the final stage, with formation of protected bays, which main elongation depends upon the main discontinuity systems in the rock mass, and the main direction of sea storms as well. These examples highlight the importance of sinkhole processes in predicting the future evolution of the coast, and may be of help to local authorities for the most proper management of such a fragile environment.