Preliminary observations on collapse sinkholes distribution in central-southern Apennines

This study focuses on karst collapse sinkholes of the southern and central Apennines region (Italy), and has the aim of outlining and discuss the factors which contribute to the occurrence of collapse phenomena. By the analysis of the morphometrical/morphological features of the about 600 initially identified sinkholes, about 50% were interpreted as collapse sinkholes related to karst phenomena, which are the object of this study. These were geo-referred and organised in a data base. In the data base was also reported information on the geological-structural and hydrogeological features of areas affected by the collapses. The collapse sinkhole census was paralleled by an analysis of the distribution of the main mineral springs (H2S and CO2 rich waters), of travertine bodies and of extensional faults with late Quaternary activity, which were all considered significant to the study due to the interrelations linking travertines, karst solution processes, CO2 rich waters and faults. Furthermore, with the aim of investigating the role of seismic shaking in the occurrence of the collapses, the karst collapse sinkhole distribution was compared with the distribution of stronger historical earthquakes epicentres.The results of this regional scale synthesis suggests a possible key to the interpretation of karst collapse phenomena. The latter, in fact, appear correlated to the combination of peculiar conditions, which may be envisaged in the presence of active faults and mineral waters. The study, in particular, suggests that karst collapse sinkholes result from enhanced dissolution phenomena related to the uprising of deeply derived fluids, for which active faults represent preferred pathways, and favoured by the presence of a relatively shallow water table. In the collapse events, an important role is possibly played by seismic shaking.