Sinkhole clusters after heavy rainstorms

Sinkholes are the most common geological hazard in karst terrains. Generally triggered by rainstorms or by changes in the hydrological/hydrogeological regime, they display a wide range of morphologies and sizes. Typically, the main difficulty in evaluating the sinkhole hazard is represented by the collection of reliable data about time of occurrence of the events, which is a mandatory requirement for the estimation of the hazard. In this paper, we document a dozen sinkholes triggered by a heavy rainstorm that occurred during the first week of September 2014 in the Gargano Promontory of Apulia (southeastern Italy). Following a description of the rainstorm, two clusters of sinkholes are described, starting with the identification of the sinkhole type and of the main morphometric characteristics. Even though it is very likely that the documented sinkholes are only a fraction of those caused by the September 2014 rainstorm, this documentation provides insights for the collection of important sinkhole data produced by a specific, triggering storm.