Definition of sinkhole prone areas and their monitoring. A case study in Latium (Pianura Pontina)

Abstract

In Italy, natural sinkhole phenomena which are not connected to karst processes are relatively frequent. In the southern plain of Latium (Pontina area), for example, several small subcircular lakes are described, whose formation is thought to have been caused by erosional processes related to vertical turbulence and/or piping in alluvial sediments. At the present it is impossible to think about an estimation attempt for the hazard/risk due to the complete lack of adequate information about the whole plain. A gravity survey carried out some years ago in whole plain shows several negative gravity anomalies. Later, in the last decade, some negative gravity areas were also studied by microgravity surveys. Microgravity results show that these phenomena could tend to develop in different geological settings, from the apex of the alluvial fans down to the lower alluvial plain, generally within relatively short distances from streams and artificial channels. Gravity information set can allow us to select a peculiar areas to be submitted to further intensive monitoring and surveys such as: 1) microgravity surveys to detect negative gravity anomalies; 2) high-resolution geophysical surveys; 3) continuous areal leveling to detect the (negative and positive) vertical motion; 4) gas seepage monitoring; 5) water seepage monitoring. In terms of hazards, at the present, it should at least ask whether the sinkholes on the inner side of embankment body could also evolve towards underseepage phenomena, where negative gravity anomalies was detected.