Sinkhole monitoring and early warning: An experimental and successful GB-InSAR application

Sinkholes represent a natural risk which may hit catastrophically without clearly detectible precursors. However, they are often overlooked by people and administrators. Therefore sinkhole monitoring and associated early warning constitute an important research topic and only few papers about sinkhole prediction can be found about this subject. In this paper an experience of sinkhole monitoring and early warning with GB-InSAR is described. The latter is a highly precise instrument able to produce displacement maps with metric special resolution. The described activities were carried out on Elba Island (Central Italy), where karstified limestone set off the occurrence of 8 sinkholes since 2008, all within less than 3000 m2, causing major damage to an important road and many indirect losses. In 1 year of monitoring two deforming areas were detected, and the point where a sinkhole was about to propagate to the street level was precisely predicted, thus permitting the preventive closure of the road. The moving area was larger than the hole thus showing a subsidence that continued for prolonged time even after that the cavity was filled up. The occurrence of a 1.5 m wide sinkhole, undetected by the GB-InSAR, also showed the lower detection limit of the instrument.