An initial approach to the analysis of alluvial plain sinkhole-clusters at Finale Emilia and Reno Finalese (Modena - Italy).

Two alluvial plain sinkhole clusters in the lowermost part of the Modena Province (Italy) are illustrated. They could probably be classified as suffusion sinkholes, according the latest Italian taxonomy suggestions. Both clusters developed in orchards, i.e. in areas undisturbed by yearly ploughing. They are characterized by similar surface evidence and ground deformations, and were surveyed by geophysical, hydrochemical, GPS and traditional topographic techniques. In the first case, the cluster is located over the subsiding limb of a vertical deformation possibly coinciding with a minor (tectonic) disturbance. In the second example, the available data do not allow us to verify the existence of a buried disturbance, but strongly suggest this possibility. Direct relationships do not appear to exist between the phreatic water-table level and nearest river flood water levels. In both cases, the phreatic aquifer consists of slightly brackish waters. In the second case, a relationship between the water chemical concentration and tectonic stresses appears to be recorded. Thus, if the two clusters prove suffusion phenomena, these must be regarded as directed vertically downwards.