May subcutaneous evaporites enhance the risk of suffusion dolines? Examples from Emilia Romagna, Piedmont, Apulia (Italy) and Cardona (Spain) and Siberia (Russia).

Evaporite rocks (mainly gypsum) crop out in many European regions and normally display a wide variety of both surface and underground dissolution landforms. On the contrary, when evaporite rocks are overlain by an even thin layer of more or less permeable material (sands, gravels etc.) the absence of turbulent flow of the percolating water does not allow for a great deal of dissolution. This can be explained by the fact that the dissolution of gypsum and halite is controlled by the diffusion from the water film in contact with the rock and the solution, which is negligible in absence of a turbulent flow. Thus, in normal conditions, the development of suffusion dolines in covered evaporite formations is a rare phenomenon. There are, however, some factors that can ultimately lead to the formation of great sinkholes in very short lapses of time (some hours) and without any warning signs in covered evaporites. There are three main mechanisms that can lead to these phenomena: 1- presence of hypogenic caves; 2- turbulent subcutaneous water flow; 3- emptying of paleokarst by piping. While the collapses of the first type can develop in a completely natural way, and for this reason are relatively difficult to predict, those of the second and third type are normally induced by human activities and therefore can be avoided or minimised through good management practices of the territory.