Surface and subsurface drainage evolution of the Corfino and Soraggio karst areas (Tuscany, Italy)

Povzetek

The Pania di Corfino and Ripa di Soraggio are two minor karst areas in Tuscany, having a surface of only 11 km2, but contain more than 100 known caves. Some caves are old epi-phreatic passages testifying to a discontinuous lowering of base level in the two major valleys that cross the carbonate outcrops: the Serchio di Soraggio and the Fiume rivers, respectively located along the NWand SE borders of the massif. The spatial-altimetric distribution of major caves, whichare found on a vertical range of a few hundreds of meters, and their relationships withthe position of surface alluvial deposits have allowed to infer a first evolutionary framework of karst during the late Quaternary. If we refer to a simple model, where fluvial deposition occurs mainly during cold stages and incision during warm stages, the discrete distribution of cave passages suggests that the different epi-phreatic phases are the responses to the alternation of cold and warm periods. In any case, the re-organization of the river network induced by the tectonic uplift had a relevant effect on cave systems. First, the underground diversion of surface drainage enhanced the downcutting of NWand SE peripheral streams, whichreceived a larger quantity of water throughkarst springs due to the favored morpho-structural setting. Successively, the backward piracy of the allogenic catchments of the karst systems by surface tributaries led to the dewatering of caves and to the present situation.