Hypogenic Caves in the Apennine Mountains (Italy)

Hypogene speleogenesis is important for karstification in the Apennines because of widespread, aggressive groundwaters containing endogenic H2S and CO2. Evidence for karst processes can be found throughout the region, from solutional limestone caves to deposition of carbonate travertine. The caves are up to few tens of kilometers long and show different patterns, ranging from phreatic to almost ideal water table caves. The caves often have a maze pattern and contain large rooms, cupola roofs, blind pits, and anastomotic zones. Solutional processes prevailed in the phreatic zone, also in deep-seated conditions, but subaerial corrosion is developed as well and can play an important morphogenetic role. The main cave-forming processes are related to the H2S oxidation to sulfuric acid, a process that involves chemotrophic microbial activity, and are responsible for the diffuse deposition of replacement gypsum in subaerial conditions. The great variety of geological settings makes the Apennines a good place to study hypogene karst, and the existence of active branches in several caves also permits a direct study of the cave-forming processes and the comparison with the resultant morphologies.