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Abstract:

Through more than one century of speleological research in Italy, many hypogenic limestone caves have been explored, mapped and studied. These caves are characterized by a variety of patterns and morphological sizes including three-dimensional maze sys-tems and deep shafts, with both active endogenic CO2 and H2S vents.
An integrate approach taking in account geological, hydrological and geochemical set-tings permit to recognize the main hypogenic speleogenetic process. The H2S oxidation to sulfuric acid, by oxygen-rich groundwaters as well as in the atmosphere is actually the main active hypogenic cave-forming processes. Both phreatic and vadose corrosion reactions involve chemotropic microbial activity, with sulfur-redox bacterial communi-ties that generate sulfuric acid as metabolic product. The bedrock corrosion produce sulfate ions in the phreatic zone and gypsum replacement in the limestone walls of the vadose sectors of the caves. The caves are characterized by both fossil and active pas-sages in which water rich in H2S as well as endogenic CO2 plays a determinant role in speleogenesis. Although sulfuric acid-related speleogenesis typically produces gypsum deposits, in caves where the karstification processes are driven by subterranean CO2 sources, voids and speleothems are the only final products.
In Italy all the end-members of the karst processes can be found, from solution caves to outcrop of carbonate travertine. The hypogenic caves are concentrated for largest and both fossils and active systems in the Tuscany, Umbria, Marche and Latium regions (Menichetti, 2009). These consist of few tens of kilometers of solutional passages with galleries and shafts, which are characterized by large rooms, cupola and blind pits, anas-tomotic passages, bubble trails roof pendants, knife edges, and phreatic passages. Ac-tive smaller karst systems are known in Southern Italy in Apulia, Campania and Sicily, related to the geothermal anomaly associated with CO2 and H2S vents.