The Frasassi Caves, Italy

The Frasassi Caves are a rare and striking example of active hypogenic karst. The combined effects of tectonic uplift and river downcutting produced a succession of horizontal passage levels connected by vertical shafts, with older caves occupying higher elevations. This unique setting is an extraordinary natural laboratory that provides a bridge between cave forming processes that we can observe in real time, such as sulfuric acid speleogenesis, with “fossil” morphologies in older cave levels and other inactive caves whose genesis involved similar processes. The Frasassi Caves are also home to a spectacular and diverse chemosynthetic ecosystem that derives energy from the mixing of sulfide- and oxygen-rich fluids in the cave passages. The extraordinary beauty and size of the passages and speleothems led to the opening of a show cave in a section of the Grotta Grande del Vento in 1974, with an average of 350,000 visitors per year.