The Phlegraean Fields (Italian: Campi Flegrei, Italian: [ˈkampi fleˈɡrɛi]; Neapolitan: Campe Flegree) is a large volcanic caldera west of Naples, Italy. The Neapolitan Yellow Tuff eruption (about 12ka BP) produced just 50 cubic kilometers. It is, however, one of relatively few volcanoes large enough to form a caldera. It is part of the Campanian volcanic arc, which includes Mount Vesuvius, about 9 km (6 miles) east of Naples. The Phlegraean Fields is monitored by the Vesuvius Observatory. Part of the city of Naples is built over it.The Phlegraean Fields' largest known eruptions have an estimated volcanic explosivity index (VEI) of 7. It is often called a supervolcano in popular media, although the accepted definition for that term is a volcano that has had an eruption with a VEI of 8, the highest level.
The area of the caldera consists of 24 craters and volcanic edifices. Most of them lie under the Gulf of Naples. There are effusive gaseous manifestations in the Solfatara crater, which was believed in ancient Rome to be the home of Vulcan, the god of fire. The area features bradyseismic phenomena, which are most evident at the Macellum of Pozzuoli, misidentified by 18th-century excavators as a temple of Serapis: bands of boreholes left by marine molluscs on marble columns show that the level of the site in relation to sea level has varied. Hydrothermal activity can still be observed at Lucrino, Agnano and the town of Pozzuoli.
