Phlegraean Fields

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.

At present, the Phlegraean Fields area comprises the Naples districts of Agnano and Fuorigrotta, the area of Pozzuoli, Bacoli, Monte di Procida, Quarto, the Phlegraean Islands, Ischia, Procida and Vivara.^{[citation needed]}

The Solfatara crater was accessible on foot until 2017 and contains many steam-emitting fumaroles and over 150 pools, at the last count, of boiling mud. Several subsidiary cones and tuff craters, one filled by Lake Avernus, lie within the caldera.

The magma underlying the Phlegraean Fields produces lavas of varying composition but generally rich in potassium. Trachyte is the most common eruptive product, unusually alkali-rich in some cases. Peralkaline phonolitic trachyte and latite have also been produced, and there is rare trachybasalt.

Ash across the Mediterranean region is evidence of a major eruption 109,000 years ago, which has been named the Maddaloni Eruption, or X-6. Modelling gives a magnitude estimate of 7.6 and VEI 7, only slightly lower than the Campanian Ignimbrite of about 40,000 years ago, making it the second largest event in the eruptive history of the Campi Flegrei.

Three geological phases or periods are recognised and distinguished.

Volcanic deposits indicative of eruption have been dated by argon at 315,000, 205,000, 157,000 and 18,000 years ago.^{[citation needed]}