[a] It is part of the Campanian volcanic arc, which includes Mount Vesuvius, about 9 km (6 miles) east 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.

[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.

The magma underlying the Phlegraean Fields produces lavas of varying composition but generally rich in potassium.

[citation needed] In 1538, an eight-day eruption in the area deposited enough material to create a new hill, Monte Nuovo.

[17] A 2009 journal article stated that deformation of the caldera centre near Pozzuoli might presage an eruptive event within decades.

[21] In May 2017, a study by University College London and the Vesuvius Observatory published in Nature Communications concluded that an eruption might be closer than previously thought.

The study found that the geographical unrest since the 1950s has a cumulative effect, causing a build-up of energy in the crust and making the volcano more susceptible to eruption.

In this case activity could stop abruptly, or lead to a phreatic eruption of hot liquids, gases and rock fragments, rather than lava.

[28] A February 2020 status report indicated that earth uplift around Pozzuoli continued at steady rates, with a maximum average of 0.7 cm per month since July 2017.

A study by Italy's National Institute of Geophysics and Volcanology (INGV) and University College London (UCL) in June 2023 concluded that the volcano was edging towards "breaking point" and in an "extremely dangerous state".

[38][39] On 20 May 2024, seismic activity intensified, with a swarm of 150 earthquakes in a few hours, one of magnitude 4.4 causing fear among the population of Pozzuoli and some cracks and minor damage to buildings.

[31][37] In respect of its 18th and 19th century role in the development of geoscience, not least volcanology, this locality was included by the International Union of Geological Sciences (IUGS) in its assemblage of 100 'geological heritage sites' around the world in a listing published in October 2022.