The slumbering Campi Flegrei volcano under the Italian city of Naples shows signs of reawakening and may be nearing a critical pressure point, according to a new study.

Italian and French scientists have for the first time identified a threshold beyond which rising magma under the Earth’s surface could trigger the release of fluids and gases at a 10-fold increased rate.

This would cause the injection of high-temperature steam into surrounding rocks, said Giovanni Chiodini, a researcher at Italy’s National Institute of Geophysics and Volcanology in Bologna. “Hydrothermal rocks, if heated, can ultimately lose their mechanical resistance, causing an acceleration towards critical conditions,” he told AFP by email.

He said it was not possible to say when – or if – the volcano would erupt but “it would be very dangerous” if it did for about 500,000 people living inside and near the caldera – the bowl-like depression created after a volcano blows its top.

Chiodini said there was an urgent need to obtain a better understanding of Campi Flegrei’s behaviour because of the risk to such a dense urban population.

Since 2005, Campi Flegrei has been undergoing what scientists call uplift, causing Italian authorities to raise the alert level in 2012 from green to yellow, signalling the need for active scientific monitoring. The pace of ground deformation and low-level seismic activity has recently increased.

Two other active volcanoes – Rabaul in Papua New Guinea and Sierra Negra in the Galapagos – “both showed acceleration in ground deformation before eruption with a pattern similar to that observed at Campi Flegrei,” Chiodini said.



The Campi Flegrei caldera was formed 39,000 years ago in an explosion that threw hundreds of cubic kilometres of lava, rock and debris into the air in the largest eruption in Europe in the past 200,000 years. Campi Flegrei last erupted in 1538, though on a much smaller scale.

Nearby Mount Vesuvius, which had a massive eruption in AD79 that buried several Roman settlements including Pompeii, is also classified as an active volcano.

The study co-authored by Chiodini was published on Tuesday in the scientific journal Nature Communication.