Homes were evacuated and many people slept in their cars or on the street after the strongest earthquake in 40 years shook the area around the sprawling Campi Flegrei supervolcano close to Naples.
The 4.4-magnitude tremor in Pozzuoli, a densely populated port city, was followed by 150 quakes that were also strongly felt in Naples.
Local media reports said cracks had formed in buildings and chunks of masonry had collapsed. Schools were closed on Tuesday in Pozzuoli and a cluster of towns and districts of Naples.
“We left our home at midnight and went to our son’s in Vomero [Naples],” Mimmo Pignatelli, who lives in Solfatara, a town adjacent to one of Campi Flegrei’s 24 ancient volcanic craters, said.
“We are used to the quakes – but this one was very frightening as it was the strongest in 40 years. We could feel the ground move as we walked.”
Seismic activity on Campi Flegrei, which is home to at least 360,000 people across seven of the most at-risk inhabited hubs, has intensified in the past two years, with the frequency and strength of the quakes increasing as the caldera, the basin at the top of the volcano, weakens and pressure beneath it builds. This causes the ground to rise and the volcano’s crust to stretch.
“The earth is continuing to rise at a rate of 2cm a month, a higher rate than last year, and unfortunately it seems to be continuing at this rate,” Mauro Di Vito, the director of the Vesuvius Observatory for Italy’s National Institute of Geophysics and Volcanology (INGV), told reporters. “We expect similar earthquakes … I cannot make predictions but we can expect the swarm to continue.”
The Italian government has devised a mass evacuation plan, with test-runs expected at the end of May.
The 7-mile Campi Flegrei caldera is a much larger volcano than the nearby, cone-shaped Vesuvius, which destroyed the ancient Roman city of Pompeii in AD79, and is much more active.
The supervolcano has been in a restless state for more than 70 years as a result of a phenomenon known as bradyseism, which scientists understand to be the gradual movement of part of Earth’s surface caused by the filling or emptying of an underground magma chamber or hydrothermal activity. The last time Campi Flegrei had a comparable burst of earthquakes was in the early 1980s.
Christopher Kilburn, a professor at University College London, led a study that described the caldera as edging towards “breaking point”.
He said: “When there was a crisis 40 years ago, it came to a halt very abruptly, but it’s not clear yet whether what’s happening today is completely analogous. So we have to be very cautious. The question is, can we see an evolution in the behaviour of the fracture … is there any evidence of smaller fractures growing into bigger ones?”
Campi Flegrei was formed 39,000 years ago after an eruption emptied it of magma. Its last significant eruption was in 1538.