The risk of an eruption in the Phlegraean Fields, a volcanic region in north-west Italy near Naples, has never been higher, warns a British-Italian study published on Friday.
Half a million people are directly threatened by a supervolcano. Less well known than Mount Vesuvius, which wiped Pompeii off the map nearly two millennia ago, is the Phlegraean Fields volcano, which last erupted in 1538, exposing hundreds of thousands of residents to a torrent of lava, ash and rock.
The volcano’s energy is so great that its eruption 30,000 years ago has been hypothesized to have contributed to the extinction of Neanderthals. In fact, “it is an extremely dangerous volcano,” explained AFP Stefano Carlino, co-author of the study from London University UCL and the Italian Institute of Geophysics and Volcanology (INGV), published in the journal Communications Earth & Environment.
“We’re not saying there will be an outbreak, we’re saying conditions are more favorable for an outbreak,” said UCL’s Christopher Kilburn, the operations manager.
Weakened by a multitude of smaller earthquakes
The volcano has not been spoken of since the 1980s, when renewed activity led to the evacuation of 40,000 residents. However, according to the study, the tens of thousands of small earthquakes beginning in the 1950s weakened the caldera — a flat-bottomed volcanic depression — of which “parts were tested until they almost reached breaking point.”
These tremors, even more frequent since 2019, have thus shaken the subterranean layers. The municipality of Pozzuoli, on which the volcano is located, has also risen four meters over the decades.
In addition, the researchers noted that the effects of volcanic activity are “cumulative”: it is not necessary for the intensity of this activity to increase significantly to increase the likelihood of an eruption. “A potential eruption could be preceded by relatively weak signals, such as moderate ground uplift and a smaller number of earthquakes,” they noted.
They took the example of the Rabaul Caldera in Papua New Guinea, which erupted in 1994 when the shaking that preceded it was far less than when it erupted a decade earlier.
Yellow Alert
If the probability of a mega eruption is “very low,” small eruptions are more likely, Stefano Carlino said. But when “we can’t say for sure what’s going to happen, it’s important to be prepared for any eventuality.” Furthermore, according to Christopher Kilburn, even in the event of a crustal rupture, “the magma must rise at the right place”.
Half a million residents live in a high-risk area, with another 800,000 in a lower-risk area. In the event of an alarm, the local authorities plan to evacuate the population using public transport. The alert level – green, yellow, orange, red – is reviewed every month.
“Pozzuoli is currently on yellow alert,” local spokeswoman Giordana Mobilio told AFP. “We are in constant communication with the residents of the city and inform them about earthquakes” with a magnitude of more than 1.5, she emphasizes.