POZZUOLI, Italy — In Greek and Roman mythology, the Campi Flegrei volcano is depicted as the opening to the underworld.
Its prehistoric eruptions blocked out the sun, turning summer into winter and covering Europe and Russia in thick volcanic ash. Now this powerful seismic giant near Naples is stirring again, shaking the ground in a way that scientists say it hasn't for centuries.
"Two of the most recent earthquakes are the strongest we've ever seen," said Giovanni Macedonio, the director of the National Institute of Geophysics and Volcanology in Naples. Earthquakes in March and June this year caused by the Campi Flegrei forced people "to evacuate and there are tens of families that can't return to their homes because of the damage."
For everyone to survive an eruption, over half a million people would have to be evacuated from an area that Italian authorities have marked the "red zone" around the Campi Flegrei's eight-mile wide crater. Here, Macedonio says, "there really are no countermeasures to protect yourself" from the pyroclastic flow of volcanic particles and ash — super-heated to some 1,472 degrees Fahrenheit — that would cover terrain at a speed between 30 and 60 miles per hour.
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The Campi Flegrei volcano is considered a "national threat" for the "explosive" style of its eruptions, which, scientists believe could create an eruptive column — a kind of cloud of dust and ash — that could rise some 18 miles into the sky and spread on the wind. When that column of dust and ash eventually falls, its weight can even collapse roofs of homes.
At the observatory Macedonio oversees in Naples, a large red phone connects directly to the civil protection headquarters in Rome. The line is tested twice a day.
Vesuvius — the best known volcano in this area, whose pyroclastic flow froze in time the ancient Roman city of Pompeii — rises to the east of Naples. Hans Christian Andersen, after witnessing an eruption in 1834, described the lava as "colossal, fallen stars."
But the truth is it's the much less visible Campi Flegrei, or Phlegrean Fields (from the Greek phlegraios for "fiery"), underground, that has the potential to be devastating. This is because today, hundreds of thousands of people live right on top of this volcano — in the eight-mile-wide crater left by past eruptions.
"All of us know we are living in a completely seismic area," said Naples resident Maddalena Desario, whose neighborhood is situated on the rim of the Campi Flegrei caldera.
In the ancient city of Pozzuoli, which sits in the caldera, tourists follow a guide through winding, narrow alleyways. From a hilltop, they look out over a curving bay — the sea sparkling in the sunshine under an intense blue sky, and the island of Capri, playground of the rich, in the distance.
But this immense beauty belies the peril here. During the biggest volcanic eruption, some 39,000 years ago, the Campi Flegrei shot out 72 cubic miles of molten rock, according to Macedonio of the National Institute of Geophysics and Volcanology. Global temperatures plummeted, and the entirety of what is now Europe, as well as parts of Russia, were covered in volcanic ash. Some scientists have suggested the eruption could have contributed to the final disappearance of the Neanderthals.
Experts say an eruption today would not occur on that scale. However, it could still be large enough to wreak havoc on millions of lives and halt air travel across Europe, perhaps even further around the globe. So Macedonio and his team monitor its every grumble and tremor.
At the observatory in Naples, screens on every wall show the seismic activity of all the volcanoes in the region. On the day NPR visited in September, a loud alarm sounded across the room, signaling that an earthquake had been detected. The scientists moved fast to assess the location and power of the tremor and send the information to the Italian public safety authorities.
It was in the Campi Flegrei. And this is not unusual. Last year, the scientists logged some 2,500 earthquakes caused by this volcano in a single month. And now the tremors are intensifying in magnitude: June saw an unprecedented 4.6-magnitude earthquake — enough to crack walls and send people fleeing from their homes.
These earthquakes are coupled with bradyseism — a phenomenon in which the ground swells, slowly rising beneath people's feet. At the old port in Pozzuoli, boats now stand nestled in long grass, marooned on new land that has risen out of the sea. Ancient Roman columns have fossils of mollusks halfway up, showing how they were once underwater.
It's as if this giant volcano were breathing — the ground rising and lowering over decades, with every breath. Before a last major eruption some 15,000 years ago, scientists say the ground rose about 85 feet. Now it's steadily rising again — up by 4.6 feet since 2005, and the rate at which it's swelling is getting faster.
"One thing that you learn very soon is that we do not have control. Nature has the control," said Warner Marzocchi, a professor of geophysics and natural risk at the University of Naples, Federico II. "These kind of volcanic systems are used to having phases of unrest like this one that we are observing. The biggest scientific challenge is to understand what is driving this unrest."
To meet that challenge, Marzocchi and his team — along with Stanford University and the National Institute of Geophysics and Volcanology — are using artificial intelligence to build what they and other experts say is the most accurate picture yet. The model identifies thousands of earthquakes not previously detectable with existing technology. The research expanded the total seismicity recorded by monitoring stations in the last three years from about 12,000 to more than 54,000 earthquakes in the Campi Flegrei alone.
The developments help scientists make more educated guesses about the likely magnitude of future quakes and learn more about why the Campi Flegrei has shown increasing activity since 2005. Marzocchi says the data suggest that, for now, the tremors are more the result of gases pushing superheated water up through the earth, rather than magma rising. Scientists hope this means an eruption is not necessarily imminent. But they cannot know for sure.
Marzocchi says the risk of an eruption is still "not zero" and therefore it is vital to remain vigilant.
In Pozzuoli in September, visitors wandered into historical buildings open to the public for a contemporary art exhibition. Down one cobbled street, local artist Pina Testa stood outside her studio. Her paintings include dozens of works showing volcanic eruptions — the giant plumes of ash depicted in a bright array of colors.
"Fire, and everything that is the movement of the earth, speaks to the soul, and all this comes out in my paintings," said Testa, explaining the inspiration she finds in the volcano. She laughed: "Sometimes when the earth quakes, I feel like it is right under my studio" — which she said is so far undamaged.
She admitted there's even a kind of affection for this deadly companion. She remembers as a child the gatherings with neighbors on the street as they would evacuate their homes during an earthquake – sometimes in the middle of the night. It was a time to chat, to connect, and even share a pizza.
In the 1970s and 1980s, tens of thousands of residents were relocated from the Rione Terra, the historic district of Pozzuoli, in forced evacuations by the authorities, who believed the sharp upswell in the ground from bradyseism could be a sign of an imminent eruption. Police and military forced people from their homes. They were relocated to new apartments, and this oldest quarter of the city was seized permanently by the state. Today, tourists wander the still-empty streets of this quaint hilltop district, whose beautiful and historic buildings stand mostly uninhabited.
However, across Pozzuoli and the Campi Flegrei region, entire communities remain. The volcano and its seismicity have always been part of them, Testa explained. The real residents of Pozzuoli live in harmony with the volcano, she said. They can get scared sometimes, but never terrified. And they do not leave.
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