Residents are now keeping emergency bags packed, preparing for larger quakes, or worse, an eruption some experts fear could prove devastating. Nearly 80,000 people blithely inhabit the sulfureous caldera, playing soccer in the streets and cooking rich ragus in apartments with majestic views of Capri and Ischia, the emerald isles across the Gulf of Naples. In total, an estimated 485,000 people live in the designated danger zone of a smoke-belching behemoth the ancient Romans thought was an entrance to Hell.
The most pessimistic experts signal it may even be time to consider relocating, presenting residents with a stark choice: Should they stay - or should they go?
The crisis is escalating a debate within Italy's scientific community about the extent of the threat from the 8-mile-wide monster pockmarked with more than two dozen craters and believed to have caused the most violent eruption of prehistoric Europe. There is no indication of a sudden rise in magma that could signal an imminent eruption. But volcanic events can be highly unpredictable, and the new cycle of volcanic earthquakes - along with a measurable rise of the ground by 2 cm a month - are worrying.
An eruption could range from the kind of limited burst that upended a boardwalk in Yellowstone National Park last month to something catastrophic. The fields, experts say, have the potential to wreak more havoc than Mt. Vesuvius, about 25 miles away, during its historic destruction of Pompeii in 79 AD.
A number of scientists are warning of a possible tipping point - but no one more so than Giuseppe Mastrolorenzo, a senior researcher with Italy's National Institute of Geophysics and Volcanology (INGV) who is engaged in a public fight with the agency he serves, arguing it is not taking the threat seriously enough. He describes a worst-case scenario in which a deep fissure opens in the earth, spewing a mushroom cloud of noxious gas, superheated ash and pyroclastic material. At night, emissions would be wreathed in lightning bolts. The view of the coastline would be shrouded by a deadly black veil. In the aftermath, white-gray ash and rock would blanket the land.
Even a significantly smaller but still strong eruption, he said, "could devastate the entire metropolitan area of Naples, with its 3 million inhabitants."
"The pressure could release like a bomb," he said, standing under the scorching sun and gazing down at a massive crater lake formed during the last significant Phlegraean eruption in 1538.
Some of his own bosses - as well as Pozzuoli's Mayor Luigi Manzoni - dismiss such talk as fearmongering, arguing there is no need to abandon this sun-kissed land now. The danger is serious but manageable; the threat of a major eruption remote. The bigger threat, they say, would be a new wave of volcanic earthquakes. They believe it can be handled without the kind of costly evacuations and building reinforcements that occurred in the 1980s, the last time the Phlegraean Fields rumbled to life.
The national government, meanwhile, is sending conflicting signals. On one hand, Rome last month imposed a temporary construction ban, and a leading minister called it "criminal" that people were ever allowed to settle in the shadow of such a threat. Yet Prime Minister Giorgia Meloni has also appeared to incentivize staying. She has given in to local politicians and championed a 1.2 billion euro redevelopment of a blighted waterfront at risk from the volcano, including a new urban park, land reclamation projects, new housing and infrastructure.
The threat "has always existed in Pozzuoli," Manzoni said. "We have to learn to coexist with it."
Italy is the most volcanically active country in continental Europe, and two of the country's most active volcanoes are in the midst of minor eruptions. On the southern island of Stromboli, the eponymous volcano is spewing lava with more bark than bite. In Sicily, showy Mt. Etna is blowing her top, provoking minor inconveniences as opposed to general panic.
And then there is Campi Flegrei, the fiery or Phlegraean fields in English, a volcano with nearly half its caldera in the Mediterranean Sea. Rock samples suggest a mega eruption here 39,000 years ago touched off a volcanic winter in Europe linked to the extinction of the Neanderthals.
Though magma underneath the Phlegraean Fields is not surging upward, the volcano has been growing more dangerous, said Giovanni Chiodini, a retired geochemist formerly in charge of the area's geochemical surveillance and who has published academic articles on the Phlegraean Fields. The volcano's magma is depressurizing, releasing gas as well as vapor that rises through rock and liquefies.
"If we were talking about a volcano in Antarctica, we would all be saying that it's moving toward an eruption," says Chiodini, suggesting that there's greater reluctance to alarm people in a populated area like Italy.
Chiodini said the volcano is just as likely to settle down as erupt, but it's the uncertainty that's causing anxiety. How much warning residents would get is anybody's guess. In the 1538 eruption, earthquakes were so severe and continuous that ancient residents had days, even weeks, to leave. Current evaluation plans - now being fine-tuned for speed and efficiency - assume 72 hours to get half a million people to safety.
But Mastrolorenzo argues an eruption could happen with only a few hours' notice and threaten metropolitan Naples, Italy's third largest city. The area may not be prepared. Evacuations during the May quake were disastrous, citizens say; some drivers got stuck in gridlocked traffic and were forced walk to the safety of a beach. A subsequent evacuation saw only a handful of participants.
For decades, the Macellum of Pozzuoli, the column-studded ruins of an ancient market, haven risen and fallen as volcanic activity has alternately lifted or depressed the earth beneath its foundations. The ruins are now again in a period of lift, with a rising watermark of between 2 and 4 cm per month since last year, though still a far less than the 14 meter increase witnessed in less than a year ahead of the 1538 eruption.
Carlo Doglioni, the INGV's director, said the rise in the land is not as dramatic as the last major volcanic disturbances here four decades ago. Citizens should be concerned, he said, but he criticized Mastrolorenzo's doomsaying. There is a yellow warning in effect in the area. But current readings, he said, do not suggest "people should evacuate at this time."
"Mastrolorenzo is looking for visibility, to attract attention," he said. Still, Doglioni said it would also be "wrong" to underestimate the risk. Asked if people should leave Pozzuoli, he said: "I personally would not love to go there to live."
On July 26 at 1:46 p.m., Andrea Vitale, a 67-year-old retired schoolteacher, froze in the kitchen of his apartment built inside the Phlegraean Field's caldera. He heard a big bang and felt an undulating sensation, as if the building was riding a wave. In the living room, his young granddaughter screamed. Balou, his Pitbull mix, barked incessantly. A crack appeared on a living room wall.
"In Pompeii they had no idea," he said. "But the threat is clear to us. That's what they'll say when they find us in the ash."
July's 4.0 temblor was the second significant quake in two months. A May 20 quake, measuring 4.4, did more damage, forcing the evacuation of three schools, a women's prison and more than 100 families. Others, like Vitale, have homes that were reinforced during the 1980s, when his neighborhood was evacuated for 18 months. But even some of those structures have begun to crack.
Citizen groups insist the local government is purposely downplaying the threat and that national government should do more, for instance by offering additional, faster assistance for repairs and aid for residents who want to relocate.
"They have minimized the problem to try not to scare people because they are more concerned about the economy," said Laura Lovinelli, head of Campi Flegrei citizen's group.
Nello Musumeci, Italy's minister for civil protection, acknowledged that a government plan for massive redevelopment in a neighboring red zone town appeared to contradict efforts to discourage new construction in the area. The local government is offering stipends to residents in temporary housing from the May quake, and the national government has approved subsidies to help with construction. But the state cannot handle all the expenses, Musumeci said, suggesting that residents who choose to live here must share the cost.
As tourism drops, restaurants have closed, and business is down. Rossana Maurelli, 56, said sales at her family's ceramic shop - selling dishes emblazoned with fiery scenes of volcanic eruptions - have fallen 60 to 70 percent since last year.
She recognizes the danger. Today, the local beach is the only place where she finds peace. She said she goes there daily to avoid sitting in her apartment, where she sometimes imagines its walls caving in.
But she can't envision leaving Pozzuoli, her family's home for generations.