In the heat of a summer afternoon, Vincenzo Morra, a professor of petrology at the University of Naples, took me up into the low brown hills of Pisciarelli just west of Naples. We drove past large, out-of-town discount stores and abandoned football pitches, and parked opposite a derelict, flat-roofed building. “We are going to the place where you can touch the volcano,” he told me. As I got out of the car, two things struck me simultaneously: the smell – the pungent, rotten-egg stink of sulphur – and a great rushing sound, shockingly loud against the silence of the hillside.

Morra, who is also the co-ordinator of the Italian Volcanic Risk Committee, led the way down a track towards a small, rocky gully. Turning the corner, the noise intensified. It sounded like an immense waterfall or some sort of infernal machine. In front of us, I saw its origin: a large cloud of steam rising from a fissure in the grey rocks. Below the fissure, a pool of churning mud belched and bubbled. No vegetation grew nearby and the earth beneath my feet felt hot. We were looking at what volcanologists call a fumarole. The heat emanated from a pool of magma that had collected some 3km below the ground.

Campi Flegrei – the name means “fiery fields” – is a type of volcano known as a caldera (from the Spanish for “kettle” or “cauldron”). Other examples include Yellowstone in Wyoming, Rabaul in Papua New Guinea and Tennger in Indonesia. It was probably formed around 35,000 years ago when an immense prehistoric volcano erupted and collapsed inwards, creating a large bowl-shaped depression in the landscape. Twenty thousand years later a second eruption contorted the original caldera to give it its current shape: it is 15km across at its widest and extends beneath parts of Naples and under the Bay of Pozzuoli. Many smaller eruptions have shaken the caldera, the last of which occurred in September 1538. That eruption was fairly modest, though it still buried an entire village underneath a cone of earth 133 metres high and 700 metres across, known today as Monte Nuovo – the new mountain. Eyewitness accounts describe the ground swelling and cracking. Cold water gushed out, followed by bulging clouds of smoke and “deep-coloured flames”. Burning ashes and white-hot pumice were thrown 5.5km into the air and there was, according to an eyewitness, a “noise like the discharge of a number of great artillery”. So many birds fell dead from the sky that the ground around the eruption site was carpeted with their carcasses. Layers of ash and pumice, up to 25cm thick, covered buildings and vegetation.

For the next 400 years, the volcano dozed. The heat of the springs and the smoke from the fumaroles were the only signs of life. Most people’s attention turned to the more active and more dramatic cone of Vesuvius to the east of the city. Now, however, there are signs that Campi Flegrei is rousing. This is a major problem as the population in the area has swelled to over half a million people over the last 500 years, making it one of the most heavily populated calderas in the world.

“It’s much more dangerous than Vesuvius because we don’t know where the eruption will be,” said Morra. Unlike Vesuvius, where the eruption is likely to come from the top or side of the cone, a caldera has the potential to erupt in many different locations simultaneously. “But people are more scared of Vesuvius because with Campi Flegrei you don’t see the cone, so there is not the same perception of danger,” he said.

Hubble, bubble, boil then trouble MAIN IMAGE Hot mud around the volcanic vent at Pisciarelli, to the west of Naples ABOVE An aerial view of some of the houses under threat

In a recent survey of residents, only 14% of respondents mentioned Campi Flegrei when asked to list the active volcanoes in their area and just 0.5% of respondents listed volcanoes as one of the three greatest threats to their community (unemployment and crime were more immediate concerns). At the bottom of the hill, I spoke to a phlegmatic old man sitting on a bench outside a restaurant. “We can’t fight nature,” he told me. In a newspaper article published in the Corriere del Mezzogiorno earlier this year, the mayor of Pozzuoli complained that locals were fed up with endless gruesome speculation about the fate of the area. The Civil Protection Department – the government department responsible for volcanic risk – had everything under control, he insisted.

“It is not simple for 700,000 people to be evacuated,” Morra told me. “It is very difficult because, in an emergency, people don’t know what they need to do. If you asked my wife, she wouldn’t know what to do. This is the problem.”

The principles behind volcanic eruptions are well known but deriving forecasts from them is not simple. Each volcano has its own quirks and history that determine when it will erupt next and how large that eruption will be. In the case of Campi Flegrei, some magma appears to have travelled upwards from a large chamber at a depth of around 5km to a point some 3km beneath the surface. It was only in September 2017 that scientists actually identified the location of the hot zone of magma underground. The looming question is what will happen next.

Christopher Kilburn, a volcanologist at University College London who has been studying Campi Flegrei for over 30 years, told me that “it’s not possible to make long-term eruption forecasts.” Instead he mapped out three scenarios that could occur when magma escapes. It might burrow itself elsewhere underground. It might head towards the surface but lack the energy to break through. Or it might smash through the crust in an eruption. “The challenge is knowing which of those things is going to happen. At the moment we can’t do that because, quite simply, we can’t see through the rock to observe what the magma is doing.” Figuring out the behaviour of the underground magma is, as another scientist described it, like “looking at a giant, fiendishly complex plumbing system”.



Hot stuff A plate by Peter Fabri from “Campi Phlegrei”, a treatise from 1776 by William Hamilton, the British ambassador to the Kingdom of Naples. The picture shows Hamilton examining sulphur and arsenic deposits

With volcanoes that have been quiet for long periods, the most prominent signals that an eruption is imminent are changes in the surface of the volcano (ground deformation) and increased seismic activity (because of the movement of the magma). Other indications include increased fumarole temperature and a change in gas emissions from hydrogen sulphide to sulphur dioxide. Laymen will notice the last of these: they will stop smelling rotten eggs and start feeling their eyes sting.

“In the short term, as you get within days, you might be able to say that these signals are consistent with an eruption and make forecasts approaching the quality of a weather forecast,” Kilburn said. But there is no guarantee that an eruption will ultimately happen. A weather forecaster may be forgiven the odd damp squib; when it comes to eruptions, the public tends to be somewhat more exacting. Diligent volcanologists cannot offer the certainty demanded of them.

But every time there is a major eruption, scientists learn something new about volcanic behaviour. In 1995, Chances Peak in Montserrat erupted. A year later, Kilburn flew out to join a team monitoring the ongoing eruption. In the Montserrat Volcano Observatory he happened upon a graph that showed a jagged upward curve of peaks and troughs, representing a series of earthquakes that had occurred prior to the eruption. He was reminded of a talk given by Barry Voight, a distinguished volcanologist, on common eruption trends. At the time of the talk, Kilburn was working in a completely different field – lava flow – but Voight’s words stayed with him and in Montserrat, looking at the graph, he could see a trend – the number of earthquakes had accelerated prior to the eruption.

During the 1980s, volcanology was changing from an almost purely observational science to a more quantitative one, which sought mathematical patterns and built models. Before Voight, volcanologists made forecasts based on simple measurements of phenomena. For example, if a certain number of earthquakes per day were recorded, they might judge the situation critical. Voight’s crucial insight lay in seeing that the rate at which physical processes changed was as important when making forecasts. Kilburn decided to use this insight to develop a model that could be applied to Campi Flegrei and used as a forecasting tool. To produce this, he needed to look at the underlying physics that determine when a rock fractures. He moved from studying very large things (volcanoes) to very small ones (atoms). “It took bloody ages!” he said, shaking his head. Kilburn thought he’d be ready to publish by the new millennium but teaching, other projects and a series of false starts intervened. It wasn’t until May 2017 that his results were published.

At Campi Flegrei, monitoring and forecasting is the responsibility of the Vesuvius Observatory. Founded in 1841 by King Ferdinand II, this is the world’s oldest institute of volcanology. Inside, the walls of the main monitoring room are covered with screens displaying information from remote sensors. The observatory is staffed 24 hours a day, every day of the year. It was here, back in 2005, that the director, Francesca Bianco, first noticed something worrying in the Campi Flegrei feeds: the land in the caldera was moving upwards. This had happened three times before – between 1950 and 1952, between 1969 and 1972 and between 1982 and 1984. In the last instance, the land rose by as much as two metres and the accompanying earthquakes forced around 40,000 residents to evacuate Pozzuoli. Some never returned.

Each time the land started moving, volcanologists waited nervously. Yet no eruption occurred. A new period of uplift convinced Morra and the other members of the Volcanic Risk Committee to raise the alert level in December 2012 from green (“base”) to yellow (“attention”). In 2016 a paper by Giovanni Chiodini and others from the National Institute of Geophysics and Volcanology (the observatory’s parent body) in Nature Communications reported patterns of magma behaviour that resembled those seen before caldera eruptions in the Galapagos Islands and Papua New Guinea. “The presence of more than half a million people living in the proximity of the caldera…highlights the urgency of obtaining a better understanding,” they wrote. A year later, Kilburn published his model, co-authored by Stefano Carlino and Giuseppe De Natale, two researchers at the Observatory, which shed light on the rumblings.

Eruptions occur when the crust stretches and breaks. Magma travels towards the surface and the crust has to expand to accommodate it. Imagine an elastic band. You can stretch it so far but there comes a point when the band snaps. Something analogous happens in the crust; when it breaks an eruption may occur. Kilburn produced the first full physical model of the relationship between the movement of the ground, the amount of seismicity and the chance of the crust breaking. “It brings a structure that allows us to quantify all these things,” he said. “Up until now it’s all been gut feeling.”

Applied to Campi Flegrei, Kilburn’s model challenged the prevailing assumption that during the periods of unrest between 1950 and 1985, the stretched crust had returned each time to something like its original state. In fact, they were all part of one prolonged sequence of seismic activity. If he is correct, the next major uplift is not going to start from where the last one started; it’s going to start from where the last one finished. The volcano’s crust is getting ever closer to breaking point. “And the difficulty is that people might have been frightened in the first incident but they’re less frightened in the second and even less in the third,” he said. “And of course it should be exactly the other way around! You don’t want to frighten people unnecessarily, but you want to get the message across.”



Clearing its throat A spume of ash from Mount Bromo in the Tengger caldera in Indonesia

“All of this is in the red zone,” Morra told me cheerfully. We were standing outside Campi Flegrei railway station on the Via Diocleziano, a long, dusty street running between tall apartment blocks. Clothes dried on balconies in the July heat and locals sat outside the cafés that spilled onto the pavement beside budget clothing shops and dim greengrocers. The red zone, home to around 700,000 people and the Vesuvius Observatory itself, is the area most likely to be destroyed when Campi Flegrei erupts. The Civil Protection Department envisages four possible scenarios: an explosive eruption, which will be classed as small, medium, large or very large; multiple, simultaneous eruptions from different vents; a phreatic eruption, which is driven by steam; and an effusive eruption, in which the lava flows steadily. They have calculated that there is a 95% chance that the eruption will be no bigger than medium sized. Because of the large number of people in the caldera, this will still be incredibly dangerous.

But more spectacular conflagrations have happened before and may happen again. The Agnano-Monte Spina eruption, for example, took place in the caldera 4,100 years ago. Some volcanologists use it as a point of reference for a “large” Campi Flegrei eruption. In such a scenario, repeated earthquakes would shake the ground. A large grey cloud would spread over the caldera, swathing the ground in darkness. The only illumination would come from the lightening bolts it shot out. This cloud would, in reality, be a column of hot water, toxic gases, ash and pumice propelled up to 25km into the air. Anyone caught near the eruption vent would be bombarded with fragments of white-hot rocks and boulders. Deposits of hot ash, thick enough to destroy buildings, would fall as far as 40km away.





In the red zone Tourists visiting one of the fumaroles

“Ash fall is particularly nasty,” Amy Donovan, a lecturer in geohazards at King’s College London told me. “I’ve been at volcanoes where it just goes completely dark and you have to get somebody else to walk in front of the truck to show you where the road is.” A heavy fall of ash may look like sprinkled flour but it is, essentially, rock. It is hard to brush off and can destroy mechanical and electrical parts. Breathing becomes impossible without a mask. As the erupting column collapsed, it would turn into the most dangerous thing of all: a pyro­clastic flow. Covering dozens of metres in seconds, pyroclastic flows are superhot streams of gas, rock, soil and ash capable of reaching between 200° C and 700° C . The extreme heat will kill everything alive, vaporising clothes and flesh in seconds.

For Bianco and the observatory staff, one of the greatest challenges will be deciding when to trigger the final red alert. There are currently no set criteria for deciding this. (Kilburn’s model may explain crust failure but even that does not guarantee an eruption.) “A lot still involves considerable amounts of expert judgment. What have you seen before?” Donovan explained. Because major eruptions are relatively rare, it can take a lifetime to build up that knowledge. The United States Geological Survey, for example, is currently facing the retirement of a tranche of experienced volcanologists and must consider how best to preserve their expertise.

The stakes are incredibly high. In the L’Aquila earthquake in Italy in 2009 (a low-probability event with high stakes, much like an eruption), more than 300 people died. Some of the victims’ families claim that reassuring statements by the then-deputy head of the Civil Protection Department fatally prompted their relatives to stay indoors when the quake struck. At the other extreme, volcanology is still haunted by the example of the 1976 Guadeloupe eruptive crisis, when 72,000 people were evacuated for between three and nine months at huge economic and personal cost. A major eruption never occurred.

When the Campi Flegrei red alert is finally triggered, the heads of the emergency services and the scientific and technical advisers will meet at the CPD ’s headquarters in Rome. Here, a belt-and-braces approach to safety is observed: there is plenty of gleaming modern technology but also a crucifix on the wall and, in the small vestibule, a richly painted gold icon. “We have calculated that 72 hours is the minimum amount of time we need to complete the evacuation,” David Fabi from the emergency management office told me when I visited. This breaks down as 12 hours for organisation, 48 hours for exfiltration and an extra 12-hour security margin. It will require a mammoth feat of logistics.

Fabi and his colleagues have divided the red zone into 15 sectors. Each sector has been twinned with another area of Italy where the evacuees will be hosted. For example, residents from the municipality of Pozzuoli will travel to Lombardy, and residents of the Naples neighbourhood of Chiaia will go to Sicily. It is assumed that many people will leave in their own vehicles, though there are concerns about the quality of rural roads and their capacity to support such large amounts of traffic. For those not using their own vehicles, transport will be laid on. The details of the Campi Flegrei evacuation plan are still being finalised but in the equivalent plan for Vesuvius – where a population of around 700,000 lives inside the red zone – the CPD expects to provide hundreds of buses, trains and ships for each day of the evacuation.

The undertaking is complicated by the fact that no one knows where the eruption will occur and which routes out of the caldera might be blocked. The plans assume that there will be a 72-hour advance warning. But in his report on the 1994 eruption at Rabaul, Hugh Davies, a professor of geology at the University of Papua New Guinea, wrote that there was now “clear evidence that a caldera-collapse volcano can erupt with as little as 27 hours of precursor activity”. Indeed, the speed with which the Rabaul eruption developed meant that the authorities effectively had only 12 hours’ warning, making it impossible to put into place many of the safety measures.





Fire watchers LEFT Vincenzo Morra, co-ordinator of the Italian Volcanic Risk Committee. RIGHT Francesca Bianco, the director of the Vesuvius Observatory

Communication between the scientists, the authorities and the population will be the key to a successful evacuation at Campi Flegrei. At Rabaul, despite the rush, only five of the 45,000 people in need of evacuation lost their lives. In his report Davies speculates that the high level of hazard awareness among the community was a major factor in this success.

At Campi Flegrei, Kilburn has been interviewing residents who witnessed the evacuations at Pozzuoli in the 1970s and 1980s. Their responses are alarming. There is “an underlying cynicism about whether evacuations are motivated wholly by scientific concern”, he told me. Many believe that evacuations benefit property speculators, who have taken advantage of the collapse in housing prices in Pozzuoli during emergencies. “It is not clear that the suspicions are well founded. However, even if they are incorrect, if the allegations are believed to be true, they encourage resistance.”

Donovan recognises the problem. “Trust is hard won and easily lost. Some of it is about communication. It’s about getting people to understand how much uncertainty there is in forecasting. Scientists are not deliberately withholding or giving bad information – they just don’t know exactly what is going to happen and when.”

This mistrust of scientists and the authorities is one of many factors that may make people reluctant to leave their homes. Other concerns include fear of looting and worries about pets. “Can you take your cat with you? That can be a big issue for a lot of people, especially in developed countries,” Donovan said. For others, the prospect of living for a long period of time in temporary accommodation is a major deterrent. During the evacuation of Montserrat in 1995 some elderly islanders chose to remain – and die – in their homes rather than face unsanitary and undignified conditions in overcrowded evacuation shelters. Evacuees worry whether they will ever be able to return home. Unlike, say, a hurricane, an eruption can last for months or even years.

Working with Lux in Fabula, a cultural association in Pozzuoli, Kilburn and the observatory scientists are seeking to rebuild trust between the caldera residents, the scientific community and the authorities. According to Kilburn, effective messaging is as important as accurate forecasting. One promising way of disseminating information is through schoolchildren. “We give the information to the kids and they pass it on to their parents and grandparents,” Bianco told me. The effectiveness of these sorts of bottom-up tactics is well documented. Digital technology can also be employed to raise awareness. Lara Mani, a researcher at the University of Plymouth, recently developed a game that helps residents of the Caribbean island of St Vincent visualise the hazards posed by their volcano. But no one yet knows whether this knowledge will be retained and applied in the chaos of an eruption.

In the rocky gully, I turned away from the fumarole to look down the browning hillside. The houses of the red zone shimmered in the heat. Pink and white and purple bougainvillea grew in startlingly bright profusion along the roadside. Considered one way, everything I could see had come about because of the volcano. Around 35,000 years earlier, it had collapsed in on itself and formed the bowl of the caldera. Compacted ash turned into rock; lava flows solidified into outcrops; volcanic cones became tree-covered hills. More than 2,000 years ago, the Romans established the town of Pozzuoli in the middle of the caldera. The fertile volcanic soil encouraged people to settle there, to plant vineyards and citrus groves, to take the rocks formed from ash and construct the buildings that wind up the hillside.

Whether this landscape will exist in 2,000 years’ time depends very much on what the volcano does next. Three kilometres beneath the streets of Campi Flegrei, the magma is stirring in its subterranean chamber. Up on the surface, the scientists bend anxiously over their instruments. Standing on the hillside, listening to the roar of the fumarole, I felt, for a moment, that a human being was a very small thing. I turned back to look again at the steam and vapour escaping from the fissure. I prodded, with the toe of my boot, a charred stub of vegetation. Morra had walked closer to the vent. “Look,” he said, smiling. “For me, this is something very beautiful. The breath of the volcano.”

PHOTOGRAPHS ENRICO SACCHETTI