Just across the Gulf of Naples from Pompeii, the Campi Flegrei volcano — a caldera that stretches as wide as 15km across — threatens some 700,000 people living within its red zone. As Helen Gordon shows in her 1843 Magazine story on the volcanologists tasked with predicting an eruption, managing a natural disaster in a dense metro area like Naples is going to be daunting, and made even more complicated by the skepticism of many residents and the region’s aging infrastructure. Scientists like Francesco Bianco, the director of the Vesuvius Observatory, are caught in an impossible dilemma: if they sound too alarmist, people could end up not heeding their warnings; but if they stay too laissez-faire, thousands might perish.

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 organization, 48 hours for exfiltration and an extra 12-hour security margin. It will require a mammoth feat of logistics.

Read the story