In the Bay of Naples, Europe’s most notorious giant is showing signs of reawakening from its long slumber.
Campi Flegrei, a name that aptly translates as “burning fields”, is a supervolcano. It consists of a vast and complex network of underground chambers that formed hundreds of thousands of years ago, stretching from the outskirts of Naples to underneath the Mediterranean Sea.
About half a million people live in Campi Flegrei’s seven-mile-long caldera, which was formed by vast eruptions 200,000, 39,000, 35,000 and 12,000 years ago.
The past 500 years have been fairly peaceful ones for Campi Flegrei. There have been no eruptions at all since 1538, and that was a comparatively small event that resulted in the formation of the “New Mountain”, Monte Nuovo. But recent events suggest that this period of quiescence may be coming to an end.
An acceleration of processes causing deformation and heating within the caldera saw the Italian government raise the volcano’s threat level in December 2016. Fears are growing that magma deep inside Campi Flegrei could be reaching the “critical degassing pressure”, where a sudden large-scale release of volcanic gases could abruptly inject heat into surrounding hydrothermal fluids and rocks.
When this happens on a significant scale, it can cause catastrophic rock failure within the volcano, triggering an eruption. In line with this, a study published in May 2017 found evidence that the supervolcano has been building towards an eruption for decades.
But the difficult question is not if, but when, and just how big an event this would be.
“Campi Flegrei is in a critical state,” says Antonio Costa of the National Institute of Geophysics and Volcanology in Bologna, who is part of a team monitoring the supervolcano. “In probabilistic terms, we expect something called a ‘violent Strombolian eruption’.
This is relatively small-scale to a supereruption. However, it’s not easy to say if there will definitely be an eruption in the coming years. Campi Flegrei has not erupted during the timescale that it’s been under observation, so we don’t know entirely what to expect.”
A violent Strombolian eruption would blast molten rock and volcanic gases a few thousand feet into the atmosphere. It would surely be a major event, potentially requiring the evacuation of hundreds of thousands of people. But in the context of Campi Flegrei’s past, it would be minor.
The volcano’s most notorious supereruption was the Campanian Ignimbrite eruption, which occurred some 39,000 years ago. It punched an estimated 300 cubic kilometres of molten rock 70km up into the stratosphere, along with an estimated 450,000 tons of sulphur dioxide. The ash cloud was carried as far as central Russia, some 2,000km away.
The eruption occurred at a time when much of Europe was already going through a lengthy glacial period, and the consequences are thought to have devastated much of the continent for centuries.
Entire swathes of land, including Italy, the Mediterranean coast and the entirety of eastern Europe, were left covered in up to 20cm of ash. This would have destroyed vegetation and created a vast desert. Much of Russia was immersed in 5cm of ash, enough to disrupt plant life for decades or more.
“We know from chemical analysis that the ash contained fluorine, which has a strong impact on vegetation, and it would have produced a disease called fluorosis in animals,” Costa says. “This would have had a knock-on impact on humans.”
In addition, the huge quantity of sulphur dioxide released would have created a volcanic winter. Sulphur dioxide backscatters the Sun’s radiation in the upper atmosphere, preventing it from reaching the ground. The 1991 Mount Pinatubo eruption, one of the biggest of the 20th Century, did exactly this, temporarily lowering the global temperature by around 0.6C.
But the Campanian Ignimbrite eruption may have had a far greater impact, with some scientists estimating that it decreased temperatures in Europe by as much as 4C, drastically altering the climate for many years.