Campi Flegrei, “burning fields”, is a supervolcano that 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 and last erupted in 1538.
According to the BBC, about half a million people live in its seven-mile-long caldera, which was formed by vast eruptions 200,000, 39,000, 35,000 and 12,000 years ago. Recent events suggest that the monster is awakening: deformation and heating within the caldera saw the Italian government raise the volcano’s threat level in December 2016. A study published in May 2017 found evidence that the supervolcano has been building towards an eruption for decades. Fears are growing, says the BBC, 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.
“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.”
The volcano’s most notorious supereruption was the Campanian Ignimbrite eruption, which occurred some 39,000 years ago when much of Europe was going through a lengthy glacial period. The consequences are thought to have created a volcanic winter that devastated much of the continent for centuries. 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.
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.”
The timing of this huge eruption is suspicious, because many archaeologists believe that 39,000 years ago is roughly when our cousins the Neanderthals died out in Europe. According to the BBC, it has long been speculated that the eruption triggered extreme environmental conditions across Europe, contributing to the extinction of the Neanderthals, at least in some regions.