When one thinks of Naples and volcanoes, the mind goes straight to Mount Vesuvius, the volcano responsible for the destruction of Pompeii and Herculaneum in 79 CE and a stark reminder of the immense power of nature ever since. But a more worrying volcano exists just to the west of the city, Campi Flegrei. Also referred to as the Phlegraean Fields, this supervolcano has a large crater (caldera) that's 13 kilometers (8 miles) across. A potential eruption would be deadly and catastrophic.

New research, published in Science Advances, has shown that the magma reservoir underneath Campi Flegrei has begun to fill up. This build-up phase will likely lead to a large-volume eruption in the distant future, and while the danger is not imminent, it shows that the supervolcano needs to be kept under constant surveillance. About 1.5 million people live next to or right on top of the caldera.

The new assessment shows that the chemical composition of the magma entering the caldera has changed lately. Volatile substances, in particular, are being separated from the magma, which is increasing the pressure within the caldera.

The team studied rocks and minerals from the area that formed during one of the 23 eruptions that have taken place on this site in recent geological history. The focus is clearly on the two major ones, 39,000 and 15,000 years ago, which formed the caldera and led to part of it ending up underwater. Several minor eruptions contributed to the landscape of the region, and the researchers were curious to see whether they could learn about the future of the supervolcano from its recent past.

In 1538, an eight-day eruption led to the formation of Monte Nuovo (literally “new mountain”), a cinder cone volcano, and was the first eruption in modern times to be described by many people. The researchers studied the rocks before and after the eruption and saw the distinct changes. The more modern rocks were similar in composition to the ones that tend to form before major eruptions.

While the analysis gives important insights into the changes within the supervolcano, the team states clearly that there is no evidence to draw conclusions on when the next eruption will be, or if it will be a major one. There is even the possibility that the system will become dormant.

There are many uncertainties when it comes to supervolcanoes worldwide and a good deal of alarmism is unfounded. That said, it is important to be vigilant because an eruption would be devastating and have worldwide consequences.