Over the past 40,000 years, three major eruptions have burst forth from Italy’s Campi Flegrei volcano. Two of said eruptions carved massive calderas, or craters, in the landscape, and the third, which happened in 1538, created a new mountain in the region. Since then, the volcano has been relatively quiet; today, in fact, some 1.5 million people live within one of the calderas.
As Robin George Andrews reports for the New York Times, a new study tracing the geologic history of Campi Flegrei has revealed that the volcano’s major eruptions seem to follow a pattern. What’s more, the researchers behind the study posit that the volcano could be entering into a new phase of activity; though a massive eruption, if it happens at all, is not likely to happen during our lifetime.
Previous studies have looked at discrete periods of Campi Flegrei’s activity, but the new report, published in Science Advances, is by comparison quite broad in scope. A team of researchers led by Francesca Forni, who at the time was a PhD student at ETH Zürich, analyzed geologic samples from 23 eruptions, both large and small, that have occurred over the past 60,000 years. The researchers also relied on computer models to get a picture of what has been happening inside the volcano over the past 15,000 years, when the last caldera-forming eruption took place. (The other caldera-forming eruption happened 39,000 years ago).
They found that Campi Flegrei’s eruptions seem to take place in stages. First, as National Geographic’s Maya Wei-Haas explains, magma builds up in the chamber, which results in huge eruptions. The subsequent blasts are frequent and smaller, shooting out hot, dry magma. As the magma cools, the eruptions become less scorching in temperature as well.
Eventually, even the minor eruptions become infrequent, but magma continues to accumulate. Water-rich “mush,” a slushy mixture of magma and solid crystals, starts to form, and pushes bubbles into the magma. This, according to the researchers, could spark a major eruption, setting the cycle in motion again.
The researchers write in their study that since the 1538 eruption, “the caldera has gone through recurrent episodes of unrest, suggesting that the magmatic system is active and potentially prone to erupt again in the future.” But the scientists have no idea when that blast might spew forth. The last two caldera-forming events happened 24,000 years apart. Another cycle could be longer, or shorter, or the eruption might not happen at all if the volcano goes extinct.
“We don’t have any constraints at the moment about time,” Forni tells Mary Beth Griggs of the Verge. “Volcanoes are not clocks, either in terms of time, or behavior.”
Other experts have noted that the present activity remarked upon in the paper, like ground deformation or changes in gas emissions, doesn’t necessarily mean much when it comes to predicting eruptions that could happen many, many years from now.
“We have to be cautious … about connecting the long-term behavior over thousands of years to short-term changes over years to decades, and their implications about the potential for eruption,” volcanologist Christopher Kilburn of the University College London, tells Wei-Haas.
Still, because so many people live within reach of Campi Flegrei’s blast, the volcano is very closely monitored for any changes in activity. Emergency plans are in place to protect residents from big or small eruptions—if they ever do occur.