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Sitting within the Bay of Naples in southern Italy is Campi Flegrei, a vast and restless volcanic caldron. The history of this sleeping colossus includes two massive eruptions, 39,000 and 15,000 years ago, that left deep calderas in the landscape. Its last significant volcanic event a 1538 eruption known as Monte Nuovo that spawned a small new mountain. Since then, it has been curiously eruption-free.
Today, 1.5 million people live within the volcano'S caldera and its surroundings, and the cache of magma that could make it one of the most hazardous areas on earth. In a study published Wednesday in Science Advances, volcanologists report that Campi Flegrei is at the beginning of an eruption cycle, one that may result in a massive outburst at some point in the likely distant future.
The researchers arrived at this conclusion by the 60,000-year-long history of the volcano, which reveals what appears to be a rhythm at Campi Flegrei's upsurges. Fortunately, there are no signs that an eruption is imminent. And because the volcano is one of the world's most closely monitored, scientists are likely to pick up on any warning signs.
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Previous studies of Campi Flegrei have focused on one or a handful of its eruptions. But the new study, led by Francesca Forni, a postdoctoral researcher at Nanyang Technological University in Singapore, who conducted the work at ETH Zurich, used fresh geological samples taken from 23 eruptions across its history, both larger and smaller, to see how the chemistry of the magma changed over deep time. Her team also used computers to simulate what may have happened to the volcano since the last caldera-forming eruption 15,000 years ago.
The team found Campi Flegrei has gone through stages. First, a massive eruption occurs, resulting in the formation of a caldera. Then the volcano enters a period of regular, small eruptions as magma escapes through new fractures in the crust.
Finally, the volcano enters a pre-caldera phase. Minor eruptions become infrequent, and magma accumulates in the subterranean reservoir. As it pools, the magma evolves into a water-rich, gassy form, and the most drunk, bubble-rich patches gather at the top. This magma buildup may eventually culminate in another major eruption, and the cycle would begin anew.
But geological cycles can be broken, and the current lack of volcanism at Campi Flegrei does not necessarily increase to major eruption. Christopher Kilburn, an expert at University College London who was not involved in the study, said that the volcano's sustained period of relative calm could point to "on the wane."
But Dr. Forni found that the chemistry of the Monte Nuovo eruption in 1538 is similar to that seen in the past, when the volcano slowly built up to caldera-forming blasts. The presence of two calderas suggests that Campi Flegrei has probably completed this cycle, and that this pattern is indeed real, then the theory that "we are potentially at the beginning of a new cycle," Dr. Forni said.
But, she said, predicting when a major eruption will occur is beyond the current ability of science: "The best we can do for the system behaved in the past."
One of the study's co-authors, Gianfilippo De Astis, a researcher at Italy's National Institute of Geophysics and Volcanology, said that the magmatic reservoir is currently at rest. "It can keep these physical and chemical conditions for a long time," he said.
Lara Smale, a doctoral student at University College London who is researching Campi Flegrei was not involved in the study, which pointed out that "the chance of a very large eruption at Campi Flegrei in our lifetimes is extremely low."
Even then, the next eruption probably will be a small event, compared with the massive outbursts of tens of thousands of years ago. Most of the eruptions in Campi Flegrei's past were minor.
The study's use of geochemistry to understand long-term magmatic evolution, Dr. Kilburn said, "may help to improve our understanding of wide calderas worldwide."
Campi Flegrei 's Cyclical Nature is significant. If corroborated, said Ms. Smale, then so far volcanoes elsewhere have cycles too – meaning their future could also come into sharper focus.
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