The smoking crater of Campi Flegrei. (Image credit: ALBERTO PIZZOLI via Getty Images)
The history of Italy's Campi Flegrei volcano may have been more explosive than experts thought.
A new study has shown that the volcano — or its neighbor — left behind a huge layer of ash and volcanic rock about 109,000 years ago. The event, called the Maddaloni/X-6 eruption, was comparable in size to the largest known eruption, Campi Flegrei, 40,000 years ago, which was so large it formed a caldera 9 miles (15 kilometers) across.
“Despite the relatively large uncertainties, the Maddaloni/X-6 eruption may be, by a significant margin, at least the second largest explosive event to have occurred in the Phlegraean Fields region since 109,000 years ago,” lead study author Giada Fernandez, a PhD student in the Department of Earth Sciences at Sapienza University of Rome, wrote in a new paper published Jan. 15 in the journal Communications Earth & Environment.
The Phlegraean Fields are located east of Naples, on the southern edge of the fertile Campanian Plain. The soil of this plain is rich in nutrients and consists of decomposed volcanic ash left over from an eruption 40,000 years ago.
Confirmation of an earlier eruption that was nearly as powerful has hidden implications for the risk to the estimated 400,000 people living in the caldera.
The volcano has about 75 years of unrest that may or may not lead to an eruption. If one does occur, it will likely be small, said Christopher Kilburn, a volcanologist at University College London who was not involved in the new study. But if Campi Flegrei has experienced several caldera-forming eruptions in the past, that could indicate the volcano’s capacity for more destructive explosions in the long term.
“This changes our perception of the risk of Campi Flegrei reactivating,” Kilburn told Live Science.
However, the new paper does not specify whether Maddaloni/X-6 erupted directly from Campi Flegrei or whether magma flowed from fissures located a few dozen miles north of the caldera. That would not matter much to anyone caught in the eruption zone in the event of such a devastating event, Kilburn said. But it is important for researchers studying the volcano, as it can help them zero in on the signals that are most likely to herald a major eruption.
Scientists knew the volcano left behind layers of ash before its eruption 40,000 years ago. The problem with understanding these eruptions is that most of their traces were erased by the last major eruption. The remains of Maddaloni/X-6 are now mostly visible in small outcrops in the Apennines, Kilburn explained, or in boreholes drilled deep into the Earth.
Fernandez and her colleagues used these outcrops to create a model of what the 109,000-year-old eruption might have looked like. They found that it occurred in the Campi Flegrei region and began with an explosive eruption of ash and rock that created the characteristic billowing volcanic cloud. This was followed by a period of huge pyroclastic flows — avalanches of hot gas and rock that formed a layer of rock known as ignimbrite. This ignimbrite reaches depths of 6.5 feet (2 meters) in places.
The eruption would have removed more than 36 cubic miles (150 cubic kilometers) of magma from beneath the surface, not much less than the largest known eruption, which occurred 40,000 years ago, Fernandez and her colleagues note.
By comparison, the last eruption at the Phlegraean Fields occurred in 1538, when about 0.005 cubic miles (0.02 cubic
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