Campi Flegrei: One of World's Most Dangerous Supervolcanoes Could Erupt Sooner Than Expected

Pozzuoli has risen by over three meters since uplift began in the 1950s. Ferdinando Marfella/Flickr

One of the world's most dangerous supervolcanoes appears to be closer to erupting than we once thought, scientists have warned. Campi Flegrei in southern Italy has been showing signs of reawakening over the past 67 years, and new research indicates the volcano has been building energy throughout this period, increasing the risk that it will erupt.

Campi Flegrei is a huge volcanic field that sits about 9 miles to the west of Naples, a city home to over a million people. It is made up of 24 craters and edifices, and appears as a large depression on the surface of the land.

The volcano last erupted in 1538 after almost a century of pressure building up. But though it lasted over a week, this was a comparably small one—40,000 years ago, it produced a "super-colossal" eruption. This is the second highest measure on the volcanic explosivity index, the first being "mega-colossal," like those seen at the Yellowstone supervolcano in the U.S. thousands of years ago.

In a study published in Nature Communications, scientists have created a model looking at unrest and ground uplift at Campi Flegrei since the 1950s to work out whether it could be preparing for an eruption.

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Two-year episodes of unrest were recorded in the '50s, '70s and '80s. The movement of magma 1.8 miles beneath the surface was responsible for the activity, with a series of small earthquakes and uplift taking place each time.

Previous research has shown the ground around Campi Flegrei has been moving upwards, rising by 13 inches in the last 10 years. In total, the three episodes of uplift have caused the port of Pozzuoli—which is near the epicenter of the unrest—to rise over three meters out of the sea. Similar uplift was recorded before the 1538 eruption.

While it is impossible to predict exactly when a volcano will erupt, there are tell-tale signs that can help scientists work out the risk. When the ground around a volcano has been stretched so much it reaches breaking point, the magma is able to escape—the surface splits and an eruption can take place. But this does not always happen. Sometimes the magma stalls before reaching the surface.

campi flegrei volcano
Volcanic activity on Campi Flegrei. The supervolcano has shown signs of unrest since the 1950s. Daniel Enchev/Flicrk

In the latest study, scientists at University College London (UCL) and the Vesuvius Observatory in Naples showed how each period of unrest had led to a cumulative build-up of energy needed to stretch the crust.

"Individual episodes have conventionally been treated as independent events," the authors write. "Only data from an ongoing episode are considered pertinent to evaluating eruptive potential." Scientists had previously thought the crust of the volcano would relax after each episode of unrest.

Instead, the team showed that each successive episode led to the "long-term accumulation of stress" and that their findings provide "the first quantitative evidence that Campi Flegrei is evolving towards conditions more favorable to eruption."

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Study author Christopher Kilburn, director of the UCL Hazard Centre, said in a statement: "By studying how the ground is cracking and moving at Campi Flegrei, we think it may be approaching a critical stage where further unrest will increase the possibility of an eruption, and it's imperative that the authorities are prepared for this."

He added, "We don't know when or if this long-term unrest will lead to an eruption, but Campi Flegrei is following a trend we've seen when testing our model on other volcanoes, including Rabaul in Papua New Guinea, El Hierro in the Canary Islands, and Soufriere Hills on Montserrat in the Caribbean." In the study, the scientists said the field data indicated uplift at Campi Flegrei will reach between 16 and 33 feet before an eruption is likely.

Piton de la Fournaise volcano
Representational image. Molten lava erupts from the Piton de la Fournaise, Réunion island, in 2015. Campi Flegrei in Italy has not erupted since the 1500s. Gilles Adt/Reuters

In an interview with Newsweek, Kilburn says: "We're not saying there will be an eruption. There's a big difference between 'there will be one' and 'it's more likely than previously thought.' If you evaluate the probability of it occurring, you have to understand the crust is becoming increasingly broken up, so the chances are increasing with time."

He says they only have data from two or three other periods of activity, so drawing conclusions from this is not ideal. "But if we do draw an analogy, before the last eruption there was 17 meters [56 feet] uplift. The question is do we wait for another 17 meters or could it come earlier? Our conclusion is it could come earlier—and also that the way the crust is breaking, it's reaching a point where its behavior may change and we get more seismicity with each meter of additional uplift.

"For all we know, the volcano won't do any more. We might not have any more problems for another 500 years. But if we go into another rapid uplift, like we've seen in the past, we just have to bear in mind that…it might be taking to a state closer to an eruption. The probability would be higher."

In terms of how large an eruption would be, Kilburn said the biggest would be on a par with Vesuvius 79AD—the eruption that destroyed Pompeii and Herculaneum. "But that's quite unlikely," he says. "It's much more likely to be about 100 times smaller. The real problem is not knowing where it's going to happen… We'll have to evacuate more than the area that's likely to be affected because they won't know quite where it's going to come out until the last moment, whereas a volcano like Vesuvius the magma normally comes out of the top."

In the '70s and '80s, thousands of people living around Campi Flegrei were evacuated over concerns the volcano would erupt. Study co-author Giuseppe De Natale, former director of the Vesuvius Observatory, said: "Most damage in previous crises was caused by the seismic shaking of buildings. Our findings show that we must be ready for a greater amount of local seismicity during another uplift and that we must adapt our preparations for another emergency, whether or not it leads to an eruption."

To predict more about Campi Flegrei, scientists need to get a better understanding of the structure down to a depth of 1.8 miles, as this is where the magma causing the disturbances is located. "How it will behave will depend on the shape of the body it forms, how much is there,"says Kilburn.