Italy’s super-volcano Campi Flegrei is close to a possible eruption – it last erupted in 1538

Italy’s super-volcano Campi Flegrei is close to a possible eruption – it last erupted in 1538

A new study indicates that the Campi Flegrei volcano in southern Italy is becoming weaker and more likely to erupt. The volcano, which last erupted in 1538, has been turbulent for more than 70 years, with major unrest and thousands of small earthquakes over the decades. The latest research applied a unique model to the volcano’s fracking, interpreting earthquake and ground-lift patterns and inferring that parts of the volcano were stretched almost to the breaking point. (Artist’s illustration of a volcanic eruption).

According to new research, the giant Campi Flegrei volcano in southern Italy has become weaker, making it more likely to erupt. Using a unique model to interpret earthquake and ground-lift patterns, the study found that parts of the volcano were stretched almost to breaking point. However, a volcanic eruption is not guaranteed, and more research is needed to get accurate predictions.

The Campi Flegrei volcano in southern Italy is becoming weaker and more likely to erupt, increasing the likelihood of an eruption, according to a new study by researchers at UCL (University College London) and Italy’s National Research Institute of Geophysics and Volcanology (INGV).

The volcano, which last erupted in 1538, has been turbulent for more than 70 years, with two-year spikes of unrest in the 1950s, 70s and 80s, and a slower phase of unrest over the past decade. Tens of thousands of small earthquakes occurred during these periods, and the port city of Pozzuoli was lifted about 4 meters (13 ft), roughly the height of a double-decker bus.

The new study, published today (June 9) in Nature’s Earth and Environment Communications Journal, a model of volcanic fracturing, developed at UCL, to interpret seismic and ground-lift patterns, concluding that parts of the volcano were stretched almost to the breaking point.

Campi Flegrei, also known as the Phlegraean Fields, is a large volcanic area west of Naples, Italy. It is considered a supervolcano due to the nature and history of its eruptions and the large caldera system. This caldera was formed 39,000 years ago in an eruption that was one of the largest in European history. Its eruption ejected so much material that it triggered a volcanic winter, greatly affecting life across the planet.

Lead author Professor Christopher Kilburn (UCL Earth Sciences) said: “Our new study confirms that Campi Flegrei is close to rupturing. However, this does not mean that a volcanic eruption is guaranteed. The rupture may open a crack through the crust, but magma still needs to be pushed out at the site.” correct for the occurrence of a volcanic eruption.

“This is the first time we’ve applied our model, which is based on the physics of how rocks break, in real time to any volcano.

“Our first use of this model was in 2017 and since then Campi Flegrei has behaved as we expected it to, with more and more small earthquakes indicating pressure from below.

“We will now have to adjust our procedures to estimate the chances of opening up new routes for magma or gas to reach the surface.

“This study is the first of its kind to predict the occurrence of ruptures in an active volcano. It represents a step change in our goal to improve forecasts of eruptions worldwide.”

Dr Nicola Alessandro Pino of the Vesuvius Observatory representing INGV in Naples said: “Our results show that parts of the volcano are becoming weaker. This means that it may fracture even though the stresses that keep it apart are smaller than during the last crisis 40 years ago.”

A supervolcano denotes an eruptive volcano with a magnitude 8 on the Volcano Explosivity Index (VEI), meaning it is capable of erupting more than 1,000 cubic kilometers (240 cubic miles) of material. Supervolcanoes can produce devastation on an almost unimaginable scale, and such eruptions can lead to extreme changes in the global climate.

Campi Flegrei is the closest active volcano to London. It is not an obvious volcano because, rather than growing into a traditional mountain, it has a gentle depression shape 12–14 km (7.5–8.5 miles) in diameter (hence it is known as a caldera). This explains why now 360 thousand people live on its surface.

Over the past decade, the ground under Pozzuoli has been creeping up about 10 cm (4 in) a year. Continuous small earthquakes have also been recorded for the first time since the mid-1980s. More than 600 were registered in April, the largest monthly number to date.

Turbulence is caused by fluid movement about 3 kilometers (2 miles) below the surface. Some of the fluids may be molten rock, or magma, and some may be natural volcanic gas. The final phase of the unrest appears to have been caused by volcanic gas seeping into fissures in the rock, filling the 3-kilometer-thick crust like a sponge.

Earthquakes occur when faults (fissures) slip due to expansion of the crust. The pattern of earthquakes from 2020 indicates that the rocks respond in an inelastic way, by breaking rather than bending.

Dr. Stefania Danesi from INGV Bologna said: “We cannot see what is happening underground. Instead, we have to decipher the clues that the volcano gives us, such as earthquakes and the lifting of the earth.”

In their paper, the team explained that the impact of disturbances since the 1950s is cumulative, meaning that a final eruption could be preceded by relatively weak signals such as a lower rate of ground elevation and fewer earthquakes. Such was the case for the eruption of Papua New Guinea’s Rabaul caldera in 1994, which was preceded by small earthquakes that occurred at a tenth the rate that occurred during a crisis a decade earlier.

The researchers said that Campi Flegrei’s current tensile strength (the maximum stress a material can withstand before breaking when stretched) is likely to be about a third of what it was in 1984.

The team emphasized that the volcanic eruption was not inevitable. Dr Stefano Carlino of the Vesuvius Observatory explained: “The same applies to all volcanoes that have been quiet for generations. Campi Flegrei may settle into a new routine of gently rising and falling, as seen in similar volcanoes around the world, or simply return to rest. We can’t yet say for sure what will happen. The point is to be prepared for all the consequences.”

Professor Kilburn and colleagues will now apply the UCL model of volcanic rupture to other volcanoes that have reawakened after a long period of time, in an effort to establish more reliable criteria for deciding whether an eruption is likely to occur. Currently, volcanic eruptions are predicted using statistical data that is unique to each volcano, rather than relying on basic principles that can be applied to multiple volcanoes.

Reference: “Possible pre-eruption rupture of the Campi Flegrei caldera, southern Italy” by June 9, 2023, Available here. Earth and Environment Communications.
DOI: 10.1038/s43247-023-00842-1

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