The Campi Flegrei volcano in southern Italy has weakened and is more prone to erupt, making it more likely to erupt, according to a new study by researchers at UCL and Italy’s National Institute of Geophysics and Volcanology (INGV).
The volcano, which last erupted in 1538, has been dormant for more than 70 years, with biannual eruptions in the 1950s, 1970s and 1980s and a slow period of eruptions in the last decade. Tens of thousands of small earthquakes occurred during these periods, and the coastal city of Pozzuoli rose about 4 m (13 ft), about the height of a double-decker bus.
The new study, published in the journal Nature’s Communications Earth & Environment, used a model of volcanic eruptions developed at UCL to explain patterns of earthquakes and uplift, and concluded that parts of the volcano were stretched to breaking point.
Lead author Professor Christopher Kilburn (UCL Earth Sciences) said: “Our new study confirms that Campi Flegrei is approaching eruption. However, this does not mean that an eruption is guaranteed. A fissure can open a fissure through the Earth’s crust, but magma still has to rise in the right place for an eruption to occur.
“For the first time, we applied a model based on the physics of rock fracture in real time to any volcano.
“We first used the model in 2017, and since then Campi Flegrei has behaved as we predicted, with an increase in small earthquakes exerting downward pressure.
“We now have to adjust our procedures to assess the possibility of new pathways for magma or gas to escape to the surface.
“The study is the first of its kind to predict the eruption of an active volcano. This represents a step change in our goal to improve eruption forecasting around the world.”
Dr. Nicola Alessandro Pino of the Vesuvius Observatory, INGV in Naples, said: “Our results show that parts of the volcano have weakened. This means that it can be disrupted, although less than during the crisis 40 years ago.
Campi Flegrei is the closest active volcano to London. It is not an obvious volcano, as instead of growing into a traditional mountain, it has the shape of a gentle depression 12–14 km (7.5–8.5 mi) wide (and thus known as a caldera). This explains why 360,000 people live on its roof.
Over the past decade, the ground beneath Pozzuoli has been moving up about 10 cm (4 inches) per year. Regular small earthquakes were also recorded for the first time since the mid-1980s. More than 600 were registered in April, the largest monthly number so far.
The concern was caused by fluids moving about 3 km (2 miles) underground. Some fluids may be molten rock or magma, and some may be natural volcanic gas. The final stage of disturbance may have been caused by magmatic gas seeping into voids in the rock and filling the 3 km thick crust like a sponge.
Earthquakes occur when cracks (cracks) slide due to stretching of the earth’s crust. The pattern of earthquakes in 2020 shows that the rock responds in an inelastic manner by fracturing rather than bending.
Dr Stefania Danesi from INGV Bologna said: ‘We cannot see what is happening underground. Instead, we have to deal with details like volcanoes, earthquakes, and uplift.”
In their paper, the team explained that the effects of the upheavals since the 1950s are cumulative, meaning that the latest eruption may have been preceded by relatively weak signals such as reduced uplift rates and fewer earthquakes. This was the case with the 1994 eruption of the Rabaul caldera in Papua New Guinea, which was preceded by a small earthquake one-tenth the magnitude of the crisis a decade earlier.
Campi Flegrei’s current tensile strength (the maximum stress a material can withstand before breaking when stretched) may be a third of what it was in 1984, the researchers said.
The team noted that eruptions are not inevitable. Dr. Stefano Carlino of the Vesuvius Observatory explained: “This is the same for all volcanoes that have been dormant for generations. Campi Flegrei may simply transition to a new routine of rising and falling, or simply return to rest, as seen in similar volcanoes around the world. We cannot say for sure what will happen. The main thing is to be ready for all results.”
Professor Kilburn and his colleagues will now apply the UCL model of volcanic eruptions to other volcanoes that have reawakened after a long period of time, in an attempt to identify more reliable criteria for determining the likelihood of an eruption. Currently, eruptions are predicted using statistical data specific to each volcano, rather than relying on fundamental principles that can be applied to multiple volcanoes.
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