The Phlegraean Fields in the south of Italy are considered a supervolcano. (archive image) © imago/Milestone Media
In Italy, a supervolcano is attracting attention with numerous small earthquakes, among other things. Experts fear that a volcanic eruption could be imminent.
London/Naples – Mount Etna, Vesuvius, Stromboli – there are numerous volcanoes in Italy that attract attention from time to time with activity. One of these volcanoes is considered particularly delicate: Mount Vesuvius in southern Italy is one of the most dangerous volcanoes on Earth. However, very close to it is another particularly dangerous area classified as a "supervolcano": the Phlegraean Fields (Campi Flegrei).
It is an area that extends over more than 150 square kilometers and begins right on the outskirts of Naples. The Italian islands of Ischia, Procida and Nisida are also included. In the region of the Phlegraean Fields there are countless thermal springs, the ground can become very hot due to volcanic activity, there are more than 50 eruption foci. The volcano's caldera, the cauldron-shaped structure created by eruptions, for example, is two-thirds submerged. About 360,000 people live on the supervolcano. The Phlegraean Fields and the volcano Vesuvius have a common magma chamber at a depth of about ten kilometers.
Italian supervolcano Phlegraean Fields last erupted in 1538
The last eruption of the Phlegraean Fields supervolcano is dated to 1538, but over the past 70 years the volcano has been very turbulent. According to experts, tens of thousands of small earthquakes have been measured during this period, raising the coastal town of Pozzuoli by almost four meters.
In a new study, researchers from University College London and the National Research Institute for Geophysics and Volcanology in Italy (INGV) have taken a close look at the supervolcano. The study was published in the journal NatureCommunications Earth & Environment and shows that the Phlegraean Fields became weaker and more susceptible to cracks, making an eruption more likely.
Research group investigates supervolcano Campi Flegrei in Italy
To come to this conclusion, the research team led by lead author Christopher Kilburn applied a model of volcanic fractures to the supervolcano. The model helps to interpret the patterns of earthquakes and ground uplifts. The conclusion of the research group: Parts of the volcano were stretched almost to the point of rupture. Co-author Nicola Allesandro Pino explains in a statement: "Our results show that parts of the volcano are weakening. This means that it could rupture, even if the tensions that are pulling it apart are less than they were during the last crisis 40 years ago."
Lead author Kilburn adds: "Our new study confirms that the Campi Flegrei are getting closer to the outbreak." However, he also qualifies: "This does not mean that an eruption is guaranteed. The fracture could open a crack through the crust, but the magma still needs to be pushed up in the right place for an eruption to occur."
Supervolcano in Italy behaves as predicted
Kilburn's research group applied their model to the supervolcano for the first time in 2017 and found that the Campi Flegrei have since behaved as predicted: There has been an increasing number of small earthquakes – more than 600 small quakes were recorded in April alone, more than ever before in one month. In addition, the soil under the city was raised annually by about ten centimeters.
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This activity is related to the movement of fluids about three kilometers below the surface, according to a statement on the study. The last turbulent phase of the supervolcano was probably caused by igneous gas that penetrates crevices in the rock and fills the three-kilometer-thick crust like a sponge. Earthquakes occur when faults are shifted due to the stretching of the crust. The pattern of the 2020 earthquakes suggests that the rock does not react elastically: it breaks rather than bends. "We can't see what's happening underground," recalls co-author Stefania Danesi. "Instead, we need to decipher the clues that the volcano gives us, i.e. earthquakes and ground uplifts."
We can't say for sure what will happen yet. It is important that we are prepared for all developments.
Stefano Carlino, Vesuvius Observatory
Eruption of the Italian supervolcano is not inevitable
In the study, the research team explains that the unrest since the 1950s has been cumulative, which means that an eventual eruption may be preceded by relatively weak signals, such as lower ground uplift and fewer earthquakes. But an eruption of the supervolcano is not inevitable, as the research group emphasizes. "It's the same as for all volcanoes that have been quiet for generations," explains co-author Stefano Carlino. "The Campi Flegrei could transition into a new routine of gentle rising and falling, as seen in similar volcanoes around the world, or simply come to rest. We can't say for sure what will happen yet. It is important that we are prepared for all developments."
In the next step, the research team wants to apply its volcano model to other volcanoes that have reawakened after a long period of dormancy. The aim is to find more reliable criteria as to whether a volcanic eruption is likely. Currently, eruptions are predicted based on statistical data for each individual volcano, rather than applying basic principles to multiple volcanoes. "This study is the first of its kind to predict eruptions at an active volcano. It is an important step towards our goal of improving the prediction of eruptions worldwide," emphasizes lead author Kilburn. (tab)