Italy's supervolcano is bubbling: "An eruption could happen at any time"

Giuseppe Mastrolorenzo moves up and down in his chair. "It's like a vertical shaking," says the volcanologist, "like a series of explosions." This is how he describes the earthquakes that have occurred in recent months around the Phlegraean Fields, Italy's supervolcano. He lives near Monte Nuovo, a volcanic cone west of Naples that is part of the supervolcano.

Mr. Mastrolorenzo, what is going on in the Phlegraean Fields right now?

What we're seeing there is a new bradyseism crisis. Bradyseism is a slow ground movement: Part of the Earth's surface gradually rises and falls, which is typical of the Phlegraean Fields. In 1538, this phenomenon, with the associated earthquakes, caused the eruption of the Monte Nuovo volcano. After that, there was a relatively quiet period without any activity. Since 2005, we've been experiencing a new bradyseism crisis with some ground deformation, always in the center of the caldera. And since 2011, earthquake activity has also been increasing.

How pronounced is the earthquake activity?

In recent years, many thousands of earthquakes have occurred—some stronger, others weaker. One of the strongest was the earthquake that struck the center of Pozzuoli in May of last year. With a magnitude of 4.4, it was the strongest earthquake of the last 40 years.

This record was then broken on March 13, 2025. This earthquake had a magnitude of 4.6. Its epicenter was located here (pointing to a map of the Phlegraean Fields hanging behind it), between Pozzuoli and Naples. Recently, another earthquake with a magnitude of 4.6 was located very close to the center of the caldera. Compared to earthquakes that occur in tectonic areas—regions where tectonic plates interact—the local acceleration and local effects are very strong.

What causes these earthquakes?

The earthquakes are the result of these ground movements and the tensions in the Earth's upper crust caused by gas pressure. For years, the Phlegraean Fields have been emitting increasing amounts of gases such as carbon dioxide – recently 5,000 tons per day. Other gases such as hydrogen sulfide are also increasing. This indicates that there is a large magma body deep underground, from which these gases emanate and penetrate into higher rock layers. This causes ground deformation at a rate of currently about 1.5 centimeters per month, sometimes as much as 3 centimeters per month, and is associated with the release of tension in the form of earthquakes.

Unlike in previous years, earthquakes are now occurring throughout the caldera. It's likely that the entire upper crust of the caldera is expanding and being stressed by the gas flow. The intensity of the phenomenon is increasing, and we don't know what the maximum magnitude might be or when the next earthquake will occur.

Are earthquakes of this kind still normal?

Nothing is normal in this area. For me, there is no end to risk assessment—both for volcanic risk and for bradyseism and seismic risk. Because nothing is predictable. We don't know how things might develop. Events in recent years have shown that the energy and magnitude of earthquakes could increase, and we don't know where the limits lie. If ground movements occur along the caldera's boundary faults, there could theoretically be earthquakes with a magnitude of more than five. Buildings could collapse and even cause casualties. But we don't know whether these movements will occur.

Giuseppe Mastrolorenzo is a senior researcher at the Istituto Nazionale di Geofisica e Vulcanologia (INGV), Italy's largest research institute for geophysics and volcanology.

Source: Private

Are the earthquakes and ground deformations a sign of another volcanic eruption?

In fact, we usually know these phenomena—bradyseismos, ground deformation, gas emissions, and earthquakes—as possible precursors to a volcanic eruption. However, this usually applies to a different type of volcano, such as Mount Etna or Stromboli. In the case of the Phlegraean Fields, we don't know whether an eruption will occur during such a bradyseismic phase or perhaps even during a relatively quiet period.

In my estimation, an eruption could occur at any time. The magma could rise to the surface directly from the magma chamber about eight kilometers deep within a few hours. So we won't have much lead time. But it's impossible to make precise predictions. We also have no experience with pre-eruption monitoring, because the only eruption occurred in 1538, about 500 years ago. So we have no experience, and the system is chaotic by nature. And chaotic systems are unpredictable. So an eruption could happen in 1,000 years, in a century, in 10 years, or even tomorrow.

How well would you say the local people are prepared for a volcanic eruption?

We are completely unprepared. The risk has been severely underestimated for a long time. The current emergency plan, for example, assumes that we can predict an eruption 72 hours in advance, simply because civil defense needs those 72 hours to evacuate hundreds of thousands of people from the center of the caldera, from the red zone. But that's not true. We simply don't know how quickly and how severely an eruption could escalate.

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My advice to the authorities is that, given previous experience and the limitations of research, we must be prepared at all times in such a critical and unpredictable system. We need evacuation routes down to the center of the caldera. Roads, railway lines, and so on. (Moves his hands back and forth over the map.) One of the few advantages of the caldera is that part of it is coastal. So we have ports like Pozzuoli and other small tourist ports, so we could leave the area by ship or boat if necessary. However, we must bear in mind that an eruption will raise the ground, which will lower the sea level in the harbor, and within a short time it will be impossible for ships to dock there.

What might a volcanic eruption look like?

In the past, the region has mainly experienced explosive eruptions – similar to the eruption in Pompeii. That is, with huge plumes of smoke containing gases and particles such as volcanic ash. With pyroclastic flows, that is, Avalanches of hot gas and rock flow down the slope at high speed. At temperatures of several hundred degrees Celsius. In Naples, we can still find deposits several hundred meters underground that date back to eruptions of the Phlegraean Fields thousands of years ago.

This worst-case scenario could also occur in the event of a new eruption. Even a moderate eruption would not only affect the Phlegraean Fields, but the entire Neapolitan area could be hit by hot, devastating pyroclastic flows. In the optimistic scenario, only the center of the caldera would be affected by the eruption. But at this point, I estimate that at least three million people, the inhabitants of the greater Naples area, are at risk. That's why we must expand the red zone.

Could a volcanic eruption also have consequences for neighboring countries, perhaps even global consequences?

Only in the event of a super-eruption could other countries be affected. For example, a super-eruption of the Phlegraean Fields about 40,000 years ago scattered ash throughout the Mediterranean. If such an eruption were to occur, I believe it could trigger long-lasting climate changes through the injection of ash and gas into the stratosphere. This is also known as a volcanic winter. A global temperature drop could occur and last for several years.

The yellow alert level has been in effect since 2012. Will it soon need to be raised to orange?

That depends on how the situation develops. The problem, however, is that we haven't had a threshold for declaring the orange level for many years. So, it's not the case that, for example, the orange level is declared as soon as an earthquake reaches a magnitude of 5, or when more than 2,000 earthquakes occur in a certain period, or something like that. In principle, the orange level could already be declared now.

What you have to consider is that the orange level implies a lot of government resources. Because once this alert level is reached, all residents can leave the region and receive government aid to rent a house or pay for a hotel. Therefore, declaring the orange level will be very critical for the government.