The ground beneath Naples is rising, and scientists are watching closely

Nature · Published 30 September 2026 Swipe more like this →

In short: The Phlegraean Fields is a massive volcanic caldera where the earth itself is physically swelling. With recent ground uplift reaching 2 cm per month, researchers are debating whether this movement signals a looming eruption or merely a shift in hydrothermal pressure.

The Phlegraean Fields, a large caldera west of Naples, is currently experiencing significant geological unrest. Since 2012, the area has seen rapid ground uplift, with a peak rate of approximately 3 cm per month recorded in December 2012. By May 2024, the rate of rising ground had reached 2 cm per month. This swelling is accompanied by intense seismic activity; for instance, a swarm of 150 earthquakes occurred in just a few hours on 20 May 2024, causing minor structural damage and evacuations in Pozzuoli.

The mechanism driving this deformation remains a subject of scientific debate. One 'shallow magma model' suggests magma is pushing toward the surface to trigger an explosive event. Conversely, the 'hot fluids model' proposes that steam and gases, generated by deeper magma, are inflating the crust. If the latter is true, the result might be a phreatic eruption—an explosion of steam and rock fragments—which is generally less destructive than a lava-producing eruption. Recent data suggests the driving force changed around 2012 from hydrothermal dynamics to the periodic arrival of magma in a flat, sill-shaped reservoir roughly 3,000 meters deep.

The stakes are high, as parts of Naples are built directly over the caldera. While many volcanologists do not expect an imminent major eruption, the situation is described as an 'extremely dangerous state' by some researchers. In late 2023, a magnitude 4.2 earthquake prompted officials to prepare contingency plans to evacuate up to 360,000 people. While the area's history includes massive events like the Maddaloni Eruption 109,000 years ago, modern monitoring remains focused on preventing a repeat of the catastrophic 1538 Monte Nuovo event.

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