West of Naples, beneath a densely populated coastline that Italians have inhabited since antiquity, the ground has been slowly heaving upward for years. The area is Campi Flegrei, a sprawling volcanic caldera that has no towering cone but instead reveals itself through a phenomenon called bradyseism, the gradual rise and fall of the land surface driven by pressures deep below. In recent seasons the trend has been upward, and that persistent lift has kept volcanologists on close watch.
Campi Flegrei is not a single mountain but a roughly 13-kilometer-wide depression, much of it hidden beneath the town of Pozzuoli and the western suburbs of Naples. Its restlessness matters because roughly half a million people live inside or immediately around the caldera, one of the most densely settled volcanic zones on Earth. The central question researchers keep returning to is whether the current unrest is a slow-burning nuisance or the prelude to something larger.
What bradyseism is and why Pozzuoli keeps rising
Bradyseism, from the Greek for slow movement, describes ground that swells and subsides over months and years rather than jolting in an instant. At Campi Flegrei the effect is dramatic enough to be measured with everyday reference points: docks that once sat at the waterline drift higher above it, and buildings shift as the land beneath them lifts. As reporting on the caldera has documented, the movement is tied to pressure changes in the fluids and gases beneath the surface, and it can reverse direction when that pressure eases.
The current episode has been one of sustained uplift. Italy’s National Institute of Geophysics and Volcanology, known by its Italian acronym INGV, has tracked ground rising at roughly 10 millimeters per month during early 2026, with Pozzuoli lifted by about 24 centimeters since January 2025. Those figures are small in absolute terms but relentless, and the accumulated rise has stressed structures and stretched the patience of residents who periodically feel the accompanying earthquakes.
The debate over magma versus hydrothermal fluids
The scientific heart of the matter is what, exactly, is pushing the ground up. For years the leading explanation focused on the hydrothermal system, the network of hot water and gas circulating in the rock, which can pressurize and expand without any fresh magma moving toward the surface. A quieter hydrothermal driver would imply a lower likelihood of imminent eruption than a rising body of molten rock.
More recent analysis has complicated that picture. Research published in the journal Science examined the current phase of unrest and pointed toward magma accumulating at depth as a significant contributor to the uplift, even as researchers cautioned that no direct signature of magma migrating upward toward the surface had been detected. The distinction is critical: magma accumulating in a deep reservoir is not the same as magma on the move, and the presence of one does not guarantee the other.
What INGV monitoring actually measures
The institute maintains a dense monitoring network across the caldera, combining satellite and ground-based measurements of deformation with seismometers that catch the frequent small earthquakes accompanying the uplift. In a technical assessment, INGV quantified the relationship between ground uplift and seismic activity, giving officials a clearer framework for interpreting whether a given burst of tremors reflects escalating pressure or routine adjustment.
Those measurements feed Italy’s civil-protection alert levels for the caldera, which range from a base condition through progressively higher states of concern. The seismic swarms tend to cluster under the Pozzuoli and Agnano areas, and while individual quakes have generally been small, occasional stronger events have cracked walls and rattled residents enough to prompt evacuations of specific buildings. Monitoring cannot predict an eruption date, but it is designed to detect the kind of accelerating change that would precede one.
The long shadow of a supervolcano
Campi Flegrei carries an outsized reputation because of its deep history. As geological summaries note, the caldera formed in enormous prehistoric eruptions, including one about 39,000 years ago that ranks among the largest volcanic events in European history and blanketed a vast region in ash. That catastrophic past is why the site is sometimes described as a supervolcano, a label that captures its worst-case potential but says little about what any current episode of unrest will actually do.
Volcanologists are careful to separate that ancient ceiling from present-day expectations. The most likely outcomes of the current phase range from the uplift eventually reversing, as it has in past cycles, to a comparatively small eruption rather than a cataclysm on the scale of the caldera-forming events. No credible scientific source has issued a firm eruption forecast, and researchers have repeatedly warned against treating speculative timelines as predictions.
For now the situation remains one of vigilance rather than emergency. The ground keeps rising, the small quakes keep coming, and the monitoring instruments keep feeding data to the scientists whose job is to tell the difference between a caldera breathing and a caldera preparing to erupt. That watchful uncertainty is the defining condition of life above one of the world’s most closely studied volcanic systems.
This article was researched and drafted with the assistance of AI and reviewed before publication.
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