Beneath Naples’ western suburbs lies Campi Flegrei, a vast volcanic crater that shakes more intensely now than it has in decades.
A June 2025 magnitude-4.6 earthquake rattled buildings across the bay—the strongest jolt in roughly forty years.
Scientists confirm this quake marks the latest in a pattern of intensifying tremors that locals can no longer overlook.
Pressure Builds
One earthquake tells only part of the story. For twenty years, the ground has heaved upward steadily.
Since 2005, GPS stations around Pozzuoli have measured over 3.3 feet of uplift, with recent data suggesting a total of closer to 4.6 feet.
Each uplift burst brings swarms of small quakes, signaling rising pressure beneath the crater.
Gates Below
Romans once feared this volcanic landscape as a literal gateway to hell itself.
Lake Avernus, a crater lake within Campi Flegrei, was described by ancient writers as Hades’ entrance, with its fumes supposedly lethal to birds. Solfatara nearby—now closed to visitors—vents sulfurous steam from a boiling crater.
Modern science articles invoke this mythology, referring to Campi Flegrei as the “gateway to the underworld” as unrest resurges.
Cycles Of Unrest
This region has risen menacingly before. During the early 1980s, ground uplift forced authorities to evacuate tens of thousands from Pozzuoli’s historic Rione Terra neighborhood.
Streets cracked, buildings warped, and entire blocks were abandoned permanently.
The current unrest phase—which began around 2005 and accelerated after 2012—mirrors that crisis but persists far longer.
Ancient Super-Blast
When Campi Flegrei last reshaped itself catastrophically, it produced a massive eruption that blanketed much of Europe in ash.
Geologic studies date the Neapolitan Yellow Tuff eruption to roughly 14,000–15,000 years ago—one of two massive collapses that carved today’s 8-mile-wide crater.
Major outlets refer to this as the volcano’s “last major eruption,” distinguishing it from the much smaller 1538 Monte Nuovo blast.
Life In The Red Zone
Roughly 500,000 people live on this restless ground inside Italy’s official Campi Flegrei “red zone.”
This high-risk area includes Pozzuoli, Bacoli, Monte di Procida, Quarto, and western Naples neighborhoods—all positioned within or directly atop the caldera.
Civil Protection evacuation plans assume moving all 500,000 residents within roughly 72 hours if alert levels reach the highest level, red. Home literally sits inside a supervolcano.
Shaken Daily Life
For Pozzuoli residents, the crisis translates to rattling dishes and sleepless nights rather than abstract statistics.
Earthquake swarms—sometimes exceeding 1,000 quakes monthly—strike frequently, with shaking strong enough to force people into the streets.
Yet this has bred a weary acceptance: schools operate, cafés open, locals insist evacuation talk risks needless panic. How long will this fragile balance persist?
Watching Every Tremor
Italy’s National Institute of Geophysics and Volcanology monitors Campi Flegrei with unprecedented intensity.
Seismic stations, GPS receivers, tiltmeters, and gas sensors blanket the caldera, transmitting real-time data to the Vesuvius Observatory in Naples.
Civil Protection staff maintain constant contact, testing emergency communication lines multiple times daily. Their goal: detect any shift from “unrest” toward eruption, enabling evacuation of hundreds of thousands.
A Supervolcano Club
Scientists often rank Campi Flegrei alongside global heavyweights like Yellowstone and Toba. Its largest eruptions reach Volcanic Explosivity Index 7—just below the VEI-8 threshold, sometimes defining “supervolcanoes.”
Yet, science writers and many researchers still apply the supervolcano label due to its massive caldera and eruption power. That designation explains why any activity spike here captures the attention of worldwide volcanologists.
AI’s Quiet Alarm
The most significant, yet overlooked, development involved re-examining three years of seismic data using artificial intelligence.
A 2025 study and INGV announcement reported that machine-learning models expanded the earthquake catalog from roughly 12,000 manually identified events to over 54,000 quakes.
Though many were tiny, together they reveal dense, shallow fracturing. This fourfold increase in detected quakes suggests a far more stressed crust than previously believed.
Managing Public Fear
Officials face a challenging communication task: to warn sufficiently to boost preparedness without triggering mass evacuations or economic disruption.
Civil Protection maintains Campi Flegrei at “yellow” alert—heightened watchfulness—rather than upgrading to “orange” or “red,” despite the strongest quakes.
Some residents accuse authorities of minimizing risks for political gain, while others claim the media exaggerates threats. Institutional trust may matter as much as magma behavior.
Evolving Risk Models
Scientists continuously refine their understanding of how Campi Flegrei might fail. Recent Nature and Science papers propose that a hot, gas-charged hydrothermal system in the upper crust drives much of the uplift and seismicity, not necessarily massive fresh magma volumes.
This suggests a potential for dangerous phreatic or moderate magmatic eruptions, rather than an imminent catastrophe, although models remain uncertain. Each new data set subtly shifts the risk picture.
Preparing To Move
On paper, red-zone evacuation plans appear thorough and detailed. Authorities mapped transport routes, receiving centers, and phased movements designed to relocate roughly 500,000 residents within three days.
Drills and public information campaigns aim to ensure residents know their destinations. Yet, local reports reveal uneven awareness, and skeptics doubt that such a massive operation could execute smoothly under intense pressure.
Cautious Optimists
Many volcanologists emphasize that, despite alarming signals, a catastrophic super-eruption remains unlikely in the near future.
A Nature commentary described the risk as “non-negligible but still low,” urging stronger monitoring and preparation over panic. Others warn that even a smaller eruption beneath this densely populated region could cause widespread devastation.
The real debate focuses not on danger itself, but on what type of eruption proves most plausible.
Living On The Edge
Campi Flegrei poses a difficult question for Naples and Italy: how long can so many people safely inhabit an awakening volcanic crater?
Economic ties, cultural heritage, and family bonds keep residents rooted despite intensifying quakes and uplift.
Scientists continue to refine models; officials update emergency plans, but the risk never reaches zero. At what point does this restless “underworld” finally force people to leave?
Sources:
NPR, 25 Nov 2025
Popular Mechanics, 6 Jul 2023
Nature “Weighing the risk at Campi Flegrei”, 2023
Geographical, 19 Dec 2023
Phlegraean Fields Red Zone documentation, 6 Oct 2023
INGV bulletins, 2012–2024