The Monster beneath Campi Flegrei

[Nik_SpeakerToCats]

It was long suspected.
It was inferred from on-shore and off-shore investigations.
But the vast caldera which *had* to underlay area could not be confirmed beyond a short arc.
Until now...

First graphic is scary enough, several significant, twitchy faults aligned with activity.
The second is scarier, as reveals the ancient caldera's 'ring fault', most of it off-shore..

Fortunately, the yo-yo Bradyseism --It is a real word-- for which that area is infamous seems to be due to ground-water, not actual magma shifts. But that's another story...

AI model reveals hidden earthquake swarms and faults in Italy's Campi Flegrei
https://phys.org/news/2025-09-ai-reveal ... warms.html
quote:
Campi Flegrei is an active volcano located within the densely populated Neapolitan area. This volcanic region, which is home to more than 500,000 people, has experienced episodes of unrest dating back to the late 1950s.

The last period of unrest started in 2005, with a significant increase in the seismicity in 2018, including five earthquakes above a magnitude 4 in the first eight months of 2025. The new research expands the seismicity recorded by monitoring stations from 2022 to 2025 from about 12,000 to more than 54,000 earthquakes.

The data revealed two faults converging under the town of Pozzuoli west of Naples, which has been continuously monitored since the early 1980s, when unrest caused the land to rise more than 6 feet and more than 16,000 earthquakes prompted the evacuation of 40,000 residents.
...
Campi Flegrei is an 8-mile-wide caldera, a massive depression formed by major volcanic eruptions about 39,000 and 15,000 years ago. In addition to eruptions, the caldera experiences uplift and subsidence—rising and sinking of the land called bradyseism.
/

[Rocket J Squrriel]

The Volcano Cafe has done several articles about the monster:

https://www.volcanocafe.org/volcano-for ... i-flegrei/

https://www.volcanocafe.org/the-shaking ... i-flegrei/

[David Newton]

But the vast caldera which *had* to underlay area could not be confirmed beyond a short arc.

Wrong. The geometry of the caldera has been well known for decades. Onshore it's patently obvious and offshore the location of the ring fault has been fairly well known.

This work appears to have made things rather more precise and it has certainly helped to make the exact earthquake threat clear. It's evolutionary and clarifying rather than revolutionary.

[Nik_SpeakerToCats]

Fair point.
Improvement in resolution merely comparable to 'Before' vs 'After' Hubble Fix.

IIRC, active coring, geo-phone pinging etc had been limited to off-shore, beyond Naples' city authority. Seems there's Italian law & precedent that, if you 'interfere' with a volcano, in whatever way, you are liable for all subsequent damage.
{ FX: Icelandic Face-Palm }
This, being purely passive, a re-working of prior data, incurred no such issues.

Meanwhile, not far to the West, the picturesque island of Ischia continues to slowly rise as is summit of slowly extruding 'plug' of mostly-dormant volcano. How is it connected to the Campi Flegrei sub-structure ? IIRC, unclear, given geology differs...

Upside, the 'Gulf of Naples', the 'Looks like a Mega-Caldera' oval running clock-wise from Naples, via Vesuvius / Pompeii, Sorrento, Capri and Ischia, is apparently 'Sedimentary' to great depth.

Ischia arises, Vesuvius is scary, Campi Flegrei is potentially much, much worse, but finding those were but flank eruptions of a Toba-scale mega-caldera might rattle even Neapolitan nerves...

[David Newton]

Oh there are a LOT more active volcanoes in Italy than people realise.

Of the Campanian Arc people have mostly only heard of Vesuvius, with some having heard of Campi Flegri and very few knowing about Ischia.

Etna is Etna!

Of the Lipari Islands people have likely heard of Stromboli, some have heard of Vulcano (ironic since it's the root namesake volcano!) and very few will know of Lipari itself being a volcano or Vulsini which is a large submarine stratovolcano and an extremely significant tsunami threat to Italy.

Beyond that there's the island of Pantelleria south of Sicily that is volcanic and the Campi Flegrei del Mar di Sicilia as well which saw a naval race to claim the temporary island it created in 1867.

I'm using the volcanological definition of active here. As in erupted at some point during the Holocene.

[Rocket J Squrriel]

People don't realizae that there are volcanoes all over Europe. There is even an 'active' area in the Eifel in Germany. Last eruption may have been 13,000+ years ago and Mt Pinatubo sized. There is still outgassing, earthquakes, and inflation (in millimeters per year). Pele is letting everyone know that she is still around.

[Johnnie Lyle]

People don't realizae that there are volcanoes all over Europe. There is even an 'active' area in the Eifel in Germany. Last eruption may have been 13,000+ years ago and Mt Pinatubo sized. There is still outgassing, earthquakes, and inflation (in millimeters per year). Pele is letting everyone know that she is still around.

People also forget that the US has a lot of active volcanoes too.

Unfortunately, lots of people would rather forget about a threat than move away from pleasant locales within range of their wrath.

[Rocket J Squrriel]

I was surprised that 1.1 billion years ago one of the largest lava flow, the Greenstone Flow, in Earth's history started from what became Lake Superior. The flow to the southwest reached Kansas and to the south east Ohio. Some spots it was 450 meter thick.

Earth has its moments today but was bada$$ back in the day.

[Johnnie Lyle]

I was surprised that 1.1 billion years ago one of the largest lava flow, the Greenstone Flow, in Earth's history started from what became Lake Superior. The flow to the southwest reached Kansas and to the south east Ohio. Some spots it was 450 meter thick.

Earth has its moments today but was bada$$ back in the day.

Youth and skill lose to old age and treachery :p

Conversely, Earth and God seem to be on the same trajectory. Brash and aggressive as youths, but more restrained as they enter adulthood and/or have kids.

[Nik_SpeakerToCats]

Tangential, the latest Volcano Café post is about calderas, including a tour of the Tibesti caldera zoo.

For too long, that area was 'Here Be Dragons', variously spears, muskets, AKs: Mars was better known !!