The Campania Plain, Part 5: Neapolitan Volcano Hazards


Campania has good reason to be proud of its volcanoes:

  • Asleep, these beautiful but strange mountains draw tourists and also serve as ground water aquifers during the dry heat of a Mediterranean summer
  • Awake, they build new land, while their ash nourishes both the soil and the sea

But locals are also aware of the risks that come with living near a Neapolitan volcano. We need to check these out, too.

What hazards are there?

Short answer: Tephra (ash, pumice, falling rocks, etc.), pyroclastic flows, deadly gases, earthquakes, tsunamis, lava flows, debris avalanches, and at least for Vesuvius, floods.

Details: The Campanian Ignimbrite eruption and other major episodes of volcanic violence were all cataclysmic events, but they weren’t disasters until they affected human beings (which the Campanian Ignimbrite did, during Upper Paleolithic times).

It’s the presence of people that makes normal Earth processes like these so problematical. (Torrence)


Bronze Age neighbors fleeing Vesuvius’ wrath during the Avellino eruption left behind footprints, as well as their homes and belongings.
(Pierpaolo Petrone via Wikimedia, public domain.)

Around the world, human experience with volcanoes goes back hundreds of centuries, long before the modern era’s technology and scientific research gave us clues into what goes on before and during an eruption.

Folklore and practical tips passed down through generations help people who live near a volcano survive eruptions.

The rest of us know about volcanic hazards thanks to global media reports.

Most of us have learned, for instance, that ash can irritate lungs and eyes, collapse roofs, and mess up machinery, water supplies, and electronics.

But did you know that simple ash fall can also kill you through suffocation and burial?

There hasn’t been an eruption large enough to provide that much ash during historic times, but such big events have happened more than once in Campania and could some day happen again.

That’s just stuff falling out of the sky. Then there are pyroclastic flows, which bring wind and heat into the hazardous mix.

Oppenheimer (see source list at post’s end) describes these high-speed clouds of ash, rock, and gas as:

. . . an atomic bomb blast, an immense avalanche, and a Category Five hurricane, with the added complication that the temperatures can reach hundreds of degrees Celsius.



Hollywood is not unaware of the dramatic, as well as physical, impact of pyroclastic flows. (And this volcanophile thoroughly enjoyed “Dante’s Peak”!)


Smaller ones, Oppenheimer writes, may travel up to 12 miles from the vent, depending on topography (which funnels the moving volcanic material just as it does water).

Many of these flows travel under the influence of gravity, just as a stream or river does, which is why technically they’re called “pyroclastic density currents.”

But most of us know them as “flows,” and we’ve also heard of pyroclastic surges — those high-energy monstrous clouds that can cross barriers and race down slopes and across plains for many tens of miles.

Katia and Maurice Krafft, along with 41 other people, died in such a surge at Japan’s Unzen Volcano in 1991.

So did hundreds of people (at least) in Pompeii, many of them after they went back home to check on things during a temporary slow-down in the eruption and were trapped when Vesuvius entered its climactic phase a few hours later.

There are surge beds on Ischia, too, from the VEI 3 Cretaio eruption there around 40 AD. (Petrini et al.)

Campi Flegrei is also capable of such powerful activity. Its Neapolitan Yellow Tuff eruption, some 15,000 years ago, began as a steam-and-magma-driven plinian eruption (VEI 5-6). Then came enormous pyroclastic flows and surges. These have left deposits more than 160 feet thick (Perrotta et al.) in Naples.

Campi Flegrei’s role in the Campanian Ignimbrite eruption is still open to debate, but there’s no doubt whatsoever that, during that VEI 6-7 eruption, pyroclastic surges buried some of the foothills and travelled almost 3,000 feet up into the nearby Apennine Mountains!

Could such a big eruption happen again on the Campanian Plain?

There certainly are no indications, in this heavily monitored volcanic zone, that such a thing is even starting to brew.

But as De Vivo et al. (2010) point out, there have been other, somewhat smaller ignimbrite eruptions on the Plain during the last 250,000 years, some erupted before and some of them after the big event.

Whatever spawned the Campanian Ignimbrite was not a unique process.

Of course, volcanologists are constantly on the lookout for precursors of an eruption. Such signs include earthquakes due to underground magma and hydrothermal fluid movement, as well as changes in volcanic degassing at fumaroles and other sites.



Sampling fumaroles is a common volcano monitoring technique throughout the world.


Sometimes you don’t need instruments to spot a precursor.

The 62 AD earthquake that reportedly damaged parts of Pompeii may have been related somehow to magma movement into nearby Vesuvius.

When the volcano erupted 17 years later — almost immediately afterwards, in geologic terms — repairs were ongoing (and Imperial reps were investigating alleged shenanigans involving shady property transfers in this elite resort town after the temblor).

Ground deformation is another eruption precursor, and it can cause hazards, too.

If a volcano’s conduit gets plugged, pressure builds up not only from rising magma but also from gas and steam that exsolve — the opposite of “dissolve” — out of the molten rock. This makes rock walls bulge.

GPS stations and other land- and satellite-based geophysical instruments can pick up even very small bulges.


In the right circumstances, rock is surprisingly flexible. This is Mount St. Helens before the 1980 eruption (left) and about two weeks before the lateral blast in May 1980 (right). Images from USGS (left)/Peter Lipman, USGS (right)

By changing the shape of a fire mountain’s flanks, ground deformation sometimes causes a debris avalanche. Yes, that’s just like a snow avalanche but with rocks and mud.


It all happened in seconds, but the famous 1980 eruption of Mount St. Helens began as a debris avalanche. Once all that overlying flank rock was gone, the magma inside the mountain “popped” and a VEI 5 eruption began. (USDA)

Steep hillsides aren’t a problem at Campi Flegrei, but nearby Ischia Caldera is almost all mountain (Mount Epomeo). It has had at least 4 major debris avalanches. These happened between roughly 6000 and 3500 BC, removing over 2 km3 of rock. (Vezzoli)

At Vesuvius, debris avalanches reached Naples Bay during the Pompeii eruption, as did some pyroclastic flows.

Volcanoes have many ways to reach out and touch us. But don’t let that worry you into canceling your vacation trip to Campania.

Vesuvius, after all, is the birthplace of modern volcanology, and back in the 19th century, they built the world’s first volcano observatory there, on an old Avellino Pumice flow near the crater.


Notice how different the top of Vesuvuis looked in the 19th century! Almost every eruption reshapes this volcano’s summit. (Wikimedia, public domain)

That location seems to be tempting fate — indeed, the 1906 eruption briefly trapped volcanologists, including Frank Perret, inside — but the building still stands. It now houses archives and a public museum that is a must-see for anyone visiting the volcano. (The actual monitoring nowadays is done from Naples.)

It’s not likely that tourists will ever be caught by a surprise eruption from any of these Neapolitan volcanoes. (Note, though, that earthquakes on Ischia probably result from rock stresses as Monte Epomeo slowly subsides rather than from magmatism; it’s not easy to predict when those rocks will reach a breaking point.)

Still, millions of Campanians live and work here. For them, the #1 question is . . .

How likely is an eruption?

Short answer: It’s almost certain. However, no one can yet pin down exactly when that will happen, how big the eruption will be, or what specific hazards will be present.

Details: Let’s start with Ischia because of its unusual structure.

Monte Epomeo. (Andrey Korchagin, public domain)

The last eruption here happened in the early 1300s. As we’ve seen, the island’s most prominent feature — Mount Epomeo — is not the volcano.

The volcano here is a submarine caldera that isn’t much bigger than the island.

Mount Epomeo is an uplifted block of leftover ignimbrite from this caldera’s Monte Epomeo Green Tuff eruption, some 55,000 years ago.

The block was submerged on the caldera floor for tens of thousands of years until something, probably the intrusion of new magma, began to push it up some 30,000 years ago.

Today, Carlino et al. suspect that there is a magma body, about 6 miles wide, sitting a little over half a mile below the mountain. Over millennia, they say, some of this melt has leaked up to the surface through the same geologic faults that Mount Epomeo moves along.

The last such leak was the eruption mentioned above, which occurred in 1302.

It’s unlikely that another eruption is pending on Ischia, because Mount Epomeo is now slowly subsiding.

Not to worry. Ischia isn’t about to do an Atlantis.

It’s just a restless caldera, like its much larger neighbor Campi Flegrei and many other volcanoes, including Yellowstone. (Carlino et al.)

Ground that slowly rises and falls seems to be typical behavior at such places (although, as we’ll soon see, Campi Flegrei carries this to extremes).

At Ischia, the geologic record suggests that Mount Epomeo either stops moving or goes into an uplift phase for a while before eruptions. (Carlino et al.)

So, for the moment, anyway, earthquakes — particularly in the northern end of the island in and around Casamicciola Terme — and landslides are probably the major hazards at Ischia Caldera.

J. M. W. Turner was only one of the many artists to portray Vesuvius during its almost 2,000 years of activity after the Pompeii eruption. (Wikimedia, public domain)

Mount Vesuvius caught the Romans by surprise in 79 AD because it had been sound asleep for many centuries before that terrible day. Pliny the Elder hadn’t even included it in his list of active volcanoes.

But Vesuvius became the birthplace of modern volcano science because of its frequent eruptions between 79 AD and 1944 (the last eruption to date).

Those Vesuvian fireworks, while not constant for 1,865 years, were frequent enough to draw writers, painters, elite youth on the Grand Tour, and many others who also enjoyed Campania’s accessibility and laidback beauty.

Most notably, Vesuvius attracted the attention of William Hamilton, whose reports laid a solid foundation for the new scientific field of volcanology. (Scarth)

If Vesuvius hadn’t attracted so much attention by being in what the boffins call “open-conduit” conditions during this crucial part of Western history, we might know much less about volcanoes now, and Campania might therefore face even higher hazard levels.

There is ongoing debate over why this volcano has such Jekyll-Hyde behavior.

One hypothesis is that Vesuvius has cycles, during which the open conduit through which magma rises to the surface eventually closes and the volcano goes to sleep again for centuries, only to reawaken with a big bang. (De Vivo and others, 2010)

Not everyone is on board with this. Scandone et al., for instance, suspect that what appears in the geologic record as cycling activity is just artifact left by a few strong eruptions that were followed by crater collapse.

It would be really nice to know which interpretation is correct because Vesuvius has now been quiet for almost 75 years — a much longer span of time than any other interval between eruptions since its last big blast in 1631.

Is it settling down for another long snooze or will it rumble back to life soon?

Most eruptions here between the late 1600s and 1944 were what volcanologists call effusive (lava flows) or strombolian (basically lava fountaining and explosions as big magma bubbles burst).

Vesuvius gets meaner than that after a long sleep has built up internal pressure from gas and steam.

Today’s emergency planners are modeling their Vesuvius eruption plans on the 1631 eruption, in which (per Scarth, page 140):

After [a lengthy repose] Vesuvius burst into eruption soon after 7 a.m. on Tuesday 16 December . . . For the rest of the day, a Plinian eruption column soared some 21 km [13 miles] skywards, and the whole area around Vesuvius shook almost continuously. At about 10 a.m. on Wednesday 17 December, loud explosions heralded the collapse of the crest of the mountain. At once, pyroclastic flows poured up over the enlarged crater, swept down the southern flanks of Vesuvius and devastated everything in their path. That same day, the erupted steam and violent thunderstorms combined to cause heavy rains that provoked disastrous mudflows and floods on the northern flanks of the mountain and dowsed the other slopes with wet ash.

Activity began to wane within 48 hours of the start of the eruption and, by the end of the week, the eruption had calmed down enough for some rescue operations to begin. . .

Eruptions at Vesuvius killed 796 people between 1682 and 1944. Some 4,000 died on December 16 and December 17, 1631 — 500 more than the known death toll from the Pompeii eruption. (Oppenheimer)

Against that terrifying background, it’s difficult to wrap our minds around the fact that Vesuvius is not the biggest player here.

Campi Flegrei is the “elephant in the room” that no one is ignoring.

Its recent eruptions haven’t been as intense as some of those at Vesuvius. There have been more than 50 of these, all comparatively small and mostly monogenetic, since the Neapolitan Yellow Tuff eruption, shortly before the end of the last ice age.

The last Campi Flegrei eruption happened in 1538, forming the Monte Nuovo spatter cone.

Per Scarth, “It was large enough to provide a superb spectacle (especially at night), but small enough to be approached . . . closely . . .”

‘Pon my word it was a fine fire.
— Francesco del Nero, eyewitness, quoted by Scarth


Today, life has reclaimed the crater that Signor del Nero saw filled with fire in 1538. (yiftah-s via Wikimedia, CC BY-SA 3.0)

Vesuvius has had some larger eruptions than Campi Flegrei recently, but it is a much smaller volcano.

And while Vesuvius has had eruptions, including the Avellino Pumice, that were even more intense than its activity in 1631 and 79 AD, this volcano is not associated with the enormous Campanian Ignimbrite ash “hurricane” that buried the whole Plain under hundreds of feet of volcanic debris.

Campi Flegrei is. Depending on who you ask, it was either the sole source of the Campanian Ignimbrite or a contributing vent.

That’s impressive enough, but Campi Flegrei also “breathes.”

For one thing, its Solfatara Crater is larger and more productive than any Vesuvian fumarole.

For another, the ground here moves up and down so much that it damages buildings. With cracks appearing in building walls and amid concerns that there might be an eruption, the town of Pozzuoli was evacuated for a while during a particularly intense episode of bradyseism (as this ground movement is called) in the early 1980s.



There was no eruption, fortunately, but bradyseism, which also alternately submerges and raises local Roman ruins, has been going on since at least the Neapolitan Yellow Tuff eruption, according to geologic evidence from the La Starza cliffs behind Pozzuoli.

Possible connections between bradyseism and eruptions are still being investigated.

This ground movement at Campi Flegrei also makes it hard to spot precursory earthquakes and deformation that might otherwise be detected weeks to months in advance of volcanic activity.

So getting enough warning time for an evacuation is a problem here. While it’s good to be proactive, as authorities were in the 1980s, how many false alarms can people and businesses stand?

Another challenge is predicting how large an impending eruption might be.

That’s true at every active volcano, by the way, but given the size of Campi Flegrei caldera and its link to two large-volume events (the Campanian Ignimbrite and Neapolitan Yellow Tuff), it’s of particular concern here.

Signals from a lot of magma moving around down there — say, a Neapolitan Yellow Tuff’s 49 cubic kilometers’ worth — should come through long before it reaches the surface, but we can’t be sure of that.

Such a big eruption has never occurred during historic times or while instruments were available, so volcanologists don’t have much solid data to work with.

Fortunately, plinian events have been rare here, compared to Vesuvius, at least during the last 15,000 years.

Mastrolorenzo et al. assessed volcanic hazard at Campi Flegrei and found that the statistically most likely eruption might be a VEI 3.

Such an intermediate-sized event, they say, would cause serious problems in and near the caldera, where over 1.5 million people live, as well as to the east (in the direction of downtown Naples), thanks to local wind patterns.

Ash fall would be the main problem in Naples, since any relatively low-energy pyroclastic flows from VEI 3 activity would probably be deflected by local topography rather than surge over it into the downtown area. Lava flows would probably remain inside the caldera and break up as they moved through the rugged landscape. (Mastrolorenzo and others)

Of course, this is just one study, and “probably” is not a very comforting word in such a context.

But probability statistics will have to do. Emergency planners need something to go on when setting up guidelines to save as many Campanian lives as possible during a volcano emergency.

Next time, we’ll take a general look at those plans, as well as see how people have coped with volcanoes down through the years, even before emergency management was a thing.


Featured image: KirkandMimi, at Pixabay, public domain.



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