Campi Flegrei volcano: Europe's Yellowstone?

01/04/2020

The metropolis of Naples lies ten kilometres from Mount Vesuvius. Some consider this a safe distance. But they forget a much bigger volcano below their feet: the Campi Flegrei. A past eruption was so violent, that it may have delivered a final blow to waning Neanderthal populations. 

The Campi Flegrei volcano is so big you hardly see it. 

Text © Kathelijne Bonne.

Can one talk about Naples and not mention the infamous Vesuvius, the buried city of Pompei and Pliny the Younger? These three are inextricably linked by the eruption of the year 79 A.D., perhaps the most famous eruption in history. Then, seventeen-year-old Pliny described the course of the eruption as objectively as possible. His account is, therefore, one of the first scientific descriptions of an eruption. 

Caput mundi

Pompei was a thriving city of the Roman Empire and nobody will ever know whether Pompei, and not Rome, would have been the caput mundi, were it not for the Vesuvius to change the course of history. Would this sun-drenched, almost subtropical part of Italy have been equally attractive for agriculture and thus civilization, without the fertile volcanic soils? Today Pompeii is a small town, hosting the famous archaeological site. 

But while Vesuvius is the only clearly present volcano in the area, it is only one of many volcanoes of southern Italy, and certainly not the largest. 

It is dwarfed by Europe's biggest, most dangerous, yet unnoticed volcano: the Campi Flegrei.

Vesuvius, seen from Posillipo, Naples. A typical, visible volcano.
Vesuvius, seen from Posillipo, Naples. A typical, visible volcano.

Invisible volcano

On the mainland west of Naples lies the Campi Flegrei, meaning 'burning fields'. Contrary to what the name suggests, this is a region of lovely green hills with vineyards and lemon and orange orchards, so different from the barren, brown Vesuvius. But if you take a closer look, you'll see that all these hills are actually small volcanoes. 

These volcanoes are part of a larger volcanic complex, which is about twelve kilometers wide. It stretches over the entire area of the bay of Pozzuoli, including the municipalities of Bacoli and Baia, and the western suburbs of Naples. The jagged coastline with many coves, bays, inlets, capes and cliffs is entirely sculpted by volcanic activity. 

Campi Flegrei is one of the few supervolcanoes in the world. If that is not bad enough, the region of the province of Naples is overpopulated. 

Supervolcanoes slumber for thousands to tens of thousands of years, in such a way that their existence is not anchored in humanity's collective memory. In the event of an eruption, the destruction in the area is total and the impact is global. The so-called super-eruptions have the power to put history and evolution on a different track. 

Satellite image of Campi Flegrei at the Bay of Pozzuoli. Count the craters!
Satellite image of Campi Flegrei at the Bay of Pozzuoli. Count the craters!

Yellowstone

But what is a supervolcano? And why do we speak of a supervolcano when we see many small volcanoes? Is this not-so-scientific word an apocalyptic fabrication of the media to frighten people? No, the name refers to the exceptionally large volume of magma that is released during an eruption, and the explosive nature of such an event. 

Hundreds to more than a thousand cubic kilometers of magma are released during a single eruption. Scientists use an index to express the power of an eruption: the VEI, or volcanic explosivity index. A VEI of 8 is the largest, like that of Yellowstone 640,000 years ago. The largest eruption of the Campi Flegrei had a VEI of 7, and the eruption of the Vesuvius of AD 79 was only a four. 

A supervolcano does not look like an ordinary volcano. There is no mountain to be seen. Its destructive power leaves only a large, collapsed area, a caldera, with hot springs, sulfur fumes, geysers and crater lakes. And fertile soils. 

Large volcanic eruptions. Pinatubo in 1991. It had a Volcanic Explosivity Index of 6.
Large volcanic eruptions. Pinatubo in 1991. It had a Volcanic Explosivity Index of 6.

The last Ice Age

The coast of Campania was not always dotted by volcanoes. It's actually a fairly recent phenomenon. Long ago, the coastline lay further land inward, near the Apennine mountains. The mainland was populated by homo sapiens and groups of Neanderthals, who were then already decreasing in number. The sea gradually retreated when the volcanic activity began some 47 thousand years ago [i], during the Last Ice Age. 

Then a few small volcanic craters formed, now forming part of the island of Procida and Monte de Procida, a mountain in the west of the Campi Flegrei, famous for its incredible panoramas over land and sea. Later, relatively small eruptions took place now and then. 

But something bigger was imminent. 

Stratospheric heights

Hot, molten rock began to fill a gigantic magma chamber located below the region of Campania. The pressure under the ground increased steadily. One day, 39 thousand years ago, the pressure reached an unbearable critical point. The land surface broke apart and in a giant eruption, 150 cubic kilometers of pulverized magma were released into the sky. Europe shook under a super eruption. 

Volcanologists calculated that the eruption column climbed 40 km up into the sky, all the way through the atmosphere, reaching the troposphere [ii]. Such an eruption is referred to as ultraplinian (more powerful than what Pliny observed), and the magnitude as 'super colossal'. 

Humps, as large as houses, rained down upon Campania. Humans in large parts of Italy perished. Europe and western Asia were covered below a thick blanket of ash and stones. Tsunamis ravaged the Mediterranean shores. Nothing was left of the volcano itself, just an enormous gaping caldera that probably filled with seawater and volcanic ash when the 'storm' subsided. 

Volcanic winter

The finest particles and gases orbited the Earth, carried by the winds. A dark mist, an aerosol, blocked the passage of sunlight. A volcanic winter followed and lasted several years. Ecosystems were disrupted, as was the balance between prey, predators and hominids. 

Some anthropologists suggest that the extinction of Neanderthals in Europe may have something to do with the Campi Flegrei catastrophe [iii]. 

Disasters aside, I'd like to think that elsewhere in the world, the homo sapiens and the last groups of Neanderthals may have enjoyed extra fiery sunsets that are known to occur after large eruptions. 

Ashes in Greenland

A greyish rock that can be found in several places in the Campania region and far beyond, is the petrified, deposited ash of this gigantic eruption, known as the Campanian Ignimbrite. Ignimbrite, from Latin igni and imbri, fire and rain, is hardened, deposited volcanic ash. 

Far beyond Italy, e.g. in Greenland [iv], a layer of ash from this eruption  was found in an ice core. 

After this catastrophic eruption, the Campi Flegrei volcano became peaceful, at least for a period of about 25 thousand years.

Grey rocks are the ash layers of the Campanian Ignimbrite, the mega-eruption of 39,000 years ago. Islands of Procida and Ischia at the horizon.
Grey rocks are the ash layers of the Campanian Ignimbrite, the mega-eruption of 39,000 years ago. Islands of Procida and Ischia at the horizon.

Yellow buildings

Many historic buildings in the city of Naples and surroundings are built of a porous stone with a characteristic pale-yellow color. It may be a coincidence, but the color happens to match that of the artist's pigment Naples Yellow. The stone is the famous Tufo Giallo Napoletano, or Neapolitan yellow tuff [v]. 

The Neapolitan Yellow Tuff is the legacy of a second gigantic eruption, which took place 15 thousand years ago [vi]. It was not as gigantic as the previous eruption, but still 40 square kilometers of magma blew into the sky. That's four times as much as the Pinatubo in 1991. The yellow petrified ash is now part of Campania's natural and cultural heritage and has a protected status. 

First colony

Despite its violent history, the Campi Flegrei has been a very attractive location for colonizers. The area has been inhabited by humans for a very long time thanks to its fertile soils under an ideal climate. The oldest Greek colony of the Italian peninsula, Kyme, now Cuma, is located on the edge of the Campi Flegrei. 

From Kyme the Greeks founded the other great colonies of Magna Graecia, such as Neapolis (Naples) and Zancle (Messina). Several world-class Greek and Roman archaeological sites in the Campi Flegrei bear witness to a rich past. 

Campi Flegrei/ Looking from Capo Miseno to the town of Bacoli.
Campi Flegrei/ Looking from Capo Miseno to the town of Bacoli.

Pozzuoli evacuated

The last eruption took place in 1538. It was nowhere as big as the previous ones. A new mountain then rose from the surface, aptly named Monte Nuovo, now a national reserve. 

More recently, in the eighties of last century, the town of Pozzuoli was evacuated for fear of an imminent eruption. The ground had started to heave and rise, slowly, but notably, suggesting that magma from below was rising [i]. The eruption never came and the magma stayed were it is. 

But for how long?

Unpredictable

Today, locals are reminded of the volcanism by the whiff of sulfur in the air, the hot water springs and fumes and small earthquakes. The famous Solfatara volcano near Pozzuoli now smokes, bubbles, smells and hisses. 

Until recently it was open to visitors, but it has been closed off due to its erratic, unpredictable behavior, having taken the lives of some who came too close to the hot boiling springs. 

Under Pliny's feet

Pliny the Younger was near the Cape of Miseno, a huge rock in the Tyrrhenean Sea, when he witnessed the spectacle of Vesuvius in the year 79. Would he have suspected that beneath his feet there was a much larger volcano than Vesuvius?

Capo Miseno in Campi Flegrei, with yellow rocks from an eruption of 15000 years ago.
Capo Miseno in Campi Flegrei, with yellow rocks from an eruption of 15000 years ago.

Do you want to read in Italian, and learn more about the cultural and natural richness of Campi Flegrei in general? I recommend Campi Flegrei of Attilio Wanderlingh. 

A very complete book on the volcanology of Campi Flegrei and other volcanoes of Southern Italy is the first one in the list below. "Volcanoes of Southern Italy". 

Cited works

[i] Guest J., Cole P., Duncan A. & Chester D. 2003. Volcanoes of Southern Italy. The Geological Society of London. 284 p.

[ii] Sigurdsson H., Carey S., Cornell W., Pescatore T. 1985 The eruption of Mount Vesuvius in 79 AD. National geographic research, 1 (3): 332-387

[iii] Black B.A., Neely R.R. & Manga M. 2015 Campanian Ignimbrite volcanism, climate, and the final decline of the Neanderthals. Geology (2015) 43 (5): 411-414.

[iv] Fedele F.G. Giaccio B., Isaia R., Orsi G. 2002 Ecosystem Impact of the Campanian Ignimbrite Eruption in Late Pleistocene Europe. Quaternary Research 57(3): 420-424

[v] Colella A., Di Benedetto C., Calcaterra D. et al. 2017 The Neapolitan Yellow Tuff: An outstanding example of heterogeneity Construction and Building Materials, 136, p. 361-373.

[vi] Deino A.L., Orsi G., Vita S. & Piochi M. 2004 The age of the Neapolitan Yellow Tuff caldera-forming eruption (Campi Flegrei caldera - Italy) assessed by 40Ar/39Ar dating method. Journal of Volcanology and Geothermal Research, 133 (1-4), p. 157-170.