A large circular depression surrounds the Bay of Naples on Italy's southwestern coast. Extending into the ocean, it can only be truly seen from the air. From the ground, you'd never know the area, which is home to several towns and villages, is actually a caldera - a massive volcanic crater seated above an extensive network of magma chambers and tunnels.
The land beneath Naples occasionally rumbles, and even rises, as the magma chambers beneath it bulge with molten rock. The people who live within the circumference of the ancient caldera do so in the hopes that the Campi Flegrei supervolcano will never blow in their lifetimes. If it does one day erupt, the results could be dire.
Looking back at past volcanic activity and eruptions, scientists have a pretty clear picture of the destructive potential of Campi Flegrei and the impact it would have on Italy and the world. One explosion nearly 40,000 years ago is believed to have contributed to the extinction of Neanderthals and was a level 7 on the Volcanic Explosivity Index. By comparison, the catastrophic eruption of Mount Vesuvius in 79 AD was only a level 5.
Here's a look at the general anatomy of the Campi Flegrei supervolcano, and what people in Naples and across the globe could expect if it went off today.
Animals And Plants Would Suffer From Overexposure To Fluorine
One of the major elements present in the ash and pyroclasts ejected by the Campi Flegrei volcano is fluorine, which today is used in the creation of fluoride, a chemical intended to prevent tooth decay. However, the level of fluorine that plants would be exposed to could cause an epidemic in the animal groups that eat those plants.
As explained by Antonio Costa of the National Institute of Geophysics and Volcanology in Bologna, "We know from chemical analysis that the ash [from Campi Flegrei] contained fluorine, which has a strong impact on vegetation, and it would have produced a disease called fluorosis in animals."
Modern examinations of volcanic incidents have shown that fluorosis can lead to infection or damage to animals' skin and respiratory tracts. A volcanic eruption could lead to massive population drops in animal groups that are unable to feed or hunt.
The Bay Of Naples Would Be Covered By Meters Of Debris
If the Campi Flegrei supervolcano experienced a significant explosion, as it did in the distant past, the debris ejected from the volcano would cover a truly incredible amount of land. The Bay of Naples wouldn't just be blanketed in ash like so many other areas of Europe. Instead, it would be downright buried.
When the Neapolitan Yellow Tuff eruption occurred approximately 15,000 years ago, the Campi Flegrei volcano ejected 40 cubic kilometers of volcanic debris. To understand how big that is, just one cubic kilometer of volcanic debris would fill 400,000 Olympic swimming pools. And the Neapolitan Yellow Tuff eruption pales in comparison to the Campanian Ignimbrite, which ejected an estimated 200 cubic kilometers of debris.
Needless to say, scientists believe the Bay of Naples and the cities around the caldera would be covered in several meters of ash and other detritus. Homes and buildings could potentially be buried forever.
More Than 6 Million People Would Have To Leave Their Homes
The Campi Flegrei supervolcano is located just west of Naples, an Italian city in the region of Campania. Numerous towns have been built and developed within its caldera over the last few thousand years. Populations inside the caldera and closely bordering it would be in immediate jeopardy if the various volcanic cones and edifices began to blow, and this would require a mass-evacuation of an enormous number of people.
The Naples metropolitan area alone has a population of over 3 million residents. If you include the populations of all the small towns and villages that would be directly in harm's way - such as Pozzuoli, Quarto, Qauliano, Monte di Procida, and others - the number of volcanic refugees would be close to 6 million. All of them would be looking for places to escape to in neighboring cities and countries already bracing for a catastrophic disaster, creating an additional logistical nightmare.
The Ground Itself Could Crack And Spew Out Magma
If you stood in the middle of the caldera, it would be easy to assume that any of the individual vents or craters are the volcano. In reality, numerous magma chambers and tubes - essentially, volcanic plumbing - run underneath the caldera. The entire region, both on land and underwater, is an enormous volcano - and new vents, peaks, and fissures can occur anywhere at points of pressure. It's one reason the area is called the "fields of fire" in Italian.
The most recent significant eruption at Campi Flegrei happened on September 29, 1538. A new volcanic cone rose from the ground and grew to over 400 feet in one week. This peak became known as Monte Nuovo, or "New Mountain." Contemporary accounts state that a crack formed at the highest point and burst open. Monte Nuovo ejected enormous amounts of fire, muddy ash, and pyroclastic flow described as white and gray smoke. The eruption lasted for three days, with the majority of activity happening within the first 24 hours, and then came to an end.
As described by historians William Davis and William Snyder in National Geographic in 1902:
Masses of lava "as big as an ox" were shot into the air by the bursting of great bubbles of gas or steam that ascended through the lava in the vent. Finer ashes fell over the country for several miles around. The people in the neighboring villages fled in terror from their homes.
This particular eruption was miniscule in comparison to the eruption that occurred 40,000 years ago. If Campi Flegrei burst to its true explosive potential, no structure inside the caldera would be spared from destruction.