If Italy's Campi Flegrei Supervolcano Erupts, It Could Be Even Worse Than Mount Vesuvius

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.

  • Campi Flegrei Is Made Up Of 24 Different Volcanic Craters And Vents
    Photo: Sir Charles Lyell / New York Public Library / CC0 1.0

    Campi Flegrei Is Made Up Of 24 Different Volcanic Craters And Vents

    The Campi Flegrei supervolcano doesn't have the structure that is generally imagined when people think of volcanoes. Instead of a single, steep-sided mountain, it's made up of 24 smaller craters, volcanic edifices, and vents that all reside inside a large, circular depression known as a caldera. Its broader name is the Phlegraean Fields.

    The caldera is a massive crater that was formed 40,000 years ago when Campi Flegrei erupted. Significant volcanic activity routinely occurs in the numerous submarine vents off the coast, and two dozen volcanic edifices can be found both above ground and under the waters of the Mediterranean. 

  • The Eruption Would Send Ash Into Africa, The Middle East, And Central Russia

    On multiple occasions in the past, Campi Flegrei exploded to catastrophic effect. One of the most destructive eruptions is known as the Campanian Ignimbrite event (CI), which occurred around 38,000 BC. Using this as a guide, it's possible to estimate how the ash cloud from a massive explosion would spread across the world.

    During a survey for new archeological sites in Romania, the Max Planck Institute for Evolutionary Anthropology discovered ash from the CI event in deposits "up to 50-100 centimeters thick." That means that researches found 4-foot layers of ash over 750 miles from the actual volcano. Ash from the massive eruption of Campi Flegrei has also been found in areas of North Africa, across multiple countries in the Middle East, and deep into Central Russia - over 2,000 miles from Naples.

  • The Color Of The Sky Would Change

    A massive explosion of the Campi Flegrei volcano would alter the color of the sky. The ash alone would cause an overall graying of the air as it muddied the light from the sun, and sunsets would become much more frightening.

    When the Campanian Ignimbrite event occurred, volcanologist Benjamin Black explained, "Sunsets would have been dark red for a year after the eruption due to sulfur in the atmosphere." 

    This eruption occurred during a transitional stage in human history, when Neanderthal populations were dwindling and Homo sapiens were on the rise. For the people at the time, the change would have been a confusing and foreboding sight. "Imagine what that must have been like to see and wonder about," Black said.

  • It Would Decrease The Average Temperature Across Europe And Lead To A Mini Ice Age
    Photo: Sanchit Maharjan / Wikimedia Commons / CC BY-SA 4.0

    It Would Decrease The Average Temperature Across Europe And Lead To A Mini Ice Age

    If Campi Flegrei erupted to its full potential, or to the degree that it did 40,000 years ago, it would spew a massive ash cloud into the air that could lower temperatures throughout Western Europe and as far away as Central Russia. According to volcanologist Benjamin Black, who has studied the impact of the Campi Flegrei eruption on Neanderthals, average temperatures dropped nearly 9 degrees Celsius in parts of Russia.

    In areas less directly affected by the ash cloud, average temperatures could drop by 3 to 5 degrees. That may not sound like a lot, but the so-called "Little Ice Age" that lasted from the 1300s to the 1800s was a result of average temperatures dropping as little as 2 degrees from present-day levels. The last ice age, which saw massive freezing across large swaths of the Earth, was 10 to 12 degrees colder than today - meaning a 9-degree drop in Russian would definitely lead to massive freezing conditions, and potentially the beginning of a modern-day ice age.

  • Animals And Plants Would Suffer From Overexposure To Fluorine
    Photo: Bark / Flickr / CC BY 2.0

    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.