J - 209 : Campi Flegrei - Ticking Time Bomb?

View over the "Phlegarean Fields" east of Pozzuoli towards Sorrento (l.) and Capri (r.)

The “Phlegarean Fields” or Campi Flegrei were in the news last week. During one single night, local Emergency Services received more than 800 reports of new gas vents opening up in the middle of villages, streets, parks and open fields. The “Campi Flegrei”, the often overlooked twin to the Vesuvius volcano, seem to be wakening up.

Under upward pressure and volcanic steam one road

in Pozzuoli cracked open - luckily only one street

The year before, between March and June, there were three powerful earthquakes with a magnitude of > 4.0 on the Richter scale. In addition, tens of thousands smaller quakes preceeded the big ones. Some of the tremors came from very deep. Geologists spotted the source in 8 km depth. Data indicates that pressure waves travelled through a network of ancient magma tunnels which were dormant for centuries. A 8 km long network crosses the Gulf of Naples and reaches Monte Vesuvio. The Flegrei Caldera and the Vesuvio are linked.

Schematic Illustration of the Magma Channel Network linking Campi Flegrei and Vesuvio

Would probably not cover this event were Pozzuoli not our disembarkation port on 16 Sept 2026. This year we are sailing along Italy’s Arch of Fire. In week 1 we will see Mount Etna in the distance, then climb Monte Vulcano in week 2 and sail past the Stromboli. In week 3 we cruise around the Gulf of Naples, always in the vicinity of Mount Vesuvius.

The Caldera of Campi Flegrei is 13 km wide and contains 17 Volcanic Craters

The volcanic activities on Italy’s West coast are the result of the African continental plate sliding below the European plate. I covered the subject in 2021. On the descent, water locked inside the African plate turns into powerful steam. The explosive steam cracks rock formations - magma streams upwards and forms chambers and volcanos. The Flegrei Fields form a 13 km wide caldera which Wikipedia explains better than I ever could. It is 600’000 years old and erupted powerfully 39’000 years ago during the last ice age. As southern Europe was ice free, the meters thick layers of ash and pumice can still be found.

The Cloud of Ejecta from 39'000 years ago covered large parts of Europe in Ash and Pumice

Thereafter the caldera became dormant and was inactive even during the eruption of the Vesuvio in 79 AD when Herculaneum and Pompeii were destroyed. But earthquakes and slow land up-lifts and subsidence, called Bradisismo, continued and changed ground levels and costal lines constantly. The Gulf of Pozzuoli was once the playground for Rome’s rich and powerful. Their villas lined the hills and shores of Baiae. Now the costal area is partially covered by the sea. The Empire’s largest naval base, Misenio was just around the corner to the west and the commercial port where lots of money was to be made in Pozzuoli.

The Remains of the Roman Market (Macellum) are above Sea Levels again

Macellum, the Roman market next to the ancient port, was once at sea level, then inundated by the waves for a few hundred years and now sits a few meters above the sea again. Over the last few decades, Pozzuoli was lifted by 2 cm p.a. The moving ground causes the cracks in houses and opens the ground where volcanic gases from deep below the earth escape.

Changes in Altitude 2007 - 2011 (left) and 2011 - 2023 (right)

The Campi Flegri and the Mount Vesuvius are one of the most intensively monitored volcanic areas. With a good 3 million people living in the region of Naples, this is not a surprise. Nobody wants a repeat of Herculaneum and Pompeii. Elaborate evacuation plans have been drawn up to bring people to safety – just in case. Now that geologists discovered the connection between the Vesuvius and the caldera of the Campi Flegrei they have to adjust the emergency procedures. The simultaneous eruption of both is quite a challenge.

Naples Rescue and Emergency Services regularly train together for an Evacuation

Evacuating 3 million people from Naples in an orderly fashion and on time is not easy and could become very messy. That eruptions often occur quickly was shown by the Monte Nuovo in Pozzuoli. In 1538, during the last period of caldera activity, a 100 meters high volcanic edifice built within a few weeks. It was the first volcanic eruption well observed and documented. Renaissance men were deeply interested and kept detailed records.

View from the Campi Flegrei over Pozzuoli in 1829

Having no crystal ball, I do not know whether there will be any volcanic activity when we arrive in Pozzuoli. Experts believe there is not enough magma in the chambers for an eruption. It would need about three times the current volume. But we may witness vents spuing out smelly gasses and smaller tremors. Authorities are now so well prepared that there are even simulations for potential tsunamis. In case there is one, we best sit it out on the open sea. Most likely though we will disembark in Pozzuoli without any friction.

Tsunami Simulaions in the Gulf of Pozzuoli