from the pen of icarus blake

Campi Flegrei, also known as the Phlegrean fields, is a series of 24 volcanic calderas in the ocean outside of Naples, Italy.  One of these, the Solfatara crater, was considered the home of the Roman God of Fire Vulcan due to the amount of volcanic activity evident in the area.  The caldera itself underlies the districts of Agnano and Fuorigrotta in southwestern Naples, as well as the cities of Pozzuoli, Bacoli, Monte di Procida, Quarto, and the Phlegrean Islands.  The area is densely populated, more than 180,000 people live directly atop the caldera.  

Campi Flegrei’s history of seismic activity can be tracked back multiple thousands of years, but it’s more recent history has worrying implications for our modern world.  Geological evidence (rock formations generated by eruptions in the preceding 20,000 years) that indicate a pattern of uplift and subsidence — ie. a process of magma filling a chamber beneath the caldera, preceding eruption.  Data collected in the area since 1969 indicates this process of gradual uplift has been ongoing, and suggests an eruption in the coming “decades to century”.

Between the years of 1984 and 1985, a major uplift event occurred and authorities in Campania and Italy at large seriously considered evacuating the overlying and surrounding communities at Campi Flegrei, but before the order was given, the caldera began to subside once more.  This may have been an internal rift opening, allowing magma to flow away from the surface, or an encounter with a pocket of CO2 within the earth.  Either way, the fears of an eruption were assuaged until uplift began again in 2000.

The uplift event in 1984-85 stretched the overlying crust to the breaking point, reaching maximum tensile stress (think filling a balloon until it pops).  A similar situation arose in 1994 in Papua New Guinea, when the Rabul caldera erupted following seismic activity 10 times less intense than the last period of recorded activity.  The last recorded period of activity stressed the crust overlying the caldera to a breaking point, allowing a much smaller uplift event to trigger an eruption.  This eruption was about as destructive as the eruptions Campi Flegrei has had in the past, but resides in a less populated area, and occurred with enough warning to minimize casualties (5, mostly to lightning storms triggered by ash clouds entering the atmosphere).  In addition to its location, Campi Flegrei erupts at multiple points over an extended period during a single eruption cycle.  Periods of volcanic activity at Campi Flegrei can last up to 150 years (based on geological dating of rock formations laid down during the last major active period).  This means that, if evacuation for an eruption is necessary, the area may be uninhabitable for decades.

Fears of an eruption intensified following a number of studies that found that uplift in the caldera beneath the city of Pozzuoli was reaching levels that matched those of 1984-85, including an increase in volcanic activity that could indicate a larger event on the horizon.  The seismic uplift that stretched the rock of the caldera to its breaking point in 1984-85 is repeating itself, this time with the stressed and weakened crust underlying a highly populated region of Italy.  By 2020, geological monitoring noticed that the crust reached an inelastic state — it can no longer stretch, the balloon has to pop.  The pressure may still be relieved by a fissure opening in the bedrock below the magma, but Campi Flegrei is approaching a probable surface eruption.

On September 27th of this year, Campi Flegrei experienced the strongest earthquake in 40 years (4.2 on the Richter scale).  An eruption would displace 360,000 people — the inhabitants of the cities overlying the crater as well as those within the eruption zone who would be directly impacted by related events such as ash clouds and pyroclastic flows (like the ones that buried Pompeii) emitted by the eruption.  In addition, an eruption in Italy is likely to impact multiple aspects of modern life as the eruption of the Eyjafjallajökull volcano in 2010.  Major disruptions in air travel and global trade can be expected.  The eruption of Campi Flegrei will be far larger than the eruption in Iceland, and may be large enough to disrupt climate patterns worldwide as the Tambora eruption of 1815 did (though not as intensely — the Tambora eruption was the largest in human history) resulting in worldwide temperature drops.  As of October 8, authorities in Italy are running drills and considering evacuation plans if the seismic activity continues and no subsidence is observed.  If we are to see a world-changing volcanic event in our lifetime, it’s likely to be Campi Flegrei.

Sources:

Isaia R, Marianelli P, Sbrana A, “Caldera unrest prior to intense volcanism in Campi Flegrei (Italy) at 4.0 ka B.P.: Implications for caldera dynamics and future eruptive scenarios” Geophysical Research Letters 36:21 (2009)

Kilburn C, Carlino S, Danesi S, Pino N, “Potential for rupture before eruption at Campi Flegrei caldera, Southern Italy” Communications Earth and Environment 4:1 (2023)

Angela Giuffrida, “Fears rise of volcanic eruption near Naples after strongest earthquake in 40 years” The Guardian, September 28, 2023

Erik Klemetti, “Is It Time to Start Worrying About an Eruption at the Campi Flegrei?” Discover Magazine, October 8, 2023

Smithsonian Institution National Museum of Natural History Global Volcanism Program (https://volcano.si.edu)