Campi Flegrei: The Stirring Giant Beneath Italy

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Campi Flegrei Seismic Activity: Interpreting Recent Geodynamics.


Italy’s Campi Flegrei, also known as the Phlegraean Fields, has been a significant point of discussion in recent years due to its heightened geological activity. This captivating volcanic complex, located in the Campania region of southern Italy, comprises 24 craters and volcanic edifices, marking its place as one of the most significant geological formations on the planet.

The 2023 Campi Flegrei Earthquake

The attention towards Campi Flegrei further intensified on June 11, 2023, when an earthquake of magnitude 3.6 occurred, originating 3 kilometers beneath the heart of the Phlegraean Fields. This seismic event, alongside another comparable incident of the same magnitude in March 2022, underscored the most potent tremor experienced in the area since the seismic period of 1982-1984. During this historical period, the region was bombarded with more than 1,200 earthquakes, with magnitudes extending up to 4.

The earthquakes recorded in May 2023 in the Phlegraean Fields (Vesuvian Observatory of the National Institute of Geophysics and Volcanology).
Earthquakes recorded in May 2023 in the Phlegraean Fields (Vesuvian Observatory of the National Institute of Geophysics and Volcanology).

Although these seismic events did not lead to structural damages in the nearby towns and cities, including Pozzuoli, they serve as a strong indication of the vital geological forces that continue to shape the region. Thus, a close examination of these tremors is critical to unravel the geological past of the area and draw accurate predictions for the future based on the available data.

The Geological Complexity of Campi Flegrei: Unraveling the Intricacies

The geological intrigue of the Phlegraean Fields is not just in its surface manifestation, but also in what lies beneath. Unlike its nearby counterpart, Vesuvius, Campi Flegrei does not possess a single, dominant volcanic cone. Instead, it presents an intricate system of various volcanic centers that lie within a depression, or caldera. This geological structure is a result of a massive reservoir of magma collapsing post two significant eruptions around 40,000 and 15,000 years ago, followed by gradual subsidence.

The Caldera and Its Surroundings

The region that the caldera and the associated volcanic system span is vast – roughly 12 kilometers by 15 kilometers. This area encapsulates several municipalities, including Bacoli, Monte di Procida, Pozzuoli, Quarto, and Giugliano, in addition to a section of Naples. Since the last eruption in 1538, the volcanic activity has been restricted to fumaroles and thermal waters.

Solfatara (volcano), source

The Solfatara of Pozzuoli, one among the forty volcanoes constituting the Phlegraean Fields, resides nearly three kilometers away from the heart of Pozzuoli. Despite being an age-old volcanic crater, its active status remains, albeit currently dormant. Over the past two thousand years, it has consistently displayed the phenomena of sulfur dioxide fumaroles, jets of scorching mud, and high soil temperatures; these activities, also observable in various parts of the globe, are coined as “solfatara” due to their shared characteristics with the one in Pozzuoli. The formation of the Solfatara occurred within the Phlegraean Fields’ third eruption period, dating back 3,700-3,900 years ago. During the epoch of the Roman Empire, its prominence was well-recognized, as reflected in Strabo’s “Strabonis Geographica,” which portrayed it as the domicile of Vulcan, the god of fire, identifying it as the gateway to the Underworld or the Forum Vulcani. Pliny the Elder also made reference to it as the “Fontes Leucogei” for the alum-like, white waters that continue to emanate from it. Around the same era, mining pursuits for the bianchetto, a type of plaster, commenced. The extraction process involved a fee of 20,000 sesterces. In the year 1198, under the rule of Frederick II of Swabia, Scipione Mazzella documented a calamitous eruption of the Solfatara, which was accompanied by an intense earthquake.

Campi Flegrei’s Geological Past: Journey Through Time

The Phlegraean Fields’ recent seismic activities can be better comprehended by examining its historical geodynamic patterns. Throughout the twentieth century, the caldera’s soil experienced an uplift in three distinct periods. Each phase primarily affected Pozzuoli, leading to a substantial elevation of up to 3.5 meters in the ground level. The uplift process began again in 2004 and continues to this day, but at a slower pace and causing fewer earthquakes than in the 70s and 80s.

Sulfur at the Solfatara crater
Sulfur at the Solfatara crater, source

Seismic Patterns in Campi Flegrei: The Rhythm of the Earth

Campi Flegrei’s seismic activity is not just a series of sporadic tremors. Each quake is a piece of a larger puzzle that, when put together, tells the story of the region’s geodynamics. In April and May 2023 alone, an astounding 675 and 661 earthquakes were recorded, respectively. Although most of these were weak and barely perceptible to inhabitants, they are clear signals of the ongoing geological processes in the region.

Bradisism: Deciphering the Mystery

The main theory put forth to explain the observed bradyseism or slow, vertical ground movement in the area involves magma deep within the earth. As this magma releases large quantities of steam, the steam heats the rocks separating the magma from the ground surface, leading to terrain deformation, seismic activity, and intensifying fumarolic activity. The exact mechanisms and implications of this process, however, are subject to ongoing research and discussion.

What the Experts Say

On June 9, 2023, an international team of scientists from the National Institute of Geophysics and Volcanology (INGV) published a study. The research contemplated the possibility of the caldera’s movements causing a rupture in its crust, the most superficial layer. While it’s not entirely ruled out that magma may be implicated in this process, there are currently no concrete reasons to anticipate a traditional volcanic eruption involving lava outflow.

The current alert state for Civil Protection is “yellow” due to earthquakes, not because of an eruption threat. Understanding the nuanced geodynamics of the Phlegraean Fields is crucial for risk assessment and prevention.

Miniature from the Angelic Code
Miniature from the Angelic Code. Pietro da Eboli (13th century) “De Balneis Puteolanis”. Miniature from the Angelic Code Ms. 1474 (Angelic Library of Rome), showing the “Balneum Sulphatara”, which in the Middle Ages was considered miraculous for the treatment of female infertility and for numerous other ailments. The miniature depicts a group of women immersed in a hexagonal bath to regain fertility, while in the background a hooded figure stokes the emanations released from small volcanoes and fumaroles with a bellows.

Featured image source: wikipedia

Topics: Seismic Activity in Campi Flegrei, Ground Deformation in Campi Flegrei, Analysis of Earthquakes in Campi Flegrei, Geological Formation of Campi Flegrei, Theories of Bradisism, Recent Scientific Findings in Campi Flegrei, Volcanic Activity in Pozzuoli, Role of INGV in Campi Flegrei Studies


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