The Phlegraean Fields, known as Campi Flegrei in Italian, has once again grabbed the headlines following the potent earthquake tremors experienced on September 27, 2023. Positioned in Campania, within the Gulf of Pozzuoli, this active volcanic region stretches across several municipalities, including Bacoli, Giugliano, Monte di Procida, Naples, Pozzuoli, and Quarto. The term 'Campi Flegrei', translating to 'burning fields' from Greek, perfectly captures the essence of this region, brimming with volcanic activity since ancient times.
Understanding the Distinct Volcanic Nature of the Phlegraean Fields
Unlike its famous counterpart, Vesuvius, the National Institute of Geophysics and Volcanology outlines that the Phlegraean Fields aren't a single volcano. Instead, it's a volcanic field that has remained active for over 80,000 years, comprising multiple volcanic centers scattered across a depression termed the 'caldera'. This caldera came into existence following two significant eruptions - the Campanian Ignimbrite (40,000 years ago) and the Neapolitan Yellow Tuff (15,000 years ago). Both eruptions resulted in the depletion of the magma reservoir, leading to the collapse of the roof.
Tracing the Volcanic History of the Phlegraean Fields
The first eruption (Campanian Ignimbrite) is noted as the most powerful eruption ever witnessed in the Mediterranean, causing climate alterations on a global scale. Conversely, the second eruption (Neapolitan Yellow Tuff) triggered an epoch of heightened activity, accounting for 27 eruptions in the last 5,500 years. Among these, the most recent one in 1538 resulted in the formation of the tuff cone, dubbed Monte Nuovo.
The Phlegraean Fields and the Phenomenon of Bradyseism
This volcanic area is known for bradyseism - a gradual shift in the ground level due to uplift and subsidence. Documented since the 4th century AD, this phenomenon significantly impacted the region during the 1970s and 1980s, with Pozzuoli experiencing an uplift of approximately 3.5 meters. A period of subsidence ensued, only to be disrupted by an uplift trend in 2005, which continues to date.
Current State of Affairs in the Phlegraean Fields
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A recent INGV report from July 2023 noted a 4.2 magnitude tremor in the Phlegraean Fields on September 27, 2023 - the strongest in recent history. Preceding this, August witnessed numerous tremors, including two of 3.6 and 3.1 magnitudes, felt by a substantial populace on August 18.
Additionally, the report recorded 206 earthquakes in July 2023, with a maximum magnitude of 1.9 (±0.3). Out of these, six (approximately 2.9%) ranged between 1.0 and 1.9 magnitudes, while 200 (approx. 97.1%) registered magnitudes less than 1.0 or were undeterminable.
Furthermore, soil deformation monitoring networks identified a radial uplift pattern centered in Pozzuoli, reaching a peak velocity of around 1.5 cm per month. However, a reduction in uplift velocity has been observed since May-end 2023. As per the latest data from the INGV monitoring network, the Phlegraean Fields currently hold a yellow alert status.
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