The Phlegraean Fields is a vast active volcanic area with a structure called "caldera," a lowered area with an almost circular shape caused by significant eruptions in the past. The Phlegrean Fields caldera stretches from Monte di Procida to Posillipo and includes an underwater part of the Gulf of Pozzuoli.
In 1538, the Phlegraean Fields witnessed its last eruption. Despite being one of the smallest in its eruptive history, this event marked the end of 3000 years of quiescence. Within just a few days, the eruption gave birth to the cone of Monte Nuovo, standing about 130m high. Since then, the caldera has been quiescent, that is, "dormant," but shows signs of activity such as seismicity, fumaroles, and ground deformation.
The Phlegraean Fields caldera is notably affected by a phenomenon known as bradyseism. This involves slow phases of ground lowering, or subsidence, interspersed with more rapid uplift phases. While the associated seismic activity generally doesn't reach high magnitudes, it can still cause damage due to its superficial nature. This activity is easily perceived and can lead to damage to infrastructure and buildings.
The main recent bradyseismic crises occurred during 1970-1972 and 1982-1984 and registered a total ground uplift of more than three meters along with hundreds of earthquakes. During these events, Pozzuoli's historic center residents were evacuated and relocated to neighborhoods on the city's outskirts. Since 2005, a new stage of uplift has been observed as the ground has risen by more than a meter, resulting in many earthquakes.
Since 2012, the continued shifts in some of the geophysical and geochemical parameters tracked by the networks of the INGV-Vesuvius Observatory (increased seismicity, changes in the geochemical composition of fumaroles and gases coming from the ground, and, of course, ground uplift) necessitated raising the alert to the yellow level and activating the operational phase of “attention”.
The volcanic activity status and the phenomenon of bradyseism in the Phlegraean Fields are in constant evolution.
The Civil Protection Department usually holds monthly videoconferences to assess the volcanic activity status and alert level with the Centers of Expertise in charge of observing volcanic activity on the Phlegraean Fields: the Vesuvius Observatory of INGV and the Institute for Electromagnetic Sensing of the Environment (IREA) of the CNR-National Research Council. Also involved in the videoconferences are the General Directorate for Territorial Government, Public Works and Civil Protection of the Campania Region and the PLINIVS Study Center of the University of Naples Federico II, the Department's Center of Expertise for studies on seismic and volcanic vulnerability.
According to the phenomena and risk assessments made available by the Centers of Expertise, the Civil Protection Department declares the alert levels in strict coordination with the civil protection structure of the Campania Region after consulting with the National Commission for the Forecasting and Prevention of Major Risks - Volcanic Risk Sector. The steps to be taken by the National Civil Protection Service are set out in the operational phases (attention, pre-alarm, and alarm) provided in the civil protection plans. The Prime Minister announces the stages of pre-alarm and alarm.
The outcomes of the videoconferences can be viewed at the end of this page in the "Attachments" section. The last available report is dated September 2023; due to the intensification of the ongoing bradyseismic crisis, the National Commission for the Forecasting and Prevention of Major Risks met several times in October, November, and December 2023 and confirmed the yellow alert level for volcanic risk in the Phlegraean Fields. For more details, please visit this page.
The red zone is the area where preventive evacuation is, in case of "alarm," the only safeguard measure for the population. This area is exposed to the danger of invasion by pyroclastic flows, which represent the most dangerous phenomenon for the people due to their high temperatures and speed. The municipalities of Pozzuoli, Bacoli, Monte di Procida, and Quarto; part of the municipalities of Giugliano in Campania and Marano di Napoli; some neighborhoods of Naples: Soccavo, Pianura, Bagnoli, Fuorigrotta and part of the neighborhoods of San Ferdinando, Posillipo, Chiaia, Arenella, Vomero, Chiaiano and Montecalvario are included in the red zone. About 500,000 residents live in this area.
The yellow zone is the area exposed to significant volcanic ash fallout in the event of an eruption. For this area, temporary evacuations of the population residing in buildings made vulnerable or difficult to access by the accumulation of ash may be required. The yellow zone includes the municipalities of Villaricca, Calvizzano, Marano di Napoli, Mugnano di Napoli, Melito di Napoli, and Casavatore and 24 neighborhoods of the City of Naples: Arenella, Avvocata, Barra, Chiaia, Chiaiano, Mercato, Miano, Montecalvario, Pendino, Piscinola, Poggioreale, Porto, San Carlo all'Arena, San Ferdinando, San Giovanni a Teduccio, San Giuseppe, San Lorenzo, San Pietro a Patierno, Scampia, Secondigliano, Stella, Vicaria, Vomero, and Zona Industriale. More than 800,000 residents live in this area.
For more details on national emergency planning for volcanic risk in the Phlegraean Fields and to view the map where the red zone and yellow zone are located, you can read this article.
The Phlegraean Fields are a volcanic caldera and pose a very high threat due to the risk of volcanic phenomena, the presence of many inhabited centers in the area, and their immediate proximity to the city of Naples.
The definition of risk for the Phlegraean Fields is more complex than for other types of volcanoes. The definition of an eruptive scenario requires the determination of the most expected kind of eruption, with its possible expected phenomena, as well as the likelihood of the opening of eruptive vents in different areas of the caldera, which affects the potential distribution of products over the territory. Unlike volcanoes with a central apparatus, in the Phlegraean Fields, the area of possible opening of eruptive vents is extensive.
Nevertheless, it is expected that a future eruption at the Phlegraean Fields could produce several phenomena, which can be summarized essentially as the launching of bombs and large blocks near the eruptive center, the flow of pyroclastic flows within a radius of several kilometers, and the fallout of ash and lapilli from a distance of many kilometers. Concerning the latter phenomenon, it should be considered that, unlike Vesuvius, Naples is located downwind of the dominant wind direction and is likely to be affected.
The monitoring system of the Phlegraean Fields, managed by the INGV - Vesuvius Observatory, constantly tracks parameters related to seismicity, ground deformation, and physicochemical characteristics of fumaroles. Data related to the monitoring of the Phlegraean Fields volcanic area are submitted to the Department and constantly updated on the INGV - Vesuvius Observatory website.
In addition to INGV, the Institute for Electromagnetic Sensing of the Environment (IREA) of the CNR-National Research Council also helps with satellite monitoring of ground deformation. Furthermore, the PLINIVS Study Center of the University of Naples Federico II researches the vulnerability of elements exposed to volcanic phenomena in the Phlegraean area.
The eruptive history of the Phlegraean Fields is marked by two significant eruptions: the Campanian Ignimbrite eruption, which occurred 39,000 years ago, and the Neapolitan Yellow Tuff eruption, which occurred 15,000 years ago. These eruptions were followed by two subsidence episodes that, overlapping, gave rise to a complex caldera that today is the most evident structure in the Phlegrean area.
During the Campanian Ignimbrite eruption, the most violent in the Mediterranean area with a volume of magma emitted between 100 and 150km3, pyroclastic flows buried two-thirds of Campania under a thick blanket of tuff deposits. This was the occasion of an initial sinking of the area above the magma chamber that gave rise to the caldera, which was subsequently invaded by the sea.
The Neapolitan Yellow Tuff eruption, in which the volume of magma emitted was 20-30km3, resulted in the formation of a smaller caldera inside the first one.
Over the past 15,000 years, more than 70 eruptions have occurred, forming volcanic structures, craters, and volcanic lakes that are still clearly visible, such as Astroni, Solfatara, and Lake Averno. The most recent eruption, which occurred in 1538 after a period of stagnation of about 3,000 years, was anticipated by a ground uplift that reached 19 meters in two years and gave rise to the volcano Monte Nuovo, a mountain about 130m high on the eastern shore of Lake Averno.
Today, the Phlegraean area experiences significant fumarolic activity, accompanied by seismic activity and bradyseism, a slow uplift and lowering of the ground.
The major recent bradyseismic crises occurred during 1970-1972 and 1982-1984, resulting in a total ground uplift of more than three meters and thousands of earthquakes. During these events, Pozzuoli's historic center residents were evacuated and relocated to neighborhoods on the city's outskirts. Since 2005, a new phase of ground uplift has started, which, in 18 years, has increased by more than a meter and registered many earthquakes.
Since 2012, the variations of some parameters monitored in the caldera area (increased seismicity, changes in the geochemical composition of fumaroles and gases coming from the ground, and, of course, ground uplift) necessitated raising the alert to the yellow level and activating the operational phase of “attention”.
Note of the Head of Department of December 12, 2023
DL No.140/2023 - Art. 4. Transmission of the Rapid Emergency Planning document for the bradyseism in the Phlegraean Fields
Conversion Law No. 183 of December 7, 2023
Urgent measures to prevent seismic risk related to bradyseismic phenomenon in the Phlegraean Fields area
Resolution of the Campania Regional Council No. 679 del 23 novembre 2023
Article 3 of Decree-Law No. 140 of October 12, 2023 - Urgent measures to prevent seismic risk related to the bradyseismic phenomenon in the Phlegraean Fields area. Communication plan to the population
Decree-Law No. 140 of October 12, 2023
Urgent measures to prevent seismic risk related to the bradyseismic phenomenon in the Phlegraean Fields area
Resolution of the Regional Council No. 187 of April 19, 2023
Phlegraean Fields Volcanic Risk. Pathways for the assisted removal and autonomous removal of the population from the red zone
Resolution of the Campania Regional Council No. 547 of September 4, 2018
(Removal planning, approval of meeting areas and gates)
Decree of the President of the Council of Ministers of June 24, 2016
Provisions for updating emergency planning for volcanic risk in the Phlegraean Fields
(red zone, yellow zone and twinning Map)
Decree of the Head of Department of February 2, 2015
Indications to the components and operational structures of the National Service for the updating of emergency plans for the precautionary removal of the population of the red zone of the Vesuvian area