In the Phlegraean Fields area, bradyseism has shown signs of intensification in the last two years, as the uplift of the ground, due to variations in magmatic hydrothermal pressure in the subsurface, has been accompanied by a gradual increase in seismic activity, both in the number of earthquakes and in their magnitude. In 2023, the strongest events occurred on 27 September and 2 October and had magnitudes of 4.2 and 4.0 respectively; while in 2024, the largest event was recorded on 20 May with a magnitude of 4.4. But what is the situation today? What phase are we experiencing? To answer these questions, we interviewed Dr Pierluigi Musto, geologist and author of numerous articles on the subject.
by Roberta Imbimbo

Dott. Musto, bradyseism in the Phlegraean Fields is a phenomenon that has always aroused great interest from a scientific point of view, in order to better understand volcanic processes and prevent any risks connected with possible eruptions or earthquakes. What phase are we experiencing today in terms of the rate of ground uplift and consequently seismic frequency/intensity?
Seismicity in the Phlegraean Fields is influenced by the speed at which the ground is rising: the greater the speed, the higher the seismicity, always bearing in mind that the maximum intensity expected in the area is estimated to be around 5 magnitude by experts. It has to be said that Prof. De Natale – Research Director of the Vesuvius Observatory, INGV headquarters in Naples – already in 2017 published (along with others) a paper in which he stated that, as the maximum uplift approached and exceeded the crisis of the 1980s, we would have an increase in seismicity, both in frequency and magnitude. Today we are a few tens of cm above this level. August is 10 mm/month with a fairly low seismic energy released compared to even the recent past. However, a significant seismic event was recorded on 6 December 2024 of Md 3.4 within a discrete sequence of less energetic events. It interrupted a period of absence of earthquakes of magnitude >3 (the last one was recorded at the end of August 2024). During periods of greater seismic intensity, the average rate of uplift was greater: in May 2024 of 20 mm/month, between September and October 2023 of 15 mm/month (with a peak of 10 mm in just three days between 21 and 23 September). We can therefore state that as long as the ground continues to rise, we will have seismicity. However, it must be emphasised that it is not possible to predict earthquakes or even the way in which energy is released (isolated earthquakes, seismic sequences). The Phlegraean caldera is a complex system and the phenomena that occur within it do not have a linear trend.
Can you give us a brief comparison with the bradyseismic crisis of the 1980s?
The two crises have different characters: in 1982-84 the rate of ground uplift was much higher. At that time we had values close to and sometimes above 10 cm/month, and in two years overall the ground rose by about 1.80 metres; in this crisis we are having a much lower rate of uplift. Suffice it to note that from November in 2005 until today the ground has risen by about 135 cm in the area of maximum deformation, at Rione Terra. However, it is necessary to remember that from 1985 to 2005, the beginning of the current ‘unrest’, the ground had lowered by about 95 cm. In the preceding crisis, after an initial period of moderate seismicity, there was a significant increase from 4 September 1983 and even more so from 4 October 1983, when an event with a magnitude of around 4.0 – 4.2 (the most energetic in those years) occurred. On 1 April 1984 there was a major seismic swarm with about 500 events in four hours. This has never happened again.

At what depth is the magma chamber now located? The director of the Vesuvius Observatory, Mauro Antonio Di Vito, spoke a few days ago of the magma rising from the previous 8 km to its current depth of 6 km. Is this confirmed? If so, what does this mean in practical terms? Is it plausible to think that there will soon be openings for the magma to rise?
Various specialised studies have been conducted with different methods on the situation of the Phlegraean subsurface and its evolution. All agree that there is currently a rather extensive magma chamber at a depth of about 8 km. It cannot be responsible for the thrust that generates the deformation of the ground, the source of this phenomenon is located higher up, between 3 and 4 km and would have limited extension (reference is mainly made to the model of Mogi – 1958). This is evident from the deformation itself, which is maximum in the Rione Terra area and tends to decrease rapidly laterally to become almost zero at the limits of the caldera. Prof Roberto Scandone, in a recent speech on the occasion of the celebrations for the 25th anniversary of INGV’s establishment, called this deformation ‘a resurgent dome’: it is a definition I particularly like. Researchers do not agree on what the origin of this source is: some say that it is gas that has risen to such depths and comes from the magma chamber, others claim that there are small portions of magma that have risen from below and are able to directly determine the deformation. A third hypothesis points to ‘a middle ground’ between the first two. The various hypotheses are formulated through various methods of indirect investigation which, by their nature, never provide certain data. The fact that there are conflicting hypotheses should not be surprising, as the various methods applied do not always converge into a single model, all of which is a starting point for further study and investigation, which is the ‘salt of science’ provided it is supported by data obtained according to the scientific method.
Do we now have state-of-the-art instruments to predict a possible imminent volcanic eruption well in advance?
The Phlegraean area is monitored 365 days a year – 24 hours a day by the Vesuvius Observatory (INGV headquarters in Naples) with state-of-the-art instruments and highly specialised personnel. This is ‘multi-parametric’ monitoring that not only detects seismicity and ground deformation but other parameters such as geochemistry, gravimetry, etc. In this way, it is possible to effectively keep an eye on the territory. I would like to emphasise how the monitoring system has made great strides since the crisis of the 1980s, and is now being implemented. In the 1980s, seismographs were not digital, ground deformation analysis was not carried out by satellites, and various other instruments did not have the technology of today.
What could be the anticipatory signs of an eruption?
Researchers study what has already happened in other parts of the world; in the Phlegraean area we have the only example of an eruption that occurred in historical times and is therefore also supported by chronicles of the time (Monte Nuovo 1538). Studies are continually implemented in various fields of research also through constant comparison. For example, one can observe the trend of deformation over time: it has taken on an almost constant form since the crisis of the 1980s (maximum near the Rione Terra and gradually decreasing away from its centre). This suggests the stationarity of the source; if an asymmetry were to develop, with a significant increase in velocity, it would indicate a major movement from below. Reference is made to the seismicity that would increase significantly by providing other parameters of a specialised nature. It is essential to emphasise that these and other elements can only be assessed by the highly specialised personnel of the research institutes involved in monitoring, the only ones able to have all the parameters necessary for such a delicate prediction. I would also like to emphasise that international researchers are involved in various capacities in the study of the entire Neapolitan volcanic area. In Naples in May 2023, there was a very interesting conference that I had the honour of attending (as an auditor).
In the event of an eruption of the Phlegraean Fields, what would happen to Pozzuoli, Naples and all the districts within the red zone? Do you think that the population is sufficiently informed about the guidelines to be adopted in the event of imminent danger?
A possible volcanic eruption would presumably result in the emergence of yet another volcanic crater within the Phlegrean caldera. Where? It is impossible to know! How big would the eruption be? Experts rule out the possibility that it could be compared to the eruptions of the Campania Ignimbrite and the Neapolitan Yellow Tuff. The most probable event hypothesised is expected to be of small to medium magnitude, however it is assumed to be explosive in character with the expulsion of pyroclastic material into the atmosphere (Plinian or Sub-Plinian eruption). With the inevitable fallout, a high-temperature, high-velocity ‘pyroclastic cloud’ could be generated that would destroy everything it encounters; its path is totally unpredictable. Such a scenario would suggest the need to evacuate the entire Flegrean caldera and several areas on its rim, according to the Civil Protection’s evacuation plan. The inhabited centre of Naples would be exposed to ash fallout. At present, there are no indications of an imminent volcanic eruption. Since 2012, a state of ‘unrest’ has been ‘made official’ by raising the alert level for volcanic phenomena: from green (quiet) to yellow (attention). Any worsening in the state of the volcano would induce the competent bodies to raise the alert level to orange (pre-alarm) before a possible evacuation (red). The hazard for seismic events is different: it has been calculated that the highest energy event could reach a magnitude of about 5 (maximum theoretical event). The territory is already exposed to earthquakes with a magnitude > 3, which determines the need for an adequate prevention plan for both buildings and the behaviour of the population.

Awareness-raising on the subject starts with the youngest and starts right from the schools.
Several years ago, the Civil Protection and the INGV promoted an information campaign in schools aimed at teachers and students on the subject of prevention in the Neapolitan volcanic area (Project ‘I do not risk’) This project is aimed at the entire population and can be consulted at https://iononrischio.protezionecivile.it/it/. Recently, on the occasion of the 44th anniversary of the Irpinia earthquake, the Order of Geologists of the Campania Region promoted the event ‘The Geologist in the Schools’ in which a geologist (internal or external to the participating school institution) illustrated the dangers of potentially catastrophic natural phenomena. Educational initiatives on the geological aspects of the Phlegraean Fields are often promoted in various schools in the Phlegraean area, and I am often involved in them, as in the Comprehensive Institute where I teach (I.C.Madonna Assunta di Bagnoli).
Possible future scenarios?
First of all, it is essential that research goes ahead, that technological progress continues to support the instruments used for monitoring, that the competent bodies continue to improve in their functions, and, allow me, that the world of young people can become passionate about knowledge in this scientific field, providing new impulses for knowledge and doing in Neapolitan volcanology.