"The district of the universe where volcanoes, history and poetry have left more traces". This is how the French baroness Madame de Staël described the Campi Flegrei. A fascinating and mysterious region, which over the centuries has been the backdrop for ancient myths and legends. Gateway to Hades according to the Greeks and Romans, it is here that Virgil, in his Aeneid, begins the descent of Aeneas into the underworld. But in this handkerchief of land, as Roman tradition wanted, the sacred and the profane were indissolubly united, in an unrepeatable mix of veneration and otium, with the entire landscape from Posillipo to Monte di Procida dotted with sumptuous patrician and imperial residences, spas, piers, villas, fish ponds for breeding oysters and moray eels and an imposing amphitheater, the third largest in Roman times Italy after the Colosseum and that of Capua.
Testimonies of a pleasant and memorable past, therefore, which has not always come down to us precisely because of the changing morphology of the area. “The most wonderful region in the world; under the purest sky, the treacherous ground" wrote Goethe at the end of the XNUMXth century, to underline how maternal and welcoming nature did not hide here its most disturbing and at times dangerous side.
After the lively volcanic activity of antiquity, today the Campi Flegrei caldera, although active, is in a state of quiescence and continues to preserve a very important natural value. We talked about it with Rosella Nave, a geologist and volcanologist from INGV who, at the Vesuvius Observatory in Naples, is responsible for monitoring volcanic activity and communicating the danger and risk associated with it.
Rosella, which volcanoes are we talking about when we refer to the "Neapolitan volcanoes"?
Vesuvius, Campi Flegrei and Ischia, the active volcanoes of the area, monitored in real time by INGV through its seismic, geochemical and geodetic monitoring networks. We also have another volcanic island, Procida, which last erupted more than 20.000 years ago and is considered an extinct volcano.
What characterizes the area that we refer to as Campi Flegrei?
Definitely the caldera. It is a structure linked to two large caldera collapses (which occurred 39.000 and 15.000 years ago), i.e. formed during two large, high-energy explosive eruptions. In such cases, the magma chamber, i.e. the magma reservoir of a volcano, empties very quickly causing the overlying rocks to collapse and giving rise to a sub-circular or elliptical depressed area.
"Caldera" is a term that in Spanish also means "pan" and indicates the typical pan used to prepare paella: wide and with very low edges. Here, the Campi Flegrei have precisely this structure: a collapsed structure whose limits range from the hill of Posillipo to Monte di Procida, with a submerged edge in the gulf of Pozzuoli. It is a very characteristic area, unmistakable even from the photos from above, with a circular structure of about 12 kilometers in diameter "riddled" inside by various volcanic craters.
Is it correct to define Campi Flegrei as a "super-volcano"?
Let's say that this is not actually a volcanological term. It had been invented for an American volcano around the 2000s and then fell into disuse. More recently, around XNUMX, the BBC made a documentary about supervolcanoes focusing on Yellowstone and bringing the term back into the limelight. In reality, the super-volcano does not exist, a super-eruption of a volcano can exist, but always reminding us that this prefix is used above all in journalism.
In volcanology these "super-eruptions" correspond to those that have an explosivity index (VEI) of 8: explosive eruptions of very high magnitude which are generally classified as catastrophic. Yellowstone has historically given eruptions like this, but it should be remembered that even these so-called super-volcanoes in most cases produce much more frequent eruptions of much more modest entities.
The most violent eruption of Campi Flegrei, that of Ignimbrite Campana 39.000 years ago, was classified as VEI 7. However, this eruption, like other very large volcanic events, had a very significant impact on the environment. In fact, the large quantity of particles and gases emitted in these cases, and in particular of sulphur, interacting with the atmosphere determines a certain reflection of the sun's rays with the consequent cooling of the atmospheric temperature for a certain period of time. The Campi Flegrei, with the eruption of the Ignimbrite Campana, effectively produced a change in the climate of the northern hemisphere with a decrease in temperature of at least 3-4 degrees.
What kind of volcanism characterizes this area?
The reconstruction of the eruptive history of Campi Flegrei tells us that this volcano tends to produce explosive eruptions, preferably of medium and small size, with very rare effusive eruptions: just think that in the last 15.000 years there have been more than 70 eruptions, and of these only four were effusive.
As far as the major ones are concerned, these are eruptions that had a great impact on the territory, on which it was then built and re-built: in Naples, for example, it is enough to look around a little to realize that many of the buildings and monuments of the city are built in yellow tuff and gray tuff, which are among the main products of the Phlegrean eruptions.
Has this volcanism undergone variations over time?
Without a doubt it was gradually conditioned by the structural evolution of the caldera which controlled, through the systems of active faults, the rise of the magma to the surface. In particular, in the last 10.000 years it has been seen that the bottom of the caldera has begun to have resurgence movements due to changes in the structural response of the caldera bottom.
All this is part of the extremely peculiar geological phenomenon of the area, bradyseism. The term derives from the Greek and indicates a very slow movement of the ground, characterized by an uplift followed by a lowering of a much smaller entity. This phenomenon is linked to thrusts coming from slightly deeper parts of the crust, due to the ascent of magma or the introduction of hotter and deeper gases which expand the geothermal system which lies under our feet in Campi Flegrei and which is evident in the demonstrations at the Solfatara.
When did Campi Flegrei last erupt?
To 1538. It was an eruption that came after about 3.400 years of eruptive "silence", preceded by a brief but substantial phase of ground deformation in which the area rose and then reached an ascent of magma in the Monte Nuovo area. the cone about 130 meters high clearly visible also from the nearby coast.
What is the current state of the volcano?
It is currently in a state of quiescence. This means that there is no eruptive activity but there is background volcanic, seismic and deformation activity. Furthermore, since December 2012 the Campi Flegrei have risen in alert level going from the green level (Base) to the yellow one (Attention), precisely because of the variations in the seismic, deformation and geochemical parameters which for about ten years have indicated an evolving trend . However, this does not mean that the alert level must in the future necessarily vary from orange (Pre-alarm) to red (Alarm): over time, the parameters could in fact return to more stable values and the alert could then reenter.
Furthermore, these variations in the alert levels can take a very long time: the yellow alert level must however remind us that the Campi Flegrei are, yes, in a state of quiescence, but that it is not the same state of quiescence in which it is found , for example, Vesuvius.
How important is the issue of communicating the danger of this volcano alongside research and monitoring?
It's very important. It is in general for all volcanoes, but it becomes particularly important in the case of volcanoes where urbanization is intense and practically inside the volcanic area itself, such as Campi Flegrei.
It is important both to study the danger of a volcano in terms of eruptive probability, to contribute to the regular updating of the risk maps essential for an operational response to a possible emergency; and communicate this danger adequately to increase the awareness of citizens in the area where you live.
The conformation of the Campi Flegrei caldera does not help much in this sense, since it is not a central volcano with the characteristic cone shape as is, for example, Vesuvius, which already inspires a certain "fear" to the eye. In the Campi Flegrei caldera we have many small, more or less evident "volcanetti": the Solfatara, the small Monte Nuovo, the large crater of the Astroni and the other volcanic forms are decidedly more evident if seen from above, in aerial images where one can note how the inner area of the caldera is “riddled” with small craters.
I'm from Vesuvius and I know well that living under a volcano that dominates the landscape gives you a much better awareness of risk: it's as if you could more easily reach a greater degree of "conscious acceptance" of the area in which you live.
In the case of Campi Flegrei I would certainly say that the proximity to Vesuvius, which is the most famous volcano in the world due to the eruption of Pompeii in 79 AD, tends to shift much of the attention and concern of the inhabitants towards the volcano clearly visible, to the detriment of what you actually live in.
What level of awareness and perception of risk is there among the people who live in the Phlegraean area?
This is a very important issue, which we have been dealing with for some time: even the reflections made a little while ago are in fact the result of some works that we published about ten years ago on the perception of risk both at Campi Flegrei and at Vesuvius. These studies allowed us to clearly highlight the difference in awareness between those who live on the slopes of these two volcanoes.
We are currently working on new research on risk perception in Campi Flegrei, with a project financed by the Civil Protection, because many things have changed in ten years: we have passed the yellow alert level, we have conducted information campaigns for the population, people began to feel small tremors and seismic swarms that they hadn't felt for several years, the type of communication has changed with the outstretched entry of social networks... With this new work we therefore want to understand if something has really changed in these years, not only in the way of informing ourselves: if we have reached a greater ability to recognize ourselves as inhabitants of an active volcanic area and if this has somehow modified the degree of acceptance of this risk. Because we must not forget that knowing a danger and accepting it means above all being prepared for a possible emergency.
It will therefore be essential for all of us to analyze the results of this work also to understand if we are operating correctly and, above all, how to continue to behave: as citizens, of course, but also as INGV, as Civil Protection, as Mayors of the various Municipalities in the area and as the Campania Region.
What is, for you, the most "fascinating" aspect of this peculiar volcano?
As I said before, I'm from Vesuvius: up until my high school years, although I've always had a passion for volcanoes, I wasn't particularly interested in the other volcano in Naples. The spark broke out thanks to archeology and the great and fascinating bond that the Campi Flegrei have with this discipline. The Campi Flegrei, in fact, preserve very important archaeological remains from the Greek era, as well as the Roman one, which have coexisted for centuries with the volcanic nature of the place.
Many eras later, in 1830, Charles Lyell published his treatise "Principles of geology" choosing the columns of the Serapeum, the Macellum of Pozzuoli, as the cover image. The discovery of small holes at different heights on these columns, a sign of the presence of microorganisms that live on the surface of the water and "consume" the material of which the columns are made, was the first evidence of the fact that these columns, in the various phases of their history, they have been in and out of sea water several times.
When I was studying geology and saw the cover of this book, which in fact marked the birth of the discipline, for me it was as if a circle had come full circle on the Campi Flegrei: the connection of the volcano with the history of man read from an archaeological point of view it is among its most peculiar aspects and perhaps, for me, the most fascinating.
Cover: panorama of Lake Miseno (photograph by Domenico del Sorbo)