In recent days, as with any publication concerning the Phlegraean Fields, numerous newspapers have released extremely sensationalist articles in which an imminent eruption of this caldera is feared.
All this hype arose last year 15 May when a new research paper was published in Nature Communications, produced by a group of researchers from INGV and the University College of London. This publication presents a new methodology to be able to predict the eruptions of dormant volcanoes through a comparative analysis of seismic events and deformations suffered by the soil. In this study, particular attention was paid to the analysis of the effort to which the rocks can be subjected in relation to the maximum sustainable effort, beyond which the entire volcanic system could erupt.
The rocks, when subjected to stresses that produce small deformations, they behave in an elastic way or deform proportionally to the intensity of the effort suffered e, the elimination of the latter, they recover their original form. However, beyond a certain threshold of effort, the behavior of the rocks becomes elasto-brittle and they can fracture. Further increasing efforts, the rock behaves only in a fragile way, producing numerous fractures capable of connecting the deep areas of the caldera to the surface, thus triggering an eruptive event. By monitoring and studying the simultaneous trend of deformations and seismicity, one is therefore able to understand the evolution of the system from an elastic to a fragile behavior.
The researchers applied this approach to the case of Campi Flegrei, analyzing the phenomenon of bradyseism (periodic lowering and lifting of the soil of a volcanic area) which for hundreds of years has affected this area of Campania. From the 1950 to date they have occurred 3 main bradyseismic episodes that have produced an uplift of over 4 meters in the port of Pozzuoli and approx 26.000 earthquakes.
In an area like the Phlegraean Fields, in which recurring phenomena of lifting occur, the model shows how each further bradyseismic episode affects a system already modified by the efforts produced by the previous events. This involves a much more complex and more critical evolution of the system, as each deformation moment can follow a different path.
Once the volcanic system has undergone large cumulative deformations it is possible that it may evolve towards complete fracturing and, then, towards a probable eruption. In particular, it was possible to quantify the extent of the uplift beyond which the volcanic system could enter a fragile regime and increase the probability of an eruptive event. The calculated lift is between 6,25 e 12,5 meters, lower values than the 17 observed before its last eruption occurred in 1538 (Eruption of Monte Nuovo). This discrepancy could be due to differences in the mechanical characteristics of the deformed rocks or to the presence of mechanisms that can reduce the resistance.
A correct application of this model pays off, however, a good knowledge of the real physical state of the rocks in the depths of the Phlegraean subsoil is necessary, in order to understand how close the volcanic system is to the critical point. In order to achieve this, it is necessary to drill deep holes, useful to be able to sample and investigate the non-elastic mechanical properties of rocks in the deep areas of the system.
In conclusion, the Phlegraean area is undergoing upheavals in this period not related to the intrusion of new magma masses in the shallow portions of the caldera, contrary to what happened in the period 1982-1984. The absence of magma in these areas is in fact evidenced by the geochemical evidence of the fluids emitted by the fumaroles and by the particular trend of soil deformations: si è infatti notato come negli ultimi anni sono avvenuti fenomeni di sollevamento e abbassamento del terreno non imputabili ad un magma in risalita. However, l’attenzione deve continuare a rimanere alta poiché possibili future intrusioni di magma potrebbero produrre nuovi sollevamenti, maggiori rispetto a quelli osservati durante la crisi degli anni 70′-80′.I Campi Flegrei sono pur sempre una delle aree vulcaniche più a rischio del pianeta.
Di F. Mu.
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