For decades, the Campi Flegrei have been at the center of attention of volcanologists and the local population due to the frequent episodes of bradyseism, those slow movements of the ground that testify to the restlessness of the volcanic subsoil. Now, however, the situation seems to be getting worse, and leaves room for apprehension and inferences that do not help. What is really hidden in the bowels of this giant? What are the mechanisms that govern his behavior?
In a new study, a team of Italian researchers tried to answer these questions using a cutting-edge technique that provides high-resolution images of the caldera's internal structure to follow its evolution over time.
The findings, published in Earth and Planetary Science Letters (I'll link them here), reveal a complex and evolving magmatic system, with three magma reservoirs at different depths and fluid movements that can be the warning signs of a future crisis.
A window on the caldera
The study, conducted by a team of researchers from the National Institute of Geophysics and Volcanology (INGV) and the University of Milan Bicocca, used a technique called 4D non-linear seismic tomography. In simple words, it is a method that uses seismic waves generated by earthquakes to "illuminate" the interior of the Earth, a bit like a medical CT scan uses X-rays to visualize the inside of the human body.
The innovation of this study lies in having applied a non-linear and trans-dimensional algorithm, which allows us to obtain more detailed and faithful images of the internal structure of the caldera, overcoming the limits of traditional methods. Furthermore, the temporal dimension (which is why it is called 4D) allows us to follow the evolution of the system over time, identifying even small but potentially significant changes.
The result is a real "map" of the subsoil of the Campi Flegrei, which as mentioned reveals for the first time the existence of three main magmatic reservoirs: two more superficial, about 2-4 km deep, and one deeper, about 5 km. Let's take a look.
Campi Flegrei, three evolving magma reservoirs
The first surface tank (called “A” in the study) lies between 2 and 2,5 km deep, just below the center of the caldera. It is characterized by low seismic wave speeds (indicating hot and/or partially molten rocks) and a progressive increase in the ratio between P and S wave speeds between 1984 and 2019. According to the researchers, this could indicate a process of cooling and degassing of the magma, perhaps starting after the bradyseismic crisis of 1982-84.
The second surface tank (“B”) it lies slightly deeper, between 3,5 and 4 km. It also shows low seismic velocities, but unlike the first, here the Vp/Vs ratio has decreased over time. This suggests a possible recharge process by magmatic fluids, which occurred during the current unrest phase that began in 2005.
But perhaps the most surprising discovery concerns the deep reservoir (“C”), detected at approximately 5 km depth. This area is characterized by very low P wave speeds and very high Vp/Vs ratios, compatible with the presence of magma. Furthermore, the shape and location of this anomaly have changed over time. After almost disappearing between 1984 and 2019, it reappeared starting from April 2019, more superficial and with a strong increase in the Vp/Vs ratio. A signal, according to the authors, of a possible new injection of magma coming from even deeper sources.
What does all this mean?
The results shed new light on the mechanisms that govern the evolution of the Campi Flegrei caldera. A complex and dynamic system in which magma and fluids interact at different spatial and temporal scales. The discovery of three magma reservoirs at different depths, and above all the evidence of magma movements in the last period, are a crucial step forward.
Naturally, we are still far from being able to predict with certainty if and when the Campi Flegrei will seriously awaken, with strong earthquakes or even eruptions. Studies like this, however, provide us with increasingly precise tools to follow the evolution of the system in real time, identify precursory signals and evaluate the level of risk.
In a densely populated area like the Phlegraean one (we are over half a million people), having detailed and updated information is essential for planning mitigation and emergency management strategies. And 4D seismic tomography is a candidate to become one of the most valuable tools in this sense.
Campi Flegrei, towards the future: the challenges of living with an active volcano
The study by INGV and the University of Milan Bicocca confirms that the Campi Flegrei are a living and evolving system. The challenge now is to translate this knowledge into concrete actions to reduce volcanic risk. This means strengthening monitoring, but also investing in the education and preparation of the population, in territorial planning, in the development of resilient infrastructure.
Because living with an active volcano is not impossible, we have always done it (not without a certain amount of madness): but it requires awareness, responsibility and constant attention to the signals that the Earth sends us. With respect, caution, but also with trust in research and in our ability to face even the greatest challenges.