Under the Campi Flegrei the magma seems organized in a more complex way than imagined: not a large single chamber, but a complex system of deep zones, transfer areas and reservoirs located at different depths. This was reconstructed by an international study published in Scientific Reportswhich for the first time offers a 3D geophysical map of the caldera’s power system down to about 50 kilometers below the surface.
The study does not indicate an imminent eruption, but adds an important piece of knowledge about one of the most monitored volcanoes in the world. In a densely inhabited area that has been affected by bradyseism for years, understanding how the deep and superficial parts of the system communicate is essential to better read the signals measured on the surface.
The map under the volcano
The work used the receiver functions technique, that is, the analysis of how seismic waves change as they pass through different materials underground. In practice, distant earthquakes become a kind of natural x-ray: the waves arrive, pass through the crust and mantle, slow down or change behavior, and from those variations it is possible to reconstruct a part of the hidden architecture of the caldera.
The most important result concerns two areas of low velocity of seismic waves. The first is located about 10 kilometers deep, in the eastern part of the caldera, with an elongated shape and dimensions estimated at around 6 × 5 × 4 kilometers. The authors interpret it as a possible localized area of magmatic transfer or intrusion. Further down, a second structure appears: its roof is about 25 kilometers away, it is about 17 kilometers thick, it is inclined towards the north and could contain up to 30% of molten material by weight. This area is interpreted as a possible deep source of primitive magma, located between the deep crust and the upper mantle.
Translated without making it a scene from a disaster film: a multi-level structure emerges under the Campi Flegrei. A deep part where magma can originate or accumulate, an intermediate zone where it can move, and sectors closer to the surface where fluids, hot rocks, gases, fractures and pressure come into play. The volcano looks a lot less like a room full of magma and a lot more like an ancient, crooked, hot, valve-filled plumbing system that scientists are trying to name without breaking anything.
The pieces already known
This new deep map dovetails with other recent work. A 2024 study on geodetic and petrological data had already followed the evolution of the crisis that began in 2005, indicating a progressively larger and more superficial deformation source, which went from about 5.9 to 3.9 kilometers, and a deeper source around 8 kilometers. According to that model, the inflation of the shallowest source would be explained by the ascent of 0.06-0.22 cubic kilometers of magma from depths greater than or equal to 8 kilometers.
Also in 2024, a CNR-IREA group had estimated an irregular source in a region of the crust between approximately 3 kilometers and 500 meters deep, in the area between Solfatara and Pisciarelli, precisely where many surface phenomena become more evident: uplift, seismicity, temperatures, geochemical variations.
Then in 2025, another study published in Communications Earth & Environment used 3D magnetotelluric imaging to look up to about 20 kilometers below the caldera. There a large low resistivity anomaly had emerged between 8 and 20 kilometres, interpreted as a “crystal mush” zone: a kind of hot paste made of crystals, rocks, fluids and a melt share estimated at around 10%, with around 90 cubic kilometers of melt in the overall modeled volume.
Placed side by side, these studies tell the same thing from different depths. Under the Campi Flegrei deep portions, intermediate zones, channels, more superficial reservoirs and a very active hydrothermal system coexist.
The correct reading
The magma map at Campi Flegrei increases knowledge of the volcanic system. It marks an important scientific step. It offers better tools to interpret bradyseism, seismicity, degassing and ground deformations. From here to turning it into a countdown to an eruption is an enormous distance.
The Civil Protection currently indicates a yellow alert level for the Campi Flegrei, with the state of the volcano in “medium disequilibrium” and Phase 2 of Attention. A new phase of uplift of the caldera has been underway since 2005; since 2018 the uplift has been accompanied by a gradual increase in seismic activity, intensified since 2023, with events up to magnitude 4.6 and an overall uplift exceeding 150 centimeters since 2005.
The same official framework specifies a decisive step: the scientific results strengthen the evidence of the presence of magma in depth as the cause of the bradyseismic crisis, while the absence of evidence of magmatic ascent led to the confirmation of the yellow alert level.
The earthquake of May 21, 2026, magnitude Md 4.4 in the Gulf of Pozzuoli at about 3 kilometers deep, reminded us of how alive the system is and how much it is perceived by the population, even in the city of Naples. The INGV indicated impacts up to MCS degree V, with an earthquake swarm underway since 05:50 local time.
The operational point remains the same: more knowledge, more monitoring, more prevention, more clarity. The new map of the magma under the Campi Flegrei serves to better understand how the caldera works, to connect what happens in depth with what is measured on the surface, to read the signals with less fog.
You might also be interested in:
