There is a new method to predict the eruptions of Europe’s most active volcano: following the movements of the magma under Mount Etna.
A new method for following the movements of magma under Mount Etna opens up more precise perspectives for anticipating eruptions of Europe’s most active volcano. The study, conducted by the National Institute of Geophysics and Volcanology (INGV) and published in the journal Science Advances, places the seismological parameter known as “b” valuewhich describes the distribution between low- and high-magnitude earthquakes. In other words the “b value” (or b-value) is a parameter used in seismology that indicates the ratio between the number of small earthquakes and that of large ones in a given area.
Always active. Etna is the largest active volcano in Europe and we have regularly recorded its volcanic activity for the last 2,700 years. However, the system’s eruptive origins date back approximately 500,000 years. The most recent eruptive phase dates back to June 2025: the event produced a column of ash approximately 6.5 kilometers high and a flow of incandescent blocks. The authorities managed to spread the alert already on the morning of the eruption, but researchers underline that forecasts are not always so timely.
What changes? The INGV research examined 20 years of seismic data (from 2005 to 2024) in the Etna area, focusing on the spatial and temporal variation of the “b value”. According to the authors, this variation reflects the evolution of stress within the crust and may mark the phases in which the magma rises towards the surface. «The variations in the b value over time reflect the evolution of stress within the volcano», explained INGV geophysicist and first author of the study, Marco Firetto Carlino, in an interview. “Since magma upwelling induces stress changes in the crust, b-value monitoring can help reveal different stages of magma transfer from depth to the surface.”
In practice, in active zones of magmatic accumulation — where the magma exerts pressure on the surrounding rocks — higher b values are observed: this means that there are many small earthquakes compared to large ones. This is because the rocks become more fragmented and “weak” due to the magma fracturing the crust. On the contrary, in more stable crusts, little stressed by the magma, rarer but higher magnitude earthquakes prevail, associated with lower b values.
Etna magmatic system. The study describes Etna’s internal system as complex and stratified: a deep magma storage zone is located about 11 km below sea level, feeding a system of intermediate deposits (between 3 and 7 km deep) and finally a more superficial zone within the volcanic edifice.
The crust around Etna reaches thicknesses of up to 30 km and is found in the context of the collision between the African and European plates. A vertical strike-slip fault facilitates the rise of magma towards the surface.
Why it matters. Monitoring the b-value can offer a new tool for estimating when the magma is transiting from a deep area to a shallower one, allowing volcano eruptions to be defined more in advance. “Monitoring the b value offers an effective way to track the movement of magma within the crust and evaluate the evolutionary state of the volcano before eruptions,” says Firetto Carlino.
Thanks to Etna’s frequent activity and the vast seismic archive, scientists have been able to emerge a very strong correlation between the “b value” and the eruptive phases of the volcano. If confirmed in other volcanic contexts, the methodology could be applied to other active volcanoes, provided there is sufficient seismic data and a good spatial distribution of the events.
Limits and prospects. Eruption prediction continues to be a complex field: the “b value” is not an immediate “warning light” of imminent eruption, but an additional tool to evaluate the internal state of the volcano. Each volcano has its own characteristics and Etna represents an “ideal” case for this type of study thanks to the intense activity and good data availability. The researchers now intend to extend the analysis to other Italian and international volcanic areas, as well as combine the “b value” with other indicators (geochemical, deformational, thermal) to improve predictions.