A newly discovered way to monitor the movements of magma beneath Etna could help scientists predict when it might erupt.
Mount Etna, located on the Italian island of Sicily, is the largest active volcano in Europe. Humans have documented its activity for the past 2,700 years, but the volcano’s eruptive history spans 500,000 years ago.
This new method could make it easier to predict Etna eruptions. In a new study, researchers from Italy’s National Institute of Geophysics and Volcanology (INGV) analyzed a parameter called b-value, which describes the ratio of low-magnitude earthquakes to high-magnitude earthquakes in a region of the Earth’s crust. This ratio can change as magma rises through the crust to the top of a volcano, the researchers reported in a study published October 8 in the journal Scientific advances.
“Changes in the b value over time reflect changing stresses inside the volcano,” lead author of the study. Marco Firetto Carlinogeophysicist at the INGV Etna Observatory, told Live Science in an email. “Since magma ascent induces stress changes within the crust, monitoring the b-value can help reveal different stages of magma transfer from depth to the surface.”
The b value is an established parameter in volcanology, but the researchers looked at it in a new way, with an updated statistical model. By compiling 20 years of data on Etna’s earthquakes, they discovered a “very strong” correlation between the b value and Etna’s volcanic activity, Firetto Carlino said.
Etna is located in the collision zone between the African and European tectonic plates. As a result, a vertical fracture in the Earth’s crust, known as a strike-slip fault, is causing the volcanothus facilitating the rise of magma to the surface, according to the study.
The crust beneath Etna is up to 30 km thick. Magma rises through this volume before an eruption, but instead of replenishing a single magma chamber, the molten rock feeds a series of interconnected storage zones that are embedded in the crust at different depths.
The deepest magma storage zone is 7 miles (11 km) below sea level, Firetto Carlino explained, and it feeds an intermediate storage system with different zones probably extending 2 to 4 miles (3 to 7 km) deep. As the magma rises, it passes through a complex network of fractures and eventually reaches the final storage zone, located above sea level, within the volcanic edifice.
The researchers had a wealth of data to work with and extract b-values, due to Etna’s frequent activity. They analyzed seismic patterns in the 19 miles of crust beneath the volcano from 2005 to 2024, paying particular attention to how these patterns varied between crustal regions.
Generally, regions of the Earth’s crust with active magma storage areas show higher b-values than more stable regions, because active areas experience smaller values. earthquakes than the biggest.
“This happens because rocks affected by moving magma become weak and highly fractured,” explained Firetto Carlino. “For example, when magma inside a repository releases volatile substances, these permeate the surrounding rocks, making it easier for small fractures to slide.”
Conversely, regions of the Earth’s crust that are more stable generally experience more large earthquakes than smaller ones, because it takes more force to break rock. “Rocks with good mechanical properties can store stress for longer periods of time,” Firetto Carlino said. “When they eventually break, they produce larger earthquakes, corresponding to lower b-values.”
So, by tracking the b value over time, it might be possible for researchers to track the movement of magma through the deep crust to the first storage zone, from there to the intermediate storage system, and back to the shallow storage zone. This method could help experts estimate the times of Etna’s eruptions.
“B-value monitoring provides a powerful way to track the movement of magma in the crust and assess the evolutionary state of the volcano before eruptions,” said Firetto Carlino.
Etna was a good test case for the study because of its layered magma storage areas and enormous seismic catalog, but the results could also apply elsewhere.
“In principle, the b-value could also be used to track magma movements in other volcanic areas, provided that a sufficient number of earthquakes are available and their locations are distributed over different sectors of the Earth’s crust, well limited by previous geological studies,” said Firetto Carlino.
