A newly discovered way to monitor the movement of magma beneath Mount Etna could help scientists predict when it will erupt.
Mount Etna, located on the Italian island of Sicily, is Europe’s largest active volcano. Humans have been recording its activity for the past 2,700 years, but the volcano’s history of eruptions dates back 500,000 years.
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This new method could make it easier to predict Mount Etna’s eruptions. In a new study, researchers at Italy’s National Institute of Geophysics and Volcanology (INGV) analyzed a parameter called the b value, which measures 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 Earth’s crust to the top of a volcano, researchers reported in a study published Oct. 8 in the journal Science Advances.
“Changes in the b value over time reflect how the stresses inside the volcano are evolving,” study lead author Marco Filet Carlino, a geophysicist at the INGV Etna Observatory, told Live Science via email. “Magma ascent causes stress changes within the Earth’s crust, so tracking b-values can help reveal the different stages of magma movement from depth to the surface.”
The b-value is a well-established parameter in volcanology, but the researchers used modern statistical models to examine it in a new way. A compilation of 20 years of seismic data from Mount Etna found a “very strong” correlation between b-values and Etna’s volcanic activity, Filet-Carlino said.
Mount Etna is located in the collision zone between the African and European tectonic plates. As a result, vertical cracks in the Earth’s crust, known as strike-slip faults, exist beneath the volcano, allowing magma to rise to the surface.
The crust beneath Mount Etna is up to 19 miles (30 km) thick. Magma rises through this volume before erupting, but rather than replenishing a single magma chamber, the lava is fed into a series of interconnected storage zones embedded at various depths in the Earth’s crust.
The deepest magma storage zone is 7 miles (11 km) below sea level, which feeds into an intermediate storage system, with different zones likely extending 2 to 4 miles (3 to 7 km) deep, Fillet-Carlino explained. As the magma rises, it moves through a complex network of fractures, eventually reaching a final storage zone above sea level inside the volcanic edifice.
Because Etna is frequently active, researchers had a wealth of data from which to work and extract b values. They analyzed seismic patterns in the volcano’s crust 30 miles below the surface from 2005 to 2024, paying particular attention to how these patterns changed between crustal regions.
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In general, regions of the crust with active magma accumulation zones exhibit higher b values than more stable regions. This is because active regions have more small earthquakes than large ones.
“This happens because the rocks affected by the moving magma become weaker and crack into larger fractures,” Fillet-Carlino said. “For example, when magma in a reservoir releases volatile substances, they seep into the surrounding rock, making small cracks slippery.”
Conversely, more stable regions of the Earth’s crust typically have more large earthquakes than small ones because more force is required to break the rocks. “Rocks with good mechanical properties can accumulate stress for long periods of time,” Fillet-Carlino said. “When they eventually break, larger earthquakes occur, corresponding to lower b values.”
Therefore, by tracking b-values over time, researchers could potentially track the movement of magma through the deep crust to the first storage zone, from there to intermediate storage systems, and again to shallow storage zones. This method could help experts estimate the timing of Mount Etna’s eruption.
“Monitoring b-values provides a powerful way to track the movement of magma within the Earth’s crust and assess the evolutionary state of volcanoes before an eruption,” said Firetto Carlino.
Etna was a good test for the study because of its layered magma storage zone and vast earthquake catalog, but the results may apply elsewhere.
“In principle, b-values could also be used to track magma movements in other volcanic regions, provided that a sufficient number of earthquakes are available, their locations distributed in different crustal sectors, and well constrained by previous geological studies,” Filet-Carlino said.
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