A newly discovered way to monitor the movement of magma beneath Mount Etna could help scientists predict when it might erupt.
Mount Etna, located on the Italian island of Sicily, is Europe's largest active volcano. People have been documenting its activity for the past 2,700 years, but the history of the volcano's eruptions extends back many years. as early as 500,000 years ago.
A new method could make it easier to predict Etna's 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 to high magnitude earthquakes in a certain region of the Earth's crust. This ratio may change as magma rises through the Earth's crust to the volcano's summit, the researchers reported in a study published Oct. 8 in the journal. Achievements of science.
“Changes in b-value over time reflect how stress develops inside the volcano,” says the study's lead author. Marco Firetto Carlinoa geophysicist at the INGV Etna Observatory, told Live Science via email. “Because rising magma causes stress changes in the Earth's crust, monitoring the b-value can help identify the different stages of magma transport from depth to the surface.”
The b-value is a common parameter in volcanology, but the researchers examined it in a new way, using an updated statistical model. By collecting 20 years of earthquake data on Mount Etna, they found a “very strong” correlation between the b-value and Etna's volcanic activity, Firetto Carlino said.
Mount Etna is located in the collision zone of the African and European tectonic plates. As a result, a vertical fault known as a strike-slip fault lies at the base of the earth's crust. volcanowhich, according to the study, contributes to the rise of magma to the surface.
The crust beneath Etna is up to 19 miles (30 km) thick. Magma rises through this volume before an eruption, but rather than replenishing a single magma chamber, the molten rock feeds a series of interconnected storage zones that are embedded in the Earth's 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 likely extending to depths of 2 to 4 miles (3 to 7 km). As the magma rises, it passes through a complex network of cracks and eventually reaches the final storage zone, which is located above sea level inside the volcano's edifice.
Due to Etna's frequent activity, researchers had a wealth of data to work with and extract b values from. They analyzed seismic patterns in 12 miles of crust beneath the volcano from 2005 to 2024, focusing on how these patterns varied between regions of the Earth's crust.
In general, crustal regions with active magma storage zones exhibit higher b values than more stable regions because active zones experience smaller earthquakes than larger ones.
“This happens because rocks exposed to moving magma become weak and highly fragmented,” Firetto Carlino said. “For example, when magma inside a repository releases volatiles, they penetrate into the surrounding rocks, facilitating the sliding of small cracks.”
Conversely, more stable regions of the Earth's crust tend to experience more large earthquakes than smaller ones because it takes more force to break the rock. “Rocks with good mechanical properties can maintain stress for a longer time,” Firetto Carlino said. “When they finally collapse, they produce larger earthquakes corresponding to lower b values.”
Thus, by tracking the b value over time, researchers will be able to trace the movement of magma through the deep crust to the first storage zone, from there up to the intermediate storage system, and up again to the shallow storage zone. This method could help experts estimate the timing of Etna's eruptions.
“B-value monitoring offers a powerful way to track the movement of magma within the Earth's crust and assess the developing state of a volcano before eruptions,” Firetto Carlino said.
Mount Etna provided a good test case for the study because of its layered magma storage zones and huge seismic catalog, but the results could be applicable elsewhere.
“In principle, the b value can also be used to track magma movements in other volcanic areas, provided that there are a sufficient number of earthquakes and that their locations are distributed across different sectors of the earth's crust, which is well constrained by previous geological studies,” Firetto Carlino said.
