CO2 and water diverged in Etna’s two explosions

A new study reconstructs two historic Mount Etna eruptions and finds that carbon dioxide and water helped drive them in different ways: one involved water-rich magma that stalled near the surface, while the other was powered by carbon dioxide-rich magma rising

On Mount Etna in Sicily, the volcano’s calm today can feel like a promise. Climbers and skiers come for the views. But the mountain has a different past—one that includes extremely explosive eruptions—and the plumbing underneath didn’t behave the same way twice.

Scientists have now reconstructed the underground magma pathways behind two historic Mount Etna explosions and found that carbon dioxide and water pushed the eruptions forward through different routes. The results. published in Geochemistry. Geophysics. Geosystems. suggest that even within one volcano. the mechanisms that trigger explosivity can shift dramatically.

The research was led by Cornell University, with contributions from the Lamont-Doherty Earth Observatory, part of the Columbia Climate School. Lamont geochemist Terry Plank. a coauthor of the study. helped collect field samples from Mount Etna that the team used to rebuild the volcano’s hidden “plumbing.”.

Volcanic explosivity depends on multiple factors, from magma viscosity to volatile gases that separate from magma as it rises. The study focuses on the most important volcanic gases: water and carbon dioxide. For years. the geological community leaned toward water as the primary volatile driver of eruptions—but in 2023. Cornell professor Esteban Gazel’s research group showed that carbon dioxide can also trigger explosive eruptions. In that earlier work, researchers used Raman spectroscopy to analyze tiny bubbles trapped inside crystals formed in magma. Those bubbles. called inclusions. can preserve information about how deep the magma was stored and the pressure it experienced before an eruption.

Gazel compared the process to a bottle of soda: if you open it without disturbing it, you can drink it; if you shake it, bubbles separate quickly and you get an explosion. “Volcanoes work in a similar way, and my lab is trying to quantify these processes,” he said.

In the new study, researchers applied Raman spectroscopy to these inclusions to infer how the magma moved. First author Maxim Gavrilenko. from Cornell. explained that the technique provides the density of carbon dioxide; using a state equation. scientists transform that density into pressure. and pressure can be transformed into depth. With those steps, the team reconstructed the plumbing system with “unprecedented precision.”.

Etna’s eruptions make for an unusually revealing test case because. as volcanoes go. it’s often described as a relatively gentle giant. Yet the mountain has still produced violent eruptions in its deep past. One of the largest on record came in 122 B.C. That eruption was both “mafic. ” meaning it involved low-viscosity magma rich in magnesium and iron. and Plinian—the most explosive category of eruption. named for Pliny the Elder. who first described the violent eruption of Mount Vesuvius in 79 A.D.

Plank. who is a Lamont-Doherty Earth Observatory scientist. stressed the mismatch between how Etna is seen today and what the older eruptions actually were. “Etna is such a tourist destination today for climbers and skiers. but it had these very explosive eruptions in the past. ” he said. He also pointed to a contradiction in the textbook picture. “The textbooks say that these hot, mafic magmas that erupt from Etna can’t be explosive. Our work shows the power of CO2.”.

That “power of CO2” is reflected in what the team found for 122 B.C. In 2018, Plank traveled to Mount Etna with coauthors Bruce Houghton of the University of Hawaii at Manoa and U.C. Berkeley’s Anna Barth, then Plank’s graduate student at Lamont, to collect tephra—rocky fragments ejected during past eruptions. After sequencing and measuring magma crystals from those fragments, the researchers determined that the 122 B.C. eruption involved magma originating from about 22 km deep. Rather than surging straight to the surface. it slowly made its way upward and paused for several weeks at a shallow depth of 2 to 5 km. where it gradually released gas before eventually erupting.

Then the team compared that volcanic behavior to an earlier eruption event known as the Fall Stratified event. which occurred nearly 4. 000 years ago. In that case, the magma had risen quickly from the mantle at a depth roughly estimated at 24 to 30 km. The eruption unfolded in a matter of hours, propelled by a much higher concentration of carbon dioxide.

Gazel’s group is now taking the same method forward. They are applying it to volcanoes in Chile, Hawaii, and many other locations. The goal is to gather the kind of data needed to build physical models of eruptions—models that are the foundation for volcanic risk assessment.

The study adds another piece to a broader message about volcanoes: their plumbing systems aren’t uniform. even within the same mountain. And when the volatiles behave differently—carbon dioxide racing up from deep while water-rich magma stalls and releases gas later—two eruptions can look equally dramatic on the surface while being driven by very different underground stories.

The work was supported by the National Science Foundation, and additional co-authors included Cornell postdoctoral researchers Kyle Dayton and Ellyn Huggins.

Mount Etna volcanic eruptions carbon dioxide water Raman spectroscopy magma pathways volcanic hazards Geochemistry Geophysics Geosystems