Summary

A Cornell-led collaboration reconstructed the magma pathways behind two major Mount Etna eruptions and found sharply different roles for carbon dioxide and water. One eruption paused underground for weeks before erupting, while another reached the surface in hours.

A Cornell-led collaboration has reconstructed the underground pathways behind two historic eruptions of Mount Etna and found that they were driven by markedly different combinations of carbon dioxide and water in the magma.

The 122 B.C. eruption took several weeks to develop after magma paused at shallow depth and gradually released gas. A much older eruption, known as the Fall Stratified event, rose from deeper in the Earth and erupted within hours, propelled by a higher concentration of carbon dioxide.

The findings were published June 2, 2026, in Geochemistry, Geophysics, Geosystems. The research was led by Esteban Gazel of Cornell University, with collaborators from Columbia University, the University of Hawaii at Manoa and the University of California, Berkeley.

Contents

How the two eruptions differed

Volcanic explosivity depends partly on magma viscosity and on volatiles—dissolved gases that separate from magma as pressure changes. Water has traditionally been treated as the main volatile controlling eruptions, but carbon dioxide can also contribute to explosive behaviour.

The 122 B.C. event was both mafic, meaning it involved relatively low-viscosity magma rich in magnesium and iron, and Plinian, the most explosive category of eruption. The researchers concluded that magma first rose from a depth of about 22 kilometres. It then paused for several weeks at roughly 2 to 5 kilometres below the surface, where it gradually released gas before the eruption began.

The Fall Stratified event, which occurred nearly 4,000 years ago, followed a different route. Its magma rose quickly from a deeper part of the mantle, approximately 24 to 30 kilometres down, and erupted in a matter of hours. The team linked that rapid ascent to a much higher concentration of carbon dioxide.

The comparison shows why eruptions from the same volcano can develop on very different timescales. In the researchers’ interpretation, a sufficiently high carbon-dioxide contribution can be associated with a deep, rapid ascent, while a stronger water-driven process can be controlled at shallower levels.

Reading volcanic pressure in tiny bubbles

To reconstruct the magma pathways, the team analysed crystals formed inside the magma. The crystals contain microscopic bubbles that preserve information about the gases and pressures present as the magma moved through the volcano.

The researchers used Raman spectroscopy to examine these bubbles. Raman spectroscopy measures how light interacts with a material; in this study, it was used to determine the density of carbon dioxide in bubbles only about 1 to 10 percent of the thickness of a human hair.

The carbon-dioxide density can be converted into pressure using an equation of state, a physical relationship that describes how a substance behaves under changing temperature and pressure. Pressure can then be used to estimate the depth at which the bubble formed. Applying the measurements across crystals allowed the team to reconstruct parts of Etna’s subterranean magma plumbing with what it describes as unprecedented precision.

Why the result matters for eruption risk

Mount Etna is generally considered a relatively gentle volcano, but its history includes powerful explosive events. Its contrasting eruptions provide a natural test of how different volatile systems affect the timing and style of an eruption.

For geologists, identifying whether magma is likely to be controlled by carbon dioxide at depth or by water at shallower levels can improve the physical models used in volcanic risk assessment. The research does not turn the measurements into an eruption timetable by itself; its contribution is to provide more detailed information about the conditions and pathways that models need to represent.

Gazel’s group is applying the same approach to volcanoes in Chile, Hawaii and other locations. The broader applicability of the carbon-dioxide and water patterns is therefore being examined across different volcanic settings, including volcanoes where one volatile may dominate rather than compete with the other.

Sources