𝗦𝗰𝗶𝗲𝗻𝘁𝗶𝘀𝘁𝘀 𝗗𝗶𝘀𝗰𝗼𝘃𝗲𝗿 𝗪𝗵𝘆 𝘁𝗵𝗲 𝗦𝗮𝗺𝗲 𝗩𝗼𝗹𝗰𝗮𝗻𝗼 𝗘𝗿𝘂𝗽𝘁𝗲𝗱 𝗶𝗻 𝗧𝘄𝗼 𝗖𝗼𝗺𝗽𝗹𝗲𝘁𝗲𝗹𝘆 𝗗𝗶𝗳𝗳𝗲𝗿𝗲𝗻𝘁 𝗪𝗮𝘆𝘀

New research has revealed that a single volcano can erupt through very different underground pathways, depending on how magma, gas, and pressure behave beneath the surface.

The study focuses on Mount Etna in Italy, one of the world’s most active volcanoes. Although Etna is often seen as a relatively mild volcano compared with many others, its past contains several powerful explosive eruptions. Now, scientists have shown that two of those historic eruptions were driven by very different internal processes.

The research was led by a Cornell University collaboration and published in Geochemistry, Geophysics, Geosystems. The first author of the study is former postdoctoral researcher Maxim Gavrilenko, and the project was led by Professor Esteban Gazel of Cornell’s Department of Earth and Atmospheric Sciences.

Volcanic systems are often described as underground plumbing networks. These networks can extend many kilometres below the surface, carrying magma and gases through cracks, chambers, and pathways before an eruption occurs. But the new study shows that even within the same volcano, these pathways do not always behave in the same way.

According to the researchers, understanding these hidden differences is important because it can help geologists better assess volcanic hazards and improve models used to forecast future eruptions.

One of the key factors that determines how explosive a volcano becomes is the amount of gas trapped inside the magma. Professor Gazel compared the process to opening a bottle of soda. If the bottle is opened calmly, the gas escapes slowly. But if the bottle is shaken, bubbles separate rapidly and the liquid can burst out forcefully.

Volcanoes behave in a similar way. When gases inside magma separate quickly and build pressure, the eruption can become explosive.

The most important volcanic gases are water and carbon dioxide. For many years, scientists considered water the main volatile substance controlling volcanic eruptions. However, recent work by Gazel’s research group has shown that carbon dioxide can also play a major role in triggering explosive eruptions.

To study this, the team used a method involving Raman spectroscopy, a technique that allows scientists to examine crystals formed inside magma. These crystals can contain tiny bubbles of gas, some only a few microns in size. By measuring the density of carbon dioxide inside these bubbles, researchers can estimate the pressure at which the bubbles formed. That pressure can then be converted into depth, allowing scientists to reconstruct where magma was stored and how it moved before an eruption.

Using this approach, the team was able to reconstruct Mount Etna’s ancient volcanic plumbing system with unusual precision.

The researchers focused on two major eruptions. One occurred in 122 before Christ, and the other, known as the Fall Stratified eruption, happened nearly 4,000 years ago.

The 122 before Christ eruption was one of Mount Etna’s largest recorded explosive events. It involved mafic magma, which is low-viscosity magma rich in magnesium and iron. It was also a Plinian eruption, the most explosive category of volcanic eruption, named after Pliny the Elder, who described the famous eruption of Mount Vesuvius in 79 after Christ.

By studying crystals from this eruption, the researchers found that the magma rose slowly from about 22 kilometres below the surface. It then stalled for several weeks at a much shallower depth of about 2 to 5 kilometres. During this period, the magma gradually lost gas before finally erupting.

The older Fall Stratified eruption followed a very different pattern. In that case, magma rose rapidly from a much deeper level, about 24 to 30 kilometres beneath the surface. Instead of stalling for weeks, it surged upward and erupted within hours. This fast movement was driven by a much higher concentration of carbon dioxide.

The comparison showed that Mount Etna can erupt through two very different mechanisms. One eruption was controlled mainly by shallow processes and water-rich magma, while the other was driven by deep, carbon dioxide-rich magma that moved quickly toward the surface.

Professor Gazel explained that some volcanoes are mainly controlled by carbon dioxide, especially those found on oceanic islands. Others, such as volcanoes in subduction zones, are often controlled more strongly by water. Mount Etna is unusual because both volatile substances appear to compete within the same volcanic system.

The researchers found that when carbon dioxide reaches a certain threshold, magma can rise from deep underground very quickly, leading to a rapid eruption. When water plays a stronger role, the process tends to be controlled at shallower depths and may unfold more slowly.

These findings challenge the idea that a volcano always erupts in one predictable way. Instead, they show that the same volcano can follow different underground routes depending on the balance of gases, magma movement, and pressure conditions.

Gazel’s team is now applying the same method to volcanoes in Chile, Hawaii, and other parts of the world. According to the researchers, collecting this kind of data from many volcanoes could improve physical models of eruptions and strengthen volcanic risk assessment.

Mount Etna also carries a deep cultural history. In Greek mythology, the volcano was linked to the defeated giants Typhon and Enceladus, who were said to be buried beneath it. Gazel noted that the reconstructed plumbing systems of Etna’s eruptions almost seem to echo those mythological figures: one long and serpentine, the other smaller and more compact.

Beyond the mythology, the scientific message is clear. Mount Etna’s past shows that volcanoes can be far more internally complex than they appear from the surface.

By looking inside ancient magma crystals, scientists are now uncovering the hidden routes that magma once followed underground and those routes may help explain why the same volcano can erupt in completely different ways.

Reference: M. Gavrilenko, E. Gazel, K. Dayton, A. Barth, T. Plank, E. G. Huggins, and B. Houghton, “Deep Origin and Shallow Launch for the Etna 122 B.C. Mafic Plinian Eruption,” Geochemistry, Geophysics, Geosystems, 2 June 2026. DOI: https://doi.org/10.1029/2026GC012924.