Scientists Finally Figured Out Why the Same Volcano Can Erupt in Two Completely Different Ways
Two of Mount Etna’s most powerful eruptions took dramatically different paths beneath the volcano, revealing that its underground plumbing can change over time, according to a new study. The findings suggest that even a single volcano may erupt through entirely different mechanisms.
Although volcanoes often appear unchanged on the surface, the movement of magma deep underground is far more complex. Before reaching the surface, molten rock travels through a maze of reservoirs and conduits that can shift from one eruption to another, making volcanic behavior difficult to predict.
To uncover how these hidden systems evolve, researchers compared two major eruptions of Mount Etna in Italy separated by nearly 4,000 years. Their analysis, published in Geochemistry, Geophysics, Geosystems, revealed striking differences in the way magma rose to the surface during each event.
Tiny Gas Bubbles Revealed What Happened Underground
The strength of a volcanic eruption depends on several factors, including the amount of gas trapped inside rising magma. As pressure drops on the way to the surface, those gases expand and can turn an eruption explosive. Scientists have traditionally focused on water as the main gas involved in that process. More recently, researchers have shown that carbon dioxide can also play a major role.
To understand what happened beneath Mount Etna, the team used Raman spectroscopy to examine microscopic bubbles trapped inside crystals that formed in the magma. According to Cornell University, those bubbles are incredibly small, just 1 to 10% as thick as a human hair, but they preserve information about the pressure and depth at which they formed.
“The technique gives us the density of CO₂, and using a state equation we can transform that density into pressure, and pressure can be transformed into depth,” said first author Maxim Gavrilenko. “Then we apply those techniques to these explosive eruptions, and we are able to reconstruct the plumbing system with an unprecedented precision.”
The Same Volcano Took Two Very Different Routes
One of the eruptions studied took place in 122 B.C. and is one of the largest known events in Mount Etna’s history. It was a mafic Plinian eruption, meaning it involved magma rich in magnesium and iron and produced an exceptionally explosive eruption.
The researchers found that the magma rose from around 22 kilometers below the surface before stopping at a depth of 2 to 5 kilometers. It remained there for several weeks, gradually releasing gas before finally erupting. The second eruption, known as the Fall Stratified event, happened nearly 4,000 years ago. It unfolded very differently.
Instead of slowing down near the surface, the magma shot upward from a depth of 24 to 30 kilometers and erupted within just a few hours.The new study noted that eruption contained much higher levels of carbon dioxide than the later event.
The Hidden Battle Beneath Mount Etna
The comparison revealed something unusual about Mount Etna. Unlike many volcanoes, where one volcanic gas tends to dominate, Etna is influenced by both water and carbon dioxide. As stated by the latest research, lead researcher Esteban Gazel explained that volcanoes on oceanic islands are often controlled by carbon dioxide, while volcanoes in subduction zones are usually driven by water-rich magma. Mount Etna is one of the few places where both gases compete.
“This shows that at a certain threshold of CO₂, the eruption will come from very deep and really fast, but when you have a higher threshold of water, then the process is controlled at shallow levels,” Gazel said.
The team is now applying the same method to volcanoes in Chile, Hawaii, and other parts of the world. Gazel noted that the goal is to gather the data needed to improve the physical models that scientists use for volcanic risk assessment.
