When “Extinct” Volcanoes Reawaken

It is difficult to have more dead than extinct. Things that have disappeared are considered definitively destroyed: no second chance, no descendants, no return. Except, it turns out, extinct volcanoes may not be as dead as geologists thought. New data suggests that although they appear to be in permanent dormancy, these volcanoes may actually be quietly simmering, accumulating larger and potentially more dangerous underground magma reserves.

These are the findings of an international team of scientists, led by researchers from ETH Zurich, who have pieced together the long history of a 1,400-foot volcano known as Methana, near Athens, Greece, which dominates the Saronic Gulf in the Aegean Sea. Methana’s last eruption was around 2,200 years ago. The ancient Greek historian Strabo was there – or close enough: “A seven-story high mountain rose from a fiery eruption, inaccessible during the day because of the heat and sulphurous odor, but at night fragrant, glowing from afar and warming the sea for five stadiums, and murky,” he wrote.

Methana was thought to be an active, not extinct, volcano, but when the team of scientists pieced together its history, they discovered that at the midpoint of its 700,000-year lifespan, it had remained dormant for more than 100,000 years. And all the while, magma was quietly accumulating in the volcano’s underground chambers.

This was a surprise: Geologists have long classified volcanoes as extinct if they remained quiet for just 10,000 years. The idea was that if a volcano had not erupted for so long, the magma source should have been extinguished. Never again would it pour lava down its sides or into the villages, forests, rivers and valleys below. Scientists have determined that the opposite may be true: the quiet period may mask the growth of magma underground. The findings have implications for many volcanoes around the world that are classified as extinct and therefore not monitored.

“We strongly believe that we need to re-evaluate how we define active, dormant and extinct volcanoes, and we hope that our work will be a step forward in this direction,” study author Răzvan-Gabriel Popa, a volcanologist and principal investigator at ETH Zurich in Switzerland, said in an email. “This is essential for risk assessment, especially in areas where many people live.”

Read more: “The volcano that enveloped the Earth and gave birth to a monster”

Scientists were already skeptical about the accuracy of the definition of “extinct” for volcanoes. In recent years, some volcanoes thought to be extinct have awakened: Taftan in Iran, for example, has shown signs of trouble since 2023, and Hayli Gubbi in Ethiopia erupted in 2025 after 12,000 years of silence, Popa says.

The team decided to investigate Methana in part because of her physical configuration. Most of its volcanic domes stood side by side rather than stacked on top of each other, meaning that different eruptions from different periods are all accessible and recognizable on the surface.

“We wanted to study Methana because this volcano has a huge advantage: the different lava flows do not pile up and bury each other,” explains Popa. They extend over a large area, “each eruption forming its own hill”. This allowed them to study specific prehistoric eruptions and reconstruct the long-term evolution of the volcano. “The fact that it had an eruption 2,200 years ago, combined with its proximity to Athens, a densely populated urban center, also prompted us to examine it in detail,” notes Popa.

The team found that the magma in the volcano’s chambers was rich in water, which caused the molten rock to crystallize, slowing its movement and helping to limit eruptions as the magma reservoir spread. Researchers have studied these crystals, known as zircon, which form when magma cools and can act as time machines, recording information about volcano conditions. They dated 1,250 of these crystals over 700,000 years of volcanic history and learned that during the quiet 100,000-year period, zircon growth reached its peak, evidence of intense magma accumulation.

Methana is a subduction zone volcano, a steep-walled volcano located at a tectonic boundary where a dense oceanic plate dips beneath a younger continental plate or oceanic plate. As the sinking upper plate descends into the mantle, it tends to release water and gases, which melt the surrounding rock. Scientists believe that many other subduction zone volcanoes may similarly be periodically flooded by wet primitive magma that then builds up over time, forming crystals that prevent eruption.

Today, many subduction zone volcanoes in Greece, Italy, Indonesia, the Philippines, South and North America, and Japan are considered extinct and are therefore not currently monitored. But they may be more alive than we think.

Ciomadul, in Romania’s Eastern Carpathians, is one such volcano that deserves closer monitoring, according to Popa. Its last eruption dates back 30,000 years and is traditionally considered extinct. But recent research shows that there is a supply of active magma underground. “This is a clear example of a Methana-type volcano that has been dormant for a very long time but is building its magma chamber,” he says. “A quiet volcano is not necessarily safe.”

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Main image: Ggia / Wikimedia Commons