Greek volcano’s "silent" phase may hide ongoing magma activity, scientists warn

A Greek volcano long considered dormant for over 100,000 years may not be as inactive as once thought, according to new research that suggests some “extinct” volcanoes could still be quietly building the conditions for future eruptions.

Deep beneath the Methana volcano, near Athens, scientists have found evidence that magma was still evolving during periods when the volcano appeared to be silent at the surface. The study, published April 22 in Science Advances, points to zircon crystals as key evidence of hidden underground activity, Science News writes. 

“I think that we definitely have to start reevaluating how we classify extinct volcanoes,” says Razvan-Gabriel Popa, a volcanologist at ETH Zurich in Switzerland.

Traditionally, small volcanoes are classified as extinct if they have not erupted in around 10,000 years, though larger systems can remain inactive for far longer due to slower magma accumulation. However, the Methana findings suggest surface inactivity may not reflect what is happening deep below ground.

Popa and colleagues reconstructed a 700,000-year eruption history of Methana by analysing more than 1,250 volcanic rock samples and dating zircon crystals formed in underground magma chambers. These crystals are brought to the surface during eruptions, preserving a record of subsurface activity.

Their results showed two major eruptive phases: one ending around 280,000 years ago and another beginning about 168,000 years ago. Crucially, instead of finding a lack of activity between these phases, researchers identified a peak in zircon formation during the volcano’s so-called quiet period.

This indicates that magma remained active beneath the surface even during long stretches without eruptions, challenging the assumption that such volcanoes are truly dormant.

The researchers suggest that changes in water content within magma may explain this behaviour. Under high pressure, water helps keep magma fluid. But as pressure drops closer to the surface, gases begin to escape.

“It’s like a fizzy drink,” Popa says. “We open the bottle, and — pssshht — all the gas comes out.”

As gas escapes, the magma becomes thicker and more solid, eventually halting its upward movement before it can erupt.

Experts say this process could help explain why many magma systems never reach the surface. “Most magmas that enter Earth’s crust don’t erupt,” says Kari Cooper, a geochemist at the University of California, Davis. She adds that magma water content may play a key role in determining eruption potential.

The findings could have broader implications for volcanic risk assessment, particularly in identifying systems that appear inactive but may still be evolving underground.

“Part of that calculation is how recently they have erupted,” says Adam Kent, who studies igneous rocks and volcanoes at Oregon State University in Corvallis but was not involved in the study. “In that sense, there are probably volcanoes out there that are threatening but not evaluated as such because they haven’t erupted for a while.”

Researchers say the study highlights the need to rethink how volcanoes are classified and monitored, especially as modern techniques reveal more about the hidden dynamics beneath Earth’s surface.

By Sabina Mammadli