This Greek Volcano Appeared Dormant for 100,000 Years. Then It Erupted Once More. Should Researchers Reassess ‘Extinct’ Volcanoes?

By reconstructing a 700,000-year narrative of the Methana volcano, geologists identified a prehistoric era during which it seemed dormant on the surface, even as magma accumulated underground.

The most recent eruption of Greece’s Methana volcano occurred around 250 B.C.E. Following that event, documented by the Greek historian Strabo, the mountain has remained unperturbed, directly across the Saronic Gulf from Athens. However, the volcano’s serene surface may conceal a tumultuous—and potentially hazardous—inner reality.

“It’s vital for our society to realize that for volcanoes, a calm appearance doesn’t always imply safety,” Razvan-Gabriel Popa, a volcanologist at ETH Zurich in Switzerland, informs Reuters’ Marta Serafinko.

In a research paper published on April 22 in the journal Science Advances, Popa and a group of geologists chronicled 700,000 years of Methana’s volcanic history, which included 31 eruptions. Given the eruption around 250 B.C.E.—considered relatively recent in geological terms—Methana is classified as an active volcano, not a dead one. Its newly detailed history suggests that researchers may need to reconsider the classification of certain volcanoes currently seen as extinct, for they might harbor concealed activities.

Typically, for volcanoes like Methana, a quiet period of just 10,000 years is sufficient for geologists to declare them extinct and unlikely to erupt again. However, the recent analysis revealed that Methana experienced an approximately 100,000-year interval—between approximately 168,000 and 280,000 years ago—without any eruptions. Afterward, it resumed lava emissions.

The possibility of volcanoes remaining dormant for thousands of years before erupting indicates that scientists must reassess the potential risks posed by some of them.

“Part of that assessment involves how recently they have erupted,” notes Adam Kent, a volcanologist at Oregon State University who wasn’t part of the study, to Science News’ Skyler Ware. “In this regard, there are likely volcanoes that are threatening yet not classified as such due to their lack of recent eruptions.”

To investigate Methana’s past, Popa and his team gathered and examined over 1,250 zircon mineral crystals sourced from the volcano’s ancient lava flows. Zircon crystals are exceptionally resilient and form as magma cools, capturing small amounts of radioactive uranium. By analyzing the decay of uranium, geologists can determine the age of each crystal and its formation timeline relative to the lava flow it was extracted from.

“We aimed to study Methana because this volcano possesses a significant advantage: The various lava flows are not stacked and do not obscure one another,” Popa tells Nautilus’ Kristen French. The flows are distributed over a considerable area, with “each eruption forming its own hill,” allowing geologists to readily access rocks of different ages.

Unexpectedly, Methana’s peak in zircon production occurred during the 100,000-year lull between eruptions. This indicates that magma was actively building up beneath the volcano, even when it seemed inactive from the surface.

The explanation they uncovered was related to the chemistry of the magma. Methana is positioned above a subduction zone, where one tectonic plate slides beneath another, causing its magma to originate from melting parts of the ocean floor that have descended below the Earth’s crust. This ocean floor is replete with water, resulting in water-rich, or “superhydrous,” magma.

Deep within the Earth’s crust, where massive pressure from overlying rock exists, water assists superhydrous magma in remaining molten. However, as it ascends toward the surface, the pressure decreases, leading to the escape of water molecules from the magma.

“As they rise through the crust, they start to bubble like a carbonated beverage,” Popa explains to Reuters. “This gas bubbling triggers crystallization, transforming the magma into a sticky and viscous substance, slowing it down significantly—by a factor of 100 to 1,000—rendering it too sluggish to continue toward the surface.”

The result is a silent buildup of magma underground, creating an extensive and potentially more hazardous reservoir.

up2metric | Drone Survey in Methana Volcano (Panoramic View 1)

This revelation could be concerning for individuals residing near volcanoes situated along subduction zones that are believed to be dormant. Subduction zones are found around the boundaries of the Pacific Ocean, as well as in the Caribbean and Mediterranean seas.

Olivier Bachmann, a volcanologist at ETH Zurich and co-author of the research, states that their findings impact volcanic authorities globally, from Europe to Japan, Southeast Asia, and the Americas. “This necessitates a reassessment of the risk posed by volcanoes that have experienced long periods of dormancy but exhibit intermittent signs of magmatic activity.”