Extinct Volcanoes May Still Grow: New Crystal Evidence

Scientists have discovered that volcanoes long considered “extinct” may still be capable of eruption, as magma can continue to accumulate deep underground for hundreds of thousands of years after a volcano’s last known eruption. A new study focusing on the Methana volcano near Athens, Greece, revealed ongoing magma activity during a 100,000-year period of dormancy, challenging conventional classifications of volcanic inactivity.

The research, published April 22 in Science Advances, analyzed zircon crystals found in volcanic rock samples from Methana. These crystals form in magma chambers and are carried to the surface during eruptions. By dating over 1,250 samples, researchers reconstructed a 700,000-year history of the volcano’s activity.

Reassessing Volcanic Risk

The findings suggest that the current definition of an “extinct” volcano – typically considered inactive for 10,000 years or more – may be insufficient. “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, smaller volcanoes are considered extinct if they haven’t erupted in the last 10,000 years, while larger volcanoes can remain dormant for much longer due to the time required to build up sufficient magma for an eruption. However, the Methana study demonstrates that significant magma accumulation can occur even during extended periods of quiescence.

During Methana’s longest dormant period, lasting over 100,000 years, the team discovered the highest concentration of zircon crystal formation, indicating substantial magma activity beneath the surface. This suggests that volcanoes can remain potentially active for far longer than previously thought, even without exhibiting surface signs of unrest.

Methana’s Volcanic History

Methana, located approximately 50 kilometers from Athens, is part of the South Aegean Volcanic Arc, a region known for volcanic activity due to plate tectonics. The volcano experienced two primary periods of eruption, the first ending around 280,000 years ago and the second beginning around 168,000 years ago. The surprising discovery was the evidence of magma generation *between* these eruptive periods.

“What we learned is that volcanoes can ‘breathe’ underground for millennia without ever breaking the surface,”

Olivier Bachmann, ETH Zurich volcanologist

Researchers analyzed rock samples from 31 locations across the volcano to understand the relationship between eruptive activity and magma accumulation. The zircon crystals provided a timeline of Methana’s volcanic history, revealing the prolonged period of subsurface activity.

Implications for Future Eruption Forecasting

The study’s findings have significant implications for volcanic hazard assessment. Current forecasting models often rely on the assumption that volcanoes become extinct after a certain period of inactivity. This research suggests that this assumption may be flawed and that seemingly dormant volcanoes could pose a greater risk than previously recognized.

By identifying ongoing magma accumulation in volcanoes considered extinct, scientists may be able to better predict future eruptions and mitigate potential hazards. This is particularly important in densely populated areas near potentially active volcanoes.

The South Aegean Volcanic Arc, which includes the well-known Thera volcano (Santorini), is a region of particular interest. The devastating eruption of Thera around 3,600 years ago destroyed the Minoan civilization, highlighting the potential for catastrophic events in this area. Understanding the long-term behavior of volcanoes like Methana is crucial for improving eruption forecasting and protecting vulnerable communities.

Further research is needed to determine how widespread this phenomenon of prolonged subsurface activity is among other volcanoes globally. However, the Methana study provides compelling evidence that the definition of an “extinct” volcano requires reevaluation, and that long periods of dormancy do not necessarily equate to complete inactivity.