Zircon Crystals Indicate Extinct Volcanoes May Still Develop Underground

Tiny zircon crystals from a volcano in Greece indicate that magma can continue to form underground even during long periods without eruptions, according to a study published April 22 in Science Advances. The volcano, located about 50 kilometers from Athens, has not erupted for more than 100,000 years in some periods, but evidence shows subterranean growth persisted.

Researchers collected volcanic rock samples and examined zircon crystals, which form in deep magma chambers. By dating crystals from over 1,250 samples, the team constructed a 700,000-year timeline of the volcano's activity. The timeline revealed two main eruption periods: one ending around 280,000 years ago and another starting around 168,000 years ago.

During the interval between these periods, zircon crystal formation was at its highest, indicating ongoing magma activity despite no surface eruptions.

The study suggests that volcanoes considered extinct—typically those without eruptions in the last 10,000 years for small ones, or longer for larger ones—may still have active processes underground. Razvan-Gabriel Popa, a volcanologist at ETH Zurich in Switzerland, stated that classifications of extinct volcanoes may need reevaluation.

Water-saturated magma could explain the long quiescence, as it remains molten under high pressure but solidifies when rising and losing water vapor, similar to bubbles escaping from a fizzy drink.

Kari Cooper, a geochemist at the University of California, Davis, noted that most magmas entering Earth's crust do not erupt, and magma water content might influence eruption timing. Linking magma chemistry to volcanic life cycles could aid in forecasting hazards and prioritizing monitoring efforts.

Adam Kent, who studies igneous rocks and volcanoes at Oregon State University in Corvallis, said that recent eruption history factors into risk calculations for volcanoes.