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Large magma bodies found beneath dormant volcanoes, surprising scientists

New Cornell University led-research challenges the long-standing belief that active volcanoes have large magma bodies that are expelled during eruptions and then dissipate over time as the volcanoes become dormant.

Researchers used seismic waves to identify magma chambers beneath the surface of six volcanoes of various sizes and dormancy within the Cascade Range, which includes half of the U.S. volcanoes designated by the U.S. Geological Survey as "very high threat." The team found that all of the volcanoes, including dormant ones, have persistent and large magma bodies.

The study, led by postdoctoral researcher Guanning Pang, was in Nature Geoscience and co-authored by Geoffrey Abers, professor in geological sciences.

Their results are surprising given that some of these volcanoes, such as the Crater Lake volcano in Oregon, have not been active in millennia.

"Regardless of eruption frequency, we see large magma bodies beneath many volcanoes," Pang said. "It appears that these magma bodies exist beneath volcanoes over their whole lifetime, not just during an active state."

The fact that more volcanoes have sustained magma bodies is an important consideration for how researchers may monitor and predict future volcanic activity. The U.S. Geological Survey has been expanding and upgrading its volcanic monitoring networks in the Cascade Range and elsewhere as part of the National Volcano Early Warning System, with the aim of detecting signals of an impending eruption as early as possible.

"We used to think that if we found a large amount of magma, that meant increased likelihood of eruption," Pang said, "but now we are shifting perception that this is the baseline situation."

The results suggest that an eruption does not completely drain a magma chamber, instead, it lets off some of the excess volume and pressure. The chamber can be slowly expanded and refilled over time due to gradual melting of the crust.

"If we had a better general understanding of where magma was, we could do a much better job of targeting and optimizing monitoring," Abers said, noting that there are a "great many volcanoes that are sparsely monitored or have not been subject to intensive study."

Plans are already in the works to expand the magma monitoring system and see if the Cascade discovery translates to other locations, including Alaska.