Detecting a pocket of magma doesn’t necessarily mean a volcanic eruption is imminent. Magma may hang out near the surface of the Earth for hundreds of thousands of years before exploding out in an eruption, according to new research.

Previous hypotheses about magma held that an eruption could only occur after magma moved quickly to the surface and erupted before it had time to cool.

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However, recent observations of the chemical structure of some magma along with the molten rock’s ability to transmit heat suggests that liquid rock may be able to remain in reservoirs near the surface for long periods of time. The new study, published in the journal Geology, suggests that magma may be able to stay liquid as long as it is fed by fresh magma from deeper in the Earth.

“These time scales are in the hundreds of thousands, even up to a million, years and these chambers can sit there for that long,” said lead author Sarah Gelman, a doctoral student at the University of Washington.

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Understanding how long a magma reservoir can remain liquid could improve geologists ability to assess the risk from particular deposits.

“If you see melt in an area, it’s important to know how long that melt has been around to determine whether there is eruptive potential or not,” Gelman said. “If you image it today, does that mean it could not have been there 300,000 years ago? Previous models have said it couldn’t have been. Our model says it could. That doesn’t mean it was there, but it could have been there.”

IMAGE: Lava fountain in Hawaii (J.D. Griggs, Wikimedia Commons)