Scientists Can Listen For Sounds Volcanoes Make Just Before They Erupt

Eavesdropping on the rumblings of a volcano may help scientists predict when an eruption is coming, according to a recent study published in the journal Geophysical Research Letters.

The study used data from a volcano called Villarrica in Chile, which erupted in March 2015. Coincidentally, the eruption began just two months after scientists had started monitoring the noises it produces—in particular, infrasound, or noises pitched deeper than humans can hear.

"Volcanoes are complicated and there is currently no universally applicable means of predicting eruptions," Eric Dunham, a geoscientist at Stanford University, said in a press release. "In all likelihood, there never will be." But infrasound could be a piece of the puzzle for certain volcanoes.

Specifically, for volcanoes like Villarrica, which is classified as an open vent volcano—which is exactly what it sounds like, a volcano where magma reaches all the way up to the surface through vents in the rock and gas is constantly leaking out. That's unlike a volcano like Mount St. Helens, where all the magma was trapped underground until its dramatic eruption in 1980.

But when vents are open, volcano scientists have a couple extra options for keeping an eye on what's happening. First, there's the literal take: They can monitor the level of the lava lake in a volcano's crater from the sky to see if there's a sudden rise or fall, a signal that something big may happen.

But that's not always an easy observation to make. So the team behind the new paper studied a second, related factor, the inaudible infrasound rumblings that moving magma produces.

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The March 3, 2015 eruption, which ended three decades of quiet at Villarrica, destroyed two of the 10 infrasound monitors scientists had installed around the volcano's summit earlier that year. But the remaining devices showed that in the week before the eruption began, the sound rose in pitch.

That suggests that infrasound could be one of a suite of characteristics scientists monitor to try to see an eruption beginning with enough time to protect people nearby. Other possible warning signs, which scientists already watch at major volcanoes, include the release of certain gases, an increase in small earthquakes in the area, and warping in the ground that satellites orbiting Earth can measure.