A MARTINEZ, HOST:
Scientists have recorded a song made by a volcano. NPR's Geoff Brumfiel says it could help predict future eruptions.
GEOFF BRUMFIEL, BYLINE: There's a big volcano in Hawaii called Kilauea.
LEIF KARLSTROM: In 2008, there started an eruptive episode where there was an active lava lake at the summit.
BRUMFIEL: That's Leif Karlstrom, a professor of volcanology at the University of Oregon. As the volcano's crater filled with lava, rocks from the wall began falling into it.
KARLSTROM: These are big rock falls - like, bus-sized.
BRUMFIEL: These giant boulders would plunge into the lava lake several times a week for the next 10 years. And scientists were listening to the splashes they made as they fell.
(SOUNDBITE OF BOULDER SPLASHING)
BRUMFIEL: This audio recording is what your ears would have heard. But researchers also used seismographs placed around the crater to record low-frequency vibrations. And when Karlstrom and graduate student Josh Crozier sped up those recordings, it made music.
(SOUNDBITE OF LAVA VIBRATING)
KARLSTROM: What you're listening to here, you know, might sound like an old field recording of a marimba.
BRUMFIEL: Now, that's pretty cool. But what's even cooler is that the song actually reveals something important about the makeup of the molten rock deep inside the volcano. Karlstrom says the notes of the song depend on how many bubbles of gas are in the liquid rock.
KARLSTROM: The speed of sound of a bubbly mixture is actually very significantly different.
BRUMFIEL: You could hear this for yourself in your kitchen with a spoon and a couple of glasses.
(SOUNDBITE OF CAN OPENING)
BRUMFIEL: All right, so I've filled these two glasses to exactly the same level. They have the same amount of water in them, but one of them is still.
(SOUNDBITE OF GLASS RESONATING)
BRUMFIEL: And the other one is sparkling.
(SOUNDBITE OF GLASS PLINKING)
BRUMFIEL: So the amount of bubbles in the drink changes the way it sounds. The sounds at Kilauea matter to volcano scientists because they care a lot about bubbles.
KARLSTROM: Bubbles are the primary driver of volcanic eruptions generally, actually.
BRUMFIEL: He hopes the volcano's song could be used as a bubble detector to help predict when an eruption has the potential to turn even more violent.
KARLSTROM: There's quite a bit of effort right now in the volcanology community to develop techniques that might allow us to peer into the plumbing system while the event is occurring or before it happens so that we can forecast hazards, for example.
BRUMFIEL: Karlstom's work appears in the journal Science Advances. He says this trick may not work all the time. Not every volcano makes music. But Kilauea's song is worth a listen. Geoff Brumfiel, NPR News.
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