RACHEL MARTIN, HOST:
Every few million years or so, the Earth burps up a gargantuan volcano, a supervolcano that can erupt continuously for thousands of years. Now, a scientist who is mapping the planet's interior has an idea about what causes these supervolcanoes and when we might expect another one. NPR's Christopher Joyce has the story.
CHRISTOPHER JOYCE, BYLINE: Sure, these giant eruptions may be rare, but look out when they hit. The ash and volcanic gases can wipe out most living things over large parts of the planet. Now, a seismologist at the University of Utah has some clues about what causes these big eruptions. Michael Thorne uses seismic waves to get a picture of what's going on deep beneath the Earth's surface, where the Earth's core meets the outer mantle. Think of an avocado: the pit is the core, the stuff you make guacamole with is the outer mantle. Thorne's been watching two enormous piles of rock that sit on the boundary between the core and the mantle. One pile is underneath the Pacific Ocean, the other under Africa. Scientists have known about these but Thorne saw something different.
MICHAEL THORNE: I think this is the first study that might point to evidence that these piles are moving around.
JOYCE: Moving very, very slowly. But these piles are maybe 3,000 miles across. Thorne thinks, in fact, that the pile under the Pacific is actually two piles crushing up against each other. And where they meet, there's a blob.
THORNE: We call it a blob of partially molten material. I mean, it's big size. This one that we found is an order of magnitude, maybe 10 times larger than any of the other ones that we've observed before.
JOYCE: This blob is the size of Florida, and there are other, smaller blobs around the edges of the piles, too. So, we've got these great rock piles smushing together and squeezing this huge molten blob at the middle of it like some kind of balloon, and it is going on right underneath us - at least under Samoa. Should we care about these blobs?
THORNE: A possibility is that these blobs might represent sort of a deep-seated root, you know, to where plumes arise all the way to the surface, giving hot-spot volcanism.
JOYCE: Hot spots like Yellowstone supervolcano, for example. It's blown its top three times in the past two million years. Thorne published all this in the journal Earth and Planetary Science Letters. He's rather calm about it. He says it's a slow process from blob to blowout - maybe 100 million years or so. He says he has no plans to move. Christopher Joyce, NPR News.
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