Yellowstone National Park
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Yellowstone Supervolcano Bigger Than Once Thought
Published December 27, 2009 4:00 PMYou know that supervolcano beneath Yellowstone National Park? The one responsible for the steam that makes the place famous? Well, it turns out that supervolcano is super indeed — both bigger and deeper than scientists had previously known. Host Guy Raz speaks with geophysicist Robert Smith of the University of Utah about his new research on the larger-than-thought volcanic system beneath Yellowstone.
The supervolcano beneath Yellowstone National Park is bigger, much bigger, than scientists had previously thought. A team of researchers found that the plume of hot and molten rock that feeds the volcano rises from a depth of more than 400 miles below the earth's surface. And the reservoir that holds that molten rock, well, it's 20 percent larger than we once knew.
University of Utah geophysicist Robert Smith led that team and joins us from member station KUER in Salt Lake City.
Professor ROBERT SMITH (Geology and Geophysics, University of Utah; Geophysicist): Thank you. Glad to be here.
RAZ: Can you put this supervolcano into a perspective for us? I mean, how have its past eruptions compared to, you know, a volcano like Mount St. Helens?
Prof. SMITH: Well, recall that Yellowstone National Park, of course, is the quintessential geology park with hot springs and geysers. They derive their heat from magma from an active volcanic system that has been in the Yellowstone area active for about two million years.
In the two-million-year span, there's been three giant eruptions. And these, you know, occurred, well, two million years, 1.3 million and 640,000 years ago. And in between these eruptions and since the last one, there's been smaller eruptions, many much bigger than those of Mount St. Helens.
RAZ: Now, Professor Smith, presumably, you and your team could not start digging underground to find this magma chamber and actually measure it because you wouldn't be speaking to us now, how did you actually figure this out?
Prof. SMITH: Well, we use a method called seismic tomography, which is similar to a CAT scan of a human body.
RAZ: Mm-hmm.
Prof. SMITH: And we measure the speed of earthquake-produced waves that propagate through the earth. And we record them on a large array of seismographs at the surface. And when a seismic wave, just like a sound wave I'm talking to you is a seismic wave, if it's speeded up or slowed down by the rock material, and hot rock produces generally lower speeds of sound than cold rocks, and so what we then do is record, you know, literally thousands of earthquakes and do a computer reconstruction of where they were slowed down or speeded up. And from that, we can construct an image. We're illuminating a body just like turning on a light or like taking a CAT scan or an X-ray.
RAZ: Now, there are two components to this, right? I mean, there's the magma chamber, which is 20 percent larger.
Prof. SMITH: Right.
RAZ: But then there's this volcanic plume that is about 400 miles below the earth's surface, below - actually below the town of Wisdom, Montana, which is, what, about 100 miles from Yellowstone?
Prof. SMITH: Yeah, that discovery we've made in the sense that most people had originally implied that plumes in the earth, they're just vertical features like boiling water in a teapot. And what we found is, in fact, it's tilted because the Earth's mantle is moving at a few centimeters per year, and it's tilted because the hot material is caught in the wind of the mantle.
I'd like to use the analogy you see smoke rising, and when it gets into a breeze, it gets slightly tilted by the breeze. Well, that's what's happening in the Earth's mantle beneath the Yellowstone area.
RAZ: So, any reaction from the folks in Wisdom, Montana? I mean, are they sort of preparing to become a vacation destination in the next million years or so?
(Soundbite of laughter)
Prof. SMITH: I'm not sure that they've heard my story lately, but I doubt that they're too concerned about that. Nothing that's going to have any effect on the surface of the Earth there at all.