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University of Utah scientists recently determined that there's twice as much magma below the Yellowstone super volcano as they found in a 2004 study.

But that doesn't mean it's about to blow.

Rather, it's a testament to improved data from seismic tomography, a technique in which earthquakes are used to paint a picture of the world beneath our feet. U. scientists recorded the precise time and location of more than 4,500 quakes in the constantly active park and measured the time it took for those seismic waves to reach the surface. Slower times mean the waves are likely passing through hot magma.

"It's important to note that the magma reservoir isn't actually getting any bigger," said Jamie Farrell, a postdoctoral fellow at the U. "The implications are: 1. We understand the system better than we did before. We understand how the volcano works, how it's built underground, and 2. We can use this data to understand the potential for future hazards."

Yellowstone National Park is a huge bowl-like caldera left over from the last massive volcanic event in the region, which is currently situated over a hot spot in the Earth's mantle.

Its magma reservoir — about 7 percent full of magma (or underground lava) located between 4 and 10 miles deep — is now thought to be about 80 kilometers long and 20 kilometers wide, after data was crunched from roughly 4,500 earthquakes.

Robert Smith, U. emeritus professor of geophysics, spoke about the new data at the end of October at the Geological Society of America in Denver, and his presentation was reported by the journal Nature. The researchers will share their data with the general public and the National Park Service, both for educational and safety purposes.

"These large volcanic eruptions that have occurred at Yellowstone in the past, nobody's ever witnessed those," Farrell said. "So we really don't know what they're like when they're going to erupt."

Past Yellowstone eruptions have covered half of North America with a sheet of ash.

Farrell cautions, however, that there's no reason to take shelter just yet. There have been three giant eruptions in the last 2.1 million years, he said, but that's not enough data to determine a "typical" interval. And even if you figure the average interval at 700,000 years, we are still tens of thousands of years from being overdue.

"At any given time, there's a much higher probability of having a large earthquake than even a small volcano," Farrell said.

The park is a hub of seismic activity. There are often many small quakes in a single day, and Smith has theorized that they are aftershocks from a magnitude-7.3 earthquake at Hebgen Lake in 1959 that killed 28 people, caused 160 features which had no previous record of geysers to erupt, and was felt 285 miles away in Salt Lake City.

That volatility makes it a very fun place to be a geophysicist, Farrell said. "It's a very active region. There's a lot of neat data, and it's one of the most seismically active places in the Intermountain West. [For us], it's not just a place with large animals."

Twitter: @matthew_piper

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