Volcano under Yellowstone bigger than previously thought

Yellowstone is an active volcano. Surface features such as geysers and hot springs are direct results of the region's underlying volcanism. (National Park Service)

SALT LAKE CITY – Yellowstone's underground volcanic plumbing is bigger and better connected than scientists thought, researchers reported Wednesday, April 17, at the Seismological Society of America's annual meeting.

"We are getting a much better understanding of the volcanic system of Yellowstone," said Jamie Farrell, a seismology graduate student at the University of Utah. "The magma reservoir is at least 50 percent larger than previously imaged."

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Knowing the volume of molten magma beneath Yellowstone is important for estimating the size of future eruptions, Farrell told OurAmazingPlanet.

Supervolcano trail
Geologists believe Yellowstone sits over a hotspot, a plume of superheated rock rising from Earth's mantle. As North America slowly drifted over the hotspot, the Yellowstone plume punched through the continent's crust, leaving a bread-crumb-like trail of calderas created by massive volcanic eruptions along Idaho's Snake River Plain, leading straight to Yellowstone. The last caldera eruption was 640,000 years ago. Smaller eruptions occurred in between and after the big blasts, most recently about 70,000 years ago. [Infographic: Geology of Yellowstone]

The magma chamber seen in the new study fed these smaller eruptions and is the source of the park's amazing hydrothermal springs and geysers. It also creates the surface uplift seen in the park, said Bob Smith, a seismologist at the University of Utah and author of a related study presented at the meeting.

The volcanic plume of partly molten rock that feeds the Yellowstone supervolcano. Yellow and red indicate higher conductivity, green and blue indicate lower conductivity. Made by University of Utah geophysicists and computer scientists, this is the first large-scale 'geoelectric' image of the Yellowstone hotspot.

"This crustal magma body is a little dimple that creates the uplift," Smith said. "It's like putting your finger under a rubber membrane and pushing it up and the sides expand."

Clearer picture
A clearer picture of Yellowstone's shallow magma chamber emerged from earthquakes, whose waves change speed when they travel through molten or solid rock. Farrell analyzed nearby earthquakes to build a picture of the magma chamber.

The underground magma resembles a mutant banana, with a knobby, bulbous end poking up toward the northeast corner of Yellowstone National Park, and the rest of the tubular fruit angling shallowly southwest. It's a single connected chamber, about 37 miles long, 18 miles wide, and 3 to 7 miles deep.

Previously, researchers had thought the magma beneath Yellowstone was in separate blobs, not a continuous pocket.

The shallowest magma, in the northeast, also matches up with the park's most intense hydrothermal activity, Farrell said. The new study is the best view yet of this zone, which lies outside the youngest caldera rim.

Additional molten rock, not imaged in this study, also exists deeper beneath Yellowstone, scientists think.

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