Old Faithful erupts under blue skies

Old Faithful erupts under blue skies in Yellowstone National Park.

BOB ZELLAR/Billings Gazette

JACKSON, Wyo. – New research indicates the magma chamber underlying Yellowstone National Park may not be as volatile as previously believed.

University of Utah geophysicist Bob Smith and a student, Jamie Farrell, used seismic data from 26 years of earthquakes to map the composition of the Yellowstone caldera.

The study, published in Geophysical Research Letters earlier this month, revised the best estimate for the percentage of the magma chamber that is molten as opposed to solid. Magma chambers that have higher percentages of solids are generally thought to be less eruptible.

“The percentage of actual melt in Yellowstone is only about 10 percent,” Smith said. “We see anywhere from 7 to 13 or 14 percent, depending on where we do the calculation.”

Researchers previously estimated that the magma chamber was 32 percent liquid based on data from five seismic stations and 570 earthquakes.

The study by Farrell and Smith uses data from 4,520 earthquakes recorded between 1984 and 2011 in Yellowstone, which includes parts of Wyoming, Montana and Idaho.

Their study is based on the fact that seismic waves from earthquakes travel at different speeds in different materials. That in turn gives geophysicists glimpses into the compositions of what the waves are passing through.

Estimated at between 5 to 15 percent liquid, the fluid portion of the magma chamber is believed to be somewhere between 200 cubic kilometers and 600 cubic kilometers in size. That liquid area equates to significantly less material than two of the past three Yellowstone supervolcano eruptions, the last occurring 640,000 years ago, the research paper said.

The remaining 85 percent to 95 percent of the Yellowstone magma chamber is solid.

While there remains much uncertainty about the Yellowstone chamber, the Farrell and Smith research advances what’s known about the larger Yellowstone volcanic field and how it interacts with the magma reservoir.

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