Yellowstone National Park

Yellowstone National Park

Scientists confirm 500-mile finger of molten rock under Yellowstone

December 14, 2009, 8:19 am

Research has confirmed a 500-mile-deep magma plume under Yellowstone is slowly obliterating mountains in its path as it travels an inch a year to the northeast.

The plume rises at a southeast angle from its origin 500 miles beneath the surface under western Montana, causing the swell that forms the Yellowstone Plateau, according to one of the paper’s authors, Dr. Robert Smith. A Moose resident, professor of geophysics with the University of Utah Department of Geology and Geophysics, and coordinating scientist with Yellowstone Volcano Observatory, Smith teamed with scientists from Utah, Massachusetts, Michigan, Norway, Taiwan and Switzerland on the discovery.

They made their announcement in a paper published in the Nov. 20 issue of the Journal of Volcanology and Geothermal Research. Other researchers recently discovered a similar plume under Hawaii.

While scientists have long suspected that magma plumes create volcanos such as Yellowstone, recently some researchers have doubted their existence. Instead of plumes, or fingers of magma – molten rock – that rise from the depths of the Earth, these doubters suspected shallow pockets of magma.

“There was a large crowd that was against plumes in general and against plumes in Yellowstone,” Smith said. “That’s been a bone of contention since the mid-’90s. No one had any data.”

The article, “Geodynamics of the Yellowstone hotspot and mantle plume: Seismic and GPS imaging, kinematics, and mantle flow,” used data from a seismograph network to confirm the presence of the plume, Smith said.

“Now we can see it clear down into the earth’s midmantle,” Smith said. Earth’s mantle – the layer between the crust and the outer core – is flowing from northwest to southeast and deforming the Yellowstone plume like smoke in the wind. Meantime, the North American tectonic plate is sliding to the southwest, effectively moving the top of the plume increasingly toward Billings, Mont.

“This hot, melted material is coming up [at an angle],” Smith said of the plume and the mantle’s “wind.” “It would normally rise vertically.”

Smith and his colleagues used a network of 150 seismographs over an area 435 miles long and 310 miles wide from Missoula, Mont., to Evanston to make a 3-dimensional picture of the plume. The network functioned as a type of antenna to record seismic waves from earthquakes from around the world, including places such as South America and the western Pacific.

Those seismic waves travel at different speeds through features such as magma plumes compared to the surrounding subsurface material, Smith explained. Thus researchers were able to create the image, as a CAT scan would, of Yellowstone’s plume up to 500 miles deep.

“What we record is the travel times,” Smith said of the earthquakes’ seismic waves. “We can compare the travel times verses those we had with standard earth waves. The mathematics that we use is very similar to the mathematics they use in radiology, for example.”

While the measurements show the plume descending about 500 miles into the mantle, it’s possible the plume reaches all the way to the core. The earth’s outer core is about 1,800 miles deep, its inner core about 3,000 miles deep. The center of the planet is almost 4,000 miles below the surface.

“It wouldn’t surprise me that it would go deeper,” Smith said of the plume and its deepest tracing to 500 miles.

This new picture of the structure beneath Yellowstone not only helps researchers understand what’s happening now, but also gives them a better idea of what happened in the past and what will happen in the future.

Seventeen million years ago, the plume reached the surface as a vertical column beneath eastern Oregon and eastern Washington. It caused a bulge in the crust and eventually several volcanic eruptions.

Starting about 12 million years ago, the mantle wind began deforming the plume. At the same time, the Earth’s tectonic plates, or crust, traveled over the plume causing the Yellowstone swell to effectively move across Idaho and create the Snake River Plain.

The traveling hot spot, volcanic eruptions and subsequent erosion created the wide, flat Idaho valley through which the Snake River now runs. Even mountain ranges in the path of the hot spot were obliterated.

After effectively moving from western Nevada to eastern Idaho, the hot spot is in its current location at the northwest corner of Wyoming, where it is responsible for the geothermal features in the world’s first national park.

“Yellowstone has affected five or six states in the western United States over the last 17 million years,” Smith said. “Yellowstone’s had a profound affect on the topography and the drainage and the mountain ranges for millions of years.” The plate will keep moving, Smith said.

“I always use the joke the Park Service should be buying property to the northeast,” he said. “Eventually, it could destroy the mountains northeast of Yellowstone.”

The magma plume won’t blow the mountains “all to smithereens,” Smith said, but will gradually consume them on its slow march northeast. Yellowstone’s swell creeps along at about an inch per year toward Billings, Mont.,  or, rather, the earth’s crust under Billings creeps southwest over Yellowstone’s magma plume.