U. researcher uses vibrations to look into Yellowstone's magma chamber

SALT LAKE CITY — Scientists have studied Yellowstone National Park's magmatic system for decades, which makes the iconic geysers, mud pots and various hydrothermal wonders possible. But it wasn't until recently that a University of Utah professor found a new way to look at the region and the conditions underground.

It started in 2020, when Jamie Farrell, then a research associate professor of geology and geophysics and chief seismologist at the U.S. Geological Survey's Yellowstone Volcano Observatory, and researchers from the University of New Mexico set out to better understand the volcanic system through higher-resolution images of subsurface features.

Since the system is underground, Farrell explained, researchers used a technique called tomography, which is essentially the same thing the medical field uses to image the human body in a CT scan or an MRI.

Farrell and his team harnessed devices called seismometers that record artificial, mechanical vibrations that mimic seismic waves emitted from natural events.

"We put out around 650 temporary seismometers all throughout the Yellowstone park area, mainly along the roadway system," he said.

Then, they brought in a vibroseis truck, typically used in oil and gas exploration, to image subsurface formations and deposits. Using the truck, the team vibrated the ground at 110 locations, delivering 20 treatments lasting 40 seconds each.

"In a sense, we're causing our own earthquakes, and we record all that data on the seismometers," Farrell said. "And since we put so many (seismometers) out, we can get a higher resolution image of the subsurface."

Using artificial seismic waves, the team determined that the top of the chamber is 3.8 kilometers, or about 12,500 feet, below Earth's surface and is sharply delineated from the rock strata above, according to findings published in the journal Nature. The researchers also determined that the portion of the uppermost magma chamber is comprised of "about a 50/50 mixture" of volatile gases and liquids.

"What this tells us is that the Yellowstone magmatic system, effectively, is degassing, which is a good thing. That gas is coming out of solution and making its way up towards the surface, and that is good because as you trap gases inside a reservoir and they can't escape, pressure builds up and you could get explosive eruptions," Farrell said.

Basically, the long-dormant Yellowstone volcano is at no immediate risk of eruption.

"We're only seeing ... seven to 15% molten material in this magmatic system, and typically, you need to have at least 50% for magma to be mobile and be able to move around, and depth, and then be able to erupt. It doesn't look like the system is anywhere near ready for an impending eruption," Farrell said.

Mike Poland, the scientist in charge of the Yellowstone Volcano Observatory, said this research provides important clues about the structure of Yellowstone's magma body.

"That helps us understand more about the heat engine that's powering Yellowstone and about how melt is distributed. That can have ramifications for how we perceive the volcanic hazard," Poland said. "Yellowstone, in many ways, is a laboratory volcano, and what we learn at Yellowstone can be used to better understand volcanoes in other parts of the world that are a lot more active but are harder to study."

Those might include Campi Flegrei in Italy or Santorini in Greece, which is mostly submarine, he said.

Farrell added that this research shows promise for the ability to collect high-resolution images of magmatic systems, specifically looking at things like how Yellowstone's magmatic system interacts with the area's overriding hydrothermal system.

"I think we could use something like this to get a better idea of why these large, high-thermal basins are where they're at," he said.

The full study can be found online at nature.com.

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