Ask any geologist about the magma reservoir beneath Yellowstone, and they’ll tell you that it’s there. But where, exactly, is a lot tougher to explain.
A new paper published in Nature suggests, however, that a team of researchers has finally found the exact location of the upper boundary of Yellowstone’s magma reservoir. Locating the top of the chamber and characterizing its contents, the research reveals important insights into the future activity of the volcano at Yellowstone, indicating that the volcanic system is unlikely to erupt any time soon.
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Revealing the Yellowstone Magma Reservoir
Though the existence of the magma reservoir beneath Yellowstone has been well-established, its location and contents are a lot less clear. That’s because researchers have long struggled to pinpoint the precise location and the exact contents of the chamber’s upper portion, which have important implications for predicting the future activity of the volcano.
Setting out to precisely map the top of the chamber for the first time, the authors of the new paper sent artificial seismic vibrations through the subsurface beneath Yellowstone. They then used a network of portable geophones to map the subsurface.
The seismic reflection images that resulted revealed that the upper boundary of the magma reservoir sits at around 3.8 kilometers (about 12,500 feet) beneath Yellowstone’s surface, and that it is filled with a mixture of solid and molten rock and gas, the latter exsolved (or released) from the magma.
“The depth of 3.8 kilometers is important,” said Jamie Farrell, a paper author, a geologist at the University of Utah, and the chief seismologist at the U.S. Geological Survey’s Yellowstone Volcano Observatory, according to a press release. In fact, that depth tells geologists information about the volcano’s future threats. “We know what pressures are going to be and how bubbles are going to come out of the magma,” Farrell said in the release.
While bubbles of exsolved gases are an important factor in explosive eruptions, they aren’t accumulating at Yellowstone today. “One thing that makes these eruptions so devastating is that if gases are trapped, they become very explosive,” Farrell said in the release. But most of the gases beneath the volcano at Yellowstone are not trapped, emerging through geothermal features at Yellowstone’s surface.
“When the magma rises from the deeper crust, volatile materials such as CO2 and H2O exsolve from the melt. Due to their buoyancy, they tend to accumulate at the top of the magma chamber,” said Fan-Chi Lin, a paper author and a geologist at the University of Utah, according to the release. “But if there’s a channel, they can escape to the surface.”
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Vibrating the Volcano
To trace Yellowstone’s magma chamber, past research has turned to the University of Utah’s array of permanent seismograph stations, which monitor seismic activity throughout Yellowstone. Readings taken from these seismograph stations after earthquakes have helped scientists map Yellowstone’s magma chamber in the past, albeit blurrily, leaving the precise limits of the magma chamber unknown.
As such, the paper authors looked to the readings of 650 portable geophones scattered around Yellowstone’s roads, which revealed its seismic activity in sharper detail. They then induced seismic activity themselves, using a Vibroseis truck to send artificial vibrations through Yellowstone’s subsurface in 110 separate locations.
“In a sense, we’re causing our own earthquakes, and we record all that data on the seismometers,” Farrell said in the release. “And since we put so many out, we can get a higher resolution image of the subsurface.”
Rendering seismic reflection images from the readings, the paper authors identified the chamber’s top and contents. While around 86 percent of the top portion of the reservoir is composed of solid rock, around 14 percent is composed of pore spaces, they found, which contain molten rock, liquid, and gas.
“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,” said Mike Poland, the scientist in charge at the Yellowstone Volcano Observatory, according to the release. “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.”
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Sam Walters is a journalist covering archaeology, paleontology, ecology, and evolution for Discover, along with an assortment of other topics. Before joining the Discover team as an assistant editor in 2022, Sam studied journalism at Northwestern University in Evanston, Illinois.
