A team of geoscientists led by University of New Mexico researchers has revealed an unprecedented look inside Yellowstone National Park's massive underground magma system. Using cutting-edge seismic imaging, the team identified a sharply defined, gas-rich cap just 3.8 kilometers below the surface—a feature that suggests the reservoir is in active state but not building toward a catastrophic eruption.
The study published in Nature, was led by scientists from UNM, Rice University, the University of Utah, and the University of Texas at Dallas. It reveals a sharply defined, volatile-rich cap just 3.8 kilometers beneath the surface providing new insights into how gas and magma move through Earth's crust.
Brandon Schmandt, professor of Earth and Planetary Sciences during his time at UNM, led the project involving hundreds of portable seismometers and controlled vibration sources. The collaborative team captured some of the clearest seismic images ever recorded of the Yellowstone magma chamber, and specifically addressed the question of how far beneath the surface it is located. UNM postdoctoral researcher Chenglong Duan's innovative use of wave-equation seismic imaging helped visualize previously obscured signals.
"We collected a massive amount of data, a few million digital seismic signals. There was a long path from the raw data samples, that don't look like much individually, to eventually creating clear images of the top of the magma reservoir. Chenglong did excellent work adapting to the challenges of the data," said Schmandt.
Tobias Fischer, distinguished professor of Earth and Planetary Sciences, is co-author on this research. Fischer and his former Ph.D. student Kristen Rahilly have worked extensively on the gas emissions of Yellowstone National Park. Their research showed that the areas of high fluxes of CO2 and other gases lie directly above the imaged location of the volatile-rich part of the magma chamber.
"This work really shows an unprecedented image of magmatic gases accumulating at the very top of a massive magma chamber," said Fischer. "The gases are stored in this region and slowly leak out to the surface giving rise to the spectacular hydrothermal features, such as geysers, bubbling mud pots and diffuse degassing areas that the park is known for."
For decades, scientists have known that magma lies beneath Yellowstone's surface, but its exact structure and behavior remained unclear. That changed when researchers deployed over 600 portable seismometers throughout the park and used a 53,000-pound Vibroseis truck to generate artificial seismic waves—creating a CT-scan-like image of the underground system.
The cap, composed of partially molten rock interlaced with volatile gases like water and carbon dioxide, acts like a lid over the magma reservoir. This helps regulate pressure and release gas slowly through Yellowstone's numerous surface features—like geysers and mud pots—reducing eruption risk.
"One of the most fundamental properties one can know about magma is the depth at which it is stored. Yellowstone has been highly studied but the depth and sharpness of the top of the reservoir remained uncertain. Finding a sharp boundary at only 3.8 km depth is exciting because magma ascending to such shallow depths can release a lot of gas," explained Schmandt.
Much of this new detail came from a field campaign involving 600+ sensors, several nights of vibration truck surveying, and careful coordination within Yellowstone's protected environment. The fieldwork was primarily conducted by researchers from UNM and the University of Utah working under tight constraints, including pandemic-era travel and weather challenges.
"Knowing that we can locally measure the top of the reservoir makes us think forward about how magma reservoirs like Yellowstone's might be better monitored through time and how the sharp top at Yellowstone compares to other settings that erupt different kinds of magma," said Schmandt.
The study also found that the volatile-rich cap is about 14% porous, with half of those pores filled with gas and the other half with melt—a ratio consistent with a dynamic but stable system. While Yellowstone remains geologically active, the findings show that it's effectively "venting" rather than building toward an eruption.
The volatile-rich cap may act as a pressure regulator, allowing gases to escape gradually through Yellowstone's famous surface vents—such as Old Faithful and the Mud Volcano—rather than building up explosively.
That natural release valve, researchers say, means there is a low risk of sudden eruption and offers a model for other volcanic systems around the world.
Authors from The University of New Mexico include Chenglong Duan, Wenkai Song, Brandon Schmandt, Tobias Fischer, and Lindsay Worthington. The work was supported by the National Science Foundation.
