Geoscientists have discovered a magma cap at Yellowstone National Park that is likely playing a critical role in preventing a massive eruption in one of the largest active volcanic systems in the world.
The “volatile rich” cap made of magma is about 2.4 miles below the Earth’s surface and essentially acts as a lid — trapping pressure and heat below it, according to the team of researchers that uncovered it.
It was found after scientists used a 53,000-pound vibroseis truck to generate tiny earthquakes that send seismic waves into the ground, according to the paper, published last week in Nature. The waves measured reflected off subsurface layers, revealing a sharp boundary at the depth where the magma cap lies.
The scientists were surprised to see “something physically happening” at that depth, said Brandon Schmandt, professor of Earth, environmental and planetary sciences at Rice University and co-author of the study, in a statement.
Steaming Morning Glory Pool in the Upper Geyser Basin, Yellowstone National Park, Wyoming.
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The stability of hazardous volcanic systems is “strongly influenced” by the uppermost magma storage depth, according to the paper. In addition, the magma reservoir at the upper crust beneath Yellowstone’s caldera has not been well constrained, the researchers said.
“For decades, we’ve known there’s magma beneath Yellowstone, but the exact depth and structure of its upper boundary has been a big question,” Schmandt said. “What we’ve found is that this reservoir hasn’t shut down — it’s been sitting there for a couple million years, but it’s still dynamic.”
In 2022, researchers discovered that Yellowstone’s supervolcano has substantially more magma reservoir under the caldera than previously thought. The lava is also flowing at shallow depths that fueled prior eruption.
The researchers modeled various rock, melt and volatile conditions to determine what materials the magma cap consists of — a mixture of silicate melt and supercritical water bubbles within porous rock. The bubbles are formed as the magma rises and decompresses, causing gases like water and carbon dioxide to separate from the melt.
The Grand Prismatic hot spring is among the national parks myriad hydrothermal features created by the Yellowstone supervolcano. Photographed on July 22, 2014 in Yellowstone National Park, WY.
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Volcanic eruptions can then occur as the bubbles accumulate and increase in buoyancy, driving an explosion.
However, an eruption at Yellowstone is likely not imminent, the researchers said.
Data from seismic imaging and advanced computer modeling indicates that the magma reservoir is actively releasing gas but remains in a stable state. The system was described by Schmandt as “steady breathing,” with the bubbles rising and releasing through the porous rock of the magma cap.
“Although we detected a volatile-rich layer, its bubble and melt contents are below the levels typically associated with imminent eruption,” Schmandt said. “Instead, it looks like the system is efficiently venting gas through cracks and channels between mineral crystals.”
Yellowstone’s complex geology proved to be a challenging environment to obtain the data, the researchers said. The scattering seismic waves produced noisy data that was hard to interpret.
“When you see noisy, challenging data, don’t give up,” Chenlong Duan, a co-author on the study, said.
The geoscientists were able to capture one of the first “super clear” images of the top of the magma reservoir beneath the Yellowstone caldera using the structural seismic imaging technique, said Duan, who developed the technique.
The discovery could offer clues to future activity amid Yellowstone’s extensive volcanic system, the researchers said.