A Surprising Amount of Magma Is Under Yellowstone’s Supervolcano

One of the magma reservoirs underneath the Yellowstone Caldera, a huge crater and supervolcano, holds more liquid molten rock than scientists previously estimated, suggests new research published Thursday in the journal Science.

The amount of melted rock beneath a volcano helps researchers determine how close it might be to erupting. But though there may be more liquid magma underneath Yellowstone than scientists had assumed, the behemoth is still unlikely to erupt anytime in the near future.

Magma consists of rocks and crystals at varying stages of solidity—the more melted, or liquid, the magma is, the more likely a volcano is to erupt. Two large reservoirs full of magma exist beneath the Yellowstone Caldera—one that’s about three to ten miles beneath the surface, and another that’s 12 to 30 miles below ground.

Based on previous research, scientists thought the shallower reservoir was mostly solid, with just 5 to 15 percent melted rock. Now, however, after using powerful supercomputers to re-analyze existing seismic data from the past 20 years, they believe that proportion is actually 16 to 20 percent.

That’s still well below the threshold of liquid magma—about 35 to 50 percent—that scientists believe will trigger an eruption. While the new findings don’t change the volcano’s risk level, they do represent a “big improvement in our ability to understand what’s beneath Yellowstone,” says Kari Cooper, an Earth and planetary scientist at the University of California, Davis, who was not involved in the study, to New Scientist’s James Dinneen.

The Earth hasn’t created more liquid magma. Rather, scientists say they now have a more accurate understanding of what was already there.

“It’s a bit like getting a new lens on an old camera,” says Michael Poland, a research geophysicist and the scientist-in-charge at the U.S. Geological Survey’s Yellowstone Volcano Observatory who was not involved in the study, to the New York Times’ Robin George Andrews. “It’s the same camera, but you’ve got finer resolution now. You see with more clarity.”

The Yellowstone supervolcano, located in northwestern Wyoming in Yellowstone National Park, is one of the largest volcanoes in the world. It’s erupted multiple times over the past 2.1 million years, including three massive eruptions that smothered the surrounding landscape in ash. The Yellowstone Caldera, which spans 30 by 45 miles wide, formed during one of those eruptions roughly 631,000 years ago.

Seismic waves, produced by earthquakes, must move through layers of materials inside the Earth before reaching seismometers on the surface. The waves slow down when they reach molten rock, so researchers can use the time it takes them to reach the seismometers to glean insights into how much magma is below ground.

Past analyses have assumed that seismic waves emanate linearly from the quake toward the seismometer. But the reality of their journey is much more nuanced than that. This time around, supercomputers modeled the seismic waves in three dimensions, which gave scientists a more complete picture of the “crystal mush” below Yellowstone, as study co-author Ross Maguire, a seismologist at the University of Illinois Urbana-Champaign, tells New Scientist.

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Sarah Kuta is a writer and editor based in Longmont, Colorado. She covers history, science, travel, food and beverage, sustainability, economics and other topics.