Scientists have found a vast reservoir of hot, partly molten rock beneath the supervolcano at Yellowstone National Park that is big enough to fill the Grand Canyon 11 times over.
The newly discovered magma chamber — 12 to 28 miles underground — is four times bigger than the previously known chamber above it, according to imaging by University of Utah researchers.
In a big eruption, Yellowstone would eject 1,000 times as much material as the 1980 Mount St. Helens eruption. This would be a disaster felt on a global scale, which is why scientists are looking at this thing closely.
The study published Friday in the journal Science fills in a missing link of the system. It describes the large reservoir of hot rock, mostly solid but with some melted rock in the mix, that lies beneath a shallow, already-documented magma chamber. The reservoir is on top of a long plume of magma that emerges from deep within the Earth’s mantle.
“This is like a giant conduit. It starts down at 1,000 kilometers. It’s a pipe that starts down in the Earth,” said Robert Smith, emeritus professor of geophysics at the University of Utah and a co-author of the new paper. The lead author is his colleague Hsin-Hua Huang.
This system has been in place for roughly 17 million years, with the main change being the movement of the North American tectonic plate, creeping at the rate of roughly an inch a year toward the southwest.
A trail of remnant calderas — large volcanic craters — can be detected across Idaho, Oregon and Nevada, looking like a string of beads, marking the migration of the tectonic plate.
This new picture doesn’t change, fundamentally, the risk assessment of Yellowstone, but it will help scientists understand the mechanics of the volcano.
“Really getting an idea of how it works and understanding how these large caldera-forming eruptions may occur, and how they might happen, would be a good thing to understand,” said paper co-author Jamie Farrell, another geophysicist at the university. “No one’s ever witnessed one of these really large volcanic eruptions. We kind of scale smaller eruptions up to this size and say, ‘This is probably how it happens,’ but we really don’t know that for sure.”
The next major calderic eruption could be within the boundaries of the park, northeast of the old caldera.
“If you have this crustal magma system that is beneath the pre-Cambrian rocks, eventually if you get enough fluid in that system, enough magma, you can create another caldera, another set of giant explosions,” Smith said. “There’s no reason to think it couldn’t continue that same process and repeat that process to the northeast.”
The report is based on the equivalent of an MRI of the crust beneath Yellowstone. Nature itself supplies the key diagnostic tool: earthquakes.
The Yellowstone region is seismically active, and in any given year there can be hundreds of small earthquakes. These tremors send seismic waves racing through the planet’s crust.
Seismographs stationed around Yellowstone and across the United States record the arrival of these waves and carefully measure how long it took for them to reach the instruments. The speed of the waves carries information: When the seismic waves hit hot rock, they go slower; when they pass through cold rock, they’re faster.
By combining the data from many sensors, scientists can get a picture of the hot and cold rock beneath Yellowstone. This is known as “seismic tomography.”
This is a volcano that can erupt either in a big way or a truly colossal and catastrophic way. The big eruptions can send lava flowing over a big portion of the park; the really huge ones can form a giant crater, or caldera.
The last time Yellowstone had a calderic eruption was 640,000 years ago, and the misshapen hole it created was about 25 miles by 37 miles across. The Associated Press contributed to this report.
