Imma Perfetto
Cosmos science journalist
Seismologists who created their own artificial earthquakes to peer inside the Yellowstone caldera have revealed important hidden features of its reservoir of molten and superheated rocks and gas.
Due to limitations in imaging techniques, researchers haven’t been able to precisely locate the reservoir’s upper boundary, nor get a good understanding of its contents, before.
These characteristics strongly influence the stability of hazardous volcanic systems such as the Yellowstone volcanic field, which spans parts of the US states of Wyoming, Idaho, and Montana. It’s last supereruption, which occured about 630,000 years ago, blanketed much of North America.
The newest insights, published in a study in the journal Nature, reinforces the Yellowstone volcano is in no danger of immediate eruption.
Researchers have long used a network of fixed seismometers at Yellowstone National Park to monitor its frequent earthquakes. Because seismic waves behave differently when they encounter molten rock, they have also been used to image subsurface features such as the magma chamber.
For this study, the team deployed an array of 650 portable detectors at 100-150m intervals along Yellowstone National Park’s roads. And, instead of waiting for earthquakes to happen, they brought in a seismic vibrator to inject low-frequency vibrations into the ground.
“In a sense, we’re causing our own earthquakes, and we record all that data on the seismometers,” says study coauthor Jamie Farrell, professor of geology and geophysics at the University of Utah and chief seismologist for the Yellowstone Volcano Observatory, operated by the US Geological Survey (USGS).
“And since we put so many out, we can get a higher resolution image of the subsurface.”
Their findings indicates that the top of the chamber is 3.8km below the Earth’s surface.
“The depth of 3.8km is important. We know what pressures are going to be and how bubbles are going to come out of the magma,” says Farrell.
“One thing that makes these eruptions so devastating is that if gases are trapped, they become very explosive as they decompress.”
The artificial seismic imaging revealed the uppermost magma chamber is comprised of 86% solid rock, with pore spaces filled with molten rock and volatile gas and liquid comprising the remaining 14%.
“When the magma rises from the deeper crust, volatile materials such as CO2 and H2O exsolve from the melt,” says co-author Fan-Chi Lin, a professor in the Department of Geology & Geophysics.
“Due to their buoyancy, they tend to accumulate at the top of the magma chamber.
“But if there’s a channel, they can escape to the surface.”
The good news is that much of this gas escapes through Yellowstone’s surface geothermal features without accumulating to dangerous levels.
According to Mike Poland, scientist-in-charge of the Yellowstone Volcano Observatory, these recent breakthroughs in seismic imaging are allowing scientists to see into volcanoes in unprecedented ways.
“That helps us understand more about the heat engine that’s powering Yellowstone and about how melt is distributed,” says Poland.
“That can have ramifications for how we perceive the volcanic hazard.”
He adds that the learnings from Yellowstone can be used to better understand volcanoes in other parts of the world that are a lot more active but harder to study, such as Campi Flegrei in Italy or Santorini in Greece.
