Yellowstone supervolcano contains more magma, new study finds

Volcanologists identify magma deposits by tracking earthquakes. Seismic waves plunge through the bowels of the Earth before being detected by surface seismometers. They move more slowly through hot, partially molten rock, and scientists use their travel times to interpret how the molten parts of the subsurface are doing.

But this traditional seismic imaging technique is imperfect. Seismic waves sometimes bend around molten pockets. This method also assumes that seismic waves travel in a simplified manner, from the earthquake directly to the seismometer; in reality, seismic waves emanate in all directions and critical information about the Earth’s belly is lost.

For the new study, the authors turned to a 20-year recording of Yellowstone’s background seismic noise, generated by waves from the distant ocean, wind and human activity, to focus on the melting of the volcano They dispelled traditional seismic simplifications and used supercomputers to represent the travel of seismic waves more accurately.

The team found that the seismic waves slowed to a crawl when they traveled from 2 miles to 5 miles down, which corresponds to the upper segment where Yellowstone Volcano’s shallowest magma reservoir is believed to be. This suggests that up to 20 percent of this entire deposit is molten.

Fortunately, this is nothing to lose sleep over. A rule of thumb is that reservoirs can’t erupt without being 35 to 50 percent molten, when things are “kind of like a crystal soup,” said Ross Maguire, a seismologist at the University of Illinois at Urbana-Champaign. -Champaign and author of the study. This value, often debated by volcanologists, is likely to vary between volcanoes. Regardless, Yellowstone’s 20 percent is “still well below that critical threshold,” Dr. Maguire said.

For those hoping to uncover the secrets of other volcanoes, this study confirms that this relatively new technique “is a very good way to go,” said Diana Roman, a geophysicist at the Carnegie Institution for Science in Washington, DC, who did not it was involved in the study.

“It’s a bit like getting a new lens on an old camera,” Dr. Poland said. “It’s the same camera, but now you have a finer resolution. You see it more clearly.”