Have you seen this video of bison running out of Yellowstone? If you haven’t, here’s a version with dramatic music.
It’s no secret that Yellowstone National Park sits atop a “supervolcano.” But now, accounts of animals supposedly fleeing the park before an earthquake last Sunday have sparked fear that one of the world’s biggest supervolcanoes is about to produce an apocalyptic eruption.
That is very likely not going to happen. And if you don’t believe me, here’s Al Nash, chief of public affairs for Yellowstone: “We have seen no signs to suggest the Yellowstone volcano is about to erupt.” No signs of imminent eruption.
In his “Rumor Control” video, Nash explains the natural geological system of the park, which has between 1,000 and 3,000 earthquakes a year. “Frankly, we are just a few miles above some really hot magma,” he says. That magma serves as the heat that fuels the geysers, hot springs, and fumaroles in the park -- you know, the iconic things that attract three million visits a year.
This past Sunday, a magnitude 4.8 event -- later updated to 4.7 -- occurred at 6:34 am local time about four miles north of Norris Geyser Basin in Wyoming, according to the U.S. Geological Survey. It was most likely a strike-slip motion and may not even be linked to any volcanic processes. To be fair, it was the biggest earthquake in Yellowstone since the early 1980, though there are no reports of injuries or damage.
Precursors to volcanic eruptions do, in fact, include strong earthquakes that typically take place days to weeks before an actual eruption. The Yellowstone Volcano Observatory (YVO) -- a partnership between the USGS, Yellowstone NP, and the University of Utah -- closely monitors volcanic activity at the park. We’re talking about real-time data for everything, from ground deformation to stream temperatures. And on their site right now, the current volcano alert level is “normal.” The March 30 event was part of an earthquake series that began on March 27 and continues into April, according to the YVO update released this week. By the end of March, the series already consisted of about a hundred earthquakes, at least four of which were magnitude 3.
“Yellowstone never stops shaking,” geophysicist Robert Smith of University of Utah tells Science. Sunday’s quake was centered in a region where instruments have measured the landscape rising and falling for several months already. And it’s normal: A previous period of “uplift” in the same area between 1996 and 2003 was also accompanied by increased seismic activity.
So why fleeing bison? Yellowstone tweeted this earlier today, channeling House Stark: “The real reason animals leave the park? Winter.” Mammals tend to migrate to lower elevations outside of the park where food resources are likely to be more abundant. When the snow melts, "those very same animals will walk right back to the park,” Nash adds. Oh and also, the video of running bison was filmed weeks (at least) before Sunday’s earthquake.
But that’s not to say a cataclysmic eruption can’t happen. The Yellowstone region has produce three exceedingly large volcanic eruptions in the past 2.1 million years. Enormous volumes of magma erupted at the surface and into the atmosphere as mixtures of pumice, volcanic ash, and gas spread as pyroclastic flows in all directions, a USGS report describes. The ground collapsed, creating the broad, cauldron-shaped volcanic depressions called calderas. The last time this happened was 640,000 years ago, and since then, about 80 (far less devastating) eruptions of lava have occurred.
If another explosive, caldera-forming eruption were to occur at Yellowstone, thick ash would bury vast areas of the U.S., and the injection of volcanic gases into the atmosphere could affect global climate. But again, the probability of a large caldera-forming eruption within the next few thousand years is exceedingly low.
Images: Bison jam on the road by Neal Herbert (top), bison walking through deep snow by Jim Peaco (middle) / Yellowstone National Park Flickr