Lurking under Yellowstone National Park is a reservoir of hot magma, reaching five miles deep and fed by a gigantic plume of molten rock welling up from hundreds of miles below. The powerful heat is responsible for many of the park’s famous geysers and hot springs, but it also holds the potential for disaster. On rare occasions throughout history, the magma chamber has erupted—and though most of those have been smaller lava flows, there is a continuous threat of “super eruptions.”
Super-eruptions measure at least a magnitude 8 on the Volcano Explosivity Index and have at least 1,000 cubic kilometers of material ejected. Super-eruptions are thousands of times more powerful than the biggest eruptions we could ever imagine. If one ever occurred at Yellowstone National Park, it could spew ash for thousands of miles across the United States—damaging buildings, destroying groups, and disrupting power.
Fortunately, the chances of another super-eruption in the area are very low. The Yellowstone supervolcano has only had three enormous eruptions in history; one occurred 2.1 million years ago, one 1.3 million years ago, and one 664,000 years ago. At present, there is no indication that we’re due for another “super-eruption” anytime soon.
Still, the potential is a source of ‘apocalyptic fascination.’ Years ago, a team of scientists published a paper of what a super-eruption at Yellowstone might actually look like. States like Wyoming, Montana, Idaho, and Colorado could be buried in harsh volcanic ash. Meanwhile, the Midwest would also get a few inches of ash. But Jacob Lowenstern of the US Geological Survey points out the paper is not necessarily a prediction of the future.
“Even if Yellowstone did erupt again, you probably wouldn’t get that worst-case scenario,” he says. “What’s much, much more common are small eruptions—that’s a point that often gets ignored in the press.”
The most likely eruption scenario in Yellowstone is a smaller event that produces lava flows and a typical volcanic explosion. But in the event of a super-eruption, things would be much more intense. The warning signs would be bigger too.
“We’d likely first see intense seismic activity across the entire park,” Lowenstern says.
The main damage from this type of explosion would come from volcanic ask, that would be scattered across the country. It would also create an umbrella cloud, expanding in all directions. That much volcanic ash is capable of killing people, plants, and animals. It could even crush buildings, clog roadways, and destroy farms.
The climate would take a major hit too. Volcanoes can emit sulfur aerosols that reflect sunlight back into the atmosphere and cool the planet. When Pinatubo erupted in 1991, it cooled the planet by 1°C for a few years.