Yellowstone Supervolcano Erupted Twice 630,000 Years Ago, Plunging Earth Into Volcanic Winter

Yellowstone, favorite site of family vacations, looks so innocent in photographs—but that wasn't the case 630,000 years ago, when it would have been the source of only vacation horror stories.

That's according to a poster being displayed today at the Geological Society of America's annual conference in Seattle by Jim Kennett, a geologist at the University of California Santa Barbara. He is presenting new evidence that he believes suggests the supervolcano lurking below Yellowstone erupted not once but twice.

That's the same supervolcano that sent the internet into a tizzy of panic just last week, so let's just stop for a minute to remember that a supereruption is almost certainly definitely not going to happen any time soon. The U.S. Geological Survey ranks its probability over the next few millennia as "exceedingly low." (And we would have plenty of warning if we happened to draw that very short straw.)

But the research Kennett is presenting sheds light on what happened the last time the Yellowstone supervolcano supererupted. That was the third of three major eruptions that formed what we now know as the caldera. Kennett argues that this eruption was actually two separate eruptions.

Yellowstone's geysers are powered by its volcanic past. Karen Bleier/AFP/Getty Images

Kennett found his new evidence far from the geyser-watching tourists—in fact, the new information comes from the bottom of the ocean off the coast of California, in a location called the Santa Barbara Basin. That's a little pocket of deep water tucked between the coastline and the Channel Islands of Santa Cruz and Santa Rosa.

When the Yellowstone supervolcano experiences a full-fledged eruption, it has consequences at every scale: It remakes the land around the volcano, it spreads ash over a huge swath of the United States, and it affects climate around the world.

That's why Kennett could see two thick layers of ash in that seafloor sediment from off the coast of California. Also trapped in that sediment are the microscopic shells of sea creatures that lived at the time—and that can tell scientists about the sea temperatures their owners experienced.

According to Kennett's analysis, which may still need to be revised as it has yet to be published in a scientific paper or debated by other experts, the two layers of ash line up with two periods of global cooling, suggesting that each eruption triggered a separate "volcanic winter," which could have lasted about 80 years, putting Westeros' unpredictable seasons to shame.