It's one of the America's mosts majestic natural wonders, but deep beneath Yellowstone National Park lies a volcano more powerful than any average volcano. Now, one scientist from Arizona State University is questioning when it will go from quiet, to the edge of an eruption.
It's over 600,000 years since the last super-eruption at the Yellowstone National Park, but scientists suspect that an eruption of that magnitude scars the planet every 100,000 years.
Christy Till, a geologist at ASU, studies Yellowstone's past, in hopes of spotting future super-eruptions in the making.
However, what exactly is a supervolvano?
"It is any eruption that produces more than 1,000 cubic kilometers of erupted material," said Till.
That amount of material could cover most of the United States in a thick layer of ash.
Till said other than a natural accumulation of magma, an earthquake may be the only thing to produce an eruption of this size. Till said, however, the chance of getting touched by an eruption in Phoenix are very small, and scientists say the odds of Yellowstone -- or any other supervolcano erupting anytime soon -- are very small.