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What Would Happen If Yellowstone's Supervolcano Erupted?
By Becky Oskin, Contributing Writer | May 2, 2016 07:31am ET

Although fears of a Yellowstone volcanic blast go viral every few years, there are better things to worry about than a catastrophic supereruption exploding from the bowels of Yellowstone National Park.
Scientists at the U.S. Geological Survey's (USGS) Yellowstone Volcano Observatory always pooh-pooh these worrisome memes, but that doesn't mean researchers are ignoring the possible consequences of a supereruption. Along with forecasting the damage, scientists constantly monitor the region for signs of molten rock tunneling underground. Scientists scrutinize past supereruptions, as well as smaller volcanic blasts, to predict what would happen if the Yellowstone Volcano did blow.


Here's a deeper look at whether Yellowstone's volcano would fire up a global catastrophe.

Probing Yellowstone's past
Most of Yellowstone National Park sits inside three overlapping calderas. The shallow, bowl-shaped depressions formed when an underground magma chamber erupted at Yellowstone. Each time, so much material spewed out that the ground collapsed downward, creating a caldera. The massive blasts struck 2.1 million, 1.3 million and 640,000 years ago. These past eruptions serve as clues to understanding what would happen if there was another Yellowstone megaexplosion.

An example of the possible ashfall from a month-long Yellowstone supereruption.
Credit: USGS
If a future supereruption resembles its predecessors, then flowing lava won't be much of a threat. The older Yellowstone lava flows never traveled much farther than the park boundaries, according to the USGS. For volcanologists, the biggest worry is wind-flung ash. Imagine a circle about 500 miles (800 kilometers) across surrounding Yellowstone; studies suggest the region inside this circle might see more than 4 inches (10 centimeters) of ash on the ground, scientists reported Aug. 27, 2014, in the journal Geochemistry, Geophysics, Geosystems.

The ash would be pretty devastating for the United States, scientists predict. The fallout would include short-term destruction of Midwest agriculture, and rivers and streams would be clogged by gray muck.

People living in the Pacific Northwest might also be choking on Yellowstone's fallout.

"People who live upwind from eruptions need to be concerned about the big ones," said Larry Mastin, a USGS volcanologist and lead author of the 2014 ash study. Big eruptions often spawn giant umbrella clouds that push ash upwind across half the continent, Mastin said. These clouds get their name because the broad, flat cloud hovering over the volcano resembles an umbrella. "An umbrella cloud fundamentally changes how ash is distributed," Mastin said.

But California and Florida, which grow most of the country's fruits and vegetables, would see only a dusting of ash.

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A smelly climate shift
Yellowstone Volcano's next supereruption is likely to spew vast quantities of gases such as sulfur dioxide, which forms a sulfur aerosol that absorbs sunlight and reflects some of it back to space. The resulting climate cooling could last up to a decade. The temporary climate shift could alter rainfall patterns, and, along with severe frosts, cause widespread crop losses and famine.

The walls of the Grand Canyon of Yellowstone are made up predominantly of lava and rocks from a supereruption some 500,000 years ago.
The walls of the Grand Canyon of Yellowstone are made up predominantly of lava and rocks from a supereruption some 500,000 years ago.
Credit: USGS
But a Yellowstone megablast would not wipe out life on Earth. There were no extinctions after its last three enormous eruptions, nor have other supereruptions triggered extinctions in the last few million years. [Wipeout: History's 7 Most Mysterious Extinctions]

"Are we all going to die if Yellowstone erupts? Almost certainly the answer is no," said Jamie Farrell, a Yellowstone expert and assistant research professor at the University of Utah. "There have been quite a few supereruptions in the past couple million years, and we're still around."

Amos would see only 5 mm of ash on his roof.