Yellowstone National Park poses a potential global risk due to its supervolcano. 1) Yellowstone sits atop one of the largest supervolcanoes on Earth, which last erupted 640,000 years ago. 2) An eruption could have devastating consequences, ejecting huge amounts of volcanic material into the atmosphere and potentially cooling the climate globally for years. 3) Millions of people living throughout North America would be at risk from the far-reaching effects of ash and gas from an eruption of the Yellowstone supervolcano.