Anyone who has visited Yellowstone can agree that it is one of the most breathtakingly beautiful places in the world. It's also a frightening ticking time bomb. The colorful hot springs and majestic geysers are nature's way of saying, "hey, great news, you're standing on a supervolcano." You could fit Tokyo, the world's biggest city, into the Yellowstone caldera. And by the way, a supervolcano isn't just a big volcano — it's a whole other beast, never witnessed by humanity. When Yellowstone blows, it will erupt with about 25,000 times the force of Mount St. Helen's, and may eject enough dust into the atmosphere to threaten the entire world's food supply. Old Faithful? More like Old Fearful!