If you told your friends or family that you were going to spend some of your vacation in an active volcano, they might think you were crazy. Yet every year more than three million people do exactly that. Yellowstone National Park is a volcano. Almost everything that is special in Yellowstone is the result of being one of the world’s largest active volcanoes, in fact, a super-volcano. Fortunately, Yellowstone’s current volcanic activity is limited to hot water and earthquakes -- no eruptions, flowing magma, or cataclysmic explosions. Yellowstone did the cataclysmic explosion thing about 640,000 years ago and is resting for a possible encore in some more tens of thousands of years. Yellowstone the volcano is not going to erupt anytime soon.