Yellowstone National Park spans an area over 3,000 square miles comprising lakes, canyons, rivers, and mountain ranges. One of its most interesting features is that the park is centered over the largest supervolcano on the continent. The last huge eruption in Yellowstone was 640,000 years ago and it formed the Yellowstone caldera as we now see it. Recent geothermal activity in the area has caused some alarm. Should we worry?