For over a century, tens of millions of visitors have marveled at the natural beauty of Yellowstone National Park, home to the largest concentration of geysers in the world, including the iconic Old Faithful. Visitors may not realize it, but Yellowstone is situated directly above one of the largest volcanic systems on Earth-a supervolcano. For the past two million years, this volcano has erupted roughly every 600,000 years. The last major eruption, which produced a caldera that stretches over 1,500 square miles across the park-two-thirds the size of Prince Edward Island-occurred 640,000 years ago. So, is it overdue for another eruption?