The source of heat that powers the volcanic system of Yellowstone National Park in the western US dates back to at least 50 million years ago, scientists say. Known as Yellowstone hotspot, this vast volcanic system has long been thought to have initiated about 17 million years ago. It's responsible for Yellowstone National Park's famous volcanic activity that draws swarms of tourists from around the world. This includes one of the park's most famous geothermal features, the Old Faithful geyser, which spews jets of boiling water every 44-125 minutes, as well as the Yellowstone Caldera, a dormant 'supervolcano'. 'A growing volume of geological evidence', however, suggests Yellowstone hotspot has been around much longer – at least 50 million years and maybe even earlier, US experts now reveal.