The Yellowstone caldera is a supervolcano which spans beneath the US states of Wyoming, Montana and Idaho, and gets its chilling nickname due to its ability to inflict devastation on a global scale if it erupts. It is constantly monitored by the United States Geological Survey (USGS) for signs that a supereruption is on its way, something that has only happened three times in history, 2.1 million years ago, 1.3 million years ago and 640,000 years ago. In a video on YouTube last week, Scientist-in-Charge of the Yellowstone Volcano Observatory – Mike Poland – gave an update on activity during March.