The 3rd and most recent supervolcano eruption to occur within the present-day park boundary happened about 640,000 years ago. The resulting caldera, which is outlined on the official park map and our Interactive Map, is visible from the road near the Madison Junction. The caldera rim is expressed as a ridge that parallels the river to the south. This supervolcano eruption was unlike anything recorded in modern human history. Think of cataclysmic destruction; the stuff sci-fi movies are made of. Ash from this eruption would spread across the earth and alter global weather patterns. And, of course, all nearby life would have been destroyed. However, we caution visitors to Yellowstone not to get caught up in any sensationalist media reports about the threat of another eruption. There are no signs of an imminent eruption, notwithstanding Yellowstone’s many earthquakes. An eruption of this size would likely be proceeded by many unique warning signs.