The Yellowstone Caldera (a collapse is triggered by the emptying of the magma chamber below the volcano) is the largest volcanic system in North America. It has been termed a “supervolcano” because the caldera was formed by exceptionally large explosive eruptions.
The most violent known eruption occurred 2.1 million years ago. A smaller eruption happened 1.3 million years ago. The current caldera was created by an eruption that occurred 640,000 years ago. Each of the three climactic eruptions released vast amounts of ash that blanketed much of central North America, falling many hundreds of miles away.
Since the last supereruption, a series of smaller eruptive cycles between 640,000 and 70,000 years ago has nearly filled in the Yellowstone Caldera with 80 different eruptions. Layered lavas were formed with each eruption. The volcanic activity is much alive as manifested by the hotspots below the Crust of the Earth.