The Yellowstone Caldera 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 magma chamber that lies under Yellowstone is estimated to be a single connected chamber , about long , wide , and 3 to 7 miles ( 5 to 12 km ) deep . The current caldera was created by a cataclysmic eruption that occurred 640,000 years ago , which released more than 240 cubic miles ( 1,000 km ³ ) of ash , rock and pyroclastic materials . This eruption was more than 1,000 times larger than the 1980 eruption of Mount St. Helens . It produced a caldera nearly five eighths of a mile ( 1 km ) deep and in area and deposited the Lava Creek Tuff , a welded tuff geologic formation . The most violent known eruption , which occurred 2.1 million years ago , ejected 588 cubic miles ( 2,450 km ³ ) of volcanic material and created the rock formation known as the Huckleberry Ridge Tuff and created the Island Park Caldera . A smaller eruption ejected 67 cubic miles ( 280 km ³ ) of material 1.3 million years ago , forming the Henry 's Fork Caldera and depositing the Mesa Falls Tuff
1980 eruption of Mount St. Helens
1980 eruption of Mount St. Helens
Yellowstone National Park