<P> The Yellowstone Caldera is a volcanic caldera and supervolcano in Yellowstone National Park in the Western United States, sometimes referred to as the Yellowstone Supervolcano . The caldera and most of the park are located in the northwest corner of Wyoming . The major features of the caldera measure about 34 by 45 miles (55 by 72 km). </P> <P> The caldera formed during the last of three supereruptions over the past 2.1 million years: the Huckleberry Ridge eruption 2.1 million years ago (which created the Island Park Caldera and the Huckleberry Ridge Tuff); the Mesa Falls eruption 1.3 million years ago (which created the Henry's Fork Caldera and the Mesa Falls Tuff); and the Lava Creek eruption approximately 630,000 years ago (which created the Yellowstone Caldera and the Lava Creek Tuff). </P> <P> Volcanism at Yellowstone is relatively recent, with calderas that were created during large eruptions that took place 2.1 million, 1.3 million, and 630,000 years ago . The calderas lie over a hotspot where light, hot, magma (molten rock) from the mantle rises toward the surface . While the Yellowstone hotspot is now under the Yellowstone Plateau, it did help to create the eastern Snake River Plain (to the west of Yellowstone) through a series of huge volcanic eruptions . The hotspot appears to move across terrain in the east - northeast direction, but in fact the hotspot is much deeper than terrain and remains stationary while the North American Plate moves west - southwest over it . </P> <P> Over the past 18 million years or so, this hotspot has generated a succession of violent eruptions and less violent floods of basaltic lava . Together these eruptions have helped create the eastern part of the Snake River Plain from a once - mountainous region . At least a dozen of these eruptions were so massive that they are classified as supereruptions . Volcanic eruptions sometimes empty their stores of magma so swiftly that the overlying land collapses into the emptied magma chamber, forming a geographic depression called a caldera . </P>

How do geologists know what occurred during yellowstone’s past eruptions