Yellowstone National Park lies on top of a magma chamber that is 35-miles wide, waiting to erupt.
The Yellowstone Caldera is the volcanic caldera and supervolcano located in Yellowstone National Park in the United States, sometimes referred to as the Yellowstone Supervolcano. The caldera is located in the northwest corner of Wyoming, in which the vast majority of the park is contained. The major features of the caldera measure about 34 by 45 miles (55 by 72 km). The caldera formed during the last of three supereruptions over the past 2.1 million years. First came the Huckleberry Ridge eruption 2.1 million years ago, which created the Island Park Caldera and the Huckleberry Ridge Tuff. Next came the Mesa Falls eruption 1.3 million years ago, which created the Henry's Fork Caldera and the Mesa Falls Tuff. Finally came the Lava Creek eruption 640,000 years ago, which created the Yellowstone Caldera and the Lava Creek Tuff.
The last full-scale eruption of the Yellowstone Supervolcano, the Lava Creek eruption which happened nearly 640,000 years ago, ejected approximately 240 cubic miles (1,000 km3) of rock, dust and volcanic ash into the sky.
Geologists are closely monitoring the rise and fall of the Yellowstone Plateau, which measures on average 0.6 inches (1.5 cm) yearly, as an indication of changes in magma chamber pressure.
The upward movement of the Yellowstone caldera floor between 2004 and 2008 — almost 3 inches (7.6 cm) each year — was more than three times greater than ever observed since such measurements began in 1923. From mid-summer 2004 through mid-summer 2008, the land surface within the caldera moved upward as much as 8 inches (20 cm) at the White Lake GPS station. By the end of 2009, the uplift had slowed significantly and appeared to have stopped. In January 2010, the USGS stated that "uplift of the Yellowstone Caldera has slowed significantly" and that uplift continues but at a slower pace. The U.S. Geological Survey, University of Utah and National Park Service scientists with the Yellowstone Volcano Observatory maintain that they "see no evidence that another such cataclysmic eruption will occur at Yellowstone in the foreseeable future. Recurrence intervals of these events are neither regular nor predictable." This conclusion was reiterated in December 2013 in the aftermath of the publication of a study by University of Utah scientists finding that the "size of the magma body beneath Yellowstone is significantly larger than had been thought." The Yellowstone Volcano Observatory issued a statement on its website stating,
" Although fascinating, the new findings do not imply increased geologic hazards at Yellowstone, and certainly do not increase the chances of a 'supereruption' in the near future. Contrary to some media reports, Yellowstone is not 'overdue' for a supereruption. "