Yellowstone caldera complex, sometimes called the Yellowstone supervolcano, is a large volcanic area that lies underneath Yellowstone National Park in northwest Wyoming . An eruption has not occurred there since prehistoric times. But evidence suggests that Yellowstone’s past eruptions have been among the most powerful on Earth. These eruptions covered much of western North America in several feet or meters of ash. Ash and debris from Yellowstone’s eruptions also entered Earth’s atmosphere, changing the climate for years after each eruption.
Scientists measure the strength of volcanic eruptions by using a scale called the Volcanic Explosivity Index (VEI). Eruptions are assigned numbers from 0, for the weakest ones, to 8, for the strongest. Eruptions at Yellowstone have reached a VEI of 8. To reach this magnitude, a volcano must eject more than 240 cubic miles (1,000 cubic kilometers) of material. An erupting volcano ejects magma (molten rock), which lies underground in an area called the magma chamber. Following an eruption, the ground above may collapse into the empty chamber, forming a crater called a caldera.
The Yellowstone caldera complex consists of three overlapping calderas that formed during three enormous eruptions. The first eruption occurred about 2.1 million years ago. It was one of the largest eruptions ever discovered, about 2,500 times more powerful than the eruption of Mount Saint Helens on May 18, 1980. The Yellowstone eruption spewed about 600 cubic miles (2,500 cubic kilometers) of ash and other debris into the atmosphere.
Yellowstone’s second eruption, 1.3 million years ago, was significantly less powerful. Its third eruption, 640,000 years ago, left beds of ash that were 660 feet (200 meters) thick. This massive eruption formed the most recent caldera. The caldera measures about 47 miles (76 kilometers) long and 28 miles (45 kilometers) wide and is one of the largest on Earth.
Yellowstone has undergone about 80 nonexplosive eruptions in the last 640,000 years. The most recent eruption occurred 70,000 years ago. Scientists monitor Yellowstone closely for signs of volcanic activity. Another major eruption is considered extremely unlikely, although smaller eruptions may occur.
Yellowstone’s volcanic activity is fueled by a hot spot , an underground upwelling of hot rock in Earth’s mantle that causes magma to form. The mantle is the layer of hot, soft rock between Earth’s crust and its core. Yellowstone’s hotspot has been active for about 16 million years. Heat from the magma beneath the volcano powers Yellowstone National Park’s many geysers and hot springs .
