Yellowstone National Park is a United States National Park and a UNESCO World Heritage Site. It was the world’s first national park, set aside in 1872 to preserve the vast number of geysers, hot springs, and other thermal areas, as well as to protect the incredible wildlife and rugged beauty of the area. The park contains 3,472 square miles (8,990 square kilometres), mostly within the northwest corner of Wyoming, but with portions extending into the states of Idaho and Montana.
Long before any recorded human history in Yellowstone, a massive volcanic eruption spewed an immense volume of ash that covered all of the western U.S., much of the Midwest, northern Mexico and some areas of the eastern Pacific Coast. The eruption may have been as much as one thousand times more powerful than the 1980 eruption of Mt. St. Helens, and it left a caldera approximately 34 by 45 miles (55 by 72 km). The Yellowstone super volcano is believed to erupt every 600,000 to 900,000 years with the last event occurring 640,000 years ago. Its eruptions are among the largest known to have ever occurred on Earth, producing drastic climate change in the aftermath. Although it is commonly assumed that the park was named for the yellow rocks seen in the Grand Canyon of the Yellowstone, the park’s name comes from the Yellowstone River that flows through it, which is in turn named after sandstone bluffs found farther down its course in eastern Montana.
On March 1, 1872, Yellowstone became the first National Park reserve declared anywhere in the world, by President Ulysses S. Grant. In 1978 it was designated a World Heritage Site.
See volcanoes for background; Yellowstone is classed as a super volcano and its last eruption is thought to have been a VE-8 event with over 1000 km3 of ejecta.
With half of the earth’s geothermal features, Yellowstone holds the planet’s most diverse and intact collection of geysers, hot springs, mudpots, and fumaroles. Its more than 300 geysers make up two thirds of all those found on earth. Combine this with more than 10,000 thermal features comprised of brilliantly colored hot springs, bubbling mudpots, and steaming fumaroles, and you have a place like no other.
Yellowstone’s hydrothermal features would not exist without the underlying magma body that releases tremendous heat. They also depend on sources of water, such as from the mountains surrounding the Yellowstone Plateau. There, snow and rain slowly percolate through layers of permeable rock riddled with cracks. Some of this cold water meets hot brine directly heated by the shallow magma body. The water’s temperature rises well above the boiling point but the water remains in a liquid state due to the great pressure and weight of the overlying water. The result is superheated water with temperatures exceeding 400 °F (200 °C).
The superheated water is less dense than the colder, heavier water sinking around it. This creates convection currents that allow the lighter, more buoyant, superheated water to begin its journey back to the surface following the cracks and weak areas through rhyolitic lava flows. This upward path is the natural “plumbing” system of the park’s hydrothermal features. Once it reaches the surface, the various colors of the pools are due to different types of bacteria growing in different temperatures.