Established in 1872 by Presidential decree, Yellowstone National Park became not only the first National Park in the United States, but also the first in the world. Occupying a 63 by 54 mile (101 by 87 km) box of the northwestern most corner of the state of Wyoming, it has since been declared by the United Nations as both a World Biosphere Reserve and World Heritage Site. It is one of the most geothermally active places on earth. A systematic geological survey of the area that began in the 1960s has confirmed the presence of several Yellowstone volcanoes which collectively constitute one massive "supervolcano."
There are in excess of 10,000 geothermal features within the park — more than the rest of the planet combined. The geysers of Yellowstone alone, numbering more than 300, represent 60% of the world's known spouts of superheated water. The most famous of these is the cone geyser named "Old Faithful" that sprays thousands of gallons (1,000 gallons = 3,785 liters) of boiling water and gases 130 feet (40 m) into the sky every 92 minutes from a low earthen mound topped by a nozzle.
Geysers, boiling hot springs, gas-spewing fumaroles and other features are created by fractures in the earth's crust around the edges of the Yellowstone volcanoes. Molten rock from deep beneath the earth pushes up the center of the volcano, bulging the land into a dome. From this pressure and the dome's distension of the land, fractures and vents develop around the margins. Despite some of their apparent violence, Yellowstone's features are releasing miniscule amounts of energy in relation to what is increasingly building below the park.
Geologists have identified two major Yellowstone volcanoes. One is near Old Faithful, and the other lies just north of Yellowstone Lake. Survey measurements at the latter site show that the land rose nearly 3 feet (0.9 m) from 1923 to 1985. From 2004 to 2008, scientists became alarmed by an 8 inch (20 cm) uplift, but the rate subsequently subsided.
Some scientists are not so much concerned with a central dome's collapse and a catastrophic eruption of one of the Yellowstone volcanoes. Lesser volcanic events are still devastating on the human scale, however. Studies have identified over 20 large craters that have been produced in the past 14,000 years, some as a result not of volcanic but rather explosive geothermal activity. Some areas of the park reveal geological evidence of repeated lava flows, though the most recent of these was 70,000 years ago.
Approximately 2.1 million years ago, the entire Yellowstone area exploded as possibly the largest volcano eruption ever in earth's history. The supervolcano was an estimated 2,400 times larger than the 1980 eruption of Washington state's Mt. St. Helens. It has happened twice again since, in an interval of 600,000 to 800,000 years. The last occurrence was 640,000 years ago. If nature holds to this timetable, the so-called Yellowstone caldera, a collapsed oval crater measuring 47 by 28 miles (76 by 45 km), is due for another cataclysmic eruption.