- Yellowstone National Park
- United States ()
According to UNESCO, Yellowstone National Park, which lies mostly within the borders of Wyoming, USA, contains more than 10,000 geothermal features - more than half of the world's known examples. The park's extensive, intact ecosystem is home to thousands of hot springs, mudpots and fumeroles, and boasts at least 300 geysers - two-thirds of the planet's total - with up to 250 of those active. Geysers are hot springs of boiling water that erupt periodically into the air as the underground steam expands up to 1,500 times its normal volume. Yellowstone was opened in 1872 and covers 9,000 km2 (3,475 miles2) of the American west. It occupies Wyoming (97%), Montana (2%) and Idaho (1%).