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Sunday, May 13, 2012

USA : Yellowstone National Park (1978)


The vast natural forest of Yellowstone National Park covers nearly 9,000 km2 ; 96% of the park lies in Wyoming, 3% in Montana and 1% in Idaho. Yellowstone contains half of all the world's known geothermal features, with more than 10,000 examples. It also has the world's largest concentration of geysers (more than 300 geyers, or two thirds of all those on the planet). Established in 1872, Yellowstone is equally known for its wildlife, such as grizzly bears, wolves, bison and wapitis.

 
Yellowstone National Park, established in 1872, covers 9,000 km2 of a vast natural forest of the southern Rocky Mountains in the North American west. It boasts an impressive array of geothermal phenomena, with more than 3,000 geysers, lava formations, fumaroles, hot springs and waterfalls, lakes and canyons. It is equally known for its wildlife: grizzly bears, bison, wolves and wapiti, North American elk.
The park is part of the most seismically active region of the Rocky Mountains, a volcanic 'hot spot'. The Yellowstone Plateau, now a forested area of 650,000 ha with an average elevation of 2,000 m, was formed out of the accumulation of rhyolite magma. The plateau is flanked on the north, east and south by mountains that rise to 4,000 m. Crustal uplifts 65 million years ago raised blocks of crust to form the southern Rocky Mountains. After that, volcanic outflows of andesitic composition were common to about 40 million years ago. Andesitic ashflows and mudflows of the Eocene age covered forests, which became petrified. Some 200 species of petrified plant have been found. A more recent period of rhyolitic volcanism began in the region about 2 million years ago, during which time thousands of cubic kilometres of rhyolitic magma filled immense chambers under the plateau and then erupted to the surface. Three cycles of eruption produced huge explosive outbursts of ash. The latest eruptive cycle formed a caldera 45 km wide and 75 km long, when the active magma chambers erupted and collapsed. The crystallizing magma is the source of heat for hydrothermal features such as geysers, hot springs, mud pots and fumaroles.
Yellowstone contains 200-250 active geysers and perhaps 10,000 thermal features. Most of the area was glaciated during the Pleistocene and many glacial features remain. The park lies at the headwaters of three major rivers. Yellowstone River is a major tributary of the Missouri River that flows via the Mississippi to the Gulf of Mexico. Firehole and Gibbon rivers unite to form the Madison, which also joins the Missouri. Snake River arises near the park's south boundary and joins the Columbia to flow into the Pacific. Yellowstone Lake is the largest lake at high elevation (2,357 m) in North America. Lower Yellowstone Falls is the highest of more than 40 named waterfalls in the park.
The park is dominated by lodgepole pine. Great elevational differences produce a range of plant communities, from semi-arid steppe to alpine tundra. There are seven species of coniferous tree and some 1,100 species of vascular plant growing in the park, including an endemic grass. The thermal areas contain unique assemblages of thermal algae and bacteria.
Six species of ungulate are native to the park. Grizzly bear has been the subject of intensive study and management for 30 years. There are currently some 50 breeding females and 150 cubs have been born in the last three years. Native fishes are protected by regulations that also permit the taking of non-native introduced species.
Palaeontological study of Lamar Cave has yielded remains of over 30 species of mammal. This suggests a diversity of fauna in prehistoric times much like that found in Yellowstone today.
Archaeological investigations of numerous important sites show that human groups visited the park area for 10,000 years, but none made it a permanent home.

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