148 USA - Mammoth Hot Springs in Yellowstone National Park (UNESCO)

Mammoth Hot Springs is a large complex of hot springs on a hill of travertine in Yellowstone National Park adjacent to Fort Yellowstone and the Mammoth Hot Springs Historic District. It was created over thousands of years as hot water from the spring cooled and deposited calcium carbonate (over two tons flow into Mammoth each day in a solution). Although these springs lie outside the caldera boundary, their energy has been attributed to the same magmatic system that fuels other Yellowstone geothermal areas. The hot water that feeds Mammoth comes from Norris Geyser Basin after traveling underground via a fault line that runs through limestone and roughly parallel to the Norris-to-Mammoth road. The limestone from rock formations along the fault is the source of the calcium carbonate. Shallow circulation along this corridor allows Norris' superheated water to slightly cool before surfacing at Mammoth, generally at about 170 °F (80 °C). Algae living in the warm pools have tinted the travertine shades of brown, orange, red, and green. 

Thermal activity here is extensive both over time and distance. The thermal flows show much variability with some variations taking place over periods ranging from decades to days. Terrace Mountain at Mammoth Hot Springs is the largest known carbonate-depositing spring in the world. The most famous feature at the springs is the Minerva Terrace, a series of travertine terraces. The terraces have been deposited by the spring over many years but, due to recent minor earthquake activity, the spring vent has shifted, rendering the terraces dry. The Mammoth Terraces extend all the way from the hillside, across the Parade Ground, and down to Boiling River. The Mammoth Hotel, as well as all of Fort Yellowstone, is built upon an old terrace formation known as Hotel Terrace. There was some concern when construction began in 1891 on the fort site that the hollow ground would not support the weight of the buildings. Several large sink holes (fenced off) can be seen out on the Parade Ground. This area has been thermally active for several thousand years. The Mammoth area exhibits much evidence of glacial activity from the Pinedale Glaciation. The summit of Terrace Mountain is covered with glacial till, thereby dating the travertine formation there to earlier than the end of the Pinedale Glaciation. Several thermal kames, including Capitol Hill and Dude Hill, are major features of the Mammoth Village area. Ice-marginal stream beds are in evidence in the small, narrow valleys where Floating Island Lake and Phantom Lake are found. In Gardner Canyon one can see the old, sorted gravel bed of the Gardner River covered by unsorted glacial till.

061 USA - Yellowstone National Park (WHS)

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.

About the sender

When I've been an exchange student, I've been to Yellowstone two times and when I came back, I have been another third time. I bought this postcard while I have been in this amazing National Park, definitly a place to visit. I have some postcards left from Yellowstone, check the swap folder.