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Chráněná území Aljašky

24.01.2010
Geologie
Chráněná území Aljašky

Wrangell-St. Elias National Park

Wrangell-St. Elias and its adjacent park in the Yukon Territory of Canada is the world's largest parkland, in fact, it is larger than the combined area of all national parks in the other 49 states combined! It contains three different mountain ranges, the St. Elias Mountains and Chugach Mountains which are composed of dominantly metamorphic and sedimentary rocks and the Wrangell Mountains which consist of andesitic volcanic rock. The St. Elias Mountains are the world´s highest coastal mountain range with the Yukon's Mt. Logan at19,850 feet (second highest mountain in North America) and St. Elias Mountain at 18,008 feet. The height of these mountains and their proximity to the coast where rainfall is very high allows them to maintain the largest assemblage of glaciers in North America.
The geologic history of this park is as follows:
  1. The rocks of the 5 major exotic terranes that make up Wrangell-St. Elias National Park were formed at different distant locations south of Alaska.
  2. Accretion of these microplates began in early Cenozoic time. Associated with microplate collision was volcanic activity, metamorphism, faulting, folding and uplift of rock units into the present mountains.
  3. The last microplate, the Yakutat terrane is still in the process of accreting to North America and the force of this ongoing collision is responsible for many large earthquakes in this region and for continued uplift of the mountains.
  4. Recent andesitic volcanism in the Wrangell range is due to ongoing subduction of the Pacific Plate beneath N.America
Denali National Park
Denali shares a similar geologic history to Wrangell-St. Elias National Park. It too consists of several exotic terranes, many are the same as seen in Wrangell-St. Elias, that accreted to North America in early Cenozoic time. The Alaskan Range which comprises much of Denali and which contains Mt. McKinley at over 20,000 feet, is primarily granitic and represents a batholith that was intruded into the various terranes during their collisions with North America. The uplift of this batholith resulted from continued collision and the high altitude of Mt. McKinley is due to its unique position at the boundary between the Pacific and North American plates where subduction and strike-slip motion are both occurring and pushing Mt. McKinley up. As in Wrangell-St. Elias, continued tectonic motions generate abundant earthquakes in this area. Of course much of the scenery in Denali is presently being shaped by a number of active glaciers.

ZDROJ:http://geology.about.com, kráceno

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