The USA physical geography

The contiguous United States may be divided into seven broad physiographic divisions: from east to west, the Atlantic–Gulf Coastal Plain; the Appalachian Highlands; the Interior Plains; the Interior Highlands; the Rocky Mountain System; the Intermontane Region; and the Pacific Mountain System. An eighth division, the Laurentian Uplands, a part of the Canadian Shield, dips into the United States from Canada in the Great Lakes region. It is an area of little local relief, with an irregular drainage system and many lakes, as well as some of the oldest exposed rocks in the United States.

The Atlantic–Gulf Coastal Plain begins at Cape Cod and Long Island (moraines and outwash plains) and contains southeastern Atlantic and Gulf continental shelf – includes all of Florida and Louisiana. It is low and flat.

The Appalachian Highlands sweeping from Newfoundland to Alabama dominate the landscape of the Eastern seaboard. Their peaks, ridges, hills, and valleys form a belt almost 3,200 kilometers long and up to 580 kilometers wide.

The Interior Plains may be divided into two sections: the fertile central lowlands, the agricultural heartland of the United States; and the Great Plains, a treeless plateau that gently rises from the central lowlands to the foothills of the Rocky Mountains.

The Interior Highlands are located just West of the Mississippi River between the Interior Plains and the Gulf Coastal Plain. This region consists of the rolling Ozark Plateau to the north and the Ouachita Mountains, which are similar in structure to the ridge and valley section of the Appalachians, to the east.

The Rocky Mountain System is a geologically young and complex system that extends into northwest United States from Canada and runs south into New Mexico. There are numerous high peaks in the Rockies; the highest is Mountain Elbert (4,399 m). The Rocky Mountains are divided into four sections – the Northern Rockies, the Middle Rockies, the Wyoming (Great Divide) Basin, and the Southern Rockies. Along the crest of the Rockies is the Continental Divide, separating Atlantic-bound drainage from that heading for the Pacific Ocean.

The Intermontane Region is between the Rocky Mountains and the ranges to the west. It is an arid expanse of plateaus, basins, and ranges. The Columbia Plateau, in the north of the region, was formed by volcanic lava and is drained by the Columbia River and its tributary the Snake River, both of which have cut deep canyons into the plateau. The enormous Colorado Plateau, an area of sedimentary rock, is drained by the Colorado River and its tributaries; there the Colorado River has entrenched itself to form the Grand Canyon, one of the world’s most impressive scenic wonders. West of the plateaus is the Basin and Range province, an area of extensive semidesert.

the Grand Canyon

The Pacific Mountain System is between the Intermontane Region and the Pacific Ocean. It is a series of ranges generally paralleling the coast, formed by faulting and volcanism. The Cascade Range, with its numerous volcanic peaks extends south from southwest Canada into northern California, and from there is continued south by the Sierra Nevada, a great fault block. Mountain Whitney (4,418 m), in the Sierra Nevada, is the highest peak in the contiguous United States.

Alaska contains some of the most dramatic and untapped scenery in the country. Tall, prominent mountain ranges rise up sharply from broad, flat tundra plains. On the islands off the south and southwest coast are many volcanoes. Hawaii, far to the south of Alaska in the Pacific Ocean, is a chain of tropical, volcanic islands, popular as a tourist destination for many from East Asia and the mainland United States.

Date: 2015-01-02; view: 1493