Monday, August 20, 2007


A plateau is a large highland area of fairly level land separated from surrounding land by steep slopes. Some plateaus, like the plateau of Tibet, lie between mountain ranges. Others are higher than surrounding land. Plateaus are widespread, and together with enclosed basins they cover about 45 percent of the Earth's land surface. Some plateaus, such as the Deccan of India and the Columbia Plateau of the United States, are basaltic and were formed as the result of many lava flows covering hundreds of thousands of square kilometers that built up the land surface. Others are the result of upward folding; still others have been left elevated by the erosion of nearby lands. Plateaus, like all elevated regions, are subject to erosion, which removes great amounts of the upland surface. Low plateaus are often farming regions, while high plateaus are usually suitable for livestock grazing. Many of the world's high plateaus are deserts. Other plateaus are the Colorado Plateau of the United States, the Bolivian plateau in South America, and the plateaus of Anatolia, Arabia, Iran, and the Tibet region of China and the Canadian Shield or Laurentian Plateau, a U-shaped region of ancient rock, the nucleus of North America, stretching north from the Great Lakes to the Arctic Ocean. Covering more than half of Canada, it also includes most of Greenland and extends into the United States as the Adirondack Mountains and the Superior Highlands. The first part of North America to be elevated above sea level, it has stayed almost wholly untouched by many encroachments of the sea upon the continent.

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