Plateau, elevated, level or nearly level portion of the earth's surface, larger in summit area than a mountain and bounded on at least one side by steep slopes, occurring on land or in oceans. Some plateaus, such as the Deccan of India and the Columbia Plateau of the NW United States, are basaltic and were formed as the result of a succession of lava flows covering hundreds of thousands of square miles that built up the land surface. Others are the result of upward folding; still others have been left elevated by the erosion of adjacent lands. Plateaus, like all elevated regions, are subject to dissection by erosion, which removes greater amounts of the upland surface. Low plateaus are often agricultural regions, while high plateaus are usually fit chiefly for stock grazing. Many of the world's high plateaus are deserts. Other notable plateaus are the Colorado Plateau of the W United States, the Bolivian plateau in South America, and the plateaus of Anatolia, Arabia, Iran, and the Tibet region of China.
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In geology and earth science, a plateau (alternatively spelt in a false French spelling plâteau, the real spelling in French being plateau) is an area of highland, usually consisting of relatively flat open country if the uplift was recent in geologic history. Plateaus (or plâteaux), like mesas and buttes, are formed when land has been uplifted by tectonic activity and then eroded by wind or water. Flat-topped, sheer-sided plateaus, like the tepuis of Guiana, are formed when a section of land is uplifted that is topped with a layer of particularly resistant rock, and underlain by softer rock.
Plateau is also used to describe undersea geologic formations. Some undersea plateaus, like the Seychelles plateau, are fragments of continental crust that lie separate from continents; they are analogous to continental shelves, but without the continents. Some, like the Seychelles, have peaks that rise from the sea as islands; others rest entirely below the surface. Other undersea plateaus were formed by outpourings of flood basalts, and were never associated with continents; the vast Ontong Jaya Plateau of the western Pacific is an example of such.