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PLATEAU
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In geology and earth science, a plateau, also called a high plateau or tableland, is an area of highland, usually consisting of relatively flat open country.
Genesis
Plateaus are generally attributed to either uplift of areas of low relief (as problably in the Tibet), or to accumulation of sediments (as in intramountain endorheic basins), or to a combination of both (as in the Andean Altiplano). Sediment accumulation results usually in very low depositional angles, consitent with the definiton of high plateau. As for uplift, if this was recent in geologic history, then the low relief can be mostly preserved. Plateaus (or plateaux), like mesas and buttes, are formed when a flat 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. Other types of plateaus can be formed due to collisions of sections of Earth's crust, due to lava flows forming the land surface (known as lava or basalt plateaus), or simply when the erosion wears away the side of a land region. Plateaus cover about 45 percent of Earth's surface.
Examples
[1] The largest and highest plateau in the world is the Chang Tang of Tibet, called the "roof of the world", which is still being formed by the collisions of the Indo-Australian and Eurasian tectonic plates. Second in the list is the Andean Altiplano, 3600-4000 m in altitude, located within the Central Andes and including Lake Titicaca.
Oceanic plateaus
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.
Dissected plateaus
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A highly eroded plateau is called a dissected plateau. These older uplifts have been eroded by creeks and rivers to develop steep relief not immediately distinguishable from mountains. Many areas of the Allegheny Plateau and the Cumberland Plateau, which are at the western edge of the Appalachian Mountains of eastern North America, are called "mountains" but are actually dissected plateaus. One can stand on a high "mountain" and note that all the other tops are at the same height, which represents the original plain before uplift.
A dissected plateau may also be formed, usually on a comparatively small scale, by the levelling of terrain by planing and deposition beneath an ice sheet or perhaps, an ice cap. Subsequently, during the same or a later glacial, the margins of the glacial till plain are removed by glaciers, leaving the plateau into which erosion by water incises valleys. Such a plateau may be level or gently sloping but may be distinguished by the till caps on its hills. Glacial till is still widely known in Britain by the older name of boulder clay.
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