Plateau
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In geology and earth science, a plateau is an area of highland, usually consisting of relatively flat open country if the uplift was recent in geologic history. Plateaus (or pl�teaux), 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.
Examples of plateaus
The Tibetan plateau is one of the most famous examples of this landform, but there are many other notable examples of it from around the world, including:
- Allegheny/Cumberland Plateau (a continuous landform with different local names)
- Chota Nagpur Plateau
- Colorado Plateau
- Deccan Plateau
- Highveld
- Iranian plateau
- Khorat Plateau
- Loess Plateau
- Pennyroyal Plateau/Highland Rim (a continuous landform with different local names)
- Vercors Plateau
A more complete list of plateaus is available.
Dissected plateaus
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.