Plateau
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 if the uplift was recent in
geologic history. 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. [
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.
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.
|
Escarpment face of a cuesta, broken by a fault. Cumberland Plateau, Tennessee |
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.
