In geography, a plain, commonly known as flatland, is a flat expanse of land that generally has few rapid or steep changes in elevation. Natural vegetation in plains can include prairies/grasslands, forests, savanah, tundra, and desert biomes, among others. Plains occur as lowlands along valleys or at the base of mountains, as coastal plains, and as plateaus or uplands. Plains are one of the major landforms on earth, being present on all continents and covering more than one-third of the world's land area. Plains in many areas are important for agriculture. There are various types of plains, and biomes on them.
A plain or flatland is a flat expanse of land with few rapid or steep changes in elevation. Plains occur as lowlands along valleys or at the base of mountains, as coastal plains, and as plateaus or uplands.[1] Plains are one of the major landforms on earth, where they are present on all continents, and cover more than one-third of the world's land area.[2]
In a valley, a plain is enclosed on two sides, but in other cases a plain may be delineated by a complete or partial ring of hills, by mountains, or by cliffs. Where a geological region contains more than one plain, they may be connected by a pass (sometimes termed a gap). Coastal plains mostly rise from sea level until they run into elevated features such as mountains or plateaus.[3] Plains can be formed from flowing lava; from deposition of sediment by water, ice, or wind; or formed by erosion by the agents from hills or mountains.
Plains in many areas are important for agriculture because where the soils were deposited as sediments they may be deep and fertile, and the flatness facilitates mechanization of crop production; or because they support grasslands which provide good grazing for livestock.[5]
Alluvial plains, which are formed by rivers and which may be one of these overlapping types:
Alluvial plains, formed over a long period of time by a river depositing sediment on their flood plains or beds, which become alluvial soil. The difference between a flood plain and an alluvial plain is: a flood plain represents areas experiencing flooding fairly regularly in the present or recently, whereas an alluvial plain includes areas where a flood plain is now and used to be, or areas which only experience flooding a few times a century.[8]File:雪山下的成都市天际线 Chengdu skyline with snow capped mountains.jpgChengdu Plain, Sichuan
Flood plain, adjacent to a lake, river, stream, or wetland that experiences occasional or periodic flooding.
Glacial plains, formed by the movement of glaciers under the force of gravity:
Outwash plain (also known as sandur; plural sandar), a glacial out-wash plain formed of sediments deposited by melt-water at the terminus of a glacier. Sandar consist mainly of stratified (layered and sorted) gravel and sand.[9][10]
Till plains, plain of glacial till that form when a sheet of ice becomes detached from the main body of a glacier and melts in place depositing the sediments it carries. Till plains are composed of unsorted material (till) of all sizes.
Erosional plains have been leveled by various agents of denudation such as running water, rivers, wind and glacier which wear out the rugged surface and smoothens them. Plain resulting from the action of these agents of denudation are called peneplains (almost plain) while plains formed from wind action are called pediplains.[13]
Structural plains are relatively undisturbed horizontal surfaces of the Earth. They are structurally depressed areas of the world that make up some of the most extensive natural lowlands on the Earth's surface.[14]
↑Whittow, John (1984). Dictionary of Physical Geography. London: Penguin. p. 467. ISBN978-0-14-051094-2.
↑Gornitz, Vivien, ed. (2009). Encyclopedia of Paleoclimatology And Ancient Environments. Dordrecht: Springer. p. 665. ISBN9781402045516.
↑Powell, W. Gabe. 2009. Identifying Land Use/Land Cover (LULC) Using National Agriculture Imagery Program (NAIP) Data as a Hydrologic Model Input for Local Flood Plain Management. Applied Research Project, Texas State University.
↑Goudie, A. S., ed. (2004). "Denudation chronology". Encyclopedia of Geomorphology. pp. 244–248.
↑Vinogradova, N.G. (1997). "Zoogeography of the Abyssal and Hadal Zones". The Biogeography of the Oceans. Advances in Marine Biology. 32. pp. 325–387. doi:10.1016/S0065-2881(08)60019-X. ISBN9780120261321.
↑Magilligan F.J., Gomez B., Mertes L.A.K., Smith, L.C. Smith N.D., Finnegan D., Garvin J.B., Geomorphic effectiveness, sandur development, and the pattern of landscape response during jökulhlaups: Skeiðarársandur, southeastern Iceland, Geomorphology 44 (2002) 95–113
↑Smith L.C., Sheng Y., Magilligan F.J., Smith N.D., Gomez B., Mertes L., Krabill W.B., Garven J.B., Geomorphic impact and rapid subsequent recovery from the 1996 Skeiðarársandur jökulhlaup, Iceland, measured with multi-year airborne lidar. Geomorphology vol. 75 Is. 1–2 (2006) 65–75
↑United States. Department of Conservation. Division of Geology. Glacial Sluceways and Lacustrine Plains of Southern Indiana. By William D. Thornburry. Bloomington: n.p., 1950. Web. <"Archived copy"(PDF). Archived(PDF) from the original on 2016-03-03. Retrieved 2015-12-16.CS1 maint: archived copy as title (link)>.
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