In geography , a plain , commonly known as flatland , is a flat expanse of land that generally does not change much in elevation , and is primarily treeless. 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.
20-520: Arcadia Planitia is a smooth plain with fresh lava flows and Amazonian volcanic flows on Mars . It was named by Giovanni Schiaparelli in 1882 after the Arcadia region of ancient Greece . It dates from the Amazonian period 's Arcadia formation's lava flows and small cinder cones . It includes a more recently developed large region of aeolian materials derived from periglacial processes. It
40-1040: A riffle and pool structure and cooler water temperatures. Rivers with a course that drops in elevation very slowly will have slower water flow and lower force. This in turn produces the other characteristics of a lowland river—a meandering course lacking rapids , a river bed dominated by fine sediments and higher water temperatures. Lowland rivers tend to carry more suspended sediment and organic matter as well, but some lowland rivers have periods of high water clarity in seasonal low-flow periods. The generally clear, cool, fast-flowing waters and bedrock and coarse sediment beds of upland rivers encourage fish species with limited temperature tolerances, high oxygen needs, strong swimming ability and specialised reproductive strategies to prevent eggs or larvae being swept away. These characteristics also encourage invertebrate species with limited temperature tolerances, high oxygen needs and ecologies revolving around coarse sediments and interstices or "gaps" between those coarse sediments. The term "upland"
60-563: A plain that are conditionally categorized by their elevation above the sea level . Lowlands are usually no higher than 200 m (660 ft), while uplands are somewhere around 200 m (660 ft) to 500 m (1,600 ft). On unusual occasions, certain lowlands such as the Caspian Depression lie below sea level. Uplands areas tend to spike into valleys and mountains , forming mountain ranges while lowland areas tend to be uniformly flat, although both can vary such as
80-638: A subsurface layer of excess ice, which subsequently sublimates. With sublimation , the ice changes directly from a solid to gaseous form. In the impact, the excess ice is broken up, resulting in an increase in surface area. Ice will sublimate much more if there is more surface area. After the ice disappears into the atmosphere, dry soil material will collapse and cause the crater diameter to become larger. Places on Mars that display expanded craters may indicate where future colonists can find water ice. Martian gullies are small, incised networks of narrow channels and their associated downslope sediment deposits, found on
100-512: 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. Plains can be formed from flowing lava ; from deposition of sediment by water, ice, or wind; or formed by erosion by
120-408: Is a flat expanse of land with a layer of grass that generally does not change much in elevation , and is primarily treeless. 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, where they are present on all continents, and cover more than one-third of the world's land area. In
140-539: Is also found cut into the faces of sand dunes which themselves considered to be quite young. On the basis of their form, aspects, positions, and location amongst and apparent interaction with features thought to be rich in water ice, many researchers believed that the processes carving the gullies involve liquid water. However, this remains a topic of active research. The pictures below show gullies in Arcadia Planitia. Planitia A plain or flatland
160-727: Is also used in wetland ecology , where "upland" plants indicate an area that is not a wetland. The generally more turbid , warm, slow-flowing waters and fine sediment beds of lowland rivers encourage fish species with broad temperature tolerances and greater tolerances to low oxygen levels, and life history and breeding strategies adapted to these and other traits of lowland rivers. These characteristics also encourage invertebrate species with broad temperature tolerances and greater tolerances to low oxygen levels and ecologies revolving around fine sediments or alternative habitats such as submerged woody debris ("snags") or submergent macrophytes ("water weed"). Lowland alluvial plains form when there
180-413: Is generally considered to be land that is at a higher elevation than the alluvial plain or stream terrace , which are considered to be "lowlands". The term "bottomland" refers to low-lying alluvial land near a river. Much freshwater fish and invertebrate communities around the world show a pattern of specialization into upland or lowland river habitats. Classifying rivers and streams as upland or lowland
200-404: Is important in freshwater ecology , as the two types of river habitat are very different, and usually support very different populations of fish and invertebrate species. In freshwater ecology, upland rivers and streams are the fast-flowing rivers and streams that drain elevated or mountainous country, often onto broad alluvial plains (where they become lowland rivers). However, elevation is not
220-586: Is located northwest of the Tharsis region in the northern lowlands, spanning roughly the region 33.9–64.2° North and 165.9–210.4° East, straddling partly in the Cebrenia quadrangle (MC-07), and partly in the Diacria one (MC-02), and centered at 47°12′N 184°18′E / 47.2°N 184.3°E / 47.2; 184.3 . Arcadia marks a transition from the thinly cratered terrain to its north and
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#1732788019289240-469: The Mongolian Plateau . Upland habitats are cold, clear and rocky whose rivers are fast-flowing in mountainous areas; lowland habitats are warm with slow-flowing rivers found in relatively flat lowland areas, with water that is frequently colored by sediment and organic matter. These classifications overlap with the geological definitions of "upland" and "lowland". In geology an "upland"
260-456: 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. Lowland Upland and lowland are conditional descriptions of a plain based on elevation above sea level . In studies of the ecology of freshwater rivers , habitats are classified as upland or lowland. Upland and lowland are portions of
280-404: The agents from hills or mountains. Biomes on plains include grassland ( temperate or subtropical ), steppe ( semi-arid ), savannah ( tropical ) or tundra ( polar ). In a few instances, deserts and rainforests may also be considered plains. Plains in many areas are important for agriculture because where the soils were deposited as sediments they may be deep and fertile , and
300-595: The flatness facilitates mechanization of crop production; or because they support grasslands which provide good grazing for livestock . The types of depositional plains include: 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 . Structural plains are relatively undisturbed horizontal surfaces of
320-492: The ground. Expanded craters have lost their rims, which may be because any rim that was once present has collapsed into the crater during expansion or lost its ice if composed of ice. Excess ice (ice in addition to what is in the pores of the ground) is widespread throughout the Martian mid-latitudes, especially in Arcadia Planitia. In this region are many expanded secondary craters that probably form from impacts that destabilize
340-503: The planet of Mars . They are named for their resemblance to terrestrial gullies . First discovered on images from Mars Global Surveyor , they occur on steep slopes, especially on the walls of craters. Usually, each gully has a dendritic alcove at its head, a fan-shaped apron at its base, and a single thread of incised channel linking the two, giving the whole gully an hourglass shape. They are believed to be relatively young because they have few, if any craters. A subclass of gullies
360-489: The slow flow of near-surface materials. This supports the proposition that ground ice exists in the near-surface of Arcadia Planitia, and therefore this location is an area of interest for potential exploration missions. Large impacts often create swarms of small secondary craters from the debris that is blasted out as a consequence of the impact. Studies of a type of secondary craters, called expanded craters, have given us insights into places where abundant ice may be present in
380-426: The sole determinant of whether a river is upland or lowland. Arguably the most important determinants are those of stream power and stream gradient . Rivers with a course that drops rapidly in elevation will have faster water flow and higher stream power or "force of water". This in turn produces the other characteristics of an upland river—an incised course , a river bed dominated by bedrock and coarse sediments,
400-470: The very old cratered terrain to the south. On its east it runs into the Alba Mons volcanoes. Its elevation relative to the geodetic datum varies between 0 and -3 km. Many low-lying areas of Arcadia are marked by grooves and sub-parallel ridges. These features indicate glaciation and appear similar to those on Earth, where the freezing and thawing of water located between ground layers contributes to
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