erosion(redirected from marginal erosion)
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erosion(ĭrō`zhən), general term for the processes by which the surface of the earth is constantly being worn away. The principal agents are gravity, running water, near-shore waves, ice (mostly glaciers), and wind. All running water gathers and transports particles of soil or fragments of rock (formed by weatheringweathering,
collective term for the processes by which rock at or near the earth's surface is disintegrated and decomposed by the action of atmospheric agents, water, and living things. Some of these processes are mechanical, e.g.
..... Click the link for more information. ), and every stream carries, in suspension or rolling along its bottom, material received from its tributaries or detached from its own banks. These transported particles strike against the bedrock of the stream channel, literally grinding it away and eventually settle out along the channel or find their way to the sea. The Mississippi River is being reduced by erosion at the rate of 1 ft (30 cm) in about 9,000 years. Seacoasts are eroded by ocean waves, which detach loose or nonresistant material. Waves wear the rock by both the force of their own impact and the abrasive action of the detritus they carry. Global warmingglobal warming,
the gradual increase of the temperature of the earth's lower atmosphere as a result of the increase in greenhouse gases since the Industrial Revolution. Global warming and its effects, such as more intense summer and winter storms, are also referred to as climate
..... Click the link for more information. , by increasing sea levels, accelerates coastal erosion and also inundates coasts; in the Arctic, ice, a major component of the coasts, also is melted by global warming, compounding the effects of coastal erosion. Ice can erode rocks by a freezing-thawing cycle; and ice in the form of glaciersglacier,
moving mass of ice that survives year to year, formed by the compacting of snow into névé and then into granular ice and set in motion outward and downward by the force of gravity and the stress of its accumulated mass.
..... Click the link for more information. erodes by plucking off loose rocks, by its abrasive action on the surface over which it passes, and by glacial meltwater rivers and streams. In deserts and along beaches, wind transports sand, eroding one area and depositing in another. The wind can also drive sand and other particles against rocks, abrading them. Before human modification, landmasses were probably eroding at rates close to 1 inch (2 to 3 centimeters) per 1,000 years; now rates have doubled. In the United States 30% is natural erosion, while 70% is because of human intervention. Suspended sedimentsediment,
mineral or organic particles that are deposited by the action of wind, water, or glacial ice. These sediments can eventually form sedimentary rocks (see rock).
..... Click the link for more information. from erosion is one of the world's greatest pollutants. Sediment can fill reservoirs and navigable waterways, impair wildlife habitats, increase flooding and water treatment costs, and deplete valuable topsoil. It can also concentrate harmful chemicals and bacteria. The continuous washing away of the fine rich topsoil of farmland due to poor agricultural practices is a problem in many parts of the world. Accelerated erosion from removal of acres of trees and vegetation, which diminishes the natural erosion protection, is becoming increasingly common in populated areas. Strip mining also removes vegetation and can be a localized cause of erosion. Among the methods of preventing soil erosion are reforestation, maintenance of fallow strips, terracing, underdraining, ditching, deep plowing, and plowing across slopes rather than up and down. See conservation of natural resourcesconservation of natural resources,
the wise use of the earth's resources by humanity. The term conservation came into use in the late 19th cent. and referred to the management, mainly for economic reasons, of such valuable natural resources as timber, fish, game, topsoil,
..... Click the link for more information. .
the destruction of rocks and soils by running water.
Erosion is manifested in various forms: the direct mechanical effect of water flow, which causes solid particles to be suspended and be carried away or transported along the bottom by the stream of water; the dissolution of rocks by water (corrosion); the abrasion and wearing away of the bottom of a stream by water-transported particles (corrasion); and the excitation of electrical charges of opposite sign in the water-solid system, which promotes the suspension of fine particles. The erosive capacity of a stream increases with increasing current velocity; it is also dependent on the nature of the underlying surface (bed).
Erosion is one of the principal factors responsible for the formation of the earth’s relief. A distinction is made between surface erosion (slope wash), which tends to even out irregularities in the relief; and stream erosion (the formation of ditches, gullies, and valleys), which leads to dissection of the earth’s surface. Stream erosion is subdivided into downcutting erosion, including retrograde, or backward, erosion, which spreads from the lower part of the runoff to the upper part and leads to the formation of a longitudinal profile of equilibrium; and lateral erosion, which causes the valley floor to broaden through the meandering or shifting of the channel owing to the deflecting effect of the earth’s rotation. Geologic (natural) erosion occurs everywhere there is running water. Accelerated erosion is caused by careless human economic activity.
In the foreign literature, the term ’erosion” includes the direct destructive action of the sea, wind, glaciers, and other factors. This is the origin of such terms as “wind erosion,” “glacial erosion,” and “marine erosion.” The term “soil erosion” is also included in this group.
REFERENCESMakkaveev, N.I. Rush reki i eroziia v ee basseine. Moscow, 1955.
Voprosy erozii istoka. (Sbornik.) Moscow, 1962.
Zvonkov, V. V. Vodnaia i vetrovaia eroziia Zemli. Moscow, 1962.
Mirtskhulava, Ts. E. Inzhenernye melody rascheta i prognoza vodnoi erozii. Moscow, 1970.
in medicine, a superficial injury to the epithelium of the skin or mucous membrane. Among the causes of erosion are mechanical injuries (abrasions of the skin), dystrophic and inflammatory processes in the mucous membrane (for example, gastric erosion), and the irritating effect of pathological secretions (as in cervical erosion). Erosion of the mucous membrane of the stomach is clinically significant; it is characteristic of the condition known as erosive gastritis, which is often marked by multiple erosions and complicated gastric bleeding. Unlike ulcers, erosions heal without scarring.