Erosion

In earth science, erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location[1] (not to be confused with weathering which involves no movement). This natural process is caused by the dynamic activity of erosive agents, that is, water, ice (glaciers), snow, air (wind), plants, animals, and humans. In accordance with these agents, erosion is sometimes divided into water erosion, glacial erosion, snow erosion, wind (aeolic) erosion, zoogenic erosion, and anthropogenic erosion.[2] The particulate breakdown of rock or soil into clastic sediment is referred to as physical or mechanical erosion; this contrasts with chemical erosion, where soil or rock material is removed from an area by its dissolving into a solvent (typically water), followed by the flow away of that solution. Eroded sediment or solutes may be transported just a few millimetres, or for thousands of kilometres.

Natural rates of erosion are controlled by the action of geological weathering geomorphic drivers, such as rainfall;[3] bedrock wear in rivers; coastal erosion by the sea and waves; glacial plucking, abrasion, and scour; areal flooding; wind abrasion; groundwater processes; and mass movement processes in steep landscapes like landslides and debris flows. The rates at which such processes act control how fast a surface is eroded. Typically, physical erosion proceeds fastest on steeply sloping surfaces, and rates may also be sensitive to some climatically-controlled properties including amounts of water supplied (e.g., by rain), storminess, wind speed, wave fetch, or atmospheric temperature (especially for some ice-related processes). Feedbacks are also possible between rates of erosion and the amount of eroded material that is already carried by, for example, a river or glacier.[4][5] Processes of erosion that produce sediment or solutes from a place contrast with those of deposition, which control the arrival and emplacement of material at a new location.[1]

While erosion is a natural process, human activities have increased by 10-40 times the rate at which erosion is occurring globally.[6] At well-known agriculture sites such as the Appalachian Mountains, intensive farming practices have caused erosion up to 100x the speed of the natural rate of erosion in the region.[7] Excessive (or accelerated) erosion causes both "on-site" and "off-site" problems. On-site impacts include decreases in agricultural productivity and (on natural landscapes) ecological collapse, both because of loss of the nutrient-rich upper soil layers. In some cases, the eventual end result is desertification. Off-site effects include sedimentation of waterways and eutrophication of water bodies, as well as sediment-related damage to roads and houses. Water and wind erosion are the two primary causes of land degradation; combined, they are responsible for about 84% of the global extent of degraded land, making excessive erosion one of the most significant environmental problems worldwide.[8]:2[9]:1

Intensive agriculture, deforestation, roads, anthropogenic climate change and urban sprawl are amongst the most significant human activities in regard to their effect on stimulating erosion.[10] However, there are many prevention and remediation practices that can curtail or limit erosion of vulnerable soils.

KharazaArch
A natural arch produced by the wind erosion of differentially weathered rock in Jebel Kharaz, Jordan
大连国家地质公园9-海蚀崖
A wave-like sea cliff produced by coastal erosion, in Jinshitan Coastal National Geopark, Dalian, Liaoning Province, China
Eroding rill in field in eastern Germany
An actively eroding rill on an intensively-farmed field in eastern Germany

Physical processes

Rainfall and surface runoff

Water and soil splashed by the impact of a single raindrop
Soil and water being splashed by the impact of a single raindrop

Rainfall, and the surface runoff which may result from rainfall, produces four main types of soil erosion: splash erosion, sheet erosion, rill erosion, and gully erosion. Splash erosion is generally seen as the first and least severe stage in the soil erosion process, which is followed by sheet erosion, then rill erosion and finally gully erosion (the most severe of the four).[9]:60–61[11]

In splash erosion, the impact of a falling raindrop creates a small crater in the soil,[12] ejecting soil particles.[13] The distance these soil particles travel can be as much as 0.6 m (two feet) vertically and 1.5 m (five feet) horizontally on level ground.

If the soil is saturated, or if the rainfall rate is greater than the rate at which water can infiltrate into the soil, surface runoff occurs. If the runoff has sufficient flow energy, it will transport loosened soil particles (sediment) down the slope.[14] Sheet erosion is the transport of loosened soil particles by overland flow.[14]

Rummu aherainemägi2
A spoil tip covered in rills and gullies due to erosion processes caused by rainfall: Rummu, Estonia

Rill erosion refers to the development of small, ephemeral concentrated flow paths which function as both sediment source and sediment delivery systems for erosion on hillslopes. Generally, where water erosion rates on disturbed upland areas are greatest, rills are active. Flow depths in rills are typically of the order of a few centimetres (about an inch) or less and along-channel slopes may be quite steep. This means that rills exhibit hydraulic physics very different from water flowing through the deeper, wider channels of streams and rivers.[15]

Gully erosion occurs when runoff water accumulates and rapidly flows in narrow channels during or immediately after heavy rains or melting snow, removing soil to a considerable depth.[16][17][18]

Rivers and streams

Dobbingstone Burn - geograph.org.uk - 1291882
Dobbingstone Burn, Scotland, showing two different types of erosion affecting the same place. Valley erosion is occurring due to the flow of the stream, and the boulders and stones (and much of the soil) that are lying on the stream's banks are glacial till that was left behind as ice age glaciers flowed over the terrain.
Erosion
Soil erosion from a stream

Valley or stream erosion occurs with continued water flow along a linear feature. The erosion is both downward, deepening the valley, and headward, extending the valley into the hillside, creating head cuts and steep banks. In the earliest stage of stream erosion, the erosive activity is dominantly vertical, the valleys have a typical V cross-section and the stream gradient is relatively steep. When some base level is reached, the erosive activity switches to lateral erosion, which widens the valley floor and creates a narrow floodplain. The stream gradient becomes nearly flat, and lateral deposition of sediments becomes important as the stream meanders across the valley floor. In all stages of stream erosion, by far the most erosion occurs during times of flood when more and faster-moving water is available to carry a larger sediment load. In such processes, it is not the water alone that erodes: suspended abrasive particles, pebbles, and boulders can also act erosively as they traverse a surface, in a process known as traction.[19]

Bank erosion is the wearing away of the banks of a stream or river. This is distinguished from changes on the bed of the watercourse, which is referred to as scour. Erosion and changes in the form of river banks may be measured by inserting metal rods into the bank and marking the position of the bank surface along the rods at different times.[20]

Thermal erosion is the result of melting and weakening permafrost due to moving water.[21] It can occur both along rivers and at the coast. Rapid river channel migration observed in the Lena River of Siberia is due to thermal erosion, as these portions of the banks are composed of permafrost-cemented non-cohesive materials.[22] Much of this erosion occurs as the weakened banks fail in large slumps. Thermal erosion also affects the Arctic coast, where wave action and near-shore temperatures combine to undercut permafrost bluffs along the shoreline and cause them to fail. Annual erosion rates along a 100-kilometre (62-mile) segment of the Beaufort Sea shoreline averaged 5.6 metres (18 feet) per year from 1955 to 2002.[23]

Most river erosion happens nearer to the mouth of a river. On a river bend, the longest least sharp side has slower moving water. Here deposits build up. On the narrowest sharpest side of the bend, there is faster moving water so this side tends to erode away mostly.

Coastal erosion

Wavecut platform southerndown pano
Wave cut platform caused by erosion of cliffs by the sea, at Southerndown in South Wales
Erosion of Boulder Clay in Filey Bay
Erosion of the boulder clay (of Pleistocene age) along cliffs of Filey Bay, Yorkshire, England

Shoreline erosion, which occurs on both exposed and sheltered coasts, primarily occurs through the action of currents and waves but sea level (tidal) change can also play a role.

Hydraulic action takes place when the air in a joint is suddenly compressed by a wave closing the entrance of the joint. This then cracks it. Wave pounding is when the sheer energy of the wave hitting the cliff or rock breaks pieces off. Abrasion or corrasion is caused by waves launching sea load at the cliff. It is the most effective and rapid form of shoreline erosion (not to be confused with corrosion). Corrosion is the dissolving of rock by carbonic acid in sea water.[24] Limestone cliffs are particularly vulnerable to this kind of erosion. Attrition is where particles/sea load carried by the waves are worn down as they hit each other and the cliffs. This then makes the material easier to wash away. The material ends up as shingle and sand. Another significant source of erosion, particularly on carbonate coastlines, is boring, scraping and grinding of organisms, a process termed bioerosion.[25]

Sediment is transported along the coast in the direction of the prevailing current (longshore drift). When the upcurrent amount of sediment is less than the amount being carried away, erosion occurs. When the upcurrent amount of sediment is greater, sand or gravel banks will tend to form as a result of deposition. These banks may slowly migrate along the coast in the direction of the longshore drift, alternately protecting and exposing parts of the coastline. Where there is a bend in the coastline, quite often a buildup of eroded material occurs forming a long narrow bank (a spit). Armoured beaches and submerged offshore sandbanks may also protect parts of a coastline from erosion. Over the years, as the shoals gradually shift, the erosion may be redirected to attack different parts of the shore.[26]

Chemical erosion

Chemical erosion is the loss of matter in a landscape in the form of solutes. Chemical erosion is usually calculated from the solutes found in streams. Anders Rapp pioneered the study of chemical erosion in his work about Kärkevagge published in 1960.[27]

Glaciers

Glaciers erode predominantly by three different processes: abrasion/scouring, plucking, and ice thrusting. In an abrasion process, debris in the basal ice scrapes along the bed, polishing and gouging the underlying rocks, similar to sandpaper on wood. Scientists have shown that, in addition to the role of temperature played in valley-deepening, other glaciological processes, such as erosion also control cross-valley variations. In a homogeneous bedrock erosion pattern, curved channel cross-section beneath the ice is created. Though the glacier continues to incise vertically, the shape of the channel beneath the ice eventually remain constant, reaching a U-shaped parabolic steady-state shape as we now see in glaciated valleys. Scientists also provide a numerical estimate of the time required for the ultimate formation of a steady-shaped U-shaped valley—approximately 100,000 years. In a weak bedrock (containing material more erodible than the surrounding rocks) erosion pattern, on the contrary, the amount of over deepening is limited because ice velocities and erosion rates are reduced.[28]

Glaciers can also cause pieces of bedrock to crack off in the process of plucking. In ice thrusting, the glacier freezes to its bed, then as it surges forward, it moves large sheets of frozen sediment at the base along with the glacier. This method produced some of the many thousands of lake basins that dot the edge of the Canadian Shield. Differences in the height of mountain ranges are not only being the result tectonic forces, such as rock uplift, but also local climate variations. Scientists use global analysis of topography to show that glacial erosion controls the maximum height of mountains, as the relief between mountain peaks and the snow line are generally confined to altitudes less than 1500 m.[29] The erosion caused by glaciers worldwide erodes mountains so effectively that the term glacial buzzsaw has become widely used, which describes the limiting effect of glaciers on the height of mountain ranges.[30] As mountains grow higher, they generally allow for more glacial activity (especially in the accumulation zone above the glacial equilibrium line altitude),[31] which causes increased rates of erosion of the mountain, decreasing mass faster than isostatic rebound can add to the mountain.[32] This provides a good example of a negative feedback loop. Ongoing research is showing that while glaciers tend to decrease mountain size, in some areas, glaciers can actually reduce the rate of erosion, acting as a glacial armor.[30] Ice can not only erode mountains but also protect them from erosion. Depending on glacier regime, even steep alpine lands can be preserved through time with the help of ice. Scientists have proved this theory by sampling eight summits of northwestern Svalbard using Be10 and Al26, showing that northwestern Svalbard transformed from a glacier-erosion state under relatively mild glacial maxima temperature, to a glacier-armor state occupied by cold-based, protective ice during much colder glacial maxima temperatures as the Quaternary ice age progressed.[33]

These processes, combined with erosion and transport by the water network beneath the glacier, leave behind glacial landforms such as moraines, drumlins, ground moraine (till), kames, kame deltas, moulins, and glacial erratics in their wake, typically at the terminus or during glacier retreat.[34]

The best-developed glacial valley morphology appears to be restricted to landscapes with low rock uplift rates (less than or equal to 2 mm per year) and high relief, leading to long-turnover times. Where rock uplift rates exceed 2 mm per year, glacial valley morphology has generally been significantly modified in postglacial time. Interplay of glacial erosion and tectonic forcing governs the morphologic impact of glaciations on active orogens, by both influencing their height, and by altering the patterns of erosion during subsequent glacial periods via a link between rock uplift and valley cross-sectional shape.[35]

Floods

At extremely high flows, kolks, or vortices are formed by large volumes of rapidly rushing water. Kolks cause extreme local erosion, plucking bedrock and creating pothole-type geographical features called Rock-cut basins. Examples can be seen in the flood regions result from glacial Lake Missoula, which created the channeled scablands in the Columbia Basin region of eastern Washington.[36]

Wind erosion

Im Salar de Uyuni
Árbol de Piedra, a rock formation in the Altiplano, Bolivia sculpted by wind erosion

Wind erosion is a major geomorphological force, especially in arid and semi-arid regions. It is also a major source of land degradation, evaporation, desertification, harmful airborne dust, and crop damage—especially after being increased far above natural rates by human activities such as deforestation, urbanization, and agriculture.[37][38]

Wind erosion is of two primary varieties: deflation, where the wind picks up and carries away loose particles; and abrasion, where surfaces are worn down as they are struck by airborne particles carried by wind. Deflation is divided into three categories: (1) surface creep, where larger, heavier particles slide or roll along the ground; (2) saltation, where particles are lifted a short height into the air, and bounce and saltate across the surface of the soil; and (3) suspension, where very small and light particles are lifted into the air by the wind, and are often carried for long distances. Saltation is responsible for the majority (50-70%) of wind erosion, followed by suspension (30-40%), and then surface creep (5-25%).[39]:57[40]

Wind erosion is much more severe in arid areas and during times of drought. For example, in the Great Plains, it is estimated that soil loss due to wind erosion can be as much as 6100 times greater in drought years than in wet years.[41]

Mass movement

NegevWadi2009
A wadi in Makhtesh Ramon, Israel, showing gravity collapse erosion on its banks

Mass movement is the downward and outward movement of rock and sediments on a sloped surface, mainly due to the force of gravity.[42][43]

Mass movement is an important part of the erosional process and is often the first stage in the breakdown and transport of weathered materials in mountainous areas.[44]:93 It moves material from higher elevations to lower elevations where other eroding agents such as streams and glaciers can then pick up the material and move it to even lower elevations. Mass-movement processes are always occurring continuously on all slopes; some mass-movement processes act very slowly; others occur very suddenly, often with disastrous results. Any perceptible down-slope movement of rock or sediment is often referred to in general terms as a landslide. However, landslides can be classified in a much more detailed way that reflects the mechanisms responsible for the movement and the velocity at which the movement occurs. One of the visible topographical manifestations of a very slow form of such activity is a scree slope.

Slumping happens on steep hillsides, occurring along distinct fracture zones, often within materials like clay that, once released, may move quite rapidly downhill. They will often show a spoon-shaped isostatic depression, in which the material has begun to slide downhill. In some cases, the slump is caused by water beneath the slope weakening it. In many cases it is simply the result of poor engineering along highways where it is a regular occurrence.[45]

Surface creep is the slow movement of soil and rock debris by gravity which is usually not perceptible except through extended observation. However, the term can also describe the rolling of dislodged soil particles 0.5 to 1.0 mm (0.02 to 0.04 in) in diameter by wind along the soil surface.[46]

Factors affecting erosion rates

Climate

The amount and intensity of precipitation is the main climatic factor governing soil erosion by water. The relationship is particularly strong if heavy rainfall occurs at times when, or in locations where, the soil's surface is not well protected by vegetation. This might be during periods when agricultural activities leave the soil bare, or in semi-arid regions where vegetation is naturally sparse. Wind erosion requires strong winds, particularly during times of drought when vegetation is sparse and soil is dry (and so is more erodible). Other climatic factors such as average temperature and temperature range may also affect erosion, via their effects on vegetation and soil properties. In general, given similar vegetation and ecosystems, areas with more precipitation (especially high-intensity rainfall), more wind, or more storms are expected to have more erosion.

In some areas of the world (e.g. the mid-western USA), rainfall intensity is the primary determinant of erosivity (for a definition of erosivity check,[47]) with higher intensity rainfall generally resulting in more soil erosion by water. The size and velocity of rain drops is also an important factor. Larger and higher-velocity rain drops have greater kinetic energy, and thus their impact will displace soil particles by larger distances than smaller, slower-moving rain drops.[48]

In other regions of the world (e.g. western Europe), runoff and erosion result from relatively low intensities of stratiform rainfall falling onto the previously saturated soil. In such situations, rainfall amount rather than intensity is the main factor determining the severity of soil erosion by water.[16]

In Taiwan, where typhoon frequency increased significantly in the 21st century, a strong link has been drawn between the increase in storm frequency with an increase in sediment load in rivers and reservoirs, highlighting the impacts climate change can have on erosion.[49]

Vegetative cover

Vegetation acts as an interface between the atmosphere and the soil. It increases the permeability of the soil to rainwater, thus decreasing runoff. It shelters the soil from winds, which results in decreased wind erosion, as well as advantageous changes in microclimate. The roots of the plants bind the soil together, and interweave with other roots, forming a more solid mass that is less susceptible to both water[50] and wind erosion. The removal of vegetation increases the rate of surface erosion.[51]

Topography

The topography of the land determines the velocity at which surface runoff will flow, which in turn determines the erosivity of the runoff. Longer, steeper slopes (especially those without adequate vegetative cover) are more susceptible to very high rates of erosion during heavy rains than shorter, less steep slopes. Steeper terrain is also more prone to mudslides, landslides, and other forms of gravitational erosion processes.[48]:28–30[52][53]

Tectonics

Tectonic processes control rates and distributions of erosion at the Earth's surface. If the tectonic action causes part of the Earth's surface (e.g., a mountain range) to be raised or lowered relative to surrounding areas, this must necessarily change the gradient of the land surface. Because erosion rates are almost always sensitive to the local slope (see above), this will change the rates of erosion in the uplifted area. Active tectonics also brings fresh, unweathered rock towards the surface, where it is exposed to the action of erosion.

However, erosion can also affect tectonic processes. The removal by erosion of large amounts of rock from a particular region, and its deposition elsewhere, can result in a lightening of the load on the lower crust and mantle. Because tectonic processes are driven by gradients in the stress field developed in the crust, this unloading can in turn cause tectonic or isostatic uplift in the region.[44]:99[54] In some cases, it has been hypothesised that these twin feedbacks can act to localize and enhance zones of very rapid exhumation of deep crustal rocks beneath places on the Earth's surface with extremely high erosion rates, for example, beneath the extremely steep terrain of Nanga Parbat in the western Himalayas. Such a place has been called a "tectonic aneurysm".[55]

Development

Human land development, in forms including agricultural and urban development, is considered a significant factor in erosion[56] and sediment transport. In Taiwan, increases in sediment load in the northern, central, and southern regions of the island can be tracked with the timeline of development for each region throughout the 20th century.[49]

Erosion at various scales

Mountain ranges

Mountain ranges are known to take many millions of years to erode to the degree they effectively cease to exist. Scholars Pitman and Golovchenko estimate that it takes probably more than 450 million years to erode a mountain mass similar to the Himalaya into an almost-flat peneplain if there are no major sea-level changes.[57] Erosion of mountains massifs can create a pattern of equally high summits called summit accordance.[58] It has been argued that extension during post-orogenic collapse is a more effective mechanism of lowering the height of orogenic mountains than erosion.[59]

Examples of heavily eroded mountain ranges include the Timanides of Northern Russia. Erosion of this orogen has produced sediments that are now found in the East European Platform, including the Cambrian Sablya Formation near Lake Ladoga. Studies of these sediments indicate that it is likely that the erosion of the orogen began in the Cambrian and then intensified in the Ordovician.[60]

Soils

If the rate of erosion is higher than the rate of soil formation the soils are being destroyed by erosion.[61] Where soil is not destroyed by erosion, erosion can in some cases prevent the formation of soil features that form slowly. Inceptisols are common soils that form in areas of fast erosion.[62]

While erosion of soils is a natural process, human activities have increased by 10-40 times the rate at which erosion is occurring globally. Excessive (or accelerated) erosion causes both "on-site" and "off-site" problems. On-site impacts include decreases in agricultural productivity and (on natural landscapes) ecological collapse, both because of loss of the nutrient-rich upper soil layers. In some cases, the eventual end result is desertification. Off-site effects include sedimentation of waterways and eutrophication of water bodies, as well as sediment-related damage to roads and houses. Water and wind erosion are the two primary causes of land degradation; combined, they are responsible for about 84% of the global extent of degraded land, making excessive erosion one of the most significant environmental problems.[9][63]

See also

References

  1. ^ a b "Erosion". Encyclopædia Britannica. 2015-12-03. Archived from the original on 2015-12-21. Retrieved 2015-12-06.
  2. ^ Apollo, M., Andreychouk, V., Bhattarai, S.S. (2018-03-24). "Short-Term Impacts of Livestock Grazing on Vegetation and Track Formation in a High Mountain Environment: A Case Study from the Himalayan Miyar Valley (India)". Sustainability. 10 (4): 951. doi:10.3390/su10040951. ISSN 2071-1050.CS1 maint: Multiple names: authors list (link)
  3. ^ Cheraghi, M., S. Jomaa, G.C. Sander, and D.A. Barry (2016 ), Hysteretic sediment fluxes in rainfall-driven soil erosion: Particle size effects, Water Resour. Res., 52, doi:10.1002/2016WR019314 file [http://onlinelibrary.wiley.com/doi/10.1002/2016WR019314/full link]
  4. ^ Hallet, Bernard (1981). "Glacial Abrasion and Sliding: Their Dependence on the Debris Concentration In Basal Ice". Annals of Glaciology. 2 (1): 23–28. Bibcode:1981AnGla...2...23H. doi:10.3189/172756481794352487. ISSN 0260-3055.
  5. ^ Sklar, Leonard S.; Dietrich, William E. (2004). "A mechanistic model for river incision into bedrock by saltating bed load" (PDF). Water Resources Research. 40 (6): W06301. Bibcode:2004WRR....40.6301S. doi:10.1029/2003WR002496. ISSN 0043-1397. Archived (PDF) from the original on 2016-10-11. Retrieved 2016-06-18.
  6. ^ Dotterweich, Markus (2013-11-01). "The history of human-induced soil erosion: Geomorphic legacies, early descriptions and research, and the development of soil conservation – A global synopsis". Geomorphology. 201: 1–34. Bibcode:2013Geomo.201....1D. doi:10.1016/j.geomorph.2013.07.021.
  7. ^ Reusser, L.; Bierman, P.; Rood, D. (2015). "Quantifying human impacts on rates of erosion and sediment transport at a landscape scale". Geology. 43 (2): 171–174. Bibcode:2015Geo....43..171R. doi:10.1130/g36272.1.
  8. ^ Blanco-Canqui, Humberto; Rattan, Lal (2008). "Soil and water conservation". Principles of soil conservation and management. Dordrecht: Springer. pp. 1–20. ISBN 978-1-4020-8709-7.
  9. ^ a b c Toy, Terrence J.; Foster, George R.; Renard, Kenneth G. (2002). Soil erosion : processes, prediction, measurement, and control. New York: Wiley. ISBN 978-0-471-38369-7.
  10. ^ Julien, Pierre Y. (2010). Erosion and Sedimentation. Cambridge University Press. p. 1. ISBN 978-0-521-53737-7.
  11. ^ Zachar, Dušan (1982). "Classification of soil erosion". Soil Erosion. Vol. 10. Elsevier. p. 48. ISBN 978-0-444-99725-8.
  12. ^ See Figure 1 in Obreschkow, D.; Dorsaz, N.; Kobel, P.; De Bosset, A.; Tinguely, M.; Field, J.; Farhat, M. (2011). "Confined Shocks inside Isolated Liquid Volumes – A New Path of Erosion?". Physics of Fluids. 23 (10): 101702. arXiv:1109.3175. Bibcode:2011PhFl...23j1702O. doi:10.1063/1.3647583.
  13. ^ Cheraghi, M., S. Jomaa, G.C. Sander, and D.A. Barry (2016 ), Hysteretic sediment fluxes in rainfall-driven soil erosion: Particle size effects, Water Resour. Res., 52, doi:10.1002/2016WR019314
  14. ^ a b Food and Agriculture Organization (1965). "Types of erosion damage". Soil Erosion by Water: Some Measures for Its Control on Cultivated Lands. United Nations. pp. 23–25. ISBN 978-92-5-100474-6.
  15. ^ Nearing, M.A.; Norton, L.D.; Bulgakov, D.A.; Larionov, G.A.; West, L.T.; Dontsova, K.M. (1997). "Hydraulics and erosion in eroding rills". Water Resources Research. 33 (4): 865–876. Bibcode:1997WRR....33..865N. doi:10.1029/97wr00013.
  16. ^ a b Boardman, John; Poesen, Jean, eds. (2007). Soil Erosion in Europe. Chichester: John Wiley & Sons. ISBN 978-0-470-85911-7.
  17. ^ J. Poesen, L. Vandekerckhove, J. Nachtergaele, D. Oostwoud Wijdenes, G. Verstraeten, B. Can Wesemael (2002). "Gully erosion in dryland environments". In Bull, Louise J. & Kirby, M.J. Dryland Rivers: Hydrology and Geomorphology of Semi-Arid Channels. John Wiley & Sons. pp. 229–262. ISBN 978-0-471-49123-1.CS1 maint: Uses authors parameter (link) CS1 maint: Uses editors parameter (link)
  18. ^ Borah, Deva K. et al. (2008). "Watershed sediment yield". In Garcia, Marcelo H. Sedimentation Engineering: Processes, Measurements, Modeling, and Practice. ASCE Publishing. p. 828. ISBN 978-0-7844-0814-8.CS1 maint: Uses authors parameter (link)
  19. ^ Ritter, Michael E. (2006) "Geologic Work of Streams" Archived 2012-05-06 at the Wayback Machine The Physical Environment: an Introduction to Physical Geography University of Wisconsin, OCLC 79006225
  20. ^ Nancy D. Gordon (2004). "Erosion and Scour". Stream hydrology: an introduction for ecologists. ISBN 978-0-470-84357-4.
  21. ^ "Thermal Erosion". NSIDC Glossary. National Snow and Ice Data Center. Archived from the original on 2010-11-19. Retrieved 21 December 2009.
  22. ^ Costard, F.; Dupeyrat, L.; Gautier, E.; Carey-Gailhardis, E. (2003). "Fluvial thermal erosion investigations along a rapidly eroding river bank: application to the Lena River (central Siberia)". Earth Surface Processes and Landforms. 28 (12): 1349–1359. Bibcode:2003ESPL...28.1349C. doi:10.1002/esp.592.
  23. ^ Jones, B.M.; Hinkel, K.M.; Arp, C.D.; Eisner, W.R. (2008). "Modern Erosion Rates and Loss of Coastal Features and Sites, Beaufort Sea Coastline, Alaska". Arctic. 61 (4): 361–372. doi:10.14430/arctic44. Archived from the original on 2013-05-17.
  24. ^ Geddes, Ian. "Lithosphere." Higher geography for cfe: physical and human environments, Hodder Education, 2015.
  25. ^ Glynn, Peter W. "Bioerosion and coral-reef growth: a dynamic balance." Life and death of coral reefs (1997): 68-95.
  26. ^ Bell, Frederic Gladstone. "Marine action and control." Geological hazards: their assessment, avoidance, and mitigation, Taylor & Francis, 1999, pp. 302–306.
  27. ^ Dixon, John C.; Thorn, Colin E. (2005). "Chemical weathering and landscape development in mid-latitude alpine environments". Geomorphology. 67 (1–2): 127–145. Bibcode:2005Geomo..67..127D. doi:10.1016/j.geomorph.2004.07.009.
  28. ^ Harbor, Jonathan M.; Hallet, Bernard; Raymond, Charles F. (1988-05-26). "A numerical model of landform development by glacial erosion". Nature. 333 (6171): 347–349. Bibcode:1988Natur.333..347H. doi:10.1038/333347a0.
  29. ^ Egholm, D. L.; Nielsen, S. B.; Pedersen, V.K.; Lesemann, J.-E. (2009). "Glacial effects limiting mountain height". Nature. 460 (7257): 884–887. Bibcode:2009Natur.460..884E. doi:10.1038/nature08263. PMID 19675651.
  30. ^ a b Thomson, Stuart N.; Brandon, Mark T.; Tomkin, Jonathan H.; Reiners, Peter W.; Vásquez, Cristián; Wilson, Nathaniel J. (2010). "Glaciation as a destructive and constructive control on mountain building". Nature. 467 (7313): 313–317. Bibcode:2010Natur.467..313T. doi:10.1038/nature09365. PMID 20844534.
  31. ^ Tomkin, J.H.; Roe, G.H. (2007). "Climate and tectonic controls on glaciated critical-taper orogens" (PDF). Earth Planet. Sci. Lett. 262 (3–4): 385–397. Bibcode:2007E&PSL.262..385T. CiteSeerX 10.1.1.477.3927. doi:10.1016/j.epsl.2007.07.040. Archived (PDF) from the original on 2017-08-09. Retrieved 2017-10-24.
  32. ^ Mitchell, S.G. & Montgomery, D.R. "Influence of a glacial buzzsaw on the height and morphology of the Cascade Range in central Washington State". Quat. Res. 65, 96–107 (2006)
  33. ^ Gjermundsen, Endre F.; Briner, Jason P.; Akçar, Naki; Foros, Jørn; Kubik, Peter W.; Salvigsen, Otto; Hormes, Anne (2015). "Minimal erosion of Arctic alpine topography during late Quaternary glaciation". Nature Geoscience. 8 (10): 789. Bibcode:2015NatGe...8..789G. doi:10.1038/ngeo2524.
  34. ^ Harvey, A.M. "Local-Scale geomorphology – process systems and landforms." Introducing Geomorphology: A Guide to Landforms and Processes. Dunedin Academic Press, 2012, pp. 87–88. EBSCOhost.
  35. ^ Prasicek, Günther; Larsen, Isaac J.; Montgomery, David R. (2015-08-14). "Tectonic control on the persistence of glacially sculpted topography". Nature Communications. 6: 8028. Bibcode:2015NatCo...6E8028P. doi:10.1038/ncomms9028. ISSN 2041-1723. PMC 4557346. PMID 26271245.
  36. ^ See, for example: Alt, David (2001). Glacial Lake Missoula & its Humongous Floods. Mountain Press. ISBN 978-0-87842-415-3.
  37. ^ Zheng, Xiaojing & Huang, Ning (2009). Mechanics of Wind-Blown Sand Movements. Mechanics of Wind-Blown Sand Movements by Xiaojing Zheng. Berlin: Springer. Springer. pp. 7–8. Bibcode:2009mwbs.book.....Z. ISBN 978-3-540-88253-4.CS1 maint: Uses authors parameter (link)
  38. ^ Cornelis, Wim S. (2006). "Hydroclimatology of wind erosion in arid and semi-arid environments". In D'Odorico, Paolo & Porporato, Amilcare. Dryland Ecohydrology. Springer. p. 141. ISBN 978-1-4020-4261-4.CS1 maint: Uses editors parameter (link)
  39. ^ Blanco-Canqui, Humberto; Rattan, Lal (2008). "Wind erosion". Principles of soil conservation and management. Dordrecht: Springer. pp. 54–80. ISBN 978-1-4020-8709-7.
  40. ^ Balba, A. Monem (1995). "Desertification: Wind erosion". Management of Problem Soils in Arid Ecosystems. CRC Press. p. 214. ISBN 978-0-87371-811-0.
  41. ^ Wiggs, Giles F.S. (2011). "Geomorphological hazards in drylands". In Thomas, David S.G. Arid Zone Geomorphology: Process, Form and Change in Drylands. John Wiley & Sons. p. 588. ISBN 978-0-470-71076-0.
  42. ^ Van Beek, Rens (2008). "Hillside processes: mass wasting, slope stability, and erosion". In Norris, Joanne E. et al. Slope Stability and Erosion Control: Ecotechnological Solutions. Slope Stability and Erosion Control: Ecotechnological Solutions. Springer. Bibcode:2008ssec.conf.....N. ISBN 978-1-4020-6675-7.CS1 maint: Uses authors parameter (link) CS1 maint: Uses editors parameter (link)
  43. ^ Gray, Donald H. & Sotir, Robbin B. (1996). "Surficial erosion and mass movement". Biotechnical and Soil Bioengineering Slope Stabilization: A Practical Guide for Erosion Control. John Wiley & Sons. p. 20. ISBN 978-0-471-04978-4.CS1 maint: Uses authors parameter (link)
  44. ^ a b Nichols, Gary (2009). Sedimentology and Stratigraphy. John Wiley & Sons. ISBN 978-1-4051-9379-5.
  45. ^ Sivashanmugam, P. (2007). Basics of Environmental Science and Engineering. New India Publishing. pp. 43–. ISBN 978-81-89422-28-8.
  46. ^ "Britannica Library". library.eb.com. Retrieved 2017-01-31.
  47. ^ Zorn, Matija; Komac, Blaž (2013). Bobrowsky, Peter T., ed. Encyclopedia of Natural Hazards. Encyclopedia of Earth Sciences Series. Springer Netherlands. pp. 289–290. doi:10.1007/978-1-4020-4399-4_121. ISBN 978-90-481-8699-0.
  48. ^ a b Blanco-Canqui, Humberto; Rattan, Lal (2008). "Water erosion". Principles of soil conservation and management. Dordrecht: Springer. pp. 21–53 [29–31]. ISBN 978-1-4020-8709-7.
  49. ^ a b Montgomery, David R.; Huang, Michelle Y.-F.; Huang, Alice Y.-L. (2014-01-01). "Regional soil erosion in response to land use and increased typhoon frequency and intensity, Taiwan". Quaternary Research. 81 (1): 15–20. Bibcode:2014QuRes..81...15M. doi:10.1016/j.yqres.2013.10.005. ISSN 0033-5894. Archived from the original on 2017-02-24. Retrieved 2017-02-23.
  50. ^ Gyssels, G.; Poesen, J.; Bochet, E.; Li, Y. (2005-06-01). "Impact of plant roots on the resistance of soils to erosion by water: a review". Progress in Physical Geography. 29 (2): 189–217. doi:10.1191/0309133305pp443ra. ISSN 0309-1333.
  51. ^ Styczen, M.E. & Morgan, R.P.C. (1995). "Engineering properties of vegetation". In Morgan, R.P.C. & Rickson, R. Jane. Slope Stabilization and Erosion Control: A Bioengineering Approach. Taylor & Francis. ISBN 978-0-419-15630-7.CS1 maint: Uses authors parameter (link) CS1 maint: Uses editors parameter (link)
  52. ^ Whisenant, Steve G. (2008). "Terrestrial systems". In Perrow Michael R. & Davy, Anthony J. Handbook of Ecological Restoration: Principles of Restoration. Cambridge University Press. p. 89. ISBN 978-0-521-04983-2.CS1 maint: Uses editors parameter (link)
  53. ^ Wainwright, John & Brazier, Richard E. (2011). "Slope systems". In Thomas, David S.G. Arid Zone Geomorphology: Process, Form and Change in Drylands. John Wiley & Sons. ISBN 978-0-470-71076-0.CS1 maint: Uses authors parameter (link)
  54. ^ Burbank, Douglas W.; Anderson, Robert S. (2011). "Tectonic and surface uplift rates". Tectonic Geomorphology. John Wiley & Sons. pp. 270–271. ISBN 978-1-4443-4504-9.
  55. ^ Zeitler, P.K. et al. (2001), Erosion, Himalayan Geodynamics, and the Geomorphology of Metamorphism, GSA Today, 11, 4–9.
  56. ^ Chen, Jie (2007-01-16). "Rapid urbanization in China: A real challenge to soil protection and food security". CATENA. Influences of rapid urbanization and industrialization on soil resource and its quality in China. 69 (1): 1–15. doi:10.1016/j.catena.2006.04.019.
  57. ^ Pitman, W. C.; Golovchenko, X. (1991). "The effect of sea level changes on the morphology of mountain belts". Journal of Geophysical Research: Solid Earth. 96 (B4): 6879–6891. Bibcode:1991JGR....96.6879P. doi:10.1029/91JB00250. ISSN 0148-0227.
  58. ^ Beckinsale, Robert P.; Chorley, Richard J. (2003) [1991]. "Chapter Seven: American Polycyclic Geomorphology". The History of the Study of Landforms. Volume Three. Taylor & Francis e-Library. pp. 235–236.
  59. ^ Dewey, J.F.; Ryan, P.D.; Andersen, T.B. (1993). "Orogenic uplift and collapse, crustal thickness, fabrics and metamorphic phase changes: the role of eclogites". Geological Society, London, Special Publications. 76 (1): 325–343. Bibcode:1993GSLSP..76..325D. doi:10.1144/gsl.sp.1993.076.01.16.
  60. ^ Orlov, S.Yu.; Kuznetsov, N.B.; Miller, E.D.; Soboleva, A.A.; Udoratina, O.V. (2011). "Age Constraints for the Pre-Uralide–Timanide Orogenic Event Inferred from the Study of Detrital Zircons". Doklady Earth Sciences. 440 (1): 1216–1221. Bibcode:2011DokES.440.1216O. doi:10.1134/s1028334x11090078. Retrieved 22 September 2015.
  61. ^ Lupia-Palmieri, Elvidio (2004). "Erosion". In Goudie, A.S. Encyclopedia of Geomorphology. p. 336.
  62. ^ Alexander, Earl B. (2014). Soils in natural landscapes. CRC Press. p. 108. ISBN 978-1-4665-9436-4.
  63. ^ Blanco, Humberto & Lal, Rattan (2010). "Soil and water conservation". Principles of Soil Conservation and Management. Springer. p. 2. ISBN 978-90-481-8529-0.CS1 maint: Uses authors parameter (link)

Further reading

External links

Aeolian processes

Aeolian processes, also spelled eolian or æolian, pertain to wind activity in the study of geology and weather and specifically to the wind's ability to shape the surface of the Earth (or other planets). Winds may erode, transport, and deposit materials and are effective agents in regions with sparse vegetation, a lack of soil moisture and a large supply of unconsolidated sediments. Although water is a much more powerful eroding force than wind, aeolian processes are important in arid environments such as deserts.

The term is derived from the name of the Greek god Aeolus, the keeper of the winds.

Beach

A beach is a landform alongside a body of water which consists of loose particles. The particles composing a beach are typically made from rock, such as sand, gravel, shingle, pebbles. The particles can also be biological in origin, such as mollusc shells or coralline algae.

Some beaches have man-made infrastructure, such as lifeguard posts, changing rooms, showers, shacks and bars. They may also have hospitality venues (such as resorts, camps, hotels, and restaurants) nearby. Wild beaches, also known as undeveloped or undiscovered beaches, are not developed in this manner. Wild beaches can be appreciated for their untouched beauty and preserved nature.

Beaches typically occur in areas along the coast where wave or current action deposits and reworks sediments.

Canyon

A canyon (Spanish: cañón; archaic British English spelling: cañon) or gorge is a deep cleft between escarpments or cliffs resulting from weathering and the erosive activity of a river over geologic timescales. Rivers have a natural tendency to cut through underlying surfaces, eventually wearing away rock layers as sediments are removed downstream. A river bed will gradually reach a baseline elevation, which is the same elevation as the body of water into which the river drains. The processes of weathering and erosion will form canyons when the river's headwaters and estuary are at significantly different elevations, particularly through regions where softer rock layers are intermingled with harder layers more resistant to weathering.

A canyon may also refer to a rift between two mountain peaks, such as those in ranges including the Rocky Mountains, the Alps, the Himalayas or the Andes. Usually a river or stream and erosion carve out such splits between mountains. Examples of mountain-type canyons are Provo Canyon in Utah or Yosemite Valley in California's Sierra Nevada. Canyons within mountains, or gorges that have an opening on only one side, are called box canyons. Slot canyons are very narrow canyons that often have smooth walls.

Steep-sided valleys in the seabed of the continental slope are referred to as submarine canyons. Unlike canyons on land, submarine canyons are thought to be formed by turbidity currents and landslides.

Cirque

A cirque (French, from the Latin word circus) is an amphitheatre-like valley formed by glacial erosion. Alternative names for this landform are corrie (from Scottish Gaelic coire, meaning a pot or cauldron) and cwm (Welsh for "valley", pronounced [kʊm]). A cirque may also be a similarly shaped landform arising from fluvial erosion.

The concave shape of a glacial cirque is open on the downhill side, while the cupped section is generally steep. Cliff-like slopes, down which ice and glaciated debris combine and converge, form the three or more higher sides. The floor of the cirque ends up bowl-shaped as it is the complex convergence zone of combining ice flows from multiple directions and their accompanying rock burdens: hence it experiences somewhat greater erosion forces, and is most often overdeepened below the level of the cirque's low-side outlet (stage) and its down slope (backstage) valley. If the cirque is subject to seasonal melting, the floor of the cirque most often forms a tarn (small lake) behind a dam which marks the downstream limit of the glacial overdeepening: the dam itself can be composed of moraine, glacial till, or a lip of the underlying bedrock.The fluvial cirque or makhtesh, found in karst landscapes, is formed by intermittent river flow cutting through layers of limestone and chalk leaving sheer cliffs. A common feature for all fluvial-erosion cirques is a terrain which includes erosion resistant upper structures overlying materials which are more easily eroded.

Cliff

In geography and geology, a cliff is a vertical, or nearly vertical, rock exposure. Cliffs are formed as erosion landforms by the processes of weathering and erosion. Cliffs are common on coasts, in mountainous areas, escarpments and along rivers. Cliffs are usually formed by rock that is resistant to weathering and erosion. Sedimentary rocks most likely to form cliffs include sandstone, limestone, chalk, and dolomite. Igneous rocks such as granite and basalt also often form cliffs.

An escarpment (or scarp) is a type of cliff, formed by the movement of a geologic fault or landslide, or by differential erosion of rock layers of differing hardness.

Most cliffs have some form of scree slope at their base. In arid areas or under high cliffs, they are generally exposed jumbles of fallen rock. In areas of higher moisture, a soil slope may obscure the talus. Many cliffs also feature tributary waterfalls or rock shelters. Sometimes a cliff peters out at the end of a ridge, with tea tables or other types of rock columns remaining. Coastal erosion may lead to the formation of sea cliffs along a receding coastline.

The Ordnance Survey distinguishes between cliffs (continuous line along the top edge with projections down the face) and outcrops (continuous lines along lower edge).

Coastal erosion

There are two common definitions of coastal erosion. It is often defined as the loss or displacement of land along the coastline due to the action of waves, currents, tides, wind-driven water, waterborne ice, or other impacts of storms. In this case, landward retreat of the shoreline, measured to a given spatial datum, is described over a temporal scale of tides, seasons, and other short-term cyclic processes. Alternatively, it is defined as the process of long-term removal of sediment and rocks at the coastline, leading again to loss of land and retreat of the coastline landward. Coastal erosion may be caused by hydraulic action, abrasion, impact and corrosion by wind and water, and other forces, natural or unnatural.On non-rocky coasts, coastal erosion results in rock formations in areas where the coastline contains rock layers or fracture zones with varying resistance to erosion. Softer areas become eroded much faster than harder ones, which typically result in landforms such as tunnels, bridges, columns, and pillars. Over time the coast generally evens out. The softer areas fill up with sediment eroded from hard areas, and rock formations are eroded away. Also abrasion commonly happens in areas where there are strong winds, loose sand, and soft rocks. The blowing of millions of sharp sand grains creates a sandblasting effect. This effect helps to erode, smooth and polish rocks. The definition of abrasion is grinding and wearing away of rock surfaces through the mechanical action of other rock or sand particles.

Cycle of erosion

The geographic cycle or cycle of erosion is an idealized model that explains the development of relief in landscapes. The model starts with the erosion that follows uplift of land above a base level and ends – if conditions allow – in the formation of a peneplain. Landscapes that show evidence of more than one cycle of erosion are termed "polycyclical". The cycle of erosion and some of its associated concepts have, despite popularity, been a subject of much criticism.

Fluvial processes

In geography and geology, fluvial processes are associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluvioglacial is used.

Generic trademark

A generic trademark, also known as a genericized trademark or proprietary eponym, is a trademark or brand name that, due to its popularity or significance, has become the generic name for, or synonymous with, a general class of product or service, usually against the intentions of the trademark's holder. The process of a product's name becoming genericized is known as genericide.A trademark is said to become genericized when it begins as a distinctive product identifier but changes in meaning to become generic. This typically happens when the products or services with which the trademark is associated have acquired substantial market dominance or mind share, such that the primary meaning of the genericized trademark becomes the product or service itself rather than an indication of source for the product or service. A trademark thus popularized has its legal protection at risk in some countries such as the United States and United Kingdom, as its intellectual property rights in the trademark may be lost and competitors enabled to use the genericized trademark to describe their similar products, unless the owner of an affected trademark works sufficiently to correct and prevent such broad use.Thermos, Kleenex, Q-Tip, ChapStick, Aspirin, Dumpster, Band-Aid, Velcro, Hoover, Jet Ski, and Speedo are examples of trademarks that have become genericized in the US and elsewhere.

Glacial landform

Glacial landforms are landforms created by the action of glaciers. Most of today's glacial landforms were created by the movement of large ice sheets during the Quaternary glaciations. Some areas, like Fennoscandia and the southern Andes, have extensive occurrences of glacial landforms; other areas, such as the Sahara, display rare and very old fossil glacial landforms.

Mountain range

A mountain range or hill range is a series of mountains or hills ranged in a line and connected by high ground. A mountain system or mountain belt is a group of mountain ranges with similarity in form, structure, and alignment that have arisen from the same cause, usually an orogeny. Mountain ranges are formed by a variety of geological processes, but most of the significant ones on Earth are the result of plate tectonics. Mountain ranges are also found on many planetary mass objects in the Solar System and are likely a feature of most terrestrial planets.

Mountain ranges are usually segmented by highlands or mountain passes and valleys. Individual mountains within the same mountain range do not necessarily have the same geologic structure or petrology. They may be a mix of different orogenic expressions and terranes, for example thrust sheets, uplifted blocks, fold mountains, and volcanic landforms resulting in a variety of rock types.

Ravine

A ravine is a landform that is narrower than a canyon and is often the product of streamcutting erosion. Ravines are typically classified as larger in scale than gullies, although smaller than valleys.

Sediment

Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand and silt can be carried in suspension in river water and on reaching the sea bed deposited by sedimentation and if buried, may eventually become sandstone and siltstone (sedimentary rocks).

Sediments are most often transported by water (fluvial processes), but also wind (aeolian processes) and glaciers. Beach sands and river channel deposits are examples of fluvial transport and deposition, though sediment also often settles out of slow-moving or standing water in lakes and oceans. Desert sand dunes and loess are examples of aeolian transport and deposition. Glacial moraine deposits and till are ice-transported sediments.

Skin condition

A skin condition, also known as cutaneous condition, is any medical condition that affects the integumentary system—the organ system that encloses the body and includes skin, hair, nails, and related muscle and glands. The major function of this system is as a barrier against the external environment.Conditions of the human integumentary system constitute a broad spectrum of diseases, also known as dermatoses, as well as many nonpathologic states (like, in certain circumstances, melanonychia and racquet nails). While only a small number of skin diseases account for most visits to the physician, thousands of skin conditions have been described. Classification of these conditions often presents many nosological challenges, since underlying causes and pathogenetics are often not known. Therefore, most current textbooks present a classification based on location (for example, conditions of the mucous membrane), morphology (chronic blistering conditions), cause (skin conditions resulting from physical factors), and so on.Clinically, the diagnosis of any particular skin condition is made by gathering pertinent information regarding the presenting skin lesion(s), including the location (such as arms, head, legs), symptoms (pruritus, pain), duration (acute or chronic), arrangement (solitary, generalized, annular, linear), morphology (macules, papules, vesicles), and color (red, blue, brown, black, white, yellow). The diagnosis of many conditions often also requires a skin biopsy which yields histologic information that can be correlated with the clinical presentation and any laboratory data. The introduction of cutaneous ultrasound has allowed the detection of cutaneous tumors, inflammatory processes, nail disorders and hair diseases.

Soil erosion

Soil erosion is the displacement of the upper layer of soil, one form of soil degradation. This natural process is caused by the dynamic activity of erosive agents, that is, water, ice (glaciers), snow, air (wind), plants, animals, and humans. In accordance with these agents, erosion is sometimes divided into water erosion, glacial erosion, snow erosion, wind (aeolean) erosion, zoogenic erosion, and anthropogenic erosion.

Soil erosion may be a slow process that continues relatively unnoticed, or it may occur at an alarming rate causing a serious loss of topsoil. The loss of soil from farmland may be reflected in reduced crop production potential, lower surface water quality and damaged drainage networks.

Human activities have increased by 10–40 times the rate at which erosion is occurring globally. Excessive (or accelerated) erosion causes both "on-site" and "off-site" problems. On-site impacts include decreases in agricultural productivity and (on natural landscapes) ecological collapse, both because of loss of the nutrient-rich upper soil layers. In some cases, the eventual end result is desertification. Off-site effects include sedimentation of waterways and eutrophication of water bodies, as well as sediment-related damage to roads and houses. Water and wind erosion are the two primary causes of land degradation; combined, they are responsible for about 84% of the global extent of degraded land, making excessive erosion one of the most significant environmental problems worldwide.Intensive agriculture, deforestation, roads, anthropogenic climate change and urban sprawl are amongst the most significant human activities in regard to their effect on stimulating erosion. However, there are many prevention and remediation practices that can curtail or limit erosion of vulnerable soils.

Stack (geology)

A stack or sea stack is a geological landform consisting of a steep and often vertical column or columns of rock in the sea near a coast, formed by wave erosion. Stacks are formed over time by wind and water, processes of coastal geomorphology. They are formed when part of a headland is eroded by hydraulic action, which is the force of the sea or water crashing against the rock. The force of the water weakens cracks in the headland, causing them to later collapse, forming free-standing stacks and even a small island. Without the constant presence of water, stacks also form when a natural arch collapses under gravity, due to sub-aerial processes like wind erosion. Erosion causes the arch to collapse, leaving the pillar of hard rock standing away from the coast—the stack. Eventually, erosion will cause the stack to collapse, leaving a stump. Stacks can provide important nesting locations for seabirds, and many are popular for rock climbing.

Isolated steep-sided, rocky oceanic islets, typically of volcanic origin, are also loosely called "stacks" or "volcanic stacks".

Surface runoff

Surface runoff (also known as overland flow) is the flow of water that occurs when excess stormwater, meltwater, or other sources flows over the Earth's surface. This might occur because soil is saturated to full capacity, because rain arrives more quickly than soil can absorb it, or because impervious areas (roofs and pavement) send their runoff to surrounding soil that cannot absorb all of it. Surface runoff is a major component of the water cycle. It is the primary agent in soil erosion by water.Runoff that occurs on the ground surface before reaching a channel is also called a nonpoint source. If a nonpoint source contains man-made contaminants, or natural forms of pollution (such as rotting leaves) the runoff is called nonpoint source pollution. A land area which produces runoff that drains to a common point is called a drainage basin. When runoff flows along the ground, it can pick up soil contaminants including petroleum, pesticides, or fertilizers that become discharge or nonpoint source pollution.In addition to causing water erosion and pollution, surface runoff in urban areas is a primary cause of urban flooding which can result in property damage, damp and mold in basements, and street flooding.

Valley

A valley is a low area between hills or mountains typically with a river running through it. In geology, a valley or dale is a depression that is longer than it is wide. The terms U-shaped and V-shaped are descriptive terms of geography to characterize the form of valleys. Most valleys belong to one of these two main types or a mixture of them, at least with respect to the cross section of the slopes or hillsides.

Weathering

Weathering is the breaking down of rocks, soil, and minerals as well as wood and artificial materials through contact with the Earth's atmosphere, water, and biological organisms. Weathering occurs in situ (on site), that is, in the same place, with little or no movement, and thus should not be confused with erosion, which involves the movement of rocks and minerals by agents such as water, ice, snow, wind, waves and gravity and then being transported and deposited in other locations.

Two important classifications of weathering processes exist – physical and chemical weathering; each sometimes involves a biological component. Mechanical or physical weathering involves the breakdown of rocks and soils through direct contact with atmospheric conditions, such as heat, water, ice and pressure. The second classification, chemical weathering, involves the direct effect of atmospheric chemicals or biologically produced chemicals also known as biological weathering in the breakdown of rocks, soils and minerals. While physical weathering is accentuated in very cold or very dry environments, chemical reactions are most intense where the climate is wet and hot. However, both types of weathering occur together, and each tends to accelerate the other. For example, physical abrasion (rubbing together) decreases the size of particles and therefore increases their surface area, making them more susceptible to chemical reactions. The various agents act in concert to convert primary minerals (feldspars and micas) to secondary minerals (clays and carbonates) and release plant nutrient elements in soluble forms.

The materials left over after the rock breaks down combined with organic material creates soil. The mineral content of the soil is determined by the parent material; thus, a soil derived from a single rock type can often be deficient in one or more minerals needed for good fertility, while a soil weathered from a mix of rock types (as in glacial, aeolian or alluvial sediments) often makes more fertile soil. In addition, many of Earth's landforms and landscapes are the result of weathering processes combined with erosion and re-deposition.

Large-scale features
Alluvial rivers
Bedrock river
Bedforms
Regional processes
Mechanics

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.