A natural arch produced by the erosion of differentially weathered rock in Jebel Kharaz, Jordan

Erosion is the process by which soil and rock are removed from the Earth's surface by natural processes such as wind or water flow, and then transported and deposited in other locations.

While erosion is a natural process, human activities have dramatically increased (by 10-40 times) the rate at which erosion is occurring globally. Excessive erosion causes problems such as desertification, decreases in agricultural productivity due to land degradation, sedimentation of waterways, and ecological collapse due to loss of the nutrient rich upper soil layers. Water and wind erosion are now the two primary causes of land degradation; combined, they are responsible for 84% of degraded acreage, making excessive erosion one of the most significant global environmental problems we face today.^[1][2]

Industrial agriculture, deforestation, roads, anthropogenic climate change and urban sprawl are amongst the most significant human activities in regards to their effect on stimulating erosion.^[3][4] However, there are many available alternative land use practices that can curtail or limit erosion—such as terrace-building, no-till agriculture, and revegetation of denuded soils.

Physical processes[link]

Water erosion[link]

Rainfall[link]

A hillside covered in rills and gullies due to erosion processes caused by rainfall

There are three primary types of erosion that occur as a direct result of rainfall -- sheet erosion, rill erosion, and gully erosion. Sheet erosion is generally seen as the first and least severe stage in the soil erosion process, which is followed by rill erosion, and finally gully erosion (the most severe of the three).^[5][6]

The impact of a falling raindrop creates a small crater in the soil, ejecting soil particles. The distance these soil particles travel (on level ground) can be as much as 2 feet vertically, and 5 feet horizontally. Once the rate of rain fall is faster than the rate of infiltration into the soil, surface runoff occurs and carries the loosened soil particles down slope.^[7]

Sheet erosion is the transport of loosened soil particles by surface runoff that is flowing downhill in thin sheets.^[7]

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 on the order of a few centimeters or less and slopes may be quite steep. This means that rills exhibit very different hydraulic physics than water flowing through the deeper, wider channels of streams and rivers.^{[citation needed]}

Gully erosion occurs when runoff water accumulates, and then rapidly flows in narrow channels during or immediately after heavy rains or melting snow, removing soil to a considerable depth.^[8][9][10]

Rivers and streams[link]

Dobbingstone Burn, Scotland -- This photo illustrates 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 edges are glacial till that was left behind as ice age glaciers flowed over the terrain.

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. 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.^[11]

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.^[12]

Thermal erosion is the result of melting and weakening permafrost due to moving water.^[13] 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.^[14] 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-kilometer segment of the Beaufort Sea shoreline averaged 5.6 meters per year from 1955 to 2002.^[15]

Coastal erosion[link]

Wave cut platform caused by erosion of cliffs by the sea, at Southerndown in South Wales

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 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 seaload 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. Limestone cliffs are particularly vulnerable to this kind of erosion. Attrition is where particles/seaload 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 the boring, scraping and grinding of organisms, a process termed bioerosion.^{[citation needed]}

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 build up 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.^{[citation needed]}

Glaciers[link]

Glacial moraines above Lake Louise, in Alberta, Canada.

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

Floods[link]

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.^[16]

Freezing and thawing[link]

Cold weather causes water trapped in tiny rock cracks to freeze and expand, breaking the rock into several pieces. This can lead to gravity erosion on steep slopes. The scree which forms at the bottom of a steep mountainside is mostly formed from pieces of rock (soil) broken away by this means. It is a common engineering problem wherever rock cliffs are alongside roads, because morning thaws can drop hazardous rock pieces onto the road.^{[citation needed]}

In some places, water seeps into rocks during the daytime, then freezes at night. Ice expands, thus, creating a wedge in the rock. Over time, the repetition in the forming and melting of the ice causes fissures, which eventually breaks the rock down. This process is also called freeze-thaw weathering.^{[citation needed]}

Wind erosion[link]

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.^[17][18]

Wind erosion is of two primary varieties: deflation, where the wind picks up and carries loose soil 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%).^[19][20]

Wind erosion is much more severe in arid areas, and during times of drought. For example, in the Great Plains, it is estimated that wind erosion soil loss can be as much as 6100 times greater in drought years, than in wet years.^[21]

Gravitational erosion[link]

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.^[22][23]

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.^[24] 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.^{[citation needed]}

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.^{[citation needed]}

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 in diameter by wind along the soil surface.^{[citation needed]}

Exfoliation[link]

Exfoliation is a type of erosion that occurs when a rock is rapidly heated up by the sun. This results in the expansion of the rock. When the temperature decreases again, the rock contracts, causing pieces of the rock to break off. Exfoliation occurs mainly in deserts due to the high temperatures during the day and cold temperatures at night.^[25]

Factors affecting erosion rates[link]

Precipitation and wind speed[link]

Climatic factors include the amount and intensity of precipitation, the average temperature, as well as the typical temperature range, seasonality, wind speed, and storm frequency. In general, given similar vegetation and ecosystems, areas with high-intensity precipitation, more frequent rainfall, more wind, or more storms are expected to have more erosion.^{[citation needed]}

Rainfall intensity is the primary determinant of erosivity, with higher intensity rainfall generally resulting in more erosion. 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.^[26]

Soil structure and composition[link]

Erosional gully in unconsolidated Dead Sea (Israel) sediments along the southwestern shore. This gully was excavated by floods from the Judean Mountains in less than a year.

The composition, moisture, and compaction of soil are all major factors in determining the erosivity of rainfall. Sediments containing more clay tend to be more resistant to erosion than those with sand or silt, because the clay helps bind soil particles together.^[27] Soil containing high levels of organic materials are often more resistant to erosion, because the organic materials coagulate soil colloids and create a stronger, more stable soil structure.^[28] The amount of water present in the soil before the precipitation also plays an important role, because it sets limits on the amount of water that can be absorbed by the soil (and hence prevented from flowing on the surface as erosive runoff). Wet, saturated soils will not be able to absorb as much rain water, leading to higher levels of surface runoff and thus higher erosivity for a given volume of rainfall.^[28][29] Soil compaction also affects the permeability of the soil to water, and hence the amount of water that flows away as runoff. More compacted soils will have a larger amount of surface runoff than less compacted soils.^[28]

Vegetative cover[link]

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 and wind erosion. The removal of vegetation increases the rate of surface erosion.^[30]

Topography[link]

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.^[31][32][33]

Human activities that increase erosion rates[link]

Agricultural practices[link]

Tilled farmland such as this is very susceptible to erosion from rainfall, due to the destruction of vegetative cover and the loosening of the soil during plowing.

Unsustainable agricultural practices are the single greatest contributor to the global increase in erosion rates.^[34] The tillage of agricultural lands, which breaks up soil into finer particles, is one of the primary factors. The problem has been exacerbated in modern times, due to mechanized agricultural equipment that allows for deep plowing, which severely increases the amount of soil that is available for transport by water erosion. Others include mono-cropping, farming on steep slopes, pesticide and chemical fertilizer usage (which kill organisms that bind soil together), row-cropping, and the use of surface irrigation.^[35][36] Tillage also increases wind erosion rates, by dehydrating the soil and breaking it up into smaller particles that can be picked up by the wind. Exacerbating this is the fact that most of the trees are generally removed from agricultural fields, allowing winds to have long, open runs to travel over at higher speeds.^[37] Heavy grazing reduces vegetative cover and causes severe soil compaction, both of which increase erosion rates.^[38]

Deforestation[link]

In this clearcut, almost all of the vegetation has been stripped from surface of steep slopes, in an area with very heavy rains. Severe erosion occurs in cases such as this, causing stream sedimentation and the loss of nutrient rich topsoil.

In an undisturbed forest, the mineral soil is protected by a layer of leaf litter and an humus that cover the forest floor. These two layers form a protective mat over the soil that absorbs the impact of rain drops. They are porous and highly permeable to rainfall, and allow rainwater to slow percolate into the soil below, instead of flowing over the surface as runoff.^[39] The roots of the trees and plants^[40] hold together soil particles, preventing them from being washed away.^[39] The vegetative cover acts to reduce the velocity of the raindrops that strike the foliage and stems before hitting the ground, reducing their kinetic energy.^[41] However it is the forest floor, more than the canopy, that prevents surface erosion. The terminal velocity of rain drops is reached in about 8 meters. Because forest canopies are usually higher than this, rain drops can often regain terminal velocity even after striking the canopy. However, the intact forest floor, with its layers of leaf litter and organic matter, is still able to absorb the impact of the rainfall.^[41][42]

Deforestation causes increased erosion rates due to exposure of mineral soil by removing the humus and litter layers from the soil surface, removing the vegetative cover that binds soil together, and causing heavy soil compaction from logging equipment. Once trees have been removed by fire or logging, infiltration rates become high and erosion low to the degree the forest floor remains intact. Severe fires can lead to significant further erosion if followed by heavy rainfall.^[43]

Globally one of the largest contributors to erosive soil loss in the year 2006 is the slash and burn treatment of tropical forests. In a number of regions of the earth, entire sectors of a country have been rendered unproductive. For example, on the Madagascar high central plateau, comprising approximately ten percent of that country's land area, virtually the entire landscape is sterile of vegetation, with gully erosive furrows typically in excess of 50 meters deep and one kilometer wide. Shifting cultivation is a farming system which sometimes incorporates the slash and burn method in some regions of the world. This degrades the soil and causes the soil to become less and less fertile.^{[citation needed]}

Roads and urbanization[link]

Urbanization has major effects on erosion processes—first by denuding the land of vegetative cover, altering drainage patterns, and compacting the soil during construction; and next by covering the land in an impermeable layer of asphalt or concrete that increases the amount of surface runoff and increases surface wind speeds.^[44] Much of the sediment carried in runoff from urban areas (especially roads) is highly contaminated with fuel, oil, and other chemicals.^[45] This increased runoff, in addition to eroding and degrading the land that it flows over, also causes major disruption to surrounding watersheds by altering the volume and rate of water that flows through them, and filling them with chemically polluted sedimentation. The increased flow of water through local waterways also causes a large increase in the rate of bank erosion.^[46]

Climate change[link]

The warmer atmospheric temperatures observed over the past decades are expected to lead to a more vigorous hydrological cycle, including more extreme rainfall events.^[47] The rise in sea levels that has occurred as a result of climate change has also greatly increased coastal erosion rates.^[48][49]

Studies on soil erosion suggest that increased rainfall amounts and intensities will lead to greater rates of erosion. Thus, if rainfall amounts and intensities increase in many parts of the world as expected, erosion will also increase, unless amelioration measures are taken. Soil erosion rates are expected to change in response to changes in climate for a variety of reasons. The most direct is the change in the erosive power of rainfall. Other reasons include: a) changes in plant canopy caused by shifts in plant biomass production associated with moisture regime; b) changes in litter cover on the ground caused by changes in both plant residue decomposition rates driven by temperature and moisture dependent soil microbial activity as well as plant biomass production rates; c) changes in soil moisture due to shifting precipitation regimes and evapo-transpiration rates, which changes infiltration and runoff ratios; d) soil erodibility changes due to decrease in soil organic matter concentrations in soils that lead to a soil structure that is more susceptible to erosion and increased runoff due to increased soil surface sealing and crusting; e) a shift of winter precipitation from non-erosive snow to erosive rainfall due to increasing winter temperatures; f) melting of permafrost, which induces an erodible soil state from a previously non-erodible one; and g) shifts in land use made necessary to accommodate new climatic regimes.^{[citation needed]}

Studies by Pruski and Nearing indicated that, other factors such as land use not considered, we can expect approximately a 1.7% change in soil erosion for each 1% change in total precipitation under climate change.^[50]

Global environmental effects[link]

World map indicating areas that are vulnerable to high rates of water erosion.

During the 17th and 18th centuries, Easter Island experienced severe erosion due to deforestation and unsustainable agricultural practices. The resulting loss of topsoil ultimately led to ecological collapse, causing mass starvation and the complete disintegration of the Easter Island civilization.^[51][52]

Due to the severity of its ecological effects, and the scale on which it is occurring, erosion constitutes one of the most significant global environmental problems we face today.^[2]

Land degradation[link]

Water and wind erosion are now the two primary causes of land degradation; combined, they are responsible for 84% of degraded acreage.^[1]

Each year, about 75 billion tons of soil is eroded from the land—a rate that is about 13-40 times as fast as the natural rate of erosion.^[53] Approximately 40% of the world's agricultural land is seriously degraded.^[54] According to the UN, an area of fertile soil the size of Ukraine is lost every year because of drought, deforestation and climate change.^[55] In Africa, if current trends of soil degradation continue, the continent might be able to feed just 25% of its population by 2025, according to UNU's Ghana-based Institute for Natural Resources in Africa.^[56]

The loss of soil fertility due to erosion is further problematic because the response is often to apply chemical fertilizers, which leads to further water and soil pollution, rather than to allow the land to regenerate.^[57]

Sedimentation of aquatic ecosystems[link]

Soil erosion (especially from agricultural activity) is considered to be the leading global cause of diffuse water pollution, due to the effects of the excess sediments flowing into the world's waterways. The sediments themselves act as pollutants, as well as being carriers for other pollutants, such as attached pesticide molecules or heavy metals.^[58]

The effect of increased sediments loads on aquatic ecosystems can be catastrophic. Silt can smother the spawning beds of fish, by filling in the space between gravel on the stream bed. It also reduces their food supply, and causes major respiratory issues for them as sediment enters their gills. The biodiversity of aquatic plant and algal life is reduced, and invertebrates are also unable to survive and reproduce. While the sedimentation event itself might be relatively short-lived, the ecological disruption caused by the mass die off often persists long into the future.^[59]

One of the most serious and long-running water erosion problems worldwide is in the People's Republic of China, on the middle reaches of the Yellow River and the upper reaches of the Yangtze River. From the Yellow River, over 1.6 billion tons of sediment flows into the ocean each year. The sediment originates primarily from water erosion in the Loess Plateau region of the northwest.^{[citation needed]}

Airborne dust pollution[link]

Soil particles picked up during wind erosion are a major source of air pollution, in the form of airborne particulates -- "dust". These airborne soil particles are often contaminated with toxic chemicals such as pesticides or petroleum fuels, posing ecological and public health hazards when they later land, or are inhaled/ingested.^{[60][61][62][63]}

Dust from erosion acts to suppress rainfall and changes the sky color from blue to white, which leads to an increase in red sunsets. Over 50% of the African dust that reaches the United States affects Florida.^[64] Dust events have been linked to a decline in the health of coral reefs across the Caribbean and Florida, primarily since the 1970s.^[65] Similar dust plumes originate in the Gobi desert, which combined with pollutants, spread large distances downwind, or eastward, into North America.^[66]

Tectonic effects[link]

This section requires expansion.

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. This can cause tectonic or isostatic uplift in the region.^[67][68]

Monitoring, measuring, and modeling erosion[link]

Terracing is an ancient technique that can significantly slow the rate of water erosion on cultivated slopes.

This section requires expansion.

Monitoring and modeling of erosion processes can help us better understand the causes, make predictions, and plan how to implement preventative and restorative strategies. However, the complexity of erosion processes and the number of areas that must be studied to understand and model them (e.g. climatology, hydrology, geology, chemistry, physics, etc.) makes accurate modelling quite challenging.^[69][70] Erosion models are also non-linear, which makes them difficult to work with numerically, and makes it difficult or impossible to scale up to making predictions about large areas from data collected by sampling smaller plots.^[71]

The most commonly used model for predicting soil loss from water erosion is the Universal Soil Loss Equation (USLE), which estimates the average annual soil loss Failed to parse (Missing texvc executable; please see math/README to configure.): A

as[72]:

Failed to parse (Missing texvc executable; please see math/README to configure.): A = RKLSCP

where R is the rainfall erosivity factor, K is the soil erodibility factor, L and S are topographic factors representing length and slope, and C and P are cropping management factors.

Erosion is measured and further understood using tools such as the micro-erosion meter (MEM) and the traversing micro-erosion meter (TMEM). The MEM has proved helpful in measuring bedrock erosion in various ecosystems around the world. It can measure both terrestrial and oceanic erosion. On the other hand, the TMEM can be used to track the expanding and contracting of volatile rock formations and can give a reading of how quickly a rock formation is deteriorating.^{[citation needed]}

Prevention and remediation[link]

A windbreak (the row of trees) planted next to an agricultural field, acting as a shield against strong winds. This reduces the effects of wind erosion, and provides many other benefits.

The most effective known method for erosion prevention is to increase vegetative cover on the land, which helps prevent both wind and water erosion.^[73] Terracing is an extremely effective means of erosion control, which has been practiced for thousands of years by people all over the world.^[74] Windbreaks (also called shelterbelts) are rows of trees and shrubs that are planted along the edges of agricultural fields, to shield the fields against winds.^[75] In addition to significantly reducing wind erosion, windbreaks provide many other benefits such as improved microclimates for crops (which are sheltered from the dehydrating and otherwise damaging effects of wind), habitat for beneficial bird species,^[76] carbon sequestration,^[77] and aesthetic improvements to the agricultural landscape.^[78][79] Traditional planting methods, such as mixed-cropping (instead of monocropping) and crop rotation have also been shown to significantly reduce erosion rates.^[80][81]

See also[link]

Notes[link]

This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (April 2012)

Further reading[link]

• Boardman, John; Poesen, Jean (2006). Soil erosion in Europe. Wiley. ISBN 978-0-470-85910-0. 
• Montgomery, David R. (2007) Soil erosion and agricultural sustainability PNAS 104: 13268-13272.
• Brown, Jason; Drake, Simon (2009). Classic Erosion. Wiley. 
• Vanoni, Vito A., ed. "The nature of sedimentation problems". Sedimentation Engineering. ASCE Publications. ISBN 978-0-7844-0823-0. http://books.google.com/books?id=TxGTDYz_FnwC&pg=PA1. 

External links[link]

Find more about Erosion on Wikipedia's sister projects:
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	Learning resources from Wikiversity
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	Source texts from Wikisource
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• The Soil Erosion Site
• International Erosion Control Association
• USDA National Soil Erosion Laboratory
• The Soil and Water Conservation Society
• International Soil Conservation Organization
• Bioerosion website at The College of Wooster
• Pulawy Erosion Research Center
• Southwest Watershed Research Center

For the Australian tree commonly known as "Billy Blue", see Acacia sclerosperma.

Billy Blue or William Blue (c.1767 - 1834) was an Australian convict. Although Billy Blue’s place and date of birth are uncertain, convict records suggest he was born in Jamaica around 1767.

Conviction[link]

By 1796 he was living at Deptford, London, and working as a chocolate-maker and also labouring on ships on the Thames.

On 4 October 1796 he was convicted, at Maidstone, in Kent, of stealing raw sugar and sentenced to seven years transportation. After serving over four years in the convict hulks (ships used for housing criminals), he was transported to Botany Bay, Australia, in the convict ship Minorca. He was described in the ship’s records as 'a Jamaican Negro sailor', aged 29 in 1796.

Personal life[link]

He arrived in Sydney in 1801 and served out the remaining part of his sentence. In 1804, records show him living in ‘the Rocks’, then a very tough part of the city. There he met Elizabeth Williams, a 30-year-old convict from Hampshire, England, who had arrived in June 1804. On 27 April 1805, they were married at the old St. Philip's Anglican church in Sydney, where 5 of their 6 children were later christened.^[1]

Career[link]

He became a boatman that ferried passengers across Sydney Harbour. He was also made a water bailiff and watched boat traffic on Port Jackson from a special tower. Despite being a bailiff, it seems Billy didn't do everything by the book. It was said that his law infringements were frequent, but due to his colourful personality, they were looked upon with a "benevolent air" by the authorities.

In 1818, tolerance of his practices temporarily waned. Billy was found to be carrying liquor on his boat, and was accused of smuggling. Billy protested that he had found the liquor floating in the harbour and was simply bringing it to shore. It seems his story was vaguely believable because he was stripped of his right to be a bailiff, but was still allowed to operate his ferry service.

Legacy[link]

Aside from providing a valued service to the colony, Billy's eccentric nature helped him attain the status of what could be defined as Australia’s first celebrity. Billy was a very popular member of the community. Governor Macquarie once remarked jokingly: "I shall have to make you the Commodore". For the rest of his life, he was referred to as “the Commodore." In tribute to his legacy, many streets, landmarks, hotels and businesses in North Sydney have been named in his honour. These include Blues Point, William Street, Blues Point Road, The Commodore Hotel, and the Billy Blue Design School.^[2]

See also[link]

• John Caesar
• African Australians

References[link]

Simon Baron-Cohen
Born	(1958-08-15) 15 August 1958 (age 53) London, England
Residence	England
Citizenship	British and Canadian
Nationality	British
Fields	Psychologist
Institutions	University of Cambridge
Alma mater	New College, Oxford King's College London University College London
Doctoral advisor	Uta Frith
Known for	Autism research

Simon Baron-Cohen FBA^[1] (born 15 August 1958) is professor of Developmental Psychopathology in the Departments of Psychiatry and Experimental Psychology at the University of Cambridge in the United Kingdom. He is the Director of the University's Autism Research Centre,^[2] and a Fellow of Trinity College.^[3] He is best known for his work on autism, including his early theory that autism involves degrees of "mind-blindness" (or delays in the development of theory of mind); and his later theory that autism is an extreme form of the "male brain", which involved a re-conceptualisation of typical psychological sex differences in terms of empathizing–systemizing theory.

Education[link]

Baron-Cohen completed an MA in Human Sciences at New College, Oxford, and an MPhil in Clinical Psychology at the Institute of Psychiatry, King's College London. He did his PhD in Psychology at University College London under the supervision of Uta Frith.

Research areas[link]

Baron-Cohen was a co-author of the first study to show that children with autism have delays in the development of a theory of mind (ToM) (Cognition, 1985).^[4]

Baron-Cohen’s research over the subsequent 10 years provided much of the evidence for the ToM deficit, culminating in two edited anthologies (Understanding Other Minds, 1993, and 2000). His research group have linked the origins of the ToM deficit to joint attention (Brit J. Dev Psychol, 1987) and showed that absence of joint attention at 18 months is a predictor of later autism (British Journal of Psychiatry, 1992, 1996).^[5] Based on these and other findings, he proposed a model of the development of ‘mindreading’ in his widely cited monograph (Mindblindness, 1995 MIT Press). Baron-Cohen has also conducted brain imaging work examining the autistic brain. These studies highlighted differences between the typical and autistic brain in the orbitofrontal cortex (Brit. J. Psychiatry, 1994) PMID 7866679 and the amygdala (Euro. J. Neuroscience, 1999), the latter leading him to propose the amygdala theory of autism (Neurosci. Behav. Rev. 2000). In 2010, with his former doctoral student Michael Lombardo, they showed that the ventromedial prefrontal cortex does not differentiate self from other in autism and accounts for variation in social deficits.^[6] In 2011, with Lombardo, they also showed that the right temporoparietal junction was hypoactive in autism during ToM tasks and also accounted for variation in social deficits.^[7]

In the late 1990s Baron-Cohen developed the hypothesis that typical sex differences may provide a neurobiological and psychological understanding of autism (the empathizing–systemizing theory). The theory proposes that autism is an extreme of the male brain (J. Cog. Neurosci, 1997; TICS, 2002). This led to him situating ToM within the broader domain of empathy, and to the development of a new construct (systemizing). The extreme male brain (EMB) theory of autism sees autism as being on a continuum with individual differences in the general population (sex differences). Baron-Cohen proposes that the cause of autism at a biological level may be hyper-masculinization. This hypothesis posits that certain features of autism (‘obsessions’ and repetitive behaviour, previously regarded as ‘purposeless’) as being highly purposive, intelligent (hyper-systemizing), and a sign of a different way of thinking. He wrote a popular book on the topic of sex differences and its relationship to autism (The Essential Difference, 2003).

Baron-Cohen launched the Cambridge Longitudinal Foetal Testosterone (FT) Project in the late 1990s, a research program following children of mothers who had amniocentesis. This aimed to study the effects of individual differences in FT on later child development. This is summarised in a technical monograph (Prenatal Testosterone in Mind, 2004 MIT Press). This study revealed that FT is negatively correlated with social and language development, and is positively correlated with attention to detail and a number of autistic traits (Brit. J. Psychology, 2009). His work studying FT led him to test the hyper-masculinization of autism at the psychometric level and in regard to developmental neurobiology (Science, 2005; PLOS Biology, 2011). The role of foetal testosterone in autism remains to be assessed in clinical cases, but gains some support from the recent discovery from Baron-Cohen's lab of androgen-related genes being associated with autistic traits, empathy, and Asperger Syndrome (Autism Research, 2009), and from the finding that a precursor to testosterone (androstenedione) is elevated in autism (Psychoneuroendocrinology, 2011). With Mike Lombardo he conducted the first study in humans of where FT influences grey matter in the brain (J. Neuroscience 2012). He is currently collaborating with the Danish Biobank to test if FT is elevated in people who go on to develop autism.

Baron-Cohen has developed software for special education (Mindreading)^[8] and an animation series to teach children with autism to recognise and understand emotions (The Transporters)^[9] both of which were BAFTA nominated and have been scientifically evaluated to show that they have benefit to emotional and social learning in autism. Baron-Cohen's work was applied to intervention in the book "Teaching Children With Autism To Mindread" (Wiley, 1997).

Baron-Cohen has worked in another research area: synaesthesia, a neurological condition in which a sensation in one modality (e.g., hearing) triggers a perception in another modality (e.g., colour). He and his colleagues were the first to develop the Test of Genuineness (Perception, 1987) and suggest that synaesthesia is the result of a breakdown in modularity (Perception, 1993). They were also the first to confirm the existence of synaesthesia using neuroimaging (Brain, 1995 and Nature Neuroscience, 1999) and to demonstrate that it is a heritable condition, conducting the first genetic study of synaesthesia (Perception, 1996; American Journal of Human Genetics, 2009).

Baron-Cohen is co-editor in chief of the journal Molecular Autism.^[10] and is Chair of the NICE Guideline Development Group for adults with autism.

Media[link]

Baron-Cohen appeared on Private Passions, on 13 April 2008, the biographical music discussion programme hosted by Michael Berkeley on BBC Radio 3.^[11]

He was featured on the BBC news page calling for an ethical debate on the issue of a prenatal test for autism, arguing it is important to debate this in advance of such a test existing, given the pace of biomedical research in autism.^[12] In an article in 2000 (Development and Psychopathology) Baron-Cohen argued that high-functioning autism or Asperger Syndrome need not just lead to disability, but can also lead to talent.^[13] He has found over 25 years that the media largely report his work accurately but in March 2009, he wrote a piece in New Scientist on the misrepresentation over his group's research into foetal testosterone in typically developing children.^[14]

He has appeared in many television science documentaries, one example being Brainman in which he diagnosed Daniel Tammet (who has extreme memory) with both synaesthesia and Asperger Syndrome.

In 2008 Baron-Cohen assessed Gary McKinnon, the British computer hacker who had been accused of breaking into 97 United States military and NASA computer networks in 2001 and 2002, and diagnosed him as having Asperger Syndrome. McKinnon's lawyers used this diagnosis in their appeal against his extradition to the U.S., but the British High Court nonetheless ruled that McKinnon should be extradited to the U.S. to face trial.

He appeared in TIME Magazine, featuring his 'assortative mating' theory of autism.^[15]

Personal life and awards[link]

Baron-Cohen was awarded the Spearman Medal from the British Psychological Society (BPS), the McAndless Award from the American Psychological Association, the May Davison Award for Clinical Psychology from the BPS, and the Presidents Award from the BPS. He was President of the British Association for the Advancement of Science Section for Psychology in 2007, and was Vice President of the International Society for Autism Research (INSAR) for 2009-11. He is also a Vice President of the National Autistic Society (UK). He is a Fellow of the BPS, the BA, and the Association of Psychological Science.

Baron-Cohen is the son of Judith and Vivian Baron-Cohen. He is married to Bridget Lindley^[16] and together they have three children: independent film maker Sam Baron, Robin Lindley-Baron, and songwriter Kate Baron.^[17] His brothers are film director Ash Baron Cohen and Dan Baron Cohen (International Drama and Education Association). His sisters are Suzannah Baron Cohen and acupuncturist Aliza Baron Cohen. His cousins include computer scientist Amnon Baron Cohen, composer and musician Erran Baron Cohen, comic actor Sacha Baron Cohen,^[18] composer Lewis Furey, film producer Daniel Louis, playwright Richard Greenblatt, University of Washington chemistry professor Seymour Rabinovitch, University of Montana Japanese professor Judith Rabinovitch, and film-director Mark Robson.

Selected publications[link]

Books[link]

Baron-Cohen's single authored books:

• Baron-Cohen, S (1995) Mindblindness: an essay on autism and theory of mind. MIT Press/Bradford Books.
• Baron-Cohen, S (2003) The Essential Difference: men, women and the extreme male brain. Penguin/Basic Books. ISBN 978-0-7139-9671-5
• Baron-Cohen, S (2008) Autism and Asperger Syndrome: The Facts. OUP.
• Baron-Cohen, S (2011) Zero Degrees of Empathy: A new theory of human cruelty. Penguin/Allen Lane. This appears under a different title in the US:
• Baron-Cohen, S (2011) The Science of Evil: On empathy and the origins of human cruelty. Basic Books. ISBN 978-0-465-02353-0

His multi-authored and edited books include:

• Baron-Cohen, S, and Bolton, P, (1993) Autism: the facts. Oxford University Press.
• Baron-Cohen, S, Tager-Flusberg, H, and Cohen, D.J. (eds,) (1993) Understanding other minds: perspectives from autism. Oxford University Press.
• Baron-Cohen, S, & Harrison, J, (eds: 1997) Synaesthesia: classic and contemporary readings. Blackwells.
• Baron-Cohen S, ed. (1997). The maladapted mind: classic readings in evolutionary psychopathology. East Sussex, UK: Psychology Press/Taylor Francis Group. ISBN 0-86377-460-1. http://books.google.com/?id=Rdz8voFlsZAC&printsec=frontcover&dq=maladapted+mind#v=onepage&q&f=false. Retrieved 21 January 2011 </ref>
• Howlin, P, Baron-Cohen, S, Hadwin, J, & Swettenham, J, (1999). Teaching children with autism to mind-read. Wiley.
• Robertson, M, & Baron-Cohen, S, (1998) Tourette Syndrome: The facts. Oxford University Press.
• Baron-Cohen, S, Tager-Flusberg, H, & Cohen, D, (eds. 2000). Understanding other minds: perspectives from developmental cognitive neuroscience. Oxford University Press.
• Baron-Cohen, S & Wheelwright, S, (2004) An exact mind. Jessica Kingsley Ltd. Artwork by Peter Myers.
• Baron-Cohen, S, Lutchmaya, S, & Knickmeyer, R, (2005) Prenatal testosterone in mind: Studies of amniotic fluid. MIT Press/Bradford Books.
• Baron-Cohen, S, Tager-Flusberg, H, and Cohen, D.J. (eds,) (2007) Understanding other minds: perspectives from developmental cognitive neuroscience – 2nd Edition. Oxford University Press.
• Hadwin, J, Howlin, P, & Baron-Cohen, S, (2008) Teaching children with autism to mindread: a handbook. Wiley.

Papers[link]

Baron-Cohen has authored over 250 peer-reviewed papers, including:

• Baron-Cohen, S, Leslie, A.M., & Frith, U, (1985) Does the autistic child have a “theory of mind?” Cognition, 21, 37-46.
• Baron-Cohen, S, Wyke, M, & Binnie, C, (1987) Hearing words and seeing colours: an experimental investigation of a case of synaesthesia. Perception, 16, 761-67.
• Baron-Cohen, S, Allen, J, & Gillberg, C, (1992) Can autism be detected at 18 months? The needle, the haystack, and the CHAT. British Journal of Psychiatry, 161, 839-843.
• Baron-Cohen, S, (1994) How to build a baby that can read minds: Cognitive mechanisms in mindreading. Cahiers de Psychologie Cognitive/ Current Psychology of Cognition, 13, 513-552.
• Baron-Cohen, S, Ring, H, Moriarty, J, Shmitz, P, Costa, D, & Ell, P, (1994) Recognition of mental state terms: a clinical study of autism, and a functional neuroimaging study of normal adults. British Journal of Psychiatry, 165, 640-649.
• Baron-Cohen, S, Cox, A, Baird, G, Swettenham, J, Drew, A, Nightingale, N, Morgan, K, & Charman, T, (1996) Psychological markers of autism at 18 months of age in a large population. British Journal of Psychiatry, 168, 158-163.
• Baron-Cohen, S, Jolliffe, T, Mortimore, C, & Robertson, M (1997) Another advanced test of theory of mind: evidence from very high functioning adults with autism or Asperger Syndrome. Journal of Child Psychology and Psychiatry, 38, 813-822.
• Baron-Cohen, S, Wheelwright, S, Stott, C, Bolton, P, & Goodyer, I, (1997) Is there a link between engineering and autism? Autism, 1, 101-108.
• Baron-Cohen, S, Ring, H, Wheelwright, S, Bullmore, E, Brammer, M, Simmons, A, & Williams, S, (1999) Social intelligence in the normal and autistic brain: an fMRI study. European Journal of Neuroscience, 11, 1891-1898.
• Baron-Cohen, S, Ring, H, Bullmore, E, Wheelwright, S, Ashwin, C, & Williams, S, (2000) The amygdala theory of autism. Neuroscience and Behavioural Reviews, 24, 355-364.
• Connellan, J, Baron-Cohen, S, Wheelwright, S, Ba’tki, A, & Ahluwalia, J, (2000) Sex differences in human neonatal social perception. Infant Behavior and Development, 23, 113-118.
• Baron-Cohen, S, & Wheelwright, S, Skinner, R, Martin, J, & Clubley, E, (2001) The Autism-Spectrum Quotient: Evidence from Asperger Syndrome/high-functioning autism, males and females, scientists, and mathematicians. Journal of Autism and Developmental Disorders, 31, 5-17.
• Baron-Cohen, S, (2002) The extreme male brain theory of autism. Trends in Cognitive Sciences, 6, 248-254.
• Lutchmaya, S, Baron-Cohen, S, & Raggatt, P, (2002) Foetal testosterone and eye contact in 12-month-old infants. Infant Behaviour and Development, 25, 327-335.
• Nunn, J, Gregory, L, Morris, R, Brammer, M, Bullmore, E, Harrison, J, Williams, S, Baron-Cohen, S, and Gray, J, (2002) Functional magnetic resonance imaging of synaesthesia: activation of colour vision area V4/V8 by spoken words. Nature Neuroscience, 5, 371-375.
• Baron-Cohen, S, & Wheelwright, S, (2004) The Empathy Quotient (EQ). An investigation of adults with Asperger Syndrome or High Functioning Autism, and normal sex differences. Journal of Autism and Developmental Disorders, 34, 163-175.
• Baron-Cohen, S, Knickmeyer, R, & Belmonte, M (2005) Sex differences in the brain: implications for explaining autism. Science, 310, 819-823.
• Chapman, E, Baron-Cohen, S, Auyeung, B, Knickmeyer, R, Taylor, K & Hackett, G (2006) Foetal testosterone and empathy: evidence from the Empathy Quotient (EQ) and the ‘Reading the Mind in the Eyes’ Test’. Social Neuroscience, 1, 135-148.
• Auyeung, B, Baron-Cohen, S, Chapman, E, Knickmeyer, R, Taylor, K & Hackett, G, (2009) Foetal testosterone and autistic traits. British Journal of Psychology, 100, 1-22.
• Baron-Cohen, S, Scott, F, J, Allison, C, Williams, J, Bolton, P, Matthews, F, E, & Brayne, C, (2009) Autism Spectrum Prevalence: a school-based U.K. population study. British Journal of Psychiatry, 194, 500-509.
• Chakrabarti, B, Dudridge, F, Kent, L, Wheelwright, S, Hill-Cawthorne, G, Allison, C, Banerjee-Basu, S, & Baron-Cohen, S, (2009) Genes related to sex-steroids, neural growth and social-emotional behaviour are associated with autistic traits, empathy and Asperger Syndrome. Autism Research, 2, 157-177.
• Asher, J, Lamb, J, A, Brocklebank, D, Cazier, J-B, Maestrini, E, Addis, L, Sen, M, Baron-Cohen, S, & Monaco, A, P, (2009) A whole-genome scan and fine-mapping linkage study of autidory-visual synthethesia reveals evidence of linkage to chromosomes 2q24, 5q33, 6p12 and 12p12. The American Journal of Human Genetics, 84, 279-285.
• Baron-Cohen, S, Golan, O, & Ashwin, E, (2009) Can emotion recognition be taught to children with autism spectrum conditions? Proceedings of the Royal Society, Series B, Special Issue, 364, 3567-3574.
• Auyeung, B, Taylor, K, Hackett, G, & Baron-Cohen, S, (2010) Fetal testosterone and autistic traits in 18 to 24-month-old children, Molecular Autism, 1:11.
• Chura, L, Lombardo, M, Ashwin, E, Auyeung, B, Chakrabarti, B, Bullmore, E, T, & Baron-Cohen, S, (2010) Organizational effects of fetal testosterone on human corpus callosum size and asymmetry. Psychoneuroendocrinology, 35, 122-132.
• Golan, O, Baron-Cohen, S, Ashwin, E, Granader, Y, McClintock, S, Day, K, & Leggett, V, (2010) Enhancing emotion recognition in children with autism spectrum conditions: an intervention using animated vehicles with real emotional faces. Journal of Autism and Developmental Disorders, 40, 269-279.
• Lombardo, M, Chakrabarti, B, Bullmore, E, Sadek, S, Pasco, G, Wheelwright, S, Suckling, J, MRC AIMS Consortium & Baron-Cohen, S, (2010) Atypical neural self-representation in autism. Brain, 133, 611-624.
• Lombardo, M, Chakrabarti, B, Bullmore, E, & Wheelwright, S, Sadek, S, Suckling, J, MRC AIMS Consortium & Baron-Cohen, S, (2010) Shared neural circuits for mentalizing about the self and others. Journal of Cognitive Neuroscience, 277, 1623-1635.
• Wheelwright, S, Auyeung, B, Allison, C, & Baron-Cohen, S, (2010) Defining the broader, medium and narrow autism phenotype among parents using the Autism Spectrum Quotient (AQ). Molecular Autism,1, 10.
• Lombardo, M, Chakrabarti; B, Bullmore, E, MRC AIMS Consortium and Baron-Cohen, S, (2011). Specialization of right temporo-parietal junction for mentalizing and its relation to social impairments in autism. NeuroImage 2011 Feb 26 [Epub ahead of print].
• Baron-Cohen, S, Lombardo, M, Auyeung, B, Ashwin, E, Chakrabarti, B, & Knickmeyer, R, (2011) Why are Autism Spectrum Conditions more prevalent in males? Public Library of Science Biology. 9, 1-10 And Supplementary Material to ‘Why are autism spectrum conditions more prevalent in males?’.

See also[link]

• Autism Spectrum Quotient
• Empathizing-systemizing theory
• Sally-Anne test
• Empathy
• Gender differences

References[link]

External links[link]

• They just can't help it, Simon Baron-Cohen, The Guardian (17 April 2003)
• The Male Condition, Simon Baron-Cohen, The New York Times Op-Ed Section, (8 August 2005)
• The Assortative Mating Theory: A Talk with Simon Baron-Cohen, Edge Foundation discussion, 2005
• Autism Research Centre - ARC people : Simon Baron-Cohen
• The Short Life of a Diagnosis Simon Baron-Cohen, The New York Times Op-Ed Section, (November 9, 2009)
• Why a lack of empathy is the root of all evil, Clint Witchalls, The Independent Featured Book Review in Health and Families Section, (5 April 2011)
• The Psychology of Evil Radio interview on Philosophy Talk
• The Science of Evil: On Empathy and the Origins of Cruelty, Simon Baron-Cohen, (The Montréal Review, October, 2011)

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