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Soil erosion is the displacement of the
upper
upper
layer of
soil Soil is a mixture In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, comp ...

soil
; it is a form of
soil degradation Soil retrogression and degradation are two regressive evolution processes associated with the loss of equilibrium of a stable A stable is a building in which livestock Livestock is commonly defined as domesticated Domestication is a sust ...
. This natural process is caused by the dynamic activity of erosive agents, that is,
water Water (chemical formula H2O) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known li ...

water
,
ice Ice is water Water (chemical formula H2O) is an , transparent, tasteless, odorless, and , which is the main constituent of 's and the s of all known living organisms (in which it acts as a ). It is vital for all known forms of , eve ...

ice
(glaciers),
snow Snow comprises individual ice Ice is water Water (chemical formula H2O) is an , transparent, tasteless, odorless, and , which is the main constituent of 's and the s of all known living organisms (in which it acts as a ). ...

snow
,
air The atmosphere of Earth is the layer of gas Gas is one of the four fundamental states of matter In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (ph ...
(wind),
plants Plants are predominantly photosynthetic Photosynthesis is a process used by plants and other organisms to convert Conversion or convert may refer to: Arts, entertainment, and media * Conversion (Doctor Who audio), "Conversion" (''Docto ...

plants
,
animals Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells ...

animals
, and
humans Humans (''Homo sapiens'') are the most abundant and widespread species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A speci ...

humans
. In accordance with these agents, erosion is sometimes divided into water erosion,
glacial erosion In earth science Earth science or geoscience includes all fields of natural science Natural science is a branch of science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific ...
, snow erosion, wind (aeolean) erosion, zoogenic erosion and anthropogenic erosion such as tillage 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 Topsoil is the upper, outermost layer of soil Soil is a mixture In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements t ...
. The loss of soil from farmland may be reflected in reduced
crop A crop is a plant that can be grown and harvested extensively for profit or subsistence. Crops may refer either to the harvested parts or to the harvest in a more refined state. Most crops are cultivated in agriculture Agriculture is th ...

crop
production potential, lower surface
water quality Water quality refers to the chemical A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touche ...

water quality
and damaged drainage networks. Soil erosion could also cause
sinkholes A sinkhole, also known as a cenote, sink, sink-hole, swallet, swallow hole, or doline (the different terms for sinkholes are often used interchangeably), is a depression or hole in the ground caused by some form of collapse of the surface lay ...

sinkholes
. Human activities have increased by 10–50 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 Agricultural productivity is measured as the ratio of agricultural Agriculture is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary Image:Family watching television 1958.jpg, ...
and (on
natural landscape A natural landscape is the original landscape that exists before it is acted upon by human culture. The natural landscape and the cultural landscape are separate parts of the landscape. However, in the 21st century, landscapes that are totally u ...

natural landscape
s)
ecological collapse Ecological collapse refers to a situation where an ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together t ...
, both because of loss of the nutrient-rich upper soil layers. In some cases, the eventual end result is
desertification Desertification is a type of land degradation Land degradation is a process in which the value of the biophysical environment is affected by a combination of human-induced processes acting upon the land. It is viewed as any change or distu ...
. Off-site effects include sedimentation of waterways and
eutrophication Eutrophication (from Greek ''eutrophos'', "well-nourished") is the process by which an entire body of water (Lysefjord) in Norway Norway, officially the Kingdom of Norway,Names in the official and recognised languages: Bokmål Bokm ...

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 Land degradation is a process in which the value of the biophysical environment A biophysical environment is a life, biotic and Abiotic component, abiotic surrounding of an organism or population, and consequently includes the factors that ...
; combined, they are responsible for about 84% of the global extent of degraded land, making excessive erosion one of the most significant
environmental problems Environmental issues are harmful effects of human activity on the biophysical environment. Environmental protection Environmental protection is the practice of protecting the natural environment by individuals, organizations and governments. Its o ...
worldwide.
Intensive agriculture Intensive agriculture, also known as intensive farming (as opposed to extensive farming Extensive farming or extensive agriculture (as opposed to intensive farming) is an agricultural Agriculture is the science, art and practice of cultiv ...
,
deforestation deforestation in 1750-2004 (net loss) showing anthropogenic modification of remaining forest. File:MODIS (2020-08-01).jpg, 300px, Dry seasons, exacerbated by climate change, and the use of slash-and-burn methods for clearing tropical forest ...

deforestation
,
road A road is a wide way leading from one place to another, typically one with a specially prepared surface which vehicles and bikes can use. Roads consist of one or two roadway A carriageway (British English British English (BrE) is the ...

road
s, anthropogenic
climate change Contemporary climate change includes both the global warming caused by humans, and its impacts on Earth's weather patterns. There have been previous periods of climate change, but the current changes are more rapid than any known even ...
and
urban sprawl Urban sprawl (also known as suburban sprawl or urban encroachment) is the unrestricted growth in many urban area An urban area, or built-up area, is a human settlement with a high population density and infrastructure of built environment. ...
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.


Physical processes


Rainfall and surface runoff

Rainfall Rain is liquid water in the form of droplet Rain water flux from a canopy. Among the forces that govern drop formation: cohesion, Van der Waals force">Cohesion_(chemistry).html" ;"title="surface tension, Cohesion (chemistry)">cohesion, ...

Rainfall
, and the
surface runoff Surface runoff (also known as overland flow) is the flow of water Water (chemical formula H2O) is an , transparent, tasteless, odorless, and , which is the main constituent of 's and the s of all known living organisms (in which it ac ...
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). In ''splash erosion'', the impact of a falling raindrop creates a small crater in the soil,See figure 4 in ejecting soil particles. 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 Transport (in British English British English (BrE) is the standard dialect A standard language (also standard variety, standard dialect, and standard) is a language variety that has undergone substantial codification of grammar and ...
loosened soil particles (
sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently sediment transport, transported by the action of wind, water, or ice or by the force of gravity acting on the particles. ...

sediment
) down the slope. ''Sheet erosion'' is the transport of loosened soil particles by overland flow. ''
Rill In hillslope geomorphology, a rill is a shallow Channel (geography), channel (no more than a few tens of centimetres deep) cut into soil by the erosion, erosive action of Overland flow, flowing water. Similar but smaller incised channels are kno ...
erosion'' refers to the development of small,
ephemeral Ephemerality (from the Greek language, Greek word , meaning 'lasting only one day') is the concept of things being transitory, existing only briefly. Typically the term ephemeral is used to describe objects found in nature, although it can descr ...
concentrated flow paths which function as both sediment source and
sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently sediment transport, transported by the action of wind, water, or ice or by the force of gravity acting on the particles. ...

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 centimeters (about an inch) or less and along-channel slopes may be quite steep. This means that rills exhibit
hydraulic Hydraulics (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is a ...

hydraulic
physics very different from water flowing through the deeper wider channels of streams and rivers. ''
Gully erosion A gully is a landform created by running water, mass movement, or commonly a combination of both erosion, eroding sharply into soil or other relatively erodible material, typically on a hillside or in river floodplains or terraces. Gullies resem ...

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.


Rivers and streams

''Valley'' or ''stream erosion'' occurs with continued water flow along a linear feature. The erosion is both downward, deepening the valley, and , 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 In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology), rocks of which it is composed, and the processe ...
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
meander A meander is one of a series of regular sinuous curves in the channel of a river or other watercourse. It is produced as a watercourse erodes the sediment Sediment is a naturally occurring material that is broken down by processes of weath ...

meander
s 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,
pebble A pebble is a clast Clastic rocks are composed of fragments, or clasts, of pre-existing minerals In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth ...

pebble
s and
boulder In geology Geology (from the Ancient Greek Ancient Greek includes the forms of the Greek language Greek ( el, label=Modern Greek Modern Greek (, , or , ''Kiní Neoellinikí Glóssa''), generally referred to by speake ...

boulder
s can also act erosively as they traverse a
surface File:Water droplet lying on a damask.jpg, Water droplet lying on a damask. Surface tension is high enough to prevent floating below the textile. A surface, as the term is most generally used, is the outermost or uppermost layer of a physical obje ...
, in a process known as ''traction''. ''Bank erosion'' is the wearing away of the banks of a
stream A stream is a body of water (Lysefjord) in Norway Norway, officially the Kingdom of Norway,Names in the official and recognised languages: Bokmål Bokmål (, ; literally "book tongue") is an official written standard for the No ...

stream
or
river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of wate ...

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. ''Thermal erosion'' is the result of melting and weakening
permafrost Permafrost is ground that continuously remains below 0 °C (32 °F) for two or more years, located on land or under the ocean The ocean (also the or the world ocean) is the body of that covers approximately 70.8% of the surfa ...

permafrost
due to moving water. It can occur both along rivers and at the coast. Rapid
river channel migrationRiver channel migration is the geomorphological process that involves the lateral migration of an alluvial channel (geography), river channel across its floodplain. This process is mainly driven by the combination of bank erosion of and point bar dep ...
observed in the
Lena River The Lena (russian: link=no, Ле́на, ; evn, Елюенэ, ''Eljune''; sah, Өлүөнэ, ''Ölüöne''; bua, Зүлхэ, ''Zülkhe''; mn, Зүлгэ, ''Zülge'') is the easternmost of the three great Siberian rivers that flow into the Arcti ...
of
Siberia Siberia (; rus, Сибирь, r=Sibir', p=sʲɪˈbʲirʲ, a=Ru-Сибирь.ogg) is an extensive geographical region, constituting all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has been a part of R ...

Siberia
is due to thermal erosion, as these portions of the banks are composed of permafrost-cemented non-cohesive materials. Much of this erosion occurs as the weakened banks fail in large slumps. Thermal erosion also affects the
Arctic The Arctic ( or ) is a polar regions of Earth, polar region located at the northernmost part of Earth. The Arctic consists of the Arctic Ocean, adjacent seas, and parts of Alaska (United States), Canada, Finland, Greenland (Danish Realm, ...

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 segment of the Beaufort Sea shoreline averaged per year from 1955 to 2002.


Floods

At extremely high flows,
kolk KOLK 94.3 FM broadcasting, FM is a radio station licensed to Lakeside, Montana. The station broadcasts a country music format and is owned by KOFI, Inc.
s, or
vortices , revealed by colored smoke In fluid dynamics In physics and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids—liquids and gases. It has several subdisciplines, including aerodynamics (the ...

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 basin A rock-cut basin, in this usage of the term, is a natural phenomenon. They are cylindrical depressions cut into stream or river beds, often filled with water. Such plucked-bedrock pits are created by kolks; powerful vortices within the water curren ...
s. Examples can be seen in the flood regions result from glacial
Lake Missoula Sediment deposited by the lake with a hammer for scale. Lake Missoula was a prehistoric proglacial lake in western Montana Montana () is a U.S. state, state in the Mountain states, Mountain West region of the United States. It is borde ...
, which created the
channeled scablands Drumheller Channels The Channeled Scablands at one time were a relatively barren and soil-free region of interconnected relict and dry flood channels, coulees and cataracts A cataract is a cloudy area in the lens (anatomy), lens of the ey ...

channeled scablands
in the Columbia Basin region of eastern
Washington Washington commonly refers to: * Washington (state), United States * Washington, D.C., the capital of the United States ** Federal government of the United States (metonym) ** Washington metropolitan area, the metropolitan area centered on Washingt ...
.


Wind erosion

Wind erosion is a major
geomorphological incised into shale at the foot of the North Caineville Plateau, Utah, within the pass carved by the Fremont River (Utah), Fremont River and known as the Blue Gate. Grove Karl Gilbert, GK Gilbert studied the landscapes of this area in great detail, ...
force, especially in
arid A region is arid when it is characterized by a severe lack of available water, to the extent of hindering or preventing the growth and development Development or developing may refer to: Arts *Development hell, when a project is stuck in d ...
and
semi-arid A semi-arid climate, semi-desert climate, or steppe climate is the climate Climate is the long-term pattern of weather Weather is the state of the atmosphere An atmosphere (from the greek words ἀτμός ''(atmos)'', meaning ' ...
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 deforestation in 1750-2004 (net loss) showing anthropogenic modification of remaining forest. File:MODIS (2020-08-01).jpg, 300px, Dry seasons, exacerbated by climate change, and the use of slash-and-burn methods for clearing tropical forest ...

deforestation
,
urbanization Urbanization (or urbanisation) refers to the population shift from rural File:Rural landscape in Finland.jpg, A rural landscape in Lappeenranta, South Karelia, Finland. 15 July 2000. In general, a rural area or a countryside is a geographi ...
, and
agriculture Agriculture is the science, art and practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary Image:Family watching television 1958.jpg, Exercise trends, Increases in sedentary behaviors su ...

agriculture
. Wind erosion is of two primary varieties: ''
deflation In economics Economics () is a social science that studies the Production (economics), production, distribution (economics), distribution, and Consumption (economics), consumption of goods and services. Economics focuses on the behav ...

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 Saltation may refer to: * Saltation (biology), an evolutionary hypothesis emphasizing sudden and drastic change * Saltation (geology), a process of particle transport by fluids * Cutaneous rabbit illusion (sensory saltation), a perceptual illusion ...
'', where particles are lifted a short height into the air, and bounce and saltate across the surface of the soil; and (3) ''
suspension Suspension or suspended may refer to: Science and engineering * Suspension (topology), in mathematics * Suspension (dynamical systems), in mathematics * Suspension of a ring, in mathematics * Suspension (chemistry), small solid particles suspende ...
'', 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%). Silty soils tend to be the most affected by wind erosion; silt particles are relatively easily detached and carried away. Wind erosion is much more severe in arid areas and during times of drought. For example, in the
Great Plains The Great Plains (french: Grandes Plaines), sometimes simply "the Plains", is a broad expanse of flatland ''Flatland: A Romance of Many Dimensions'' is a satire, satirical novella by the English schoolmaster Edwin Abbott Abbott, first publi ...
, 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.


Mass movement

''
Mass movement A mass movement denotes a political party or movement which is supported by large segments of a population. Political movements that typically advocate the creation of a mass movement include the ideologies of communism Communism (from L ...
'' is the downward and outward movement of rock and sediments on a sloped surface, mainly due to the force of
gravity Gravity (), or gravitation, is a by which all things with or —including s, s, , and even —are attracted to (or ''gravitate'' toward) one another. , gravity gives to s, and the causes the s of the oceans. The gravitational attracti ...

gravity
. 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. It moves material from higher elevations to lower elevations where other eroding agents such as streams and
glacier A glacier (; ) is a persistent body of dense ice Ice is into a state. Depending on the presence of such as particles of soil or bubbles of air, it can appear transparent or a more or less bluish-white color. In the , ice is abunda ...

glacier
s 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 Landslides, also known as landslips, are several forms of mass wasting Mass wasting, also known as mass movement, is a general term for the movement of rock Rock most often refers to: * Rock (geology) A rock is any naturally occurri ...

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 Scree is a collection of broken rock Rock most often refers to: * Rock (geology) A rock is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the minerals included, its Chemical compound ...

scree
slope. ''
Slumping Slumping is a technique in which items are made in a kiln , Wrecclesham, Surrey Surrey () is a county in South East England which borders Kent to the east, East Sussex to the southeast, West Sussex to the south, Hampshire to the west, B ...
'' happens on steep hillsides, occurring along distinct fracture zones, often within materials like
clay Clay is a type of fine-grained natural soil Surface-water- gley developed in glacial till, Northern Ireland.">Northern_Ireland.html" ;"title="glacial till, Northern Ireland">glacial till, Northern Ireland. Soil is a mixture of organic m ...

clay
that, once released, may move quite rapidly downhill. They will often show a spoon-shaped
isostatic depression Isostatic depression is the sinking of large parts of the Earth's crust into the asthenosphere The asthenosphere ( grc, ἀσθενός 'asthenos''meaning "without strength", and thus "weak", and 'sphaira''meaning "sphere") is the highly vis ...
, 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
highway A highway is any public or private road A road is a wide way leading from one place to another, typically one with a specially prepared surface which vehicles and bikes can use. Roads consist of one or two roadways (British English: ...

highway
s where it is a regular occurrence. ''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 in diameter by wind along the soil surface.


Tillage erosion


Factors affecting soil erosion


Climate

The amount and intensity of
precipitation In meteorology Meteorology is a branch of the (which include and ), with a major focus on . The study of meteorology dates back , though significant progress in meteorology did not begin until the 18th century. The 19th century saw mod ...

precipitation
is the main 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 Vegetation is an assemblage of plant Plants are predominantly photosynthetic Photosynthesis is a process used by plants and other organisms to Energy transformation, convert light energy into chemical energy that, through cellular re ...

vegetation
. This might be during periods when leave the soil bare, or in
semi-arid A semi-arid climate, semi-desert climate, or steppe climate is the climate Climate is the long-term pattern of weather Weather is the state of the atmosphere An atmosphere (from the greek words ἀτμός ''(atmos)'', meaning ' ...
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, with higher intensity rainfall generally resulting in more soil erosion by water. The size and velocity of
rain drop Raindrops in a plant. A drop or droplet is a small column of liquid, bounded completely or almost completely by free surfaces. A drop may form when liquid accumulates at the lower end of a tube or other surface boundary, producing a hanging dr ...

rain drop
s is also an important factor. Larger and higher-velocity rain drops have greater
kinetic energy In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regular ...
, and thus their impact will displace soil particles by larger distances than smaller, slower-moving rain drops. In other regions of the world (e.g.
western Europe Western Europe is the western region of Europe Europe is a continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven geographical r ...

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


Soil structure and composition

The composition, moisture, and compaction of soil are all major factors in determining the erosivity of rainfall. Sediments containing more
clay Clay is a type of fine-grained natural soil Surface-water- gley developed in glacial till, Northern Ireland.">Northern_Ireland.html" ;"title="glacial till, Northern Ireland">glacial till, Northern Ireland. Soil is a mixture of organic m ...

clay
tend to be more resistant to erosion than those with sand or silt, because the clay helps bind soil particles together. 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. 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 rainwater, leading to higher levels of surface runoff and thus higher erosivity for a given volume of rainfall.
Soil compaction In geotechnical engineering Geotechnical engineering, also known as geotechnics, is the branch of concerned with the engineering behavior of . It uses the principles of and for the solution of its respective problems. It also relies on k ...
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.


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 and wind erosion. The removal of vegetation increases the rate of surface erosion.


Topography

The topography of the land determines the velocity at which
surface runoff Surface runoff (also known as overland flow) is the flow of water Water (chemical formula H2O) is an , transparent, tasteless, odorless, and , which is the main constituent of 's and the s of all known living organisms (in which it ac ...
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.


Human activities that increase soil erosion


Agricultural practices

Unsustainable agricultural practices increase rates of erosion by one to two
orders of magnitude An order of magnitude is an approximation of the logarithm In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geome ...
over the natural rate and far exceed replacement by soil production. The
tillage Tillage is the agricultural Agriculture is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary Image:Family watching television 1958.jpg, Exercise trends, Increases in sedentary ...
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 Deep plowing is a plowing A plough or plow ( US; both ) is a farm tool for loosening or turning the soil before sowing Sowing is the process of planting. An area or object that has had seeds planted in it will be described as a sowed area ...
, 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. A complex overall situation with respect to defining nutrient losses from soils, could arise as a result of the size selective nature of soil erosion events. Loss of total phosphorus, for instance, in the finer eroded fraction is greater relative to the whole soil. Extrapolating this evidence to predict subsequent behaviour within receiving aquatic systems, the reason is that this more easily transported material may support a lower solution P concentration compared to coarser sized fractions. 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. Heavy grazing reduces vegetative cover and causes severe soil compaction, both of which increase erosion rates.


Deforestation

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 porosity, porous and highly permeability (earth sciences), permeable to rainfall, and allow rainwater to slow percolate into the soil below, instead of flowing over the surface as surface runoff, runoff. The roots of the trees and plants hold together soil particles, preventing them from being washed away. 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 In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regular ...
. However it is the forest floor, more than the canopy, that prevents surface erosion. The terminal velocity of rain drops is reached in about . Because forest canopies are usually higher than this, rain drops can often regain terminal velocity even after striking the canopy. However, the intact forest landscape, intact forest floor, with its layers of leaf litter and organic matter, is still able to absorb the impact of the rainfall. Deforestation causes increased erosion rates due to exposure of mineral
soil Soil is a mixture In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, comp ...

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. 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 Vegetation is an assemblage of plant Plants are predominantly photosynthetic Photosynthesis is a process used by plants and other organisms to Energy transformation, convert light energy into chemical energy that, through cellular re ...

vegetation
, with gully erosive furrows typically in excess of deep and 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.


Roads and urbanization

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. Much of the sediment carried in runoff from urban areas (especially roads) is highly contaminated with fuel, oil, and other chemicals. 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.


Climate change

The warmer atmospheric temperatures observed over the past decades are expected to lead to a more vigorous hydrological cycle, including more extreme rainfall events. The rise in sea levels that has occurred as a result of climate change has also greatly increased coastal erosion rates. Studies on soil erosion suggest that increased rainfall amounts and intensities will lead to greater rates of soil 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. Studies by Pruski and Nearing indicated that, other factors such as land use unconsidered, it is reasonable to expect approximately a 1.7% change in soil erosion for each 1% change in total precipitation under climate change. In recent studies, there are predicted increases of rainfall erosivity by 17% in the United States, by 18% in Europe, and globally 30 to 66%


Global environmental effects

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.


Land degradation

Water and wind erosion are now the two primary causes of
land degradation Land degradation is a process in which the value of the biophysical environment A biophysical environment is a life, biotic and Abiotic component, abiotic surrounding of an organism or population, and consequently includes the factors that ...
; combined, they are responsible for 84% of degraded acreage. 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. Approximately 40% of the world's agricultural land is seriously degraded. According to the United Nations, an area of fertile soil the size of Ukraine is lost every year because of drought,
deforestation deforestation in 1750-2004 (net loss) showing anthropogenic modification of remaining forest. File:MODIS (2020-08-01).jpg, 300px, Dry seasons, exacerbated by climate change, and the use of slash-and-burn methods for clearing tropical forest ...

deforestation
and
climate change Contemporary climate change includes both the global warming caused by humans, and its impacts on Earth's weather patterns. There have been previous periods of climate change, but the current changes are more rapid than any known even ...
. 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 United Nations University, UNU's Ghana-based Institute for Natural Resources in Africa. Recent modeling developments have quantified rainfall erosivity at global scale using high temporal resolution (<30 min) and high fidelity rainfall recordings. The results is an extensive global data collection effort produced the Global Rainfall Erosivity Database (GloREDa) which includes rainfall erosivity for 3,625 stations and covers 63 countries. This first ever Global Rainfall Erosivity Database was used to develop a global erosivity map at 30 arc-seconds(~1 km) based on sophisticated geostatistical process. According to a new study published in Nature Communications, almost 36 billion tons of soil is lost every year due to water, and deforestation and other changes in land use make the problem worse. The study investigates global soil erosion dynamics by means of high-resolution spatially distributed modelling (ca. 250 × 250 m cell size). The geo-statistical approach allows, for the first time, the thorough incorporation into a global soil erosion model of land use and changes in land use, the extent, types, spatial distribution of global croplands and the effects of different regional cropping systems. 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.


Sedimentation of aquatic ecosystems

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. 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. 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 Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently sediment transport, transported by the action of wind, water, or ice or by the force of gravity acting on the particles. ...

sediment
originates primarily from water erosion in the Loess Plateau region of the northwest.


Airborne dust pollution

Soil particles picked up during wind erosion of soil 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. Dust from erosion acts to suppress rainfall and changes the sky color from blue to white, which leads to an increase in red sunsets. Dust events have been linked to a decline in the health of coral reefs across the Caribbean and Florida, primarily since the 1970s. Similar dust plumes originate in the Gobi desert, which combined with pollutants, spread large distances downwind, or eastward, into North America.


Monitoring, measuring and modeling soil erosion

Monitoring and modeling of erosion processes can help people better understand the Soil erosion#Factors affecting soil erosion, causes of soil erosion, make predictions of erosion Scenario planning, under a range of possible conditions, and plan the implementation of Soil erosion#Prevention and remediation, preventative and restorative strategies for erosion. However, the complexity of erosion processes and the number of scientific disciplines that must be considered to understand and model them (e.g. climatology, hydrology, geology, soil science, agriculture, chemistry, physics, etc.) makes accurate modelling challenging. 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. The most commonly used model for predicting soil loss from water erosion is the ''Universal Soil Loss Equation, Universal Soil Loss Equation (USLE)''. This was developed in the 1960s and 1970s. It estimates the average annual soil loss ''A'' on a plot-sized area as: : ''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, ''C'' is the cover and management factor and ''P'' is the support practices factor. Despite the USLE's Universal Soil Loss Equation#Description of USLE, plot-scale spatial basis, the model has often been used to estimate soil erosion on much larger areas, such as Drainage basin, watersheds, continents, and globally. One major problem is that the USLE cannot simulate gully erosion, and so erosion from gullies is ignored in any USLE-based assessment of erosion. Yet erosion from gullies can be a substantial proportion (10–80%) of total erosion on cultivated and grazed land. During the 50 years since the introduction of the USLE, many other soil erosion models have been developed. But because of the complexity of soil erosion and its constituent processes, all erosion models can only roughly approximate actual erosion rates when Forecast verification, validated i.e. when model predictions are compared with real-world measurements of erosion. Thus new soil erosion models continue to be developed. Some of these remain USLE-based, e.g. the G2 model. Other soil erosion models have largely (e.g. the WEPP, Water Erosion Prediction Project model) or wholly (e.g. RHEM, the Rangeland Hydrology and Erosion Model ) abandoned usage of USLE elements. Global studies continue to be based on the USLE


Prevention and remediation

The most effective known method for erosion prevention is to increase vegetative cover on the land, which helps prevent both wind and water erosion. Terrace (agriculture), Terracing is an extremely effective means of erosion control, which has been practiced for thousands of years by people all over the world. 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. 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, carbon sequestration, and aesthetic improvements to the agricultural landscape. Traditional planting methods, such as mixed-cropping (instead of monocropping) and crop rotation have also been shown to significantly reduce erosion rates. Crop residues play a role in the mitigation of erosion, because they reduce the impact of raindrops breaking up the soil particles. There is a higher potential for erosion when producing potatoes than when growing cereals, or oilseed crops. Forages have a fibrous root system, which helps combat erosion by anchoring the plants to the top layer of the soil, and covering the entirety of the field, as it is a non-row crop. In tropical coastal systems, properties of mangroves have been examined as a potential means to reduce soil erosion. Their complex root structures are known to help reduce wave damage from storms and flood impacts while binding and building soils. These roots can slow down water flow, leading to the deposition of sediments and reduced erosion rates. However, in order to maintain sediment balance, adequate mangrove forest width needs to be present.Spalding M, McIvor A, Tonneijck FH, Tol S and van Eijk P (2014) Mangroves for coastal defence. Guidelines for coastal managers & policy makers. Published by Wetlands International and The Nature Conservancy. 42 p


See also

* Badlands * Biorhexistasy * Bridge scour * Cellular confinement * Coastal sediment supply * Food security * Geomorphology * Groundwater sapping * Highly erodible land * Ice jacking * Lessivage * Riparian zone * Sediment transport * Soil horizon * Soil type * Sphericity * TERON (Tillage erosion) * Tillage erosion * Vegetation and slope stability * Vetiver System


Notes


Further reading

* * * Montgomery, David R. (2007
Soil erosion and agricultural sustainability
PNAS 104: 13268–13272. * *
Mainguet M. & Dumay F., 2011. Fighting wind erosion. One aspect of the combat against desertification. Les dossiers thématiques du CSFD. N°3. May 2011. CSFD/Agropolis International, Montpellier, France. 44 pp.
*


External links


The Soil Erosion Site

International Erosion Control Association

Soil Erosion Data
in the European Soil Portal


The Soil and Water Conservation Society
{{Authority control Soil erosion,