Eolian processes
Encyclopedia
Aeolian processes pertain to the activity of the wind
s and more specifically, to the winds' ability to shape the surface of the Earth
and other planet
s. Winds may erode, transport, and deposit materials, and are effective agents in regions with sparse vegetation
and a large supply of unconsolidated sediment
s. Although water is a much more powerful eroding force than wind, aeolian processes are important in arid environments such as desert
s.
The term is derived from the name of the Greek god, Æolus, the keeper of the winds.
the Earth's surface by deflation (the removal of loose, fine-grained particles), by the turbulent
eddy
action of the wind and by abrasion
(the wearing down of surfaces by the grinding action and sandblasting of windborne particles).
Regions which experience intense and sustained erosion are called deflation zones. Most aeolian deflation zones are composed of desert pavement
, a sheet-like surface of rock fragments that remains after wind and water have removed the fine particles. Almost half of Earth's desert surfaces are stony deflation zones. The rock mantle
in desert pavement
s protects the underlying material from deflation.
A dark, shiny stain, called desert varnish
or rock varnish, is often found on the surfaces of some desert rocks that have been exposed at the surface for a long period of time. Manganese
, iron oxide
s, hydroxide
s, and clay
minerals form most varnishes and provide the shine.
Deflation basins, called blowout
s, are hollows formed by the removal of particles by wind. Blowouts are generally small, but may be up to several kilometers in diameter.
Wind-driven grains abrade landform
s. Grinding by particles carried in the wind creates grooves or small depression
s. Ventifact
s are rocks which have been cut, and sometimes polished, by the abrasive action of wind.
Sculpted landforms, called yardang
s, are up to tens of meters high and kilometers long and are forms that have been streamlined by desert winds. The famous Great Sphinx of Giza
in Egypt may be a modified yardang
.
(skipping or bouncing) and creeping (rolling or sliding) along the ground.
Small particles may be held in the atmosphere
in suspension. Upward currents of air support the weight of suspended particles and hold them indefinitely in the surrounding air. Typical winds near Earth's surface suspend particles less than 0.2 millimeters in diameter and scatter them aloft as dust
or haze
.
Saltation is downwind movement of particles in a series of jumps or skips. Saltation normally lifts sand-size particles no more than one centimeter above the ground, and proceeds at one-half to one-third the speed of the wind. A saltating grain may hit other grains that jump up to continue the saltation. The grain may also hit larger grains that are too heavy to hop, but that slowly creep forward as they are pushed by saltating grains. Surface creep accounts for as much as 25 percent of grain movement in a desert.
Aeolian turbidity current
s are better known as dust storm
s. Air over deserts is cooled significantly when rain passes through it. This cooler and denser air sinks toward the desert surface. When it reaches the ground, the air is deflected forward and sweeps up surface debris
in its turbulence as a dust storm.
Crops
, people, village
s, and possibly even climate
s are affected by dust storms. Some dust storms are intercontinental, a few may circle the globe
, and occasionally they may engulf entire planets. When the Mariner 9
spacecraft entered its orbit around Mars
in 1971, a dust storm lasting one month covered the entire planet, thus delaying the task of photo-mapping the planet's surface.
Most of the dust carried by dust storms is in the form of silt
-size particles. Deposits of this windblown silt are known as loess
. The thickest known deposit of loess, 335 meters, is on the Loess Plateau
in China
. In Europe
and in the Americas
, accumulations of loess are generally from 20 to 30 meters thick.
Aeolian transport from deserts plays an important role in ecosystems globally, e.g. by transport of minerals from the Sahara
to Amazonia. Aeolian processes are affected by human activity, such as the use of 4x4 vehicles on deserts.
Small whirlwinds, called dust devil
s, are common in arid lands and are thought to be related to very intense local heating of the air that results in instabilities of the air mass. Dust devils may be as much as one kilometer high.
s, ripples, and dune
s.
Sand sheets are flat, gently undulating sandy plots of sand surfaced by grains that may be too large for saltation. They form approximately 40 percent of aeolian depositional surfaces. The Selima Sand Sheet, which occupies 60,000 square kilometers in southern Egypt
and northern Sudan
, is one of the Earth's largest sand sheets. The Selima is absolutely flat in some places; in others, active dune
s move over its surface.
Wind blowing on a sand surface ripples the surface into crest
s and troughs whose long axes are perpendicular
to the wind direction. The average length of jumps during saltation corresponds to the wavelength
, or distance between adjacent crests, of the ripples. In ripples, the coarsest materials collect at the crests causing inverse grading
. This distinguishes small ripples from dunes, where the coarsest materials are generally in the troughs. This is also a distinguishing feature between water laid ripples and aeolian ripples.
Wind-blown sand moves up the gentle upwind side of the dune by saltation or creep. Sand accumulates at the brink, the top of the slipface. When the buildup of sand at the brink exceeds the angle of repose
, a small avalanche
of grains slides down the slipface. Grain by grain, the dune moves downwind.
Accumulations of sediment blown by the wind into a mound
or ridge
, dunes have gentle upwind slopes on the windward side. The downwind portion of the dune, the lee slope, is commonly a steep avalanche
slope referred to as a slipface. Dunes may have more than one slipface. The minimum height of a slipface is about 30 centimeters.
Some of the most significant experimental measurements on aeolian sand movement were performed by Ralph Alger Bagnold
, a British engineer who worked in Egypt
prior to World War II
. Bagnold investigated the physics of particles moving through the atmosphere
and deposited by wind. He recognized two basic dune types, the crescentic dune, which he called "barchan
," and the linear dune, which he called longitudinal or "seif" (Arabic for "sword").
Wind
Wind is the flow of gases on a large scale. On Earth, wind consists of the bulk movement of air. In outer space, solar wind is the movement of gases or charged particles from the sun through space, while planetary wind is the outgassing of light chemical elements from a planet's atmosphere into space...
s and more specifically, to the winds' ability to shape the surface of the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
and other planet
Planet
A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...
s. Winds may erode, transport, and deposit materials, and are effective agents in regions with sparse vegetation
Vegetation
Vegetation is a general term for the plant life of a region; it refers to the ground cover provided by plants. It is a general term, without specific reference to particular taxa, life forms, structure, spatial extent, or any other specific botanical or geographic characteristics. It is broader...
and a large supply of unconsolidated sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
s. Although water is a much more powerful eroding force than wind, aeolian processes are important in arid environments such as desert
Desert
A desert is a landscape or region that receives an extremely low amount of precipitation, less than enough to support growth of most plants. Most deserts have an average annual precipitation of less than...
s.
The term is derived from the name of the Greek god, Æolus, the keeper of the winds.
Wind erosion
Wind erodesErosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
the Earth's surface by deflation (the removal of loose, fine-grained particles), by the turbulent
Turbulence
In fluid dynamics, turbulence or turbulent flow is a flow regime characterized by chaotic and stochastic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time...
eddy
Eddy (fluid dynamics)
In fluid dynamics, an eddy is the swirling of a fluid and the reverse current created when the fluid flows past an obstacle. The moving fluid creates a space devoid of downstream-flowing fluid on the downstream side of the object...
action of the wind and by abrasion
Ventifact
Ventifacts are rocks that have been abraded, pitted, etched, grooved, or polished by wind-driven sand or ice crystals. These geomorphic features are most typically found in arid environments where there is little vegetation to interfere with aeolian particle transport, where there are frequently...
(the wearing down of surfaces by the grinding action and sandblasting of windborne particles).
Regions which experience intense and sustained erosion are called deflation zones. Most aeolian deflation zones are composed of desert pavement
Desert pavement
A desert pavement is a desert surface that is covered with closely packed, interlocking angular or rounded rock fragments of pebble and cobble size.-Formation:Several theories have been proposed for their formation...
, a sheet-like surface of rock fragments that remains after wind and water have removed the fine particles. Almost half of Earth's desert surfaces are stony deflation zones. The rock mantle
Mantle (geology)
The mantle is a part of a terrestrial planet or other rocky body large enough to have differentiation by density. The interior of the Earth, similar to the other terrestrial planets, is chemically divided into layers. The mantle is a highly viscous layer between the crust and the outer core....
in desert pavement
Desert pavement
A desert pavement is a desert surface that is covered with closely packed, interlocking angular or rounded rock fragments of pebble and cobble size.-Formation:Several theories have been proposed for their formation...
s protects the underlying material from deflation.
A dark, shiny stain, called desert varnish
Desert varnish
Desert varnish, or rock varnish is a orange-yellow to black coating found on exposed rock surfaces in arid environments. Desert varnish is usually around one micron thick and present nanometre-scale layering...
or rock varnish, is often found on the surfaces of some desert rocks that have been exposed at the surface for a long period of time. Manganese
Manganese
Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...
, iron oxide
Iron oxide
Iron oxides are chemical compounds composed of iron and oxygen. All together, there are sixteen known iron oxides and oxyhydroxides.Iron oxides and oxide-hydroxides are widespread in nature, play an important role in many geological and biological processes, and are widely utilized by humans, e.g.,...
s, hydroxide
Hydroxide
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and a hydrogen atom held together by a covalent bond, and carrying a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, as a ligand, a nucleophile, and a...
s, and clay
Clay
Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...
minerals form most varnishes and provide the shine.
Deflation basins, called blowout
Blowout (geology)
Blowouts are sandy depressions in a sand dune ecosystem caused by the removal of sediments by wind.Blowouts occur in partially vegetated dunefields or sandhills. A blowout forms when a patch of protective vegetation is lost, allowing strong winds to "blow out" sand and form a depression...
s, are hollows formed by the removal of particles by wind. Blowouts are generally small, but may be up to several kilometers in diameter.
Wind-driven grains abrade landform
Landform
A landform or physical feature in the earth sciences and geology sub-fields, comprises a geomorphological unit, and is largely defined by its surface form and location in the landscape, as part of the terrain, and as such, is typically an element of topography...
s. Grinding by particles carried in the wind creates grooves or small depression
Depression (geology)
A depression in geology is a landform sunken or depressed below the surrounding area. Depressions may be formed by various mechanisms.Structural or tectonic related:...
s. Ventifact
Ventifact
Ventifacts are rocks that have been abraded, pitted, etched, grooved, or polished by wind-driven sand or ice crystals. These geomorphic features are most typically found in arid environments where there is little vegetation to interfere with aeolian particle transport, where there are frequently...
s are rocks which have been cut, and sometimes polished, by the abrasive action of wind.
Sculpted landforms, called yardang
Yardang
A yardang is a streamlined hill carved from bedrock or any consolidated or semiconsolidated material by the dual action of wind abrasion, dust and sand, and deflation. Yardangs become elongated features typically three or more times longer than wide, and when viewed from above, resemble the hull of...
s, are up to tens of meters high and kilometers long and are forms that have been streamlined by desert winds. The famous Great Sphinx of Giza
Great Sphinx of Giza
The Great Sphinx of Giza , commonly referred to as the Sphinx, is a limestone statue of a reclining or couchant sphinx that stands on the Giza Plateau on the west bank of the Nile in Giza, Egypt....
in Egypt may be a modified yardang
Yardang
A yardang is a streamlined hill carved from bedrock or any consolidated or semiconsolidated material by the dual action of wind abrasion, dust and sand, and deflation. Yardangs become elongated features typically three or more times longer than wide, and when viewed from above, resemble the hull of...
.
Transport
Particles are transported by winds through suspension, saltationSaltation (geology)
In geology, saltation is a specific type of particle transport by fluids such as wind or water. It occurs when loose material is removed from a bed and carried by the fluid, before being transported back to the surface...
(skipping or bouncing) and creeping (rolling or sliding) along the ground.
Small particles may be held in the atmosphere
Atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...
in suspension. Upward currents of air support the weight of suspended particles and hold them indefinitely in the surrounding air. Typical winds near Earth's surface suspend particles less than 0.2 millimeters in diameter and scatter them aloft as dust
Dust
Dust consists of particles in the atmosphere that arise from various sources such as soil dust lifted up by wind , volcanic eruptions, and pollution...
or haze
Haze
Haze is traditionally an atmospheric phenomenon where dust, smoke and other dry particles obscure the clarity of the sky. The World Meteorological Organization manual of codes includes a classification of horizontal obscuration into categories of fog, ice fog, steam fog, mist, haze, smoke, volcanic...
.
Saltation is downwind movement of particles in a series of jumps or skips. Saltation normally lifts sand-size particles no more than one centimeter above the ground, and proceeds at one-half to one-third the speed of the wind. A saltating grain may hit other grains that jump up to continue the saltation. The grain may also hit larger grains that are too heavy to hop, but that slowly creep forward as they are pushed by saltating grains. Surface creep accounts for as much as 25 percent of grain movement in a desert.
Aeolian turbidity current
Turbidity current
A turbidity current is a current of rapidly moving, sediment-laden water moving down a slope through water, or another fluid. The current moves because it has a higher density and turbidity than the fluid through which it flows...
s are better known as dust storm
Dust storm
A dust / sand storm is a meteorological phenomenon common in arid and semi-arid regions. Dust storms arise when a gust front or other strong wind blows loose sand and dirt from a dry surface. Particles are transported by saltation and suspension, causing soil to move from one place and deposition...
s. Air over deserts is cooled significantly when rain passes through it. This cooler and denser air sinks toward the desert surface. When it reaches the ground, the air is deflected forward and sweeps up surface debris
Debris
Debris is rubble, wreckage, ruins, litter and discarded garbage/refuse/trash, scattered remains of something destroyed, or, in geology, large rock fragments left by a melting glacier etc. The singular form of debris is debris...
in its turbulence as a dust storm.
Crops
Crop (agriculture)
A crop is a non-animal species or variety that is grown to be harvested as food, livestock fodder, fuel or for any other economic purpose. Major world crops include maize , wheat, rice, soybeans, hay, potatoes and cotton. While the term "crop" most commonly refers to plants, it can also include...
, people, village
Village
A village is a clustered human settlement or community, larger than a hamlet with the population ranging from a few hundred to a few thousand , Though often located in rural areas, the term urban village is also applied to certain urban neighbourhoods, such as the West Village in Manhattan, New...
s, and possibly even climate
Climate
Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods...
s are affected by dust storms. Some dust storms are intercontinental, a few may circle the globe
Globe
A globe is a three-dimensional scale model of Earth or other spheroid celestial body such as a planet, star, or moon...
, and occasionally they may engulf entire planets. When the Mariner 9
Mariner 9
Mariner 9 was a NASA space orbiter that helped in the exploration of Mars and was part of the Mariner program. Mariner 9 was launched toward Mars on May 30, 1971 from Cape Canaveral Air Force Station and reached the planet on November 13 of the same year, becoming the first spacecraft to orbit...
spacecraft entered its orbit around Mars
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
in 1971, a dust storm lasting one month covered the entire planet, thus delaying the task of photo-mapping the planet's surface.
Most of the dust carried by dust storms is in the form of silt
Silt
Silt is granular material of a size somewhere between sand and clay whose mineral origin is quartz and feldspar. Silt may occur as a soil or as suspended sediment in a surface water body...
-size particles. Deposits of this windblown silt are known as loess
Loess
Loess is an aeolian sediment formed by the accumulation of wind-blown silt, typically in the 20–50 micrometre size range, twenty percent or less clay and the balance equal parts sand and silt that are loosely cemented by calcium carbonate...
. The thickest known deposit of loess, 335 meters, is on the Loess Plateau
Loess Plateau
The Loess Plateau , also known as the Huangtu Plateau, is a plateau that covers an area of some 640,000 km² in the upper and middle reaches of China's Yellow River. Loess is the name for the silty sediment that has been deposited by wind storms on the plateau over the ages...
in China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
. In Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
and in the Americas
Americas
The Americas, or America , are lands in the Western hemisphere, also known as the New World. In English, the plural form the Americas is often used to refer to the landmasses of North America and South America with their associated islands and regions, while the singular form America is primarily...
, accumulations of loess are generally from 20 to 30 meters thick.
Aeolian transport from deserts plays an important role in ecosystems globally, e.g. by transport of minerals from the Sahara
Sahara
The Sahara is the world's second largest desert, after Antarctica. At over , it covers most of Northern Africa, making it almost as large as Europe or the United States. The Sahara stretches from the Red Sea, including parts of the Mediterranean coasts, to the outskirts of the Atlantic Ocean...
to Amazonia. Aeolian processes are affected by human activity, such as the use of 4x4 vehicles on deserts.
Small whirlwinds, called dust devil
Dust devil
A dust devil is a strong, well-formed, and relatively long-lived whirlwind, ranging from small to large . The primary vertical motion is upward...
s, are common in arid lands and are thought to be related to very intense local heating of the air that results in instabilities of the air mass. Dust devils may be as much as one kilometer high.
Deposition
Wind-deposited materials hold clues to past as well as to present wind directions and intensities. These features help us understand the present climate and the forces that molded it. Wind-deposited sand bodies occur as sand sheetSand sheet
Sand sheets are flat, gently undulating plots of sand surfaced by grains that may be too large for saltation. They form approximately 40 percent of aeolian depositional surfaces....
s, ripples, and dune
Dune
In physical geography, a dune is a hill of sand built by wind. Dunes occur in different forms and sizes, formed by interaction with the wind. Most kinds of dunes are longer on the windward side where the sand is pushed up the dune and have a shorter "slip face" in the lee of the wind...
s.
Sand sheets are flat, gently undulating sandy plots of sand surfaced by grains that may be too large for saltation. They form approximately 40 percent of aeolian depositional surfaces. The Selima Sand Sheet, which occupies 60,000 square kilometers in southern Egypt
Egypt
Egypt , officially the Arab Republic of Egypt, Arabic: , is a country mainly in North Africa, with the Sinai Peninsula forming a land bridge in Southwest Asia. Egypt is thus a transcontinental country, and a major power in Africa, the Mediterranean Basin, the Middle East and the Muslim world...
and northern Sudan
Sudan
Sudan , officially the Republic of the Sudan , is a country in North Africa, sometimes considered part of the Middle East politically. It is bordered by Egypt to the north, the Red Sea to the northeast, Eritrea and Ethiopia to the east, South Sudan to the south, the Central African Republic to the...
, is one of the Earth's largest sand sheets. The Selima is absolutely flat in some places; in others, active dune
Dune
In physical geography, a dune is a hill of sand built by wind. Dunes occur in different forms and sizes, formed by interaction with the wind. Most kinds of dunes are longer on the windward side where the sand is pushed up the dune and have a shorter "slip face" in the lee of the wind...
s move over its surface.
Wind blowing on a sand surface ripples the surface into crest
Crest (physics)
A crest is the point on a wave with the maximum value or upward displacement within a cycle. A trough is the opposite of a crest, so the minimum or lowest point in a cycle.-Interference:...
s and troughs whose long axes are perpendicular
Perpendicular
In geometry, two lines or planes are considered perpendicular to each other if they form congruent adjacent angles . The term may be used as a noun or adjective...
to the wind direction. The average length of jumps during saltation corresponds to the wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
, or distance between adjacent crests, of the ripples. In ripples, the coarsest materials collect at the crests causing inverse grading
Graded bedding
In geology, a graded bed is one characterized by a systematic change in grain or clast size from the base of the bed to the top. Most commonly this takes the form of normal grading, with coarser sediments at the base, which grade upward into progressively finer ones...
. This distinguishes small ripples from dunes, where the coarsest materials are generally in the troughs. This is also a distinguishing feature between water laid ripples and aeolian ripples.
Wind-blown sand moves up the gentle upwind side of the dune by saltation or creep. Sand accumulates at the brink, the top of the slipface. When the buildup of sand at the brink exceeds the angle of repose
Angle of repose
The angle of repose or, more precisely, the critical angle of repose, of a granular material is the steepest angle of descent or dip of the slope relative to the horizontal plane when material on the slope face is on the verge of sliding. This angle is in the range 0°–90°.When bulk granular...
, a small avalanche
Avalanche
An avalanche is a sudden rapid flow of snow down a slope, occurring when either natural triggers or human activity causes a critical escalating transition from the slow equilibrium evolution of the snow pack. Typically occurring in mountainous terrain, an avalanche can mix air and water with the...
of grains slides down the slipface. Grain by grain, the dune moves downwind.
Accumulations of sediment blown by the wind into a mound
Mound
A mound is a general term for an artificial heaped pile of earth, gravel, sand, rocks, or debris. The most common use is in reference to natural earthen formation such as hills and mountains, particularly if they appear artificial. The term may also be applied to any rounded area of topographically...
or ridge
Ridge
A ridge is a geological feature consisting of a chain of mountains or hills that form a continuous elevated crest for some distance. Ridges are usually termed hills or mountains as well, depending on size. There are several main types of ridges:...
, dunes have gentle upwind slopes on the windward side. The downwind portion of the dune, the lee slope, is commonly a steep avalanche
Avalanche
An avalanche is a sudden rapid flow of snow down a slope, occurring when either natural triggers or human activity causes a critical escalating transition from the slow equilibrium evolution of the snow pack. Typically occurring in mountainous terrain, an avalanche can mix air and water with the...
slope referred to as a slipface. Dunes may have more than one slipface. The minimum height of a slipface is about 30 centimeters.
Some of the most significant experimental measurements on aeolian sand movement were performed by Ralph Alger Bagnold
Ralph Alger Bagnold
Brigadier Ralph Alger Bagnold, FRS OBE, was the founder and first commander of the British Army's Long Range Desert Group during World War II. He is also generally considered to have been a pioneer of desert exploration, an acclaim earned for his activities during the 1930s...
, a British engineer who worked in Egypt
Egypt
Egypt , officially the Arab Republic of Egypt, Arabic: , is a country mainly in North Africa, with the Sinai Peninsula forming a land bridge in Southwest Asia. Egypt is thus a transcontinental country, and a major power in Africa, the Mediterranean Basin, the Middle East and the Muslim world...
prior to World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
. Bagnold investigated the physics of particles moving through the atmosphere
Atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...
and deposited by wind. He recognized two basic dune types, the crescentic dune, which he called "barchan
Barchan
A barchan dune, also barkhan is an arc-shaped sand ridge, comprising well-sorted sand. This type of dune possesses two "horns" that face downwind, with the slip face at the angle of repose of sand, or approximately 35 degrees . The upwind side is packed by the wind, and stands at about 15 degrees...
," and the linear dune, which he called longitudinal or "seif" (Arabic for "sword").
See also
- Aeolian landformAeolian landformAeolian landforms are features of the Earth's surface produced by either the erosive or constructive action of the wind. This process is not unique to earth, and it has been observed and studied on other planets, including Mars.-Terminology:...
- Asian dustAsian DustAsian Dust is a seasonal meteorological phenomenon which affects much of East Asia sporadically during the springtime months...
- Bagnold formulaBagnold FormulaThe Bagnold formula, named after Ralph Alger Bagnold, relates the amount of sand moved by the wind to wind speed by saltation. It states that the mass transport of sand is proportional to the third power of the friction velocity...
- BarchanBarchanA barchan dune, also barkhan is an arc-shaped sand ridge, comprising well-sorted sand. This type of dune possesses two "horns" that face downwind, with the slip face at the angle of repose of sand, or approximately 35 degrees . The upwind side is packed by the wind, and stands at about 15 degrees...
- Blowout (geology)Blowout (geology)Blowouts are sandy depressions in a sand dune ecosystem caused by the removal of sediments by wind.Blowouts occur in partially vegetated dunefields or sandhills. A blowout forms when a patch of protective vegetation is lost, allowing strong winds to "blow out" sand and form a depression...
- Cross-beddingCross-beddingIn geology, the sedimentary structures known as cross-bedding refer to horizontal units that are internally composed of inclined layers. This is a case in geology in which the original depositional layering is tilted, and the tilting is not a result of post-depositional deformation...
- DreikanterDreikanterA Dreikanter is a type of ventifact that typically forms in desert or periglacial environments due to the abrasive action of blowing sand.Dreikanters exhibit a characteristic three-faced pyramidal shape. The word Dreikanter is a German word meaning "a three-sider."right|thumb|300px| Unusually large...
- DuneDuneIn physical geography, a dune is a hill of sand built by wind. Dunes occur in different forms and sizes, formed by interaction with the wind. Most kinds of dunes are longer on the windward side where the sand is pushed up the dune and have a shorter "slip face" in the lee of the wind...
- Médanos (geology)
- Saltation (geology)Saltation (geology)In geology, saltation is a specific type of particle transport by fluids such as wind or water. It occurs when loose material is removed from a bed and carried by the fluid, before being transported back to the surface...
- SandhillSandhillA sandhill is a type of ecological community or xeric wildfire-maintained ecosystem. It is not the same as a sand dune. It features very short fire return intervals, one to five years. Without fire, sandhills undergo ecological succession and become more oak dominated.Entisols are the typical...
- SedimentSedimentSediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
- Sediment transportSediment transportSediment transport is the movement of solid particles , typically due to a combination of the force of gravity acting on the sediment, and/or the movement of the fluid in which the sediment is entrained...
- The Physics of Blown Sand and Desert Dunes
- VentifactVentifactVentifacts are rocks that have been abraded, pitted, etched, grooved, or polished by wind-driven sand or ice crystals. These geomorphic features are most typically found in arid environments where there is little vegetation to interfere with aeolian particle transport, where there are frequently...
- Wind Erosion on European Light SoilsWind Erosion on European Light SoilsWEELS was a research project funded as part of the EU Environment and Climate Programme, intended to develop a small-scale model of wind erosion at the level of individual farms and fields, based on research at three test sites in Lower Saxony, Scania, and Suffolk.WEELS was a collaborative project...
- YardangYardangA yardang is a streamlined hill carved from bedrock or any consolidated or semiconsolidated material by the dual action of wind abrasion, dust and sand, and deflation. Yardangs become elongated features typically three or more times longer than wide, and when viewed from above, resemble the hull of...