Erg Chebbi, Morocco

Dunes of Maspalomas in Gran Canaria

Avalanche deposits on a crest of the Kelso Dunes, Mojave National Preserve, California.

In physical geography, a dune is a hill of sand built either by wind or water flow. Dunes occur in different forms and sizes, formed by interaction with the flow of air or water. 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. The valley or trough between dunes is called a slack. A "dune field" is an area covered by extensive sand dunes. Large dune fields are known as ergs.

Some coastal areas have one or more sets of dunes running parallel to the shoreline directly inland from the beach. In most cases the dunes are important in protecting the land against potential ravages by storm waves from the sea. Although the most widely distributed dunes are those associated with coastal regions, the largest complexes of dunes are found inland in dry regions and associated with ancient lake or sea beds.

Dunes also form under the action of water flow (alluvial processes), and on sand or gravel beds of rivers, estuaries and the sea-bed.

The modern word "dune" came into English from French circa 1790. In ancient times, words cognate to "dune" probably had the meaning of a built-up hill or citadel fortification.^[1]

Conservation[link]

Dune habitats provide niches for highly specialised plants and animals, including numerous rare species and some endangered species. Due to widespread human population expansion, dunes face destruction through land development and recreational usages, as well as alteration to prevent the encroachment of sand onto inhabited areas. Some countries, notably the United States, Australia, Canada, New Zealand, the United Kingdom, and Netherlands, have developed significant programs of dune protection through the use of sand dune stabilization. In the U.K., a Biodiversity Action Plan has been developed to assess dunes loss and to prevent future dunes destruction.

Aeolian dune shapes[link]

Crescentic[link]

"Crescent-shaped mounds are generally wider than they are long. The slipfaces are on the concave sides of the dunes. These dunes form under winds that blow consistently from one direction, and they also are known as barchans, or transverse dunes. Some types of crescentic dunes move more quickly over desert surfaces than any other type of dune. A group of dunes moved more than 100 metres per year between 1954 and 1959 in the China's Ningxia Province, and similar speeds have been recorded in the Western Desert of Egypt. The largest crescentic dunes on Earth, with mean crest-to-crest widths of more than 3 kilometres, are in China's Taklamakan Desert."^[2]

Linear[link]

Straight or slightly sinuous sand ridges typically much longer than they are wide are known as linear dunes. They may be more than 160 kilometres (100 miles) long. Some linear dunes merge to form Y-shaped compound dunes. Many form in bidirectional wind regimes. The long axes of these dunes extend in the resultant direction of sand movement.

Linear loess hills known as pahas are superficially similar. These hills appear to have been formed during the last ice age under permafrost conditions dominated by sparse tundra vegetation.

Star[link]

Radially symmetrical, star dunes are pyramidal sand mounds with slipfaces on three or more arms that radiate from the high center of the mound. They tend to accumulate in areas with multidirectional wind regimes. Star dunes grow upward rather than laterally. They dominate the Grand Erg Oriental of the Sahara. In other deserts, they occur around the margins of the sand seas, particularly near topographic barriers. In the southeast Badain Jaran Desert of China, the star dunes are up to 500 metres tall and may be the tallest dunes on Earth.

Dome[link]

Oval or circular mounds that generally lack a slipface, dome dunes are rare, and these occur at the far upwind margins of sand seas.

Parabolic[link]

U-shaped mounds of sand with convex noses trailed by elongated arms are parabolic dunes. These dunes are formed from blowout dunes where the erosion of vegetated sand leads to a U-shaped depression. The elongated arms are held in place by vegetation; the largest arm known on Earth reaches 12 km. Sometimes these dunes are called U-shaped, blowout, or hairpin dunes, and they are well known in coastal deserts. Unlike crescent shaped dunes, their crests point upwind. The bulk of the sand in the dune migrates forward.

In plan view, these are U-shaped or V-shaped mounds of well-sorted, very fine to medium sand with elongated arms that extend upwind behind the central part of the dune. There are slip faces that often occur on the outer side of the nose and on the outer slopes of the arms.

These dunes often occur in semiarid areas where the precipitation is retained in the lower parts of the dune and underlying soils. Parabolic dunes are dependent on the vegetation that covers them—grasses,shrubs,and trees, which help anchor the trailing arms. In inland deserts, parabolic dunes commonly originate and extend downwind from blowouts in sand sheets only partly anchored by vegetation. They can also originate from beach sands and extend inland into vegetated areas in coastal zones and on shores of large lakes.

Most parabolic dunes do not reach heights higher than a few tens of metres except at their nose, where vegetation stops or slows the advance of accumulating sand.

Simple parabolic dunes have only one set of arms that trail upwind, behind the leading nose. Compound parabolic dunes are coalesced features with several sets of trailing arms. Complex parabolic dunes include subsidiary superposed or coalesced forms, usually of barchanoid or linear shapes.

Parabolic dunes, like crescent dunes, occur in areas where very strong winds are mostly unidirectional. Although these dunes are found in areas now characterized by variable wind speeds, the effective winds associated with the growth and migration of both the parabolic and crescent dunes probably are the most consistent in wind direction.

The grain size for these well-sorted, very fine to medium sands is about 0.06 to 0.5 mm. Parabolic dunes have loose sand and steep slopes only on their outer flanks. The inner slopes are mostly well packed and anchored by vegetation, as are the corridors between individual dunes. Because all dune arms are oriented in the same direction, and, the inter-dune corridors are generally swept clear of loose sand, the corridors can usually be traversed in between the trailing arms of the dune. However to cross straight over the dune by going over the trailing arms, can be very difficult. Also, traversing the nose is very difficult as well because the nose is usually made up of loose sand without much if any vegetation.

Longitudinal (Seif) dunes[link]

Rub' al Khali seen by the ASTER instrument on NASA's Terra satellite

Longitudinal dunes (also called Seif dunes, after the Arabic word for "sword"), elongate parallel to the prevailing wind, possibly caused by a larger dune having its smaller sides blown away. Seif dunes are sharp-crested and are common in the Sahara. They range up to 300 m (980 ft) in height and 300 km (190 mi) in length. In the southern third of the Arabian Peninsula, a vast erg called the Rub' al Khali or the Empty Quarter, contains seif dunes that stretch for almost 200 km and reach heights of over 300 m.

Seif dunes are thought to develop from barchans if a change of the usual wind direction occurs. The new wind direction will lead to the development of a new wing and the over development of one of the original wings. If the prevailing wind then becomes dominant for a lengthy period of time the dune will revert to its barchan form, with one exaggerated wing. Should the strong wind then return the exaggerated wing will further extend so that eventually it will be supplied with sand when the prevailing wind returns. The wing will continue to grow under both wind conditions, thus producing a seif dune. On a seif dune the slip face develops on the side facing away from the strong wind, while the slip face of a barchan faces the direction of movement. In the sheltered troughs between highly developed seif dunes barchans may be formed because the wind is unidirectional.

A transverse dune is perpendicular to the prevailing wind, probably caused by a steady build-up of sand on an already existing minuscule mound.

Reversing dunes[link]

Complex dune: Dune 7 in the Namib desert, one of the tallest in the world.

Occurring wherever winds periodically reverse direction, reversing dunes are varieties of any of the above shapes. These dunes typically have major and minor slipfaces oriented in opposite directions.

All these dune shapes may occur in three forms: simple, compound, and complex. Simple dunes are basic forms with a minimum number of slipfaces that define the geometric type. Compound dunes are large dunes on which smaller dunes of similar type and slipface orientation are superimposed, and complex dunes are combinations of two or more dune types. A crescentic dune with a star dune superimposed on its crest is the most common complex dune. Simple dunes represent a wind regime that has not changed in intensity or direction since the formation of the dune, while compound and complex dunes suggest that the intensity and direction of the wind has changed.

Dune types[link]

The Great Dune of Pyla is the largest dune in Europe.

Sub-aqueous lithified dune (megaripple) from Utah.

Sub-aqueous dunes[link]

Sub-aqueous (underwater) dunes (also known in geology as megaripples) form on a bed of sand or gravel under the actions of water flow. They are ubiquitous in natural channels such as rivers and estuaries, and also form in engineered canals and pipelines. Dunes move downstream as the upstream slope is eroded and the sediment deposited on the downstream or lee slope in typical bedform construction.^[3]

These dunes most often form as a continuous 'train' of dunes, showing remarkable similarity in wavelength and height.

Dunes on the bed of a channel significantly increase flow resistance, their presence and growth playing a major part in river flooding.

Lithified dunes[link]

A lithified (consolidated) sand dune is a type of sandstone that is formed when a marine or aeolian sand dune becomes compacted and hardened. Once in this form, water passing through the rock can carry and deposit minerals, which can alter the color of the rock. Cross-bedded layers of stacks of lithified dunes can produce the cross-hatching patterns, such as those seen in the Zion National Park in the western United States.

A slang term that is used in the Southwestern States (of the U.S.A.) for those consolidated and hardened sand dunes is "slickrock", a name that was introduced by pioneers of the Old West because their steel-rimmed wagon wheels could not gain traction on the rock.

Coastal dunes[link]

Coastal dunes on the Kurnell Peninsula in Southern Sydney

Dunes form where constructive waves encourage the accumulation of sand, and where prevailing onshore winds blow this sand inland. There need to be obstacles—for example, vegetation, pebbles and so on—to trap the moving sand grains. As the sand grains get trapped they start to accumulate, starting dune formation. The wind then starts to affect the mound of sand by eroding sand particles from the windward side and depositing them on the leeward side. Gradually this action causes the dune to “migrate” inland, as it does so it accumulates more and more sand. Dunes provide privacy and shelter from the wind.

Ecological succession on coastal dunes[link]

Coastal dunes in Curonian spit.

As a dune forms, plant succession occurs. The conditions on an embryo dune are harsh, with salt spray from the sea carried on strong winds. The dune is well drained and often dry, and composed of calcium carbonate from seashells. Rotting seaweed, brought in by storm waves adds nutrients to allow pioneer species to colonize the dune. These pioneer species are marram grass, sea wort grass and other sea grasses in the United Kingdom. These plants are well adapted to the harsh conditions of the foredune typically having deep roots which reach the water table, root nodules that produce nitrogen compounds, and protected stoma, reducing transpiration. Also, the deep roots bind the sand together, and the dune grows into a foredune as more sand is blown over the grasses. The grasses add nitrogen to the soil, meaning other, less hardy plants can then colonize the dunes. Typically these are heather, heaths and gorses. These too are adapted to the low soil water content and have small, prickly leaves which reduce transpiration. Heather adds humus to the soil and is usually replaced by coniferous trees, which can tolerate low soil pH, caused by the accumulation and decomposition of organic matter with nitrate leaching.^[4] Coniferous forests and heathland are common climax communities for sand dune systems.

Young dunes are called yellow dunes and dunes which have high humus content are called grey dunes. Leaching occurs on the dunes, washing humus into the slacks, and the slacks may be much more developed than the exposed tops of the dunes. It is usually in the slacks that more rare species are developed and there is a tendency for the dune slacks soil to be waterlogged and where only marsh plants can survive. These plants would include: creeping willow, cotton grass, yellow ins, reeds, and rushes. As for the species, there is a tendency for natterjack toads to breed here.

Desertification[link]

Sand dunes can have a negative impact on humans when they encroach on human habitats. Sand dunes move via a few different means, all of them helped along by wind. One way that dunes can move is by saltation, where sand particles skip along the ground like a bouncing ball. When these skipping particles land, they may knock into other particles and cause them to move as well, in a process known as creep. With slightly stronger winds, particles collide in mid-air, causing sheet flows. In a major dust storm, dunes may move tens of metres through such sheet flows. Also as in the case of snow, sand avalanches, falling down the slipface of the dunes - that face away from the winds - also move the dunes forward.

Sand threatens buildings and crops in Africa, the Middle East, and China. Drenching sand dunes with oil stops their migration, but this approach is quite destructive to the dunes' animal habitats and uses a valuable resource. Sand fences might also slow their movement to a crawl, but geologists are still analyzing results for the optimum fence designs.^{[citation needed]} Preventing sand dunes from overwhelming towns, villages, and agricultural areas has become a priority for the United Nations Environment Programme. Planting dunes with vegetation also helps to stabilise them.

Examples[link]

Sand dunes of Khongoryn Els, Gurvansaikhan NP, Mongolia.

Africa[link]

• Alexandria Coastal Dunefields, in the Eastern Cape, South Africa ^[5]
• Western Sahara

Asia[link]

• The dunes in the Thar desert in Rajasthan, India
• Tottori Sand Dunes, Tottori Prefecture, Japan
• Rig-e Jenn in the Central Desert of Iran.
• Rig-e Lut in the Southeast of Iran.
• The Ilocos Norte Sand Dunes in the Philippines, particularly Paoay Sand Dunes.
• Mer'eb Dune (also written as Merheb) in United Arab Emirates, used as an arena for motor sports and skiing.
• Gumuk Pasir Parangkusumo near Parangtritis beach in Yogyakarta, Indonesia.

Europe[link]

• The Dune of Pyla, not far from Bordeaux, France, is the largest known sand dune in Europe
• Sands of Forvie within the Ythan Estuary complex, Aberdeenshire, Scotland.
• Oxwich Dunes, near Swansea, is on the Gower Peninsula in Wales.
• Winterton Dunes – Norfolk, England
• Słowiński National Park, Poland
• Akrotiri Sand Dune, Lemesos, Cyprus

North America[link]

Gypsum sand at White Sands National Monument, New Mexico

Parabolic dune in Hoffmaster State Park. Note damage to dune grass on unauthorized trail in center of photograph.

• The Athabasca Sand Dunes, the northmost sand dunes in the world, located in the Athabasca Sand Dunes Provincial Park, Saskatchewan.
• The Kelso Dunes in the Mojave Desert of California.
• Great Sand Dunes National Park, Colorado.
• White Sands National Monument, New Mexico.
• Little Sahara Recreation Area, Utah.
• Indiana Dunes National Lakeshore, Indiana, on the south shore of Lake Michigan.
• Warren Dunes State Park and Sleeping Bear Dunes National Lakeshore, Michigan, on the east shore of Lake Michigan.
• Grand Sable Dunes, in the Pictured Rocks National Lakeshore, Michigan.
• Algodones Dunes near Brawley, California.
• Guadalupe-Nipomo Dunes, on the central coast of California.
• Monahans Sandhills State Park near Odessa, Texas.
• Beaver Dunes State Park near Beaver, Oklahoma.
• The Killpecker sand dunes of the Red Desert in southwestern Wyoming.
• Jockey's Ridge State Park – on the Outer Banks, North Carolina.
• Oregon Dunes National Recreation Area near Florence, Oregon, on the Pacific Coast.
• Bruneau Dunes State Park - Owyhee Desert, Idaho
• Hoffmaster State Park - Muskegon, Michigan

South America[link]

• Lençóis Maranhenses National Park in the state of Maranhão, Brazil
• Jericoacoara National Park, in the state of Ceará, Brazil
• Genipabu in Natal, Brazil
• Medanos de Coro National Park near the town of Coro, in Falcón State, Venezuela
• in Nasca Province in Peru
• Cerro Blanco in Nasca Province in Peru
• Cerro Medanoso in Atacama Region in Chile
• Valdivian Coastal Reserve in Chile

Oceania[link]

• Fraser Island in Queensland, Australia
• Stockton Beach in NSW

World's highest dunes[link]

Sand dune systems[link]

The examples and perspective in this article deal primarily with the United Kingdom and do not represent a worldwide view of the subject. Please improve this article and discuss the issue on the talk page. (November 2010)

An example of fencing at Studland

(coastal dunes featuring succession)

• Ashdod Sand Dune, Israel
• Crymlyn Burrows, Wales
• Kenfig Burrows, Wales
• Margam burrows, Wales
• Studland, Dorsetshire, England
• Athabasca Sand Dunes Provincial Park, Alberta and Saskatchewan
• Murlough Sand Dunes, Newcastle, Co Down, Northern Ireland
• Morfa Harlech sand dunes, Gwynedd, Wales
• Newborough Warren, North Wales
• Bamburgh Dunes, Northumberland, England
• Oregon Dunes National Recreation Area, near North Bend, Oregon
• Circeo National Park, a Mediterranean dune area on the southwest coast of the Lazio region of Italy
• Winterton, Norfolk, England
• Ynyslas Sand Dunes, Wales
• Sleeping Bear Dunes National Lakeshore, Michigan
• Fraser Island, Queensland Australia, largest sand island in the world

Extraterrestrial dunes[link]

Dunes can likely be found in any environment where there is a substantial atmosphere, winds, and dust to be blown. Dunes are common on Mars, and they have also been observed in the equatorial regions of Titan using the radar system of the Cassini space probe.

Titan's dunes include large expanses with modal lengths of about 20–30 km. The regions are not topographically confined, resembling sand seas. These dunes are interpreted to be longitudinal dunes whose crests are oriented parallel to the dominant wind direction, which generally indicates west-to-east wind flow. The sand is likely composed of hydrocarbon particles, possibly with some water ice mixed in.^[8]

Images[link]

• 

  A diagram showing the formation of a dune with a slipface

• 

  Mesquite Flat Dunes in Death Valley National Park

• 

  Erg Awbari (Idehan Ubari) in the Sahara desert region of Fezzan in Libya

• 

  Some dunes are suitable for dune-boarding

• 

  Sand dunes in Death Valley National Park. The image shows coppice dunes,which are formed around vegetation

• 

  A footbridge provides beach access and protects dunes

• 

  A sand dune in Namibia

• 

  A dune in Morocco

• Sanddune.JPG

  Sand dunes with scattered vegetation in UAE

• 

  Parabolic dune partially stabilized by marram grass

• 

  Sand blowing off a crest in the Kelso Dunes of the Mojave Desert, California

• 

  Cat Dune sand ramp, Cronese Mountains, California

• 

  Satellite image of dune fields near Luís Correia.

• Dunadopordosol.jpg

  Dune by the sea in Jericoacoara.

See also[link]

Wikimedia Commons has media related to: Dune

• Antidune
• Barchan
• Earth science
• Erg (landform)
• Ice dune
• List of landforms
• Machair
• Masseira
• Médanos
• Sandhill
• Singing sand
• Strand plain
• Sand dune stabilization
• Cliff-top dune

References and notes[link]

• "Nouakchott, Mauritania". NASA Earth Observatory. http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=17168. Retrieved 2006-04-28. 
• V. Badescu, R. B. Cathcart and A. A. Bolonkin, "Sand Dune Fixation: a solar-powered Sahara seawater pipeline macroproject", in: Land Degradation & Development; 19, (2008): doi:10.1002/ldr.864.
• "Types of Dunes". USGS. http://pubs.usgs.gov/gip/deserts/dunes/. Retrieved 2010-10-06. 
• "Summary: Dunes, Parabolic". Desert Processes Working Group; Knowledge Sciences, Inc.. http://www.agc.army.mil/research/products/desert_guide/lsmsheet/lspara.htm. Retrieved 2010-10-06. 
• "Fighting wind erosion. One aspect of the combat against desertification". Les dossiers thématiques du CSFD. http://www.csf-desertification.org/index.php/bibliotheque/publications-csfd/les-dossiers-du-csfd-english/doc_details/142-mainguet-monique-a-dumay-frederic-2011-fighting-wind-erosion-. Retrieved 2011-01-04. 

Further reading[link]

• Bagnold, Ralph ([1941] 2005). The Physics of Blown Sand and Desert Dunes. Dover Publications. ISBN 978-0-486-43931-0. 
• Anthony J. Parsons, A. D. Abrahams, ed. (2009). Geomorphology of Desert Environments. Springer. ISBN 978-1-4020-5718-2. 
• Pye, Kenneth; Tsoar, Haim (2009). Aeolian Sand and Sand Dunes. Springer. ISBN 978-3-540-85909-3. 

External links[link]

• Coastal Sand Dunes
• Magilligan Dunes, Northern Ireland
• Dune pattern identification, U.S. Army
• Treading Lightly: Minimum Impact Dune Hiking
• Dune Racers of the Empty Quarter – video of sand dunes in the United Arab Emirates
• The Bibliography of Aeolian Research
• Sahara sand dunes forms – as investigated by native offroaders from Egypt
• Gold Coast Dune Management Policy
• USGS page on dune types
• Great Sand Dunes National Park
• Photo gallery dedicated to the dune, by Nikbarte, the desert photographer

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. (June 2008)

Close-up of sand from the Gobi Desert, Mongolia, showing a surface area of 1 square centimetre.

Sand dunes in Libya.

Heavy minerals (dark) in a quartz beach sand (Chennai, India).

Sand is a naturally occurring granular material composed of finely divided rock and mineral particles. The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal settings is silica (silicon dioxide, or SiO₂), usually in the form of quartz.

The second most common form of sand is calcium carbonate, for example aragonite, which has mostly been created, over the past half billion years, by various forms of life like coral and shellfish. It is, for example, the primary form of sand apparent in areas where reefs have dominated the ecosystem for millions of years, like the Caribbean.

Composition[link]

In terms of particle size as used by geologists, sand particles range in diameter from 0.0625 mm (or ⅟16 mm) to 2 mm. An individual particle in this range size is termed a sand grain. Sand grains are between gravel (with particles ranging from 2 mm up to 64 mm) and silt (particles smaller than 0.0625 mm down to 0.004 mm). The size specification between sand and gravel has remained constant for more than a century, but particle diameters as small as 0.02 mm were considered sand under the Albert Atterberg standard in use during the early 20th century. A 1953 engineering standard published by the American Association of State Highway and Transportation Officials set the minimum sand size at 0.074 mm. A 1938 specification of the United States Department of Agriculture was 0.05 mm.^[1] Sand feels gritty when rubbed between the fingers (silt, by comparison, feels like flour).

ISO 14688 grades sands as fine, medium and coarse with ranges 0.063 mm to 0.2 mm to 0.63 mm to 2.0 mm. In the United States, sand is commonly divided into five sub-categories based on size: very fine sand (⅟16 – ⅛ mm diameter), fine sand (⅛ mm – ¼ mm), medium sand (¼ mm – ½ mm), coarse sand (½ mm – 1 mm), and very coarse sand (1 mm – 2 mm). These sizes are based on the Krumbein phi scale, where size in Φ = -log base 2 of size in mm. On this scale, for sand the value of Φ varies from −1 to +4, with the divisions between sub-categories at whole numbers.

Sand from Pismo Beach, California. Components are primarily quartz, chert, igneous rock and shell fragments. Scale bar is 1.0 mm.

Close up of black volcanic sand from Perissa, in Santorini, Greece

Sand from Kalalau Beach, Hawaii (Field width = 5.5 mm). We see a few grains of olivine, which is the green sand of some beaches of Hawaii.

The most common constituent of sand, in inland continental settings and non-tropical coastal settings, is silica (silicon dioxide, or SiO₂), usually in the form of quartz, which, because of its chemical inertness and considerable hardness, is the most common mineral resistant to weathering.

Correlative analysis of Icelandic volcanic beach sand from Reynisfjara beach, using a Stereo Microscope and an Scanning Electron Microscope with EDS detection system for element analysis.

The composition of sand is highly variable, depending on the local rock sources and conditions. The bright white sands found in tropical and subtropical coastal settings are eroded limestone and may contain coral and shell fragments in addition to other organic or organically derived fragmental material, suggesting sand formation depends on living organisms, too.^[2] The gypsum sand dunes of the White Sands National Monument in New Mexico are famous for their bright, white color. Arkose is a sand or sandstone with considerable feldspar content, derived from the weathering and erosion of a (usually nearby) granitic rock outcrop. Some sands contain magnetite, chlorite, glauconite or gypsum. Sands rich in magnetite are dark to black in color, as are sands derived from volcanic basalts and obsidian. Chlorite-glauconite bearing sands are typically green in color, as are sands derived from basaltic (lava) with a high olivine content. Many sands, especially those found extensively in Southern Europe, have iron impurities within the quartz crystals of the sand, giving a deep yellow color. Sand deposits in some areas contain garnets and other resistant minerals, including some small gemstones.

Environments[link]

Sand from Coral Pink Sand Dunes State Park, Utah. These are grains of quartz with a hematite coating providing the orange color. Scale bar is 1.0 mm.

Sand is transported by wind and water and deposited in the form of beaches, dunes, sand spits, sand bars and related features. In environments such as gravel-bed rivers and glacial moraines it often occurs as one of the many grain sizes that are represented. Sand-bed rivers, such as the Platte River in Nebraska, USA, have sandy beds largely because there is no larger source material that they can transport. Dunes, a distinctive geographical feature of desert environments, are on the other hand sandy because larger material is generally immobile in wind. Sand is a component of soil.

Study[link]

An electron micrograph showing grains of sand

Photomicrograph of a volcanic sand grain; upper picture is plane-polarized light, bottom picture is cross-polarized light, scale box at left-center is 0.25 millimeter.

The study of individual grains can reveal much historical information as to the origin and kind of transport of the grain. Quartz sand that is recently weathered from granite or gneiss quartz crystals will be angular. It is called grus in geology or sharp sand in the building trade where it is preferred for concrete, and in gardening where it is used as a soil amendment to loosen clay soils. Sand that is transported long distances by water or wind will be rounded, with characteristic abrasion patterns on the grain surface. Desert sand is typically rounded.

People who collect sand as a hobby are known as arenophiles. Organisms that thrive in sandy environments are psammophiles.

Uses[link]

At 300 km/h, an ICE 3 (DB class 403) releases sand from several bogies to the rails.

Sand sorting tower at a gravel extraction pit.

• Agriculture: Sandy soils are ideal for crops such as watermelons, peaches, and peanuts, and their excellent drainage characteristics make them suitable for intensive dairy farming.
• Aquaria: Sand makes a low cost aquarium base material which some believe is better than gravel for home use. It is also an absolute necessity for saltwater reef tanks, which emulate environments composed largely of aragonite sand broken down from coral and shellfish.
• Artificial reefs: Geotextile bagged sand can serve as the foundation for new reefs.
• Beach nourishment: Governments move sand to beaches where tides, storms or deliberate changes to the shoreline erode the original sand.^[3]
• Brick: Manufacturing plants add sand to a mixture of clay and other materials for manufacturing bricks.
• Cob: Coarse sand makes up as much as 75% of cob.
• Mortar: Sand is mixed with cement and sometimes lime to be used in masonry construction.
• Concrete: Sand is often a principal component of this critical construction material.
• Hydraulic Fracturing: The drilling technique for natural gas also known as fracing use "frac sand". The rounded silica sand is used as a "proppant" a material that holds the cracks open that is caused by the hydraulic fracturing process.
• Glass: Sand is the principal component in common glass.
• Landscaping: Sand makes small hills and slopes (for example, in golf courses).
• Paint: Mixing sand with paint produces a textured finish for walls and ceilings or non-slip floor surfaces.
• Railroads: Train operators use sand to improve the traction of wheels on the rails.
• Roads: Sand improves traction (and thus traffic safety) in icy or snowy conditions.
• Sand animation: Performance artists draw images in sand. Makers of animated films use the same term to describe their use of sand on frontlit or backlit glass.
• Sand casting: Casters moisten or oil molding sand, also known as foundry sand and then shape it into molds into which they pour molten material. This type of sand must be able to withstand high temperatures and pressure, allow gases to escape, have a uniform, small grain size and be non-reactive with metals.
• Sand castles: Shaping sand into castles or other miniature buildings is a popular beach activity.
• Sandbags: These protect against floods and gunfire. The inexpensive bags are easy to transport when empty, and unskilled volunteers can quickly fill them with local sand in emergencies.
• Sandblasting: Graded sand serves as an abrasive in cleaning, preparing, and polishing.
• Water filtration: Media filters use sand for filtering water.
• Zoanthid "skeletons": Animals in this order of marine benthic cnidarians related to corals and sea anemones, incorporate sand into their mesoglea for structural strength, which they need because they lack a true skeleton.

Hazards[link]

A stingray about to bury itself in sand

While sand is generally non-toxic, sand-using activities such as sandblasting require precautions. Bags of silica sand used for sandblasting now carry labels warning the user to wear respiratory protection to avoid breathing the resulting fine silica dust. Material safety data sheets (MSDS) for silica sand state that "excessive inhalation of crystalline silica is a serious health concern".^[4]

In areas of high pore water pressure sand and salt water can form quicksand, which is a colloid hydrogel that behaves like a liquid. Quicksand produces a considerable barrier to escape for creatures caught within, who often die from exposure (not from submersion) as a result.

Environmental Issues[link]

Sand's many uses require a significant dredging industry, raising environmental concerns over fish depletion, landslides, and flooding. Countries such as China, Indonesia, Malaysia and Cambodia ban sand exports, citing these issues as a major factor.^[5]

See also[link]

Wikimedia Commons has media related to: Sand

• Beach
• Dry quicksand
• Sandstorm
• Heavy mineral sands ore deposits
• Oil sands
• Particle size
• Quicksand
• Sand island
• Sand Rat
• Sandstone
• Singing sand
• Tar sands
• White Sands National Monument

References[link]

External links[link]

Look up sand in Wiktionary, the free dictionary.

• Beach Sand: What It Is, Where It Comes From and How It Gets Here Beaufort County, SC
• ISO

v t e Coastal geography Landforms Anchialine pool Avulsion Archipelago Atoll Ayre Barrier bar Barrier island Bay Baymouth bar Bight Brackish marsh Cape Channel Cliff Cliffed coast Cliff-top dune Coast Coastal plain Coastal waterfall Continental margin Continental shelf Coral reef Cove Dune Estuary Firth Fjard Fjord Flat coast Freshwater marsh Fundus Gat Geo Graded shoreline Gulf Headland Inlet Intertidal wetland Island Islet Isthmus Lagoon Marine terrace Mouth bar Raised shorelines Machair Mega delta Mudflat Natural arch Peninsula Reef Regressive delta Ria River delta Rocky shore Salt marsh Shore Sound Stack Steep coast Strait Strand plain Submarine canyon Tied island Tidal island Tidal marsh Tide pool Tombolo More... Beaches Beach cusps Beach evolution Beach ridge Beachrock Modern recession of beaches Pocket beach Raised beach Storm beach Shingle beach Processes Blowhole Coastal erosion Concordant coastline Current Cuspate foreland Discordant coastline Emergent coastline Feeder bluff Fetch Headlands and bays Large scale coastal behaviour Longshore drift Marine regression Marine transgression Rip current Sea cave Sea foam Shoal Spit Submergent coastline Surf break Surf zone Surge channel Swash Volcanic arc Wave-cut platform Wave shoaling Wind wave Wrack zone Management Coastal management Accretion Integrated coastal zone management Submersion Related Bulkhead line Coastline length Intertidal zone Littoral zone Particle size boulder shingle pebble sand silt clay Physical oceanography Region of freshwater influence Scree More...