Dune

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Dune 

 

Coastal dunes in De Panne Belgium.

 

Erg Chebbi, Morocco

 

Sand dunes of the Empty Quarter to the east of Liwa Oasis, United Arab Emirates.

Dunes are large masses of wind-blown sand, and are most common in deserted environments, such as the Sahara, and also near beaches. An area with dunes is called a dune system. In physical geography, a dune is a hill of loose sand built by aeolian processes (wind) or the flow of water. Dunes occur in different shapes and sizes, formed by interaction with the flow of air or water. Dunes can be natural, but also man-made (artificial). Most kinds of dunes are longer on the stoss (upflow) side, where the sand is pushed up the dune, and have a shorter "slip face" in the lee side. The valley or trough between dunes is called a slack.

An erg or sand sea is a large broad, flat area covered with wind-swept sand and/or dunes with little or no vegetation. Smaller areas are called dune fields.

Dunes occur in some deserts, inland and along some coasts. 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 can form under the action of water flow (fluvial processes), and on sand or gravel beds of rivers, estuaries and the sea-bed.

The modern word "dune" came into English from French around 1790, which in turn came from Middle Dutch dūne.

Formation

Sand hitting sand is more likely to stick; sand hitting a more coherent surface is more likely to bounce (saltation). This exacerbating feedback loop helps sand accumulate into dunes.

 

Dunes are made of sand-sized particles, and may consist of quartz, calcium carbonate, snow, gypsum, or other materials. The upwind/upstream/upcurrent side of the dune is called the stoss side; the downflow side is called the lee side. Sand is pushed (creep) or bounces (saltation) up the stoss side, and slides down the lee side. A side of a dune that the sand has slid down is called a slip face (or slipface). 

The Bagnold formula gives the speed at which particles can be transported.

Aeolian dunes

Aeolian dune shapes

Five basic dune types are recognized: crescentic, linear, star, dome, and parabolic. Dune areas may occur in three forms: simple (isolated dunes of basic type), compound (larger dunes on which smaller dunes of same type form), and complex (combinations of different types).

Barchan or crescentic

Isolated barchan dunes on the surface of Mars. Dominant wind direction would be from left to right.

 

Barchan dunes are crescent-shaped mounds which are generally wider than they are long. The lee-side slipfaces are on the concave sides of the dunes. These dunes form under winds that blow consistently from one direction (unimodal winds). They form separate crescents when the sand supply is comparatively small. When the sand supply is greater, they may merge into barchanoid ridges, and then transverse dunes (see below).

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 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 three kilometres, are in China's Taklamakan Desert.

See lunettes and parabolic dunes, below, for dunes similar to crescent-shaped ones.

Transverse dunes

Abundant barchan dunes may merge into barchanoid ridges, which then grade into linear (or slightly sinuous) transverse dunes, so called because they lie transverse, or across, the wind direction, with the wind blowing perpendicular to the ridge crest.

Seif or longitudinal dunes

Seif dunes are linear (or slightly sinuous) dunes with two slip faces. The two slip faces make them sharp-crested. They are called seif dunes after the Arabic word for "sword". They may be more than 160 kilometres (100 miles) long, and thus easily visible in satellite images (see illustrations).

Seif dunes are associated with bidirectional winds. The long axes and ridges of these dunes extend along the resultant direction of sand movement (hence the name "longitudinal"). Some linear dunes merge to form Y-shaped compound dunes.

Formation is debated. Bagnold, in The Physics of Blown Sand and Desert Dunes, suggested that some seif dunes form when a barchan dune moves into a bidirectional wind regime, and one arm or wing of the crescent elongates. Others suggest that seif dunes are formed by vortices in a unidirectional wind. In the sheltered troughs between highly developed seif dunes, barchans may be formed, because the wind is constrained to be unidirectional by the dunes.

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  Rub' al Khali (Arabian Empty Quarter) sand dunes imaged by Terra (EOS AM-1). Most of these dunes are seif dunes. Their origin from barchans is suggested by the stubby remnant "hooks" seen on many of the dunes. Wind would be from left to right.
  
  
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  Large linear seif dunes in the Great Sand Sea in southwest Egypt, seen from the International Space Station. The distance between each dune is 1.5–2.5 km.
  
  
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  The average-direction-longitudinal model of seif dune formation.
  
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  By contrast, transverse dunes form with the wind blowing perpendicular to the ridges, and have only one slipface, on the lee side. The stoss side is less steep.
  
  
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  Transverse dunes lie perpendicular to the wind, which moves them forwards, producing the cross-bedding shown here.
  

Seif dunes 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 Empty Quarter, contains seif dunes that stretch for almost 200 km and reach heights of over 300 m.

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

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

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

Lunettes

Fixed crescentic dunes that form on the leeward margins of playas and river valleys in arid and semiarid regions in response to the direction (s) of prevailing winds, are known as lunettes, source-bordering dunes, bourrelets and clay dunes. They may be composed of clay, silt, sand, or gypsum, eroded from the basin floor or shore, transported up the concave side of the dune, and deposited on the convex side. Examples in Australia are up to 6.5 km long, 1 km wide, and up to 50 metres high. They also occur in southern and West Africa, and in parts of the western United States, especially Texas.

Parabolic

Schematic of coastal parabolic dunes

 

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 slipfaces 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. The stability of the dunes was once attributed to the vegetative cover but recent research has pointed to water as the main source of parabolic dune stability. The vegetation that covers them—grasses, shrubs, and trees—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.

A type of extensive parabolic dune that lacks discernible slipfaces and has mostly coarse grained sand is known as a zibar. The term zibar comes from the Arabic word to describe "rolling transverse ridges ... with a hard surface". The dunes are small, have low relief, and can be found in many places across the planet from Wyoming (United States) to Saudi Arabia to Australia. Spacing between zibars ranges from 50 to 400 metres and they don't become more than 10 metres high. The dunes form at about ninety degrees to the prevailing wind which blows away the small, fine-grained sand leaving behind the coarser grained sand to form the crest.

Reversing dunes

Reversing dune showing short minor slipface atop the major stoss (upwind) face

 

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. The minor slipfaces are usually temporary, as they appear after a reverse wind and are generally destroyed when the wind next blows in the dominant direction.

Draas

Dune Nine in Sossusvlei, Namibia, is over 300m high.

 

Draas are very large-scale dune bedforms; they may be tens or a few hundreds of metres in height, kilometres wide, and hundreds of kilometres in length. After a draa has reached a certain size, it generally develops superimposed dune forms. They are thought to be more ancient and slower-moving than smaller dunes, and to form by vertical growth of existing dunes. Draas are widespread in sand seas and are well-represented in the geological record.

Dune complexity

All these dune shapes may occur in three forms: simple (isolated dunes of basic type), compound (lager dunes on which smaller dunes of same type form), and complex (combinations of different types). Simple dunes are basic forms with the 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. 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 movement

The sand mass of dunes can move either windward or leeward, depending on if the wind is making contact with the dune from below or above its apogee. If wind hits from above, the sand particles move leeward. If sand hits from below, sand particles move windward. The leeward flux of sand is greater than the windward flux. Further, when the wind carrying sand particles when it hits the dune, the dune's sand particles will saltate more than if the wind had hit the dune without carrying sand particles.

Coastal dunes

Coastal dunes covered in grasses around the mouth of the Liver Å river in Denmark

 

Play media

Newborough Dune Rejuvenation, Wales; video of work done by Natural Resources Wales; 2015

Coastal dunes form when wet sand is deposited along the coast and dries out and is blown along the beach.^[26] Dunes form where the beach is wide enough to allow for the accumulation of wind-blown sand, and where prevailing onshore winds tend to blow sand inland. The three key ingredients for coastal dune formation are a large sand supply, winds to move said sand supply, and a place for the sand supply to accumulate. Obstacles—for example, vegetation, pebbles and so on—tend to slow down the wind and lead to the deposition of sand grains. These small "incipient dunes or "shadow dunes" tend to grow in the vertical direction if the obstacle slowing the wind can also grow vertically (i.e., vegetation). Coastal dunes expand laterally as a result of lateral growth of coastal plants via seed or rhizome. Models of coastal dunes suggest that their final equilibrium height is related to the distance between the water line and where vegetation can grow. Coastal dunes can be classified by where they develop, or begin to take shape. Dunes are commonly grouped into either the Primary Dune Group or the Secondary Dune Group. Primary dunes gain most of their sand from the beach itself, while secondary dunes gain their sand from the primary dune. Along the Florida Panhandle, most dunes are considered to be foredunes or hummocks. Different locations around the globe have dune formations unique to their given coastal profile.

Coastal sand dunes can provide privacy and/or habitats to support local flora and fauna. Animals such as sand snakes, lizards, and rodents can live in coastal sand dunes, along with insects of all types. Often the vegetation of sand dunes is discussed without acknowledging the importance that coastal dunes have for animals. Further, some animals, such as foxes and feral pigs can use coastal dunes as hunting grounds to find food. Birds are also known to utilize coastal dunes as nesting grounds. All these species find the coastal environment of the sand dune vital to their species' survival. 

Over the course of time coastal dunes may be impacted by tropical cyclones or other intense storm activity, dependent on their location. Recent work has suggested that coastal dunes tend to evolve toward a high or low morphology depending on the growth rate of dunes relative to storm frequency. During a storm event, dunes play a significant role in minimizing wave energy as it moves onshore. As a result, coastal dunes, especially those in the foredune area affected by a storm surge, will retreat or erode. To counteract the damage from tropical activity on coastal dunes, short term post-storm efforts such as fences can be made by individual agencies through fencing to help with sand accumulation.

How a much a dune erodes during any storm surge is related to its location on the coastal shoreline and the profile of the beach during a particular season. During the summer, a beach tends to take on more of a convex appearance due to gentler waves, while the same beach in the winter may take on more of a concave appearance. As a result, coastal dunes can get eroded much more quickly in the winter than in the summer.

Ecological succession on coastal dunes

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. 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. In Europe these plants include: creeping willow, cotton grass, yellow iris, reeds, and rushes. As for vertebrates in European dunes, natterjack toads sometimes breed here.

Coastal dune floral adaptations

Dune ecosystems are extremely difficult places for plants to survive. This is due to a number of pressures related to their proximity to the ocean and confinement to growth on sandy substrates. These include:

• Little available soil moisture
• Little available soil organic matter/nutrients
• Harsh winds
• Salt spray
• Erosion/shifting and sometimes ephemeral substrate
• Tidal influences

There are many adaptations plants have evolved to cope with these pressures:

• Deep taproot to reach water table (Pink Sand Verbena)
• Shallow but extensive root systems
• Prostrate growth form to avoid wind/salt spray (Abronia spp., Beach Primrose)
• Krummholz growth form (Monterrey Cypress-not a dune plant but deals with similar pressures)
• Thickened cuticle/Succulence to reduce moisture loss and reduce salt uptake (Ambrosia/Abronia spp., Calystegia soldanella)
• Pale leaves to reduce insolation (Artemisia/Ambrosia spp.)
• Thorny/Spiky seeds to ensure establishment in vicinity of parent, reduces chances of being blown away or swept out to sea (Ambrosia chamissonis)

Nabkha dunes

A nabkha, or coppice dune, is a small dune anchored by vegetation. They usually indicate desertification or soil erosion, and serve as nesting and burrow sites for animals.

Sub-aqueous dunes

Sub-aqueous (underwater) dunes 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. In the case of sub-aqueous barchan dunes, sediment is lost by their extremities, known as horns.

These dunes most often form as a continuous 'train' of dunes, showing remarkable similarity in wavelength and height. The shape of a dune gives information about its formation environment. For instance, rivers produce asymmetrical ripples, with the steeper slip face facing downstream. Ripple marks preserved in sedimentary strata in the geological record can be used to determine the direction of current flow, and thus an indication of the source of the sediments.

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

Lithified dunes

Cross-bedding in lithified aeolian sand dunes preserved as sandstone in Zion National Park, Utah

 

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 Zion National Park in the western United States.

A slang term, used in the southwest US, for 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.

Desertification

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 uses a valuable resource and is quite destructive to the dunes' animal habitats. Sand fences might also slow their movement to a crawl, but geologists are still analyzing results for the optimum fence designs. 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.

Conservation

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

 

Dune habitats provide niches for highly specialized 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, Netherlands, and Sri Lanka 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.

Examples

Africa

A dune in Sossusvlei, in the greater Namib-Naukluft National Park, Namibia. Note the trees being engulfed for scale.

 

Camelthorn trees and bushes scattered on dunes in the Kalahari Desert in Namibia (2017)

• Alexandria Coastal Dunefields, in the Eastern Cape, South Africa
• Witsand Nature Reserve in the Kalahari Desert, South Africa
• The white dunes of De Hoop Nature Reserve, South Africa
• The dunes of the Suguta Valley, a desert part of the Great Rift Valley in northwestern Kenya
• The dunes of the Danakil Depression, northeastern Ethiopia toward the border with Eritrea
• The dunes of Sossusvlei in the greater Namib-Naukluft National Park, Namibia
• The coastal dunes of Iona National Park in the southwesternmost part of Angola
• Khawa dunes in the Kgalagadi Transfrontier Park, the southwesternmost part of Botswana
• La Dune Rose in the city of Gao in northern Mali near the Niger River
• Erg Aoukar in southeastern Mauritania extending into Mali
• Erg Chech in southwestern Algeria and northern Mali
• Erg Chebbi and Erg Chigaga in southern Morocco
• Grand Erg Oriental in northeastern Algeria and southern Tunisia
• Grand Erg Occidental in western Algeria
• The Idehan Ubari and the Idehan Murzuq in southwestern Libya
• The Corralejo dunes in the Canary Islands, Spain
• The Rebiana Sand Sea in southeastern Libya
• The Great Sand Sea in southeastern Libya and southwestern Egypt
• The Selima Sand Sheet in northwestern Sudan
• The dunes of the Bayuda Desert in northern Sudan
• The dunes of the Lompoul Desert in northwestern Senegal
• The coastal dunes of Bazaruto Island, Mozambique
• Erg du Djourab in northern Chad
• The dunes of the Mourdi Depression in northeastern Chad
• The dunes of Tin Toumma Desert, in southeastern Niger
• Grand Erg de Bilma in the Ténéré, in northern Niger
• The dunes of Oursi in the Sahel Region, northern Burkina Faso
• Tanzania's Shifting Sands near Olduvai Gorge

Wind ripples on crescent-shaped sand dunes (Barchans) in Southwest Afghanistan (Sistan)

Asia

• The dunes in the Thar Desert in India and Pakistan
• 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.
• Moreeb Dune in Liwa Oasis, United Arab Emirates, used as an arena for drag motor sports and Sandboarding.
• Gumuk Pasir Parangkusumo near Parangtritis beach in Yogyakarta, Indonesia.
• Mui Ne, Vietnam.
• Wahiba Sands, Oman
• Teri, red dune complex in southern India
• The dunes of the Taklamakan Desert in southwest Xinjiang in Northwest China
• Tukulans of the Central Yakutian Lowland, Russia

Fronting the Mediterranean Sea in Oliva, a municipality in the comarca of Safor in the Valencian Community, Spain

Europe

• The Dunes of Dyuni, near Pomorie, Bulgaria, vast area of sand dunes in the Burgas Province
• The Dune of Pilat, not far from Bordeaux, France, is the largest known sand dune in Europe
• The Dunes of Piscinas, in the south west of Sardinia island.
• 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
• Råbjerg mile, Northern Jutland, Denmark
• Thy National Park, North Denmark Region, Denmark
• Dunes of Corrubedo, Spain
• Northern Littoral Natural Park, Portugal
• São Jacinto Dunes Natural Reserve, Portugal
• Rëra e Hedhur in Shëngjin, Albania
• Hoge Veluwe National Park, Veluwe, Netherlands
• Dunes of Texel National Park, Texel, Netherlands
• Zuid-Kennemerland National Park, North Holland, Netherlands
• Ammothines Lemnou, Lemnos, Greece
• Dunes of the Curonian Spit, Lithuania and Russia
• Oleshky Sands, Ukraine
• Ullahau, Sweden, Big Parabel Dune and dune system

North America

Guadalupe-Nipomo Dunes

 

Cadiz Dunes Wilderness, California.

• Victoria Island Sand Dunes,160 km North West of Cambridge Bay, Nunavut, Canada. Approximately 600 square kilometers, the largest in Canada, third largest in North America and the largest in the Artic. There are two lakes with direct access to the Dunes from float planes.
• Herring Cove, Race Point and The Province Lands bicycle path in Provincetown, Massachusetts as part of the US National Park Service of the Cape Cod National Seashore.
• Great Kobuk Sand Dunes, the northernmost sand dunes in the world, Kobuk Valley National Park, Alaska.
• The Athabasca Sand Dunes, located in the Athabasca Sand Dunes Provincial Park, Saskatchewan.
• The Cadiz Dunes in the Mojave Trails National Monument in California.
• The Kelso Dunes in the Mojave Desert of California.
• Eureka Valley Sand Dunes and Mesquite Flat Sand Dunes in Death Valley National Park, California.
• Great Sand Dunes National Park, Colorado.
• White Sands National Park, New Mexico.
• Little Sahara Recreation Area, Utah.
• Sleeping Bear Dunes National Lakeshore, Michigan, on the east shore of Lake Michigan.
• Indiana Dunes National Park, Indiana, on the south shore of Lake Michigan.^[57][58]
• Warren Dunes State Park, Michigan, on the east shore of Lake Michigan.
• Grand Sable Dunes, in the Pictured Rocks National Lakeshore, Michigan.
• Samalayuca Dunes, in the state of Chihuahua, Mexico
• 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.
• The Great Dune found in Cape Henlopen State Park in Lewes, Delaware.
• Oregon Dunes National Recreation Area near Florence, Oregon, on the Pacific Coast.
• Bruneau Dunes State Park – Owyhee Desert, Idaho
• Hoffmaster State Park – Muskegon, Michigan
• Silver Lake State Park — a sand dunes that allows off-road vehicle use located in Mears, Michigan.

South America

White sand dunes in the Lençóis Maranhenses National Park, Maranhão, Brazil

• 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
• Duna Federico Kirbus in Catamarca Province, Argentina
• Villa Gesell in Buenos Aires Province, Argentina
• Cerro Blanco in Nazca Province, Peru
• Huacachina in Ica Region, Peru
• Cerro Medanoso in Atacama Region, Chile
• Colún Beach, Valdivian Coastal Reserve in Chile

Oceania

• Simpson Desert sand dunes in the Northern Territory, Queensland and South Australia, Australia
• Fraser Island in Queensland, Australia
• Cronulla sand dunes in New South Wales, Australia
• Stockton Beach in New South Wales, Australia
• Te Paki sand dunes near Cape Reinga, New Zealand

World's highest dunes

Note: This table is partially based on estimates and incomplete information.

Dune	Height from Base feet/metres	Height from Sea Level feet/metres	Location	Notes
Duna Federico Kirbus	≈4,035/1,230	≈9,334/2,845	Bolsón de Fiambalá, Fiambalá, Catamarca Province, Argentina	Highest in the world
Cerro Blanco	≈3,860/1,176	≈6,791/2,080	Nazca Province, Ica Region, Peru 14.868°S 74.838°W	Highest in Peru, second highest in the world
Badain Jaran Dunes	≈1,640/500	≈6,640/2,020	Badain Jaran Desert, Alashan Plain, Inner Mongolia, Gobi Desert, China	World's tallest stationary dunes and highest in Asia
Rig-e Yalan Dune	≈1,542/470	≈3,117/950	Lut Desert, Kerman, Iran	Near World the hottest place (Gandom Beryan)
Average Highest Area Dunes	1,410/430?	≈6,500/1,980?	Isaouane-n-Tifernine Sand Sea, Algerian Sahara	Highest in Africa
Big Daddy/Dune 7 (Big Mama?)	1,256/383	≈1,870/570	Sossusvlei Dunes, Namib Desert, Namibia / Near Walvis Bay Namib Desert, Namibia	according to the Namibian Ministry of Environment & Tourism the highest dune in the world
Mount Tempest	≈920/280	≈920/280	Moreton Island, Brisbane, Australia	Highest in Australia
Star Dune	>750/230	≈8,950/2,730	Great Sand Dunes National Park and Preserve, Colorado, USA	Highest in North America
Dune of Pyla	≈345/105	≈699/130	Bay of Arcachon, Aquitaine, France	Highest in Europe
Ming-Sha Dunes	?	5,660/1,725	Dunhuang Oasis, Taklamakan Desert, Gansu, China
Medanoso Dune	≈1805/550	≈5446/1,660	Atacama Desert, Chile	Highest in Chile

Sand dune systems

(coastal dunes featuring succession)

• Athabasca Sand Dunes Provincial Park, Alberta and Saskatchewan
• Ashdod Sand Dune, Israel
• Bamburgh Dunes, Northumberland, England
• Bradley Beach, New Jersey
• Circeo National Park, a Mediterranean dune area on the southwest coast of the Lazio region of Italy
• Cronulla sand dunes, NSW, Australia
• Crymlyn Burrows, Wales
• Dawlish Warren, Devon, England
• Fraser Island, Queensland Australia, largest sand island in the world
• Indiana Dunes National Park, Indiana
• Kenfig Burrows, Wales
• Margam burrows, Wales
• Murlough Sand Dunes, Newcastle, Co Down, Northern Ireland
• Morfa Harlech sand dunes, Gwynedd, Wales
• Newborough Warren, North Wales
• Oregon Dunes National Recreation Area, near North Bend, Oregon
• Penhale Sands, Cornwall, England
• Sleeping Bear Dunes National Lakeshore, Michigan
• Sandy Island Beach State Park, Richland, New York
• Studland, Dorset, England
• Thy National Park, North Denmark Region, Denmark
• Winterton, Norfolk, England
• Woolacombe, Devon, England
• Ynyslas Sand Dunes, Wales

Extraterrestrial dunes

Sand dune on Mars

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 in the equatorial regions of Titan. 

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.

Dunes are a popular theme in science fiction, featuring in depictions of dry Desert planets appearing as early as the 1956 film Forbidden Planet and Frank Herbert's 1965 novel Dune. The environment of the desert planet Arrakis (also known as Dune) in the Dune franchise Dune in turn inspired the Star Wars franchise, which includes prominent theme of dunes on fictional planets such as Tatooine, Geonosis, and Jakku.

Internationalization

From Wikipedia, the free encyclopedia

In economics, internationalization or internationalisation is the process of increasing involvement of enterprises in international markets, although there is no agreed definition of internationalization. Internationalization is a crucial strategy not only for companies that seek horizontal integration globally but also for countries that addresses the sustainability of its development in different manufacturing as well as service sectors especially in higher education which is a very important context that needs internationalization to bridge the gap between different cultures and countries. There are several internationalization theories which try to explain why there are international activities.

Entrepreneurs and enterprises

Those entrepreneurs who are interested in the field of internationalization of business need to possess the ability to think globally and have an understanding of international cultures. By appreciating and understanding different beliefs, values, behaviors and business strategies of a variety of companies within other countries, entrepreneurs will be able to internationalize successfully. Entrepreneurs must also have an ongoing concern for innovation, maintaining a high level of quality, be committed to corporate social responsibility, and continue to strive to provide the best business strategies and either goods or services possible while adapting to different countries and cultures.

Trade theories

Absolute cost advantage (Adam Smith, 1776)

Adam Smith claimed that a country should specialise in, and export, commodities in which it had an absolute advantage. An absolute advantage existed when the country could produce a commodity with less costs per unit produced than could its trading partner. By the same reasoning, it should import commodities in which it had an absolute disadvantage.

While there are possible gains from trade with absolute advantage, comparative advantage extends the range of possible mutually beneficial exchanges. In other words, it is not necessary to have an absolute advantage to gain from trade, only a comparative advantage.

Comparative cost advantage (David Ricardo, 1817)

David Ricardo argued that a country does not need to have an absolute advantage in the production of any commodity for international trade between it and another country to be mutually beneficial. Absolute advantage meant greater efficiency in production, or the use of less labor factor in production. Two countries could both benefit from trade if each had a relative advantage in production. Relative advantage simply meant that the ratio of the labor embodied in the two commodities differed between two countries, such that each country would have at least one commoditiy where the relative amount of labor embodied would be less than that of the other country.

Gravity model of trade (Walter Isard, 1954)

The gravity model of trade in international economics, similar to other gravity models in social science, predicts bilateral trade flows based on the economic sizes of (often using GDP measurements) and distance between two units. The basic theoretical model for trade between two countries takes the form of:

${\displaystyle F_{ij}=G{\frac {M_{i}M_{j}}{D_{ij}}}}$

with:

${\displaystyle F\,}$: Trade flow

${\displaystyle i,j\,}$: Country i and j

${\displaystyle M\,}$: Economic mass, for example GDP

${\displaystyle D\,}$: Distance

${\displaystyle G\,}$: Constant

The model has also been used in international relations to evaluate the impact of treaties and alliances on trade, and it has been used to test the effectiveness of trade agreements and organizations such as the North American Free Trade Agreement (NAFTA) and the World Trade Organization (WTO).

Heckscher-Ohlin model (Eli Heckscher, 1966 & Bertil Ohlin, 1952)

The Heckscher-Ohlin model (H-O model), also known as the factors proportions development, is a general equilibrium mathematical model of international trade, developed by Eli Heckscher and Bertil Ohlin at the Stockholm School of Economics. It builds on David Ricardo's theory of comparative advantage by predicting patterns of commerce and production based on the factor endowments of a trading region. The model essentially says that countries will export products that utilize their abundant and cheap factor(s) of production and import products that utilize the countries' scarce factor(s).

The results of this work has been the formulation of certain named conclusions arising from the assumptions inherent in the model. These are known as:

• Heckscher-Ohlin theorem
• Rybczynski theorem
• Stolper-Samuelson theorem
• Factor-Price Equalization theorem

Leontief paradox (Wassily Leontief, 1954)

Leontief's paradox in economics is that the country with the world's highest capital-per worker has a lower capital:labour ratio in exports than in imports. 

This econometric find was the result of Professor Wassily W. Leontief's attempt to test the Heckscher-Ohlin theory empirically. In 1954, Leontief found that the U.S. (the most capital-abundant country in the world by any criteria) exported labor-intensive commodities and imported capital-intensive commodities, in contradiction with Heckscher-Ohlin theory.

Linder hypothesis (Staffan Burenstam Linder, 1961)

The Linder hypothesis (demand-structure hypothesis) is a conjecture in economics about international trade patterns. The hypothesis is that the more similar are the demand structures of countries the more they will trade with one another. Further, international trade will still occur between two countries having identical preferences and factor endowments (relying on specialization to create a comparative advantage in the production of differentiated goods between the two nations).

Location theory

Location theory is concerned with the geographic location of economic activity; it has become an integral part of economic geography, regional science, and spatial economics. Location theory addresses the questions of what economic activities are located where and why. Location theory rests — like microeconomic theory generally — on the assumption that agents act in their own self-interest. Thus firms choose locations that maximize their profits and individuals choose locations, that maximize their utility.

Market imperfection theory (Stephen Hymer, 1976 & Charles P. Kindleberger, 1969 & Richard E. Caves, 1971)

In economics, a market failure is a situation wherein the allocation of production or use of goods and services by the free market is not efficient. Market failures can be viewed as scenarios where individuals' pursuit of pure self-interest leads to results that can be improved upon from the societal point of view. The first known use of the term by economists was in 1958, but the concept has been traced back to the Victorian philosopher Henry Sidgwick.

Market imperfection can be defined as anything that interferes with trade. This includes two dimensions of imperfections. First, imperfections cause a rational market participant to deviate from holding the market portfolio. Second, imperfections cause a rational market participant to deviate from his preferred risk level. Market imperfections generate costs which interfere with trades that rational individuals make (or would make in the absence of the imperfection).

The idea that multinational corporations (MNEs) owe their existence to market imperfections was first put forward by Stephen Hymer, Charles P. Kindleberger and Caves. The market imperfections they had in mind were, however, structural imperfections in markets for final products.

According to Hymer, market imperfections are structural, arising from structural deviations from perfect competition in the final product market due to exclusive and permanent control of proprietary technology, privileged access to inputs, scale economies, control of distribution systems, and product differentiation, but in their absence markets are perfectly efficient.

By contrast, the insight of transaction costs theories of the MNEs, simultaneously and independently developed in the 1970s by McManus (1972), Buckley and Casson (1976), Brown (1976) and Hennart (1977, 1982), is that market imperfections are inherent attributes of markets, and MNEs are institutions to bypass these imperfections. Markets experience natural imperfections, i.e. imperfections that are because the implicit neoclassical assumptions of perfect knowledge and perfect enforcement are not realized.

New Trade Theory

New Trade Theory (NTT) is the economic critique of international free trade from the perspective of increasing returns to scale and the network effect. Some economists have asked whether it might be effective for a nation to shelter infant industries until they had grown to a sufficient size large enough to compete internationally.

New Trade theorists challenge the assumption of diminishing returns to scale, and some argue that using protectionist measures to build up a huge industrial base in certain industries will then allow those sectors to dominate the world market (via a network effect).

Specific factors model

In this model, labour mobility between industries is possible while capital is immobile between industries in the short-run. Thus, this model can be interpreted as a 'short run' version of the Heckscher-Ohlin model.

Traditional approaches

The Porter diamond

Diamond model

The diamond model is an economical model developed by Michael Porter in his book The Competitive Advantage of Nations, where he published his theory of why particular industries become competitive in particular locations.

The diamond model consists of six factors:

• Factor conditions
• Demand conditions
• Related and supporting industries
• Firm strategy, structure and rivalry
• Government
• Chance

The Porter thesis is that these factors interact with each other to create conditions where innovation and improved competitiveness occurs.

Diffusion of innovations (Rogers, 1962)

Diffusion of innovation is a theory of how, why, and at what rate new ideas and technology spread through cultures. Everett Rogers introduced it in his 1962 book, Diffusion of Innovations, writing that "Diffusion is the process by which an innovation is communicated through certain channels over time among the members of a social system."

Eclectic paradigm (John H. Dunning)

The eclectic paradigm is a theory in economics and is also known as the OLI-Model. It is a further development of the theory of internalization and published by John H. Dunning in 1993. The theory of internalization itself is based on the transaction cost theory. This theory says that transactions are made within an institution if the transaction costs on the free market are higher than the internal costs. This process is called internalization.

For Dunning, not only the structure of organization is important. He added three additional factors to the theory:

• Ownership advantages (trademark, production technique, entrepreneurial skills, returns to scale)
• Locational advantages (existence of raw materials, low wages, special taxes or tariffs)
• Internalisation advantages (advantages by producing through a partnership arrangement such as licensing or a joint venture).

Foreign direct investment theory

Foreign direct investment (FDI) in its classic form is defined as a company from one country making a physical investment into building a factory in another country. It is the establishment of an enterprise by a foreigner. Its definition can be extended to include investments made to acquire lasting interest in enterprises operating outside of the economy of the investor. The FDI relationship consists of a parent enterprise and a foreign affiliate which together form a multinational corporation (MNC). In order to qualify as FDI the investment must afford the parent enterprise control over its foreign affiliate. The International Monetary Fund (IMF) defines control in this case as owning 10% or more of the ordinary shares or voting power of an incorporated firm or its equivalent for an unincorporated firm; lower ownership shares are known as portfolio investment.

Monopolistic advantage theory

The monopolistic advantage theory is an approach in international business which explains why firms can compete in foreign settings against indigenous competitors and is frequently associated with the seminal contribution of Stephen Hymer.

Prior to Stephen Hymer’s doctoral thesis, The International Operations of National Firms: A Study of foreign direct Investment, theories did not adequately explain why firms engaged in foreign operations. Hymer started his research by analyzing the motivations behind foreign investment of US corporations in other countries. Neoclassical theories, dominant at the time, explained foreign direct investments as capital movements across borders based on perceived benefits from interest rates in other markets, there was no need to separate them from any other kind of investment (Ietto-Guilles, 2012).

He effectively differentiated Foreign Direct Investment and portfolio investments by including the notion of control of foreign firms to FDI Theory, which implies control of the operation; whilst portfolio foreign investment confers a share of ownership but not control. Stephen Hymer focused on and considered FDI and MNE as part of the theory of the firm. (Hymer, 1976: 21) 

He also dismissed the assumption that FDIs are motivated by the search of low costs in foreign countries, by emphasizing the fact that local firms are not able to compete effectively against foreign firms, even though they have to face foreign barriers (cultural, political, lingual etc.) to market entry. He suggested that firms invest in foreign countries in order to maximize their specific firm advantages in imperfect markets, that is, markets where the flow of information is uneven and allows companies to benefit from a competitive advantage over the local competition.

Stephen Hymer also suggested a second determinant for firms engaging in foreign operations, removal of conflicts. When a rival company is operating in a foreign market or is willing to enter one, a conflict situation arises. Through FDI, a multinational can share or take complete control of foreign production, effectively removing conflict. This will lead to the increase of market power for the specific firm, increasing imperfections in the market as a whole (Ietto-Guilles, 2012)

A final determinant for multinationals making direct investments is the distribution of risk through diversification. By choosing different markets and production locations, the risk inherent to foreign operations are spread and reduced.

All of these motivations for FDI are built on market imperfections and conflict. A firm engaging in direct investment could then reduce competition, eliminate the conflicts and exploit the firm specific advantages making them capable of succeeding in a foreign market.

Stephen Hymer can be considered the father of international business because he effectively studied multinationals from a different perspective than the existing literature, by approaching multinationals as national companies with international operations, regarded as expansions from home operations. He analyzed the activities of the MNEs and their impact on the economy, gave an explanation for the large flow of foreign investments by US corporations at a time where they were incomplete, and envisioned the ethical conflicts that could arise from the increase in power of MNEs.

Non-availability approach

The non-availability explains international trade by the fact that each country imports the goods that are not available at home. This unavailability may be due to lack of natural resources (oil, gold, etc.: this is absolute unavailability) or to the fact that the goods cannot be produced domestically, or could only be produced at prohibitive costs (for technological or other reasons): this is relative unavailability. On the other hand, each country exports the goods that are available at home.

Technology gap theory of trade 

The technology gap theory describes an advantage enjoyed by the country that introduces new goods in a market. As a consequence of research activity and entrepreneurship, new goods are produced and the innovating country enjoys a monopoly until the other countries learn to produce these goods: in the meantime they have to import them. Thus, international trade is created for the time necessary to imitate the new goods (imitation lag).

Uppsala model

The Uppsala model is a theory that explains how firms gradually intensify their activities in foreign markets. It is similar to the POM model. The key features of both models are the following: firms first gain experience from the domestic market before they move to foreign markets; firms start their foreign operations from culturally and/or geographically close countries and move gradually to culturally and geographically more distant countries; firms start their foreign operations by using traditional exports and gradually move to using more intensive and demanding operation modes (sales subsidiaries etc.) both at the company and target country level.

Further theories

Contingency theory

Contingency theory refers to any of a number of management theories. Several contingency approaches were developed concurrently in the late 1960s. They suggested that previous theories such as Weber's bureaucracy and Frederick Winslow Taylor's scientific management had failed because they neglected that management style and organizational structure were influenced by various aspects of the environment: the contingency factors. There could not be "one best way" for leadership or organization.

Contract theory

In economics, contract theory studies how economic actors can and do construct contractual arrangements, generally in the presence of asymmetric information. Contract theory is closely connected to the field of law and economics. One prominent field of application is managerial compensation.

Economy of scale

Economies of scale, in microeconomics, are the cost advantages that a business obtains due to expansion. They are factors that cause a producer’s average cost per unit to fall as output rises. Diseconomies of scale are the opposite. Economies of scale may be utilized by any size firm expanding its scale of operation.

Internalisation theory (Peter J. Buckley & Mark Casson, 1976; Rugman, 1981)

Product life-cycle theory

As first articulated by Raymond Vernon in 1966, a product goes through a life cycle consisting of four stages: "new product", "growth product", "maturity product" and "obsolescence product". The conditions in which a product is sold change over time and must be managed as it moves through this succession of stages. This is called product life cycle management. 

Transaction cost theory

The theory of the firm consists of a number of economic theories which describe the nature of the firm, company, or corporation, including its existence, its behaviour, and its relationship with the market.

Ronald Coase set out his transaction cost theory of the firm in 1937, making it one of the first (neo-classical) attempts to define the firm theoretically in relation to the market. Coase sets out to define a firm in a manner which is both realistic and compatible with the idea of substitution at the margin, so instruments of conventional economic analysis apply. He notes that a firm’s interactions with the market may not be under its control (for instance because of sales taxes), but its internal allocation of resources are: “Within a firm, ... market transactions are eliminated and in place of the complicated market structure with exchange transactions is substituted the entrepreneur ... who directs production.” He asks why alternative methods of production (such as the price mechanism and economic planning), could not either achieve all production, so that either firms use internal prices for all their production, or one big firm runs the entire economy.

Theory of the growth of the firm

While at Johns Hopkins, Penrose participated in a research project on the growth of firms. She came to the conclusion that the existing theory of the firm was inadequate to explain how firms grow. Her insight was to realise that the 'Firm' in theory is not the same thing as 'flesh and blood' organizations that businessmen call firms. This insight eventually led to the publication of her second book, The Theory of the Growth of the Firm in 1959.