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This article is about sand formations. For other uses, see Dune (disambiguation).

In physical geography, a dune is a hill of sand built by aeolian processes. Geography (from Greek γεωγραφία - geografia) is the study of the Earth and its lands features inhabitants and phenomena Sand is a naturally occurring Granular material composed of finely divided rock and Mineral particles Aeolian (or Eolian or Æolian) processes pertain to the activity of the Winds and more specifically to the winds' ability to shape the surface of the Dunes are subject to different forms and sizes based on their interaction with the wind. Most kinds of dune are longer on the windward side where the sand is pushed up the dune, and 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. An erg (also sand sea or dune sea) is a large relatively flat area of Desert covered with Wind -swept Sand with little to no vegetation

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. This article is about the body of water For other uses see SEA and Seas. 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. A lake (from Latin lacus) is a Terrain feature (or Physical feature) a body of Liquid on the surface of a world that is localized to the This article is about the body of water For other uses see SEA and Seas.

Dunes also form under the action of water flow (alluvial processes), on sand or gravel beds of rivers, estuaries and the sea-bed. Alluvium (from the Latin, alluvius, from alluere, "to wash against" is Soil or Sediments deposited by a river or other running Gravel is rock that is of a specific Particle size range In Geology, gravel is any loose rock that is larger than two millimeters (2mm "Riverine" redirects here For the use of that term in Maritime geography, see there An estuary is a semi-enclosed Coastal body of Water with one or more Rivers or Streams flowing into it and with a free connection to the open

The modern word "dune" came into English from French circa 1790 but it's an old Indo-European word that's found in most of the Slavic languages as well as the Germanic and Latin languages. In ancient times words cognate to "dune" probably had the meaning of a citadel or built-up hill fortification. [1]


Contents

Conservation

Dune habitats provide niches for highly specialized plants and animals, including numerous rare and endangered species. A rare species is an Organism which is very uncommon or scarce An endangered species is a population of an organism which is at risk of becoming Extinct because it is either few in numbers or threatened by changing environmental or predation Due to human population expansion dunes face destruction through recreation and land development, as well as alteration to prevent encroachment on inhabited areas. Overpopulation refers to a condition where an Organism 's numbers exceed the Carrying capacity of its Habitat. Some countries, notably the U.S., New Zealand, Great Britain, Australia, Canada and the Netherlands have developed extensive programs of dune protection. The United States of America —commonly referred to as the New Zealand is an Island country in the south-western Pacific Ocean comprising two main landmasses (the North Island and the South Island See also Kingdom of Great Britain Great Britain (Breatainn Mhòr Prydain Fawr Breten Veur Graet Breetain is the larger of the two main islands For a topic outline on this subject see List of basic Australia topics. Country to "Dominion of Canada" or "Canadian Federation" or anything else please read the Talk Page The Netherlands ( Dutch:, ˈnedərlɑnt is the European part of the Kingdom of the Netherlands, which consists of the Netherlands the Netherlands In the UK, a Biodiversity Action Plan has been developed to assess dunes loss and prevent future dunes destruction. This article is about a conservation biology topic For other uses of BAP see BAP (disambiguation.

Dune shapes

Crescentic

Crescent-shaped mounds are generally wider than they are long. The slipface is on the dune's concave side. These dunes form under winds that blow from one direction, and they also are known as barchans, or transverse dunes. A barchan Dune is an arc-shaped sand ridge comprising well-sorted sand Some types of crescentic dunes move faster over desert surfaces than any other type of dune. A desert is a Landscape or region that receives very little precipitation. A group of dunes moved more than 100 meters per year between 1954 and 1959 in the People's Republic of China's Ningxia Province; similar rates have been recorded in the Western Desert of Egypt. Talk People's Republic of China) PEOPLE'S REPUBLIC OF CHINA ARTICLE GUIDELINES This article is about the country of Egypt For a topic outline on this subject see List of basic Egypt topics. The largest crescentic dunes on Earth, with mean crest-to-crest widths of more than 3 kilometers, are in China's Taklamakan Desert. The Taklamakan Desert (Takelamagan Shamo 塔克拉玛干沙漠 also known as Taklimakan, is a Desert in Central Asia, in the Xinjiang

Linear

Straight or slightly sinuous sand ridges typically much longer than they are wide are known as linear dunes. They may be more than 160 kilometers long. Linear dunes may occur as isolated ridges, but they generally form sets of parallel ridges separated by miles of sand, gravel, or rocky interdune corridors. 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.

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. The Grand Erg Oriental (also known as the Great Eastern Erg) is an erg in Algeria. In other deserts, they occur around the margins of the sand seas, particularly near topographic barriers. An erg (also sand sea or dune sea) is a large relatively flat area of Desert covered with Wind -swept Sand with little to no vegetation In the southeast Badain Jaran Desert of China, the star dunes are up to 500 meters tall and may be the tallest dunes on Earth. The Badain Jaran Desert (Badanjilin Shamo 巴丹吉林沙漠 can be found in western Inner Mongolia.

Dome

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

Parabolic

U-shaped mounds of sand with convex noses trailed by elongated arms are parabolic dunes. Sometimes these dunes are called U-shaped, blowout, or hairpin dunes, and they are well known in coastal deserts. Blowouts are sandy depressions in a sand Dune ecosystem (psammosere caused by the removal of sediments by Wind. Unlike crescent shaped dunes, their crests point upwind. The elongated arms of parabolic dunes follow rather than lead because they have been fixed by vegetation, while the bulk of the sand in the dune migrates forward.

Longitudinal (Seif) and transverse dunes

Seif dunes.
Seif dunes.

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 (900 ft) in height and 300 km (200 mi) in length. In the southern third of the Arabian Peninsula, a region called the Empty Quarter because of its total lack of populatation, a vast erg called Rub al Khali conatins seif dunes that stretch for almost 200 km and reach heights of over 300m.

Seif dunes are thought to develop from barchans if a change of 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 buildup of sand on an already existing minuscule mound.

Reversing dunes

Complex dune: Dune 7 in the Namib desert, one of the tallest in the world.
Complex dune: Dune 7 in the Namib desert, one of the tallest in the world. The Namib Desert is a Desert in Namibia and southwest Angola which forms part of the Namib-Naukluft National Park.

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

The Great Dune of Pyla is the largest dune in Europe.
The Great Dune of Pyla is the largest dune in Europe. The Great Dune of Pilat (la Dune du Pilat is the largest sand Dune in Europe.

Sub-aqueous dunes

Sub-aqueous (underwater) dunes form on a bed of sand or gravel under the actions of water flow. Underwater is a term describing the realm below the surface of Water where the water exists in a natural feature (called a body of water) such as an Ocean They are ubiquitous in natural channels such as rivers and estuaries, and also form in engineered canals and pipelines. Physical geography, a channel is the physical confine of a River, slough or ocean Strait consisting of a bed and banks Canals are artificial channels for water There are two types of canals water conveyance canals which are used for the conveyance and delivery of water and Waterways Dunes move downstream as the upstream slope is eroded and the sediment deposited on the downstream or lee slope.

These dunes most often form as a continuous 'train' of dunes, showing remarkable similarity in wavelength and height. In Physics wavelength is the distance between repeating units of a propagating Wave of a given Frequency.

Dunes on the bed of a channel significantly increase flow resistance, their presence and growth playing a major part in river flooding. A flood is an overflow of an expanse of water that submerges land a deluge

Lithified dunes

A lithified (consolidated) sand dune is a type of sandstone that is formed when a marine or aeolian sand dune becomes compacted and hardened. Lithification (from the Greek word lithos meaning 'rock' and the Latin -derived suffix -ific) is the process in which Sediments compact Sandstone is a Sedimentary rock composed mainly of Sand -size Mineral or rock grains. Once in this form, water passing through the rock can carry and deposit minerals, which can alter the hue 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. Zion National Park is a United States National Park located in the Southwestern United States, near Springdale Utah.

A local slang term used for these consolidated dunes is "slickrock", a name that was introduced by pioneers of the old west because their steel-rimmed wagon wheels could not gain purchase on the rock.

Coastal dunes

Coastal dunes on the Kurnell Peninsula
Coastal dunes on the Kurnell Peninsula


Dunes form where constructive waves encourage the accumulation of sand, and where prevailing onshore winds blow this sand inland. The Cronulla sand dunes are located on the Kurnell Peninsula in the local government area of Sutherland Shire, Sydney Australia. There needs to be obstacles e. g. vegetation, pebbles etc. to trap the moving sand grains. As the sand grains get trapped they start to accumulate, this is the start of 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. Privacy is the ability of an individual or group to seclude themselves or information about themselves and thereby reveal themselves selectively Wind is the flow of Air or other Gases that compose an Atmosphere (including but not limited to the Earth's)

Ecological succession on coastal dunes

Coastal dunes in Curonian spit.
Coastal dunes in Curonian spit. The Curonian Spit (Kuršių Nerija Куршская коса Mierzeja Kurońska Kurische Nehrung Kuršu kāpas is a 98 km long thin curved sand- Dune 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. Sea spray is a Spray of Water that forms when Ocean waves crash 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. Seaweed is a loose colloquial term encompassing macroscopic Multicellular, benthic marine Algae. A pioneer species are Species which colonizes previously uncolonized land usually leading to Ecological succession. These pioneer species are marram grass, sea wort grass and other sea grasses in the UK. The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom, the UK or Britain,is a Sovereign state located These plants are well adapted to the harsh conditions of the fore-dune typically having deep roots which reach the water table, root nodules that produce nitrogen compounds, and protected stoma, reducing transpiration. The water table is the level at which the ground water pressure is equal to Atmospheric pressure. Root nodules occur on the roots of plants that associate with Vigna bacteria. Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 In Botany, a stoma (also stomate; plural stomata) is a tiny opening or pore found mostly on the underside of a Plant Leaf Transpiration is the Evaporation of water from the aerial parts of Plants especially leaves but also stems Flowers and Roots Also, the deep roots bind the sand together, and the dune grows into a fore dune 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. Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 Typically these are heathers and gorses. Calluna vulgaris (also known as Ling is the sole species in the Genus Calluna in the family Ericaceae. Gorse ( Ulex) comprises a Genus of about 20 species of Evergreen Shrubs in the subfamily Faboideae of the pea family These too are adapted to the low soil water content and have small, prickly leaves which reduce transpiration. Heathers add humus to the soil, but have a pH of lower than 7, so make the soil slightly acidic. Humus (Origin 1790–1800 Latin: earth ground) is the organic material in Soil lending it a dark brown or black colouration pH is the measure of the acidity or alkalinity of a Solution. In Computer science, ACID ( Atomicity Consistency Isolation Durability) is a set of properties that guarantee that Database transactions are Heathers are usually replaced by coniferous trees which can tolerate the low pH. pH is the measure of the acidity or alkalinity of a Solution. Coniferous forests and heathland are common climax communities for sand dune systems. Heaths are Shrubland habitats characterised by open low growing woody Vegetation, found on mainly infertile Acidic soils The term climax community, also described as a climatic climax community, is an ecological term for a biological community of Plants and

Young dunes are called yellow dunes, dunes which have high humus content are called grey dunes. Yellow dunes are Sand dunes that develop after the first set of embryo dunes appear Grey dunes are fixed stable Sand dunes located 50-100 m from the edge of the ocean 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

Main article: Desertification
One way of preventing sand from accumulating in roadways is planting trees and vegetation along the road.
One way of preventing sand from accumulating in roadways is planting trees and vegetation along the road. Desertification is the degradation of land in arid and dry sub-humid areas resulting primarily from human activities and influenced by climatic variations

One of the biggest problems posed by sand dunes is their encroachment on human habitats. Sand dunes move through a few different means, all of them helped along by wind. One way that dunes can move is through saltation, where sand particles skip along the ground like a rock thrown across a pond might skip across the water's surface. For definition and other use disambiguation see Saltation In Geology, saltation (from Latin, saltus, "leap" When these skipping particles land, they may knock into other particles and cause them to skip as well. With slightly stronger winds, particles collide in mid-air, causing sheet flows. In a major dust storm, dunes may move tens of meters through such sheet flows. And like snow, sand avalanches, falling down the steep slopes of the dunes that face away from the winds, also moving the dunes forward. This article refers to the natural event For other uses see Avalanche (disambiguation An avalanche is an abrupt and rapid flow of snow often

Sand threatens buildings and crops in Africa, the Middle East and China. Drenching sand dunes with oil stops their migration, but this approach is highly destructive to the dunes habitat and uses a finite resource. Sand fences might also work, but researchers are still analyzing optimum fence designs. Preventing sand dunes from overwhelming cities and agricultural areas has become a priority for the United Nations Environment Programme. The UN Environment Programme (or UNEP) coordinates United Nations environmental activities assisting developing countries in implementing environmentally sound policies

Examples

Sand dunes of Khongoryn Els, Gurvansaikhan NP, Mongolia.
Sand dunes of Khongoryn Els, Gurvansaikhan NP, Mongolia. Gobi Gurvansaikhan National Park is a national park in southern Mongolia. Mongolia (mɒŋˈɡoʊliə, literally Mongol country/nation,) is a Landlocked Country in East

World's highest dunes

Note: This table is based on estimates and incomplete information. Winterton Dunes is an extensive Dune system on the east coast of Norfolk, England, which has been designated as a National Nature Reserve and Norfolk (ˈnɔrfək is a low-lying county in East Anglia, England, United Kingdom. England is a Country which is part of the United Kingdom. Its inhabitants account for more than 83% of the total UK population whilst its mainland
Dune Height from Base feet/meters Height from Sea Level feet/meters Location Notes
Badain Jaran Dunes ~1640/500 ~6640/2,020 Badain Jaran Desert, Alashan Plain, Inner Mongolia, Gobi Desert, China World's Tallest Stationary Dunes [2]
Average Highest Area Dunes 1,526/465? ~6,500/~1,980? Isaouane-n-Tifernine Sand Sea, Algerian Sahara Highest in Africa
Big Daddy/Dune 7 1,256/383  ? Sossusvlei Dunes, Namib Desert, Namibia / Near Walvis Bay Namib Desert, Namibia
Mount Tempest ~920/280 ~920/280 Moreton Bay, 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  ? 4,921/1,500 or 7,923/2,415? Atacama Desert, Chile Highest in South America?

Sand dune systems

An example of fencing at Studland
An example of fencing at Studland
(coastal dunes featuring succession)

Extraterrestrial dunes

See also: List of extraterrestrial dune fields

Dunes can likely be found in any environment where there is a substantial atmosphere, winds, and dust to be blown. The Badain Jaran Desert (Badanjilin Shamo 巴丹吉林沙漠 can be found in western Inner Mongolia. The Gobi (Говь Govi or Gov', "gravel-covered plain" Chinese: zh-t 戈壁(沙漠 Gēbì (Shāmò) The Namib Desert is a Desert in Namibia and southwest Angola which forms part of the Namib-Naukluft National Park. The Namib Desert is a Desert in Namibia and southwest Angola which forms part of the Namib-Naukluft National Park. Moreton Bay is a large bay on the eastern coast of Australia 19 km from Brisbane, Queensland. Brisbane ( is the state capital of Queensland. Brisbane is the third most populous city in Australia and the most populous city of Queensland Great Sand Dunes National Park and Preserve is a United States National Park located in the easternmost parts of Alamosa County and Saguache County, The Great Dune of Pilat (la Dune du Pilat is the largest sand Dune in Europe. Arcachon is a commune in the Gironde department in southwestern France. Dunhuang ( also written as 燉煌 till early Qing Dynasty; is a City (pop Atacama redirects here for the political-administrative region of Chile, see Atacama Region. Ashdod Nitzanim Sand Dune Park is a Psammosere ecosystem located close to the city of Ashdod on the Israeli Coastal Plain near the Mediterranean For a topic outline on this subject see List of basic Israel topics. Kenfig (Cynffig is a Village and former Borough in Bridgend, Wales. South Wales (De Cymru is an area of Wales bordered by England and the Bristol Channel to the east and south and Mid Wales and West Wales South Wales (De Cymru is an area of Wales bordered by England and the Bristol Channel to the east and south and Mid Wales and West Wales Studland is a small village on the Isle of Purbeck in the English county of Dorset. Dorset ( (or archaically, Dorsetshire) is a county in South West England on the English Channel coast England is a Country which is part of the United Kingdom. Its inhabitants account for more than 83% of the total UK population whilst its mainland Newcastle (in Irish: An Caisleán Nua, ie The New Castle is a small town in County Down, Northern Ireland. County Down, ( Ulster Scots: Coontie Doun. is one of the nine counties that form the province of Ulster and one of six counties that form Northern Ireland (Tuaisceart Éireann Ulster Scots: Norlin Airlann) is a Country within the United Kingdom, lying in the northeast of Morfa Harlech ( is an extensive Dune system stretching northwards from the town of Harlech in North Wales. History Gwynedd was an independent kingdom from the end of the Roman period until the 13th Century when it was conquered and subjugated by England North Wales (Gogledd Cymru is the northernmost unofficial region of Wales, bordered to the south by Mid Wales and to the east by England. North Wales (Gogledd Cymru is the northernmost unofficial region of Wales, bordered to the south by Mid Wales and to the east by England. Bamburgh Dunes are a region of coastal Sand Dunes with an area of over 40 hectares situated around the village of Bamburgh in Northumberland, Northumberland is a county in the North East of England. The non-metropolitan county of Northumberland borders Cumbria to the west The Oregon Dunes National Recreation Area (or NRA) is located on the Oregon Coast, stretching approximately 40 miles north from the Coos River in North Oregon ( is a state in the Pacific Northwest region of the United States. The United States of America —commonly referred to as the For the football club see SS Lazio Lazio ( Latium in Latin) is a regione of central Italy (Italia officially the Italian Republic, (Repubblica Italiana is located on the Italian Peninsula in Southern Europe, and on the two largest Norfolk (ˈnɔrfək is a low-lying county in East Anglia, England, United Kingdom. England is a Country which is part of the United Kingdom. Its inhabitants account for more than 83% of the total UK population whilst its mainland Ynyslas Sand Dunes are Sand dunes bordering Cardigan Bay and the Dyfi Estuary between Ynyslas and Aberdyfi in Ceredigion Sleeping Bear Dunes National Lakeshore is a United States National Lakeshore located along the northwest coast of the Lower Peninsula of Michigan in Michigan ( is a Midwestern state of the United States of America. The United States of America —commonly referred to as the This is a list of Dune fields not on Earth which have been given official names by the International Astronomical Union. Dunes are common on Mars, and have also been observed in the equatorial regions of Titan by the Cassini probe's radar. TemplateInfobox Planet.--> Titan (ˈtaɪtən, or as Cassini–Huygens is a joint NASA / ESA / ASI Robotic spacecraft mission currently studying the planet Saturn and its

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. [1]

Images

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. Death Valley National Park is a mostly Arid United States National Park located east of the Sierra Nevada mountain range in southern Inyo County Death Valley National Park is a mostly Arid United States National Park located east of the Sierra Nevada mountain range in southern Inyo County 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

Sand dunes with scattered vegetation in UAE

Parabolic dune partially stabilized by marram grass

References

Footnotes

  1. ^ Peeking Through the Haze: Titan's Surface, part II - The Planetary Society Blog | The Planetary Society

External links

See also

An antidune is an upper flow regime Sedimentary structure found in aquatic environments A barchan Dune is an arc-shaped sand ridge comprising well-sorted sand Earth science (also known as geoscience, the geosciences or the Earth Sciences) is an all-embracing term for the Sciences related to the planet This article is about a geographic landform For the TV series see Machair (TV series The Gaelic word machair or machar refers to a fertile Masseira is a unique form of traditional Farming technique practised in the parishes of Estela and Aguçadoura in the north of Póvoa de Varzim in Portugal A sandhill is an ecological Community type found in many parts of the world A strand plain is a series of Dunes usually associated with and parallel to a Beach, sometimes containing small creeks or Lakes that have very

Dictionary

dune

-noun

  1. A ridge or hill of sand piled up by the wind.
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