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Barchan
A barchan or barkhan dune (from Kazakh бархан ) is a crescent-shaped dune. The term was introduced in 1881 by Russian naturalist Alexander von Middendorf, based on their occurrence in Turkestan and other inland desert regions. Barchans face the wind, appearing convex and are produced by wind action predominantly from one direction. They are a very common landform in sandy deserts all over the world and are arc-shaped, markedly asymmetrical in cross section, with a gentle slope facing toward the wind sand ridge, comprising well-sorted sand. This type of dune possesses two "horns" that face downwind, with the steeper slope known as the slip face, facing away from the wind, downwind, at the angle of repose of the sand in question, approximately 30–35 degrees for medium-fine dry sand. The upwind side is packed by the wind, and stands at about 15 degrees. Barchans may be high and wide at the base measured perpendicular to the wind. Simple barchan dunes may appear ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Barchan
A barchan or barkhan dune (from Kazakh бархан ) is a crescent-shaped dune. The term was introduced in 1881 by Russian naturalist Alexander von Middendorf, based on their occurrence in Turkestan and other inland desert regions. Barchans face the wind, appearing convex and are produced by wind action predominantly from one direction. They are a very common landform in sandy deserts all over the world and are arc-shaped, markedly asymmetrical in cross section, with a gentle slope facing toward the wind sand ridge, comprising well-sorted sand. This type of dune possesses two "horns" that face downwind, with the steeper slope known as the slip face, facing away from the wind, downwind, at the angle of repose of the sand in question, approximately 30–35 degrees for medium-fine dry sand. The upwind side is packed by the wind, and stands at about 15 degrees. Barchans may be high and wide at the base measured perpendicular to the wind. Simple barchan dunes may appear ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dune
A dune is a landform composed of wind- or water-driven sand. It typically takes the form of a mound, ridge, or hill. An area with dunes is called a dune system or a dune complex. A large dune complex is called a dune field, while broad, flat regions covered with wind-swept sand or dunes with little or no vegetation are called ''ergs'' or ''sand seas''. Dunes occur in different shapes and sizes, but 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 ''dune slack''. Dunes are most common in desert environments, where the lack of moisture hinders the growth of vegetation that would otherwise interfere with the development of dunes. However, sand deposits are not restricted to deserts, and dunes are also found along sea shores, along streams in semiarid climates, in areas of glacial outwash, and in other areas where poorly cemented sa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Megabarchan
A dune is a landform composed of wind- or water-driven sand. It typically takes the form of a mound, ridge, or hill. An area with dunes is called a dune system or a dune complex. A large dune complex is called a dune field, while broad, flat regions covered with wind-swept sand or dunes with little or no vegetation are called ''ergs'' or ''sand seas''. Dunes occur in different shapes and sizes, but 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 ''dune slack''. Dunes are most common in desert environments, where the lack of moisture hinders the growth of vegetation that would otherwise interfere with the development of dunes. However, sand deposits are not restricted to deserts, and dunes are also found along sea shores, along streams in semiarid climates, in areas of glacial outwash, and in other areas where poorly cemented san ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sandy Desert
A desert is a barren area of landscape where little precipitation occurs and, consequently, living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to denudation. About one-third of the land surface of the Earth is arid or semi-arid. This includes much of the polar regions, where little precipitation occurs, and which are sometimes called polar deserts or "cold deserts". Deserts can be classified by the amount of precipitation that falls, by the temperature that prevails, by the causes of desertification or by their geographical location. Deserts are formed by weathering processes as large variations in temperature between day and night put strains on the rocks, which consequently break in pieces. Although rain seldom occurs in deserts, there are occasional downpours that can result in flash floods. Rain falling on hot rocks can cause them to shatter, and the resulting fragments and rubble strewn over the d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Barkhane
Operation Barkhane was an anti-insurgent operation that started on 1 August 2014 and formally ended on 9 November 2022. It was led by the French military against Islamist groups in Africa's Sahel region.France sets up anti-Islamist force in Africa's Sahel bbc.co.uk. and consisted of a roughly 3,000-strong French force, which was permanently headquartered in , the capital of . The operation was led in co-operation with five countries, all of which are former French colonies that span the Sahel: |
Angle Of Repose
The angle of repose, or critical angle of repose, of a granular material is the steepest angle of descent or dip relative to the horizontal plane to which a material can be piled without slumping. At this angle, the material on the slope face is on the verge of sliding. The angle of repose can range from 0° to 90°. The morphology of the material affects the angle of repose; smooth, rounded sand grains cannot be piled as steeply as can rough, interlocking sands. The angle of repose can also be affected by additions of solvents. If a small amount of water is able to bridge the gaps between particles, electrostatic attraction of the water to mineral surfaces will increase the angle of repose, and related quantities such as the soil strength. When bulk granular materials are poured onto a horizontal surface, a conical pile will form. The internal angle between the surface of the pile and the horizontal surface is known as the angle of repose and is related to the density, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mesquite Sand Dunes
Mesquite is a common name for several plants in the genus ''Prosopis'', which contains over 40 species of small leguminous trees. They are native to dry areas in the Americas. They have extremely long roots to seek water from very far under ground. As a legume, mesquites are one of the few sources of fixed nitrogen in the desert habitat. These trees bloom from spring to summer. They often produce fruits known as "pods". ''Prosopis'' spp. are able to grow up to tall, depending on site and climate. They are deciduous and depending on location and rainfall have either deep or shallow roots. ''Prosopis'' is considered long-lived because of the low mortality rate after the dicotyledonous stage and juveniles are also able to survive in conditions with low light and drought. The Cahuilla indigenous people of western North America were known to eat the seeds of mesquite. History ''Prosopis'' spp. have been in North America since the Pliocene era and their wood has been dated to 3300 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kazakh Language
The Kazakh or simply Qazaq (Latin: or , Cyrillic: or , Arabic Script: or , , ) is a Turkic language of the Kipchak branch spoken in Central Asia by Kazakhs. It is closely related to Nogai, Kyrgyz and Karakalpak. It is the official language of Kazakhstan and a significant minority language in the Ili Kazakh Autonomous Prefecture in Xinjiang, north-western China and in the Bayan-Ölgii Province of western Mongolia. The language is also spoken by many ethnic Kazakhs throughout the former Soviet Union (some 472,000 in Russia according to the 2010 Russian Census), Germany, and Turkey. Like other Turkic languages, Kazakh is an agglutinative language and employs vowel harmony. '' Ethnologue'' recognizes three mutually intelligible dialect groups, Northeastern Kazakh, the most widely spoken variety which also serves as the basis for the standard language, Southern Kazakh and Western Kazakh. The language share a degree of mutual intelligiblity with closely related Karakalpak ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Crescent
A crescent shape (, ) is a symbol or emblem used to represent the lunar phase in the first quarter (the "sickle moon"), or by extension a symbol representing the Moon itself. In Hinduism, Lord Shiva is often shown wearing a crescent moon on his head symbolising that the lord is the master of time and is himself timeless. It is used as the astrological symbol for the Moon, and hence as the alchemical symbol for silver. It was also the emblem of Diana/Artemis, and hence represented virginity. In Christianity Marian veneration, it is associated with the Virgin Mary. From its use as roof finial in Ottoman era mosques, it has also become associated with Islam, and the crescent was introduced as chaplain badge for Muslim chaplains in the US military in 1993.On December 14, 1992, the Army Chief of Chaplains requested that an insignia be created for future Muslim chaplains, and the design (a crescent) was completed January 8, 1993. Emerson, William K., ''Encyclopedia of United St ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alexander Von Middendorf
Alexander Theodor von Middendorff (russian: Алекса́ндр Фёдорович Ми́ддендорф; tr. ; 18 August 1815 – 24 January 1894) was a zoologist and explorer of Baltic German and Estonian extraction. He is known for his expedition 1843–45 to the extreme north and east of Siberia, describing the effects of permafrost on the spread of animals and plants. Early life Middendorff's mother Sophia Johanson (1782–1868), the daughter of an Estonian farmer, had been sent to Saint Petersburg for education by her parents. There she met with the future director of the St. Petersburg Pedagogical Institute, Theodor Johann von Middendorff (1776–1856), whose father was a Baltic German pastor in Karuse, Estonia. As the two young people came from different social ranks and were unable to marry each other, their daughter Anette (b. 1809) and son Alexander were born out of wedlock. Alexander was born on 18 August 1815 in St. Petersburg, but could not be baptized until ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Turkestan
Turkestan, also spelled Turkistan ( fa, ترکستان, Torkestân, lit=Land of the Turks), is a historical region in Central Asia corresponding to the regions of Transoxiana and Xinjiang. Overview Known as Turan to the Persians, western Turkestan has also been known historically as Sogdia, "Ma wara'u'n-nahr" (by its Arab conquerors), and Transoxiana by western travelers. The latter two names refer to its position beyond the River Oxus when approached from the south, emphasizing Turkestan's long-standing relationship with Iran, the Persian Empires, and the Umayyad and Abbasid Caliphates. Oghuz Turks (also known as Turkmens), Kyrgyzs, Uzbeks, Kazakhs, Khazars, Uyghurs and Hazaras are some of the Turkic inhabitants of the region who, as history progressed, have spread further into Eurasia forming such Turkic nations as Turkey, and subnational regions like Tatarstan in Russia and Crimea in Ukraine. Tajiks and Russians form sizable non-Turkic minorities. It is subdivided into A ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Landform
A landform is a natural or anthropogenic land feature on the solid surface of the Earth or other planetary body. Landforms together make up a given terrain, and their arrangement in the landscape is known as topography. Landforms include hills, mountains, canyons, and valleys, as well as shoreline features such as bays, peninsulas, and seas, including submerged features such as mid-ocean ridges, volcanoes, and the great ocean basins. Physical characteristics Landforms are categorized by characteristic physical attributes such as elevation, slope, orientation, stratification, rock exposure and soil type. Gross physical features or landforms include intuitive elements such as berms, mounds, hills, ridges, cliffs, valleys, rivers, peninsulas, volcanoes, and numerous other structural and size-scaled (e.g. ponds vs. lakes, hills vs. mountains) elements including various kinds of inland and oceanic waterbodies and sub-surface features. Mountains, hills, plateaux, and plains are t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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