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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] |
Seif 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 san ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Erg (landform)
An erg (also sand sea or dune sea, or sand sheet if it lacks dunes) is a broad, flat area of desert covered with wind-swept sand with little or no vegetative cover. The word is derived from the Arabic word ''ʿarq'' (), meaning "dune field". Strictly speaking, an erg is defined as a desert area that contains more than of aeolian or wind-blown sand and where sand covers more than 20% of the surface. Smaller areas are known as "dune fields". The largest hot desert in the world, the Sahara, covers and contains several ergs, such as the Chech Erg and the Issaouane Erg in Algeria. Approximately 85% of all the Earth's mobile sand is found in ergs that are greater than . Ergs are also found on other celestial bodies, such as Venus, Mars, and Saturn's moon Titan. Description Ergs are concentrated in two broad belts between 20° to 40°N and 20° to 40°S latitudes, which include regions crossed by the dry, subsiding air of the trade winds. Active ergs are limited to regions ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Barchan In Noachis
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 a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ralph Bagnold
Brigadier Ralph Alger Bagnold, OBE, FRS, (3 April 1896 – 28 May 1990) was an English 20th-century desert explorer, geologist and soldier. In 1932, he staged the first recorded East-to-West crossing of the Libyan Desert. His work in the field of Aeolian processes was the basis for the book ''The Physics of Blown Sand and Desert Dunes'', establishing the discipline of aeolian geomorphology, combining field work observations, experiments and physical equations. His work has been used by United States' space agency NASA in its study of the terrain of the planet Mars, the Bagnold Dunes on Mars' surface being named after him by the organisation. During the Second World War, he was a soldier in the British Army, in which he founded the behind-the-lines reconnaissance, espionage and raiding unit the "Long Range Desert Group", serving as its first commanding officer in the North Africa Campaign. Early life Bagnold was born in Devonport, England. His father, Colonel Arthur Henry ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sand
Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class of soil or soil type; i.e., a soil containing more than 85 percent sand-sized particles by mass. The composition of sand varies, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal settings is silica (silicon dioxide, or SiO2), usually in the form of quartz. Calcium carbonate is the second most common type of sand, for example, aragonite, which has mostly been created, over the past 500million years, by various forms of life, like coral and shellfish. For example, it is the primary form of sand apparent in areas where reefs have dominated the ecosystem for millions of years like the Caribbean. Somewhat more rarely, sand may be composed of calciu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Western Desert (Egypt)
The Western Desert of Egypt is an area of the Sahara that lies west of the river Nile, up to the Libyan border, and south from the Mediterranean Sea to the border with Sudan. It is named in contrast to the Eastern Desert which extends east from the Nile to the Red Sea. The Western Desert is mostly rocky desert, though an area of sandy desert, known as the Great Sand Sea, lies to the west against the Libyan border. The desert covers an area of which is two-thirds of the land area of the country. Its highest elevation is in the Gilf Kebir plateau to the far south-west of the country, on the Egypt-Sudan-Libya border. The Western Desert is barren and uninhabited save for a chain of oases which extend in an arc from Siwa, in the north-west, to Kharga in the south. It has been the scene of conflict in modern times, particularly during the Second World War. Administratively the Western Desert is divided between various governorates; in the north and west, the Matrouh Governorate adm ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Taklamakan Desert
The Taklimakan or Taklamakan Desert (; zh, s=塔克拉玛干沙漠, p=Tǎkèlāmǎgān Shāmò, Xiao'erjing: , dng, Такәламаган Шамә; ug, تەكلىماكان قۇملۇقى, Täklimakan qumluqi; also spelled Taklimakan and Teklimakan) is a desert in Southwestern Xinjiang in Northwest China. It is bounded by the Kunlun Mountains to the south, the Pamir Mountains to the west, the Tian Shan range to the north, and the Gobi Desert to the east. Etymology While most researchers agree on being the Persian word for "place", etymology of ''Takla'' is less clear. The word may be a Uyghur borrowing of the Persian , "to leave alone/out/behind, relinquish, abandon" + ''makan''. Another plausible explanation suggests it is derived from Turki ''taqlar makan'', describing "the place of ruins". Chinese scholars Wang Guowei and Huang Wenbi linked the name to the Tocharians, a historical people of the Tarim Basin, making the meaning of "Taklamakan" similar to "Tocharistan". A ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Egypt
Egypt ( ar, مصر , ), officially the Arab Republic of Egypt, is a transcontinental country spanning the northeast corner of Africa and southwest corner of Asia via a land bridge formed by the Sinai Peninsula. It is bordered by the Mediterranean Sea to the north, the Gaza Strip of Palestine and Israel to the northeast, the Red Sea to the east, Sudan to the south, and Libya to the west. The Gulf of Aqaba in the northeast separates Egypt from Jordan and Saudi Arabia. Cairo is the capital and largest city of Egypt, while Alexandria, the second-largest city, is an important industrial and tourist hub at the Mediterranean coast. At approximately 100 million inhabitants, Egypt is the 14th-most populated country in the world. Egypt has one of the longest histories of any country, tracing its heritage along the Nile Delta back to the 6th–4th millennia BCE. Considered a cradle of civilisation, Ancient Egypt saw some of the earliest developments of writing, agriculture, ur ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Saltation (geology)
In geology, saltation () is a specific type of particle transport by fluids such as wind or water. It occurs when loose materials are removed from a bed and carried by the fluid, before being transported back to the surface. Examples include pebble transport by rivers, sand drift over desert surfaces, soil blowing over fields, and snow drift over smooth surfaces such as those in the Arctic or Canadian Prairies. Process At low fluid velocities, loose material rolls downstream, staying in contact with the surface. This is called ''creep'' or ''reptation''. Here the forces exerted by the fluid on the particle are only enough to roll the particle around the point of contact with the surface. Once the wind speed reaches a certain critical value, termed the ''impact'' or ''fluid threshold'', the drag and lift forces exerted by the fluid are sufficient to lift some particles from the surface. These particles are accelerated by the fluid, and pulled downward by gravity, causing them to t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bagnold Formula
The Bagnold formula, named after Ralph Alger Bagnold, relates the amount of sand moved by the wind to wind speed by saltation. It states that the mass transport of sand is proportional to the third power of the friction velocity. Under steady conditions, this implies that mass transport is proportional to the third power of the excess of the wind speed (at any fixed height over the sand surface) over the minimum wind speed that is able to activate and sustain a continuous flow of sand grains. The formula was derived by Bagnold in 1936 and later published in his book ''The Physics of Blown Sand and Desert Dunes'' in 1941. Wind tunnel and field experiments suggest that the formula is basically correct. It has later been modified by several researchers, but is still considered to be the benchmark formula.Sørensen, M. 2004. On the rate of aeolian sand transport. Geomorphology 59:53-62. In its simplest form, Bagnold's formula may be expressed as: :q = C \ \frac\ \sqrt u_*^3 where ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sandstone
Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) because they are the most resistant minerals to weathering processes at the Earth's surface. Like uncemented sand, sandstone may be any color due to impurities within the minerals, but the most common colors are tan, brown, yellow, red, grey, pink, white, and black. Since sandstone beds often form highly visible cliffs and other topographic features, certain colors of sandstone have been strongly identified with certain regions. Rock formations that are primarily composed of sandstone usually allow the percolation of water and other fluids and are porous enough to store large quantities, making them valuable aquifers and petroleum reservoirs. Quartz-bearing sandstone can be changed into quartzite through metamorphism, usually related to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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