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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 ''Erg (landform), ergs'' or ''sand seas''. Dunes occur in different shapes and sizes, but most kinds of dunes are longer on the wiktionary:stoss, 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 Outwash plain, glacial outwash ... [...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 language, Arabic word ''ʿirq'' (), meaning "dune field". Strictly speaking, an erg is defined as a desert area that contains more than of aeolian processes, 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 , the largest being the Rub' al Khali, the ''Empty Quarter'' of the Arabian Peninsula. Ergs are also found on other celestial bodies, such as Venus, Mars, and Saturn's moon Titan (moon), Titan. Geography Sand seas and dune fields generally occur in regions downwind of copious sourc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Barchan In Noachis
A barchan or barkhan dune (from Kazakh бархан ) is a crescent-shaped dune. Russian naturalist Alexander von Middendorf introduced the term in 1881, working from the occurrence of barchans in Turkestan and in 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 du ... [...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. Bagnold served in the First World War as an engineer in the British Army. 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 were named after him by the organisation. He returned to the forces in the Second World War, 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 wa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Desert
A desert is a landscape where little precipitation occurs and, consequently, living conditions create unique biomes and ecosystems. 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 climate, semi-arid. This includes much of the Polar regions of Earth, 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 strain the Rock (geology), 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 frag ... [...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 usually 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. One such example of this is aragonite, which has been created over the past 500million years by various forms of life, such as coral and shellfish. It is the primary form of sand apparent in areas where reefs have dominated the ecosystem for millions of years, as in the Caribbean. Somewhat more rarely, sand may be composed ... [...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 t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Western Desert (Egypt)
In Egypt, the Western Desert is an area of the Sahara that lies west of the river Nile, up to the Egypt–Libya border, Libyan border, and south from the Mediterranean Sea to the Egypt–Sudan border, 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 Reg (landform), rocky desert, though an area of Erg (landform), 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 Oasis, 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 d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Egypt
Egypt ( , ), officially the Arab Republic of Egypt, is a country spanning the Northeast Africa, northeast corner of Africa and Western Asia, southwest corner of Asia via the Sinai Peninsula. It is bordered by the Mediterranean Sea to northern coast of Egypt, the north, the Gaza Strip of Palestine and Israel to Egypt–Israel barrier, the northeast, the Red Sea to the east, Sudan to Egypt–Sudan border, the south, and Libya to Egypt–Libya border, the west; the Gulf of Aqaba in the northeast separates Egypt from Jordan and Saudi Arabia. Cairo is the capital, list of cities and towns in Egypt, largest city, and leading cultural center, while Alexandria is the second-largest city and an important hub of industry and tourism. With over 109 million inhabitants, Egypt is the List of African countries by population, third-most populous country in Africa and List of countries and dependencies by population, 15th-most populated in the world. Egypt has one of the longest histories o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
China
China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after India, representing 17.4% of the world population. China spans the equivalent of five time zones and Borders of China, borders fourteen countries by land across an area of nearly , making it the list of countries and dependencies by area, third-largest country by land area. The country is divided into 33 Province-level divisions of China, province-level divisions: 22 provinces of China, provinces, 5 autonomous regions of China, autonomous regions, 4 direct-administered municipalities of China, municipalities, and 2 semi-autonomous special administrative regions. Beijing is the country's capital, while Shanghai is List of cities in China by population, its most populous city by urban area and largest financial center. Considered one of six ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sandstone
Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar, because they are the most resistant minerals to the weathering processes at the Earth's surface. Like uncemented sand, sandstone may be imparted any color by impurities within the minerals, but the most common colors are tan, brown, yellow, red, grey, pink, white, and black. Because sandstone beds can form highly visible cliffs and other topography, topographic features, certain colors of sandstone have become strongly identified with certain regions, such as the red rock deserts of Arches National Park and other areas of the Southwestern United States, American Southwest. Rock formations composed of sandstone usually allow the p ... [...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 whe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
