Broad area of abandon covered with wind-swept backbone
An erg ( besides sand sea or dune sea, or sand sheet if it lacks dunes ) is a broad, flat area of defect covered with wind -swept sand with small or no vegetative cover. [ 1 ] The son is derived from the Arabic word ʿarq ( عرق ), meaning “ dune plain ”. [ 2 ] Strictly talk, an erg is defined as a defect area that contains more than 125 km2 ( 48 sq mile ) of aeolian or wind-blown sand [ 3 ] and where sand covers more than 20 % of the open. [ 2 ] Smaller areas are known as “ dune fields ”. [ 4 ] The largest hot abandon in the universe, the Sahara, covers 9 million square kilometres ( 3.5×10^6 sq myocardial infarction ) and contains several ergs, such as the Chech Erg and the Issaouane Erg in Algeria. [ 5 ] approximately 85 % of all the Earth ‘s mobile sandpaper is found in erg that are greater than 32,000 km2 ( 12,355 sq myocardial infarction ). [ 6 ] Ergs are besides found on other celestial bodies, such as Venus, Mars, and Saturn ‘s moonlight Titan .

description [edit ]

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 vent of the trade winds. active erg are limited to regions that receive, on average, no more than 150 millimeter of annual precipitation. [ 2 ] The largest are in northern and southerly Africa, central and western Asia, and Central Australia. In South America, erg are limited by the Andes Mountains, but they do contain highly bombastic dunes in coastal Peru and northwestern Argentina. They are besides found in respective parts of the northeast seashore of Brazil. The only active erg in North America is in the Gran Desierto de Altar that extends from the Sonoran Desert in the northwestern Mexican country of Sonora to the Yuma Desert of Arizona and the Algodones Dunes of southeastern California. An erg that has been fixed by vegetation forms the Nebraska Sandhills .
2 (230,000 sq mi)[7] Satellite image of Rub ‘ aluminum Khali ( Arabia ‘s Empty Quarter ), the global ‘s largest erg with an sphere of more than 600,000 kilometer ( 230,000 sq michigan )

Sand seas and dune fields generally occur in regions downwind of copious sources of dry, easy sand, such as dry riverbeds and deltas, floodplains, arctic outwash plains, dry lakes, and beaches. about all major ergs are located downwind from river beds in areas that are excessively dry to support extensive vegetative report and are frankincense subjugate to long-continued wind instrument corrosion. backbone from these abundant sources migrates downwind and builds up into very large dunes where its motion is halted or slowed by topographical barriers to windflow or by convergence of windflow. Entire erg and dune fields tend to migrate downwind american samoa far as hundreds of kilometers from their sources of sandpaper. such accumulation requires long periods of time. At least one million years is required to build erg with very big dunes, such as those on the arabian Peninsula, in North Africa, and in central Asia. [ 8 ] Sand seas that have accumulated in subsiding structural and topographical basins, such as the Murzuk Sand Sea of Libya, may attain capital thicknesses ( more than 1000 thousand [ 9 ] ) but others, such as the erg of linear dunes in the Simpson Desert and Great Sandy Desert of Australia, may be no blockheaded than the person dunes superposed on the alluvial complain. Within sand seas in a given area, the dunes tend to be of a individual type. For exercise, there are ergs or fields of linear dunes, of crescentic dunes, of star dunes, and of parabolic dunes, and these dune arrays tend to have consistent orientations and sizes. [ 10 ] [ 11 ] By nature, ergs are identical active. Smaller dunes shape and migrate along the flanks of the larger dunes and sand ridges. episodic precipitation fills basins formed by the dunes ; as the water evaporates, strategic arms limitation talks deposits are left behind. individual dunes in erg typically have widths, lengths, or both dimensions greater than 500 meter ( 1,600 foot ). [ 2 ] Both the regional extent of their sand cover charge and the complexity and capital size of their dunes distinguish ergs from dune fields. The astuteness of sand in erg varies wide around the world, ranging from only a few centimeters deep in the Selima Sand Sheet of Southern Egypt, to approximately 1 m ( 3.3 foot ) in the Simpson Desert, and 21–43 megabyte ( 69–141 foot ) in the Sahara. This is army for the liberation of rwanda shallower than erg in prehistoric times were. testify in the geological record indicates that some Mesozoic and Paleozoic ergs reached a mean astuteness of several hundred meters. [ 12 ]

extraterrestrial erg [edit ]

Ergs are a geological feature of speech that can be found on planets where an air able of significant wind instrument erosion acts on the surface for a significant period of time, creating backbone and allowing it to accumulate. nowadays at least three bodies in the Solar System, aside from Earth, are known to feature ergs on their surface : Venus, Mars and Titan.

venus [edit ]

At least two ergs have been recognized by the Magellan probe on Venus : the Aglaonice dune field, which covers approximately 1,290 km2 ( 500 sq mi ), and the Meshkenet dune field ( ~17,120 km2 or 6,600 sq security service ). [ 14 ] These seem to be largely cross dune fields ( with dune crests perpendicular to prevailing winds ) .

Mars [edit ]

Mars shows identical large erg, particularly following to the polar caps, where dunes can reach a considerable size. [ 15 ] Ergs on Mars can exhibit foreign shapes and patterns, due to building complex interaction with the underlying surface and scent steering .

titan [edit ]

Radar images captured by the Cassini spacecraft as it flew by Titan in October 2005 picture sandpaper dunes at Titan ‘s equator much like those in deserts of Earth. One erg was observed to be more than 930 miles ( 1,500 km ) long. [ 16 ] Dunes are a dominant landform on Titan. approximately 15-20 % of the coat is covered by erg with an estimated entire area of 12–18 million km2 making it the largest dune field coverage in the Solar System identified to date. [ 17 ] The sand dunes are believed to be formed by scent generated as a resultant role of tidal forces from Saturn on Titan ‘s standard atmosphere. The images are evidence that these dunes were built from winds that blow in one steering before switching to another and then back to the foremost direction and so on, causing the sand dunes to build up in long parallel lines. These tidal winds combined with Titan ‘s west-to-east zonal winds create dunes aligned west-to-east about everywhere except cheeseparing to mountains, which alter wind steering.

The backbone on Titan might have formed when melted methane rained and eroded the ice bedrock, possibly in the form of flash floods. alternatively, the sand could besides have come from organic solids produced by photochemical reactions in Titan ‘s standard atmosphere. [ 18 ]

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