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23-401: Jabal Aja is a granite mountain range about 100 km (62 mi) long and 10 to 35 km (6 to 22 mi) wide with an area of about 2,000 km (770 sq mi). The mountains are criss-crossed by straight valleys that have developed along fault lines and have an altitude varying between 900 and 1,550 m (3,000 and 5,100 ft). The mountain probably receives more rainfall than

46-456: A centre for migratory birds especially the demoiselle crane ( Grus virgo ). Among the important species resident in the reserve are the sand partridge , griffon vulture , Egyptian vulture , desert owl and pale rockfinch . Among the migratory species that visit the reserve in passage or over-winter here are Menetries's warbler , white-throated robin , Finsch's wheatear , cinereous bunting and several species of cranes . Mammals found in

69-529: A geological feature that can be found on planets where an atmosphere capable of significant wind erosion acts on the surface for a significant period of time, creating sand and allowing it to accumulate. Today at least three bodies in the Solar System , apart from Earth, are known to feature ergs on their surface: Venus, Mars and Titan. At least two ergs have been recognized by the Magellan probe on Venus :

92-501: 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 ʿirq ( عرق ), meaning "dune field". Strictly speaking, an erg is defined as a desert area that contains more than 125 km (48 sq mi) 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

115-434: Is dominant and is accompanied by other woody shrubs such as Searsia , Periploca , Gymnocarpos and Ephedra foliata . In the wadis and runnels, more Acacia gerrardi grows, associated with Lycium shawii , Pulicaria undulata , Ochradenus baccatus and Zilla spinosa . The combined area of Jabal Aja and Northern Ha'il has been designated an Important Bird and Biodiversity Area because of its importance as

138-613: Is halted or slowed by topographic barriers to windflow or by convergence of windflow. Entire ergs and dune fields tend to migrate downwind as far as hundreds of kilometers from their sources of sand. Such accumulation requires long periods of time. At least one million years is required to build ergs with very large dunes, such as those on the Arabian Peninsula , in North Africa, and in central Asia. Sand seas that have accumulated in subsiding structural and topographic basins, such as

161-589: The Arab Revolt in 1917, forces led by Auda ibu Tayi attacked the Turkish-held coastal town of Aqaba on its poorly defended eastern flank. The approach was via a long and wide desert route, passing close to the edge of the Nafud. Colonel T. E. Lawrence asked Auda ibu Tayi to allow their group to stray from their course into the Nafud. Auda refused because it was unnecessary. Their harsh transit did not include entering

184-447: The Arabian Peninsula at 28°18′N 41°00′E  /  28.30°N 41.00°E  / 28.30; 41.00 , occupying a great oval depression. It is 290 kilometres (180 mi) long and 225 kilometres (140 mi) wide, with an area of 103,600 square kilometres (40,000 sq mi). The Nafud is an erg , a desert region located in north-central Saudi Arabia . It is noted for its sudden violent winds, which account for

207-720: The Murzuk Sand Sea of Libya , may attain great thicknesses (more than 1000 m ) but others, such as the ergs of linear dunes in the Simpson Desert and Great Sandy Desert of Australia, may be no thicker than the individual dunes superposed on the alluvial plain . Within sand seas in a given area, the dunes tend to be of a single type. For example, 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. By nature, ergs are very active. Smaller dunes form and migrate along

230-567: The Aglaonice dune field, which covers approximately 1,290 km (500 sq mi), and the Meshkenet dune field (~17,120 km or 6,600 sq mi). These seem to be mostly transverse dune fields (with dune crests perpendicular to prevailing winds). Mars shows very large ergs, especially next to the polar caps, where dunes can reach a considerable size. Ergs on Mars can exhibit strange shapes and patterns, due to complex interaction with

253-582: The Nafud, as is depicted in the film Lawrence of Arabia . The discovery of an 85,000-year-old fossilised human finger in An Nafud in 2016 by Dr Mathieu Duval of Griffith University provided the earliest evidence of modern humans outside Africa and the Levant . This article about the geography of Saudi Arabia is a stub . You can help Misplaced Pages by expanding it . Erg (landform) An erg (also sand sea or dune sea , or sand sheet if it lacks dunes )

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276-521: The dry, subsiding air of the trade winds . Active ergs are limited to regions that receive, on average, no more than 150 mm of annual precipitation. The largest are in northern and southern Africa , central and western Asia , and Central Australia . In South America , ergs are limited by the Andes Mountains , but they do contain extremely large dunes in coastal Peru and northwestern Argentina . They are also found in several parts of

299-568: The edge of the An Nafud desert. Jabal Aja has been designated an Important Plant Area because of the richness of its plant life and the presence of many endemic and relict plant species. The reserve offers a refuge to plants from the Mediterranean and Irano-Turanian regions in an area that otherwise forms part of the Saharo-Arabian region . About 355 species of plant have been recorded in

322-462: The flanks of the larger dunes and sand ridges. Occasional precipitation fills basins formed by the dunes; as the water evaporates, salt deposits are left behind. Individual dunes in ergs typically have widths, lengths, or both dimensions greater than 500 m (1,600 ft). Both the regional extent of their sand cover and the complexity and great size of their dunes distinguish ergs from dune fields. The depth of sand in ergs varies widely around

345-597: The large crescent-shaped dunes . The sand in the Nafud is a brick-reddish color. Rain comes once or twice per year. In some lowland areas, namely those near the Hejaz Mountains, there are oases where dates, vegetables, barley, and fruits are grown. The Nafud is connected to the Rub' al Khali by the Dahna , a corridor of gravel plains and sand dunes, 800 mi (1,287 km) long and 15 to 50 miles (24.1 to 80.5 km) wide. During

368-724: The largest dune field coverage in the Solar System identified to date. The sand dunes are believed to be formed by wind generated as a result of tidal forces from Saturn on Titan's atmosphere. The images are evidence that these dunes were built from winds that blow in one direction before switching to another and then back to the first 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 nearly everywhere except close to mountains, which alter wind direction. The sand on Titan might have formed when liquid methane rained and eroded

391-975: The northeast coast 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 state 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 . Almost all major ergs are located downwind from river beds in areas that are too dry to support extensive vegetative cover and are thus subject to long-continued wind erosion. Sand from these abundant sources migrates downwind and builds up into very large dunes where its movement

414-451: The park include the Arabian wolf , sand cat and Nubian ibex , and there are a number of species of reptile and amphibian. In 1973, the country's last known cheetahs were reported in the vicinity of Ha'il. Other notes: An Nafud The Nafud desert or simply The Nafud ( Arabic : صحراء النفود , romanized :  ṣahrā' an-nafūd ) is a desert in the northern part of

437-421: The reserve, including the plants found in the adjoining desert area of An Nafud. The plains have deep sandy-loam soils and the dominant plant is Haloxylon salicornicum , with the desert gourd being common and Asphodelus tenuifolius occurring in depressions. The annual plants Stipa tortilis , Picris cyanocarpa and Anthemis appear after rains. On the thin slopes below the rocks, Acacia gerrardii

460-410: The surrounding area where Ha'il averages about 116 mm (4.6 in). This falls mainly in winter, mostly from storms approaching from the southwest, and frost is not unusual. Jabal Aja is situated to the west and southwest of the town of Ha'il and the protected area has been extended to the northeast to include an area of arid flattish terrain with low sandstone hills and granite outcrops extending to

483-529: The underlying surface and wind direction. Radar images captured by the Cassini spacecraft as it flew by Titan in October 2005 show sand 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. Dunes are a dominant landform on Titan. Approximately 15-20% of the surface is covered by ergs with an estimated total area of 12–18 million km making it

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506-578: The world, ranging from only a few centimeters deep in the Selima Sand Sheet of Southern Egypt, to approximately 1 m (3.3 ft) in the Simpson Desert, and 21–43 m (69–141 ft) in the Sahara. This is far shallower than ergs in prehistoric times were. Evidence in the geological record indicates that some Mesozoic and Paleozoic ergs reached a mean depth of several hundred meters. Ergs are

529-1157: The world, the Sahara , covers 9 million square kilometres (3.5 × 10 ^  sq mi) 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 32,000 km (12,355 sq mi), 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 . Sand seas and dune fields generally occur in regions downwind of copious sources of dry, loose sand, such as dry riverbeds and deltas , floodplains , glacial outwash plains , dry lakes , and beaches . Ergs are concentrated in two broad belts between 20° to 40°N and 20° to 40°S latitudes, which include regions crossed by

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