Desert dunes

Kasper-Zubillaga, J.J., Acevedo-Vargas, B., Morton-Bermea, O., Ortiz-Zamora, G., 2008a, Rare earth elements of the Altar Desert dune and coastal sands, Northwestern Mexico. Chemie Der Erde Geochemistry, 68, 45-69. 

Gardner, R.A.M. Pye, K. (1981) Nature, origin and paleoenvironmental significance of red coastal and desert dune sands. Progr. Phys. Geogr. 5 514—534... 

Bagnold, R.A. "The Physics of Blown Sand and Desert Dunes" Methuen, London, 1941. 

The physics of blown sand and desert dunes. New York Wm. Morrow Co. 

Lancaster, N. (1995) Geomorphology of Desert Dunes. London Routledge. 

Karnieli. A Tsoar, H., 1995. Spectral reflectance of biogenic crust developed on desert dune sand along the Israel-Egypt border. Int. J. Remote Sens. 16. 369-374. 

R. A. Bagnold. Physics of Blown Sands and Desert Dunes. William Morrow, New York, 1941. 

Wiggs, G.F.S. 2001. Desert dune processes and dynamics. Progress in Physical Geography 25(l) 53-79. 

Aeolian sands are deposited by wind action, either in dunes or in extensive sheets ( cover sand areas ) Wind action is particularly effective in hot and dry regions such as deserts but sand dunes are also common in (sub)humid regions with sparse vegetation, notably in overgrazed areas and along beaches and fluvial braid plains . The (weathering) history of the parent materials in the source area determines whether the sands are rich in quartz and/or carbonates. 

Free dunes have no fixed position, but migrate downwind by erosion on the gently inclined windward side and deposition on the leeward side (slip face) in the same way as described for fixed dunes. The smallest free dunes are common wind ripples that measure only a few centimeters in height. Large dunes are found in extensive dune areas in deserts, in sand seas known as ergs . 

Coastal dunes occur along beaches or sand-flats that form part of a non-erosional sandy or deltaic coast. The source areas of the sand will eventually lose all sand, silt and clay particles some become wet (groundwater) depressions whereas others acquire a rocky or boulder-strewn surface known as a desert pavement . 

The area of actual erg and dune formation is delimited by the 150 mm/yr isohyet. This precipitation boundary appears to have shifted strongly in the recent past. Between 20,000 and 13,000 yr BP, the southern limit of active dune formation in the Sahara desert was 800 km south of its present position and most of the now sparely vegetated Sahelian zone was an area of active dune formation at that time. These dunes, mostly of the longitudinal type, are now fixed by vegetation, but their aeolian parentage is still obvious from their well-sorted material. A similar story can be told for the Kalahari sands. Overgrazing in recent times has reactivated aeolian transport in many regions with sands. 

Dunes and sand plains form where strong winds carry sand grains in saltation over short distances. Particles finer than sand are transported in suspension and over greater distances until they settle as loess , predominantly in the steppe regions adjacent to the desert zone. 

Arid and semi-arid lands are quite widespread in Asia, where deserts make up some 11% of this continent (Table 1.1) in Central Asia, north and east of the Caspian to Aral Sea area. In the Turkestan desert, large dunes form huge sand seas (Nettleton and Peterson, 1983). West and North of China, the Takla-Makan and Gobi deserts dominate the landscapes. More to the south, the Great Indian Desert extends up to the Himalayan foothills. More to the west are the hyperarid areas of the Dasht-i-Lat and Dasht-i-Kavri deserts in Iran and Syrian deserts. Immense areas in the north-central part of the Arabian Peninsula and in the Rub al Khali deserts in its southeastern part are hyperarid or arid. 

Kasper-Zubillaga, J.J. Carranza-Edwards, A., 2005.Grain size discrimination between sands of desert and coastal dunes from northwestern Mexico. Revista Mexicana de Ciencias Geologicas, 22, 383-390. 

Kasper-Zubillaga, J.J., Carranza-Edwards, A., Morton-Bermea, O. 2008b.Heavy minerals and rare earth elements in coastal and inland dunes of El Vizcaino Desert Baja Califonia Peninsula, Mexico. Marine Georesources and Geotechnology, 26, 172-188. 

Gawler Craton, located on the edge of the Great Victoria Desert (GVD). In this part of the GVD, regolith landforms are comprised of scarce hills of weathered bedrock outcrops surrounded by sand spreads, dunes and colluvial materials the hills act as windows to the otherwise covered weathered bedrock. The outcrops themselves have been silicified and, more recently, have been overprinted with calcrete. Calcrete sampling is relatively easy on the exposed outcrops and is preferentially sampled by mineral explorers due to its near-surface location (<10-20 cm depth). However, calcrete on the colluvial slopes and in the swales is not as easily located because of concealment by GVD sand and colluvium. 

The Tsodilo Hills World Heritage Site is located in northwestern Botswana, in the Kalahari Desert, about 40 km from the Okavango River and is surrounded by relict linear sand dunes. This is one of the most interesting archaeological localities in southern Africa, in part because hills in the region are rare, the nearest to Tsodilo being about 200 km away. Evidence of human activity at the... 

Sand, such as that found in the massive sand dunes bordering the desert plain near Namib, Namibia, is composed of silicon and oxygen. 

Sounds produced by humans can also interfere with the ability of animals to communicate. Such interference can inhibit an animaPs ability to protect itself, to find food, and to live a normal life. For example, ships emit low-frequency sounds that interfere with whale communications. Other human noises can frighten whales away from their normal migration routes. In the desert, kangaroo rats Dipodomys spp.) exposed to the roar of a dune buggy lose their ability to hear snakes approaching. Japanese quail (Coturnix Coturnix Japonicd) have to call much louder than usual when they live in a noisy environment. Sooty terns (Sterna fuse at a) have been observed to abandon their nests when jets create sonic booms. Intense bursts of noise have also caused condors (Gymnogyps californianus) to abandon their nests. 

Found in a variety of habitats and elevations, from pine forests, desert flats, rolling grasslands, to the rocky slopes of mountains to about 7,000 feet or more. They are not known to occur in dunes, but have been found in sandy areas near... 

This scorpion is found in dry desert areas on different substrate types, but not in sand dunes. They hide in small natural burrows or under stones. 

But none of that mattered to the alchemist. He had already seen many people come and go, and the desert remained as it was. He had seen kings and beggars walking the desert sands. The dunes were changed constantly by the wind, yet these were the same sands he had known since he was a child. He always enjoyed seeing the happiness that the travelers experienced when, after weeks of yellow sand and blue sky, they first saw the green of the date palms. Maybe God created the desert so that man could appreciate the date trees, he thought. 

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