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Nature Creation - Earth Desert


Nature creation - Earth Desert ::-- 1.Antarctic - Desert|| 2.Sahara - Desert|| 3.Arctic - Desert|| 4.Arabian - Desert|| 5.Gobi - Desert|| 6.Kalahari - Desert|| 7.Patagonian - Desert|| 8.Victoria - Desert|| 9.Syrian - Desert|| 10.Great Basin - Desert|| Desert List||


Desert

A desert is a landscape or region that receives an extremely low amount of precipitation, less than enough to support growth of most plants. Deserts are defined as areas with an average annual precipitation of less than 250 millimetres (10 in) per year, or as areas where more water is lost by evapotranspiration than falls as precipitation. In the Koppen climate classification system, deserts are classed as BWh (hot desert) or BWk (temperate desert). In the Thornthwaite climate classification system, deserts would be classified as arid megathermal climates.



Geography

The snow surface at Dome C Station in Antarctica is representative of the majority of the continent's surface.
Deserts are part of a wide classification of regions that, on an average annual basis, have a moisture deficit (i.e. they can potentially lose more than is received). Deserts are located where vegetation cover is sparse to almost nonexistent. Deserts take up about one fifth (20%) of the Earth's land surface. Hot deserts usually have a large diurnal and seasonal temperature range, with high daytime temperatures, and low nighttime temperatures (due to extremely low humidity). In hot deserts the temperature in the daytime can reach 45 °C/113 °F or higher in the summer, and dip to 0 °C/32 °F or lower at nighttime in the winter. Water vapor in the atmosphere acts to trap long wave infrared radiation from the ground, and dry desert air is incapable of blocking sunlight during the day (due to absence of clouds) or trapping heat during the night. Thus, during daylight most of the sun's heat reaches the ground, and as soon as the sun sets the desert cools quickly by radiating its heat into space. Urban areas in deserts lack large (more than 14 °C/25 °F) daily temperature variations, partially due to the urban heat island effect.
Many deserts are formed by rain shadows; mountains blocking the path of precipitation to the desert (on the lee side of the mountain). Deserts are often composed of sand and rocky surfaces. Sand dunes called ergs and stony surfaces called hamada surfaces compose a minority of desert surfaces. Exposures of rocky terrain are typical, and reflect minimal soil development and sparseness of vegetation. The soil is rocky because of the low chemical weathering, and the relative absence of a humus fraction.
Bottomlands may be salt-covered flats. Eolian processes are major factors in shaping desert landscapes. Polar deserts (also seen as "cold deserts") have similar features, except the main form of precipitation is snow rather than rain. Antarctica is the world's largest cold desert (composed of about 98% thick continental ice sheet and 2% barren rock). Some of the barren rock is to be found in the so-called Dry Valleys of Antarctica that almost never get snow, which can have ice-encrusted saline lakes that suggest evaporation far greater than the rare snowfall due to the strong katabatic winds that evaporate even ice.
The largest hot desert is the Sahara in northern Africa, covering 9 million square kilometres and 12 countries.
Deserts sometimes contain valuable mineral deposits that were formed in the arid environment or that were exposed by erosion. Due to extreme and consistent dryness, some deserts are ideal places for natural preservation of artifacts and fossils.

Atacama is the driest place on Earth and is virtually sterile because it is blocked from moisture on both sides by the Andes mountains and by the Chilean Coast Range. The cold Humboldt Current and the anticyclone of the Pacific are essential to keep the dry climate of the Atacama. The average rainfall in the Chilean region of Antofagasta is just 1 mm per year. Some weather stations in the Atacama have never received rain. Evidence suggests that the Atacama may not have had any significant rainfall from 1570 to 1971. It is so arid that mountains that reach as high as 6,885 meters (22,590 feet) are completely free of glaciers and, in the southern part from 25°S to 27°S, may have been glacier-free throughout the Quaternary, though permafrost extends down to an altitude of 4,400 meters and is continuous above 5,600 meters.



Rank Desert Area (km²) Area (mi²)
The ten largest deserts
1 Antarctic Desert (Antarctica) 13,829,430 5,339,573
2 Sahara Desert (Africa) 9,100,000+ 3,320,000+
3 Arctic Desert (Arctic) 2,600,000+ 1,003,600+
4 Arabian Desert (Middle East) 2,330,000 900,000
5 Gobi Desert (Asia) 1,300,000 500,000
6 Kalahari Desert (Africa) 900,000 360,000
7 Patagonian Desert (South America) 670,000 260,000
8 Great Victoria Desert (Australia) 647,000 250,000
9 Syrian Desert (Middle East) 520,000 200,000
10 Great Basin Desert (North America) 492,000 190,000

libya desert

Human life in deserts

A desert is a hostile, potentially deadly environment for unprepared humans. In hot deserts, high temperatures cause rapid loss of water due to sweating, and the absence of water sources with which to replenish it can result in dehydration and death within a few days. In addition, unprotected humans are also at risk from heatstroke.
Humans may also have to adapt to sandstorms in some deserts, not just in their adverse effects on respiratory systems and eyes, but also in their potentially harmful effects on equipment such as filters, vehicles and communication equipment. Sandstorms can last for hours, sometimes even days. This makes surviving in the desert quite difficult for humans.
Despite this, some cultures have made hot deserts their home for thousands of years, including the Bedouin, Tuareg and Pueblo people. Modern technology, including advanced irrigation systems, desalinization and air conditioning have made deserts much more hospitable. In the United States and Australia for example, desert farming has found extensive use.
In cold deserts, hypothermia and frostbite are the chief hazards, as well as dehydration in the absence of a source of heat to melt ice for drinking. Falling through pack-ice or surface ice layers into freezing water is a particular danger requiring emergency action to prevent rapid hypothermia. Starvation is also a hazard; in low temperatures the body requires much more food energy to maintain body heat and to move. As with hot deserts, some people such as the Inuit have adapted to the harsh conditions of cold deserts.
Most traditional human life in deserts is nomadic. It depends in hot deserts on finding water, and on following infrequent rains to obtain grazing for livestock. In cold deserts, it depends on finding good hunting and fishing grounds, on sheltering from blizzards and winter extremes, and on storing enough food for winter. Permanent settlement in both kinds of deserts requires permanent water and food sources and adequate shelter, or the technology and energy sources to provide it.

Many deserts are flat and featureless, lacking landmarks, or composed of repeating landforms such as sand dunes or the jumbled ice-fields of glaciers. Advanced skills or devices are required to navigate through such landscapes and inexperienced travellers may perish when supplies run out after becoming lost. In addition sandstorms or blizzards may cause disorientation in severely reduced visibility.
The danger represented by wild animals in deserts has been featured in explorers' accounts but does not cause higher rates of death than in other environments such as rain forests or savanna woodland, and generally does not by itself affect human distribution. Defense against polar bears may be advisable in some areas of the Arctic, as may precautions against venomous snakes and scorpions in choosing sites at which to camp in some hot deserts.

Deserts on other planets

Mars is the only planet in the solar system in which deserts have been identified. Despite its low surface atmospheric pressure (only 1/100 of that of the Earth), the patterns of atmospheric circulation on Mars have formed a sea of circumpolar sand more than 5 million km² big, much bigger than deserts on Earth.
The Martian deserts principally consist of dunes in the form of half-moon in flat areas near the permanent polar ice caps in the north of the planet. The smaller dune fields occupy the bottom of many of the craters situated at the Martian polar regions.

 

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