Results for desert
On this page:
 
Dictionary:

desert1

  (dĕz'ərt) pronunciation
n.
  1. A barren or desolate area, especially:
    1. A dry, often sandy region of little rainfall, extreme temperatures, and sparse vegetation.
    2. A region of permanent cold that is largely or entirely devoid of life.
    3. An apparently lifeless area of water.
  2. An empty or forsaken place; a wasteland: a cultural desert.
  3. Archaic. A wild, uncultivated, and uninhabited region.
adj.
  1. Of, relating to, characteristic of, or inhabiting a desert: desert fauna.
  2. Barren and uninhabited; desolate: a desert island.

[Middle English, from Old French, from Late Latin dēsertum, from neuter past participle of dēserere, to desert. See desert3.]


de·sert2 (dĭ-zûrt') pronunciation
n.
  1. Something that is deserved or merited, especially a punishment. Often used in the plural: They got their just deserts when the scheme was finally uncovered.
  2. The state or fact of deserving reward or punishment.

[Middle English, from Old French deserte, from feminine past participle of deservir, to deserve. See deserve.]

WORD HISTORY   When Shakespeare says in Sonnet 72, “Unless you would devise some virtuous lie,/To do more for me than mine own desert,” he is using the word desert in the sense of “worthiness; deserving,” a word perhaps most familiar to us in the plural, meaning “something that is deserved,” as in the phrase just deserts. This word goes back to the Latin word dēservīre, “to devote oneself to the service of,” which in Vulgar Latin came to mean “to merit by service.” Dēservīre is made up of dē–, meaning “thoroughly,” and servīre, “to serve.” Knowing this, we can distinguish this desert from desert, “a wasteland,” and desert, “to abandon,” both of which go back to Latin dēserere, “to forsake, leave uninhabited,” which is made up of dē–, expressing the notion of undoing, and the verb serere, “to link together.” We can also distinguish all three deserts from dessert, “a sweet course at the end of a meal,” which is from the French word desservir, “to clear the table.” Desservir is made up of des–, expressing the notion of reversal, and servir (from Latin servīre), “to serve,” hence, “to unserve” or “to clear the table.”


de·sert3 (dĭ-zûrt') pronunciation

v., -sert·ed, -sert·ing, -serts.

v.tr.
  1. To leave empty or alone; abandon.
  2. To withdraw from, especially in spite of a responsibility or duty; forsake: deserted her friend in a time of need.
  3. To abandon (a military post, for example) in violation of orders or an oath.
v.intr.

To forsake one's duty or post, especially to be absent without leave from the armed forces with no intention of returning.

[French déserter, from Late Latin dēsertāre, frequentative of Latin dēserere, to abandon : dē-, de- + serere, to join.]

deserter de·sert'er n.
 
 
Sci-Tech Encyclopedia: Desert

No precise definition of a desert exists. From an ecological viewpoint the scarcity of rainfall is all important, as it directly affects plant productivity which in turn affects the abundance, diversity, and activity of animals. It has become customary to describe deserts as extremely arid where the mean precipitation is less than 2.5–4 in. (60–100 mm), arid where it is 2.5–4 to 6–10 in. (60–100 to 150–250 mm), and semiarid where it is 6–10 to 10–20 in. (150–250 to 250–500 mm). However, mean figures tend to distort the true state of affairs because precipitation in deserts is unreliable and variable. In some areas, such as the Atacama in Chile and the Arabian Desert, there may be no rainfall for several years. It is the biological effectiveness of rainfall that matters and this may vary with wind and temperature, which affect evaporation rates. The vegetation cover also alters the evaporation rate and increases the effectiveness of rainfall. Rainfall, then, is the chief limiting factor to biological processes, but intense solar radiation, high temperatures, and a paucity of nutrients (especially of nitrogen) may also limit plant productivity, and hence animal abundance. Of the main desert regions of the world, most lie within the tropics and hence are hot as well as arid. The Namib and Atacama coastal deserts are kept coot by the Benguela and Humboldt ocean currents, and many desert areas of central Asia are cool because of high latitude and altitude.

The diversity of species of animals in a desert is generally correlated with the diversity of plant species, which to a considerable degree is correlated with the predictability and amount of rainfall. There is a rather weak latitudinal gradient of diversity with relatively more species nearer the Equator than at higher latitudes. This gradient is much more conspicuous in wetter ecosystems, such as forests, and in deserts appears to be overridden by the manifold effects of rainfall. Animals, too, may affect plant diversity: the burrowing activities of rodents create niches for plants which could not otherwise survive, and mound-building termites tend to concentrate decomposition and hence nutrients, which provide opportunities for plants to colonize.

Each desert has its own community of species, and these communities are repeated in different parts of the world. Very often the organisms that occupy similar niches in different deserts belong to unrelated taxa. The overall structural similarity between American cactus species and African euphorbias is an example of convergent evolution, in which separate and unrelated groups have evolved almost identical adaptations under similar environmental conditions in widely separated parts of the world. Convergent structural modification occurs in many organisms in all environments, but is especially noticeable in deserts where possibly the small number of ecological niches has necessitated greater specialization and restriction of way of life. The face and especially the large ears of desert foxes of the Sahara and of North America are remarkably similar, and there is an extraordinary resemblance between North American sidewinding rattlesnakes and Namib sidewinding adders. See also Ecology; Physiological ecology (plant); Precipitation (meteorology).

 
Thesaurus: desert1

noun

    A tract of unproductive land: badlands, barren (often used in plural), waste, wasteland, wilderness. See rich/poor.
desert2

noun

    Something justly deserved. comeuppance, due, guerdon, recompense, reward, wage (often used in plural). Informal lump. Idioms: what is coming to one, what one has coming. See reward/punish/deserve.
desert3

verb

  1. To give up or leave without intending to return or claim again: abandon, forsake, leave, quit, throw over. Idioms: run out on, walk out on. See keep/release.
  2. To abandon one's cause or party usually to join another: apostatize, defect, renegade, tergiversate, turn. Slang rat. Idioms: change sides, turn one's coat. See approach/retreat, trust/distrust.

 
Idioms: desert

Idioms beginning with desert:
desert a sinking ship

In addition to the idiom beginning with desert, also see just deserts.

 
Antonyms: desert

adj

Definition: barren, uncultivated
Antonyms: cultivated, fertile, productive

n

Definition: wasteland; dry area
Antonyms: ocean, water

v

Definition: abandon, defect
Antonyms: aid, assist, come back, help, stay, support

 
US Military Dictionary: desert

[dǝܒzǝrt dēܒzǝrt]

dǝˈzǝrt dēˈzǝrt v. (of a soldier) illegally run away from military service.his life in the army had been such a hell that he decided to desert.

desertion n.

See the Introduction, Abbreviations and Pronunciation for further details.

 
Geography Dictionary: desert

An arid area of sparse vegetation, such that much of the ground surface is exposed. Scanty vegetation can be due to very high, or very low temperatures (as in cold deserts), or to an excess of potential evapotranspiration over precipitation. See aridity index, hot desert.

 
Music Encyclopedia: Déserts

Work for wind, piano, percussion and tape by Varèse (1954).


 
Britannica Concise Encyclopedia: desert

Agave shawii growing in a desert in North America.
Agave shawii growing in a desert in North America. (credit: © Robert and Linda Mitchell)
Large, extremely dry area of land with fairly sparse vegetation. It is one of the Earth's major types of ecosystems. Areas with a mean annual precipitation of 10 in. (250 mm) or less are generally considered deserts. They include the high-latitude circumpolar areas as well as the more familiar hot, arid regions of the low and mid-latitudes. Desert terrain may consist of rugged mountains, high plateaus, or plains; many occupy broad mountain-rimmed basins. Surface materials include bare bedrock, plains of gravel and boulders, and vast tracts of shifting sand. Wind-blown sands, commonly thought to be typical of deserts, make up only about 2% of North American deserts, 10% of the Sahara, and 30% of the Arabian desert.

For more information on desert, visit Britannica.com.

 
Architecture and Landscaping: desert

C18 landscape designed to look wild, forsaken, uninhabited, and uncultivated, with ‘ruined’ buildings, giving the impression of having been abandoned, and conducive to melancholy. A good example is the Désert de Retz, Chambourcy, Yvelines, France (1770s), with its folly in the form of a huge overscaled ruined column with an interior of three floors of apartments arranged around a central spiral stair. The rooms on the fourth floor were illuminated by means of top-lighting behind the ‘column’-shaft's broken top and through glazed ‘cracks’ in the ‘flutes’.

Bibliography

  • W. Adams (1979)
  • Muthesius & Turner (1991)
  • Racine (ed.) (2001)

The full bibliography for this book is available to download as a pdf file.
Download the bibliography for A Dictionary of Architecture and Landscape Architecture (PDF: 1.2MB)

 
Philosophy Dictionary: desert

The term denotes the idea that how a person ought to be treated depends on a fact about their actions, or their character: a proportioning of happiness to virtue, or unhappiness to vice. Treating persons as they deserve is then the exercise of justice. Problems include the distinction between moral and non-moral desert, and the question of whether the variations of treatment have a fundamental place in ethics, or whether they are to be justified, for instance on consequentialist grounds. See also free will.

 
US History Encyclopedia: Deserts

Definition has been the central problem in the history of the deserts of the United States. The need to ascertain the limits of arability and the difficulty of establishing such boundaries where precipitation fluctuates unpredictably constitute a basic developmental theme for more than half the nation. Archaeological evidences of prehistoric Native American communities indicate that droughts occasioned recurrent disaster to agricultural societies long ago, as now, in border areas. In 1803 President Thomas Jefferson, seeking congressional support for exploration of the upper Missouri River, summarized existing knowledge of newly purchased Louisiana in describing it as a region of "immense and trackless deserts" but also, at its eastern perimeter, as "one immense prairie"—a land "too rich for the growth of forest trees." The subsequent expedition of Meriwether Lewis and William Clark (1804–1806) marked the official beginning of American efforts to elaborate the description.

Until the 1860s a conception prevailed that the vast province west from the meridian of Council Bluffs, on the Missouri River, to the Rocky Mountains, between thirty-five and forty-nine degrees north latitude, was a "Great American Desert." The explorations of Lewis and Clark, Zebulon Pike, and Stephen Harriman Long, followed by the experiences of traders to Santa Fe, Rocky Mountain fur trappers, immigrants to Oregon and California, soldiers along the Gila Trail, surveyors for transcontinental railroads, and prospectors throughout the West confirmed the appellation.

While commentators agreed that agriculture could have no significant role in the region, they did occasionally recognize that the Great Plains, the mountain parks, and the interior valleys of California and the Northwest afforded excellent pasturage. As livestock industry developed in these areas during the period from 1866 to 1886, redefinition of the limits of aridity evolved. Maj. John Wesley Powell's surveys and, notably, his Report on the Lands of the Arid Region (1878) expressed the new point of view; agriculture, Powell asserted, could be profitably conducted in many parts of the West, but only as an irrigated enterprise and generally as a supplement to stock growing. The collapse of open-range ranching in the mid-1880s emphasized the need for expanded hay and forage production and gave impetus to development of Irrigation programs. But Powell's efforts to classify the public lands and the passage of the Carey Desert Land Grant Act of 1894 raised controversy. States east of the 104th meridian were excluded, at the request of their representatives, from the application of the Carey legislation. Farmers during the 1880s had expanded cultivation without irrigation nearly to that meridian in the Dakotas and even beyond it in the central plains. Many were convinced that "rainfall follows the plow." They saw no need to assume the costs and the managerial innovations of supple-mental watering. A new conception of the boundaries of aridity was emerging.

Drought in the mid-1870s had driven a vanguard of settlers eastward from the James River Valley, a prairie zone normally receiving more than twenty inches of annual rainfall. Drought in the period 1889–1894 forced thousands back from the plains farther west, where average precipitation ranges between fifteen and twenty inches annually. As normal conditions returned, however, farmers in the first two decades of the twentieth century expanded cultivation across the plains to the foothills of the Rockies—in Montana, Colorado, and New Mexico—and in many areas beyond—Utah, Idaho, the interior valleys of California, and eastern Oregon and Washington. Irrigation supplied water to only a small portion of these lands. Dry farming—a specialized program that, ideally, combines use of crop varieties adapted to drought resistance, cultivation techniques designed to conserve moisture, and management systems that emphasize large-scale operations—provided a new approach to the problem of aridity. The deserts, promoters claimed, could be made to "blossom like the rose."

When severe droughts again returned from 1919 to 1922, and from 1929 to 1936, assessment of the effectiveness of dry farming raised new concern for defining the limits of aridity—an outlook most strongly expressed in the reports of the National Resources Board of the mid-1930s but one that still permeates the writings of agricultural scientists. Long-term precipitation records, with adjustment for seasonality and rate of variability in rainfall, humidity, temperature, and soil conditions, now afford some guidance to the mapping of cultivable areas.

By established criteria a zone of outright desert (less than five inches average annual precipitation) ranges from southeastern California, northward through the western half of Nevada, nearly to the Oregon border. Because cropping without irrigation is impracticable when rainfall averages less than ten inches annually, climatic pockets found in all states west of the 104th meridian—most prevalently in Arizona, central New Mexico, eastern Nevada, Utah, and the lee side of the Cascades in Oregon and Washington—may also be defined as arid. Semiaridity—an average precipitation of from ten to fifteen inches annually—characterizes the western Dakotas, much of Montana, and large sections of eastern New Mexico, Colorado, Wyoming, Idaho, Oregon, and Washington. There dry farming may be successful but only when management programs include allowances for recurrent drought. Throughout much of the semiarid region livestock production predominates, with cropping to afford feed and forage supplementary to native short-grass pasturage. In many areas, however, the possibility of raising wheat of superior milling quality, which commands premium prices, encourages alternative land utilization. The costs of marginal productivity must be carefully weighed.

Eastward, roughly from the Missouri River to the ninety-eighth meridian and curving to the west through the central and southern plains, is a subhumid zone, in which rainfall averages from fifteen to twenty inches annually, an amount sufficient, if well distributed, to permit cultivation without recourse to specialized programs but so closely correlated to the margin of general farming requirements that a deficiency occasions failure. Almost every spring, alarms are raised that some areas of the vast wheat fields extending from the central Dakotas, through western Kansas and Nebraska and eastern Colorado and New Mexico, into the panhandles of Oklahoma and Texas have suffered serious losses. There the problem of defining limits of arability is yet unresolved; the boundaries of America's deserts and arid regions remain uncertain.

Bibliography

Fite, Gilbert C. The Farmers' Frontier, 1865–1900. New York: Holt, Rinehart and Winston, 1966.

Goetzmann, William H. Exploration and Empire: The Explorer and the Scientist in the Winning of the American West. New York: Knopf, 1966.

Hargreaves, Mary W. M. Dry Farming in the Northern Great Plains, 1900–1925. Lawrence: University Press of Kansas, 1993.

Limerick, Patricia Nelson. Desert Passages: Encounters with the American Deserts. Albuquerque: University of New Mexico, 1985.

Teague, David W. The Southwest in American Literature and Art: The Rise of a Desert Aesthetic. Tucson: University of Arizona Press, 1997.

—Mary W. M. Hargreaves/A. R.

 
Columbia Encyclopedia: desert,
arid region, usually partly covered by sand, having scanty vegetation or sometimes almost none, and capable of supporting only a limited and specially adapted animal population. The so-called cold deserts, caused by extreme cold and often covered with perpetual snow or ice, are quite distinct from the deserts of warm regions; cold deserts cover about one sixth of the world's surface. It is estimated that warm deserts form about one fifth of the land surface of the world.

The Desert Environment

An area having an annual rainfall of 10 in. (25 cm) or less is considered to be a desert. Some deserts have no rain for intervals of several years. Deserts and semideserts exist in some regions having up to about 20 in. (50 cm) of rainfall where evaporation is very high and loss by runoff is great. The largest desert regions of the world lie between 20° and 30° north and south of the equator, either where mountains intercept the paths of the trade winds or where atmospheric high-pressure areas cause descending air currents and a lack of precipitation. Other factors contributing to the formation of deserts include the amount of sunshine, rate of evaporation of water, and range of temperature. Temperature ranges in deserts are often extreme.

Plants of the desert have leaves and stems adapted to lessen their loss of water, and individual plants are more widely spaced than those in more humid regions; their roots form a spreading network sometimes penetrating to 50 ft (15 m) underground. Among the animals living in deserts of North America are species of squirrels, mice, bats, foxes, rabbits, and deer; reptiles, e.g., the Arizona coral snake, species of rattlesnakes, the desert tortoise, and the horned toad, gila monster, and many other lizards; a number of birds, e.g., the cactus wren, the road runner, species of owls, sparrows, and hawks; and spiders, scorpions, termites, and beetles. See dune; oasis.

The Deserts of the World

Europe is the only continent without deserts; there are, however, semiarid portions around the Black and Caspian seas, in parts of Ukraine and the N Caucasus. In Asia a great desert, the Gobi, exists in the middle latitudes chiefly because of its remoteness from water. Also in central Asia are the Kara Kum and Kyzyl Kum deserts. Farther south there are desert areas in NW India and through S Pakistan, Afghanistan, Iran, Iraq, and Arabia; these are largely the result of their situation in a subtropical high-pressure belt and of the distribution of pressure areas that produce cold, dry winds in winter and hot, dry winds in summer.

The Sahara, the largest desert in the world, is in Africa. Second only to the Sahara in area is the desert region of central and W Australia, lying in a high-pressure belt and in the path of the trade winds (which lose much of their moisture on the windward slopes of the east-coast mountains). South America has deserts on the coast and interior of Chile and E of the Andes in Argentina and Patagonia. In North America, deserts are found from N Mexico northward through parts of the SW and W United States. Extreme desert conditions exist in the Mojave Desert, the Imperial Valley, and Death Valley. The northern plateau region of Mexico and the adjacent portions of Texas, Arizona, and New Mexico have less extreme desert conditions with a quite abundant growth of mesquite, greasewood, creosote bush, yucca, and various species of cactus. Middle-latitude deserts are found in parts of the Great Basin.

Bibliography

See J. W. Krutch, The Voice of the Desert (1955); D. F. Costello, The Desert World (1972); G. L. Bender, ed., Reference Handbook on the Deserts of North America (1982); G. N. Louw, Ecology of Desert Organisms (1982); B. Spooner and H. S. Mann, Desertification and Development (1983); A. Grainger, Desertification (1986); L. Berkofsky and M. G. Wurtele, ed., Progress in Desert Research (1987); studies by E. C. Jaeger on desert flora and fauna (1957, 1961, 1965).

 
Word Tutor: desert
pronunciation

IN BRIEF: To abandon. Also: A dry sandy region with little or no plant life.

pronunciation Moses dragged us through the desert to the one place in the Middle East where there is no oil. — Golda Meir.

 
Wikipedia: desert
This article is about arid terrain. For other uses, see Desert (disambiguation).
For the act of abandoning or withdrawing support from an entity, see desertion.
Not to be confused with Dessert.
Erg Chebbi, Morocco
Enlarge
Erg Chebbi, Morocco

In geography, a desert is a landscape form or region that receives very little precipitation. Deserts are defined as areas that receive an average annual precipitation of less than 250 mm (10 in). In the Köppen climate classification system, deserts are classed as (BW).

Terminology

Deserts where vegetation cover is exceedingly sparse correspond to the 'hyperarid' regions of the earth, where rainfall is exceedingly rare and infrequent.

Deserts are part of a wider classification of regions that, on an average annual basis, have a moisture deficit (i.e. they can potentially lose more than is received). These areas are collectively called 'drylands' and extend over almost a third of the earth's land surface. Because desert is a vague term, the use of 'dryland', and its subdivisions of hyper arid, arid, semiarid and dry-subhumid, is preferred in some contexts, and is approved by the United Nations.[citation needed]

Geography

A satellite image of the Sahara, the world's largest hot desert and second largest desert after Antarctica.
Enlarge
A satellite image of the Sahara, the world's largest hot desert and second largest desert after Antarctica.

Deserts take up one-third of the Earth's land surface.[1] They usually have a large diurnal and seasonal temperature range, with high daytime temperatures (in summer up to 45 °C or 122 °F), and low night-time temperatures (in winter down to 0 °C; 32 °F) due to extremely low humidity. Water acts to trap infrared radiation from both the sun and the ground, and dry desert air is incapable of blocking sunlight during the day or trapping heat during the night. Thus during daylight all of the sun's heat reaches the ground. As soon as the sun sets the desert cools quickly by radiating its heat into space. Urban areas in deserts lack large (more than 25 °F/14 °C) daily temperature ranges, partially due to the urban heat island effect.

Many deserts are shielded in rain by rain shadows, mountains blocking the path of precipitation to the desert. 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 snow surface at Dome C Station in Antarctica is a representative of the majority of the continent's surface.
Enlarge
The snow surface at Dome C Station in Antarctica is a representative of the majority of the continent's surface.

Bottomlands may be salt-covered flats. Eolian processes are major factors in shaping desert landscapes. Cold deserts (also known as polar deserts) have similar features but the main form of precipitation is snow rather than rain. Antarctica is the world's largest cold desert (composed of about 98 percent thick continental ice sheet and 2 percent barren rock). The largest hot desert is the Sahara.

Deserts sometimes contain valuable mineral deposits that were formed in the arid environment or that were exposed by erosion. Because deserts are so dry, they are ideal places for artifacts and fossils to be preserved.

Etymology

The English, French (désert), Spanish (desierto), Italian (deserto), all come from the Latin desertum, meaning "an unpopulated place." This in turn is derived from the Egyptian word dSr.t, which literally means "red land" and refers to the desert.

Types of desert

High desert in Eastern Oregon, United States
Enlarge
High desert in Eastern Oregon, United States
The Agasthiyamalai hills cut off Tirunelveli (India) from the monsoons, creating a rainshadow region
Enlarge
The Agasthiyamalai hills cut off Tirunelveli (India) from the monsoons, creating a rainshadow region

In 1953, Peveril Meigs divided desert regions on Earth into three categories according to the amount of precipitation they received. In this now widely accepted system, extremely arid lands have at least 12 consecutive months without rainfall, arid lands have less than 250 millimeters (10 in) of annual rainfall, and semiarid lands have a mean annual precipitation of between 250 and 500 millimeters (10-20 in). Arid and extremely arid lands are deserts, and semiarid grasslands are generally referred to as steppes.[1]

However, lack of rainfall alone can't provide an accurate description of what a desert is. For example, Phoenix, Arizona receives less than 250 millimeters (10 in) of precipitation per year, and is immediately recognized as being located in a desert. The North Slope of Alaska's Brooks Range also receives less than 250 millimeters (10 in) of precipitation per year, but is not generally recognized as a desert region. Deserts have moderate to cool winters and hot summers.

The difference lies in something termed "potential evapotranspiration." The water budget of an area can be calculated using the formula P-PE+/-S, wherein P is precipitation, PE is potential evapotranspiration rates and S is amount of surface storage of water. Evapotranspiration is the combination of water loss through atmospheric evaporation, coupled with the evaporative loss of water through the life processes of plants. Potential evapotranspiration, then, is the amount of water that could evaporate in any given region. As an example, Tucson, Arizona receives about 300 millimeters, (12 in), of rain per year, however about 2500 millimeters, (100 in), of water could evaporate over the course of a year. In other words, about 8 times more water could evaporate from the region than actually falls. Rates of evapotranspiration in other regions such as Alaska are much lower, so while these regions receive minimal precipitation, they should be designated as specifically different from the simple definition of a desert: a place where evaporation exceeds precipitation.

With that said, there are different forms of deserts. Cold deserts can be covered in snow; such locations don't receive much precipitation, and what does fall remains frozen as snow pack; these are more commonly referred to as tundra if a short season of above-freezing temperatures is experienced, or as an ice cap if the temperature remains below freezing year-round, rendering the land almost completely lifeless.

Most non-polar deserts are hot because they have little water. Water tends to have a cooling, or at least a moderating, effect in environments where it is plentiful. In some parts of the world deserts are created by a rain shadow effect in which air masses lose much of their moisture as they move over a mountain range; other areas are arid by virtue of being very far from the nearest available sources of moisture (this is true in some middle-latitude landmass interior locations, particularly in Asia).

Deserts are also classified by their geographical location and dominant weather pattern as trade wind, mid-latitude, rain shadow, coastal, monsoon, or polar deserts. Former desert areas presently in non-arid environments are paleodeserts.

Montane deserts

Montane deserts are arid places with a very high altitude; the most prominent example is found north of the Himalaya especially in Ladakh region of Jammu and Kashmir (India), in parts of the Kunlun Mountains and the Tibetan Plateau. Many locations within this category have elevations exceeding 3,000 meters (10,000 ft) and the thermal regime can be hemiboreal. These places owe their profound aridity (the average annual precipitation is often less than 40 mm/1.5in) to being very far from the nearest available sources of moisture. Montane deserts are normally cold.

Rain shadow deserts

Rain shadow deserts form when tall mountain ranges block clouds from reaching areas in the direction the wind is going. As the air moves over the mountains, it cools and moisture condenses, causing precipitation on the windward side. Moisture almost never reaches the leeward side of the mountain, resulting in a desert. When that air reaches the leeward side, the air is dry, because it has already lost the majority of its moisture. The air then warms, expands, and blows across the desert. The warm air takes with it any remaining small amounts of moisture in the desert.

Desert features

Satellite view of Al-Dahna desert in Saudi Arabia. Different depositional features can be clearly seen.
Enlarge
Satellite view of Al-Dahna desert in Saudi Arabia. Different depositional features can be clearly seen.
Mahktesh Gadol, an erosional basin in the Negev Desert of southern Israel.
Enlarge
Mahktesh Gadol, an erosional basin in the Negev Desert of southern Israel.

Sand covers only about 20 percent of Earth's deserts. Most of the sand is in sand sheets and sand seas—vast regions of undulating dunes resembling ocean waves "frozen" in an instant of time. In general, there are six forms of deserts:

  • Mountain and basin deserts
  • Hamada deserts, which consist of plateau landforms
  • Regs, which consist of rock pavements
  • Ergs, which are formed by sand seas
  • Intermontane Basins
  • Badlands, which are located at the margins of arid lands comprising clay-rich soil

Nearly all desert surfaces are plains where eolian deflation—removal of fine-grained material by the wind—has exposed loose gravels consisting predominantly of pebbles but with occasional cobbles.

The remaining surfaces of arid lands are composed of exposed bedrock outcrops, desert soils, and fluvial deposits including alluvial fans, playas, desert lakes, and oases. Bedrock outcrops commonly occur as small mountains surrounded by extensive erosional plains.

There are several different types of dunes. Barchan dunes are produced by strong winds blowing across a level surface and are crescent-shaped. Longitudinal or seif dunes are dunes that are parallel to a strong wind that blows in one general direction. Transverse dunes run at a right angle to the constant wind direction. Star dunes are star-shaped and have several ridges that spread out around a point.

Oases are vegetated areas moistened by springs, wells, or by irrigation. Many are artificial. Oases are often the only places in deserts that support crops and permanent habitation.

Flora and fauna

Deserts have a reputation for supporting very little life, but in reality deserts often have high biodiversity, including animals that remain hidden during daylight hours to control body temperature or to limit moisture needs. Some fauna includes the kangaroo rat, coyote, jack rabbit, and many lizards. Some flora includes shrubs, Prickly Pears, and the Brittle bush.

Vegetation

Flora of Baja California Desert, Cataviña region, Mexico
Enlarge
Flora of Baja California Desert, Cataviña region, Mexico

Most desert plants are drought- or salt-tolerant, such as xerophytes. Some store water in their leaves, roots, and stems. Other desert plants have long taproots that penetrate to the water table if present, or have adapted to the weather by having wide-spreading roots to absorb water from a greater area of the ground. George Bush is the development of small, spiny leaves which shed less moisture than deciduous leaves with greater surface areas. The stems and leaves of some plants lower the surface velocity of sand-carrying winds and protect the ground from erosion. Even small fungi and microscopic plant organisms found on the soil surface (so-called cryptobiotic soil) can be a vital link in preventing erosion and providing support for other living organisms

Deserts typically have a plant cover that is sparse but enormously diverse. The giant saguaro cacti of the Sonoran Desert provide nests for desert birds and serve as "trees" of the desert. Saguaro grow slowly but may live up to 200 years. When 9 years old, they are about 15 centimeters (6 in) high. After about 75 years, the cacti develop their first branches. When fully grown, saguaro are 15 meters tall and weigh as much as 10 tons. They dot the Sonoran and reinforce the general impression of deserts as cactus-rich land.

Although cacti are often thought of as characteristic desert plants, other types of plants have adapted well to the arid environment. They include the pea and sunflower families. Cold deserts have grasses and shrubs as dominant vegetation.

Water

The shifting sands simulator at Questacon, Canberra
Enlarge
The shifting sands simulator at Questacon, Canberra

Rain does fall occasionally in deserts, and desert storms are often violent. A record 44 millimeters (1.7 in) of rain once fell within 3 hours in the Sahara. Large Saharan storms may deliver up to 1 millimeter per minute. Normally dry stream channels, called arroyos or wadis, can quickly fill after heavy rains, and flash floods make these channels dangerous.

Though little rain falls in deserts, deserts receive runoff from ephemeral, or short-lived, streams fed considerable quantities of sediment for a day or two. Although most deserts are in basins with closed or interior drainage, a few deserts are crossed by 'exotic' rivers that derive their water from outside the desert. Such rivers infiltrate soils and evaporate large amounts of water on their journeys through the deserts, but their volumes are such that they maintain their continuity. The Nile River, the Colorado River, and the Yellow River are exotic rivers that flow through deserts to deliver their sediments to the sea. Deserts may also have underground springs, rivers, or reservoirs that lay close to the surface, or deep underground. Plants that have not completely adapted to sporadic rainfalls in a desert environment may tap into underground water sources that do not exceed the reach of their root systems.

Lakes form where rainfall or meltwater in interior drainage basins is sufficient. Desert lakes are generally shallow, temporary, and salty. Because these lakes are shallow and have a low bottom gradient, wind stress may cause the lake waters to move over many square kilometers. When small lakes dry up, they leave a salt crust or hardpan. The flat area of clay, silt, or sand encrusted with salt that forms is known as a playa. There are more than a hundred playas in North American deserts. Most are relics of large lakes that existed during the last ice age about 12,000 years ago. Lake Bonneville was a 52,000 kilometers² (20,000 mi²) lake almost 300 meters (1000 ft) deep in Utah, Nevada, and Idaho during the Ice Age. Today the remnants of Lake Bonneville include Utah's Great Salt Lake, Utah Lake, and Sevier Lake. Because playas are arid landforms from a wetter past, they contain useful clues to climatic change.

When the occasional precipitation does occur, it erodes the desert rocks quickly and powerfully.Winds are the other factor that erodes deserts—they are slow yet constant.

The flat terrains of hardpans and playas make them excellent racetracks and natural runways for airplanes and spacecraft. Ground-vehicle speed records are commonly established on Bonneville Speedway, a racetrack on the Great Salt Lake hardpan. Space shuttles land on Rogers Lake Playa at Edwards Air Force Base in California.

Mineral resources

Some mineral deposits are formed, improved, or preserved by geologic processes that occur in arid lands as a consequence of climate. Ground water leaches ore minerals and redeposits them in zones near the water table. This leaching process concentrates these minerals as ore that can be mined.

Evaporation in arid lands enriches mineral accumulation in their lakes. Lake beds known as Playas may be sources of mineral deposits formed by evaporation. Water evaporating in closed basins precipitates minerals such as gypsum, salts (including sodium nitrate and sodium chloride), and borates. The minerals formed in these evaporite deposits depend on the composition and temperature of the saline waters at the time of deposition.

Significant evaporite resources occur in the Great Basin Desert of the United States, mineral deposits made famous by the "20-mule teams" that once hauled borax-laden wagons from Death Valley to the railroad. Boron, from borax and borate evaporites, is an essential ingredient in the manufacture of glass, enamel, agricultural chemicals, water softeners, and pharmaceuticals. Borates are mined from evaporite deposits at Searles Lake, California, and other desert locations. The total value of chemicals that have been produced from Searles Lake substantially exceeds US$1 billion.

The Atacama Desert of South America is unique among the deserts of the world in its great abundance of saline minerals. Sodium nitrate has been mined for explosives and fertilizer in the Atacama since the middle of the 19th century. Nearly 3 million tonnes were mined during World War I.

Valuable minerals located in arid lands include copper in the United States, Chile, Peru, and Iran; iron and lead-zinc ore in Australia; chromite in Turkey; and gold, silver, and uranium deposits in Australia and the United States. Nonmetallic mineral resources and rocks such as beryllium, mica, lithium, clays, pumice, and scoria also occur in arid regions. Sodium carbonate, sulfate, borate, nitrate, lithium, bromine, iodine, calcium, and strontium compounds come from sediments and near-surface brines formed by evaporation of inland bodies of water, often during geologically recent times.

The Green River Formation of Colorado, Wyoming, and Utah contains alluvial fan deposits and playa evaporites created in a huge lake whose level fluctuated for millions of years. Economically significant deposits of trona, a major source of sodium compounds, and thick layers of oil shale were created in the arid environment.

Some of the more productive petroleum areas on Earth are found in arid and semiarid regions of Africa and the Mideast, although the oil fields were originally formed in shallow marine environments. Recent climate change has placed these reservoirs in an arid environment. It's noteworthy that Ghawar, the world's largest and most productive oilfield is mostly under the Empty Quarter and Al-Dahna deserts.

Other oil reservoirs, however, are presumed to be eolian in origin and are presently found in humid environments. The Rotliegendes, a hydrocarbon reservoir in the North Sea, is associated with extensive evaporite deposits. Many of the major U.S. hydrocarbon resources may come from eolian sands. Ancient alluvial fan sequences may also be hydrocarbon reservoirs.

Human life in deserts

A desert is a hostile, potentially deadly environment for unprepared humans. The high heat causes rapid loss of water due to sweating, which can result in dehydration and death within days. In addition, unprotected humans are also at risk from heatstroke and venomous animals. Despite this, some cultures have made deserts their home for thousands of years, including the Bedouin, Touareg and Puebloan people. Modern technology, including advanced irrigation systems, desalinization and air conditioning have made deserts much more hospitable. In the United States and Israel, desert farming has found extensive use.

See also

References

  1. ^ a b What is a desert?
Emblem-important.svg
 This article or section is missing citations or needs footnotes.
Using inline citations helps guard against copyright violations and factual inaccuracies.

External links

Deserts

Ad-Dahna · Alvord · Arabian · Aral Karakum · Atacama · Baja California · Barsuki · Betpak-Dala · Chalbi · Chihuahuan · Dasht-e Kavir · Dasht-e Lut · Dasht-e Margoh · Dasht-e Naomid · Gibson · Gobi · Great Basin · Great Sandy Desert · Great Victoria Desert · Kalahari · Karakum · Kyzylkum · Libyan · Little Sandy Desert · Mojave · Monte · Namib · Nefud · Negev · Nubian · Ordos · Owyhee · Patagonian · Qaidam · Registan · Rub' al Khali · Ryn-Peski · Sahara · Saryesik-Atyrau · Sechura · Simpson · Sonoran · Strzelecki · Syrian · Taklamakan · Tanami · Thar · Tihamah · Ustyurt

be-x-old:Пустэльняeml:Desêrtzh-classical:沙漠zh-yue:沙漠


This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by profe