Desert

• Desert climate
• Savannah climate
• Tundra
• Eisklima

As desert is called the barren or sparsely vegetated areas of the world. In Desert vegetation covers less than 5 % of the surface. Cause of deserts are either missing heat ( cold desert, desert of ice ) and the subpolar regions subnivalen, overgrazing or drought (dry desert, desert heat ). Deserts belong to Anökumene.

• 2.1 Dry Desert 2.1.1 Subtropical dry desert
• 2.1.2 inland desert and rain shadow desert
• 2.1.3 Mist Desert

• 3.1 semi-desert
• 3.2 Edaphic desert

• 4.1 Flora and Vegetation
• 4.2 Fauna
• 4.3 Microbial life

Geomorphological classification of desert species

Sand desert

The sandy desert is called in Arabic Erg, in Western Sahara and in the Libyan desert also Edeyen. A Sandy Desert is a desert with a surface consisting predominantly of quartz sand, which was formed by the erosion of a gravel desert, or was blowing from other regions. The living conditions in the sandy deserts are harder than others. They are available with and without dunes, which can be relatively stable and solidified in its lower part, as in the southern sea of ​​sand and form so-called Gassis or as in the northern Sand Sea of Egypt about to Farafra than shifting sand dunes occur in the form of ( depending upon the prevailing wind direction) transverse, longitudinal, star or crescent dunes. The highest sand dunes are found in Algeria, the longest is the Abu Muharek with about 600 km. Good to drive, when solidified sand plains, or only with difficulty passable by car. The world's largest sand desert, the Rub al Khali in Arabia.

Gravel desert

Gravel deserts hot only in the Western Sahara Reg, in the central Sahara they are called Serir. Gravel deserts caused by erosion of stone or rocky deserts ( accumulation of coarser grain sizes by blowing out the finer grain sizes) or by the deposition of gravel in advance of glaciers. Another cause is a physical effect that is also found in freeze- dried coffee, where if you shake the container long enough to accumulate on the surface is always larger particles since the smaller more easily slide down, only that this operation in the desert where humidity, wind and temperature differences for the movement of sand grains provide, is significantly slower. Ruts hang around here very long. Good passable.

Stone or rock desert

Stone or rocky deserts also called Hammada. The surface of this desert type is dotted with dense blocky, angular rubble or rock material that accumulated as a result of physical weathering and the Auswehung of the fine material. Most are covered with boulders plateaus. By car barely passable, except on old caravan routes, which are usually, as in other forms of the desert Alamat recognizes (small stone pyramids as signposts ) and the camel carcasses, which they border. On the surface of the rocks there is increasingly desert varnish.

Salt desert

Salt desert is called in Algeria and Tunisia Schott, in the central and Eastern Sahara sebkha, Libya Grara. Salt deserts occur mostly in arid, endorheic sedimentary basins by strong evaporation. Many deserts of the type are in Iran and Central Asia. They are to be avoided and difficult to pass because of the pond and marsh fields subsalt possible. The salt of this bulkhead, however, does not represent the remains of an ancient sea - the Tethys (ocean) there is no longer since 66 million years - but it comes from the erosion of from surrounding highlands down geschwemmten deposits, which are often abundant contain salt, which is drainless sinks such as the Qattara Depression naturally accumulated and had thick, high salt enriched sound and Lehmflächen arise so-called salt flats or alkali flats. After rainfall, these were transformed into salt lakes or salt marshes, which consist of a muddy mixture of clay, sand and salt. The name of the street parallel to the Cairo - Alexandria extends north Egyptian Wadi El Natrun -, the Libyan El Atrun on Cyrenaica and the north- western Sudanese oasis El- Atrun are examples of this situation.

Ice Desert

The geomorphological type of ice desert corresponds to the climatic concept of cold desert ( see below).

Classification according to climatic mode of origin

Dry desert

Dry deserts prevented by their lack of water, the plant growth. The soils of the dry deserts are among the Aridisolen.

Subtropical dry desert

Subtropical dry deserts, also known as the Passat desert or tropic deserts, lying at a latitude up to about 30 ° either side of the Earth's equator. Examples are the biggest parts of the Sahara and the Kalahari.

Both the northern and in the southern hemisphere, the air masses are forced by coming Urpassat of the high pressure area frequently occurring there to dismount. They heated, whereby the relative humidity decreases and come up dry, cloudless climates.

The areas of high pressure coming through the intertropical convergence zone, short ITC concluded. Due to the strong sunlight through a large angle (maximum 90 °) the earth is particularly heated strongly in the equatorial region. As much water evaporates. Since there is an inversion layer in the tropopause, the air masses can not continue to rise. You are deflected to the north and south. The condensation of the water vapor it starts to rain. In the tropic region, the cooled air in which no moisture is present, begins to sink. Descending air masses cause always a resolution of the clouds. Near the ground, the air flows back into the equatorial region. By Coriolisablenkung arise the trade winds.

Inland desert and rain shadow desert

Inland deserts and rain shadow deserts are caused by the shape of the earth's surface and are therefore also called relief deserts. They occur in the interior of the continents, especially behind high mountain ranges or in basins. In such regions, falls only low rainfall, because they are too remote marine ( inland deserts ) or in the rain shadow on the leeward side of mountain ranges are ( rain shadow desert ).

The moist air masses are forced to rise before the mountains. On top of the mountain range the air is cooler and can therefore store less water: the damp, cold air masses are forced to raining. On the other side of the mountain range, the air heated for a total decrease (due to the feuchtadiabatischen cooling and heating trockenadiabatischen ) and the warm, dry air masses. Below form due to the heat and dryness of deserts.

Inland deserts are south of the southern or north of the northern tropics. Most famous are the Gobi desert, the Taklamakan and the Great Basin. A typical rain shadow desert is the desert of Judah.

Fog desert

The fog desert occurs primarily as a coastal desert and is a special form of the Passat desert. Trade winds and ocean currents, they reinforce specific. The cold rising water of the sea cools the overlying air masses over her. The humidity contained in these air masses condensed, the relative humidity rises so and clouds form. The clouds, however, have lost so much in temperature that they can no longer ascend - the result is a stable stratification and therefore fog. If these air masses now in the wilderness, so be heated and drop sharply in relative humidity, the clouds dissolve. " So close to the water and yet so low in the water," Alexander von Humboldt once described the coastal desert of Atacama.

The famous coastal deserts are the Atacama, the Namib and the Nullarbor Desert. Also sea near parts of the Sahara are under the influence of cool ocean currents. Fog deserts are found in the subtropics, especially in continental west coasts.

Cold desert

Cold deserts are found in polar regions and at high altitudes, prevent their extremely low temperatures, the spread of vegetation. Although the soil is covered by ice ( ice desert ), the air is very dry due to temperature and often lack of rainfall. Therefore, cold deserts can also be counted to the dry deserts. Many areas in Antarctica are almost entirely niederschlagslos. The Wright Valley as part of the Ross Desert in Antarctica is even considered driest area in the world.

Wind desert

Wind deserts are found on sub-Antarctic islands in the South Atlantic Ocean, south of latitude 50 degree south latitude. In this area consistently westerly storms that accompany all year round drizzle and fog, trees can not grow due to lack of wind protection. They meet at only mosses, ferns and lichens.

Other types of desert

Semi-desert

The semi-desert is a landscape zone that is slightly wetter than the real desert, but still drier than the thorn savanna. It is usually located at the edge ( the transition zone ) of such a " full desert " - see also Sahel.

Edaphic desert

In edaphic (soil- related ) deserts supplied precipitation in heavily drained soil to be removed very quickly. Water can not or only very poorly store in the ground, it lacks for plant growth. So are the huge gravel corridors in the Icelandic highlands, despite significant rainfall and snowmelt a desert landscape.

Ecology

The survival in desert areas, with their marked lack of water special environmental conditions, forcing plants and animals, but also the people at each very specific customizations. Showers are rare, but when it is raining, then usually very violent. After that, the desert blooms on: It grow colorful desert plants, but have a short life cycle due to lack of water. Nevertheless, ensure, inter alia, these short growing seasons often a surprisingly rich in wildlife.

Flora and vegetation

Deserts are characterized by poverty of vegetation or even Vegetationslosigkeit, only about a quarter of all desert surfaces are covered at all. The existing vegetation ( xerophytes, halophytes ) is carried to dryness or increased salt tolerance adapted shrubs, grasses and certain deep-rooted trees (eg Acacia in the Kalahari ) determined. They differ in water-saving, water-storing, underground enduring plants and in plants with short growing season. Thus, for example, in the fog zone of the Namib desert shrub Arthraerua leubnitziae ( a foxtail plant ) native as the most common representative of permanent vegetation, he can use the high humidity of the fog. Plants such as this succeed even during the extreme and long -lasting droughts ( the example of Arthraerua leubnitziae several thousand years) to maintain their water balance.

Fauna

In many deserts in the world numerous animal species are to be found despite the supposedly hostile conditions. Thus, the Gazelle and the steppe polecat goiter are endemic, for example, in the Gobi, among other large animals, sometimes you can also find snow leopards and wolves. Even more numerous than mammals are in the arid areas reptiles and especially the extremely adaptable arthropods (eg insects and scorpions ) encountered.

Just living in the hot sand deserts animals often have very obvious adaptations to the high surface temperatures of the sand: so have insects that daytime running on the sand, usually exceptionally long Stelzbeine because the temperature just a few centimeters decreases significantly above the sand. This and rapid locomotion, the animals are able to protect themselves from deadly overheating. The long legs of the camels could have evolved as protection against the radiation of heat.

Microbial life

Regardless of climate, temperature and latitude are in arid deserts an enormous wealth of different types of bacteria. Crucial for the growth of these microorganisms, the pH value ( acidity) of the soil: so have soils with a neutral pH, such as those found in arid deserts and forests, the bacteria optimum living conditions. In contrast, we find, surprisingly, in acidic soils, such as those of the South American rain forests, very few bacteria.

Cultural History

In cultural- historical point of playing the desert since ancient times an important role in European historiography and literature. On the one hand symbolized the desert since Herodotus the foreign and relief, that eluded the European access. On the other hand, offered the desert but also retreat. In particular, through the Bible ( Exodus from Egypt, the Israelites, temptations of Christ) and the later hagiographic literature ( hermits ) a picture of the desert was transported to Europe, which continues to act in the nucleus to the present. Through the domestication of the dromedary succeeded the people deeper into the great deserts or go through it. This allowed the desert to be human habitat.

Devastation

The emergence of new and the expansion of existing deserts is mostly caused by humans (desertification ). These include overgrazing, unadjusted agriculture and deforestation. Natural causes of desertification are drought, spread of desert sand dunes or fraying of edges. Devastation is sponsored by blowing out (wind), runoff (water), salinity and skeletonization.

The UN organization UNCCD fights against the further spread of deserts. The year 2006 was declared the International Year of Deserts and Desertification.

The largest deserts

All deserts of the earth, taken together cover about one-fifth of the total land surface of the earth, which are almost 30 million square kilometers. If the semi-deserts with added, the result is about one-third of the land area, ie slightly less than 50 million square kilometers. In total they cover almost 10% of the planet's surface.

Daily temperature fluctuation in deserts

Dry deserts may be subject to extreme temperature variations, depending on sea distance and season. During the day, the ground is scorched only superficially due to the poor thermal conductivity of the quartz-bearing and aerated desert soil. Moreover, this can compared to moist soils only little thermal energy store ( water can save about six times as much energy as sand). Due to the low cloud formation daytime heat radiation penetrates Although undamped to the ground and heats it very strong ( up to about 70 ° C ), but at night the heat radiates back unhindered into space from (clouds act as insulation layer, both from space to Earth and vice versa). This leads to a temperature difference of 50 K or more, especially in the "Winter" and far away from caring for temperature compensation sea.

This effect also allows in the driest deserts a modest life. Because of the strong cooling, a ground-level dew point is reached. Plants and other organisms can then live off the dew drops formed.

Due to the strong temperature fluctuations, the physical weathering in the desert is promoted greatly. The chemical weathering takes place, however, due to the lack of water is very slow ( cf. desert varnish ).