A desert is a barren area of landscape where little precipitation occurs and, consequently, living conditions are hostile for plant and animal life.
The lack of vegetation exposes the unprotected surface of the ground to the processes of denudation. About one-third of the land surface of the world is arid or semi-arid. This includes much of the polar regionswhere little precipitation occurs, and which are sometimes called polar deserts or "cold deserts".
Deserts can be classified by the amount of precipitation that falls, by the temperature that prevails, by the causes of desertification or by their geographical location.
Deserts are formed by weathering processes as large variations in temperature between day and night put strains on desert landscape outline 98 rocks, which consequently break in pieces. Although rain seldom occurs in deserts, there are occasional downpours that can result in flash floods. Rain falling on hot rocks can cause them to shatter, and the resulting fragments and rubble strewn over the desert floor are further eroded by the wind. This picks up particles of sand and dust and wafts them aloft in sand or dust storms.
Wind-blown sand grains striking any solid object in their path can abrade the surface. Desert landscape outline 98 are smoothed down, and the wind sorts sand into uniform deposits, desert landscape outline 98.
The grains end up as level sheets of sand or are piled high in billowing sand dunes. Other deserts are flat, stony plains where all the fine material has been blown away and the surface consists of a mosaic of smooth stones, desert landscape outline 98.
These areas are known as desert pavementsand little further erosion takes place. Other desert features include rock outcropsexposed bedrock and clays once deposited by flowing water. Temporary lakes may form and salt pans may be left when waters evaporate, desert landscape outline 98. There may be underground sources of water, in the form of springs and seepages from aquifers. Where these are found, oases can occur. Plants and animals living in the desert need special adaptations to survive in the harsh environment.
Desert landscape outline 98 tend to be tough and wiry with small or no leaves, water-resistant cuticlesand often spines to deter herbivory. Some annual plants germinatebloom and die in the course of a few weeks after rainfall, while other long-lived plants survive for years and have deep root systems able to tap underground moisture.
Animals need to keep cool and find enough food and water to survive. Many are nocturnaland stay in the shade or underground during the heat of the day. They tend to be efficient at conserving water, extracting most of their needs from their food and concentrating their urine, desert landscape outline 98.
Some animals remain in a state of dormancy for long periods, ready to become active again during the rare rainfall. They then reproduce rapidly while conditions are favorable before returning to dormancy. People have struggled to live in deserts and the surrounding semi-arid lands for millennia. Nomads have moved their flocks and herds to wherever grazing is available, and oases have provided opportunities for a more settled way of life, desert landscape outline 98.
The cultivation of semi-arid regions encourages erosion of soil and is one of the causes of increased desertification. Desert farming is possible with the aid of irrigationand the Imperial Valley in California provides an example of how previously barren land can be made productive by the import of water from an outside source.
Many trade routes have been forged across deserts, especially across the Sahara Desertand traditionally were used by caravans of camels carrying salt, gold, ivory and other goods.
Large numbers of slaves were also taken northwards across the Sahara. Some mineral extraction also Landscape Features Of The Sahara Desert takes place in deserts, and the uninterrupted sunlight gives potential for the capture of large quantities of solar energy. In English before the 20th century, desert was often used in the sense of "unpopulated area", without specific reference to aridity; [1] but today the word is most often used in its climate-science sense an area of low precipitation. A desert is a region of land that is very dry because it receives low amounts of precipitation usually in the form of rain, but it may be snow, mist or fogoften has little coverage by plants, desert landscape outline 98, and in which streams dry up unless they are supplied by water from outside the area.
Deserts have been defined and classified in a number of ways, generally combining total precipitation, number of days on which this falls, temperature, and humidity, and sometimes additional factors. Potential evapotranspiration supplements the measurement of precipitation in providing a scientific measurement-based definition of a desert.
Evapotranspiration is the combination of water loss through atmospheric evaporation and 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, desert landscape outline 98, Arizona receives about mm 12 in of rain per year, however about 2, mm 98 in of water could evaporate over the course of a year.
Rates of evapotranspiration in cold regions such as Alaska are much lower because of the lack of heat to aid in the evaporation process. Deserts are sometimes classified as "hot" or "cold", "semiarid" or "coastal". Winter temperatures vary considerably between different deserts and are often related to the location of the desert on the continental landmass and the latitude.
Cold deserts, sometimes known as temperate deserts, occur at higher latitudes than hot deserts, and the aridity is caused by the dryness of the air. Some cold deserts are far from the ocean and others are separated by mountain ranges from the sea, and in both cases, there is insufficient moisture in the air to cause much precipitation. The largest of these deserts are desert landscape outline 98 in Central Asia. Others occur on the eastern side of the Rocky Mountainsthe eastern side of the southern Andes and in southern Australia.
The air is very cold and carries little moisture so little precipitation occurs and what does fall, usually snow, is carried along in the often strong wind and may form blizzards, drifts and dunes similar to desert landscape outline 98 caused by dust and sand in other desert regions.
In Antarctica desert landscape outline 98, for example, desert landscape outline 98, the annual precipitation is about 50 mm 2 in on the central plateau and some ten times that amount on some major peninsulas, desert landscape outline 98.
Based on precipitation alone, hyperarid deserts receive less than 25 mm 1 in of rainfall a year; they have no annual seasonal cycle of precipitation and experience twelve-month periods with no rainfall at all. However, such factors as the temperature, humidity, rate of evaporation and evapotranspiration, desert landscape outline 98, and the moisture storage capacity of the ground have a marked effect on the degree of aridity and the plant and animal life that can be sustained.
Rain falling in the cold season may be more effective at promoting plant growth, and defining the boundaries of deserts and the semiarid regions that surround them on the grounds of precipitation alone is problematic. A semi-arid desert or a steppe is a version of the arid desert with much more rainfall, vegetation and higher humidity.
These regions feature a semi-arid climate and are less extreme than regular deserts. They share some characteristics of a true desert and are usually located at the edge of deserts and continental dry areas. They usually receive precipitation from mm 10 in to mm 20 in but this can vary due to evapotranspiration and soil nutrition. Coastal deserts are mostly found on the western edges of continental land masses in regions where cold currents approach the land or cold water upwellings rise from the ocean depths.
The cool winds crossing this water pick up little moisture and the coastal regions have low temperatures and very low rainfall, the main precipitation being in the form of fog and dew. Deserts of this type are often long and narrow and bounded to the east by mountain ranges. Other coastal deserts influenced by cold desert landscape outline 98 are found in Western Australiathe Arabian Peninsula and Horn of Africaand the western desert landscape outline 98 of the Sahara.
InPeveril 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 desert landscape outline 98 have at least twelve consecutive months without precipitation, desert landscape outline 98, arid lands have less than mm 10 in of annual precipitation, desert landscape outline 98, and semiarid lands have a mean annual precipitation of between and mm 10�20 in.
Both extremely arid and arid lands are considered to be deserts while semiarid lands are generally referred to as steppes when they are grasslands. Deserts are also classified, according to their geographical location and dominant weather pattern, as trade wind, mid-latitude, rain shadow, coastal, monsoon, or polar deserts. These belts are associated with the subtropical anticyclone and the large-scale descent of dry air moving from high-altitudes toward the poles. The Sahara Desert is of this type.
They are mostly in areas remote from the sea where most of the moisture has already precipitated from the prevailing winds. They include the Tengger and Sonoran Deserts. They occur in regions where large temperature differences occur between sea and land.
Moist warm air rises over the land, deposits its water content and circulates back to sea. Further inland, areas receive very little precipitation.
In some parts of the world, deserts are created by a rain shadow effect. Orographic lift occurs as air masses rise to pass over high ground. In the process they cool and lose much of their moisture by precipitation on the windward slope of the mountain range, desert landscape outline 98.
When they descend on the leeward side, they warm and their capacity to hold moisture increases so an area with relatively little precipitation occurs. Montane deserts are arid places with a very high altitude ; the most prominent example is found north of the Himalayas, in the Kunlun Mountains and the Tibetan Plateau. Many locations within this category have elevations exceeding 3, m 9, ft and the thermal desert landscape outline 98 can be hemiboreal. These places owe their profound aridity the average annual precipitation is often less than 40 mm or 1.
Montane deserts are normally cold, or may be scorchingly hot by day and very cold by night as is true of the northeastern slopes of Mount Kilimanjaro.
Polar deserts such as McMurdo Dry Valleys remain ice-free because of the dry katabatic winds that flow downhill from the surrounding mountains. In the Thornthwaite climate classification system, deserts would be classified as arid megathermal climates. Deserts usually have a large diurnal and seasonal temperature range, with high daytime temperatures falling sharply at night.
Such large temperature variations have a destructive effect on the exposed rocky surfaces. The repeated fluctuations put a strain on exposed rock and the flanks of mountains crack and shatter.
Fragmented strata slide down into the valleys where they continue to break into pieces due to the relentless sun by day and chill by night. Successive strata are exposed to further weathering. The relief of the internal pressure that has built up in rocks that have been underground for aeons can cause them to shatter. This is believed to be caused by the stresses put on the desert landscape outline 98 by repeated thermal expansions and contractions which induces fracturing parallel to the original surface, desert landscape outline 98.
The necessary moisture may be present in the form of dew or mist. Ground water may be drawn to the surface by evaporation and the formation of salt crystals may dislodge rock particles as sand or disintegrate rocks by exfoliation. Shallow caves are sometimes formed at the base of cliffs by this means.
As the desert mountains decay, large areas of shattered rock and rubble occur. The process continues and the end products are either dust or sand. Dust is formed from solidified clay or volcanic deposits whereas sand results from the fragmentation of harder graniteslimestone and sandstone. As the mountains are eroded, more and more sand is created, desert landscape outline 98. At high wind speeds, sand grains are picked up off the surface and blown along, a process known as saltation.
The whirling airborne grains act as a sand blasting mechanism which grinds away solid objects in its path as the kinetic energy of the wind is transferred to the ground. Sand and dust storms are natural events that occur in arid regions where the land is not protected by a covering of vegetation. Dust storms usually start in desert margins rather than the deserts themselves where the finer materials have already been blown away, desert landscape outline 98.
If we never wish to wait for for your grassed area desert landscape outline 98 rise upon the personal, the glow or H2O underline can beget the executive component about that we can character a rest of your landscaping as well as square decor. The Starting Back yard organisation spin a formerly new dilemma in to the family-friendly hangout just where mother as well as father can flog behind in a hammock even yet a small ones fool around hopskotch or pull upon a chalkboard circuitously ?
Substantially a single of a most some-more mostly lost options in landscaping concepts for little front yards is belligerent cover, desert landscape outline 98.
|
Landscape Maintenance Work Questions Garden Privacy Screening Ideas Uk Key |
