Major American Deserts - Research Paper Example

Lecturer Introduction The earth is made up of various terrains and climate. One good example is the desert. Well known deserts of the world include the Gobi desert in Asia, the Sahara and Kalahari desert in Africa, Mojave in the U.S. and Sonoran desert in California and Arizona. Deserts cuts across the earth along the latitudes 200-350 (United Nations Environmental Programme 5).We are going to study the deserts by looking at their unique factors. According to the National Geographic, deserts are known to cover one fifth of the earth’s land and are to be found on all the continents. This is a statling statisctics given that many of us may never have come across deserts in our life time. Yet one fifth of the earth is such a huge chunk of earth. This therefore makes deserts even more intersting to study. A desert can be defined as an area of land which is very dry because it receives very little amounts of rainfall and other forms of precipitation such as mist, snow and fog. The National Geographic estimates that any place receiving less than 10 inches of rain (approximately 25 centimeters) annually is considered to be a desert. These are very low amounts of rainfall and there is no guessing that life can be harsh in such a place. Yet as we will see later, deserts are rich in plant and animal life. Another characteristic of deserts is that they experience very high levels of evaporation from the earth’s surface and transpiration from plants. This is because of the very high levels of temperatures found in these places, mostly due to direct sunlight hitting the ground. The reason for this is that due to low levels of precipitation, there is very little clouds to reflect back the sun rays, therefore much of the sun rays actually reach the earth’s surface. The temperature levels are so high that the National Geographic estimates that in North Africa’s Sahara desert, temperatures reaches 50 degrees Celsius during the day. It is important to note that not all deserts of the world experiences very high temperatures. Indeed, we have cold deserts of the world. In these deserts, very low temperatures hinder most of the life forms and therefore the ground is largely bare and barren, just like in other deserts. Examples of cold deserts of the world are the Gobi desert in Asia and the desert found in the continent of Antarctica. From the above description, it is possible to understand why deserts are vast areas with low vegetation cover and bare soil. Principally, conditions are so harsh that normal life is almost impossible. To thrive in a desert, human beings, plants and animals have to adapt to the harsh conditions in the desert. For instance, plants have features that enables them to take up and store most of the water whenever it rains and minimises water loses during the dry period. Some of the adaptation to minimise water loss includes shedding of leavies during the dry season, shrinking of the stems and photosynthesising using stems instead of the leaves (Gallant 25). Animals on the other hand also have a number of adaptations to these climates. Some are nocturnal, only coming out at night when temperatures are low, while others would never spend time above the ground. All these enable such animals to minimise water loss and conserve most of their energy to keep them alive. Deserts of North America Map 1: Map showing the deserts of North America i.e GreatBasin, Mojave, Sonoran and Chihuahuan. (Styles 57) North American landscape is characterised by some of the world’s deserts. In this secion, we will try and get a glimpse of these landscapes. Chihuahuan Desert is found in the states of New Mexico, Arizona and Texas. It extends into North and Central Mexico. Its size is etimated to be 455,000km2 and is the largest desrt in North America with the Big Bend National Park located in it (Styles 37). Some of the plants to be found in this desert include Cacti, Chihuahuan flax and Lechuguilla. Animals to be found in tis desert include the Kangaroo rat, Javelina and Roadrunner. Great Basin desert is to be found in the states of Idaho, Nevada, Oregon and Utah in the United States. A major feature of this desert is that the Great Salt Lake is to be found in this desert. It has several mountain ranges amd large expanses of salt flats but also covered by sand, gravel and clay. Some of the plants to be found in this desert include greasewood and sagebrush while animals include pocket sheep, pronghorn antelope and side-blotched lizard (Styles 39). Mojave Desert is found in southwestern United States and covers the states of Arizona, California and Nevada. It is estimated to be approximately 65,000km2 with a major feature being the location of Death Valley in the desert. Styles (41) observes that some of the plants to be found in this desert include the Creosote bush, desert sand verbena and mesquite while animals in this desert include bighorn sheep, jackrabbit, chuckwalla and zebratailed lizard. Sonoran Desert is located in the states of Arizona and California in the United States and extends into Baja Peninsula and Sonora on Mexico. The size of this desert is estimated to be 312,000km2 and is known to have one of the most complex animal-plant community in any desert (Styles 43). Another key feature of this desert is that it gets more rainfall than any other North American desert. Some of Geological Features of a Desert Calcrete Soils in the desert are predominantly mineral soils. These soils have low orgnic content due to the fact that most of the syurface is bare and therefore no enough organisci materials in the desert to significantly contribute to the formation of the soil. Therefore, most of the soil are rich in minerals due to the intense heat. One key feature of this is the Calcrete. This is the hard crust made up of calcium carbonate. Calcrete is formed as a result of concentartion of lime due to high levels of evaporation from the soil (Halvorson, Schwalbe and Riper 29). Water is lost through the process and leaving behind the salts which form into calcrete. Calcium that dissolves to form calcrete comes from various sources syuch as dust carried and depositied by wind and carbon dioxide from respiartion of plants which dissolves in ground water. Calcrete is ususally impermiable to water and therefore makes the soil to be barren and very inhospitable to vegetation. Impermiability is even made more pronoused due to the fact that it is resistant to weathering (Halvorson, Schwalbe and Riper 31). It is mostly white though it is not uncommon to find it varying in colour from pinkish, yellowinsh to even brownish. Picture showing roots frozen in a Calcrete layer (Styles 83) Wind and Water Most of the desert features are formed through the actions of either water or wind or both. The two elements are the main agents of transportation of erosion, transposrtiation of sediments and deposit in a desert. Geologic features formed by these agents are as a result of either erosion of the land surface or depositing of materials in most cases silt or sand. Runoff from rain water transports sediments downslope. When this water, rich in sediments loses energy, ends up forming an braided stream which deposits the sediments to form an alluvial fan. ‘Alluvial’ because it is caused by water and ‘fan’ because of the shape of the feature formed (Lancater 62). Picture showing an Alluvial Fan (USGS) When two or more alluvial fans adjacent to each other merge, them we end up with a feuture called a ‘bajada’. Alluvial fans and bajadas are common in mountainous areas because in this areas, there are a lot of run offs whenecver it rains due to the bare earth. Sometimes, temporary lakes are formed in the desrt due to rain water being trapped in a shallo valleys. During the dry season, these shallow lakes dry up, leaving behind a flat, heat-creacked bed of clay. This feauture is called a playa. According to Gallant (52) we have over one hundred playas in the North American deserts. Many of these are as a consequent of large lakes which existed in the Ice Age but whch are today extinct. A good example of such lakes is the Lake Bouneville. Its remnants today includes the Utah’s Great Salt lake. Picture of the Death Valley consisting of alluvial fans and playa deposits (USGS) An arroyo is also a desert feature formed by water. It is caused by sudden heavy downpour which leads to deep cuts on the desert floor. The fast moving water from the downpoor helps create deeper gullies as sediments are easily carried away by the force of moving water. The end result is a gully with steep sides, with an almost even bed. Another way desert features are formed is through the action of wind. To begin with, wind is one of the major causes of transposrtiaon and deposition of particles. Wind shapes the desert features in two key ways. One by abrading the surface through the action of sediments being carried by wind and again through deposition of the sediments, we end up with a number of features. The action of wind in the desert is called aeolian. This distinguishes the action of wind from those of water. Sand dunes are basicallty loose sand have being accumulated together by the wind. Dunes are basically formed when winds are strong and blow in the same direction, carrying with it sands and depositing it when it loses energy. Finer materials such as silts and clay are carried further while heavier materials are left behind. The result is a gentle slopping windward side wile the leeward side forms a steep face. The cross section of a sand dune.(Source USGS) Dunes can be largely be classified into five categories namesly crescentic, star, dome, linear and parabolic. Crescentic dunes are the most common and are formed by winds blowing in the same direction, forming a crescent shaped kind of deposits. We may have sevaral of these features near each other. Crescentic Dunes (USGS) Star dunes are fomed when tends to form in areas with multidimenstional winds. Therefore the dunes ends up with several arms, raditing from a the centre which is higher than surrounding land surfaces as trthey are formed moving upwards. Star Dunes (USGS) Wind erosion on the other hand also causes a number of features on the desert surface. For instance, the rock pedestals are formed when a hard rock is left standing after many of its surrounding are torn off by the raging winds. This happens over an extended period of time and the end result is a lonely piece of rock left juting from the earths surface. Rock Pedestal (USGS) Another feature of wind deposition is the erg. An arg is basically a sea made up of sand. Therefore, we basically have kilometres of land mass covered by of waves of sand. It is thought that the Sand Hills of Nebraska are the remnants of ancient sand sea (Gray 39). A yardang is basically a series of furrows and ridges on the desrt surfaces. It is caused in areas where there exists a rock structure of alteranating hard and soft rocks. Wind erosion acts of the soft rocks, depleting it away, leaving troughs between harder materials which are left standing. The Sphinx of Giza in Egypt is thought to have been formed from a Yardang (Gray 53). A desert vanish or rock vanish is the shiny rocks found in some deserts. These rocks are as a resert of their surfaces having been eroded. As a result, R.I.C Publications (22) observes that minerals such as managenese, iron oxide and other minerals in these rocks are exposed to the environment. It is these minerals that are responsible for the shine. Conclusion Deserts have unique features formed as a rsult of either erosion or depositing of materials by either water or wind. These features are an important attraction to most deserts and some do attact thoudsands of tourists, earning local economies a lot of income. Therefore, there is need to document and preeserve such sites. At the same time, it is important to conserve the environment to avoid spread of deserts. Human activities such as cutting down of trees for firewood and buiding, use of fertilisers that deteriorates the soils and military activities that destroys the soil surface have to be controlled.This is because the spread of deserts across the world would lead human suffering due to lack of enough food and spread of new diseases. It is thus worth noting that the desert is not all doom and gloom. Works Cited Gallant, Roy. Sand on the Move: The Story of Dunes. New York: Franklin Watts, 1997. Gray, Leon. Deserts. Washington: The Rosen Publishing Group, 2011. Halvorson, William Lee, Cecil R. Schwalbe and Charles Van Riper. Southernwestern Desert Resources. Arizona : University of Arizona, 2010. Lancater, Nicholas. The Geomophology of Desert Dunes. New York: Routeledge, 1995. National Geographic. Deserts: Arid but Full of Life. 2013. 23 November 2014 Web R.I.C Publications. Wet and Dry Envrironments: Wetlands and Dry Deserts. New York: R.I.C Publications, 2007. Styles, Todd E. Missouri Botannical Garden. Gardening: Arcadia Publishing, 2012. United Nations Environmental Programme. Global Deserts Outlook. Report. Nairobi: UNEP, 2012. USGS. The Desert. Washington, 12 November 2010. Read More