Sahara Desert
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Sahara Desert
The Sahara Desert is the worlds largest desert area. The word Sahara comes from the Arabic word sahra, meaning desert. It extends from the Africas Atlantic Ocean side to the Red Sea and consists of the countries of Morocco, Algeria, Tunisia, Libya, Egypt, Mauritania, Mali, Niger, Chad, and Sudan. It is about 5,200 miles long. Overall, the Sahara Desert covers 3,500,000 square miles. The geography of the desert is varied. In the west, the Sahara is rocky with varied elevation. It does contain underground rivers, which sometime penetrate the surface, resulting in oases. The central region of the Sahara has more elevation than the other areas, with peaks such as Emi Koussi and Tahat. Even though the area lacks rainfall, these peaks are snowcapped during the winter. The Eastern part of the Sahara, the Libyan Desert, is dry with very few oases.
The Saharas landscape features include shallow basins, large oasis depressions, gravel-covered plains, plateaus, and mountains, sand sheets, dunes and sand seas. Sand sheets and dunes cover over 25 percent of the Saharas surface. The most common types of dunes include tied dunes, blowout dunes, and transverse dunes. Within the Sahara are several pyramidal dunes that reach over 500 feet in height while others reach over 1,000 feet. Researchers have for many years tried to figure out how these dunes were formed, but the case remains unsolved.
The boundaries, however, are not clearly defined and have been shifting for millennia. The Sahara was once a fertile area; millet was cultivated there over 8000 years ago. About 10,000 years ago, the Sahara was used as land for grazing in which elephants, giraffes and other animals thrived. It is estimated that in 4,000 B.C., the climate began to get drier. The fertile landscape dried up and the desert widened, creating the form that appears today. As conditions gradually became drier, however, and desertification set in, farmers abandoned their land and the animals migrated to other areas.
The Saharas climate is very hot and dry. Although it is very hot during the day, it does become cold at night. On average, it only has 8 inches of rainfall per year. The Saharas climate consists of basically two sub-climates, a dry subtropical climate in the north and a dry tropical climate in the south. The dry tropical climate is generally characterized by mild, dry winters, a hot dry season just before the rainy season, and an annual temperature cycle. The dry subtropical climate, however, is characterized by annually high temperature ranges, cold winters, hot summers and two rainy seasons. There is a narrow strip in the western portion of the Sahara, along the coast, which generally has cool temperatures compared to the rest of the Sahara because of the influence of the cold ocean currents.
The land is almost entirely without rainfall or surface water but possesses a number of underground rivers that flow from the Atlas and other mountains. Occasionally the waters of these rivers find their way to the surface; in these naturally irrigated oases, plants grow freely. The soil of this region of the Sahara is fertile and, where irrigation is possible, produces excellent crops.
The Libyan Desert is considered the most arid part of the Sahara. Moisture is almost totally absent and few oases exist. The Libyan Desert is virtually devoid of any form of animal or vegetable life. Sandy wastes and large dunes of sand that range to 400 feet or more in height characterize the land. The valley of the Nile River and the mountainous area of the Nubian Desert to the east of the Nile are, geographically, part of the Sahara, but the irrigation afforded by the Nile transforms the desert into fertile agricultural land throughout much of Egypt.
Plant and animal life is not as abundant in the Sahara as it is in other deserts. The grasses, shrubs, and trees that grow in parts of the Sahara have adapted in order to live in the dry conditions there. Plants of the Sahara obtain water in various ways. Some have long roots that reach deep into the soil and absorb