The largest tropical desert on Earth is the Sahara. It covers at least a part of ten countries in northern Africa—Morocco, Algeria, Tunisia, Libya, Egypt, Mauritania, Mali, Niger, Chad, and Sudan—plus the territory of Western Sahara. Sahara is an Arabic word meaning “desert.” The Sahara faces the Atlantic Ocean on the west. To the north are the Atlas Mountains and the Mediterranean Sea. The Red Sea lies to the east. To the south is the Sahel, a zone of transition between the desert and tropical Africa. Physical features - The Ahaggar Plateau rises from the barren landscape of the Sahara in southern Algeria.
Covering an area of about 3,320,000 square miles (8,600,000 square kilometers), the Sahara is almost as large as the entire United States. People often think of the Sahara as a vast sea of sand, but sand actually covers only about one fourth of its area. Sahara sand can be a spectacular sight where the wind piles it into hills called dunes. Some of the dunes are more than 1,000 feet (300 meters) high. They usually form in huge basins of shifting sand, called ergs. Much of the Sahara consists of gravel-covered plains and raised, rock-strewn plateaus. There are also some mountains. The highest point in the desert, at 11,204 feet (3,415 meters), is Mount Koussi, in the Tibesti Mountains of Chad. The Nile River runs along the eastern end of the Sahara. The Niger, another great river, flows through the southwestern Sahara. Several rivers empty into Lake Chad, in the southern Sahara. However, most of the waterways in the Sahara are wadis. Wadis are streams that dry up completely except for the few times in the year when it rains. In regions that see little rainfall, there are places where underground water comes to the surface in springs or is brought to the surface from wells. Such a place is called an oasis. With their reliable supply of water, oases support many of the Sahara's plants, animals, and people. ClimateThe Sahara is known for its hot weather. The highest temperature ever recorded anywhere on Earth was 136° F (58° C) at Al-?Aziziyah, Libya, in 1922. In the south, summer temperatures of 122° F (50° C) are not unusual. Winters throughout the Sahara are cool, however, averaging 55° F (13° C). In all seasons, temperatures vary widely in the course of a day. The air becomes much cooler after the sun sets. The Sahara is dry as well as hot. Precipitation averages about 5 inches (12.7 centimeters) a year in the south and only 3 inches (7.6 centimeters) a year in the north. Much of the rain falls in thunderstorms, which can cause flash floods. Snow sometimes falls on the central mountains and the northern plateaus. Winds play a major role in the climate of the Sahara. A hot wind carries dust through the northern Sahara, especially in spring. In Egypt this wind is known as the khamsin, in Libya as the ghibli, and in Tunisia as the chili. During winter a dry wind called the harmattan blows sand and dust across the southern Sahara. The sirocco is a dry wind that begins over the northern Sahara and blows northward across the Mediterranean Sea. Along the way it picks up moisture, which it carries into Southern Europe as rain and fog. The Sahara first became a desert about 5 million years ago. Since then the climate has shifted between dry and relatively moist again and again. In the latest Ice Age, which ended about 10,000 years ago, and for thousands of years afterward, the region was a pleasant grassland. The modern-day dry climate of the Sahara has been fairly constant for about 2,000 years. Plants and animalsPlants in the Sahara are found mainly near water sources or in the highlands. Shrubs, coarse grasses, and palm trees make up much of the region's plant life. The trees of the highlands include olive, cypress, and acacia. The plants of the Sahara have unusual features that help them survive despite the limited availability of water. These adaptations include long roots that can reach water deep in the ground. Some Saharan plants have developed a speeded-up life cycle to take advantage of the short season of moisture. In a period of only about three weeks, such plants can grow from a seed into a plant that sows its own seeds. The animal life of the Sahara is also limited to types that can withstand the harsh climate. Scorpions and snakes, including the cobra, are common. The desert's mammals include the oryx, gazelle, wild ass, baboon, hyena, jackal, gerbil, and desert hedgehog. Frogs, toads, and crocodiles are found in lakes and pools. More than 300 kinds of birds live in the Sahara, some for only part of the year. The ostrich, eagle owl, barn owl, and raven are among the larger types. PeopleAlthough the Sahara is a huge region, it has a population of only a few million people. Thousands of years ago, when the climate was milder, the Sahara probably had more people than it has now. The people of the Sahara live either nomadic or settled lifestyles. The nomads breed sheep, goats, and camels, roaming from place to place in search of grass for the animals to eat. Today the majority of the people of the Sahara are settled, mostly near oases. There they grow food using the artificial watering method called irrigation. The ethnic groups of the Sahara include the Regeibat of the northwest, the Chaamba of northern Algeria, and the Teda of the Tibesti Mountains. The Tuareg people live throughout a wide area. Nearly all the people of the Sahara are Muslim, but groups have maintained their own customs. Among the Tuareg, for example, men rather than women traditionally wear veils. This is the reverse of the practice in some other Muslim societies. EconomyMetals such as iron ore, copper, and manganese are present in the Sahara. Oil and natural gas have been found in Egypt, Libya, Algeria, and elsewhere in the region. Although it can be difficult to mine and transport minerals in remote areas, they are still an important source of income in the Sahara. The traditional products of the desert are animal skins, wool, salt, and fruit grown in the oases—especially dates. Grains such as millet, barley, and wheat are also grown. Tourism is on the rise, but a strong spirit of adventure is still required for travelers to the region. Study and explorationThe Sahara is difficult to cross. For thousands of years it has been a barrier between Europe to the north and tropical Africa to the south. However, the Sahara has interested Europeans since at least the 5th century BC, when the ancient Greek historian Herodotus described a desert crossing. Many Arab writers of the Middle Ages also described the Sahara in their writings. In-depth European exploration of the Sahara did not begin until the 19th century. In 1826 a Scottish explorer reached the fabled city of Timbuktu, in what is now Mali. For centuries many people outside of the Sahara had considered Timbuktu to be the most remote place on Earth. The European colonial powers who took control of the region later in the 19th century made further explorations. However, large parts of the desert remain little known and difficult to reach. Environmental issuesOver the centuries, native animals such as the lion and ostrich have been wiped out from the Sahara through hunting. The type of antelope called the addax has been killed off in the northern Sahara, and it is threatened in the southern part of the desert as well. But the most serious environmental issue connected with the Sahara is the way the desert has expanded. As people and grazing animals have removed plant cover from the ground, the soil has been exposed to the strong desert winds. Good soil has blown away, making it more and more difficult for plants to grow. The result is that the Sahara is spreading southward into the Sahel. |