The Sahara Desert

The Sahara Desert is a great desert area in North Africa that extends from the Atlantic Ocean eastward past the Red Sea to Iraq. The entire desert, the largest in the world, is about 1600 km wide and about 5000 km long from east to west.
Geographic Facts
The total domain of the Sahara Desert is more than 9,000,000 sq. km, more than 3,500,000 square miles, of which 80,000 square miles consist of partially fertile oases.
The boundaries, however, are not clearly defined, and have been shifting for a thousand years.The limits of the Sahara Desert are the Atlantic Ocean on the west, the Atlas Mountains and the Mediterranean Sea in the North, the Red Sea and Egypt in the east, and the Sudan and the valley of the Niger River in the south.
Geographically distinct is the West Sahara, which is sometimes called the Sahara Proper; the central Ahaggar Mountains and the Tibesti Massif, are plateau regions.The Libyan Desert is in the east, and the West Sahara Desert is an area of rock-strewn plains and sand deserts of varying elevation. The land is presently almost entirely without rainfall or surface water but possesses a number of underground rivers that flow fast from the Atlas and other mountains. Occasionally the waters of these rivers find their way seeping to the surface; in these naturally irrigated oases, plants grow freely. The soil of this region of the Sahara is highly fertile and, where irrigation is possible, produces excellent crops.
The central plateau region of the Sahara Desert runs for about 1600 km, about 1000 miles in a Northwest to Southeast direction. The plateau itself varies in height, from about 600 to 750 m (about 1900 to 2500 ft). Peaks in the several mountain ranges that rise from the plateau are from about 1800, to more than 3400 m (about 6000 to more than 11,200 ft) high.
Notable peaks include Emi Koussi (3415 m/11,204 ft), in the Tibesti Massif, and Tahat (3003 m / 9852 ft), in the Ahaggar Range. Although rainfall is scant in the area, several of the central Saharan peaks are snow-capped during part of the year.
The Libyan Sahara Desert is considered the most arid part of the Sahara. Moisture is almost totally absent and few oases exist. The land is characterized by sandy wastes and large dunes of sand 122 m (400 ft) or more in height.
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. However, the irrigation afforded by the Nile transforms the desert into fertile agricultural land throughout much of Egypt.