Types of deserts

SOME DESERTS OF THE WORLD

(Source: Encarta)

http://encarta.msn.com/find/MediaMax.asp?pg=3&ti=022FD000&idx=461520504

is the world's largest desert, c.3,500,000 sq mi (9,065,000 sq km), extending c.3,000 mi (4,830 km) east to west and c.1,200 mi (1,930 km) north to south across N Africa

it is bordered on the south by the SAHEL. Rainfall ranges from less than 5 in. (12.7 cm) to 10 in. (25 cm), with dry periods occasionally lasting for years.

Climate

Nighttime temperatures often drop below freezing, and daytime temperatures have been recorded at over 135°F (57°C) in the shade.

In Egypt and Algeria, limited areas, such as the Qattara Depression, are below sea level. The climate is uniformly dry; most areas average less than 127 mm (less than 5 in) of rain per year, and some get none at all for years at a time. The temperature range is extreme, ranging between freezing to more than 54.4° C (130° F) in the western and central portions.
The surface of the desert ranges from sand dunes (erg), covering about 15%, to stone plateaus (hammada) and gravel surfaces (reg), covering about 70%, to several deeply dissected mountain massifs (Ahagger, Tibesti, and Aïr), infamous in the past for the shelter they provided to marauders preying on desert travelers.

Water

Vast underground aquifers, filled with water thought to date from the Pleistocene epoch, when the Sahara was wetter, underlie much of the region, and there are important deposits of iron ore, phosphates, oil, and natural gas.

The Libyan 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, but the irrigation afforded by the Nile transforms the desert into fertile agricultural land throughout much of Egypt.

Vegetation & Animal Life

Except in the oases the desert is almost devoid of vegetation, although some stunted, thorny shrubs grow in the western Sahara. Artificial oases have been created by drilling water wells more than 1000 m (more than 3280 ft) deep. The chief trees of the oases are the date palm and a form of acacia. Gazelle and antelope are found in many parts of the desert, as are jackal, fox, badger, and hyena. The Libyan Desert is virtually devoid of any form of animal or vegetable life. The northern Sahara has assumed economic importance with the discovery of extensive petroleum deposits in Algeria and Libya.

Politically, the Sahara lies largely in Morocco, Algeria, Tunisia, Libya, Egypt, Mauritania, Mali, Niger, Chad, and Sudan.