Sahara Desert

The boundaries of the Sahara are the Atlantic Ocean on the west, the Atlas Mountains and the Mediterranean Sea on the north, the Red Sea and Egypt on the east, and the Sudan and the vale of the Niger River on the south. The Sahara is separated into western Sahara, the central Ahaggar Mountains, the Tibesti Mountains, the Aïr Mountains, Tenere desert and the Libyan desert (the most arid region). The highest crest in the Sahara is Emi Koussi (3415 m) in the Tibesti Mountains in northern Chad.

The Sahara divides the continent of Africa into North and Sub-Saharan Africa. The southern border of the Sahara is patent by a band of semiarid savanna called the Sahel; south of the Sahel lies the lusher Sudan and the Congo River Basin. Most of the Sahara consists of gravel hamada; ergs form only a minor part.

The Sahara has one of the harshest climates in the world. The existing north-easterly wind often causes the smooth to form sand storms and dust devils. Precipitation, while rare, is not unknown. Half of the Sahara receives less than 2 cm of rain a year, with the rest receiving up to 10 cm a year. The rainfall happens very infrequently, but when it does it is usually heavy when it occurs after long dry periods, which can last for years.