The Sahara is Earth’s largest hot desert by far
Spanning about 9.2 million square kilometres across North Africa, the Sahara is the world’s largest hot desert and the third-largest desert overall after Antarctica and the Arctic. Arabic ṣaḥārā is simply a plural of “desert,” yet the sand sea excludes Maghreb mountains, Mediterranean coasts, and the Nile valley.
It runs from the Red Sea and the Mediterranean to the Atlantic coastal plains, giving way in the south to the semi-arid savanna of the Sahel around the Niger valley and the Sudan region. Much of Egypt, Libya, Algeria, Mali, Niger, Chad, Sudan, Mauritania and Western Sahara lies within it, plus southern Morocco and Tunisia, about 31 percent of Africa. Counting every place that averages less than 250 millimetres of rain a year would stretch it to some 11 million square kilometres. It is so vast and bright that, in principle, near-current technology could spot it from another star.
The landscape is far more varied than endless dunes. There are rocky plateaus called hamada, sand seas or ergs with dunes topping 180 metres, gravel plains, dry wadis, dry lakes and salt flats, along with oases and oddities such as Mauritania’s Richat Structure. Deeply eroded, often volcanic mountains rise from it, including the Aïr, Ahaggar, Saharan Atlas, Tibesti, Adrar des Iforas and Red Sea Hills; the highest point is Emi Koussi, a shield volcano in northern Chad.
The core is hyperarid, with subdivisions such as the Tanezrouft, the Ténéré and the Libyan, Eastern and Nubian deserts that may go years without rain. Sparse grass and shrubs grow on the northern and southern fringes and in the highlands, with trees gathering in wadis where moisture pools.
For several hundred thousand years the region has swung between desert and grassland roughly every 20,000 years, as the wobble of Earth’s axis shifts the North African monsoon. Green Sahara phases are therefore a recurring part of its history, driven by orbital change.
Source: Sahara
