The Sahara is much more than just sand — in fact, the majority of the Sahara is made up of barren, rocky plateaus, as well as salt flats, sand dunes, mountains and dry valleys. The rivers and streams found in the Sahara are all seasonal, apart from the River Nile. There are over 20 lakes in the Sahara, most of which are saltwater lakes. Lake Chad is the only freshwater lake in the desert. In east-central Algeria lies the Isaouane-n-Tifernine Sand Sea, with sand dunes as high as m — some of the tallest in the world!
The largest dunes in Morocco are the Erg Chigaga — with some dunes reaching a massive m. The Chigaga dunes are hard to reach, with access only permitted by 4x4, camel or foot. These dunes are a relatively untouched part of the Sahara and the area we explore on our Sahara Desert Trek. Yes - dramatically! The Sahara has changed immensely! It used to be lush and green, home to a variety of plants and animals. Instead, most scientists argue that the Sahara took shape just 2 to 3 million years ago.
Terrestrial and marine evidence suggest that North Africa underwent a period of drying at that time, when the Northern Hemisphere started its most recent cycle of glaciation. The models shows that precipitation in North Africa declined by more than half about 7 million years ago, causing the region to dry out. About million years ago, a huge body of water called the Tethys Sea separated the supercontinents of Laurasia to the north and Gondwana to the south.
As those supercontinents broke apart and shuffled around, the African plate collided with the Eurasian plate, birthing the Alps and the Himalayas but closing off the bulk of the Tethys Sea. Its highest point is Chad's Mount Koussi an extinct volcanic crater that rises 11, feet above sea level at the peak , and its lowest, Egypt's Qattera Depression an oasis depression that lies feet below sea level at the deepest point.
The Sahara's fabled dune fields, which cover only about 15 percent of the entire desert's surface, lie primarily in the north central region, in the countries of Algeria and Libya. Most sand dunes -- mounds and ridges of sand sculpted by wind and gravity -- have a windward or "backslope" surface and a leeward or "slipface" surface.
Prevailing winds drive sand up the backslope until it reaches a crest and then collapses under the pull of gravity, cascading down the slipface. The wind may leave rippled surfaces in its wake. Saharan dunes as seen from the eastern edge of Morocco. Sahara's most famous features are the ergs, or sand dune seas, most of it is really hamada, or rocky plateau. The Sahara has only two permanent rivers and a handful of lakes, but it has substantial underground reservoirs, or aquifers.
Its permanent rivers are the Nile and the Niger. The Nile rises in central Africa, south of the Sahara, and flows northward through Sudan and Egypt and empties into the Mediterranean. The Niger rises in western Africa, southwest of the Sahara, and flows northeastward into Mali and the desert then turns southeastward, through Nigeria, and empties into the Gulf of Guinea.
The Sahara has some 20 or more lakes, but only one with potable water--the expansive but shallow Lake Chad, a continually expanding and shrinking body of water that lies in the country of Chad, at the southernmost edge of the Sahara. Other lakes hold a briny stew of undrinkable water.
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