If one measures from the bedrock up to an erg, the depth of the Sahara can be said to be between 21 and 43 meters. However, the sand dunes have an average height of 150 meters from the bedrock, and in windswept conditions, the height of the sand dunes can reach up to 320 meters.
Beneath the sands of the Sahara Desert scientists have discovered evidence of a prehistoric megalake. Formed some 250,000 years ago when the Nile River pushed through a low channel near Wadi Tushka, it flooded the eastern Sahara, creating a lake that at its highest level covered more than 42,000 square miles.
The Ar Rub' al Khali, or Empty Quarter, covers much of the south-central portion of the Arabian Peninsula and is the largest continuous sand desert on Earth.
The Sahara is shielded by a layer of dust believed to be up to five kilometers thick. Acting like a sunscreen for the entire desert, the ultra-fine sand repels approximately 25 percent of the sun's rays.
Emi Koussi, an extinct volcano in Chad, is the highest point in the Sahara, reaching 11,204 feet (3,415 m) above sea level, and the Qattara Depression in northwestern Egypt is the Sahara's deepest point, at 436 feet (133 m) below sea level.
Some of the world's largest supplies of underground water exist beneath the Sahara Desert, supporting about 90 major oases there.
The Sahara conceals large quantities of water stored at depth and inherited from ancient times. A recent study has just shown that this groundwater is not entirely fossil, but resupplied every year.
Sea and desert sands seldom satisfy the requirements of traditional specifications for use as a construction material, especially in their untreated state. Desert sand grains are finer and smoother so their surface chemistry would not be able to offer sufficient number of multidirectional chemical linkages.
With deserts full of it, one can easily be fooled into thinking that sand is an almost infinite resource. However, desert sand has little use; the grains are too smooth and fine to bind together, so it is not suitable for the making of for instance concrete.
Compared with standard construction sand, desert sand grains are finer and smoother so their surface chemistry would not be able to offer sufficient number of multi-directional chemical linkages. If their grain size is too small, the slurry slip and the concrete would have poor strength.
For instance, Vietnam might run out of the sand as early as 2022. The rest of the world might also face the same issue by 2050 with more than 7 billion people expected to become city-dwellers by then. If sand seems so abundant with all those deserts around the globe, then why are we running out it?
And with 50 billion metric tons consumed annually—enough to build an 88-foot-tall, 88-foot-wide wall around the world—our sand depletion is on the rise, and a completely unregulated rise at that.
It is usually a combination of minerals in the iron group: Hematite, Fe3o3, with a specific gravity of 5.26, an iron mineral that is non-magnetic and Magnetite, Fe3o4, with a specific gravity of 5.20, is magnetic. These black sands will weigh a third (1/3) to a fourth (1/4) the weight of gold (Au).
Dust from the Sahara Desert that recently pushed into Europe brought an unexpected surprise with it -- residues of radioactive pollution that is linked to the atomic bomb tests carried out by France in the 1960s.
Met Office meteorologist Dan Stroud explained that the colours were caused by a phenomenon known as Rayleigh scattering from additional particles in the air. “The dust in the atmosphere causes the light to be more refracted, so you get the dominance of the red and orange tinges of the spectrum,” he said.
Over thousands of years, as rainfall lessened and temperatures rose, what little rain there was eroded the soil and dissolved it, leaving grains of silica sand. Wind slammed sand into rocks, wearing those rocks away, which created more sand.
Desert sand is largely useless to us. The overwhelming bulk of the sand we harvest goes to make concrete, and for that purpose, desert sand grains are the wrong shape. Eroded by wind rather than water, they are too smooth and rounded to lock together to form stable concrete.
Never use sea or desert sand to build your home. These sands have a glossy, shiny look but they are too fine and rounded. Using this kind of sand can weaken the structure.
That dust is a precious fertiliser that nourishes the rainforest with much-needed iron and phosphorus minerals. In fact, by a strange symmetry, the Saharan dust adds about the same amount of phosphorus to the Amazon each year that is flushed out to sea by flood waters.
“It's a layer of dust that is picked up off the Sahara Desert and transported across the ocean.” The dust cloud typically arrives in Texas between mid-June and August and lasts for 3-5 days.
Desert Control developed a liquid natural clay to convert desert sand into fertile soil in hours. A Norwegian company is working with the University of Arizona to study a patented process to convert sandy soil into productive farm soil.
In order for the dust to get from up in the sky down to the ground, you need something to wash it out of the sky - rain. As raindrops fall, they collect particles of dust on the way down.
By around 4200 BCE, however, the monsoon retreated south to approximately where it is today, leading to the gradual desertification of the Sahara. The Sahara is now as dry as it was about 13,000 years ago.
A new paper in the Bulletin of the American Museum of Natural History describes the Trans-Saharan Seaway that existed 50 to 100 million years ago in the region of the current Sahara Desert.
There was plenty of rain in the Sahara, so nobody needed the Nile. The Holocene Wet Phase lasted for more than 6500 years, until middle of 4th millennium BC (about 3500 BC, 5500 years ago), when the amount of rain falling dropped dramatically.