Secrets of the SAHARA

It's the biggest desert in the world, a vast wilderness that covers one-third of the continent of Africa. A sailor shipwrecked on its coast in the 1800s described it as "a barren plain, extending as far as the eye could reach each way, without a tree, shrub, or spear of grass."

But there is more to this mysterious desert than miles and piles of sand. Singing sand dunes? Blue men? Blind fish? The Sahara is full of secrets.

Is the Sahara Sandy?

That sounds like a trick question. Of course there's sand in the Sahara, isn't there?

Yes, plenty. But most of the Sahara is covered with gravel and rocks. Less than a quarter of the Sahara is sand desert. Rocky desert areas called regs and lifeless plateaus called hammadas are more common.

But great seas of sand, or ergs, are there, too. One is even as big as the country of France. The ergs are where you will find the rolling miles of evershifting dunes that you see in the movies. There, a camel might sink in drifting sand up to its knees.

If you journeyed across the ergs, you could see sand dunes shaped like domes and cones and crescents, or some with arms like starfish. The shape of a dune depends on how the wind blows the sand. You might think that the sand drifts on the air as it's blown by the wind, but actually, it hops along the ground. These hopping particles bombard other grains of sand and get them hopping, too. Sand particles that are too big to hop are pushed along the ground, in a movement called sand creep.

The desert wind is fierce, and dunes can be miles long and hundreds of feet high. Dunes change all the time. They can even slowly move, sometimes burying houses and even towns. Occasionally, the buildings emerge years later, and people are able to move back into their old homes after the dune has crept on.

Travel in some parts of the Sahara and you might hear an eerie, haunting sound-the music of singing sand dunes. Some people say the dunes sound like bass violins, low-flying aircraft, or pipe organs. Others hear booming sounds or deep, beautiful, single tones that resemble the notes from a brass horn. The musical dunes often go on singing for many minutes and can be heard from miles away. Scientists know that the sounds usually occur when a dune avalanches, perhaps arising from vibrations caused when grains of sand collide. But why do only a few sand dunes in the world sing? That's a mystery scientists are still trying to solve.

Where's Water?

Of course, it's dry in the Sahara. In the eastern Sahara, known as the Great Sand Sea, not a drop of rain may fall for decades. This scorched, silent earth is no place for plants. And to come across another person is rare.

But in other parts of the Sahara, brief, violent downpours can flood old stream beds called wadis. Even when a wadi appears to be dry, desert travelers sometimes find a trickle of water flowing a foot or two under the ground. Desert people gather around such places of water, called oases.

At its smallest, an oasis may be just a spot of land with a well and a tree or two for shade. The largest oases are communities that include permanent homes and businesses. Oasis water may come from natural springs, from a river or lake, or through a human-made irrigation system. The source of many oases is artesian wells-underground water that bubbles upward naturally through cracks in the earth's surface or through holes drilled deep into the ground.

Scientists say that great quantities of water lie under much of the Sahara. Some of it is thousands of feet under the ground. It is called fossil water, and it dates from a long-ago time when the land was covered with forests, marshes, and lakes. The water bubbling up at an oasis may be tens of thousands of years old!

Water under the desert may surprise you, but so would what scientists digging a well in the 1800s once found in the water 130 feet under the ground-fish! The fish were blind from living and reproducing in darkness for thousands of years.

Why Are You Blue?

Because of the lack of water, deserts are not crowded. All together, only two and a half million people live in the Sahara. (Compare that to the United States, which is about the same size and has almost 300 million people!) Most inhabitants live around the edges of the Sahara. But some people do make their home in the desert's desolate interior region.

The Tuaregs are a seminomadic people who live mainly in the mountainous central Sahara, where few other people dare to go. In the past, they were known as fierce-and feared-warriors who raided and stole the goods of passing caravans.

The Tuaregs are known as the "Blue Men." Why? Tuareg men wrap their faces and heads in long, blue cloth. Only the men wear veils, and they never remove them, not even to eat, except when they are among their immediate family members.

The Tuaregs color their veils, as well as the robes they wear, with indigo, a natural blue dye. Because water is scarce, they do not boil their veils in a vat of dye. Instead, they use stones to pound the dye into the fabric. Over time, the dye seeps from the cloth into the wearer's skin, giving it a blue-violet cast. Indigo dye is expensive, so the darker blue a man's skin, the more wealth and status he has.