The great Sahara

All nature lovers of this world are on a huge mission to retain the green that is left on the face of the Earth, and the last thing they want to see on this planet is a desert. However, planet Earth has quite a number of deserts, and some of them are really gigantic and geologically exciting.

Therefore, let's look at one of these deserts which has earned a reputation as the largest desert of the world - the Sahara. This desert is spread over a staggering 9,000,000 square kilometres. It covers most parts of northern Africa.

You would be surprised to learn that it is almost as large as the United States and larger than Australia. The word 'sahra' in Arabic means desert. 'Ah-sahara' means 'great desert'. The word 'Sahara' has been derived from these, so, when we refer to this as the 'Sahara Desert' in English, we are more or less saying 'desert desert'.

Why is it a desert?

The Sahara is one of the hottest places on Earth. Even though temperatures there may rise to 136 degrees Fahrenheit (57.7 degrees Celsius), it is dryness, not heat that makes a place like the Sahara a desert.

However, the definition of a desert is quite ambiguous (uncertain) since sometimes scientists define deserts considering only the dryness of a region, which bring in regions like the Antarctica also in to the list of deserts. In this case, Sahara would be the second largest desert since the Antarctica is much larger than the Sahara.

The Sahara receives less than three inches (7.6 cm) of rain a year. Even in its wettest areas, rain may arrive twice in one week, then not return for years. For centuries, caravaneers have travelled through the Sahara despite its dryness and harsh conditions.

Even though there are many oases in the Sahara, the desert is so big that travellers may go for days to reach them.

Was Sahara always a desert?

Interestingly, the Sahara is believed to have been a green home to water-loving animals like hippos, many thousands of years ago. The climate has changed over thousands of years and now we see the desert. This transition is pretty scary, isn't it?

Before the Sahara became a desert, it has been home to many savanna animals, including the giraffe. People began to paint and etch the Sahara's animals in desert rock about 12,000 years ago.

Archaeologists estimate that the oldest remaining pictures date back to 6500 BC. By looking at paintings and etchings created thousands of years apart, we can see how life changed as the Sahara slowly became a desert.

Catfish, hippos and other water-dependent animals have lived in wet areas that later became part of the Sahara. Bones found in long-dry riverbeds and pictures painted or carved on rocks are the only traces of these animals.

Geography of the Sahara

The forbidding landscape of the Sahara has taken shape over thousands of years, but even today, it is constantly changing, which is yet another reason why this is considered to be a geological wonder although it is a desert.

By studying satellite photos, some scientists have come to believe that the Sahara regularly shrinks and grows. In the early 1980s, the Sahara's southern edge has expanded into the Sahel, a dry band that separates the desert from the savanna. But by the mid-1980s, this area had turned green and wet again.

As the world's biggest desert, the Sahara covers a third of the African continent. This covers huge parts of Algeria, Chad, Egypt, Libya, Mali, Mauritania, Morocco, Niger, Western Sahara, Sudan and Tunisia.

The Sahara includes many landforms such as rivers, mountain ranges, smaller deserts and ergs, lakes and oases. About 70 per cent of the Sahara consists of rocky plains covered with stones and gravel. Shale and limestone plateaus or mountain ranges make up the rest.

The longest river of the world, the Nile flows through the Sahara and the Senegal River also flows through it.

Air Mountains, Ahaggar Mountains, Saharan Atlas and Tibesti Mountains are the mountain ranges within the Sahara. Libyan Erg, Tenere, Egyptian Sand Sea, Qattara Depression, Erg of Bilma and Erg Chebbi fall under the smaller deserts and ergs.

For your knowledge, an erg, which is also known as 'Sand Sea' or 'Dune Sea', is a large, relatively flat area of desert covered with wind-swept sand with little to no vegetation cover. Out of the ergs, the Libyan Erg is as big as France.

Ergs make up only about 15 per cent of the Sahara, but the desert is so huge that even a single dune may be enormous. The Lake Chad is the prominent lake within the Sahara, and Bahariya, Ghardaia and Timimoun are the famous oases.

Aravinda Dassanayake.