The desert of Sahara is a plateau about 180 meters high
A desert is a region that gets very little rainfall. Where temperatures are high, the rate of evaporation exceeds the rainfall. The ground is dry. Such regions are called hot deserts. But there are also `cold desert’. Although these is a hardly any evaporation in such places, temperatures are so low that the little rain that falls comes in the form of snow. Plants cannot survive in such conditions. Vegetation is thus scarce in both types of deserts and the land cannot be put too much use. Desert is a kind of waste land.
Deserts cover about one –fifth of the total land surface of the world. Some deserts are like great seas of sand while some are rocky or stony deserts.
The Thar Desert is in India, Which is a hot desert because of the lack of rain. There is other hot desert in the world. You will find that the entire hot desert is found between about 15 degree cilices and 30 degree cilices north and south of the equator. These deserts are crossed either by the people of Cancer of the Tropic of Capricorn.
Another feature of the hot deserts is that they are found on the western side of the continents. Why is this? The reason is that the trade winds in this region blow across the land and carry very little moisture. The winds blow from the northeast which means that the eastern part of the continent gets the rain. By the time the winds reach the western part they are very dry. Cold currents too flow towards the equator on the western sides of the continents. Winds that blow across these currents get cooled and lose their moisture. Therefore little rain reaches the land.
Thus land becomes a dry desert. South of the equator the winds blow from the southeast.
The largest hot desert in the world is the Sahara (the Arabic word for desert) which lies south of the Mediterranean Sea and stretches right across North Africa. Smaller hot deserts are found in California in North America, in Arabia and in Central Asia. In the southern Hemisphere we find the Atacama Desert in South Africa and the great Australian desert in Central Australia.
The air in a desert is dry. During the day it is hot, sunny and cloudless. The temperature rises above 30 degree cilices. The nights are starlit, cloudless and cold. The temperature drops to about 10 degree cilices. There is little or on rain, amounting usually to less than 25 cm a year. Hot days and cold nights break up the desert rock by making it expand and contract. Thus most of the deserts are sandy and the strong winds that blow across the deserts carry the grains of sand from one place to another to form sand dunes. Sand dunes grow and often drift in the direction of the world of the wind. Sometimes entire villages have been covered by such drifting dunes.
Just as the northern part of the Thar Desert has become fertile with irrigation, so crops can be grown in all deserts where irrigation is possible.
Most of the Sahara is a plateau about 180 meters high. There are mountains in this desert but about two-thirds of the area is made up shifting sand dunes. Much of this land receives no rain for several years. Suddenly rain comes in one or two fleeting showers. This can cause flash foods, laden with sand and broken desert rock. This can cut deep gorges in the desert, called Wadis in North Africa and canyons in North America. After such storms most of the water runs off into dried up water courses called Wadis. The particles of sand carried by the wind carve the rocks into strange shapes.
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