The oasis is a fertile place in the middle of the desert, an island of life in an ocean of extreme temperatures. Any oasis always contains one or more water sources. The oases allow you to experience long walks in the desert. In large deserts such as the Sahara, cities cluster around water sources such as oases and rivers.
What causes the formation of a desert oasis? In fact, an oasis is a place in the sands where the elevation above sea level is low enough for the water table to be directly below the earth's crust, leading to springs. Even when it rains in the desert, this results in a water table just above the bedrock, usually several hundred feet below the surface. The sand is very porous in structure, so most of the water flows right through it and reaches the bedrock.
Deserts are made up of many millions of tons of sand. There is only one natural force capable of moving it in noticeable quantities - the wind. Although ten cubic feet (3.05 cubic meters) of air is retained only about an ounce of sand in an average dust storm, a cubic mile (1.6 cubic kilometers) of air can move about 4,600 tons of it, resulting in significant erosion. A violent storm can move up to 100 million tons of sand and dust.
In certain areas where large amounts of sand are transported by storms (dust storms), erosional cracks sink all the way down to the water table, lifting them straight to the surface. Seeds planted in the ground are able to germinate and spread roots in moist ground, creating an oasis.
Sometimes the oasis created by the wind can be very large when large areas of the desert are "cleared" of the sand by storms. For example, the great Kharga oasis in the Sahara is over 100 miles (161 km) long and 12 to 50 miles (19.3 to 80.5 km) wide. The oasis was created when erosion caused the edges of the great depression to sink to the water table.