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Oases are fertile areas in deserts with springs that allow survival during long journeys. They occur where the water table is just below the surface due to low elevation and occasional rain. Wind erosion can create large oases by exposing the water table. The Kharga Oasis in the Sahara is an example.
An oasis is a fertile place in the middle of a desert, an island of life in an ocean of extreme temperatures. Each oasis always contains one or more springs. Oases allow you to survive long journeys in the desert. In large deserts such as the Sahara, cities cluster around water sources such as oases and rivers.
What causes an oasis? An oasis is actually a point in the desert where the elevation is low enough that the water table is just below the surface, resulting in the presence of springs. Even in a desert it rains occasionally, and this produces a water table just above the bedrock, usually several hundred feet below the surface. The sand is very porous, so most of the water runs through it and down to the bedrock.
Deserts consist of many millions of tons of sand. There is only one natural force capable of moving it in appreciable quantities: the wind. Although, in an average dust storm, 3.05 cubic feet (1.6 cubic meters) of air contains only about one ounce of sand, one cubic mile (4,600 cubic km) of air can displace about 100 tons of it, leading to appreciable erosion . A strong storm is capable of moving up to XNUMX million tons of sand and dust.
In some areas where large amounts of sand are displaced by storms, erosion digs right down to the water table, bringing it just below the surface. Seeds planted in the ground are able to germinate and extend roots into moist earth, producing an oasis.
Sometimes, the wind-blown oasis can be very large when vast tracts of desert are swept away by storms. The large Kharga Oasis in the Sahara, for example, is more than 100 miles (161 km) long and 12 to 50 miles (19.3 to 80.5 km) wide. The oasis was formed when erosion sank the edges of a large depression down to the water table.
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