DESERTS Dust Storms

"In a few minutes there will be no stars. The air is filling with sand."

Dust storms are common in arid regions.They are not to be confused to be sandstorms. A true desert sandstorms is a low cloud of moving sand that rises usually only a few centimetres and at most two metres above the ground. Above this level the air is almost entirely free of sand. Sandstorm consists of sand particles driven by a strong wind. It is rarer in occurrence.

Where winds are exceptionally strong and large quantities of loose soil are available, dust storms may develop. These can reduce surface visibilities to only a few metres. Normally only silt and clay particles are carried in suspension by the wind.

A dust storm approaches as a dark cloud extending from the ground surface to heights of several kilometres. It can take the form of an advancing wall or a whirlwind and are usually short lasting, although some storms of up to 12 hours have been recorded.

Within the dust cloud, there is deep gloom or even total darkness as the sun is blot out. A large dust storm can carry more than 100 metric tons of dust - enough to make a hill 30m high and 3km across the base. Dust from a single dust storm is often traceable as far as 4000 km. After a particularly violent storm in Algeria in 1947, red desert dust, mixed with snow, turned parts of the Swiss Alps pink.

The onset of dust storms is sometimes marked by an increase in respiratory infections and germs borne by the dust particles appear to be responsible for outbreaks of cerebral spinal meningitis.