Wind is an active agent of transport of fine materials, especially sand and dust, and moves thousands of tons of these materials from one place to another. Wind-transportation is dependent mainly on wind-velocity.
As such, during a gale the wind often blows the smaller pebbles along the beach, and in gusts it may even move fragments of considerable size. The distance to which wind can carry the materials also varies.
There is, even, evidence of transport of dust from the Sahara by trade- winds to a distance of 2000 to 2500 Kms across the Atlantic Ocean.
It has been observed that the finer and lighter rock particles are lifted up in the air and are carried in suspension, while heyavy particles are transported through a series of bounces and more heavy materials are transported through rolling and creeping.
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Accordingly, R.A.Bagnold (1941) has distinguished three types of movement of particles by the wind as-suspension, saltation and surface creep (or traction).
Suspension
As we all know, the wind can carry with it any loose material which lies upon the surface and which is sufficiently light and fine.
It has been observed, that the finest material, derived from silts and clays and having a diameter of less than 0.05 mm like dust cloud, smoke etc. move with the wind quickly and remain in suspension in the air for quite some time and settle very slowly.
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Saltation
Medium sized particles having diameters between 0.05 mm to 2.0 mm are moved in a leaping manner. These particles are commonly too heavy to remain in suspension and lighter to be transported through rolling.
In a turbulent flow of air near the surface, the wind initially may cause a particle to roll forward and, on knocking against an immovable object, it bounces up into the air. Once entrained the particle is carried by the wind describing a parabolic path and strikes the ground with considerable force.
When it strikes the ground it either bounces up again or cause other particles to bounce. The height attained by sand grains depends on the velocity of wind, the nature of the surface and also on the velocity of the grains.
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This type of transportation which is carried out through a series of bounces is called saltation.
Wind is the moving air. Wind blowing over the solid surface of the lands is also an active agent of landform development. Its activity is particularly intensive in the deserts and semi deserts which constitute about 20% of the surface of continents.
Surface Creep
Particles too large and heavy to be lifted off the surface by the blowing wind may be gradually and erratically moved along the surface.
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During normal high winds pebbles may be rolled along the ground surface but in majority of the cases when wind blows away the finer supporting material from beneath the boulders, they start rolling forward.
This method of transportation, through rolling and creeping, is also known as traction.