94 ENVIRONMENTAL SCIENCE
Wind Erosion
Soil erosion by wind is common in dry (arid) regions Two characteristics of such region
are:
(a) The soil is chiefly sandy
(b) The vegetation is very poor or even absent.
In India erosion by wind affects approximately 50 million hectares of land, most of
which is in Rajasthan. The wind erosion also is triggered by the destruction of natural
vegetation cover of land by overfelling and overgrazing. When the top soil is laid bare to the
fury of strong gales it begins to be blown off in the form of dust storm and sand storm. The
high velocity winds blow away the soil particles. This may be of the following types:
(a) Saltation
Saltation takes place in the arid regions where:
(1) Rainfall is low,
(2) Drainages is poor,
(3) High temperatures prevail,
(4) Water evaporates quickly leaving behind the salts.
The salts are normally chlorides, sulphates, carbonates and nitrates of potassium,
magnesium and sodium, and chlorides and nitrates of calcium. The major portion of such
salty soil is carried by wind in the form of small leaps. These leaps are created by direct
pressure of wind on small particles of soil.
(b) Suspension
The wind throws away smallest soil particles into air, these particles move as fine dust
with the wind. By this way soils are transported to long distances.
(c) Surface creep
The heavier particles of soil which the wind cannot easily throw up are pushed or
spread along the surface by wind.
Landslides or slip erosion
The hydraulic pressure which is caused by heavy rains, increases the weight of the
rocks at cliffs. As a result they come under the gravitational force and finally slip or fall off.
Sometimes the whole hillock may slide down.
Stream bank erosion
The rivers during floods splash their water against the banks. In this way the water
cuts through them. Particularly at curves, water strikes with great speed and the bank
caves in alongside. This type of erosion is also known as riparian erosion.
FRIGHTENING POSITION OF SOIL EROSION IN INDIA
According to the Tiwari Committee, of the total land of 304 million hectares of India,
about 175 million hectares are exposed to serious environmental threat. This area is suffering
from degradation of various kinds. The main causes are water and wind erosion besides