Geological action of wind
Atmosphere is composed mainly of gases that are collectively known as air, Air in motion is
called wind.
Wind is one of the three major agents, which is responsible for the earth, other two being rivers
and glaciers, Wind act as agent of erosion s a carrier of transporting particles and grains so
eroded from one place and also for depositing huge quantities of such windblown material at
different places. These three principle modes of activity that is erosion, transportation and
deposition.
I.) Wind erosion
The wind accomplishes erosion by three means
1) Deflation:- Deflation is the process of removal of the blowing wind. This process
operates well in dry regions with little or no rainfall. It is the main process of wind
erosion in desert region, in fact in some desert, deflation may cause the removal of sand
from a particular location to such an created, sometimes with its base touching the water
table at quite a depth. Such depression are variously called blowout. Where the water
table is intersected and it gets partially filled up with water is called OASIS it is only
around them that some vegetation may grow and also they sustain temporarily
2) Wind abrasion
Wind becomes a powerful agents for rubbing and abrading the rock surface when
naturally loaded with sand and dust particles. This load is acquired by the strong winds
quite easily when blowing over sand dunes in deserts. This type of erosion involving
rubbing, grinding, abrading and polishing the rock surface by any natural agent with the
help of its load while passing over the rocks is termed as abrasion.
3) Attrition
Attrition is the grinding action, while on transit wind born particles often collide with one
another, such mutual collision brings about a further grinding of the particles.
Important erosional features and associated land forms
i) Hamada:- Due to deflation, when the loose particles are swept away, only the
hard mantle is left behind which is known as Hamada
ii) Yardang:- A grooved or furrowed topographic form produced by wind abrasion,
which is elongated in the direction of prevailing winds and is usually strongly
under cut, is known as yardang
iii) Pedastal rock:- A wide rock cap standing on a slender rock column, produced
because of the wind abrasion is known as a pedestal rock
iv) Ventifacts:- These are faceted by the abrasive effects of wind blown sand. These
are small sized rock fragments showing one , two or three even more typically
wind polished surfaces
v) Blowout:- These are broad shallow caves in hill broad shallow depression in
deserts
vi) Desert pavement:- It is made of a layer of residual pebbles and cobbles strewn
upon the surface while intervening finer particles have been removed as a resukt
of deflation
II) Transportation:- Wind transportation is totally dependent on wind velocity. These are
three methods of wind transportation.
i) Traction:- Where particles are removed through rolling and creeping.
ii) Saltation:- Here the particles, which are too heavy to remain in suspension and
lighter to be transported in traction are transported through a series of bounces.
iii) Suspension:- Very light particles like dust and cloud smoke etc. move with the wind
quickly but settle very slowly remain in suspension in the air.
III) Deposition
Wind formed deposits are called Aeolian deposits. Wind is an excellent agent for sorting of
materials according to their size, shape or weight, pebbles and boulders cannot be carried away
and are left back to large deposited as loess, which does not show any stratification wind
deposits take two general forms as;
i) Sheets ii) piles
sheet deposits are the dust deposits laid down on large piles deposits include the various types of
dunes which accumulate from sand and silt carried in saltation
Depositional features of wind :-
i) Sand hill:- Mounds of sand whose surface in irregular is called sand hill.
ii) Sand dune:- When the mound is in the form of a round hillock or a ridge with crest it
is called a sand dune.
Types of dunes
i) The crescentic dunes:-A crescentic dunes is characterized with two slopes in such a
way that the windward slope is convex and rises gently between 7degree and 20
degree. It has a leeward slope or downward starts abruptly. The downward slope has
two well defined parts the slip face the cusps
ii) Barchans dunes:- These are the simplest of crescentic dunes with a typically half
moon shape developed by wind blowing in the same direction for considerable length
of time with some changes in the direction of wind the simple outline of the barchans
half moon shape is destroyed.
iii) Seif:- It is similar to barchans except one wing is missing caused by an occasional
shift in wind direction
iv) Transverse dune :- Elongated dune form at right angles to the prevailing
