Denudation - Wind
The wind is the dominant agent in hot deserts.
The desert floors get heated up too much and too quickly because of being dry and barren.
Winds also move along the desert floors with great speed and the obstructions in their path create turbulence.
In the transportation process sand and silt act as effective tools to abrade the land surface.
The wind itself has a little erosive effect on rocks. the loose rock materials carried by the wind acts as their tool in the wearing of rocks.
As the solid particles are dense they are confined to heights close to the ground.
At the same time, the erosion capacity of the wind depends on the velocity and amount of particles.
If the speed of the wind is high it can carry a large number of minerals of different sizes.
Erosional Work of Winds:
The loose soil on the arid surface is blown away by the wind. This process is known as deflation.
It causes a large depression.
In some places, it also reaches the water table as a result of continuous deflation resulting in the formation of an oasis.
The sand gains wear away by the rock by abrasion, polishing, and also scouring the rock surface like a sandblasting machine.
As the wind direction changes frequently, the wind-eroded pebbles are generally angular and are called dreikanters. Finally, they are reduced to sand.
The materials picked up by the wind are transported for a long distance.
By their constant collision and ground striking, they are rounded, and ground striking they are rounded and reduced to the size of millet seeds.
Landform associated with wind erosion:
Various relief features are formed with the erosional action of wind in the form of deflation, abrasion, and attrition.
1. Mushroom rock
In the deserts, the maximum erosion of a standing mass of rock occurs slightly above the ground.
It is due to more amount of sand particles in the air near the ground level.
The intensity of cutting decreases both upwards and also downwards. So, the lower part is eroded more than the higher portion. this feature is called mushroom rock or rock pedestal.
Wind erosion is unequal over a rock consisting of different rock beds.
The soft rock beds are eroded more than the resistant layers.
The rock surface thus possesses ridges and furrows.
These ridges are known as Zeugens which rise to a height of 100 feet and warn out gradually.
These are peculiar features similar to Zeugens, much higher produced by the wind in the Mongolian desert
The rock resembles ribs with steep slopes.
The wind has formed holes in the ribs and blows fast through the holes resulting in a peculiar sound.
These are isolated residual hills comprised of hard rocks. They rise abruptly from the level of the ground and appear like islands.
Depending upon the velocity of wind, different sizes of grains are moved along the floors by rolling or saltation and carried in suspension, and in this process of transportation itself, the materials get sorted.
The name sand dune is given to refer to a mound, a hill, or a ridge of sand, with a crest or a definite summit.
For the formation of sand dunes, the supply of a large amount of sand, strong wind to move sand particles, and some forms of obstacle to break the velocity of the wind are prerequisite.
Characteristics of sand dunes:
Sand dunes vary in shape, size, height as well as direction, but their common features may be identified.
A sand dune usually has a long and gentle windward slope and a steep leeward slope.
Their height varies from a few meters to 150 meters.
Some of the sand dunes are stationary but some are migrating.
The migratory sand dunes move at the rate of 5 to 30 meters a day.
Types of sand dunes:
Sand dunes are classified into various groups and named differently according to the variation of their shape, size, alignment, extent etc.
Broadly, they may be grouped into three categories namely barchans, longitudinal and transverse dunes.
These are crescent-shaped dunes and are widely distributed in the desert lands of the world.
The word Barchan is derived from Turkish meaning a sandhill originally meant to refer to the dunes of Kirghiz steppes.
These are characterized by a convex windward and a concave leeward slope.
They are also known as seif meaning sword in Arabic.
The longitudinal dunes are parallel running for several kilometers.
They resemble the edges of a sword.
The transverse dunes are opposite the direction of wind.
They are formed where the supply of sand is large.
It is a fine material transported from far-off places to its present position by the wind.
It has no horizontal stratification.
It is yellowish in colour