Wind Action in Deserts
- Processes of Wind Action: Wind performs its geological work through three processes:
- Deflation: The lifting and removal of dust and smaller loose particles from the surface of rocks or bare soil.
- Abrasion: The process where sand and silt carried by the wind act as effective tools to abrade and sandblast the land surface.
- Impact: The sheer force of momentum generated when sand is blown directly into or against a rock surface.
Erosional Landforms of Wind
Pediments and Pediplains:
- Pediments: Gently inclined rocky floors formed close to the foot of mountains, with or without a thin cover of debris. They develop through the retreat of the mountain front, aided by a combination of erosion, lateral stream cutting, and sheet flooding.
- Pediplains: Low, featureless plains resulting from the gradual reduction of high relief in desert areas through parallel slope retreat (backwasting), leaving behind residual isolated remnants called inselbergs.
Deflation Hollows, Blow Outs, and Caves:
- Deflation Hollows (Blowouts): Shallow depressions formed when persistent wind movement in a single direction lifts and carries away weathered mantle and loose surface material. In arid regions, deep deflation hollows that reach down to the underground water table can form an oasis.
- Caves: Shallow depressions (blow outs) created on rock faces due to wind impact and abrasion that gradually deepen and widen into cave-like cavities.
- Mushroom Rocks (Table and Pedestal Rocks):
- Remnants of resistant rock outcrops polished in the shape of a mushroom, featuring a slender/narrower base and a broad, rounded top.
- They form because winds carrying sand erode and abrade the lower section of the rock more aggressively than the upper part.
- Similar variations where the upper surface remains broad are referred to as table rocks or pedestal rocks.
- Yardangs:
- Streamlined, elongated rock ridges carved and shaped by wind erosion in arid landscapes.
- Ventifacts:
- Rocks polished, shaped, and faceted by the abrasive, sandblasting action of the wind.
- Desert Pavements:
- Flat ground surfaces left behind after fine dust and sand particles have been removed by wind deflation.
Depositional Landforms of Wind
- Characteristics of Wind Deposition:
- Wind functions as a good sorting agent; materials are sorted by grain size as they roll, move by saltation, or are carried in suspension.
- When wind velocity drops, grains settle based on their critical sizes, producing well-sorted depositional features wherever sand is available.
- Sand Dunes:
- Hills or ridges of sand formed when wind-borne sand drops and accumulates after wind speed decreases or when the wind encounters an obstacle.
- Barchans: Crescent-shaped dunes with points or wings directed downwind (away from the wind direction); they form where wind direction is constant and moderate over an almost uniform surface.
- Parabolic Dunes: U-shaped dunes that develop when sandy surfaces are partially covered or stabilized by vegetation; they resemble reversed barchans under the same wind direction.
- Seif Dunes: Crescentic dunes similar to barchans, but having only one wing or point; they form when there is a shift in prevailing wind conditions and can grow into high, long ridges.
- Longitudinal Dunes: Long, low-height ridges formed parallel to the prevailing wind direction; they commonly develop where the sand supply is relatively poor and wind direction remains constant.
- Transverse Dunes: Elongated dunes aligned perpendicular (at right angles) to the constant wind direction; they form where the sand supply is elongated and oriented at right angles to the wind.
- Star Dunes: Dunes with multiple radiating arms formed in areas where winds blow from several varying directions.
- Loess:
- Extensive, fine-grained deposits formed when light, fine particles of sand and dust are carried by the wind over long distances and deposited over large areas.
- Large, prominent deposits of loess occur in China.
Reference Ncert Documents
https://ncert.nic.in/textbook/pdf/kegy206.pdf
https://ncert.nic.in/textbook/pdf/kegy205.pdf
https://ncert.nic.in/textbook/pdf/iest102.pdf
https://ncert.nic.in/textbook/pdf/gess203.pdf
