Depositional landforms

Deposition work of wind may be divided into two parts namely:

Sand Deposition:

Following landforms are classified under sand deposition:

  • Ripples:
    • Low speed winds deposit the particles in the shape of waves, which are known as layers of sands or sand ripples.
    • The inter-difference between these waves may vary from few centimeters to few meters.
    • The windward side of Ripples is generally angular at 8° to 10° while leeward side is angular at 20° to 30°. Their height rises to a few centimeters only.

 

  • Sand Dunes:
    • Velocity of wind carrying sand decreases when it faces some obstacle and therefore wind it starts depositing the sand particles on the spot of obstacle only. Resulting in the formation of sand dunes.
    • Any shrub, big rock, skeleton of an animal, upland area can act as such obstacle. The height of sand dunes may vary from some meters to 150 meters and their length may vary between 3 kilometers to 150 kilometers.
    • Shifting of Sand Dunes: Direction of wind is not fixed because of this sand dunes are not stable, they shift according to the direction of wind. Shifting sand dunes is harmful for fertile plains. Fast growing and deep root plants are planted in desert regions to control this process. They may shift from 5 to 30 meters per year.

 

    • Sand dunes may be of many types:
      • Barkhan: Half-moon and crescent shaped sand dunes are known as Barkhans. These are convex on windward side and steeper and concave on leeward side. They might be high upto 30 meters and their length varies from 150 meters to 200 meters.

 

        • Self or Longitudinal Sand Dunes: Self is an Arabic word which means ‘Sword’. These sand dunes are generally oriented in a direction parallel to prevailing wind but when the dunes blow out, sand gets deposited in parallel forms.

These may raise to 100 meter high and their breadth varies from 500 to 600 meters. These are not shifting sand dunes. These are found in areas where high velocity winds blow. These are found in Sahara Desert (Africa).

 

      • Coastal Dunes: High velocity winds blow in coastal areas because of this, waves deposit sand on the coasts of oceans. Blowing wind gives it a form of ‘Sand Dune’. With the growth of vegetation in these areas, curved sand dunes are formed and sometimes they also look like Barkhans.

 These are found in Atlantic coastal regions. In Southern France, there is 240 kilometers long dune along the coast covering 3 to 10 kilometers in inland areas. On the Western coast of India, sand dunes (coastal areas) of Goa are famous for their beauty.

Loess Plains:

  • Winds deposit light and soft soil over a large area like a blanket, these are known as plains of Loess.
  • ‘Loess’ is a word of German language which means yellow colour, porous soil with very soft particles.
  • Generally, these particles are of same size. This soil does not have layers and it is friable. When we press it crumbles easily.
  • During rainfall it becomes very sticky, on the other hand in summer it becomes very dry.
  • Loess is found in China, Europe, North America, South America and Africa.
  • The name “Yellow river” in China is also given on the basis of their soil because when it mixes with river water, water appears to be yellow in colour.