Landforms in Deserts

Introduction

Wind is one of the most powerful forces in hot deserts. The heated soil floors heat the air in direct contact with them, heating the air layers above them as well. This causes turbulence as the heated lighter air rises, and any barriers in its path cause eddies, whirlwinds, updrafts, and downdrafts to form. If there are impediments in the way of fast-moving winds along with the desert floors, turbulence results. 

Deflation, abrasion, and collision are all caused by wind. Deflation is the lifting of smaller particles and the removal of dust from the surface of rocks. The diverse landforms are the result of the wind’s sand blasting operations.

Erosional Landforms in Deserts

Pediments and Pediplains:

• • Pediments: Pediments are gently inclined rocky floors near to the foot of the mountains with or without a thin cover of the debris. These are formed because of the erosion of the mountain face, as there is  lateral erosion by streams and also by sheet flooding
  • After the formation of  pediments with a steep wash slope, followed by a cliff or free face above it, the steep wash slope and free face retreats (moves back) and this method of erosion is termed the parallel retreat of slopes through backwasting
  • The pediments extend backwards at the expense of the mountain front through the parallel retreat of slopes and slowly, the mountain gets reduced to an inselberg which is a remaining part of the original mountain

• In desert areas, the high relief is reduced to low featureless plains which are known as the pediplains

Playas:

• In basins with mountains and hills around and along, a nearly level plain forms at the centre of the basin because the drainage is towards the centre of the basin and the gradual deposition of sediment from basin margins happens
• This plain is covered up by a shallow water body when there is sufficient water. These types of shallow lakes are known as playas where water is retained for a small duration of time and as  evaporation happens, then, quite often the playas are left with  good deposition of salts
• Alkali Flats: These are the playa plain covered up by salts

Deflation Hollows and Caves:

• The weathered mantle from over the rocks or bare soil is pushed out by the continual flow of wind currents in one direction. Deflation hollows are shallow depressions generated as a result of this process
• Deflation also creates several cavities or  small pits  over rock surfaces. The face or surface of the rocks suffer impact and abrasion of wind-borne sand and this makes the first shallow depressions known as blowouts
• Few of the blowouts with time  become wider and deeper fit to be known as  caves

Mushroom, Table, and Pedestal Rocks:

• Several rock outcrops in the deserts are easily subject to wind abrasion and deflation, and hence wear out quickly, leaving remains of resistant rocks polished nicely in the mushroom shape with a slender stalk and a rounded pear-shaped cap on top
• Quite often, the remnants stand out like pedestals as the top surface is broad like a table-top

Depositional Landforms in Deserts:

• • The wind works well as a sorting agent. The materials are sorted based on wind speed and grain size, and the particles are then pushed along the floors by rolling or saltation and carried in suspension during the transportation phase

• When the wind begins to slow or die down, the grains will begin to settle, depending upon the sizes of grains and the critical velocities of the wind. So, good sorting of grains can be found in depositional landforms

Sand Dunes: The dry hot deserts are good areas for sand dune formation. To initiate the formation of dunes , hindrances and obstacles are very necessary. The various types of dune forms are as follows-

• • Barchans: These are crescent-shaped dunes with the points or wings pointing downwind, away from the wind direction, and where the original surface over which sand is drifting is almost uniform
  • Parabolic Dunes: When sandy surfaces are partially covered by vegetation, the formation of Parabolic Dunes occurs. These are reversed barchans with the same wind direction
  • Seif: It is similar to barchan with a small difference that it has only one wing or point due to shift in wind conditions. The lone wings of seifs can grow very long and high

• Longitudinal Dunes: Longitudinal Dunes are  formed if the wind direction is constant and the supply of sand is poor. They are low in height and look like long ridges of considerable length

• Transverse Dunes: Transverse Dunes  are those dunes that are aligned perpendicular to wind direction. These types of  dunes are formed when the direction of wind is constant and the source of sand is at a perpendicular angle to the wind direction. They are very long as well as low in height

• The regular shaped dunes coalesce and, thus, lose their individual characteristics when sand is plenty

• There is a shift in most of the dunes in the deserts and a few of them will get stabilized especially near human habitations

Conclusion:

Winds cause deflation, abrasion and impact. The movement of wind creates a number of erosional and depositional features in the deserts. When the sand is plenty, quite often the regular shaped dunes collapse and lose their individual characteristics. Most of the dunes in the deserts shift and a few of them will get stabilised especially near human habitations.