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Desert Landforms & erosion mechanism

Deserts

  • About 1/5th of the world’s land is made up of deserts.
  • Deserts which are absolutely barren, where nothing grows are known as true deserts.
  • Insufficient & irregular rainfall, high temperature & rapid rate of evaporation are the main causes of desert’s aridity.
  • Almost all the deserts are confined within 15* – 30* parallels to N – S of equator known as trade wind desert or tropical deserts.
  • They lie in the trade wind belt on the western parts of the continents.
  • Off shore trade winds are often bathed in cold currents which produces a desiccating (dehydrating) effect, hence moisture is not easily condensed into precipitation.

Deserts Landforms

Canyon Alluvial Fan Mesa
Butte Inselberg Salt Pan
Oasis Blowouts Sand Dunes
Yardang Zeugen Mushroom rocks

we will read about them in upcoming articles

Desert landforms

Types of deserts

Hamada / Rocky Desert

  • Consist of large stretches of bare rocks, swept clear of sand & dust by wind.
  • Exposed rocks are thoroughly smoothened, polished & highly sterile.

 

Reg / Stony Desert

  • Composed of extensive sheets of angular pebbles & gravels which the wind is not able to blow off.
  • Stony deserts are more accessible than sandy deserts & large herds of camels kept there.

 

Erg / Sandy Desert

  • Also known as sea of sand
  • Winds deposit vast stretches of undulating sand dunes in the direction of winds.

 

Badlands

  • Consists of gully & ravines formed on hill slopes & rock surfaces by the extent of water action
  • Not fit for agriculture & survival
  • Finally leads to the abandonment of entire region by its inhabitants

 

Mountain Deserts

  • Deserts which are found on the highlands such as on plateaus & mountain ranges, where erosion has dissected the desert highland into rough chaotic peaks & uneven ranges.
  • Their steep slopes consist of Wadis (dry valleys) with sharp & irregular edges carved due to action of frost.

 

Mechanism of Desert/Arid Erosion

Weathering

  • Most potent factor in reducing rocks to sand in arid regions.
  • Even though the amount of rain that falls in a desert is small, but manage to penetrate into rocks & sets up chemical reactions in various minerals it contains.
  • Intense heating during the day & rapid cooling during the night by radiations, set up stresses in already weakened rocks, hence they eventually crack.
  • When water gets into cracks of a rock, it freezes at night as the temperature drops below the freezing point & expands by 10 % of its volume.
  • Successive freezing will prise of fragments of rocks which get accumulated as screes.
  • As heat penetrates rock, its outer surface gets heated & expands, leaving its inner surface comparatively cool.
  • Hence, outer surface prise itself from the inner surface & peels off in successive thin layers, known as exfoliation.

 

Action of Wind

  • Efficient in arid regions as little vegetation or moisture to bind the loose surface materials
  • Carried out in following ways –
Deflation 
  • Involves lifting & blowing away of loose materials from the ground
  • Blowing capacity depending largely on the size of the material lifted from the surface
  • Finer dust & sands may be removed miles away from their place of origin & may get deposited even outside the desert margins.
  • Deflation results in the lowering of the land surface to form large depressions called Deflation hollows

 

Abrasion 
  • Sand blasting of rock surfaces by wind when they hurl sand particles against them
  • This results in rock surfaces being scratched, polished & worn away
  • Abrasion is most effective near the base of the rocks, where the amount of material the wind is able to carry is greatest.
  • This explains why telegraphic poles in the deserts are protected by covering of metal for a foot or two above the ground.

 

Attrition 
  • When wind borne particles roll against one another in collision, they wear each other away
  • Hence their sizes are greatly reduced & grains are rounded into millet seed sand
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