Desert Landforms and Erosion Mechanism

Desert Landforms  and Mechanism Arid Erosion  :

• About 1/5^th  of
  the world’s land is made up of deserts.

• True Desert : Deserts that are absolutely barren and where nothing
  grows at all are rare and they are better known as ‘true deserts’.

• Almost all the deserts are confined within the 15° to 30° parallels
  of latitude north and south of the equator. They lie in the trade wind belt on
  the western parts of the continents where Trade Winds are off-shore.

• They are bathed by cold currents which produce a ‘desiccating
  effect’ so that moisture is not easily condensed into precipitation.

• Dryness or aridity of deserts are tropical hot deserts or Trade
  Wind deserts’. They include the great Sahara Desert; Arabian, Iranian and Thar
  Deserts; Kalahari, Namib, and Atacama Deserts; the Great Australian Desert and
  the deserts of south-west U.S.A, and northern Mexico.

• In the continental interiors of the mid- latitudes, the deserts
  such as the Gobi and Turkestan are characterized by extremes of temperatures.

Sand Dunes

 Types of Deserts :

1.Hamada or Rocky Desert :

•  This consists of large
  stretches of bare rocks, swept clear of sand and dust by the wind.
• The exposed rocks are thoroughly smoothed and polished. The region
  is bare and sterile.
• The best known rocky deserts are those of the Sahara Desert e.g.
  the Hamada el Homra, in Libya, which covers an area of almost 20,000 square
  miles.

2. Reg or Stony Desert :

• This is composed of extensive sheets of angular pebbles and
  gravels which the winds are not able to blow off.
• Such stony deserts are much more accessible than the sandy
  deserts, and large herds of camels are kept there.
• In Libya and Egypt the term serir is used; elsewhere in Africa,
  stony deserts are called reg.

3. Erg or Sandy Desert :

• This is a sea of sand which typifies the popular idea of desert
  scenery.
• Winds deposit vast stretches of undulating sand-dunes in the heart
  of the deserts.
• The intricate patterns of ripples on the dune surfaces indicate
  the direction of the winds.
• The Calanscio Sand Sea in Libya is characteristic of a sandy
  desert. In Turkestan, sandy deserts are also known as koum.

4. Badlands :

• The term ‘badlands’ was first given to an arid area in South
  Dakota, U.S.A.
• The extent of water action on hill slopes and rock surfaces was so
  great that the entire region was abandoned by the inhabitants.
• Deserts with similar features are now referred to as badlands,
  e.g. the Painted Desert of Arizona, which lies south-east of the Grand Canyon
  of the Colorado River.

5. Mountain deserts :

• Some deserts are found on highlands such as plateaux and mountain
  ranges.
• Erosion has dissected the desert highlands into harsh, serrated
  outlines of chaotic peaks and craggy ranges.
• Their steep slopes are cut by wadis (steep-sided, often dry,
  valleys) and the action of frost has carved out sharp, irregular edges.
• In the Sahara Desert, the Ahaggar Mountains and the Tibesti
  Mountains are good examples of desert mountains.

Mechanism of Arid Erosion :

• Arid landforms are the results of many combined factors, one
  reacting upon the other.
• Lower precipitation and extreme temperature and high evaporation, are
  the chief causes of aridity.
• Sub-aerial denudation through –

1. The processes of Weathering (mechanical and chemical),
2. Wind Action and
3. The Work of Water have combined to produce a desert landscape.

Weathering Process :

• Weathering is the most potent factors in reducing rocks to sand in
  arid regions.
• Intense heating during the day and rapid cooling at night by
  radiation, set up stresses in the already weakened rocks so that they
  eventually crack.
• As heat penetrates rocks slowly when the outer surface of rocks is
  being heated by the hot sun, the inner rocks remain quite cool.
• Due to heating and cooling of rocks, peels off in successive very
  thin layers of rocks occure. Such an onion-peeling process of mechanical
  weathering is called exfoliation.

 

Wind Action :

The wind is the main geomorphic agent in the arid region. Wind in
arid region has greater speed which causes erosional and depositional
activities in the desert. The landforms which are created by erosionaland
depositional activities of wind are called as Aeolian Landforms.

Removal of sand and dust particles by wind. It forms depression in
the desert. When depression is

filled with water, it is called as Oasis.

2. Abrasion :

Action of wind in which sand particles carried by the wind strike
against the rock.

3. Attrition :

Sand particles carried by the wind striking each other is known as
attrition.

Water Action :

• Few desserts in the world are without rain or water. The annual
  precipitation may be small, 5 to 10 inches, and comes in irregular showers.
• As deserts have little vegetation to protect the surface soil,
  large quantities of rock wastes are transported in the sudden raging torrents,
  or flash-floods.
• Loose gravels, sand and fine dust are swept down the hill sides.

 

 Also Read : Tropical Cyclone in India

 

References

G.C. Leong

NCERT