Geography Chap 7 (Goh Cheng Leong + NCERT)

Chapter 7

Arid of Desert Landforms

--Location= 15° to 30° Latitude N and  S.
--Cold current on western side èno condensation of moisture.
                          
5 type of Desert land scape:
1) Hamada/ Rocky Desert:
  >Rocky desert >>> wind has eroded all sands >>> polished rocks left.
  >Identity = boulders of rocks scattered randomly.
  >Ex- “Hamada el Homara” in Libya(part of Shahara).
  > (Image ↓) :



2) Reg or Stony desert:
  >Deserts of Pebbles >>> wind has eroded sands >>> polished  
  >Identity = small pebbles uniformly spread across desert .
  >Camels are used to move across=walking diff on pebbles.
  >Stuart-stony desert, in N-E of South Australia.
  >(Image ↓):

3)Sandy/Erg desert:
>full of sand.
>wind direction = from Sand dunes.
> Ex- Thar.
>(Image ↓)

4)Badlands:
>Hills eroded by rain, river , gullies, riverine etc.
>Giving bad appearance.
>Ex- Painted desert (Arizona) +Grand canyon (Colorado).
>(Image ↓)

5)Mountain desert:
>Desert on Highland(Plateau) or Mountain.
>identity= Sharp + irregular edges || steep sided, often dry valleys||craggy slope
>ex- Tibesti mountain, Ahaggar mountain etc.
>(Image ↓):

The Mechanism of Arid erosion
--Low rainfall = less then 5 inch.
--irregular rain
--Temp ↑ + rate of evaporation ↑.
-- 2  mechanism:

1)Weathering:
  >though rainfall is less >>> water enters rock crack>>> expands in heat + chemical weathering.
      >>>leads to exfoliation(Onion peeling)
>small rocks (Screes) at the bottom of rocks = water at night freezes = breaking rocks.

2)Action of wind:
--mainly transportation (as no vegetation to hold).

  a)Deflation:
     >lift and blow loose materials(ex pebbles).
     >lowers land surface>>>> forming deflation Hollow.
     >Ex- “Qattara depression” = below sea level=in “North- west Egypt”
     >[Image of Qattara depression (forming Oasis) ↓]:

      b)Abrasion:
         >Sand blasting against the rock.
         >occurs max at base===more material in wind near base.
         >innovation= poles in desert are cover to some height from base.

      c)Attrition:
         >Particles in wind= collides with each other= forming structure “millet seed”
      
 
7 Landforms of Wind Erossion:
--combined effect= abrasion + deflation +attrition.

1) Rock pedestals or Mushroom rocks:
  >Sand blasting (Abrassion) = erodes diff layer >>> Pedastal.
  >Why= wind cant lift sand to great height.
  >with more erosion= Mushroom rocks.
  >(Image ↓)



2)Zeugen:
  >Forms “Tabular elongated” structure.
  >Why= soft rocks beneath the Hard rock.
  >(Image ↓)





3)Yardangs:
  >forms “Ridge & forrow”
  >Why= side ways alternate hard and soft layer.
  >(Image ↓)




4)Mess and buttes:
  >Flat table(in spanish) like land mass
  >resistand + horizontal = top layer.
  >Formed in =Canyon or block mountain region.
  >process = cut from top = water or wind.
 >(Image ↓)

5)Inselberg:
  >Island mountain =in German.
  >Isolated residual hill = rising abruptly from level ground.
  >features = steep slope + rounded top.
                    =Granite or Gnesis(metamorphosed Granite)
   >Desert+ semi arid = ex- N. Nigeria + W.Australia + Kalahari desert.
   >(Image ↓)

6)Ventifacts or dreikanter:
  >these are =”Pebles” >>> faceted by sand blasting (bohot saare flat surface ban gaye pebble ke alag –alag side me…….diamond jaise cutting……bcoz of “Sand blasting”)
  >Features = Flat facet + Sharp edges
  >Dreikanter = when “Ventifacts” are wind-faceted from 3 sides.
  >(Image ↓)



7)Deflation Hollows:
  >depression from deflation(Explained in “Deflation” section ↑)

Landforms of Wind Deposition in Deserts: