Role of Wind in Hot Deserts (AQA A Level Geography)

Desert Erosion

Aeolian erosion – from the Greek God of wind Aeolus

• Wind erodes arid and semi-arid surfaces and transports particles

• It does this in three ways:

  • Deflation: The carrying and removal of loose material by wind

  • Abrasion: When wind-blown sand abrades rock surfaces

  • Attrition: Loose materials collide with each other and become smaller

Deflation

• Wind removes fine sediments and lowers the desert floor

• This leaves coarser gravels, forming slag-type deposits of duricrust from the exposed bedrock

• This hardened desert floor, known as desert pavement, limits any future deflation and forms the features of a 'reg' desert

• Strong wind eddies can further hollow out the desert surface to form deflation hollows (blowouts)

• These deflation hollows are usually small but can extend several square kilometres 

Abrasion

• Wind laden with sand carves and sculpts rock (sandblasting), usually within a metre of the desert floor

• The strength, duration and direction of the wind will dictate the rate and intensity of the abrasion

• The geology of the rock also factors into the rate of abrasion, with sandstone and limestone being the easiest to erode

Attrition

• Attrition in deserts occurs during transportation and small pebbles are picked up by the wind

• These pebbles are too heavy to be carried far and attrition occurs within 0.5m of the desert floor

• As they move, the pebbles collide with each other and bits of rock are broken 

• These smaller pieces are then picked up by the wind and moved further along the desert floor colliding into each other and becoming smaller and smaller

• Eventually, these particles become part of the abrasion process 

Desert Transportation

• Aeolian (wind) transport is the carrying of sand particles away from an area in 3 ways:
  

  • Creep: When sand grains (>0.25 mm) slide and roll across the surface

    • Caused by small differences in air pressure, which creates a lift of no more than 2 mm

  • Saltation: When the wind exceeds threshold velocity, a bouncing movement of particles begins close to the ground

    • Material transported by saltation may dislodge and push larger particles too heavy to be uplifted

    • This constant bombardment moves small stones and pebbles along the desert surface

    • Particles are too heavy to be held by the wind for long distances and only reach a height of 10 cm off the desert floor

  • Suspension occurs when small dust particles (<0.15 mm) are carried by high-velocity winds high into the atmosphere

    • This is the main cause of dust storms

    • These dust particles of fine silt and clay can be taken away from the desert region entirely: The dust of the Sahara has reached the UK

Deposition

• Deposition will only occur when the wind drops below the threshold velocity 

• This is dependent on the size of the particle, and the strength of the wind

• The deposited material can then be shaped by the wind

• Only 30% of all deserts are covered in wind-blown sands called 'erg' deserts

• Sand seas (great erg deserts) are some of the most distinct landscapes on Earth 

  • The Great Sand Dunes National Park, Colorado, USA contains different types of sand dunes and covers an area of over 600 km²