Aeolian Process and Landforms Desert Landscapes

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Aeolian Process and LandformsDesert Landscapes

• Aeolus, Greek god of the winds

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Wind as a geomorphic agent
12 consecutive months with no precip
lt 10 in. precip
10 -20 in. precip
requires fine grained sediment and little
vegetation
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Arid and Semi-arid
Tunisia
Morocco
Algeria
Egypt
Libya
Sahel
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Wind Erosion

• Deflation
• removal of loose particles by wind
• max effectiveness when grain size 100mm
• silt and clay size move most easily and carried
  in suspension by turbulence
• takes a long time to move sand
• Abrasion
• bombarding of rock by airborne particles
• natural sandblasting
• sand-sized most effective
• uncommon gt 2m. above ground

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Making the Sahara Desert

• http//www.sciencefriday.com/videos/watch/10070

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by Salt Weathering
Arches NP Arch Formation
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Arches N.P.

• Greatest concentration of natural rock arches in
  the world
• Arches form by
• (Salt) weathering of vertical joints, in Entrada
  sandstone, produced by folding
• Salt-cored anticlines undergoing dissolution
• Exfoliation weathering
• Sand grains are cemented by CaCO3
• Rain forms carbonic acid dissolving bond
• Wind and water erosion exploit joints
• Groundwater sapping

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Arch formation
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Wind Erosion

• Deflation
• Variations in lithology or cementation enable
  preferential wind scour
• Desert pavement
• Abrasion
• Ventifacts

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Wind Transport

• Saltation
• bounce off the ground and other grains
• effective lt 2m. above ground
• powers the remaining 3 processes
• Reptation
• impacting grain releases shower of particles
• Suspension
• silt and clay-sized
• travel around the world
• Creep or dry ravel
• individual particles (sand and pebble size) roll
  and slide by momentum imparted by an impacting
  particle

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Wind deposition

• Where does the dust go?
• 90 on land 10 in oceans
• Sedimentation
• Grains fall to ground
• Air velocity decreases
• Air currents bring silt/clay sizes near ground
• Accretion
• Where saltating grains come to rest
• Encroachment
• Creep is stopped by surface roughness

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Aeolian Forms Transport by Suspension

• Loess
• Grain size 20-40 microns
• Accumulation rates fractions of mms/yr
• Mixed grain sizes are needed to entrain dust
• Large saltating grains disrupt the laminar
  sublayer to entrail dust
• Dust sources alluvial fans/rivers, glacial
  outwash plains
• Thickness declines with distance from source

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Chinese Loess

• 247,000 mi2 loess plateau
• Up to 300m thick
• Source deserts of interior China and Tibet

http//www.clw.csiro.au/ReVegIH/Maps.htm
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Loess Strat

• Soils separated by unweathered silt
• Used to correlate with deep sea records of
  paleoclimate
• Pleistocene
• windier and drier

glacial
Interglacial, odd numbers