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Aeolian Process and Landforms Desert Landscapes

Aeolian Process and Landforms Desert Landscapes. Aeolus, Greek god of the winds. Wind as a geomorphic agent. 12 consecutive months with no precip. < 10 in. precip. 10 -20 in. precip. requires fine grained sediment and little vegetation. Arid and Semi-arid. Tunisia. Morocco. Algeria.

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Aeolian Process and Landforms Desert Landscapes

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  1. Aeolian Process and LandformsDesert Landscapes Aeolus, Greek god of the winds

  2. Wind as a geomorphic agent 12 consecutive months with no precip < 10 in. precip 10 -20 in. precip requires fine grained sediment and little vegetation

  3. Arid and Semi-arid Tunisia Morocco Algeria Egypt Libya Sahel

  4. 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 > 2m. above ground

  5. Making the Sahara Desert • http://www.sciencefriday.com/videos/watch/10070

  6. by Salt Weathering Arches NP: Arch Formation

  7. 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

  8. Arch formation

  9. Wind Erosion • Deflation • Variations in lithology or cementation enable preferential wind scour • Desert pavement • Abrasion • Ventifacts

  10. Wind Transport • Saltation • bounce off the ground and other grains • effective < 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

  11. 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

  12. Aeolian Forms: Transport by Suspension • Loess • Grain size: 20-40 microns • Accumulation rates: fractions of mm’s/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

  13. 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

  14. Loess Strat • Soils separated by unweathered silt • Used to correlate with deep sea records of paleoclimate • Pleistocene • windier and drier glacial Interglacial, odd numbers

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