Aeolian Process and Landforms Desert Landscapes Aeolus, Greek god of the winds

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

Arid and Semi-arid Egypt Libya Tunisia Algeria Morocco

Wind Erosion Deflation –removal of loose particles by wind –max effectiveness when grain size = 100  m –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

Making the Sahara Desert

by Salt Weathering Arches NP: Arch Formation

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

Arch formation

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

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

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

Aeolian Forms: Transport by Suspension Loess –Grain size: 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

Chinese Loess 247,000 mi 2 loess plateau Up to 300m thick Source: deserts of interior China and Tibet

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