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
Libya
Egypt
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
Making the Sahara Desert
• http://www.sciencefriday.com/videos/watch/10070
Arches NP:
Arch Formation
by Salt
Weathering
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: 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
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
Loess Strat
glacial
• Soils separated by
unweathered silt
• Used to correlate with
deep sea records of
paleoclimate
• Pleistocene
– windier and drier
Interglacial, odd numbers