1. Deserts & Aeolian Processes

2. Distribution and causes of dry lands
Dry regions cover 30 percent of Earth’s land surface
Two climatic types are commonly recognized
Desert or arid
Steppe or semiarid

3. AOLIAN: WIND LANDFORMS COASTAL LANDFORMS
WIND AND WAVES
AOLIAN: WIND LANDFORMS
COASTAL LANDFORMS

4. WIND EROSIAN
SALTATION: SAND GRAINS MOVED BY THE WIND IN A SERIES OF JUMPS AND
AND BOUNCES.

7. WIND EROSIAN
DEFLATION: THE PROCESS BY WHICH WIND REMOVES THE TOP LAYER OF FINE VERY DRY SOIL OR ROCK PARTICLES AND LEAVE BEHIND LARGE ROCK PARTICLES. THESE PARTICLES OFTEN FORM A DENSLY PACKED SURFACE CALLED DESERT PAVEMENT

8. Wind Erosion Two forms of wind erosion Deflation
Removal of material by wind transport
Abrasion
Mechanical weathering of rock by wind blown sand

9. DEFLATION PROCESS

10. blowout and pillar formation
deserts: wind action
blowout and pillar formation
wind picks
up dry fine
sediment
and creates
blowout
vegetation holds
sediment
in place
and forms
pillar

11. DEFLATION AND DESERT PAVEMENT

12. Wind Erosion Two forms of wind erosion Deflation
Removal of material by wind transport
Abrasion
Mechanical weathering of rock by wind blown sand

13. WIND EROSIAN
VENTIFACTS: ROCKS PITTED, GROOVED OR POLISHED BY WIND ABRASION

14. ventifacts …wind blowing in one direction abrades up wind rock faces…

15. deserts: wind action dust suspended by wind ventifacts
…larger sand grains move by saltation (bouncing)…
ventifacts
formed by sand grains moving in high speed winds
“sand blasting”

16. Wind in the desert Wind deposits Two types of wind deposits Dunes
Slow migration of dunes in the direction of wind movement
Several types of sand dunes including barchan, transverse, longitudinal, parabolic and star dunes

17. dunes

18. deserts: wind action sand dunes: mounds of loose sand piled up by wind
• large sand supply
• winds that blow in same direction
sand erodes from and
blows up the
slope facing the wind
sand falls down the
down wind slope
(slipface)
and deposits
(calm air)
dune migrates through time

19. WIND DEPOSITION DUNES: MOUNDS OF WIND DEPOSITED SAND
TYPES: BARCHAN: CRESCENT SHAPED DUNES
PARABOLIC DUNES: U SHAPED DUNES FORM WHEN PLANTS ANCHOR THE EDGES OF BARCHAN DUNES CAUSING AN INVERTED U SHAPE

20. types of sand dunes barchan • crescent shaped • horns point down wind
• steep slip face on concave side
one direction of wind and limited sand supply

21. types of sand dunes parabolic • deeply curved
• horns anchored by vegetation
• convex in down wind direction (opposite to barchans)
one direction of wind and large sand supply

22. types of sand dunes barchan parabolic transverse longitudinal
controlled by dominant wind direction(s) and amount of sand
barchan
parabolic
transverse
longitudinal

23. ancient sand dunes

24. Sand dune migration

26. WIND DEPOSITION LONGITUDINAL DUNES: LIE PARALLELL TO THE WIND
TRANSVERSE DUNES: LIE PERPENDICULAR TO THE WIND (THESE LOOK LIKE WIND RIPPLES)

27. types of sand dunes longitudinal
• extremely long, high (100’s of meters), and straight
• long axis parallel to prevailing wind direction
• regularly spaced
• area between dunes is swept clean of sand
• cross winds may be important
large sand supply -- mechanism not fully understood

28. types of sand dunes transverse • straight • elongate • steep slip face
one direction of wind and large sand supply

31. Wind deposits
Significant depositional landforms are created by wind in some regions
Two types of wind deposits
Dunes
Mounds or ridges of sand
Often asymmetrically shaped
Windward slope is gently inclined and the leeward slope is called the slip face

33. Wind deposits Loess Blankets of windblown silt
Two primary sources are deserts and glacial outwash deposits
Extensive deposits occur in China and the central United States

34. sand pillar

35. deserts: wind action
loess: wind deposited clay and silt sized particles …sources are glacial outwash and playas
forms fertile soils that erode easily
Dust Bowl of 1930’s produced by
erosion of loess during drought

36. global distribution of loess deposits

38. deserts: wind action important agent for transportation and erosion
…caused by large daily temperature and pressure changes…
dust storms
occur if fine grained sediments are available

39. dust storm