1. Arid and Semi-Arid Landscapes
ESCI 307, Fall 2003, Lecture 14
About 10% of a non-polar desert is dune covered
1. Arid (Desert) has Precipitation (mm) < 10 x Temperature in oC
25o C Desert < 25 cm = 250 mm rain
2. UNESCO index
Desert Precipitation/Potential Evaporation < 0.25
Desert Aridity Index = Potential Evaporation/ Precipitation < 4.0
Skip Lawson's Theory pp

2. World's Deserts Types: subtropical, rain-shadow,
ESCI 307, Fall 2003, Lecture 14
about 1/5th of land
Types: subtropical, rain-shadow,
coastal, interior, polar

3. Semi-Arid Semi-arid (Steppe, Savannah, dry grassland) has
Precipitation (mm) > 10 x Temperature in oC but < than 20x
(c) Charles L. Smart. All rights reserved

4. Flash Floods Role of Desert Varnish, lack of plant cover Stream Flood
ESCI 307, Fall 2003, Lecture 14
Flash Floods
Role of Desert Varnish, lack of plant cover
Stream Flood
(c) Charles L. Smart. All rights reserved

5. Desert Landforms Produced By Water
ESCI 307, Fall 2003, Lecture 14
Desert Landforms Produced By Water
bahada
alluvial fan
Inselberg
playa
arroyo
pediment
playa

6. Arroyo - Water-Carved Canyon
ESCI 307, Fall 2003, Lecture 14
Usually dry

7. Playa, Salar, Sabkha A Playa in Death Valley, California
ESCI 307, Fall 2003, Lecture 14
Playa, Salar, Sabkha A Playa in Death Valley, California
Evaporite Pan of dried-up Playa

8. ESCI 307, Fall 2003, Lecture 14
Inselberg
Uluru (Ayers Rock)
Pediment

9. ESCI 307, Fall 2003, Lecture 14
Eolian Processes
We have been studying the physics of wind generated landforms when we consider sand grains in wind tunnels
Wind storm, Lothagam Hill dunes

10. Physics of Wind Transport
ESCI 307, Fall 2003, Lecture 14
Physics of Wind Transport
Sandstorm
Air has low density, so wind is a relatively minor agent of geomorphic change
Rock density 2000 times density same volume of air
so rock fragments are difficult to lift with air.
A one meter per second (1 m/sec) flow of water lifts the same particle as about 30 m/sec flow of air

11. ESCI 307, Fall 2003, Lecture 14
Toadstools
"Undercut, mushroom shaped pedestal rocks in desert areas are commonly attributed to wind erosion"
Ignore Bloom's comments p291 right 1 following the line above.
This area is frequently hit with high sandstorms. These remove the paint from our trucks.
Water and wind formed erosional features such as this toadstool

12. Wind-Borne Sediment causes deflation and abrasion
ESCI 307, Fall 2003, Lecture 14
Wind-Borne Sediment causes deflation and abrasion
Sahara to Caribbean
Effect on Hurricanes
Surface creep

13. Desert Pavements or Reg
ESCI 307, Fall 2003, Lecture 14
Desert Pavements or Reg
Note desert varnish, lack of sand, Iron Oxide over everything
Infiltration is slow – Flash Floods, and most water leaves the area

14. Desert Pavements (cont'd) –
ESCI 307, Fall 2003, Lecture 14
Desert Pavements (cont'd) –
Hammada (Hamada) = barren rock
Makes a great runway for supply aircraft
Just clear away a few big rocks
We tow makeshift rakes behind our Land Rovers
Desert Pavement
Source: Martin Miller

15. Erosional Landform - Deflation Hollow
ESCI 307, Fall 2003, Lecture 14
Erosional Landform - Deflation Hollow
Anecdote – How fast does this occur?

16. Abrasion Origin of Ventifacts
ESCI 307, Fall 2003, Lecture 14
Abrasion Origin of Ventifacts

17. Erosional Landforms - Ventifacts
ESCI 307, Fall 2003, Lecture 14
Wind eroded (sand blasted) surfaces

18. Erosional Landform - Yardangs
ESCI 307, Fall 2003, Lecture 14
Sphinx?
White Desert, Egypt

19. Deposition Landforms of Eolian Sands
ESCI 307, Fall 2003, Lecture 14
Deposition Landforms of Eolian Sands
Reduced wind velocity results in sediments deposition
Dunes are hills of loose wind-born sand
Size, shape, and orientation of dunes are determined by available sand, vegetation, and wind
Sand drift in Lee Of Mountains

20. Dunes form in a lee High velocity zone
ESCI 307, Fall 2003, Lecture 14
Dunes form in a lee
High velocity zone
Dunes are accumulations in the lee of local obstructions, possibly an upwind dune

21. Dune Migration Windward slope Slip face (deposition)
ESCI 307, Fall 2003, Lecture 14
Dune Migration
Windward slope
erosion and transport
Slip face (deposition)
Just like ripples in a stream

22. ESCI 307, Fall 2003, Lecture 14
Star Dunes

23. Star Dunes
Variable Wind Direction
Copyright © Frank Eckardt 2002

24. Longitudinal Dunes Constant wind direction, no vegetation
ESCI 307, Fall 2003, Lecture 14
Longitudinal Dunes
Constant wind direction, no vegetation

25. Longitudinal Dunes Constant wind direction, no vegetation
ESCI 307, Fall 2003, Lecture 14
Longitudinal Dunes
Constant wind direction, no vegetation

26. Transverse Dunes Massive volumes of sand, low consistent winds
ESCI 307, Fall 2003, Lecture 14
Massive volumes of sand, low consistent winds

27. Transverse Dunes Massive volumes of sand, low consistent winds
ESCI 307, Fall 2003, Lecture 14
Transverse Dunes
Massive volumes of sand, low consistent winds

28. Barchan Dunes Isolated Dunes, low sand supply, migrating across rock
ESCI 307, Fall 2003, Lecture 14
Isolated Dunes, low sand supply, migrating across rock

29. Barchan Dunes Isolated – low sand supply; migrating across rock
ESCI 307, Fall 2003, Lecture 14
Barchan Dunes
Isolated – low sand supply; migrating across rock

30. Parabolic Dunes Typical of coasts Horns pinned by plants
ESCI 307, Fall 2003, Lecture 14
Horns pinned by plants
Typical of coasts

31. Parabolic Dunes Stabilized “horns" point upwind
ESCI 307, Fall 2003, Lecture 14
Parabolic Dunes
Stabilized “horns" point upwind

32. Dunes in Victoria Crater - Mars
ESCI 307, Fall 2003, Lecture 14
Dunes in Victoria Crater - Mars

33. Suspended Load Transport and Deposition
ESCI 307, Fall 2003, Lecture 14
Suspended Load Transport and Deposition
In dry areas very high winds can suspend fine sand particles

34. ESCI 307, Fall 2003, Lecture 14
Suspended Load Dust

35. Loess from the Columbia River Basin
ESCI 307, Fall 2003, Lecture 14
Loess from the Columbia River Basin
Loess deposits are (usually) of glacial outwash silt. These thin downwind.

36. Global loess Origins Desert Glacial
ESCI 307, Fall 2003, Lecture 14
Global loess
Origins
Desert
Glacial
Layers of dust from Patagonia appear in Vostok cores just prior to interglacials

37. End Arid and semi-arid What type of dune? Wind
ESCI 307, Fall 2003, Lecture 14
End Arid and semi-arid
What type of dune?
Wind