1. Physical Geography Chapter 18
Arid Landscapes and Eolian Processes

2. Arid Landscapes & Eolian Processes
Eolian Erosion & Transportation
Eolian Deposition & Landforms
Human Interactions with Eolian Processes

3. Arid Landscapes 3 factors influence arid climates:
Subtropical high pressure
Rainshadow
Distance from large bodies of water

4. Desert Geomorphology
Water important to landforms in arid regions – little vegetation to slow intermittent erosion
Arroyo – steep-sided gully cut into alluvium
In undisturbed, horiz. rock layers more resistant sandstone or limestone forms flat caprock above easily eroded shale
Result is landforms flat on top w/steep sides:
Plateau -Canyon -Butte -Mesa
Pinnacle -Playa

5. Arroyo

6. Desert Landforms
Note: Tops of most landforms once part of same surface, since partially eroded away

7. Playa

8. Eolian Erosion and Transport
Wind-based processes important in deserts b/c:
Strong winds common in desert
Large supply of sand & silt to be blown
Vegetation minimal – wind free to erode

9. Threshold Velocity for wind to carry different sized particles
Fluid Behavior of Wind
Wind acts like a fluid, like water, but less dense
Faster wind can move larger particles
Threshold Velocity for wind to carry different sized particles

10. Particle Transport Silts and Clays carried in suspension
Sand bounces along – saltation, or
Sand rolls slowly along – creep

11. Eolian Erosional Landforms
2 types of wind erosion:
Deflation – wind blows loose soil away:
leaves coarser pebbles & cobbles, called Desert Pavement
when deflation causes basin to form, called Deflation Hollow

12. Eolian Erosional Landforms
Abrasion – wind blows sand along a surface to polish & abrade it
Ventifacts – rocks shaped by abrasion: pitted, grooved, polished
Yardangs – elongated, wind-sculpted ridges caused by abrasion

13. Eolian Erosional Landforms
Deflation/Desert Pavement

14. Eolian Erosional Landforms
Abrasion
Ventifacts
Yardangs

15. Loess
Fine-grained, wind-blown silt – high in calcium – usually from alluvial deposits or glacial till
Can be transported farther than sand

16. Loess Deposits around the World
Arid Landscapes and Eolian Processes
Loess Deposits around the World
Loess Deposits

17. Loess Terraces

18. Human Impact/Desertification
Desertification – transforming a vegetated landscape to one that is barren & susceptible to wind erosion
Population pressure has forced more people to clear marginal, semi-arid-to-arid land for agriculture & firewood
In wind, cleared land loses topsoil and nutrients
Vegetation unlikely to reestablish

19. Regions Prone to Desertification

20. Desertification in African Sahel
Semi-arid region in transition region from Sahara Desert in north to rainforest in south
Traditionally nomadic herders & small, sedentary farmers – north-south migrations to follow rain
Into 20th century, European borders & resource exploitation made people more sedentary – over-cultivation of soil, overgrazing, and tree removal
Add in extended drought since late 1960s, & you have desertification

21. The Sahel

22. Desertification in Great Plains
Great Plains lie east of Rocky Mts in semi-arid climate with short grass as dominant natural vegetation
Dust Bowl Region

23. Desertification in Great Plains
Early 1900s Americans moved to region to farm, plowing and clearing native grasses – unusually wet period
1930s – terrible drought hits – topsoil blows into dust storms – called “Dust Bowl”
Many migrated to California & elsewhere
Those who stayed have employed irrigation & soil conservation, including windbreaks, and conservation tillage