1. Deserts Geologic processes in arid climates
Role of water in arid climates
Streams are dry most of the time
Desert streams are said to be ephemeral
Flow only during periods of rainfall
Different names are used for desert streams including wash, arroyo, wadi, donga, and nullah

2. Deserts Geologic processes in arid climates
Role of water in arid climates
Desert rainfall
Rain often occurs as heavy showers
Causes flash floods
Poorly integrated drainage
Most erosional work in a desert is done by running water

3. A dry stream channel in the desert
Figure 6.28 A

4. The same stream channel following heavy rainfall
Figure 6.28 B

5. Deserts Basin and Range: the evolution of a desert landscape
Uplifted crustal blocks
Interior drainage into basins produces
Alluvial fans and bajadas
Playas and playa lakes

6. Deserts Basin and Range: the evolution of a desert landscape
Erosion of mountain mass causes local relief to continually diminish
Eventually mountains are reduced to a few large bedrock knobs called inselbergs projecting above a sediment-filled basin

7. Landscape evolution in a mountainous desert – early
Figure 6.29 A

8. Landscape evolution in a mountainous desert – middle
Figure 6.29 B

9. Landscape evolution in a mountainous desert – late
Figure 6.29 C

10. Deserts Wind erosion Deflation Abrasion Lifting of loose material
Produces
Blowouts
Desert pavement
Abrasion

11. Formation of desert pavement
Figure 6.34

12. Deserts Types of wind deposits Loess Deposits of windblown silt
Extensive blanket deposits
Primary sources are deserts and glacial stratified drift

13. Deserts Types of wind deposits Sand dunes
Mounds and ridges of sand formed from the wind’s bed load
Characteristic features
Slip face – the leeward slope of the dune
Cross beds – sloping layers of sand in the dune

14. Formation of sand dunes
Figure 6.37

15. Sand dune types
Figure 6.38

16. Sand dunes in the western United States