1. Deserts

2. Definition
Desert:
A region so arid that it contains no permanent streams except for those that bring water in from elsewhere, and has very sparse vegetation cover.
NOT related to temperature!
Deserts can be
Hot (>35 °C)
Cold (< 20 °C)

3. Location Dry regions cover 30 percent of Earth’s land surface
Two climatic types are commonly recognized
Desert or arid
Steppe or semiarid

4. Location of Deserts

6. Earth’s dry regions coincide with the subtropical high pressure belts & solar heating

7. Types of deserts Classified by location Subtropics
Low-latitude deserts
In the vicinities of the Tropics of Cancer and Capricorn
Areas of high pressure and sinking air that is compressed and warmed

8. Types of deserts Classified by location Middle-latitudes
Located in the deep interiors of continents
High mountains in the path of the prevailing winds produce a rainshadow desert

9. Types of deserts Classified by environment in which they are formed
subtropical: in the hot dry latitudes between 20 and 30°, both north and south
rain shadow: on the landward side of coastal mountain ranges
coastal: along coasts bordering cold ocean currents
continental interior: deep within continents, far from major water sources
polar: in the cold dry polar regions, both north and south

10. Formation of Coastal Deserts

11. Source: http://en.wikipedia.org/wiki/Desert
Deserts of Australia
Source:

12. The Saharan Desert
A satellite image of the Sahara, the world's largest hot desert and second largest desert after Antarctica. Source:

13. Weathering & Erosion in Deserts
Not as effective as in humid regions
Mechanical weathering
forms unaltered rock and mineral fragments
Wind
Water
Chemical weathering (rare)
caliche-rich soils
desert varnish

14. Water Erosion 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

16. Water Erosion 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

17. A dry stream channel in the desert

18. The same stream channel following heavy rainfall

19. Wind erosion Differs from that of running water in two ways
Wind is less capable of picking up and transporting coarse materials
Wind is not confined to channels and can spread sediment over large areas

20. Wind erosion Mechanisms of transport Bedload Suspended load
Saltation – skipping and bouncing along the surface
Suspended load
In the air as duststorms

21. Wind erosion Mechanisms of wind erosion Deflation
Lifting of loose material
Produces
Blowouts
Desert pavement

22. Deflation & Desert Pavement

23. Wind erosion Mechanisms of wind erosion Abrasion
Produces ventifacts (stones with flat faces) and yardangs (wind sculpted ridges)
Limited in vertical extent

24. Water Deposits (alluvium)
Playa
Lake Hart, S. Australia
Talus Aprons Source: Andrew Alden, licensed to About.com, Inc.
Alluvial Fans Source:
Bajada Source:

25. Wind deposits Dunes Mounds or ridges of sand
Often asymmetrically shaped
Characteristic features
Slip face
Cross beds

26. Wind deposits

27. Types of sand dunes

28. Types of sand dunes

29. Wind deposits Loess Deposits of windblown silt
Extensive blanket deposits
Primary sources are deserts and glacial stratified drift

30. Desert Landforms

31. Desert Landforms
Rocky desert areas change over time

32. Desert Landforms
Rocky desert areas change over time

33. Desert Landforms

34. 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
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

35. Basin and Range landscape

36. Landscape evolution in a mountainous desert – early stage

37. Landscape evolution in a mountainous desert – middle stage

38. Landscape evolution in a mountainous desert – late stage

39. Inselbergs in Southern California

40. ~ End ~