Characteristics of Deserts

3. Characteristics of Deserts Characteristics of Deserts Besides being dry Besides being dry > few plants > few plants > consist of nearly continuous rock > consist of nearly continuous rock and/or sand exposures and/or sand exposures > > little soil development little soil development • Weathering, erosion, & deposition • Weathering, erosion, & deposition still operate, but more slowly. still operate. > In a balance with the local climate > in a balance with the local climate

4. The Distribution of Deserts The Distribution of Deserts • Deserts form in two regions • Deserts form in two regions > areas of persistent high pressure > areas of persistent high pressure - - latitude effects related to Hadley Cell latitude effects related to Hadley Cell circulation circulation > Areas on the lee side of Topographic > Areas on the lee side of Topographic Barriers (lee= downwind side) barriers - - rainshadow effect rainshadow effect > other things influence too > other things influence too - - cold water ocean currents cold water ocean currents - - extremely cold temperatures extremely cold temperatures

5. Area of persistent arid conditions (sub-tropical desert)

6. Distribution of Arid and Semiarid Regions Distribution of Arid and Semiarid Regions • Subtropical deserts occur at 20-30° N-S latitude. Gobi Mojave Sonoran Chihuahuan Thar Sahara Arabian Atacama Kalahari Namib Australian Patagonian Antarctica

7. Rainshadow Deserts Rainshadow Deserts • Air that must cross coastal mountains loses much of its moisture, thus when it arrives over the inland areas it is drier.

8. Distribution of Arid and Semiarid Regions Distribution of Arid and Semiarid Regions • Rainshadow deserts occur in places down wind of major mountain chains like the Himalayas, Sierra Nevadas, and Andes.

9. Weathering and Soils Weathering and Soils • Mechanical weathering dominates desert regions. • Chemical weathering is not effective > Rock varnish is a thin coating of iron and/or manganese oxides on many surface rocks in deserts.

10. Agents of Change Agents of Change • Water • Water > scarce > scarce > when it rains, it really rains hard! > when it rains, it really rains hard! > erodes and deposits distinct landforms > erodes and deposits distinct landforms - - no plants to slow erosion down no plants to slow erosion down • Wind • Wind > common > common > lack of plants facilitates effectiveness as an > lack of plants facilitates effectiveness as an agent of change. agent of change. > erodes and deposits distinct landforms > erodes and deposits distinct landforms

11. Exotic & Local Streams Exotic & Local Streams Local braided streams in deserts flow • • . . infrequently- known as Arroyos • Arroyos usually exhibit braided channels • Arroyos usually exhibit braided channels > coarse-grained sediments > coarse-grained sediments > prone to severe flash floods! > prone to severe flash floods! • Exotic Streams • Exotic Streams > Perennial rivers that begin outside the desert > Perennial rivers that begin outside the desert - - Nile River, Egypt. Nile River, Egypt. - - Colorado River, Southwest US. Colorado River, Southwest US. > Can be either Meandering or Braided > Can be either Meandering or Braided

12. Arroyo- a dry, often braided stream channel in the desert

13. Nile River: An exotic stream

15. Playa lakes

16. Alluvial Fan

17. Inselbergs Inselbergs • are isolated mountains composed of more resistant rock types. • Location: Ayers Rock in central Australia.

19. New Mexico Buttes Mesa Mesa

20. Wind is a common agent of erosion and deposition in deserts The dust storm shown below transports sand, silt and clay across the Sahara desert in North Tunisia

23. Desert pavement with Inselberg

26. QTVR of dune crest

27. Barchan Barchan Dunes

28. Transverse Dunes Transverse

29. Parabolic (Blowout) Parabolic Dunes

30. Longitudinal Dunes Longitudinal

31. Star Dunes Star