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  • 1. Wind Processes and Desert Landscapes
  • 2. Overview
    • Eolian (Aeolian) processes
      • Erosion
        • deflation and abrasion
      • Transport
        • saltation and surface creep
      • Deposition
        • sand dunes and loess
    • Desert landscapes
  • 3. Eolian Erosion
    • Abrasion
      • “ sandblasting”
        • ventifacts
    • Deflation
      • Occurs where there is a mixture of cobbles and gravel with finer material (typically sand)
      • Wind removes finer material, leaving only the cobbles and gravel (desert pavement)
  • 4.  
  • 5.  
  • 6. Eolian Transport
    • Suspension
    • Saltation
    • Creep
  • 7. Eolian Deposition
    • Heavier material drops out of the wind before lighter materials
      • Sand deposited before silt and clay particles
    • Deposition of sand forms sand dunes
    • Deposition of clay and silt forms loess
  • 8. Global Sandy Areas
  • 9. Global Loess Deposits
  • 10. Global Dry Regions
  • 11. Dune Processes
  • 12. Types of Sand Dunes
    • Several factors influence the formation of the various sand dune landforms
      • Strength of the wind
      • Prevailing wind vs. shifting winds
      • Presence of vegetation
      • Amount of sand present
    • Movement
      • Free Dunes
      • Tied Dunes
  • 13.  
  • 14.  
  • 15. Crescentic Dunes
    • Barchan
      • Free dunes
      • Scarce sand
      • Consistent and effective wind from one direction
      • Single slipface
      • Horns of crescent point downwind
    • Barchanoid Ridge
      • merged barchans
  • 16.  
  • 17.  
  • 18.  
  • 19.  
  • 20.
    • Transverse dunes
      • Free dunes
      • Abundant sand supply
      • Less effective wind
      • Consistent direction of the wind
      • Single slipfaces
  • 21.  
  • 22.
    • Parabolic
      • Tied dune
      • Vegetation stabilizes movement
      • Consistent wind direction
      • multiple slipfaces
      • crescents point upwind
  • 23.  
  • 24. Linear Dunes
    • Longitudinal
      • Winds variable in one direction
      • Ridge forms parallel to consistent wind direction
      • two slipfaces
      • 100 – 400 m tall, up to 100 km long
    • Seif
      • Sharp crest
      • shorter in height
  • 25.  
  • 26.  
  • 27.  
  • 28. Star Dunes
    • Star Dunes
      • Winds variable in all directions
      • Multiple slipfaces
      • With effective winds, form high mounds
      • With less effective winds, form networks of connected sinuous arms
  • 29.  
  • 30.  
  • 31.  
  • 32. Desert Landscapes
    • Arid areas are the largest climatic region on earth (35% of earth’s surface)
    • Fluvial features
      • Flash flooding
        • Washes, arroyos, wadis
        • Bursts of vegetation growth
      • Playas
        • interior drainage
        • salinization
      • Alluvial fans
        • bajadas
    • Landscape features
      • Adapted vegetation
      • Basin and Range Province
        • Horst and Graben, interior drainage, playas, alluvial fans
  • 33.  
  • 34.  
  • 35.  
  • 36.  
  • 37. Colorado River Issues
    • Headwaters originate in the Rocky Mountains
      • High levels of rainfall
      • Snow melt
    • Flows through an extremely arid area with few feeding tributaries
    • High demand on water means that often no water actually makes it to the sea
    • Flows through seven states, into Mexico
    • Beliefs on the river’s capacity based on a 400 year high mark (greatly overestimated)
    • Subject to a variety of political treaties and agreements regulating its flow
      • In many cases, quotas are exceeded, esp. with California
  • 38. Desertification
    • Refers to the expansion of desert biomes due to a combination of poor agricultural practices and climate change
      • grazing has been identified as a major cause
    • As a global phenomenon, this idea has largely been falsified
      • Areas identified as “desertifying” were simply experiencing drought-like conditions, in conjunction with ENSO cycles; many have recovered
    • There are some areas where desertification has occurred, but it is not a global phenomenon
  • 39.