Diagram of a Sand Dune

 
Peralta Colleges, Physical Geography
Rita D. Haberlin, Instructor
DESERT LANDFORMS STUDY GUIDE

CHIEF IDEAS:

  1. Over 30% of the earth's land surface is classified as desert. Desert landforms tend to be angular rather than rounded as they are in humid areas. Weathering takes place slowly in deserts. Running water is a more important process than wind in shaping most desert landforms. Deserts have less vegetation to protect the land from sudden rainstorms.

  2.  
  3. Streams are usually short and short lived. After rainstorms, flash floods rush out of narrow box canyons over alluvial fans and onto the desert floor. Most desert streams end up in internal drainage basins rather than the sea. Exotic rivers are exceptions as they originate in more humid regions and flow across deserts to the sea (e.g., Nile, Colorado, and Indus rivers).

  4.  
  5. In the Great Basin of the American Southwest, the landscape consists of fault block basins and ranges. The ranges are eroded by streams that deposit sediments into the basins. At the center of the basins, fine silt and salts accumulate in playa lakes. These playa lakes evaporate into saltflats. Over time, erosion lowers the mountains into a pediment, a sloping bedrock surface. Eventually, the whole landscape is reduced to a surface of low relief called a pediplain with a few remnant mountains (or inselburgs).

  6.  

    On the diagram below showing desert landforms in the Great Basin, identify the alluvial fan, box canyon, fault line, pediplain, and playa.
     Diagram of desert landforms in the Great Basin
     
    A_________________________________
    B_________________________________
    C_________________________________
    D_________________________________
    E_________________________________
     

  7. In the Colorado Plateau, horizontal rock layers are sculptured by streams into plateaus, mesas, buttes, and badlands. The Grand Canyon has a "stair-step" landscape of hard rock layers forming cliffs and softer rock layers forming benches.

  8.  
  9. Wind erosion in the desert takes two forms:  abrasion and deflation. Sand abrasion is most prevalent within the first three feet of the ground and tends to form mushroom rocks and desert pavement. During dust storms, dust sized particles may be lifted into the air causing blow-outs (shallow depressions).

  10.  
  11. Fine wind-blown dust may get transported across entire continents and eventually accumulate as loess, a soft, easily eroded material that is cemented by calcium carbonate.

  12.  
  13. Sand dunes are depositional features that are shaped by the wind. Active dunes are constantly moving. Barchan dunes and transverse dunes develop at right angles to the wind. Sand dunes move slowly downwind as sand is removed from the gentle upwind slope and is deposited on the slip face downwind. Longitudinal dunes parallel the wind. Dune types depend upon wind strength and direction, sand supply, and vegetation.

 

STUDY OBJECTIVES:

  1. Describe the percentage of the land surface classified as desert. How do desert landforms differ from landforms in humid regions.
  2. Describe the characteristics of desert streams.
  3. Describe the formation of alluvial fans, playas, pediments, pediplains, and inselburgs in the basins and ranges of the Great Basin of the American Southwest.
  4. Describe the formation of plateaus, mesas, buttes, cliffs, benches and badlands in the horizontal strata of the Colorado Plateau.
  5. Describe two ways in which wind erodes. Name the landforms produced by wind erosion.
  6. Define and explain the origin of loess.
  7. Describe the role of the wind in shaping and moving transverse dunes, blow-out dunes, and longitudinal dunes.

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