Chapter18 wind erosion and deposition
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Chapter18 wind erosion and deposition

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  • Insert cover image for Chapter 18 (p. 490)
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Transcript

  • 1. Chapter 18: Arid Region Landforms and Eolian Processes Physical Geography Ninth Edition Robert E. Gabler James. F. Petersen L. Michael Trapasso Dorothy Sack
  • 2. Arid Region Landforms and Eolian Processes
  • 3. Arid Region Landforms and Eolian Processes
    • Running water does more geomorphic work than wind
      • Eolian geomorphic processes are those caused by wind
      • Arid regions provide a unique opportunity to study geomorphology as there is little vegetation
  • 4. 18.1 Surface Runoff in the Desert
    • Desert Characteristics
      • Lack of precipitation
      • High evaporation rates
      • Sparse vegetation
      • Low weathering rates and insufficient vegetation result in little moisture-retention soil
      • Running water very effective in shaping land
      • Q: Why do you think the drainage density is so high here?
  • 5. 18.1 Surface Runoff in the Desert
    • Paleogeography
      • Most deserts have not always been arid
      • Evidence:
        • Deposits
        • Wave-cut shorelines of extinct lakes
        • Immense canyons occupied by streams far too small to have eroded such a large valley
  • 6. 18.1 Surface Runoff in the Desert
    • Running Water in Deserts
      • Ephemeral channels
      • Lose water through infiltration
      • Abundance of coarse sediments
      • Braided channels
      • Discharge rates
        • Downstream decrease:
          • Infiltration
          • Evaporation
  • 7. 18.1 Surface Runoff in the Desert
    • Many desert streams terminate before sea
      • Cause
        • Diminishing discharge
        • Mountains block stream
      • Terminate in depressions and form shallow, ephemeral lakes
      • Interior drainage
  • 8. 18.1 Surface Runoff in the Desert
    • Regional base level
      • Stream that terminates in interior
      • Tectonic Activity can change regional base level
        • Floors below sea level
          • Death Valley, CA
          • Dead Sea, Middle East
          • Turfan Basin, China
          • Lake Eyre, Australia
  • 9. 18.1 Surface Runoff in the Desert
    • Many desert streams terminate before sea
      • Streams that originate in humid climates
        • Humboldt River, Nevada
        • Q: Was the gorge eroded by the streams with this amount of flow?
  • 10. 18.1 Surface Runoff in the Desert
    • Exotic Streams
      • Rivers that successfully traverse the desert and make it to the sea
        • Nile (Egypt and Sudan)
        • Tigris-Euphrates (Iraq)
        • Indus (Pakistan)
        • Murray (Australia)
      • Colorado River
        • Usually does not make due to human use
  • 11. 18.2 Water as a Geomorphic Agent in Arid Lands
    • Arid Region Landforms of Fluvial Erosion
      • Channels of ephemeral streams
        • Washes (arroyos)
        • Barrancas (Latin America)
        • Wadis (N. Africa and SE Asia)
      • Braided channels
      • Prone to flash floods
  • 12. 18.2 Water as a Geomorphic Agent in Arid Lands
    • Arid Region Landforms of Fluvial Erosion
      • Dense network of barren slopes (Badlands)
        • High drainage density
        • Dakotas
        • Death Valley, CA
        • Big Bend, TX
        • S. Alberta
  • 13. 18.2 Water as a Geomorphic Agent in Arid Lands
    • Arid Region Landforms of Fluvial Erosion
      • Plateau
        • Extensive, elevated region with fairly flat top
        • Horizontal rock layers
        • Colorado Plateau
      • Grand Canyon
        • Exposes the horizontal rock layers
        • Rim of Grand Canyon called caprock
  • 14. 18.2 Water as a Geomorphic Agent in Arid Lands
    • Arid Region Landforms of Fluvial Erosion
      • Mesas
      • Buttes
      • Monument Valley (Utah and Arizona)
  • 15. 18.2 Water as a Geomorphic Agent in Arid Lands
    • Arid Region Landforms of Fluvial Erosion
      • Pediment
        • Gentle retreat of steep mountain front
      • Inselbergs
  • 16. 18.2 Water as a Geomorphic Agent in Arid Lands
    • Arid Region Landforms of Fluvial Deposition
      • As flow of stream decreases, capacity decreases, which increases deposition
      • Alluvial Fans
        • Channels may flare out onto open plains
        • Sediment deposited along base of highlands
        • Fan apex
  • 17. 18.2 Water as a Geomorphic Agent in Arid Lands
    • Arid Region Landforms of Fluvial Erosion
      • Alluvial fan
        • Course sediment (boulders and cobbles) near fan apex
        • Steepness decreases downslope
        • Debris flow fans
  • 18. 18.2 Water as a Geomorphic Agent in Arid Lands
    • Arid Region Landforms of Fluvial Erosion
      • Bajada
        • Alluvial fans joined together
        • Q: Why would a series of alluvial fans have a tendency to eventually join to form a bajada?
      • Piedmont alluvial plain
  • 19. 18.2 Water as a Geomorphic Agent in Arid Lands
    • Playas
      • Bolsons
        • Desert basins of interior drainage surrounded by mountains
      • Playa
        • Lowest part of bolson
        • Fine-grained bed of ephemeral lake
        • Pan
  • 20. 18.2 Water as a Geomorphic Agent in Arid Lands
    • Playas
      • Salt crust playas (salt flats or salinas)
      • Bonneville Salt Flat, UT
        • Speed record
      • Edwards Air Force Base, CA
        • Space shuttle landings
  • 21. 18.3 Wind as a Geomorphic Agent
    • Eolian
      • Landform created by wind
      • Less effective than water
      • Wind Erosion and Transportation
        • Deflation
        • Suspension
        • Surface creep
        • Ripples
  • 22. 18.3 Wind as a Geomorphic Agent
    • Wind Erosion & Transportation
      • Deflation
      • Surface creep
      • Ripples
      • Abrasion
  • 23. 18.3 Wind as a Geomorphic Agent
    • Wind Erosion & Transportation
      • Dust Storms
      • Sandstorms
      • Deflation hollows
      • Q: Can you suggest a continent that might be a source of major dust storms today?
  • 24. 18.3 Wind as a Geomorphic Agent
    • Wind Erosion & Transportation
      • Desert pavement (gibber)
      • Q: Is desert pavement a surface indestructible by human activities? Why?
      • Ventifacts
        • Individual wind-fashioned rocks
  • 25. 18.3 Wind as a Geomorphic Agent
    • Wind Erosion & Transportation
      • Pedestaled, or balanced rock
        • Forms as a result of physical and chemical weathering
      • Q: What other processes or rock factors could account for such an unusual shape?
  • 26. 18.3 Wind as a Geomorphic Agent
    • Wind Erosion & Transportation
      • Yardang
        • Wind sculpted remnant ridge, often of easily eroded rock
      • Q: Which is the upwind side of the yardang?
  • 27. 18.3 Wind as a Geomorphic Agent
    • Wind Deposition
      • Sand dunes
      • Loess
        • Fine grained sediment (e.g. silt) can be transported in suspension long distances before blanketing and modifying the existing topography
  • 28. 18.3 Wind as a Geomorphic Agent
    • Sand Dunes
      • Result of wind deposition
      • Sand seas
        • Seemingly endless dune regions
      • Small dune fields (coast)
      • Dune topography
        • Sand sheets
        • Q: Why are coastlines such good locations for dune formation?
  • 29. 18.3 Wind as a Geomorphic Agent
    • Sand Dune Classification
      • Active
        • Slip face
        • Angle of repose (35 o )
      • Stabilized
      • Q: These stabilized dunes are crossed by vehicle trails. How might these trails affect the stabilized dunes?
  • 30. 18.3 Wind as a Geomorphic Agent
    • Sand Dune
      • When wind and velocity are constant, a dune can move forward by downward transfer of sediment
      • Blowout
  • 31. 18.3 Wind as a Geomorphic Agent
    • Q: Explain how plants can stabilize dunes.
  • 32. 18.3 Wind as a Geomorphic Agent
    • Types of Sand Dunes
      • Classified according to shape and relationship to the wind
      • Barchans (crescent-shaped dune)
  • 33. 18.3 Wind as a Geomorphic Agent
    • Types of Sand Dunes
      • Parabolic dunes
      • Transverse dunes
      • Longitudinal dunes
      • Star dunes
  • 34. 18.3 Wind as a Geomorphic Agent
    • Longitudinal Dune, Sahara Desert
    • Q: Estimate the ground length of the dunes in this satellite image.
  • 35. 18.3 Wind as a Geomorphic Agent
    • Dune Protection
      • Recreation
      • Fragile environment
        • White Sands, NM
        • Great Sand Dunes, CO
        • Cape Cod, MA
      • Q: Why should some dune driving need to be protected from human activities such as driving dune buggies and other recreational vehicles?
  • 36. 18.3 Wind as a Geomorphic Agent
    • Loess Deposits
      • Wind can carry in suspension dust-sized particles for thousands of km before depositing them
        • Gobi Desert, China (30-90m thick)
        • American Midwest
    • Q: Where is the origins of these loess deposits?
  • 37. 18.3 Wind as a Geomorphic Agent
    • Loess Deposits
    • Q: Why might the instability of loess cliffs be a problem?
  • 38. 18.4 Landscape Development in Deserts
    • Geomorphic differences between arid and humid climates
      • Expanse of bedrock
      • Lack of continuous water flow
      • Eolian process plays a greater role
      • Fault-block mountains in the Great Basin range
        • Orographic
        • Warner mountains
        • Panamint range
  • 39. 18.4 Landscape Development in Deserts
    • A False-color satellite image of Death Valley, CA
    • Panamint range to SW
      • Q: Why do you think the white areas are in the center of the valley?
  • 40. 18.4 Landscape Development in Deserts
    • Alluvial fans and playas (interior drainage)
    • Pediments and inselbergs (tectonically stable since a distant period of mountain formation
  • 41. 18.4 Landscape Development in Deserts
    • Inselbergs
      • Erosional remnant
      • Uluru (Ayers Rock), Australia
  • 42. 18.4 Landscape Development in Deserts
    • Green River Overlook, Utah
    • Q: What aspects of this environment make this an attractive landscape?
  • 43. Physical Geography End of Chapter 18: Arid Region Landforms and Eolian Processes