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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