Chapter18 wind erosion and deposition

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Transcript of Chapter18 wind erosion and deposition

  • Chapter 18: Arid Region Landforms and Eolian Processes Physical Geography Ninth Edition Robert E. Gabler James. F. Petersen L. Michael Trapasso Dorothy Sack
  • Arid Region Landforms and Eolian Processes
  • 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
  • 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?
  • 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
  • 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
  • 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
  • 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
  • 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?
  • 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
  • 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
  • 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
  • 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
  • 18.2 Water as a Geomorphic Agent in Arid Lands
    • Arid Region Landforms of Fluvial Erosion
      • Mesas
      • Buttes
      • Monument Valley (Utah and Arizona)
  • 18.2 Water as a Geomorphic Agent in Arid Lands
    • Arid Region Landforms of Fluvial Erosion
      • Pediment
        • Gentle retreat of steep mountain front
      • Inselbergs
  • 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
  • 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
  • 18.2 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
  • 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
  • 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
  • 18.3 Wind as a Geomorphic Agent
    • Eolian
      • Landform created by wind
      • Less effective than water