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

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