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Unformatted text preview: Chapter 12 Wind Processes and Desert Landscapes Wind Processes and Desert Landscapes Like water, wind is agent of geomorphic change Causes erosion, transportation and deposition Does not have as much force as water because it has lower viscosity (is thinner) Deserts: lack of moisture and stabilizing vegetation wind is dominant agent of change Wind Eolian processes refer to wind erosion, transportation, deposition Air less dense than water and ice, so ability of wind to move materials is small in comparison Two main wind erosion processes: Deflation Abrasion Deflation Loose or non-cohesive sediment blown away Can result in desert pavement Pebbles and gravel left behind with no sand filler Area can become deflated to a point where a basin forms blowout depression Less than meter up to hundreds of meters (or even miles) wide Chemical weathering removes materials that cement particles together, making them more likely to get blown away Many large depressions in Sahara Desert (one is almost 7000 sq. miles) Abrasion Similar to sandblasting Wind blown particles like sand continuously blown against rock polish or abrade rock away Abrasive action usually occurs in area immediately above ground sand grains relatively heavy and cannot be lifted very high Rocks become pitted, grooved or polished Rocks eroded by abrasion are called ventifacts (vent = wind) Rock structures can take on wind-blown appearance Alignment is parallel to wind direction Yardangs elongated rocks or ridges (meters to kilometers in length) Abrasion on windward side Eolian Transportation Fine particles (dust) can travel great distances think of fluvial processes Dust can be lifted much higher than heavier particles, like sand Dust can be blown over great distances dust storms Sand can only be lifted about 2 meters (6.5 ft.) Dust Bowl 1930s Poor agricultural practices and years of sustained drought caused the Dust Bowl Plains grasslands had been deeply plowed and planted to wheat During the years when there was adequate rainfall, the land produced bountiful crops Droughts in the early 1930s Farmers kept plowing and planting and nothing would grow The ground cover that held the soil in place was gone -- deflation Eolian Transportation Wind not significant in actual weathering process Plays important role in transportation of weathered materials Saltation similar process to fluvial one Due to wind, grains of sand skip and bounce along ground surface Due to saltation, particles collide with other particles and knock them loose and forward Result is surface creep particles that are too large for saltation roll and slide Depositional Landforms...
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- Spring '08