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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 Æ 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 Æ 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 Æ 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 Æ 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
- Sonoran Desert, DESERT LANDSCAPES, north american deserts, Desert Landscapes Wind, maf Water allocations