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  1. 1. Wind Processes and Desert Landscapes
  2. 2. Overview <ul><li>Eolian (Aeolian) processes </li></ul><ul><ul><li>Erosion </li></ul></ul><ul><ul><ul><li>deflation and abrasion </li></ul></ul></ul><ul><ul><li>Transport </li></ul></ul><ul><ul><ul><li>saltation and surface creep </li></ul></ul></ul><ul><ul><li>Deposition </li></ul></ul><ul><ul><ul><li>sand dunes and loess </li></ul></ul></ul><ul><li>Desert landscapes </li></ul>
  3. 3. Eolian Erosion <ul><li>Abrasion </li></ul><ul><ul><li>“ sandblasting” </li></ul></ul><ul><ul><ul><li>ventifacts </li></ul></ul></ul><ul><li>Deflation </li></ul><ul><ul><li>Occurs where there is a mixture of cobbles and gravel with finer material (typically sand) </li></ul></ul><ul><ul><li>Wind removes finer material, leaving only the cobbles and gravel (desert pavement) </li></ul></ul>
  4. 6. Eolian Transport <ul><li>Suspension </li></ul><ul><li>Saltation </li></ul><ul><li>Creep </li></ul>
  5. 7. Eolian Deposition <ul><li>Heavier material drops out of the wind before lighter materials </li></ul><ul><ul><li>Sand deposited before silt and clay particles </li></ul></ul><ul><li>Deposition of sand forms sand dunes </li></ul><ul><li>Deposition of clay and silt forms loess </li></ul>
  6. 8. Global Sandy Areas
  7. 9. Global Loess Deposits
  8. 10. Global Dry Regions
  9. 11. Dune Processes
  10. 12. Types of Sand Dunes <ul><li>Several factors influence the formation of the various sand dune landforms </li></ul><ul><ul><li>Strength of the wind </li></ul></ul><ul><ul><li>Prevailing wind vs. shifting winds </li></ul></ul><ul><ul><li>Presence of vegetation </li></ul></ul><ul><ul><li>Amount of sand present </li></ul></ul><ul><li>Movement </li></ul><ul><ul><li>Free Dunes </li></ul></ul><ul><ul><li>Tied Dunes </li></ul></ul>
  11. 15. Crescentic Dunes <ul><li>Barchan </li></ul><ul><ul><li>Free dunes </li></ul></ul><ul><ul><li>Scarce sand </li></ul></ul><ul><ul><li>Consistent and effective wind from one direction </li></ul></ul><ul><ul><li>Single slipface </li></ul></ul><ul><ul><li>Horns of crescent point downwind </li></ul></ul><ul><li>Barchanoid Ridge </li></ul><ul><ul><li>merged barchans </li></ul></ul>
  12. 20. <ul><li>Transverse dunes </li></ul><ul><ul><li>Free dunes </li></ul></ul><ul><ul><li>Abundant sand supply </li></ul></ul><ul><ul><li>Less effective wind </li></ul></ul><ul><ul><li>Consistent direction of the wind </li></ul></ul><ul><ul><li>Single slipfaces </li></ul></ul>
  13. 22. <ul><li>Parabolic </li></ul><ul><ul><li>Tied dune </li></ul></ul><ul><ul><li>Vegetation stabilizes movement </li></ul></ul><ul><ul><li>Consistent wind direction </li></ul></ul><ul><ul><li>multiple slipfaces </li></ul></ul><ul><ul><li>crescents point upwind </li></ul></ul>
  14. 24. Linear Dunes <ul><li>Longitudinal </li></ul><ul><ul><li>Winds variable in one direction </li></ul></ul><ul><ul><li>Ridge forms parallel to consistent wind direction </li></ul></ul><ul><ul><li>two slipfaces </li></ul></ul><ul><ul><li>100 – 400 m tall, up to 100 km long </li></ul></ul><ul><li>Seif </li></ul><ul><ul><li>Sharp crest </li></ul></ul><ul><ul><li>shorter in height </li></ul></ul>
  15. 28. Star Dunes <ul><li>Star Dunes </li></ul><ul><ul><li>Winds variable in all directions </li></ul></ul><ul><ul><li>Multiple slipfaces </li></ul></ul><ul><ul><li>With effective winds, form high mounds </li></ul></ul><ul><ul><li>With less effective winds, form networks of connected sinuous arms </li></ul></ul>
  16. 32. Desert Landscapes <ul><li>Arid areas are the largest climatic region on earth (35% of earth’s surface) </li></ul><ul><li>Fluvial features </li></ul><ul><ul><li>Flash flooding </li></ul></ul><ul><ul><ul><li>Washes, arroyos, wadis </li></ul></ul></ul><ul><ul><ul><li>Bursts of vegetation growth </li></ul></ul></ul><ul><ul><li>Playas </li></ul></ul><ul><ul><ul><li>interior drainage </li></ul></ul></ul><ul><ul><ul><li>salinization </li></ul></ul></ul><ul><ul><li>Alluvial fans </li></ul></ul><ul><ul><ul><li>bajadas </li></ul></ul></ul><ul><li>Landscape features </li></ul><ul><ul><li>Adapted vegetation </li></ul></ul><ul><ul><li>Basin and Range Province </li></ul></ul><ul><ul><ul><li>Horst and Graben, interior drainage, playas, alluvial fans </li></ul></ul></ul>
  17. 37. Colorado River Issues <ul><li>Headwaters originate in the Rocky Mountains </li></ul><ul><ul><li>High levels of rainfall </li></ul></ul><ul><ul><li>Snow melt </li></ul></ul><ul><li>Flows through an extremely arid area with few feeding tributaries </li></ul><ul><li>High demand on water means that often no water actually makes it to the sea </li></ul><ul><li>Flows through seven states, into Mexico </li></ul><ul><li>Beliefs on the river’s capacity based on a 400 year high mark (greatly overestimated) </li></ul><ul><li>Subject to a variety of political treaties and agreements regulating its flow </li></ul><ul><ul><li>In many cases, quotas are exceeded, esp. with California </li></ul></ul>
  18. 38. Desertification <ul><li>Refers to the expansion of desert biomes due to a combination of poor agricultural practices and climate change </li></ul><ul><ul><li>grazing has been identified as a major cause </li></ul></ul><ul><li>As a global phenomenon, this idea has largely been falsified </li></ul><ul><ul><li>Areas identified as “desertifying” were simply experiencing drought-like conditions, in conjunction with ENSO cycles; many have recovered </li></ul></ul><ul><li>There are some areas where desertification has occurred, but it is not a global phenomenon </li></ul>
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