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Wind erosion & Deposition

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  1. Wind erosion & Deposition WED V15

  2. What is wind? • Wind the horizontal flow of air. • It is caused byhorizontal differences in pressure which result from the unequal heating of Earth’s surface • http://www.classzone.com/books/earth_science/terc/content/visualizations/es1903/es1903page01.cfm?chapter_no=visualization

  3. Features caused by wind • Ripples and dunes

  4. Windward side is gentle • Leeward side is steep http://geology.wr.usgs.gov/parks/coast/dunes/index.html

  5. For dunes & ripples to form you need… • Wind • Dry sand • Wind break (drift wood, dead bird, plant, etc.)

  6. Dunes http://geology.wr.usgs.gov/parks/coast/dunes/index.html

  7. Dune Formation • steady supply of sand, wind, and a wind break • beaches and at the base of mountains in dry regions. • Wet sand will not blow around to form ripples and dunes Mesquite Flats, Death Valley, CA http://www.uoregon.edu/~millerm/sanddunes.html

  8. Grasses on the dunes help stabilize the beach http://geology.wr.usgs.gov/parks/coast/dunes/index.html

  9. Wind blows sand and makes ripples Once sand begins to pile up, ripples and dunes can form. • http://www.nps.gov/archive/grsa/resources/images/photos/dune_pattern03.jpg

  10. http://geology.wr.usgs.gov/parks/coast/dunes/index.html Ripples grow into dunes with increase of wind and sand input

  11. The collapsing sand comes to rest when it reaches just the right steepness- 30 to 34 degrees, or angle of repose- to keep the dune stable. http://geology.wr.usgs.gov/parks/coast/dunes/index.html

  12. Sand blowing off a dune http://www.uoregon.edu/~millerm/depenv.html

  13. Animation • http://highered.mcgraw-hill.com/sites/0072402466/student_view0/chapter13/animations_and_movies.html#

  14. Migration • sand inches up the windward side to the dune crest • then slips down the dune's slip face • the dune to inches forward, migrating in the direction the wind blows • this leaves its mark on the internal structure of the dune. http://geology.wr.usgs.gov/parks/coast/dunes/index.html

  15. Cross-bedding preserved in sandstone • http://www.wwnorton.com/college/geo/egeo/flash/5_1.swf • http://geology.wr.usgs.gov/parks/coast/dunes/index.html

  16. Navajo Sandstone

  17. Cross bedding in the Navajo SandstoneArches National Park

  18. Star Dune Complex • The wind blows from different directions throughout the year. http://www.nps.gov/archive/grsa/resources/images/photos/dunes_cristos03.jpg

  19. Main Dune field at White Sands National Monument • http://www.nps.gov/archive/grsa/resources/images/photos/landscape_sw02jpg.jpg

  20. http://www.nps.gov/archive/grsa/resources/photos_landscape.htmhttp://www.nps.gov/archive/grsa/resources/photos_landscape.htm

  21. http://www.nps.gov/archive/grsa/resources/photos_landscape.htmhttp://www.nps.gov/archive/grsa/resources/photos_landscape.htm

  22. http://www.nps.gov/archive/grsa/resources/photos_landscape.htmhttp://www.nps.gov/archive/grsa/resources/photos_landscape.htm

  23. Ventifacts http://earthsci.org/education/teacher/basicgeol/windes/ventifact.gif

  24. Features caused by wind • Ventifacts • rocks flattened and smoothed by wind abrasion

  25. Features caused by wind • Desert pavement • Surface where wind has blown away the smaller sediment • Deflation: removal of silt, sand, and clay by wind

  26. Desert Pavement http://media-2.web.britannica.com/eb-media/28/10728-004-83F5D724.jpg

  27. http://www.uwgb.edu/DutchS/geophoto/aeolian/DPAVMT1.jpg

  28. http://www.goldengatephoto.com/jpeg/99-29-7.jpg

  29. Evidence of wind abrasion: frosted grains http://en.wikipedia.org/wiki/File:WhiteSandsGypsum.jpg

  30. Loess • Wind-blown silt deposits • Often forms thick layers as wind deposits small particles swept from glacial outwash plains http://en.wikipedia.org/wiki/File:LoessVicksburg.jpg

  31. “When the Yellow River runs clear” Means the same as “When Pigs fly” http://upload.wikimedia.org/wikipedia/commons/e/ea/Hukou_Waterfall.jpg

  32. http://en.wikipedia.org/wiki/File:Loess_landscape_china.jpg

  33. The photograph below shows a sand dune that formed in a coastal area. This sand dune was most likely formed by (1) water flowing from the left (2) water flowing from the right (3) wind blowing from the left (4) wind blowing from the right

  34. Draw the sand