Chapter 7 Section 4 Wind


Published on

Published in: Education
1 Like
  • Be the first to comment

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

Chapter 7 Section 4 Wind

  1. 1. Chapter 7: Erosional Forces<br />Section 4: Wind<br />
  2. 2. I. Wind Erosion<br />Air <br />Differs from other erosional forces because it cannot pick up heavy sediments. <br />Wind carries and deposits sediments over large areas. <br />For example, wind is capable of picking up and carrying dust particles from fields or volcanic ash high into the atmosphere and depositing them thousands of kilometers away. <br />
  3. 3. I. Wind Erosion<br />Deflation and Abrasion<br />Wind erodes Earth’s surface by deflation and abrasion. <br />When wind erodes by deflation, it blows across loose sediment, removing small particles such as silt and sand. <br />The heavier, coarser material is left behind. <br />
  4. 4. I. Wind Erosion<br />B. Deflation and Abrasion<br />3. When wind blown sediment strikes rock, the surface of the rock gets scraped and worn away by a process called Abrasion. <br /> Abrasion is similar to sand blasting. <br />The rocks become pitted and worn down gradually over time due to abrasion. <br />
  5. 5. I. Wind Erosion<br />B. Deflation and Abrasion<br />Deflation and Abrasion happen to all land surfaces but occur mostly in deserts, beaches, and plowed fields. <br />These areas have fewer vegetation to hold the soil in place; so when wind blows over them, they can be eroded rapidly. <br />Grasslands or pasture lands have many plants to hold the soil in place, therefore there is little soil erosion caused by the wind. <br />
  6. 6. I. Wind Erosion<br />Sandstorms<br />Even when the wind blows strongly, it seldom carries sand grains higher than 0.5 m from the ground. <br />However sand storms do occur when the wind blows forcefully in the sandy parts of the deserts; sand grains bounce along and hit other sands grains, causing more and more grains to rise into the air. <br />Most sandstorms occur in deserts, but they can occur in other arid regions. <br />
  7. 7. I. Wind Erosion<br />Dust Storms<br />When soil is moist, it stays packed on the ground, but when it dries out, it can be eroded by wind. <br />Because soil is composed largely of silt and clay sized particles they are less dense than the same sized sand particles, so wind can move them high into the air. <br />When silt and clay particles stick together; a faster wind is needed to lift these fine particles of soil than is needed to lift grains of sand. <br />However after they are airborne, the wind can carry them long distances because they are less dense.<br />
  8. 8. I. Wind Erosion<br />Dust Storms<br />Where the land is dry, dust storms can cover hundreds of kilometers.<br />Dust Storms blow topsoil from open fields, overgrazed areas, and places where vegetation has disappeared. <br />Silt and dust from Kansas fell in New England and in the North Atlantic Ocean all the way from Kansas during the 1930’s Dust Bowl. <br />Dust blown from the Sahara has been traced as far away as the West Indies-a distance of at least 6,000 km. <br />
  9. 9. I. Wind Erosion<br />Which factors increase the amount of erosion?<br />
  10. 10. I. Wind Erosion<br />2. Which factors decrease the amount of erosion.<br />
  11. 11. I. Wind Erosion<br />3. Estimate the missing Erosion rating.<br />
  12. 12. II. Reducing Wind Erosion<br />Vegetation<br />One of the best ways to slow or stop wind erosion is to plant vegetation. <br />These practices helps conserve soil and protect valuable farmland. <br />Strip Cropping<br />Cover Cropping<br />No-Till Farming<br />
  13. 13. II. Reducing Wind Erosion<br />Windbreaks<br />Farmers plant trees to act as windbreaks that prevent soil erosion. <br />As the wind hits the trees, its energy of motion is reduced, therefore it is no longer able to lift particles. <br />One study showed a thin belt of cottonwood trees reduced the effect of a 25 km/h wind to about 66 percent of its normal speed. <br />
  14. 14. II. Reducing Wind Erosion<br />Windbreaks<br />Tree belts also trap snow and hold it on land. <br />This increases the moisture level of the soil, which helps prevent further erosion. <br />
  15. 15. II. Reducing Wind Erosion<br />Roots<br />Plants with fibrous root systems, such as grasses, work best at stopping wind erosion. <br />Grass roots are shallow and slender with many fibers. <br />They twist and turn between particles in the soil and hold it in place. <br />
  16. 16. II. Reducing Wind Erosion<br />Roots<br />Planting vegetation is a good way to reduce the effects of deflation and abrasion. <br />If the wind is strong and the soil is dry, nothing can stop erosion completely.<br />
  17. 17. III. Deposition by Wind<br />Loess<br />Wind deposits of fine grained sediments. <br />Examples found near the Mississippi and Missouri Rivers<br />Strong winds that blew across glacial outwash areas carried the sediments and deposited them. <br />
  18. 18. III. Deposition by Wind<br />Loess<br />Loess is as fine as talcum powder. <br />Many farmlands of the Midwestern United States have fertile soils that developed from loess deposits. <br />
  19. 19. III. Deposition by Wind<br />Dunes<br />Created when wind blows sediments against an obstacle such as a rock or clump of vegetation. <br />Wind drops sediments because is loses its energy of motion. <br />The sediment itself then becomes an obstacle, trapping even more material. <br />
  20. 20. III. Deposition by Wind<br />Dunes<br />If the wind blows long enough, the mound will become a dune. <br />A DUNE is a mound of sediments drifted by the wind. <br />
  21. 21. III. Deposition by Wind<br />Dunes<br />Dunes are common in desert regions. <br />Also along the shores of oceans, seas, or lakes. <br />Sand or other sediment will continue to build up and form a dune until the sediment runs out or the obstruction is removed. <br />Some desert sand dunes can grow to 300 feet high (100 meters), but most are much shorter. <br />
  22. 22. III. Deposition by Wind<br />Moving Dunes<br />A sand dune has two sides. <br />Side facing the wind has a gentler slope. <br />The side away from the wind is steeper. <br />The shape of the dune tells you the direction. <br />Unless sand dunes are planted with grasses, most dunes move, or migrate away from the direction of the wind. (See figure 22 next slide)<br />
  23. 23. III. Deposition by Wind<br />Moving Dunes<br />Some dunes are known as traveling dunes because they move rapidly across desert areas. <br />
  24. 24. III. Deposition by Wind<br />
  25. 25. III. Deposition by Wind<br />
  26. 26. III. Deposition by Wind<br />Dune Shape<br />The shape of the dune depends on the amount of sand or other sediment available, the wind speed and direction, and the amount of vegetation present.<br />
  27. 27. III. Deposition by Wind<br />Dune Shape<br />Barchan Dune<br />The open side of a Barchan faces the direction that the wind is blowing. <br />This type of dune forms on hard surfaces where the sand supply is limited<br />Crescent shaped. <br />
  28. 28. III. Deposition by Wind<br />Dune Shape<br />Transverse Dune.<br />Forms when sand is abundant. <br />Named because the long directions of these dunes are perpendicular to general wind direction. <br />
  29. 29. III. Deposition by Wind<br />Dune Shape<br />Star Dune<br />a. Found in areas where wind direction changes. <br />