1. Objectives Vocabulary
Wind
Objectives
Describe conditions that contribute to the likelihood that an area will experience wind erosion.
Identify wind-formed landscape features.
Describe how dunes form and migrate.
Explain the effects of wind erosion on human activities.
Vocabulary
deflation
abrasion
ventifact
dune
loess

2. Wind
Wind
Moving air can pick up and transport Earth materials in the process of erosion.
Unlike water, wind can transport sediments uphill as well as downhill.
As an erosional agent, wind can modify and change landscapes in arid and coastal areas.

3. Wind Erosion and Transport

4. Wind Erosion and Transport
Wind transport and erosion primarily occur in areas with little vegetative cover, such as deserts, semi-arid areas, seashores, and some lakeshores.
Wind erosion is a problem in many parts of the United States.

5. Wind Erosion and Transport

6. Wind Erosion and Transport
Deflation is the lowering of the land surface that results from the wind’s removal of surface particles.
In areas of intense wind erosion, coarse gravel and pebbles are usually left behind as the finer surface material is removed by winds.
The coarse surface left behind is called desert pavement.

7. Wind Erosion and Transport
Abrasion is a process of erosion that occurs when particles, such as sand, rub against the surface of rocks or other materials.
In wind abrasion, wind picks up materials such as sand particles and blows them against rocks and other objects.
Because sand is often made of quartz, a very hard mineral, wind abrasion can be a very effective agent of erosion.

8. Wind Erosion and Transport
Windblown sand causes rocks to become pitted and grooved.
Ventifacts are rocks shaped by wind-blown sediments.

9. Wind
Wind Deposition
Wind deposition occurs in areas where there are changes in wind velocity.
As wind velocity decreases, some of the wind-blown sand and other materials can no longer stay airborne, and they drop out of the airstream to form a deposit on the ground.

10. Wind Deposition Formation of Dunes
In wind-blown environments, sand particles tend to accumulate where an object blocks the particles’ forward movement.
A dune is a pile of wind-blown sand that develops over time.
Conditions, including the availability of sand, wind velocity, wind direction, and the amount of vegetation present under which a dune forms, determine its particular shape.

11. Wind Deposition Formation of Dunes
The velocity of the wind above the ground surface determines the height of a dune.
Although quartz sand is the most common component of dunes, any dry, granular material can be formed into a dune.

12. Wind Deposition Types of Dunes
Barchan dunes are solitary, crescent-shaped dunes that form in flat areas where there is little sand or vegetation.
Transverse dunes form where there is plenty of sand, little or no vegetation, and steady, prevailing winds.
Transverse dunes form in a series of long ridges that are perpendicular to the direction of the wind.
U-shaped parabolic dunes form between clumps of plants.
Longitudinal dunes form where there is limited sand available and strong prevailing winds.

13. Wind
Wind Deposition

14. Wind Deposition Types of Dunes
On offshore islands and on lakeshores, dunes are formed by winds blowing off the water toward the shore.
Coastal dunes protect against beach and coastal erosion by reducing the direct action of wind on beach sand.
They also act as buffers against the action of waves and provide shelter for vegetation.
Dune migration is caused when prevailing winds continue to move sand from the windward side of a dune to its leeward side.

15. Wind
Wind Deposition
Types of Dunes

16. Wind
Wind Deposition
Loess
Wind can carry fine, lightweight particles such as silt and clay in great quantities and for long distances.
Many parts of Earth’s surface are covered by thick layers of windblown silt known as loess.
Where precipitation is adequate, loess soils are some of the most fertile soils on Earth because they contain abundant minerals and nutrients.

17. Wind
Wind Deposition

18. Wind
Section Assessment
1. Match the following terms with their definitions.
___ deflation
___ abrasion
___ ventifact
___ loess B A C D
A. a process in which particles such as sand rub against the surface of rocks or other materials
B. the lowering of land surface that results from the wind’s removal of surface particles
C. rocks shaped by wind-blown sediments
D. thick, wind-blown silt deposits

19. Wind
Section Assessment
2. Match the description of how the dune forms to its type.
___ Most common dune, generally forms in areas of constant wind direction
___ Form in areas with high, somewhat variable winds and little sand
___ Form in areas with moderate winds and some vegetation
___ Form in areas with strong winds and abundant sand A D C B
A. Barchan
B. Transverse
C. Parabolic
D. Longitudinal

20. Section Assessment 3. How do dunes migrate?
Wind
Section Assessment
3. How do dunes migrate?
Wind blows sand particles up the windward side of the dune, depositing it on the leeward side. Over time, as sand is moved from the windward side to the leeward side, the dune shifts toward the leeward side.