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