Transcript Wind - Choteau

Chapter 8, Section 3
Wind Erosion
 Wind Erosion
 Occurs when air picks up loose material
and transports it elsewhere.
 Usually can’t pick up heavy sediments.
 Carries and deposits sediments over large
areas.
Wind Erosion
 Types of
Wind
Erosion
 Deflation and Ablation
 Happen to all land surfaces.
 Occur mostly in deserts, beaches, and
plowed fields.
Wind Erosion
 Deflation
 Occurs when wind blows across loose
sediment, removing small particles such
as silt and sand and leaving heavier,
coarser material behind.
Wind Erosion
 Abrasion  Occurs when the surfaces of rocks get
scraped and worn away by windblown
sediments that strike the rock.
 Causes rocks to become pitted and
gradually worn down.
Wind Erosion
 Sandstorms
 Occur when strong winds cause sand
grains to hit other sand grains, causing
multiple grains to rise in the air and form
a low cloud just above the ground.
 Usually winds do not carry sand grains
higher than 0.5 m above the ground.
 Most sandstorms occur in deserts.
Wind Erosion
 Dust
Storms
 Occur when wind carries smaller particles of
soil into the air.
 Soil is composed mostly of silt and clay sized
particles which can be carried higher into the
air than heavier sand grains.
 But, because the particles stick together, a
faster wind is needed to lift them into the air.
 Wind can carry the particles long distances
causing dust storms to cover hundreds of
kilometers.
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In the 1930’s dust picked up in Kansas fell in New
England and the North Atlantic Ocean.
Dust from the Sahara has been traced as far away as
the West Indies (6,000 km).
Reducing Wind Erosion
 Windbreaks  Planting vegetation to reduce wind
erosion.
 Reduces the energy of the wind.
 Traps snow, causing the moisture of the
surrounding soil to increase.
Reducing Wind Erosion
 Roots
 Plants with fibrous roots systems, such as
grasses, work best for anchoring soil.
Deposition by Wind
 Loess
 Large deposits of windblown fine-grained
sediments.
 Form when large deposits of fine-grained
sediments are packed together creating a
thick, unlayered, yellow-brown deposit.
 Produce fertile soils.
Deposition by Wind
 Dunes
 A mound of sediments drifted by the
wind.
 Form when wind blows across an obstacle
and deposits sediment behind the
obstacle where the energy is the lowest.
 Common in deserts and along the shores
of oceans, seas, and lakes.
 If the area has prevailing winds, the sand
dunes will grow.
 Some dunes are up to 100 m high.
Deposition by Wind
 Moving
Dunes
 The shape of a dune indicates the
direction that the wind usually blows.
 Side facing the wind has a gentler slope.
 Side away from the wind is steeper.
 Most dunes migrate (or move) away from
the direction of the wind.
 As the dunes loose sand on one side they
build it up on the other.
Deposition by Wind
 Dune
Shape
 The shape of a dune depends on:
 the amount of sand or other sediment
available
 the wind speed
 the wind direction
 the amount of vegetation present
Deposition by Wind
 Dune
Shape
 Types of dune shapes:
 Barchan dune
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Crescent-shape
The open side of the dune faces the direction the
wind is blowing.
Points of the crescent are directed downwind.
Forms on hard surface where the sand supply is
limited.
Deposition by Wind
 Dune
Shape
 Types of dune shapes:
 Transverse dune
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Long direction of the dune is perpendicular to the
general direction of the wind.
Form in areas where sand is abundant.
Deposition by Wind
 Dune
Shape
 Types of dune shapes:
 Star Dunes
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Form in areas where the wind blows from several
directions.