Transcript Chapter 12: Effects of Winds, Waves, and Currents

Chapter 12:
Effects of Winds, Waves, and Currents
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Wind as an Agent of Change
Rock Materials Carried by Winds
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Winds are agents of erosion.
Winds pick up and move sediments
Winds cause weathering by driving sediment
against rocks and other materials.
Deserts (dry, loose sediments) have the
most wind erosion.
Dust storms occur when strong, steady
winds lift great amounts of silt and clay from
the topsoil.
Winds of at least 18 km/h are needed to
move sand grains, and move in hops and
bounces.
Dust Storm, Texas
Abrasion by Windblown Sediments
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Windblown silt and clay particles are too small
and too soft to wear away most rocks.
Sand grains are larger and tend to be made of
more abrasive materials, they grind and scour
anything they hit.
Quartz sand grains can wear away many
materials.
Sand blasts and grinds boulders and rocks into
shapes called ventifacts.
The side of the ventifact that faces the wind
wears into a smooth flat surface, or facet
Deflation: An Erosional Effect
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Deflation is the removal of loose rock
particles by the wind
In deserts when the sands and clays are
blown away, it leaves pebbles and boulders
called desert pavement.
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In semiarid regions, deflation can form
hollows called blowouts.
Loess
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Wind can deposit sediment as well as remove it.
Large areas in China, northern Europe, and the
north central United States are covered by thick
deposits of material called loess.
1m-100m in thickness
Unlayered, yellowish particles the size of silt.
Particles are angular in shape
The particles in the US and Europe were likely from
glacial outwash plains
The particles in China are likely from the deserts of
Mongolia
Loess landscape, China
Sand Dunes
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Hills of sand deposited by winds.
Form when sand piles up against shrubs, boulders,
or other obstructions.
Dunes are found wherever there are strong winds
and enough loose sand.
Most are made of quartz sands, some are gypsum,
calcite, and may contain some feldspar, mica, and
magnetite.
If wind blows from one direction, dunes have a
long, gentle slop on the windward side, and a
shorter, steeper slope on the leeward side.
Dunes occur in many different shapes.
Four Types of Sand Dunes
Parabolic
Transverse
Barchan
Longitudinal
Migration of Dunes
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Each time the wind blows against the
windward side of a sand dune, some of the
surface sand is carried over the top.
The whole dune can move in the leeward
direction.