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Unit 5 Chapter 18
Erosion by Wind and Waves
Section 1 Wind Erosion
The wind contains energy. This energy can be used for many things. It
can pick up particles and slam them into each other
Sand is an effective abrasive tool however the winds have to be strong
in order to be effective. The winds have to be approximately 18km
per hour.
How Wind Moves Sand and Dust
Wind as an agent of erosion needs dry conditions. It picks up & moves
sediments. It drives sediments against objects.
Saltation is the bouncing and jumping of sand particles by the wind.
Winds are able to carry the dust long distances in the atmosphere.
Winds over water
Dust from the Gobi Desert (Asia) has been transported to
Western USA (across the Pacific)
Dust from the Sahara Desert (Africa) has hit the Caribbean and
Southeastern USA.
Effects of Wind Erosion
Wind erosion can shape the landscapes. Where there are few to no
plants, more erosion will occur.
Desert Pavement
Desert pavement wind removes all small particles only pebbles &
boulders left behind (Southwest US & Sarah desert)
Blowout - removal of large amounts of land due to deflation (Great Plains)
Form in dry regions with patchy vegetation (Sand Hills of
Nebraska)
Deflation Hallows
Deflation
Removal of fine dry soil particles due to lack of vegetation to keep
soil from blowing away.
Dust storm strong steady winds lift large amounts of material from
top soil (silt & clay)
More Dust Storms
1930’s Dust Storms, called the “Dust Bowl”, farmers removed
vegetation that held the soil down. Then a draught occurred. Winds
carried the dust. It looked like a curtain of dust. Many people had to
move because they could no longer grow crops there.
Ventifact
Ventifact rocks with one side worn away
Death Valley has both Desert Pavement and Ventifacts
Facet - smooth surface
Wind Deposition
Particles are deposited when the wind can no longer support them.
Eventually they are compacted together and form sedimentary
rocks.
Dunes -sand deposited by winds, formed where the soil is dry and
unprotected.
Windward side - The front side that the wind blows from (not steep)
Leeward side - The back side of a dune, mountain or hill (Steep)
White Sands National Monument
Most dunes are quartz sand. Exceptions to the rule are the White
Sands National Monument in New Mexico (gypsum), volcanic
beaches and beaches made with coral.
Types of Dunes
Dune Migration
Dunes migrate (move) toward the leeward direction. It can be as much as 30 meters per year and can
cover towns, farms & forests. Dry regions will have this migration, humid regions will not have this effect.
Loess
Loess is a deposit of un-layered siltstone particles, generally angular particles yellow in color. These
deposits range from 1 meter to 300 meters. In the US they are found mostly by the upper Mississippi &
Missouri River Valley. In Northern China they probably came from the Great Desert of Mongolia.
Section 2 Wave Erosion
As winds move over the oceans it causes waves that will erode the
shore line.
Shore Line Erosion
Mechanical Weathering- The waves break pieces of rocks by
slamming them together.
Chemical Weathering – Waves forces salt water and air into
rocks and cracks.
Sea Cliffs
Sea cliffs happen when waves strike headlands of deep water.
Headland is a resistant rock formation that projects from the shore.
Sea Caves, Arches and Stacks
Sea Cave – hard material forms a notch then a cave, then an arch.
If the arch roof caves in then it is a stack. Found in California,
Oregon, Washington, Maine, Gasped Peninsula of Canada & the
Mediterranean Sea.
A sea arch is when waves cut completely through a headland.
A Stack is an offshore column of rock that was once connected to the
headland.
Beaches
A beach is an area between high tide and low tide
Composition of Beaches
The composition is mostly quartz and some feldspar, some magnetite &
muscovite mica. There are a few beaches that can be calcite
(Bermuda) and basalt (Hawaii).
The Berm
During high and low tides sand will pile up into a sloping surface. As
more sand is deposited it raises up to form a natural berm.
A sand bar is an area of sand carried by ocean currents and deposited
near shore; usually across the mouth of a bay (by Fire Island)
Longshore-Current Deposits
Waves moving at an angle to the shore line often create currents.
A Longshore current is one that travels parallel to the shore.
Spit is a sand bar attached at one end (Dune Road)
A tombol (also known as a hook) is a split with a curved end (Sandy
Hook, NJ; Rockaway Beach;
Cape Cod, Mass)
Section 3 Coastal Erosion and Deposition
Coastal areas are among some of the most rapidly changing parts on
Earth.
Absolute Sea-Level Changes
The sea level changes (amount of water) because of glaciers, periods of
melting and other climatic changes take place.
Relative Sea-Level Changes
Are changes in the sea level due to changes in the coastal features.
Submergent Coastlines
When sea level rises or sinks.
Fiord is a submerged glacial valley that has filled in with water.
Emergent Coastlines
When sea level falls, land is raised up to create a coastline.
Barrier Islands
Barrier Islands are sand bars not attached to the main land, they run
parallel to the shore. Fire Island, NY; Atlantic City Beach, NJ;
Hatteras, N.C.; Galveston & Padre Island, TX; Palm Beach & Miami,
Fl
Lagoon
A lagoon’s water is protected by sand dunes.
Jamaica Bay is behind Rockaway Beach Hook.
Preserving the Coast Line
Don’t pollute, keep the coastal areas free from pollution.
Do not build by them. Allow nature to do what it needs to
do.