Earth Science
Chapter 8
Section 5 & 6
A. How Waves Form:
The energy in waves comes from wind that blows across the
water’s surface.
As the wind makes contact with the water, some of its energy
transfers to the water.
The energy that water picks up from the wind causes water
particles to move up and down as the wave moves on.
Water particles themselves don’t move forward, only the form
of the wave moves.
A wave changes as it approaches land. In deep water, a wave
only affects the water near the surface.
As the wave approaches shallow water, the wave begins to drag
along the bottom. The friction between the wave and the
bottom causes the wave to slow down.
Now the water will move along with the wave. This forwardmoving water provides the force that shapes the land along the
surface.
B. Erosion by Waves:
Waves are the major force of erosion along coasts.
Three ways waves erode coasts:
1. Impact – The impact of the wave causes a force that breaks
rocks apart.
2. Abrasion – Sediments picked up by the wave as it approaches
the shore wears away rock like sandpaper on wood.
3. Direction change of the wave as it approaches shore. – The
wave changes direction because different parts of the wave
come in contact with the bottom a different times.
The energy of the waves is concentrated on headlands (part
of the shore that sticks out into the ocean). Over time the
waves erode the headlands and even out the shoreline.
C. Landforms Created by Wave Erosion:
1. Sea cave – a hollow area in the rock of a cliff eroded
by wave action.
2. Wave-cut cliff – waves erode the base of a cliff so
much that the rock above collapses.
3. Sea arch – forms when waves erode a layer of softer
rock that underlies a layer of harder rock.
4. Sea stack – a collapsed sea arch.
D. Deposits by Waves:
Waves shape the coast through both erosion and deposition.
As a wave reaches the shore, they drop the sediment they carry,
forming beaches.
Beach – an area of wave-washed sediment along a coast. The
sediment along the beach is usually sand.
Longshore drift – Angled waves produce a current that runs
parallel to the coastline. As repeated waves hit the beach, some
of the beach sediment moves down the beach with the current.
Spit - a beach that projects like a finger out into the water.
Earth Science
Chapter 8
Section 6
A. How Wind Causes Erosion:
Wind by itself is the weakest agent of erosion. Yet wind can
be a powerful force in shaping the land in areas where there
are few plants to hold the soil in place.
The main way that wind causes erosion is by deflation.
Deflation is the process by which wind removes surface
material. As the wind blows it pick up and carries away
small particles of sediment.
Blowout – a bowl-shaped depression caused by deflation.
Abrasion by wind-carried sand can polish rock, but causes
little erosion. Most erosion in desert regions occurs from
weathering and water erosion.
B. Deposits Resulting from Wind erosion:
Wind erosion and deposition may form sand dunes and loess
deposits.
Loess – a fine wind deposited sediment.
Sand dunes – the build up of wind blown sediments.
Sand dunes came in many shapes.
1. Barchan dunes – form when the wind direction stays the
same and the supply of sand is limited. They are often
found as a single dune.
2. Transverse dunes – form when the wind direction stays
the same and the supply of sand is large.
3. Longitudinal dunes – form when the wind blows in two
slightly different directions and the supply of sand is
limited.
4. Star dunes – form when the wind blows in three different
directions. Star dunes are often found in a single dune.
5. Parabolic dunes – form along coasts and point away from
the wind blowing in off the water. Vegetation often
covers parts of a parabolic dune.