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5
Section
5
Waves
Waves
Reading Preview
Objectives
After this lesson, students will be able to
G.3.5.1 Identify what gives ocean waves
their energy.
G.3.5.2 Describe how ocean waves erode
a coast.
G.3.5.3 Identify features that result from
deposition by waves.
Key Concepts
Target Reading Skill
Target Reading Skill
Identifying Main Ideas Explain that
identifying main ideas and details helps
students sort the facts from the information
into groups. Each group can have a main
topic, subtopics, and details.
Identifying Main Ideas As you
read Erosion by Waves, write the
main idea in a graphic organizer
like the one below. Then write
three supporting details that
further explain the main idea.
• What gives waves their energy?
• How do waves erode a coast?
• What features result from
deposition by waves?
Key Terms
• headland • beach
• longshore drift • spit
Answers
Detail: Energy in waves breaks apart rocks.
Detail: Sediment wears away rock.
Detail: Landforms are created.
Main Idea
Waves cause erosion by impact
and . . .
Detail
Detail
Detail
Teaching Resources
• Transparency G28
1. Collect a spoonful of sand from each of
two different beaches.
2. Examine the first sample of beach sand
with a hand lens.
3. Record the properties of the sand
grains, for example, color and shape.
Are the grains smooth and rounded or angular and rough?
4. Examine the second sample and repeat Step 3. How do the
two samples compare?
Think It Over
Posing Questions What questions do you need to answer to
understand beach sand? Use what you know about erosion and
deposition to help you think of questions.
Ocean waves contain energy—sometimes a great deal of
energy. Created by ocean winds, they carry energy vast distances across the Pacific Ocean. Acting like drills or buzz saws,
the waves erode the solid rock of the coast into cliffs and caves.
Waves also carry sediment that forms features such as beaches.
How Waves Form
Preteach
Build Background
Knowledge
What Is Sand Made Of?
L1
Waves and Beaches
Encourage students who have been to
beaches to share their experiences of the
sand on the beaches and the waves that flow
over the beaches. Elicit descriptions of the
color and texture of the sand, and note any
differences among the beaches. Then ask:
How do you think waves affect beaches?
(Accept all reasonable responses.) How do you
think beaches form? (Accept all reasonable
responses.) Record students’ responses on the
board, and have them refer to the responses
at the end of the section.
Waves on the Oregon coast
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. Large ocean waves are
the result of powerful storms far out at sea. But ordinary
breezes can produce waves in lakes or small ponds.
The energy that water picks up from the wind causes water
particles to move up and down as the wave goes by. But the water
particles themselves don’t move forward.
A wave changes as it approaches land. In deep water, a wave
only affects the water near the surface. But as it approaches
shallow water, the wave begins to drag on the bottom. The friction between the wave and the bottom causes the wave to slow
down. Now the water actually does move forward with the
wave. This forward-moving water provides the force that
shapes the land along the shoreline.
304 ◆
L1
Skills Focus posing questions
Materials sand from 2 beaches, hand lens
Time 15 minutes
Tips If sand is not available locally from
either a nearby lake or ocean, obtain two
different kinds of commercial sand.
Suggest that students avoid mixing the two
samples by completely removing the first
sample before examining the second.
304
Expected Outcome Students probably
will observe differences between the two
samples. Differences might include grain
shape, size, or color.
Think It Over Questions will vary.
Possible questions: Is beach sand a result of
erosion? How is beach sand deposited? What
causes differences in beach sand at different
places?
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For: Links on Waves
Visit: www.SciLinks.org
Web Code: scn-0735
Headland
Deposition
Download a worksheet that will guide students’ review
of Internet resources on waves.
Erosion
Sea arch
Instruct
Incoming waves
How Waves Form
Teach Key Concepts
FIGURE 21
Wave Erosion
Incoming waves bend as they approach the shore,
concentrating their energy on headlands. Waves have
shaped these spectacular cliffs (right) along the coast of
Cornwall in England.
Relating Cause and Effect What will eventually happen
to the headlands?
Energy and Waves
Focus Remind students of the power of
giant waves crashing onto shore.
Teach Ask: How can wind transfer energy
to water? (By blowing over the water’s
surface) What effect does this energy cause?
(Water waves) What moves forward in
water waves? (Energy) Does water move
forward? (No, except on the beach)
Apply Ask: Why are waves near a
hurricane much higher than normal waves?
(Wind blows much faster around a hurricane,
so more energy is transferred to water
waves.) learning modality: logical/
Erosion by Waves
Waves are the major force of erosion along coasts. Waves shape
the coast through erosion by breaking down rock and transporting sand and other sediment.
How Waves Erode One way waves erode the land is by
impact. Large waves can hit rocks along the shore with great
force. This energy in waves can break apart rocks. Over time,
waves can make small cracks larger. Eventually, the waves cause
pieces of rock to break off.
Waves also erode by abrasion. As a wave approaches shallow water, it picks up sediment, including sand and gravel.
This sediment is carried forward by the wave. When the wave
hits land, the sediment wears away rock like sandpaper wearing
away wood.
Waves coming to shore gradually change direction. The
change in direction occurs as different parts of a wave begin to
drag on the bottom. Notice how the waves in Figure 21 change
direction as they approach the shore. The energy of these
waves is concentrated on headlands. A headland is a part of
the shore that sticks out into the ocean. Headlands stand out
from the coast because they are made of harder rock that resists
erosion by the waves. But, over time, waves erode the headlands and even out the shoreline.
mathematical
Independent Practice
Teaching Resources
For: Links on waves
Visit: www.SciLinks.org
Web Code: scn-0735
• Guided Reading and Study Worksheet:
Waves
Student Edition on Audio CD
Chapter 7
◆ 305
Differentiated Instruction
L3
Gifted and Talented
Investigating Beach Erosion Many
coastal communities that experience severe
beach erosion during storms are using
modern technology to rebuild and protect
their beaches from continued erosion.
Invite students to find out about this
technology and report their findings to the
class. learning modality: verbal
L2
Monitor Progress
L1
Less Proficient Readers
Making Concept Maps As students read
through this section, have them make a
concept map of Waves that is divided into
Wave Formation, Wave Erosion, and Wave
Deposition. Help students start the map,
and make sure they include linking words
between circled words. learning
L2
Writing Have students explain how energy
travels along a wave.
Answer
Figure 21 The headlands will erode, and
the shoreline will be straighter.
modality: visual
305
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Erosion by Waves
Teach Key Concepts
Erosional Features
L2
Sea cave
Formed as wave action
hollows out the cliff
Landforms Formed by Wave Erosion
Focus Refer students to Figures 21 and 22.
Teach Ask: Where will an incoming wave
first touch the bottom as it approaches the
shore? (Directly in front of the headland)
What happens when a wave touches the
bottom? (It slows down.) Point out the
arrows in the figure. Ask: What do these
arrows show? (The arrows show the wave
bending around the headland and being
concentrated on it.) How do the features
along rocky coastlines form? (The features
form because of erosion by waves.) What
feature might form where erosion occurs at
the base of a cliff? (A sea cave) How could an
arch change into a stack? (The arch could
collapse.)
Apply Ask: What is the overall effect of
erosion along rocky shorelines? (The sea
cliffs retreat through time.) learning
Wave-cut cliff
Headland
Sea arch
Formed when sea
caves on either side
of a headland join
Sea stack
Left standing when
a sea arch collapses
modality: logical/mathematical
Teaching Resources
• Transparency G29
FIGURE 22
The Changing Coast
L2
Erosion and deposition create a
variety of features along a coast.
Predicting What will eventually
happen to the sea arch?
Modeling Wave Refraction
Materials chain of students, gymnasium
Time 15 minutes
Focus Remind students that wave energy is
concentrated along rocky headlands.
Teach Have a group of at least 15 students
join hands and stand side-by-side. Instruct
them to start walking forward at the same
rate. Now tell students in the middle of the
chain that they are approaching a headland
and will have to walk more slowly. Tell the
students on the ends to continue walking
at the faster rate. Make sure that students
continue to hold hands.
Apply Ask: What happened to the ends of
the chain when the middle slowed down?
(The ends curved toward the headland.)
Why is more wave energy concentrated
on headlands? (Just as more people walked
into the headlands, more wave energy is
directed onto headlands.) learning
modality: kinesthetic
306
Landforms Created by Wave Erosion When waves hit a
steep, rocky coast, they strike the area again and again. Think
of an ax striking the trunk of a tree. The cut gets bigger and
deeper with each strike of the blade. Finally the tree falls. In a
similar way, ocean waves erode the base of the land along a
steep coast. Where the rock is softer, the waves erode the land
faster. Over time the waves may erode a hollow area in the rock
called a sea cave.
Eventually, waves may erode the base of a cliff so much that
the rock above collapses. The result is a wave-cut cliff. You can
see an example of such a cliff in Figure 22.
Another feature created by wave erosion is a sea arch. A sea
arch forms when waves erode a layer of softer rock that underlies a layer of harder rock. If an arch collapses, the result might
be a sea stack, a pillar of rock rising above the water.
Over a long period of time, what effect do waves
have on a steep, rocky coast?
306 ◆
Differentiated Instruction
L1
Special Needs
Classifying Landforms Have students
divide a piece of poster board into several
sections and title each section with the
name of one coastline feature. For example,
titles might include sea arch, sea stack, spit,
and so on. Students then collect
photographs of each landform, and mount
them in the appropriate sections. Have
students include a short caption and
labels with each photo. learning
modality: visual
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Deposits by Waves
Depositional Features
Teach Key Concepts
Beach
Formed as waves pile up
sand along the shore
Spit
Formed as longshore
drift deposits sand
along the shore
Wave Deposition
Focus Have students describe the way waves
lap up onto a beach. Encourage students to
mention the thin wash of water that moves
up and then back down the beach.
Teach Ask: Why might waves approach a
beach at an angle? (Wind causes waves to
come from that particular direction.) After
waves lap up onto the beach, what causes
the water to move back into the ocean?
(Gravity) In which direction does gravity
pull the water? (Straight down the slope of the
beach) If a sand grain were moving along
with this water, what path would it have?
(A zigzag path along the beach) Tell students
that they have just explained longshore drift.
Apply Ask: Why might a spit form where a
beach curves sharply? (The longshore current
moves sand out into the water.) learning
Sed
im
en
t
Sandbar
Formed by
wave action
L o n gsh
ore D
rift
Deposits by Waves
modality: logical/mathematical
Waves shape a coast when they deposit sediment, forming
coastal features such as beaches, spits, and barrier beaches.
Deposition occurs when waves slow down, causing the water to
drop its sediment. This process is similar to the deposition that
occurs on a river delta when the river slows down and drops its
sediment load.
Beaches As waves reach the shore, they drop the sediment
they carry, forming a beach. A beach is an area of wave-washed
sediment along a coast. The sediment deposited on beaches is
usually sand. Most sand comes from rivers that carry eroded
particles of rock into the ocean. But not all beaches are made of
sand. Some beaches are made of small fragments of coral or sea
shells piled up by wave action. Florida has many such beaches.
The sediment on a beach usually moves down the beach
after it has been deposited. Waves usually hit the beach at an
angle instead of straight on. These angled waves create a current that runs parallel to the coastline. As waves repeatedly hit
the beach, some of the beach sediment moves down the beach
with the current, in a process called longshore drift.
Calculating A sandy coast
erodes at a rate of 1.25 m
per year. But a severe storm
can erode an additional
3.75 m from the shore. If 12
severe storms occur during a
50-year period, how much
will the coast erode? If you
wish, you may use an
electronic calculator to find
the answer.
Chapter 7
◆ 307
Monitor Progress
Skills Focus calculating
L2
Materials calculator
Time 15 minutes
Tips Remind students that severe storm
erosion occurs in addition to the 1.25 m/y
rate.
Expected Outcome Students set up and
solve an equation to find the total erosion.
L2
Total Erosion = (1.25 m/y)
(50 y) + (3.75 m/storm) (12 storms) =
107.5 meters
Extend Have students perform the same
calculation if 25 severe storms occurred
during a 50-year period. learning
modality: logical/mathematical
L2
Writing Have students explain in
their own words how waves erode
the land. Students can place their
paragraphs in their portfolios.
Answers
Figure 22 The sea arch eventually will
collapse because of continued erosion.
Waves erode the base of a
rocky cliff, causing sea caves
or a collapse of the upper portion of the cliff.
307
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Monitor Progress
L2
Spits One result of longshore drift is the
formation of a spit. A spit is a beach that
projects like a finger out into the water.
Spits form as a result of deposition by
longshore drift. Spits occur where a headland or other obstacle interrupts longshore
drift, or where the coast turns abruptly.
Answers
Figure 23 Two
Barrier beaches form when
storm waves pile sand above
sea level.
Assess
Reviewing Key Concepts
1. a. Energy is transferred to ocean waves
from wind. b. An ocean wave begins to drag
at the bottom as it enters shallow water. The
wave slows, and the water moves forward
with the wave. c. Both; Ocean waves have
potential because they have height. Waves
have kinetic energy because they move.
2. a. Possible answers: sea cave, wave-cut
cliff, sea arch, sea stack b. Waves erode rock
by impact and abrasion. c. Cliff, headland,
sea cave, sea arch, sea stack
3. a. Possible answers: beach, spit, barrier
beach b. Most sand enters oceans from
rivers. Spits form as a result of sand
deposition by longshore drift where the coast
turns abruptly.
Reteach
L1
Have students make a compare-and-contrast
chart using the landforms that form by
wave erosion and those that form by wave
deposition.
Performance Assessment
L2
Drawing Have students make a labeled
drawing of the landforms created by erosion
and deposition.
Teaching Resources
• Section Summary: Waves
• Review and Reinforce: Waves
• Enrich: Waves
FIGURE 23
Spits
This aerial photograph shows how
longshore drift can carry sand and
deposit it to form a spit.
Observing How many spits can
you find in this image?
Sandbars and Barrier Beaches Incoming waves carrying sand may build up sandbars, long ridges of sand
parallel to the shore. A barrier beach is similar to a sandbar. A barrier beach forms when storm waves pile up large
amounts of sand above sea level forming a long, narrow
island parallel to the coast. Barrier beaches are found in
many places along the Atlantic coast of the United States,
such as the Outer Banks of North Carolina. People have
built homes on many of these barrier beaches. But the
storm waves that build up the beaches can also wash them
away. Barrier beach communities must be prepared for
the damage that hurricanes and other storms can bring.
How does a barrier beach form?
5
Section 5 Assessment
Target Reading Skill Identifying Main Ideas
Use your graphic organizer to help you answer
Question 2 below.
Reviewing Key Concepts
1. a. Explaining What is the source of the energy
in ocean waves?
b. Describing How does an ocean wave
change when it reaches shallow water?
c. Inferring Does an ocean wave possess
potential energy or kinetic energy? Explain.
2. a. Identifying What are two results of wave
erosion along a coast?
b. Describing What are two ways in which
waves erode rock?
c. Sequencing Place these features in the
order in which they would probably form:
sea stack, sea cave, headland, cliff, sea arch.
wave deposition?
b. Relating Cause and Effect Beginning with
the source of sand, explain the process by
which a spit forms.
Explaining a Process Suppose that you
live in a coastal area that has a barrier
beach. Write a paragraph in which you
explain the processes that formed the
barrier beach. Also describe how the forces
might change it over time.
308 ◆
Writing Mode Exposition Cause and Effect
Scoring Rubric
4 Exceeds criteria in some way, for example,
explaining the risk of building a home on a
barrier beach
3 Meets criteria but does not go beyond
requirements
2 Includes only brief description of required
elements
1 Is incorrect and incomplete
308
3. a. Listing What are three features formed by
Keep Students on Track Check that
students have completed their designs for
building their model dams. Encourage
students to begin building and testing the
dams. Have them record their observations.