Section
3
Section 3
Waves and
Wind
Waves and Wind
S 6.2.a, 6.2.c
Previously, students learned that rivers
and streams are dynamic systems that
erode, transport sediment, change course,
and flood their banks in naturally and
recurring patterns. Now, they will see how
ocean waves are active in shaping
landscapes.
S 6.2.a Framework Surface water
flow, glaciers, wind, and ocean
waves have all been and continue
to be active throughout California
and the rest of the world in shaping landscapes.
S 6.2.c Students know beaches are
dynamic systems in which the sand
is supplied by rivers and moved
along the coast by the action of
waves.
What gives waves their energy?
How do waves shape a coast?
What are the causes and effects
of wind erosion?
Objectives
After this lesson, students will be able to
3.3.1 Identify what gives ocean waves their
energy.
3.3.2 Describe how ocean waves shape
a coast.
3.3.3 Identify causes and effect of wind
erosion.
Key Terms
• headland
• beach
• longshore drift
• spit
• sand dune
• deflation
• loess
Preteach
Build Background
Knowledge
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.
Teach Academic Words
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.
4. Hold a magnet close to the sand. Are any of the sand grains
magnetic?
5. 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
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
dragging 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.
108 ◆
L2
Before teaching this section, preteach the
high-use words using the strategy on page
T45.
feature (FEE chur) n. page 110, paragraph 3
The structure, form or appearance.
The offshore sandbar is a feature of the local
beach.
108
A wave nears the shore.
What Is Sand Made Of?
L2
Skills Focus Posing questions
Materials sand from 2 beaches, hand
lens, magnet
Time 15 minutes
Tips If sand is not available from a nearby
lake or ocean, obtain two different kinds
of commercial sand. Students can avoid
mixing the two samples by removing the
first sample before examining the second.
S 6.2.c
Expected Outcome Students probably
will observe differences between the two
samples. Differences might include grain
shape, size, color, or magnetic properties.
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?
For: Links on Waves
Visit: www.SciLinks.org
Web Code: scn-0735
Download a worksheet that will guide students’ review
of Internet resources on waves.
Instruct
How Waves Form
Teach Key Concepts
FIGURE 14
Wave Erosion
Incoming waves bend as they approach the shore (left) and
focus their energy on headlands. Waves carved this sea arch
(right) in Baja California.
Predicting What will eventually happen to the headlands?
Erosion by Waves
Waves are the major force of erosion along coasts, including
the California coast.
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. Recall that abrasion is the
wearing away of rock by a grinding action. 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 14 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.
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.)
Independent Practice
L2
Teaching Resources
Reading/Notetaking Guides
• 3.3 Guided Reading/Study Worksheets
Student Edition in MP3 Format
For: Links on waves
Visit: www.SciLinks.org
Web Code: scn-0735
Chapter 3
L2
◆ 109
Universal Access
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.
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.
Monitor Progress
L2
Oral Presentation Have students explain
how energy travels along a wave.
Answer
Figure 14 The headlands will erode, and
the shoreline will be straighter.
109
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 14 and 15.
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.)
Teaching Resources
Color Transparencies
• Transparency 6.28
Wave-cut cliff
Headland
Sea stack
Left standing when
a sea arch collapses
FIGURE 15
The Changing Coast
Erosion (left) and deposition
(right) create a variety of features
along a coast. You can often see
these features along rocky parts
of the California coast.
Predicting What will eventually
happen to the sea arch?
S 6.2.c
Modeling Wave Refraction
L2
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.)
110
Sea arch
Formed when sea
caves on either side
of a headland join
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 15.
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?
110 ◆
Universal Access
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.
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.
How are beaches dynamic systems?
(Beaches can be considered dynamic systems
because they change constantly in response to
changes in the other parts of the system, such
as the supply of sand, the size and direction of
waves, and coastal features such as headlands
or structures built by people.)
Apply Ask: Why might a spit form where a
beach curves sharply? (The longshore current
moves sand out into the water.)
Sed
im
en
t
Sandbar
Formed by
wave action
L o n gsh
ore D
rift
Deposits by Waves
Waves shape a coast when they deposit sediment,
forming coastal features such as beaches, spits, sandbars,
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.
Beaches are dynamic systems. Beaches are constantly
changing as rivers supply sand and the action of waves moves
sand along the coast.
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 3
◆ 111
S 6.2.c
Skills Focus Calculating
L2
Materials calculator
Time 15 minutes
Tips Remind students that severe storm
erosion occurs in addition to the 1.25 m/yr
rate.
Expected Outcome Students set up and
solve an equation to find the total erosion.
L2
Total Erosion = (1.25 m/yr)
(50 yr) + (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.
Monitor Progress
L2
Writing Have students state in their own
words why a beach is a dynamic system.
Answers
Figure 15 The sea arch eventually will
collapse because of continued erosion, leaving
behind a sea stack.
Waves erode the base of a
rocky cliff, causing sea caves
or a collapse of the upper portion of the cliff.
111
Erosion by Wind
Teach Key Concepts
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.
L2
Deflation and Abrasion
Focus Ask students to describe being in a
sandstorm or being hit by blowing sand.
Teach Ask: How does sediment that is
blown by the wind get into the air? (It is
picked up from the ground at some locations.)
Which sizes of sediment would be picked
up? (Mostly the finer grains, such as clay, silt,
and sand) Which sizes would remain on the
ground? (Mostly the coarser grains, such as
pebbles)
Apply Ask: What effect might abrasion
have on rock surfaces? (It can make smooth,
polished rock surfaces.)
FIGURE 16
Spits
This aerial photograph shows how
longshore drift can carry sand and
deposit it to form a spit.
Inferring What feature along the
coast do you think caused the spit
to form? Explain.
Teaching Resources
Color Transparencies
• Transparency 6.29
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 seacoasts of
the United States, such as the Outer Banks of North Carolina.
In California, barrier beaches can be found at the mouths
of rivers and bays. Examples range from Silver Strand Beach in
San Diego to the barrier beach that shelters Humboldt Bay in
northern California.
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.
Erosion by Wind
FIGURE 17
Sand Dunes
In California, areas of sand
dunes are found in parts of
the Mojave Desert.
112 ◆
112
Imagine a landscape made almost entirely of sand. A sand dune
is a deposit of wind-blown sand. Over thousands of years, wind
sweeps sand across a desert, piling up huge, ever-changing dunes.
Wind by itself is the weakest agent of erosion. Water, waves,
moving ice, and even mass movement have more effect on the
land. Yet wind can be a powerful force in shaping the land in areas
where there are few plants to hold the soil in place. For example,
few plants grow in deserts, so wind can easily move the grains of
dry sand.
Wind causes erosion by deflation and abrasion.
Fine particles
carried through air.
Medium-sized
particles skip
or bounce.
Wind
FIGURE 18
Wind Erosion
Wind erosion moves sediment
particles of different sizes in the
three ways shown at the left.
Comparing and Contrasting
Compare the movement of
sediment by wind with the
movement of sediment by water
in Figure 4 earlier in the chapter.
How are the processes similar?
How are they different?
Larger particles
slide or roll.
Deflation The main way that wind causes erosion is by defla-
tion. Geologists define deflation as the process by which wind
removes surface materials. When wind blows over the land, it
picks up the smallest particles of sediment. This sediment is
made of bits of clay and silt. The stronger the wind, the larger
the particles that it can pick up. Slightly heavier particles, such
as sand, might skip or bounce for a short distance. But sand
soon falls back to the ground. Strong winds can even roll
heavier sediment particles over the ground. Figure 18 shows
how wind erodes by deflation.
Deflation does not usually have a great effect on land. However, in parts of the Great Plains in the 1930s, deflation caused
the loss of about 1 meter of topsoil in just a few years. In
deserts, deflation can sometimes create an area of rock fragments called desert pavement, shown in Figure 19. There, wind
has blown away the smaller sediment. All that remains are
rocky materials that are too heavy to be moved. Areas of desert
pavement are common in California’s Mojave Desert. Where
there is already a slight depression in the ground, deflation can
produce a bowl-shaped hollow called a blowout.
Deposition by Wind
Teach Key Concepts
L2
Sand Dunes and Loess Deposits
Focus Tell students that grains of silt are
barely visible to the unaided eye. Grains of
sand are easily seen.
Teach Ask: Which size of sediment makes
up dunes? (Sand) How high does sand blow?
(Not very) How does sand move across a
desert landscape? (The sand in dunes blows,
and the dunes move slowly across the land.)
How high do you think silt can blow? (Silt
often blows high into the atmosphere.) Do you
think that silt would form dunes when it
comes down? (No. Silt falls to form layers of
loess.)
Apply Ask: Which do you think would be
better soil—old sand dunes or old loess
deposits? (Loess deposits, such as those in the
Midwest)
Abrasion Abrasion by wind-carried sand can polish rock,
but it causes little erosion. At one time, geologists thought that
the sediment carried by wind cut the stone shapes seen in
deserts. But now evidence shows that most desert landforms
are the result of weathering and water erosion.
Where would you be most likely to see evidence of
wind erosion?
FIGURE 19
Desert Pavement
Wind erosion formed this desert
pavement in the Arizona desert.
Wind-driven sand may polish and
shape individual stones.
Chapter 3
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Universal Access
L1
English Learners/Beginning
Vocabulary: Word Analysis Explain
that the word deflate means “to lower.” Ask
students to infer the effect of deflation on
an area of Earth’s surface. Have students
look up the meaning of the word abrade.
Ask them to infer the meaning of the key
term abrasion.
English Learners/Intermediate L2
Vocabulary: Word Analysis Expand on
the Beginning activity by having students
use the words deflation and abrasion in
sentences.
Monitor Progress
L2
Skills Check Have students write a short
paragraph describing the process of
deflation.
Answers
Figure 16 The coastline turns, causing sand
to be deposited.
Figure 18 In both processes, larger grains
slide or roll, and smaller grains are carried in
suspension. One major difference is that
water carries some dissolved material.
Wind erosion often is
evident in areas where
there are few plants to hold soil in place.
113
Deposition by Wind
Assess
S 6.2.a, 6.2.c
Vocabulary Skill
Latin Word Origins deflation
Crescent-shaped dunes form where
the wind usually blows in the same
direction.
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. Waves erode the shore
directly by breaking apart rock. Waves also
carry sand, gravel, and boulders that erode
the shore by abrasion.
2. a. Possible answers: sea cave, wave-cut
cliff, sea arch, sea stack b. Possible answers:
beach, spit, barrier beach c. Most sand
enters oceans from rivers. Spits form as a
result of sand deposition by longshore drift
where the coast turns abruptly.
3. a. Deflation and abrasion b. Sand dunes
and loess deposits c. The sand would erode
much more than the rocks, so the land
surface eventually would be mostly rocks.
Remediation
L2
Writing Have students write a story from
the perspective of a sand grain that is blown
from desert pavement into a sand dune.
Teaching Resources
Reading/Notetaking Guides
• 3.3 Section Summaries
Teaching Resources, Unit 1
• 3.3 Review and Reinforce, Quiz, and
Enrich
Wind direction
FIGURE 20
Movement of Sand Dunes
Wind direction helps determine
the shape and size of sand dunes.
Sand Dunes Sand dunes come in many shapes and sizes.
Some are long, with parallel ridges, while others are U-shaped.
They can also be very small or very large—some sand dunes in
China have grown to heights of 500 meters. Sand dunes move
over time. Little by little, the sand shifts with the wind from one
side of the dune to the other. This process is shown in Figure 20.
In California, sand dunes occur along the coast where rivers have
supplied sand to bays. Examples include the dunes near Monterey Bay, Humboldt Bay, and San Diego Bay. Areas of sand dunes
can also be found in Death Valley and the Mojave desert.
Loess Deposits Sediment that is finer than sand, such as particles of clay and silt, is sometimes deposited in layers far from its
source. This fine, wind-deposited sediment is loess (les). Large
loess deposits are found in central China and in the midwestern
United States. Loess helps to form fertile soil. Many areas with
thick loess deposits are valuable farmlands.
Section 6 Assessment
S 6.2.a, 6.2.c; E-LA: Reading
6.1.0, Writing 6.2.2
3
L1
Call on students to explain how wind
transports different-sized particles.
Performance Assessment
Star-shaped dunes form where the
wind direction changes frequently.
All the sediment picked up by wind eventually falls to the
ground. This happens when the wind slows down or some
obstacle, such as a boulder or a clump of grass, traps the windblown sand sediment.
Wind erosion and deposition may
form sand dunes and loess deposits. Sand dunes can be seen on
beaches and in deserts where wind-blown sediment has built up.
Vocabulary Skill Latin Word Origins Use
what you’ve learned to complete the following
sentence. A process in which wind wears down
surface materials is called ________.
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. Applying Concepts What are two ways in
which waves cause erosion?
2. a. Identifying What are two results of wave
erosion along a coast?
b. Listing What are three features formed by
wave deposition?
c. Relating Cause and Effect Beginning with
the source of sand, explain how a spit forms.
3. a. Reviewing What are two kinds of wind
erosion?
b. Identifying What are two types of features
that result from wind deposition?
c. Predicting In a desert, soil containing a
mixture of sand and small rocks is exposed
to wind erosion. Over time, how would the
land surface change? Explain.
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.
114 ◆
Keep Students on Track Check that
students have completed their designs for
their second model. Encourage students to
begin building their model and planning
their presentation.
114
E-LA: Writing 6.2.2
Writing Mode Expository
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
1 Is incorrect and incomplete