INVESTIGATING ROCKS AND LANDFORMS
Investigation 5:
Erosional Landforms
Key Question
Materials Needed
For this investigation all
groups will need:
• stream table or similar
container
• fine sand
• water reservoir
• water
• books or blocks of
wood to elevate the
stream table
• eraser
Before you begin, first think about this key question.
How can moving water create and change
landforms?
In the last investigation you learned that rock surfaces wear
away slowly by weathering. Think about ways that water can
cause the wearing away of rocks. How does water in rivers
and streams change the landforms? How do waves crashing
on a shore result in changed landforms?
Share your thinking with others in your group and with
your class.
• paper towel
• container for collecting
overflow
• small, thin block of
wood
• index card cut to a
3 cm by 15 cm strip
• ruler or meter stick
• stopwatch or watch
with second hand
Investigate
1. In this investigation different groups will be
studying different forms of water erosion.
The goal of your group will be to find out how
your form of water erosion works. Then you
will invent a way of demonstrating it to others.
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Investigation 5: Erosional Landforms
Here are the questions you will be investigating:
Part A: Erosion by Rivers and Streams
Station A: How does a rapidly moving river erode the
land?
Station B: How does a slowly moving river erode the land?
Station C: How does erosion happen at river bends?
Station D: What erosion takes place where two rivers
meet?
Part B: Erosion by Waves at Shorelines
Station E: How does coastal erosion form cliffs?
Station F: How does erosion happen in bays?
Station G: How does wave erosion affect islands?
Station H: How does wave erosion affect spits?
In your group, discuss what you already know about each
question. Think about what you have seen and what you
have learned.
a) Record your ideas in your journal.
2. Your teacher will provide you
with a stream table, or
something similar to it.
One possible setup
is shown to
the right.
Obtain the
equipment
you will need.
Follow the
procedures
outlined for
your station.
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Inquiry
Modeling
To investigate your particular
erosion process you will set up
and use a model. Models are
very useful scientific tools.
Scientists use models to
simulate real-world events and
processes. They do this when it
is difficult to study the real
thing in a controlled way. It is
important that you try to
model what happens in the
real world as accurately as
possible.
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INVESTIGATING ROCKS AND LANDFORMS
Part A: Erosion by Rivers and Streams
Stations A to D: Model Preparation
1. Place about 3 cm of fine sand in the stream table.
2. Wet the sand thoroughly and smooth out the surface
until it is close to being a plane (flat).
3. Set up one end of the stream table in a way that will
allow you to raise it from 1 through 10 cm. To do this,
put one or two thin wooden blocks or books under one
end. Be prepared to adjust the slope of the stream table to
a value that will be suggested for your particular station.
The slope of the stream table is the height of the high end
of the stream table, divided by the horizontal distance
along the stream table. See the diagram shown.
Do not let fine sand get into
eyes. Wipe up any spills
immediately.
4. Set up the water reservoir
Stop sand here.
so it will feed into the high
end of the stream table.
Be prepared to adjust the
rate of flow of the water.
1 cm to 10 cm high
5. Follow the instructions and
suggestions below for each group to run its test.
a) In your journal, record the question you are
investigating.
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b) Record the conditions of your experiment and the
results you observe. Use both words and sketches.
Stations A to D: Running the Test
Station A: Fast-Moving Stream
With your finger, carve a narrow, fairly straight stream
through the sand, as shown in the diagram. Make the
stream about 1 cm wide and about 1 cm deep. Set the
slope of the stream table to be about 0.4. Run a small
Sand
stream of water down the channel. If necessary,
increase the rate of flow until you can see sand moving.
Observe how erosion proceeds. If your reservoir is small, you
can continue the test by adding more water to the reservoir.
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Describe how the sand is eroded and moved, and how the
size and shape of the channel change with time.
Sand
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Investigating Earth Systems
Investigation 5: Erosional Landforms
Station B: Slow-Moving Stream
With your finger, carve a wide, fairly straight
stream through the sand, as shown in the
diagram. Make the stream about 3 cm wide
and about 1 cm deep. Set the slope of the
stream table to be about 0.1. Run a small
stream of water down the channel. If
necessary, increase the rate of flow until you can see sand
moving. Observe how erosion proceeds. If your reservoir is
small, you can continue the test by adding more water to the
reservoir. Describe how the sand is eroded and moved, and
how the size and shape of the channel change with time.
Station C: River Bends
With your finger, carve two sweeping river
bends in the sand, as shown in the diagram.
Make the stream about 2 cm wide and about
Sand
1 cm deep. Set the slope of the stream table to
be about 0.1. Run a small stream of water
down the channel. If necessary, increase the rate
of flow until you can see sand moving. Observe how the bends
change their size and shape as the water flow erodes, moves,
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and deposits sand. If your reservoir is small, you can continue
the test by adding more water to the reservoir. Describe how
the sand is moved by the flow, and how the size and shape of
the bends change with time.
Station D: Where Two Rivers Meet
With your finger, carve two streams that meet to
form one stream halfway down the stream table.
See the diagram. The channels should be about
Sand
2 cm wide and about 1 cm deep. Set the slope of
the stream table to be about 0.1. Run a small
stream of water down each of the upstream
channels. Try to make the flows in the two channels about
equal. If necessary, increase the rate of flow until you can see
sand moving. Observe how the flowing water erodes theIAT.IES.SE.R.A04.07.IN.TA
sand
and shapes the channel where the two channels meet. If your
reservoir is small, you can continue the test by adding more
water to the reservoir. Describe how the sand is moved by the
flow, and how the geometry develops where the streams meet.
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INVESTIGATING ROCKS AND LANDFORMS
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Part B: Erosion by Waves at Shorelines
Stations E to H: Model Preparation
Do not let fine sand get into
eyes. Wipe up spills immediately.
1. Place the stream table on
a flat surface.
Make a shoreline “bluff”
by placing several
handfuls of wet sand at
one end of the stream
table. Flatten the top of
the material.
board to protect the bluff
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Place boards against the
as you add water
bluff to protect it as you
slowly pour water into
the container to a depth
of 2 to 3 cm.
Use the board at the other
end of the stream table to
Use board as a paddle to
make small waves that
create waves from this
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move toward the bluff.
end.
The waves should be just
large enough to move
your bluff material a little
bit. Start small. Practice your
wave-making technique.
2. Set up your station as described below.
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Station E: Cliffs
Make a cliff like the bluff you made before. This time
make it 8 cm high.
Gently place an index
card along the top,
parallel to the width of
the cliff and with the
edge of the card about
2 cm from the edge of
the cliff.
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Place index card here,
about 2 cm from the edge.
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Investigation 5: Erosional Landforms
Station F: Bays
Make a bay shape about 5 cm high at
one end of your stream table. Gently
place an index card on top of the bay.
Station G: Islands
Make an island about 5 cm high at one
end of the stream table.
Station H: Spits
Make a spit about 5 cm high, as shown
in the diagram.
3. Follow these steps to test your model:
Stations E to H: Running the Test
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As in the preparation steps, use boards to protect your
landform. Gently pour water into the stream table
to a
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depth of about 2 to 3 cm.
Remove the boards slowly and carefully when the water is still.
a) In your journal record the question you are investigating.
b) Make a sketch of the landforms in your stream table for
later comparison.
Use the board to create small waves that move toward the
landform.
Have one member of your group count the number of
waves you produce.
Gradually increase the strength of the waves to model the
wind becoming stronger.
c) As this happens, record your observations.
After 60 waves, stop and make your observations of the
condition of your landform.
d) Record your observations. Make another sketch.
Review your results. If necessary, repeat the experiment to
get more reliable results. Note all observations clearly.
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INVESTIGATING ROCKS AND LANDFORMS
Part C: Demonstrating Your Results
Inquiry
Preparing a Learning
Center
A key part of this investigation
is to educate all groups about
each station. In effect, you are
creating a “learning center”
based on your investigation. In
this way you are mirroring what
scientists do. Think carefully
about how you will do this.
Other groups are dependent on
you for their understanding.
As You Read…
Think about:
1. How are most
landscapes formed?
2. What types of
landscapes are formed
by moving water?
3. What are some
structures that people
have developed to
prevent erosion along a
shoreline?
1. Decide the best way to prepare your model for a
demonstration that will show the other groups what you
have discovered.
Keep in mind that you will only be able to do this once,
so you will need to construct a model that clearly shows
erosion.
2. Hold a session in which each group, in turn,
demonstrates its model to other groups.
As you watch each demonstration, note carefully the
erosion processes. Look for events that are similar, and
different, to your own.
a) Record your observations of each demonstration in
your journal.
Digging
Deeper
Moving Water and Landscapes
Would you have guessed that most landscapes are
formed by moving water? Almost all the land surface of
the Earth is above sea level. Everyone knows that water
runs downhill, because of the pull of gravity. At first the
part of the rain that does not immediately sink into the
ground runs off as broad sheets of water, called sheet
flow or overland flow. You probably have seen this on a
broad and gently sloping parking lot during a heavy
rain. As the overland flow collects down slope on the
land surface, it eventually forms itself into narrower
and deeper channels. The water flows much faster.
Flow in these channels can erode the soil to form
gullies, canyons, and valleys. The scale of the features
formed varies greatly. The flowing water can form
little rills a few centimeters deep on highway cuts, or
great canyons the size of the Grand Canyon.
Most canyons and valleys are not vertical slots in
the landscape. Instead, they have sloping sides. That’s
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Investigating Earth Systems
Investigation 5: Erosional Landforms
because gravity is pulling the rock and soil material on
the slopes downward, too. This downslope force moves
the material down the slope, toward the stream or
river in the bottom of the valley. These movements vary
greatly in their scale and speed.
Rivers and the Rock Cycle
Rivers carry the eroded sediment to the ocean.There it is
deposited as sediment and eventually buried to make new
sedimentary rocks. Rivers are thus an important part of the
rock cycle, which you learned about in an earlier
investigation. If rivers have been removing rock and soil
material from the continents through long periods of
geologic time, why haven’t the continents long since been
worn down to low plains? The answer is that the land of the
continents is raised up, usually very slowly, by various kinds of
Earth movements, providing new high land for rivers to
erode. That’s also an important part of the rock cycle.
Waves and Shorelines
Rivers are not the only places where moving water
shapes the landscape. Ocean waves that move toward
the shoreline deliver their energy to the shoreline in the
form of breaking waves. When waves break, they exert
enormous forces on the sediment and rock at the
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INVESTIGATING ROCKS AND LANDFORMS
shore. Even the solid rock of sea cliffs is worn back
slowly by those forces.
Beaches are masses of sand (or, in some places, gravel)
that are shaped by breaking waves. Each wave, when it
breaks, sends a sheet of water up the beach, carrying
sand up the beach. The water then turns and flows back
down the beach, carrying sand back down the slope. In
this way, grains of sand can travel enormous distances
without getting anywhere! When waves approach the
shore at an angle, however, they carry the sand not just
up and down the beach but also along the beach.
Currents flowing parallel to the beach, called longshore
currents, also move sand along the beach, if they
become strong enough. Over time, large volumes of
sand can be moved along the beach in this way.
Engineers have devised many ways to try to protect
beaches and human-built structures from coastline
erosion and keep shipping channels from being blocked
by sand moving along coastlines. Examples include
groins, jetties, and breakwaters.
Sand is deposited on the
up-current side of a groin.
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Groins are long, wall-like
structures along beaches that
extend into the ocean. Their
purpose is to act as barriers to
longshore currents in order to
control or change sand
movement. A longshore
current loses speed as it meets
the groin. This causes the
current to deposit sand on the
up-current side of the groin.
This builds up the sand on the
beach. Whenever sand on one
beach increases, however, other beaches down-current
lose a lot of sand.
Investigation 5: Erosional Landforms
Jetties are similar structures designed to keep sand from
moving into a ship channel and making it too shallow
for ship traffic. Often, two jetties are used, one on each
side of the channel.
Jetties are often built in pairs.
Breakwaters are barriers
that are built offshore to
protect part of a shoreline.
They act as a barrier to
waves, preventing erosion
and allowing the beach to
grow. However, the beach
behind the breakwater
often grows at the expense
of the shoreline that is not
protected. Seawalls are
sometimes built in places
A breakwater.
where the shoreline is
retreating because of coastal erosion.
Structures built to stop coastal erosion tend to work well
for some period of time. However, they often fail during
especially large storms, and have to be rebuilt. As you can
imagine, there is a great difference of opinion about whether
such structures should continue to be built, or whether the
coastline should be allowed to develop naturally.
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Review and Reflect
Review
1. How do streams and rivers change the shape of the land?
2. What would happen to a landscape without streams and
rivers?
3. In what different ways can lake or ocean water move
land material and shape the shoreline?
4. How can shorelines be protected from erosion?
Reflect
5. What types of land material are most likely to erode
quickly? What do you think erodes slowly? Why do you
think this is so?
6. How can human actions affect the natural process of
erosion?
7. Do you think humans should interfere with the natural
processes of erosion? Explain your answer.
Thinking about the Earth System
8. Explain why erosion is a key process in the geosphere.
9. How do erosion processes you studied in this
investigation involve the hydrosphere?
10. How is the atmosphere involved with the erosion
process?
11. What connection did you find in this investigation
between erosion and the biosphere?
Thinking about Scientific Inquiry
12. Why was modeling an important tool to use in this
investigation?
13. Which variables did you need to control in your station?
14. Which parts of the real world were you not able to
include in your models?
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