Chapter Challenge

4 Surface Processes
Getting Started
Over geologic time, the surface of the land, or landscape, is constantly
being broken down or built up. If you could watch a time-lapse film
of the landscape near you, you would see changes that you might
not notice from day to day. Some changes, such as hills wearing
down, happen very slowly. Other changes are so fast that they are
often catastrophic. These include mudslides, volcanic eruptions,
and earthquakes.
Think about how landforms are shaped in your community.
• How long does it take the surface where you live to change
by natural processes?
• How large or small are these changes?
• How do these changes affect what is happening to the land now
and in the future?
• In what ways do humans build up the landscape?
• In what ways do humans break down the landscape?
What do you think? Write down your ideas as clearly and with as
much detail as possible. Sketch diagrams to illustrate your ideas.
Be sure to look at the diagram of the Earth systems at the front of
this book. Be prepared to discuss your responses with your small
group and the class.

Scenario
The United States Olympic Committee is looking for a site in the
United States to bid for the Summer Olympic Games within the next
ten years. Bidding for this costs hundreds of thousands of dollars.
Cities have to be fairly confident that they can win even before the
process starts. The bidding city must make a very strong case that it
has the most suitable site. This year, high school Earth-science students
have been asked to help. The committee is considering bids from two
states—Florida (FL) and Alaska (AK). These two states have very
different surface and bedrock geology. They want you to use your
scientific knowledge to help find a site that is geologically suitable
to host the events.

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 Chapter Challenge
The Olympic Games are centered on a particular city. Therefore, each team will choose a
site in each state to evaluate. For example, a team might choose Miami, FL and Anchorage,
AK. Some events can be held outside of the cities as well. Your team’s job will be to
collect information about the geology of your two cities and the area around them. You
need enough information to make a report on the suitability of each city. You will need
to consider that new roads, bridges, and buildings may be necessary. The city that is most
suitable to host the Games must be able to build the following.
• A stadium
• An equestrian center for horse riding events
• A rowing center
• A volleyball center
• An aquatic center
• A tennis center
• Roads for cycling and mountain biking courses
• An artificial river for kayaking
• An athletes’ village (a place for the Olympic athletes
to stay during the games)
• New roads
• Parking lots

Your team will need to consider all of the following items in the evaluation of
your two cities.
• Bedrock geology • Landforms and surface mobility
• Relief and slopes • Soils and soil-related hazards
• Drainage basin geometry • Other important geomorphic factors
• Rivers, flow conditions, and potential • Other factors that might make
for flooding building risky
• Mass movements

The United States Olympic Committee wants a poster presentation and a written report
from each team. Your poster should include the following.
• Maps of each state and city with descriptions, diagrams, and data showing the suitability
of the land surface for development.
• Notes on the maps showing surface landforms and the processes that form them.
• Risk assessment for development (shown on the maps).
• A layout on the maps showing where you would place the various Olympic facilities.

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 Chapter Challenge

Your report should include the following.

• An introduction to the maps for each city (1–2 pages)
• Your appraisal of how stable the surface is for each city
• A list of advantages and disadvantages for hosting the games in each city
• A conclusion as to whether the Summer Olympic Games would be best held
in the Florida city or the Alaska city

laska Miami,
rage, A Florida
A n cho

Assessment Criteria
Think about what you have been asked to do. Scan ahead through the sections of the
chapter to see how they might help you to meet the challenge. Work with your classmates
and your teacher to define the criteria for assessing your work. Record all this information.
Make sure that you understand the criteria as well as you can before you begin. Your
teacher may provide you with a sample rubric to help you get started.

Engineering Design Cycle

Your Chapter Challenge is to compare the suitability
of two sites to host the Summer Olympic Games.
Then you will need to prepare a poster presentation
and a written report. Determining the best locations
in each city to develop the Olympic facilities
will be a large part of the report. You will use a
simplified Engineering Design Cycle to help your
group develop these presentations. Establishing a
clear Goal is the first step in the process. With your
group, define the project you need to create. Then,
identify the Assessment Criteria. Think through some
of the constraints that you will face. Discuss possible
ways to present your information.

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 As you experience each of the chapter sections, you will gain information. This is a part
of the Inputs you will use in the Engineering Design Cycle. These Inputs will include
vocabulary and concepts about Earth’s surface processes. Remember, it is important to
convince the committee that the
site you choose is suitable to
host the games. This includes Earth/Space Science Corner
building the necessary facilities.
After the first five sections of Surface Processes
the chapter, you will work on
part of the project and receive • Coastal processes • River-channel processes
Feedback. Your classmates and and sediments
• Drainage basins
teacher will advise you as to • River systems and
which parts of your project are • Glaciers and glacial morphology
processes
good. They may also suggest • Slopes and mass movements
which parts need to be refined. • Groundwater and aquifers
• Soils
This Mini-Challenge will be the • High- and low-gradient
streams • Streamflow and discharge
first Output of the Engineering
Design Cycle. You will evaluate • Hydrologic cycle • Topography and maps
the surface geology of each of • Landforms, erosion, • Unconsolidated and
your selected regions. It should and deposition lithified sediments
include information about • Meltwater processes • Wind erosion
surface processes, geologic
conditions, and landforms in
each city. You need to provide
suitable areas for development.
Also, you need to identify
dangerous conditions that might
make one city unsuitable. You
will then revisit the Engineering
Design Cycle after the second
half of the chapter. At that
time you will have gained the
other Inputs to complete your
final presentation.

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 Chapter 4 Surface Processes

Section 1 The Water Cycle

What Do You See?

Learning Outcomes Think About It

In this section, you will Imagine you are watching the news on television and the
• Calculate the time required meteorologist says, “We received one inch of rain yesterday.”
to melt ice.
• How much water was that?
• Graph data to determine
a heating curve for ice. • Where is all that water today?
• Identify and analyze the • How might that water be changing Earth’s surface?
various sources and distribution
of salt water and fresh water Record your ideas about these questions in your Geo log. Be
on Earth. prepared to discuss your responses with your small group and
• Generate a graphic model the class.
of the transport of water
between reservoirs within
the water cycle.
Investigate
• Understand that hydrogen In this Investigate, you will examine some of the unique
bonds can be used to explain properties of water by calculating the time required to melt ice.
some of the unique properties You will then identify the various places where salt water and
of water.
fresh water are stored on Earth. You will analyze how water is
distributed among these sources. Finally, you will look at the
various ways and rates in which water moves from place to
place within the Earth system.

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 Section 1 The Water Cycle

Part A: Calculating the Time Required a) Record the temperatures in a

to Melt Ice data table.
1. Read all of the steps of this investigation. b) Make a graph with temperature on
Before you do the experiment, write the vertical axis and time on the
down your hypothesis about how the horizontal axis. Choose the scales on
temperature of the container will the axes so that the curve you plot is
change over time. not too steep or too gentle.
a) How long will it take for the material 5. Compare your results to your hypothesis.
to reach 30°C (86°F)?
a) How do you explain any differences?
b) How will the temperature change 6. From the graph, answer the following
over time? In your log, sketch a questions in your Geo log:
graph of temperature over time.
a) At what time do you think the ice in
the container began to melt?
Goggles must be worn throughout this activity.
Wash your hands when finished. b) At what time do you think that all of
the ice in the container had melted?
c) Different slopes of the curve you
2. From a freezer or cooler of ice, obtain obtained reflect different rates of
a small metal container packed full of increase in temperature with time.
crushed ice. Place it on a hot plate. How can you explain the differing
3. Cover the container with a piece of rates of increase in temperature?
styrene foam and insert a thermometer d) In most experiments, the
into the container. The bulb of the measurement data points deviate at
thermometer should be about 2.5 cm least slightly from a perfectly smooth
from the bottom. curve. That effect is called “scatter
in the data.” How might you explain
the scatter in your data?
Part B: Water in the Hydrosphere
1. Fill five 4-L milk jugs with water. These
five jugs of water represent all the water
on Earth.
a) Calculate how many milliliters are in
the 20 L (five milk jugs). Record this
value. Note: The actual amount of
water may not be exactly 20 L, but
for the purpose of this model it will
be satisfactory.
2. Ice (mostly in the form of glaciers)
4. Take the initial temperature reading holds 1.81 percent of all the water on
and then turn the hot plate on low. Earth (see Table 1 on the next page).
Continue to read the temperature every a) If 20 L represents all the water
two minutes until the temperature on Earth, calculate the number of
reaches about 30°C. milliliters that represents the water
found in glaciers.

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 Chapter 4 Surface Processes

3. Remove this amount from the milk jugs

Clean up any spills. Dispose of the water.
and pour it into a separate container
labeled “glaciers.”
5. Develop your own model. The model
4. Repeat Steps 2 and 3 for the water should show the percentages of each
found in groundwater, saltwater and category of fresh water (ice and liquid)
freshwater lakes and streams, and and liquid fresh water. Use the values in
the atmosphere. Table 1. Use something other than water
a) Record your calculations. as the physical material for your model.
b) Calculate the number of milliliters a) From your work with the models,
of water in the oceans, but leave the write down several observations or
water in the milk jugs. discoveries that you found most
surprising or striking. Explain
c) Find the sum of the six values. your observations.
How do you account for the
“missing” water? Have your teacher check the plan for your model.

Table 1: Distribution of Water in the Hydrosphere

Percentage of Percentage of
Percentage of
Reservoir Fresh Water Fresh Water
Total Water
(Ice and Liquid) (Liquid Only)
Oceans 97.54 — —
Ice (mostly glaciers) 1.81 73.9 —
Groundwater 0.63 25.7 98.4
Saltwater lakes
0.007 — —
and streams
Freshwater lakes
0.009 0.36 1.4
and streams
Atmosphere 0.001 0.04 0.2
These figures account for 99.9 percent of all water. They do not add up to 100 percent, because
some water is tied up in the biosphere and as soil moisture.

Part C: Modeling the Water Cycle parts: reservoirs (places where water is
1. The total volume of water near Earth’s stored) and processes (ways that water
surface is almost constant. This water is moved from place to place).
is in constant motion. The water cycle a) Using blank sheets of paper, draw a
describes how Earth’s water moves from rectangular box for each reservoir
place to place in an endless cycle. Study item. Try to keep the dimensions of
the diagram on the next page that shows the boxes less than about 2.5 cm.
a simplified version of the water cycle. Write the name of each reservoir in a
2. On the following page is a more box. You will have to write small.
complete list of the components of the b) Draw a circle for each process item.
water cycle. There are also definitions Make the diameter of each circle less
of some terms with which you may not than about 2.5 cm. Write the name
be familiar. The list is divided into two of each process in a circle.

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 Section 1 The Water Cycle

Reservoirs: Definitions:
• oceans • groundwater Calving: Some glaciers end in the ocean.
• atmosphere • lakes As the glacial ice moves forward into
• clouds • rivers the ocean water, it breaks away from the
glacier in huge masses, to float away as
• glaciers • vegetation
icebergs, which gradually melt.
• soil moisture
Groundwater: Some of the liquid water at
Processes: Earth’s surface moves downward through
• evaporation from the ocean surface porous Earth materials until it reaches a
• precipitation onto the ocean surface zone where the material is saturated with
water. This water flows slowly beneath
• evaporation from the land surface
Earth’s surface until it reaches rivers, lakes,
• precipitation onto the land surface or the ocean.
• precipitation onto glaciers
Infiltration: Some of the rain that falls on
• condensation to form clouds Earth’s surface sinks directly into the soil.
• melting of glaciers Soil Moisture: Water, in the form of liquid,
• calving of glaciers vapor, and/or ice, resides in Earth’s soil
• surface runoff into rivers layer. It is the water that remains in the soil
• surface runoff into lakes after rainfall moves downward toward the
groundwater zone. Soil moisture is available
• infiltration of surface water
for plants. What is not used by plants
• groundwater flow gradually moves back up to the soil surface,
• river flow where it evaporates into the atmosphere.
• transpiration from plants
• uptake of water by plant roots

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 Chapter 4 Surface Processes

Surface Runoff: Some of the rain that falls 5. Once everyone in your small group
on Earth’s surface flows across the land has agreed upon the best version of the
surface, eventually reaching a stream, water cycle, compare your results with
a river, a lake, or the ocean. those of the other groups. Answer the
Transpiration: Water taken up by the roots following questions:
of plants is delivered to the leaves. Some of a) Is there net movement of water vapor
this water is used to make new plant tissue, from the oceans to the continents, or
and some is emitted from the leaves in the from the continents to the oceans?
form of water vapor, by a process called Explain your answer.
transpiration.
b) Is there net movement of liquid water
3. Cut out all of the boxes and circles with from the oceans to the continents, or
a pair of scissors. from the continents to the oceans?
Explain your answer.
4. On a poster board, draw a horizontal
line lengthwise across the middle of the c) How does the nature of the water
poster board. This represents Earth’s cycle vary with the seasons?
surface in a vertical cross-section view.
Part D: The Movement and Balance
a) On the left half of the poster board, of Water in the Water Cycle
draw some mountains to represent
1. Study the diagram on the next page that
a continent.
shows the rates at which water moves
b) On the right half of the poster board, from one reservoir to another within
draw a small island or a sailboat to the water cycle. Use the diagram to
represent a large ocean. answer the following:
c) Using the simplified water-cycle a) Rank the quantities of water within
diagram as a model, place the the reservoirs shown from highest
boxes and circles that you have to lowest.
created where you think they belong. b) Rank the rates at which water moves
Tape them to the poster board with among the various reservoirs from
small pieces of removable tape. Using highest to lowest.
removable tape allows you to adjust
the positions of the boxes and circles c) What is the difference between the
as needed. rates of evaporation and precipitation
over the oceans?
d) With colored pencils, draw arrows
d) What is the difference between the
between the various boxes and circles
rates of evaporation and precipitation
to show the movement or transport
over land?
of water from place to place on or
near Earth’s surface. Remember that e) How do the differences that you
a circle (process) will be located in calculated in Steps 1.c) and 1.d)
the middle of an arrow between compare to the rate at which water is
two different boxes (storage places). entering the oceans from the flow of
Think about whether the movement runoff and groundwater?
or transport is in the form of liquid
water, water vapor, or ice (or two or
three of these at the same time). Use
blue for liquid water, red for water
vapor, and green for ice.

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 Section 1 The Water Cycle

Digging Deeper
EARTH’S WATER
The Unusual Properties of Water
Did it surprise you that water is a very unusual
substance? Its unusual properties are explained
by the atomic structure of the water molecule.
This structure consists of two hydrogen atoms
bonded to an oxygen atom. (See Figure 1.)
Because of the structure of the orbits of
electrons around the three atomic nuclei, the
three atoms are not in a straight line. Instead,
they form an angle of 108°. Also, the orbiting
electrons are more strongly attracted by the
oxygen atom than by the hydrogen atoms.
(Recall that electrons have a negative charge.)
Figure 1 A water molecule
These two facts mean that the oxygen “side”
is a polar molecule.
of the molecule is negatively charged and the
hydrogen “side” of the molecule is positively Geo Words
charged. (See Figure 1.) Molecules like this are called polar molecules. polar molecule: a
A polar molecule has a negative charge on one side and a positive molecule with a
negative charge
charge on the other. on one side and a
positive charge on
the other.

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 Chapter 4 Surface Processes

Objects with the same electric charge repel one another. Objects with
different electric charges attract one another. The negative end of a water
molecule repels the negative end of another water molecule. However,
Geo Words it attracts the positive end. Attraction between opposing charges in a
hydrogen bond: a molecule creates a bond. This type of bond is called a hydrogen bond.
weak chemical bond Hydrogen bonds can explain some of the odd physical characteristics
between a hydrogen
atom in one polar
of water.
molecule and an The temperature of any material is a measure of the average thermal
electronegative
atom in a second
vibration of its atoms and molecules. As heat is added to the material, the
polar molecule. thermal vibrations increase. As a result, the temperature increases. As heat
is added to ice, the water molecules vibrate more and more. Eventually,
the vibrations break the hydrogen bonds that hold the structure together.
The ice then melts to liquid water. Would you have guessed that it takes
so much explanation to account for such a seemingly simple thing as the
melting of ice?
When liquid water freezes to form ice, the water molecules become
arranged in a specific way. The negatively charged hydrogen sides of the
molecules are bonded to the positively charged oxygen sides of neighboring
molecules. The water molecules are all bonded together with hydrogen
bonds. When the ice melts, the water molecules are free to pack themselves
more closely together. Because they are packed closely, the water molecules
occupy less space. This results in a higher density. In other words, liquid
water has a higher density than ice. That is why ice floats in water. (See
Figure 2.) Out of the millions of substances known to science, only a handful
has the property that the solid form can float in the liquid form.

Figure 2 Ice floats in water—an unusual but very important property of water.

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 Section 1 The Water Cycle

As thermal energy is added to liquid water, the temperature rises. The

thermal vibration of the water molecules becomes stronger. Yet, as you
saw in the Investigate, it takes a lot more heat to raise the temperature of
water than ice. The reason is that only some of the hydrogen bonds are
broken when ice melts. At any given time, a percentage of the molecules
in liquid water are bonded to each other. As heat is added to water, a
smaller and smaller percentage of the water molecules are hydrogen-
bonded. Heat added to water increases the thermal vibration. This breaks
more of the hydrogen bonds as well. The amount of heat needed to raise Geo Words
the temperature of a substance is called its heat capacity. Because of the heat capacity: the
heat needed to break hydrogen bonds, the heat capacity of water is far quantity of heat
higher than any other common substance. energy required
to increase the
If you add the same amount of heat to equal masses of liquid water and temperature of a
dry soil, the temperature of the soil rises much faster. That is why lakes material or system;
typically referenced
can be chilly even on sunny, warm days. Because water can absorb so as the amount of heat
much heat, the oceans are the principal heat reservoir on Earth’s surface. energy required to
For ordinary substances, higher pressure causes the melting temperature generate a 1°C rise in
to be higher. The high pressure tends to keep the solid from expanding the temperature of 1 g
of a given material.
to form the liquid. For water, however, it is the opposite. Ice shrinks
when it melts. Higher pressure helps with the shrinkage. It causes the
melting temperature to be slightly lower.
About 71 percent of Earth’s surface
is covered by water. The unusual
properties of water make it an
important substance to the whole
Earth system. The hydrogen bonds
between water molecules allow for
water to exist as a liquid over a wide
range of temperatures. It has a high
boiling point, 100ºC. It also has a
low freezing point, 0ºC. As a result,
water remains a liquid in most of
the environments on Earth. Liquid
water can store a large amount
of heat. This property protects
organisms that live in water. It is also
responsible for the ability of water
to regulate Earth’s climate. Liquid Figure 3 Nearly two percent of Earth’s
water exists as ice.
water can also dissolve a wide variety
of compounds. This ability enables
water to remove and carry materials from one part of the Earth system
to another. Liquid water has a higher density than frozen water. This
means that ice floats on top of water. If water did not have this property
then ponds, lakes, and streams would freeze from the bottom up. This
would have damaging effects on aquatic life. Finally, the expansion of
water as it freezes fractures rocks, causing rocks to break apart.
It has an important role in shaping Earth’s surface.

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 Chapter 4 Surface Processes

The Water Cycle

Water is the only common substance that exists at Earth’s surface as
a solid, a liquid, and a gas. Water is present at or near the surface
everywhere on Earth. In many places, the presence of water is obvious.
You see it in the form of lakes, rivers, glaciers, and the ocean. You will
read more about glaciers in a later section. Even in the driest of deserts,
however, it rains now and then. Although the humidity there is usually
very low, there is at least some water vapor in the air.
Water is in a continuous state of change. It can be found in the form of
liquid, solid, or vapor. It is also found in many different places. Water is
continuously moving from one place to another. It takes many different
Geo Words pathways in its movement. The combination of all of these different
water cycle (or movements is called the water cycle. It is also referred to as the hydrologic
hydrologic cycle): the cycle. The water cycle is an essential subsystem or component of the Earth
constant circulation
system. Wherever water moves, it brings with it the capacity to physically
of water from the
sea, through the and chemically change Earth’s surface.
atmosphere, to
the land, and its The water cycle is called a cycle because Earth’s surface water forms a
eventual return to the closed system. In a closed system, material moves from place to place
atmosphere by way within the system. However, it is not gained or lost from the system.
of transpiration and Earth’s surface water is actually not exactly a closed system. Relatively
evaporation from the
land and evaporation small amounts are gained or lost from the system. Some water is buried
from the sea. with sediments. It becomes locked away deep in Earth for geologically
closed system: a long times. Volcanoes release water vapor contained in the molten rock.
system in which Nonetheless, these gains and losses are very small compared to the
material moves from volume of water in Earth’s surface water cycle.
place to place but is
not gained or lost Evaporation and precipitation are the major processes in the water cycle.
from the system. The balance between these processes varies from place to place and
evaporation: the time to time. As you saw in the Investigate, there is more evaporation
change of state of
than precipitation over Earth’s oceans. On the other hand, there is more
matter from a liquid
to a gas. Heat is precipitation than evaporation over Earth’s continents. This is important
absorbed. for two reasons. There is a net movement of water vapor from the oceans
precipitation: water to the continents. There is also a net movement of liquid (and solid) water
that falls to the from the continents to the oceans as well.
surface from the
atmosphere as rain, The oceans cover about three quarters of Earth. Ocean water is constantly
snow, hail, or sleet. evaporating into the atmosphere. If enough water vapor is present in the
air, and if the air is cooled sufficiently, the water vapor condenses to form
tiny droplets of liquid water. If these droplets are close to the ground,
they form fog. (See Figure 4.) If they form at higher altitudes, by rising
air currents, they form clouds. Sometimes, water vapor in clouds reacts
chemically with compounds in the air, forming acids. These acids mix with
raindrops and fall as acid rain. Acid rain creates holes or soft spots in
rocks, causing rocks to break apart more easily.

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 Section 1 The Water Cycle

Figure 4 What part of the water cycle does the fog over the San Francisco Bay illustrate?

All of the solid or liquid water that falls to Earth from clouds is called
precipitation. Snow, sleet, and hail are solid forms of precipitation. Rain
and drizzle are liquid forms of precipitation. When rain falls on Earth’s
surface, or snow melts, several things can happen to the water. Some
evaporates back into the atmosphere. Some water flows downhill on
the surface, under the pull of gravity, and collects in streams and rivers. Geo Words
This flowing water is called surface runoff. Most rivers empty their water surface runoff: the
into the oceans. Some rivers, however, end in closed basins on land. part of the water
Death Valley and the Great Salt Lake are examples of such closed basins. that travels over
the ground surface
Running water creates many landforms. Moving water is the major agent without passing
that shapes Earth’s land surface. As water moves over the land, it carries beneath the surface.
particles of rock and soil with it. Eventually, these particles are deposited
in other places where the moving water slows down.

Figure 5 Some of the water that falls to Earth’s surface collects in streams.

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 Chapter 4 Surface Processes

Some precipitation soaks into the ground rather than evaporating or

running off. Under the pull of gravity, the water moves slowly downward.
It percolates through the open pore spaces of porous soil and rock
Geo Words material. Eventually, the water reaches a zone where all of the pore spaces
groundwater: are filled with water. This water is called groundwater. Some water, called
the part of the soil moisture, remains behind in the surface layer of soil. (See Figure 6.)
subsurface water
that is in the zone of
saturation, including
underground streams.
porosity: a measure
of the percentage of
pores (open spaces) in
a material.
permeability: a
measure of how easy
it is to force water
to flow through a
porous material.
saturated zone: the
zone, beneath the
water table where all
of the pores are filled
with water.
water table: the
surface between the
saturated zone and
the unsaturated zone
(zone of aeration). Figure 6 Schematic diagram of groundwater flow.

Several factors affect how groundwater moves through rock and

sediment. Porosity is one factor. It is a measure of the percentage of
pores (open spaces) in a material. Permeability is another factor. It is
a measure of how easy it is for water to flow through a material. In
general, permeability increases with grain size. Large-grained materials
have larger pore spaces. Also, the pore spaces are well connected. Water
passes most easily through these types of materials. Sand and gravel
are examples of permeable materials. Water passes very slowly through
finer materials. They have few and poorly connected pore spaces. These
materials are called impermeable. Clay and granite are examples of
impermeable materials.
Down to a certain depth below the surface, the pores in the sediment and
rock are mostly filled with air. The exception is when water is percolating
downward after a heavy rain. (Percolate is a term used to describe the
passing of water through a porous material.) This is called the unsaturated
zone. Eventually the downward-moving water reaches a zone called the
saturated zone. In this zone, all of the pores are filled with water. The top
of the saturated zone is called the water table. These zones are illustrated
in Figure 7. The water table can be located at the surface in places next to
rivers and lakes, and also in wetlands. In some areas it can be many tens
of meters below the surface.

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 Section 1 The Water Cycle

Figure 7 The main two

zones of the groundwater
system—saturated and
unsaturated. The water
table marks the upper
surface of the saturated
zone.
Because groundwater must move through small pores, it flows very
slowly. Groundwater speeds of one meter per day are considered high.
Speeds as low as one meter per year are common. The smaller the
pore spaces between the grains, the slower the groundwater flows.
Groundwater moves from areas where the water table is relatively high
to areas where it is relative low. Figure 8 shows the flow of groundwater
in a typical landscape.

Figure 8 The water table (WT) is shown as a dashed line. The arrows show
the direction of groundwater flow.

Precipitation that falls to Earth’s surface is important in surface processes.

Geo Words
The water breaks solid bedrock into smaller and smaller pieces. Many
organisms begin to live in these materials. Over time, the organisms die, transpiration: the
process by which
decay, and add nutrients to the materials to form soil. The roots of plants water absorbed
absorb some of the water that soaks into the soil. This water travels by plants, usually
upward through the stem and branches of the plant into the leaves and is through the roots,
released into the atmosphere as a vapor in a process called transpiration. is emitted into the
atmosphere from the
plant surface in the
form of water vapor.

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Geo Words
reservoir: a place in
the Earth system that
holds water.
flux: the rate of
movement of water
from one reservoir to
another.

Figure 9 Plants such as these broad-leaf trees play an important part in the
Checking Up water cycle.

1. In your own words,

describe the atomic Each year, about 37,000 km3 of water flows from the surface of the
structure of the continents into the oceans. That is how much more precipitation there
water molecule. is than evaporation on the continents. This water carries sediment
You may wish to
particles into the ocean. The particles come to rest on the ocean floor.
use a diagram in
your description.
It also carries dissolved minerals into the ocean. When seawater
evaporates, the dissolved materials are left behind. Over time, this
2. Why does ice float
in water?
process has made the oceans as salty as they are now.
3. Does ice melt more In Earth systems science, the water cycle is viewed as a flow of matter
or less easily under and energy. Each place that holds water is called a reservoir. The rate
pressure? Explain
at which water flows from one reservoir to another in a given time is
your answer.
called a flux. Energy is required to make water flow from one reservoir
4. In your own words,
to another. On average, the total amount of water in all reservoirs
describe the water
cycle.
combined is nearly constant. Although the data table in the Investigate
suggests that reservoirs have a constant amount of water in them, this
5. Explain why the
water cycle can be
is not the case. The amount of water stored in any one of them varies
viewed as a closed over time. For example, in many areas there may be more water in the
system. form of groundwater during the spring. During this time precipitation
6. Describe three is high, and water use and evaporation is low. There may be less in the
“paths” of the summer. That is when precipitation is low, and evaporation and water
water cycle that use are high.
precipitation can
follow once it
reaches the surface
of Earth.

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 Section 1 The Water Cycle

Think About It Again

At the beginning of this section, you imagined you were watching the news on television
and heard the meteorologist say, “We received one inch of rain yesterday.” You were then
asked the following:
• How much water was that?
• Where is all that water today?
• How might that water be changing Earth’s surface?
Record your ideas about these questions now. Refer to the ways in which water is stored
and cycled through the Earth system.

Reflecting on the Section and the Challenge

You read about several unusual properties of water. It takes a large amount of heat to
melt ice. It takes even more heat to raise the temperature of water. Unlike almost all other
substances, water is less dense in the solid form than in the liquid form. The melting
temperature of ice is slightly lower at high pressure than at low pressure. Understanding
these properties helped you understand the nature of the water cycle. You saw that water
is transported between reservoirs within the Earth system by different processes. You also
determined that the rate at which water flows from one reservoir to another in a given time
varies. This information will be important as you look at the role of water in breaking
down and building up Earth’s surface.

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Understanding and Applying

1. Which do you think responds more slowly to seasonal changes in climate: an ice
sheet or a wide ocean? Explain your answer using what you learned about the
properties of water.
2. What would happen to Earth’s oceans if ice sank instead of floated in water?
3. Prepare a table of the important physical properties of ice.
4. Describe the different conditions on Earth under which water is a solid, a liquid,
or a gas.
5. If 37,000 km3 of water flow from the surface of Earth into the oceans each year,
how many cubic kilometers of water evaporate from the oceans each year?
6. The data table in the Investigate defines the hydrosphere somewhat differently than
the image shown in the front of the book. Explain any differences you note between
the data table and the image.
7. Preparing for the Chapter Challenge
Write a few paragraphs explaining how the properties of water influence the
movement and storage of water within the Earth system. As you continue through this
chapter, you will be applying these ideas in your evaluation of the suitability of the
landscape of each city for Olympic facilities.

Inquiring Further
1. Calculating the change in volume when water freezes
With the approval of a responsible adult, try the following investigation at home.
• Take a plastic milk jug—one with a screw-top cap and dimples on the side (small
depressions in the plastic). Fill it completely full of water. Pour the water into a
large measuring cup and measure the volume of water.
a) Record the volume, then pour the water back into the jug.
• Cap the jug and put it in a freezer until it is frozen solid.
b) What happens to the shape of the jug?
• Remove the frozen jug from the freezer. Set the jug aside (perhaps until the next
day) until all the ice has melted. Keep the cap on the jug to prevent evaporation.
c) How does the water level in the jug compare with the level when you put the jug
in the freezer?
• Fill a measuring cup with water.
d) Record the volume of water in the cup.
• Using the measuring cup, pour water into the jug until it is brim-full. Be as
careful as possible not to disturb the shape of the jug as you handle it.

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 Section 1 The Water Cycle

e) Calculate and record the volume of water that you needed to add to fill the jug
to the top. To do this you will need to subtract the final volume of water in the
measuring cup from the initial volume you recorded in Step d).
f) Calculate the percentage change in volume of the jug using this equation:

percent change = additional volume of water added ⫻100%

original volume of water in jug

g) What do you think is the purpose of the dimples in the milk jug?
h) Is your result likely to be an overestimate or an underestimate? Explain your answer.
i) What do you think might happen to soil or rock when water that is trapped inside
of it freezes?

2. Volcanic eruptions and the water cycle

Volcanic eruptions release large amounts of water vapor. After you have done some
research, construct a water-cycle diagram that shows the reservoirs and flow of water
and water vapor in a volcanic region.
3. Dating water
Investigate how chlorofluorocarbons (CFCs) released from aerosols and tritium
(hydrogen 3) released during global nuclear testing in the 1950s and early 1960s
are used to determine the age of groundwater.

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 Chapter 4 Surface Processes

Section 2 Rivers and Drainage Basins

What Do You See?

Learning Outcomes Think About It

In this section, you will Look at the system of veins on a leaf. Pick a spot on a small vein
• Interpret topographic maps to near the edge of the leaf. Trace the vein until it joins the stem.
identify large and small streams Repeat this for another spot on the other side of the leaf.
within your community.
• Explore the nature of a
• How is the system of veins on a leaf similar to and different
drainage basin. from the system of streams and rivers that carry water into a
• Analyze maps to identify the
larger river, like the Mississippi?
drainage basin in which your Record your ideas about this question in your Geo log. Include
community is located.
a quick sketch. Be prepared to discuss your responses with your
• Evaluate important interactions small group and the class.
between communities and river
systems.
Investigate
In this Investigate, you will explore the factors that affect
stream drainage.
Part A: Local Stream Drainage
1. Use a topographic map of your community for the following
exercises. (See the example on the next page.) If you do not
have a river or stream in your community, use a topographic
map from a nearby community. Find a stream on the map that
flows into or joins another stream.

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 Section 2 Rivers and Drainage Basins

a) What do you notice about its b) Count the number of streams of

size relative to the stream that each size. Make a data table for
it flows into? your results.
b) In which compass direction does c) Describe one or two relationships
it flow? between smaller streams and
larger streams.
c) Describe how the relative sizes of
streams can be used to determine the d) Write a paragraph describing the
direction in which a stream flows. pattern that is formed by the rivers
and streams in your community.
d) Contour lines on a topographic
map show elevation above sea level. e) Exchange your drawing and
What is the highest elevation along explanation with another group. In
the course of the stream you chose? your log, explain any similarities and
What is the lowest elevation? Record differences that you notice.
these values in your log.
Part B: Regional Stream Drainage
e) How can you use contour lines to 1. Depending upon the region where
determine the direction in which a you live, you will need some of the
stream flows? following materials: topographic maps
(community and/or state), road maps
or road atlases (your state and the
United States), and a satellite image of
the United States. A relief map of your
state or region might be helpful as well.
Be prepared to share these resources
with other groups. Look at the local
topographic map. Find your school or a
familiar landmark on the map. Imagine
a rainstorm at your school. Consider
the rainwater that does not evaporate,
soak into the soil, or get swallowed by
a thirsty animal.

2. Use a photocopy of the topographic

map (or a clear overlay) to show the
range of stream sizes located in your
community.
a) Trace the pattern of streams on a copy
of the map or on the clear overlay.
Devise a way to show small streams,
medium streams, and large streams.
Be prepared to explain your drawing.

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 Chapter 4 Surface Processes

a) On a copy of the topographic map 3. Work with the local topographic

or on a clear overlay, trace the path map and maps that show elevation
of a drop of water that falls on your of larger regions.
school as it flows downhill from
a) Locate where the rainwater that
your school to the nearest stream.
fell on your school flowed out of
Keep in mind that water that falls
your community (or off the local
on the ground follows a path that is
topographic map). Follow the path
downhill and always perpendicular
of the water farther downstream.
to the contour lines. Where would
Name several cities that the
a drop of water that fell on your
rainwater passes.
school leave your community (or go
off the map)? b) What is the ultimate destination of
the rainwater that landed on your
2. Working with your group, figure out a
school? Explain how you know.
way to outline boundaries of the area
that drains into the stream you have c) From what you have explored so far,
chosen. Use either a photocopy of the explain why pollution that enters a
map, a sheet of tracing paper, or a clear stream near your school can affect a
overlay. The area you have drawn is community many miles away within
called a drainage basin. the same river system.
a) In your own words, summarize the
meaning of a drainage basin.

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 Section 2 Rivers and Drainage Basins

Digging Deeper
RIVER SYSTEMS
Parts of a River System
In the Investigate, you explored the factors that affect the ways in which
river water flows through a drainage basin. A river system is a network
of streams. These streams drain the surface water off a continent or part
of a continent. River systems are an essential part of the hydrologic cycle.
They transfer billions of cubic liters of water from upland areas to the
ocean. A river system has three parts: a tributary system, a trunk stream,
and a distributary system. Geo Words
• A tributary system consists of many small streams. These streams flow tributary system: a
together into slightly larger streams, which flow into larger streams, group of streams that
contribute water to
and then into even larger streams. (See Figure 1.) Tributary systems are another stream.
commonly found in mountainous areas.

Figure 1 Map of a tributary system. How many tributary streams are shown in
this map?

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 Chapter 4 Surface Processes

Geo Words
trunk stream: a • A trunk stream is a major river fed by a small number of fairly large
major river, fed by tributaries. (See Figure 2.) The word “trunk” is used because of the
a number of fairly
large tributaries; the
tree-like drainage pattern.
main stream in a river
system.
distributary system:
an outflowing branch
of a river, such as
what characteristically
occurs on a delta (a
landform that forms
at the mouth of a
river).

Figure 2 A trunk stream is fed by many smaller streams.

• A distributary system is found near the end of a main river. It consists

of a number of small channels that branch off from the main river.
Distributaries deposit undissolved materials in the ocean. They also
carry dissolved materials into the ocean. (See Figure 3.)

Figure 3 The Mississippi carries a large amount of sediment and dissolved material
into the Gulf of Mexico.

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 Section 2 Rivers and Drainage Basins

All parts of all river systems have one thing in common. The water flows
downhill. Rain that falls in the United States flows down to the Atlantic
Ocean, the Gulf of Mexico, the Gulf of California (a part of the Pacific
Ocean), or the Pacific Ocean. There are two exceptions. In northern
Alaska, water flows into the Arctic Ocean, and in some areas of the
western United States, rivers flow into large depressions rather than into
oceans. Some of the depressions are below sea level. For example, Death
Valley is more than 60 m (200 ft) below sea level. Geo Words
A drainage basin is the area from which all of the rain that falls eventually drainage basin (or
flows to the same final destination. A drainage basin is also called a watershed): the area
from which all of
watershed. The final destination of all watersheds is usually the ocean.
the rain that falls
In the United States, there are drainage systems of different sizes. (See eventually flows
Figure 4.) In the Northeast, the largest drainage basins are the Hudson, to the same final
Connecticut, Delaware, and Potomac river systems. However, even destination, usually
these are relatively small. The southeastern part of the United States the ocean.
is dominated by rivers that flow to the east and south off the high
Appalachian Mountains. Some of these, such as the Savannah River, flow
into the Atlantic Ocean. Others, such as the Apalachicola River, flow into
the Gulf of Mexico.

Figure 4 Map of the United States showing the major river systems with the
Continental Divide.

The largest river system in the United States is the Mississippi River. It
enters the Gulf of Mexico downstream of New Orleans, Louisiana. It does
so after it collects water from a huge area of the midsection of North
America. One of its giant tributaries is the Ohio River. Tributaries of

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 Chapter 4 Surface Processes

the Ohio include the Tennessee, the Allegheny, as well as many other
large rivers. Many other branches that flow into the Mississippi River
serve as tributaries as well.
Drainage Divides
Geo Words Hilltops and mountains serve as boundaries between drainage basins.
drainage divide: the These boundaries are called drainage divides. Water falling on one side of
boundary between a divide flows into one river system. Water falling on the other side of the
adjacent drainage divide flows into a different river system. In this way, raindrops that fall
basins.
within inches of each other on a mountaintop can end up thousands of
miles away from each other. There are divides between streams of all sizes
within a river system. Any hilltop or ridge causes some rainfall to flow in
one direction and some to flow in another direction. However, in some
cases, the rainfall might flow into two different tributaries that eventually
end up in the same larger stream. The Continental Divide stretches north
to south through the mountainous areas of the western United States.
It separates the United States into two major drainage systems. One
drainage system empties into the Pacific Ocean. The other empties into
the Gulf of Mexico. (See Figure 4 on the previous page.)
River Systems and Settlement Development
Why are river systems important? Humans use river systems in many ways.
Rivers provide a source of drinking water. They are used for domestic
and industrial purposes, and for irrigation of farmlands. They are also
used to wash away waste product. For example, chemicals from industrial
processes and treated sewage are dumped into rivers. Throughout history,
rivers have served as both giant water faucets and giant sewers. This is not
a good combination. As recently as the late 1960s, several major cities in
the United States allowed human waste to enter large rivers. This was part
of their waste-disposal system. From local to national scales, communities
have recognized the problems with this. They have worked to limit the use
of rivers as waste-disposal systems. However, accidental spills of industrial
and human waste continue to happen every year.

Figure 5 A barge transporting materials down a river.

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 Section 2 Rivers and Drainage Basins

People use river systems for transportation. River transportation is

relatively cheap. Barges that carry materials, such as gravel and coal,
move up and down the river systems of the United States. This is the
case in the eastern and midwestern parts of the United States. In
the northern United States, the St. Lawrence River flows from Lake
Ontario into the Atlantic Ocean. A system of canals connects the Great
Lakes to the St. Lawrence River. This makes it possible for goods to be
shipped from inland ports like Duluth, Minnesota, Chicago, Illinois, and
Detroit, Michigan, to the Atlantic Ocean. From there the goods can be
transported to ports worldwide.

Figure 6 This dam literally “stops up” the flow of the river water, generating
electricity in the process.

Rivers provide power. Since colonial times, Americans have used this
power. In the 1700s and 1800s, Americans used the energy of flowing
water to move waterwheels. The waterwheels powered mills for cutting
wood and grinding corn and wheat. In the twentieth century, dams
and hydroelectric power plants were built along rivers. A dam causes
an artificial lake to form. Some of the water runs through openings, or
conduits, in the dam. As the water moves down through the conduits,
it turns the blades of turbines. The mechanical energy of the falling
water is converted into electrical energy. Hydroelectric power plants are
common in the United States. The United States has made use of much
of its potential hydroelectric power.
Dams are also used to control water flow. This can reduce the impact
of flooding. To do this, the operators of the dam drop the level of the
water behind the dam during dry periods. This makes room for storage
of water during heavy rains. The water held by dams can supply water
to cities for domestic use. In agricultural areas the water can also be
used for irrigation. However, dams disrupt the natural flow of rivers. This
results in a disruption of the river’s natural ecosystems. It is important to
understand the negative as well as the positive aspects of dams.

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 Chapter 4 Surface Processes

Figure 7 A by-product of dams is lake formation.

Rivers also provide recreation. People are awed by waterfalls. They

love the sound of rushing mountain streams, and they can go rafting,
canoeing, or kayaking in a swift-flowing river. They can also enjoy a boat
ride or a picnic on a riverbank. Millions of Americans swim, fish, and boat
in rivers and in the lakes created by dams along rivers.

Figure 8 Recreational uses of rivers include swimming, boating, and fishing.

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 Section 2 Rivers and Drainage Basins

In addition to providing humans with water, waste disposal, power, and

fun, rivers change the surface of Earth. Water moving downhill toward Geo Words
the ocean erodes bits of soil and rock. It carries these bits downstream erode: to wear away
toward the coast. The process of picking up and transporting loose soil soil and rock by the
and rock lowers the level of mountains. It is one process that gives Earth’s action of streams,
glaciers, waves, wind,
surface its shape. In deserts, where water is scarce, streams that flow and underground
after infrequent rainstorms are important in shaping the landscape. water.
This is because there is little vegetation to hold the soil in place.

Checking Up
1. Describe the three
main parts of a
river system.
2. What is a drainage
divide?
3. Describe at least
one benefit and
one drawback to
Figure 9 This desert landscape shows how rivers shape the land.
building a dam on
a river.

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 Chapter 4 Surface Processes

Think About It Again

At the beginning of this section, you were asked the following:
• How is the system of veins on a leaf similar to and different from the system of streams
and rivers that carry water into a larger river, like the Mississippi?
Record your ideas about this question now. Use your analyses of drainage patterns to help
with your explanation.

Reflecting on the Section and the Challenge

In this section, using different kinds of maps, you found streams of different sizes in
your community and traced the water flow from higher to lower elevations. Knowing the
geology over which the water in your community flows, and how it changes both its own
composition and the land features, can help you figure out the boundaries of river systems
and sources of streamflow. This information will help you determine how parts of Earth’s
surface are affected by upstream and downstream environments. Think about these
connections as you work on the Chapter Challenge.

Understanding and Applying

1. Describe the drainage basin in which your community is located.

2. How is your local river system part of a larger drainage basin in the United States?
3. Sketch a diagram showing the aerial or map view of your concept of a river system
and how it changes from upstream to downstream. On the diagram, mark where your
community fits in.
4. Examine a copy of the
topographic map shown.
a) On a copy of the map
provided by your
teacher, draw arrows
along the streams to
show the direction of
flow. Explain the
reasons for the
direction you drew
the arrows.
b) Draw the drainage
divide shown on
the map.

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 Section 2 Rivers and Drainage Basins

5. Preparing for the Chapter Challenge

Think about the interconnections within a drainage system. Describe your regional
drainage in terms of the connections between smaller and larger streams. Brainstorm
with members of your group to make a concept map that shows the different parts
of your local drainage system. Start thinking about how river systems play a role in
landscape development. Consider how rivers might affect your Florida and Alaska
Olympic Games sites. Go to the EarthComm Web site at http://www.agiweb.org/
education/earthcomm2/ for resources to help you explore surface drainage in each
of these states. Compare the drainage patterns of the two states.

Inquiring Further
1. Water quality in your community river system
If water quality is a big issue in your community, do some in-depth research on the
causes of the water-quality problems, the effects on your community, and the solutions
that have been proposed to address the problems.
• What are some of the different strategies being suggested to improve water quality?
• What are the pros and cons of the different strategies? What course of action do
you recommend?
2. River pollution and ecosystems
How does water pollution affect ecosystems that depend on the river? Research a
particular ecosystem in your community that has been affected by water pollution.
Has anything been done to address the problem? What do you suggest?
3. Dams and river systems
Research the controversies surrounding one of the following dams, some of which have
been removed, some of which are scheduled to be removed, and some of which are still
being debated. Include reasons for and against removal of the dam.
• Edwards Dam, Kennebec River, Maine
• Quaker Neck Dam, Neuse River, North Carolina
• Kirkpatrick Dam (also known as Rodman Dam), St. Johns River, Florida
• Glen Canyon Dam, Colorado River, Arizona
• Lower Granite Dam, Snake River, Idaho
• Elwha Dam and Glines Canyon Dam, Elwha River, Washington
4. Local river systems and wastewater treatment
• Where does the sewage from your community go?
• Does sewage from your community enter the river system before or after treatment?
• Which communities downstream would this affect?
• What would happen to the drainage system and sewage system if it rained 10 cm or
more in one day?
• Are there any communities upstream of your community that might put sewage or
pollutants into your river system? If so, what are they?

Go to the EarthComm Web site at http://www.agiweb.org/education/earthcomm2/

for assistance with Inquiring Further research.

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 Chapter 4 Surface Processes

Section 3 Slopes and Landscapes

What Do You See?

Learning Outcomes Think About It

In this section, you will Many people enjoy the climate and lifestyle of California.
• Calculate the angle of repose Unfortunately, life in California can come with risks. Landslides,
for different kinds of soils and earthquakes, and flows of debris are just a few. Landslides in
other granular materials.
California have resulted in numerous deaths and millions of dollars
• Determine if any areas in your in property damage. To help prevent such tragedies, geologists
community have slopes that are
study landslides and the slopes on which they occur. Changing the
too steep for safe development.
slope of the land or even the amount of vegetation on a slope can
• Recognize the importance
have very dangerous consequences.
of considering slopes in
land development. • How does the slope of land control surface processes?
• How might changing the slope of the land create potential
hazards for citizens (for example, cutting through the land to
build a road or housing project)?
Record your ideas about these questions in your Geo log. Be
prepared to discuss your responses with your small group
and the class.

Investigate
In this Investigate, you will experiment with the factors that
result in unstable slopes. These are the kinds of slopes that can
lead to landslides.

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 Section 3 Slopes and Landscapes

Part A: The Slope of a Sand Pile

a) Record the measurement of the angle
Clean up spills immediately. Cover desk with
of the slope each time.
newspaper to make cleanup easier. Wear safety b) Does the angle of the slope change?
goggles when pouring sand or other particles.
If so, how much?

1. Slowly pour 500 mL of dry sand 6. Pour extra sand onto a pile of sand
through a funnel onto a flat surface, several times.
such as your lab table, so that it makes a) Record the measurement of the angle
a pile. of the slope each time.
a) Describe what happens to the sides b) Does the angle of the slope change?
of the pile as you pour the sand.
Part B: The Slope of Other Materials
2. Hold a protractor upright (with the
1. Obtain some or all of the following
bottom edge held against the flat
materials (make sure they are dry): fine
surface) and carefully begin to slide it
sand, coarse sand, gravel, soil, table
behind the pile as shown in the diagram.
salt, granulated sugar.

3. At the point where the curved upper a) Predict what would happen if you
edge of the protractor intersects the repeated the investigation in Part A
surface of the pile of sand, read the using these materials, which have
angle in degrees. This is the natural particles of different sizes and shapes.
angle of the side (slope) of the pile. It Record your prediction in your log.
is called the angle of repose. It is the
steepest slope that can be formed in the 2. For each of the available materials,
material without slumping or sliding of repeat the following procedures:
the material down the slope. • Place a handful of the materials in
a) Record this angle in your Geo log. a dry container, such as a can or
plastic beaker.
4. Repeat Steps 1, 2, and 3 several times.
• Cover the container with cardboard.
a) Record the measurement of the angle • Turn the container upside down onto
of the slope each time. a flat surface.
b) Do you get the same angle each time? • Lift the container very slowly. A cone-
Explain your answer. shaped pile should form.
c) Why is it important to take this • Measure the angle of the slope of
measurement several times? the pile.
• Take three measurements for
5. Repeat Steps 1, 2, and 3 using different each material.
amounts of sand.

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a) Record your measurements in a table centimeters) on the map equals 24,000

similar to the one below. units in the real world. There may also
be a scale bar on the map that indicates
b) In your log, write a summary
the relationship between map distance
paragraph discussing conclusions
and real distance (for example, one inch
you can draw from the data in your
on the map equals one kilometer in the
table. Your paragraph should address
real world). You will need to use a scale
how particle size relates to the
that makes it easy to measure distances
maximum slope angle the particles
on your map.
will maintain.
4. Convert your horizontal scale to the
Wash your hands when you are done. same units that are used for the contour
interval (probably feet or meters).
5. Choose a slope on your map and record
the following data in a table of your
own design.
a) Measure a specific horizontal
distance perpendicular to the
slope. Record the actual (not map)
horizontal distance.
b) Use contour lines to measure the
change in elevation over that specific
horizontal distance.
c) Divide the change in elevation by
the horizontal distance (make sure
they are in the same units), and then
multiply by 100. This gives you the
percent grade of the slope.

Part C: Characteristics of Slopes in 6. Repeat Step 5 for several slopes on

Your Community your map.
1. Obtain a topographic map of an area in a) Record all of the data in your table.
or around your community that shows 7. Make a second table that lists
a variety of different slopes. If your the location, percent grade, and
community is relatively flat, use a map characteristics for each slope. Some
of another area that shows both slopes characteristics you could list include:
and areas of development. kind(s) and density of vegetation, kind(s)
2. Determine the contour interval on of developments above, below, and on
your map, either from the legend or the slope, population density above,
by identifying the spacing between below, and on the slope, underlying
contour lines. geology, and surface deposits. Add any
other characteristics that you think will
3. Determine the scale of your map. This be important when evaluating land use
may be expressed as a ratio, such as on and around slopes.
1:24,000, which means one unit (of any
measure of distance, such as inches or a) Include this table in your log.

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 Section 3 Slopes and Landscapes

Digging Deeper
SLOPES AND MASS MOVEMENT
Angle of Repose
In the Investigate, you explored what makes slopes unstable and stable.
You looked at the role of gravity and different types of materials. You Geo Words
also explored slopes in your local area. Sediments are unconsolidated sediment: the solid
materials. They have not gone through the conversion into rocks. (The fragments or particles
that are transported
process by which sediments compact to solid rock is called lithification.) and deposited by
A pile of sand is unconsolidated sediment. However, sandstone is a wind, water, or ice.
rock. Mud is unconsolidated sediment. Shale is a rock. Unconsolidated unconsolidated
materials cover solid rock (bedrock) in many places. This includes places material: the
where glaciers have been (glaciated areas), layers of soil (horizons), sediment that is
loosely arranged, or
deserts, beaches, lakes, rivers, and sand dunes. that has particles that
Unconsolidated materials are far less stable than rock. Solid bedrock is are not cemented
together, either at
stable at almost any slope angle. Unconsolidated sediments, however, the surface or at a
are stable only up to a maximum slope angle. This is shown in Figure 1. depth.
You studied this angle in both Parts A and B of the Investigate. This lithification: the
maximum angle is called the angle of repose. If you add more sand to a conversion of
unconsolidated
pile of sand with sides already at the angle of repose, the extra sand just sediment into a
slides down the sides. The angle cannot become any steeper without the coherent, solid rock.
sides collapsing. In general, the angle of repose for dry, unconsolidated bedrock: the solid
sediments ranges from 30° to 35°. The angle of repose does not vary rock that is connected
much with sediment size. However, more angular (jagged) particles continuously down
into Earth’s crust,
can maintain steeper slopes than more rounded particles. rather than existing
as separate pieces or
masses surrounded
by loose materials.
angle of repose: the
maximum slope or
angle at which loose
material remains
stable, commonly
ranging between
30° and 35° on
natural slopes.

Figure 1 Developers must take care not to build on slopes that exceed the
angle of repose.

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 Chapter 4 Surface Processes

Mass Movement
An important factor to consider for your Chapter Challenge is the natural
slope of the land. You must also consider the materials on and under
these slopes as well. Sediments that were deposited by rivers or glaciers
lie beneath many areas. Some of these deposits are sloping. In that case,
you need to consider how stable the slope is before deciding to develop
the area. The stability of a slope depends on a number of factors. The
kind and amount of vegetation is an important factor. The sediment
composition, texture, and moisture content are also important. The
underlying geology needs to be considered as well.
Under certain conditions, slopes can be modified to allow for
development. Figure 2 shows one modification. Notice how the slopes
have been terraced. Retaining walls can also be used to make a slope
more stable. Drainage channels at the top of slopes are also useful. They
are placed so as to reduce areas where the particles that make up the
surfaces of the slopes can be moved away or eroded.

Figure 2 This slope has been terraced to increase its stability.

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 Section 3 Slopes and Landscapes

Buildings, roads, and other

structures built on slopes
of any angle can be
damaged or destroyed Geo Words
when mass movement mass movement: the
occurs. (See Figure 3.) downslope movement
Examples of mass of soil, sediment, or
rock at Earth’s surface
movement include by the pull of gravity.
rockfalls, landslides, debris
flows, debris avalanches,
and creep. (Creep refers
to the gradual movement
of rock and debris
movement.) The basic
cause of these types of
movement is the
downward pull of gravity.
Part of the pull of gravity
acts parallel to the sloping
surface. (See Figure 4.)
If that does not make
sense to you at first, think
about what happens to
you when you stand on Figure 3 A small seaside community north of Santa
Barbara, California felt the effects of mass movement.
a slippery slope. Gravity The slide of an unstable hill slope destroyed several
pulls you straight down homes and resulted in an evacuation of the area.
the slope.
This same downslope pull acts on the
materials that lie under a sloping land
surface as well. Under certain conditions,
the downslope pull of gravity overcomes
the strength of the material. The
material moves downslope. This
movement varies enormously in speed.
It can be so slow you cannot see it
happening. It can be as fast as tens
of meters per second. The movement
also varies in volume of material. The
amount of material can range from
single-sediment particles to cubic Figure 4 Gravity acts to pull an
kilometers of material. Adding water object toward the center of Earth.
This force can be shown using a
to the soil or sediment increases its
parallel part and a normal part.
weight. Also, water reduces the friction The greater the slope angle, the
between the grains. This allows the larger the force pulling the object
grains to slide past one another more parallel to the slope.
easily. Both of these factors increase
the chance of mass movement.

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 Chapter 4 Surface Processes

In cold regions, cycles of freezing and thawing can cause mass movements.
As the water in soil or sediment freezes, it expands. The grains are lifted
parallel to the slope. When the ice melts, the grains settle parallel to the
slope. Then they slide downhill because of the pull of gravity. Often, the
water helps to reduce the friction.
In areas where the ground freezes in the winter to a depth of several feet,
the top layers of soil are loosened during spring thaw. At the same time,
Geo Words the bottom layers remain frozen and solid. The water-saturated upper
freeze-thaw cycles: layers then slide downhill. In areas where freeze-thaw cycles are frequent,
frequent temperature building foundations and pipes carrying gas, water, or sewage must be
fluctuations around
0°C that cause the placed below the freezing zone. (That is about a meter [3–4 ft] deep in
expansion and northern states.) This helps to prevent damage from surface slides.
contraction of water
within soil pores Vegetation can help to stabilize slopes. Trees, shrubs, bushes, and grasses
or cracks in rocks can help to keep soil layers intact, depending on the depth of the roots.
resulting in an overall Most vegetated areas, however, are still subject to landslides if they
loss of strength.
become saturated with water.
relief: the general
difference in You can tell how steep slopes are by using topographic maps. The maps
elevation of the land use contour lines to show the elevation of the land. The standard to which
from place to place in
some region.
all elevations are compared is average sea level. A contour line represents
equal elevations, or heights, above sea level. Therefore, a 10-ft contour
percent grade: the
ratio of the vertical line connects all the points in a region that are 10 ft above sea level. There
and horizontal is a basic rule for drawing contour lines. Contour lines can never cross,
distance covered because two elevations cannot exist at the same location. The spacing
by a given slope,
of the contour lines is a measure of the steepness of the land. The closer
multiplied by 100.
together the contour lines are, the steeper the slope they represent. A
region showing great variation in elevation is referred to as having high
Checking Up relief. A region showing relatively little variation is referred to as having
low relief.
1. What is the
relationship When you work with a slope on a topographic map, use the contour
between particle lines to measure the steepness of the slope. The steepness is how much
size and the
angle of repose?
the land rises over a particular horizontal distance. Use the scale on the
Between the map to figure out the horizontal distance from one point on the slope
jaggedness of to another point, measured perpendicular to the contour lines. Convert
particles and the so that both the vertical change (the change in elevation) and the
angle of repose? horizontal distance are expressed in the same units. The units are usually
2. Describe two ways in feet or miles, or in meters or kilometers. Divide the vertical change by
in which slopes can the horizontal distance. Then multiply by 100, to get what is called the
be stabilized.
percent grade.
3. Describe three
human activities
that may make
slopes unstable.

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 Section 3 Slopes and Landscapes

Think About It Again

At the beginning of this section, you were asked the following:
• How does the slope of land control surface processes?
• How might changing the slope of the land create potential hazards for citizens (for
example, cutting through the land to build a road or housing project)?
Record your ideas about these questions now. Apply what you learned from your slope
models to help you revisit these questions.

Reflecting on the Section and the Challenge

In this section, you explored how gravity and particle size affect how stable a slope is.
You read that materials of a certain grain size will pile up to a maximum slope angle. You
also read that you can calculate slope and percent grade from a topographic map. You
can classify slopes on the basis of the physical characteristics you see on maps. Slopes are
important landforms for the movement of sediments toward rivers and eventually to lower
elevations. Studying slopes in lowland and upland regions will be important as you work
on your Chapter Challenge.

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 Chapter 4 Surface Processes

Understanding and Applying

1. Compare the slopes of mountainous regions with those of lowland drainage basins.
2. Which rock types are most prone to forming unstable slopes?
3. The development of roads and buildings typically involves moving and shaping the
land. What basic guidelines should be followed when cutting a slope or piling loose
material and creating a slope?
4. Why would a developer be motivated to build on a potentially unstable slope? In your
opinion, what advantages would outweigh the dangers?
5. Specifically describe how slopes might have influenced your community’s growth over
the last:
a) 5 years b) 20 years c) 50 years
6. Consider other communities you have visited or researched where slope influences
development.
a) Describe a community where slopes have limited development.
b) Describe a community where slopes have been helpful for development.
7. Preparing for the Chapter Challenge
Write a short paragraph answering each of the following questions:
a) What are the characteristics of slopes that shed the most materials?
b) Where are these slopes found?
c) Which slopes in your community cannot be safely developed? What evidence
supports your answer?
d) Which developments in your community might be at risk from mass movements?
What would have to happen for these risks to be minimized?
Apply these ideas to the assessment of slopes in your Florida and Alaska Olympic
Games sites.

Inquiring Further
1. Effect of water on mass movement
Repeat Part B of the Investigate using materials that have water added to them and see
if your results change.
• What do your results lead you to believe regarding slopes without vegetation during
times of heavy rain?
• What practices during times of heavy construction in a community does the
information support?

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 Section 3 Slopes and Landscapes

2. Slope-risk map of your community

Compile slope information onto a risk map for your community using the traffic light
colors of green = safe, yellow = proceed with caution, red = stop; do not proceed.
Include a key that classifies what type of development may be of concern in each area.
3. Underlying materials in your community
Determine what kinds of materials underlie different parts of your community by
consulting geologic maps, local developers, and/or town officials.
• Does your community lie on unconsolidated sediment or relatively solid bedrock?
• If you found areas of unconsolidated sediment, are the sediments naturally occurring
or were they deposited by human activity?
• Is building on bedrock always safer than building on sediment? Explain your answer.
• In your own words, describe how the distribution of underlying materials has shaped
your community’s building patterns.
4. Famous catastrophic mass movements
Go to the EarthComm Web
site at http://www.agiweb
.org/education/earthcomm2/
to investigate famous
examples of catastrophic
mass movements that have
affected communities.
Conduct research on these
mass movements. Answer the
following questions.
• What happened?
• How did the mass
movement affect the
community?
• What factors led to the
mass movement?
• How might the event have
been avoided?
• What lessons were learned
from the event?

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 Chapter 4 Surface Processes

Section 4 High-Gradient Streams

What Do You See?

Learning Outcomes Think About It

In this section, you will Look at the two different streams shown in the illustrations above.
• Use models and real-time
• How are the two streams different?
streamflow data to understand
the characteristics of high- • Could both streams be located in the same geographic area?
gradient streams.
Record your ideas about these questions in your Geo log. Be
• Identify characteristics of prepared to discuss your responses with your small group
high-gradient streams.
and the class.
• Calculate stream slope
or gradient.
Investigate
• Identify areas likely to have
high-gradient streams. In this Investigate, you will run a model that examines the
• Assess possible hazards and effect that a high gradient has on the way a stream flows.
benefits of a high-gradient
Part A: Investigating High-Gradient Streams Using
stream on a community.
a Stream Table

Before you begin, it would be a good idea to cover tables with

newspaper or other material to make cleanup easier. Keep paper
towels nearby for cleanup.

1. To model a high-gradient stream, set up a stream table as

follows. Use the photograph on the next page to help you
with your setup.

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 Section 4 High-Gradient Streams

• Cover the bottom of a stream table a before and after video or photo to
with a layer of sand about 2.5 cm record your observations of the
thick. stream table.
• Using additional sand, make high Be ready to turn off the flow of water at any
mountains separated by narrow river moment. Mass wasting (sand slide) is possible.
valleys at the upper end of the stream
table. a) Which parts of the landscape are
• Using pieces of toothpicks or small most prone to erosion—the steeply
blocks, set up communities of sloping or gently sloping parts?
“buildings” in the stream valleys
and on the hillsides and hilltops. b) Where is sediment deposited?
• Prop up the stream table about 30 cm c) Where does water flow fastest and
to create a steep slope. You may need where does it flow slowest?
to support the lower end to prevent it
d) Where is the largest volume of water
from sliding.
flowing in the stream and where is
• Be prepared to drain, bail, or recycle the smallest?
the water that accumulates at the
lower end of the stream table. 3. Turn off the water and rebuild your
2. Turn on a water source with a low rate landscape and “community.”
of flow or use a beaker full of water to
control the rate of flow. Observe and If toothpicks were used, be sure to retrieve them
record the changes in the stream valleys from the sand. Wash your hands after handling
and hillsides. You may wish to take the sand.

Stream table setup for a high-gradient stream.

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 Chapter 4 Surface Processes

Part B: Stream Gradients

1. Streams and rivers always flow 3. Use the two values you obtained to
downhill. The gradient, or slope, of calculate the stream slope, or gradient,
a stream or river expresses the loss in in feet per mile or in meters per
elevation of the stream or river with kilometer. To do this, divide the change
distance downstream. Obtain one or in elevation by the horizontal distance
more topographic maps that cover your between the two points. For example,
community and nearby areas. Identify if the river drops two meters over a
the stream or river nearest to your horizontal distance of four kilometers,
school. Find two adjacent contour lines the gradient of the river is one-half
that cross the river. Note the contour meter per kilometer. The gradient can
interval. It may be 5, 10, 20, or 40 ft, also be expressed as just a number, by
or it might be in meters instead. using the same units of measurement
for both the vertical drop and the
a) Record the contour interval as
horizontal distance. In the example
change in elevation.
above, the gradient would be 2 m
2. Use a piece of string to measure the divided by 4000 m, or 0.0005.
distance between the two points along
a) Record the gradient of the stream.
the river where the contour lines cross
the river. Use the scale on the map to 4. Study the data for the Mississippi River
convert this distance on the map to System in the table on the next page.
miles or kilometers on the ground.
a) Record this value.

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 Section 4 High-Gradient Streams

Data on the Mississippi River System

for Various Locations on the Mississippi River and its Tributaries,
August 2009

Contributing
Discharge Floodplain Distance to Elevation
Location Drainage Area
(ft3/s) Width (mi) Sea (mi) (ft)
(mi2)
North Fork Shoshone River,
699 628 0.04 2300 5580
Wapiti, Wyoming
Shoshone River, Cody,
1603 1190 0.2 2270 4900
Wyoming
Missouri River, Culbertson,
91,557 6960 1.4 1800 1880
Montana
Missouri River, Hermann,
522,500 81,800 2.5 780 480
Missouri
Mississippi River, Chester,
708,600 181,000 6.0 625 340
Illinois
Mississippi River, Vicksburg,
1,144,500 495,000 30 205 50
Mississippi

a) Search for patterns in the data that b) Use the data to make a graph
would allow you to characterize how showing one of the patterns that
a river changes over its course. For you have just described.
example, using the data, complete c) Calculate the stream gradients (in
the following sentence: “As the feet per mile) between the following
distance from the sea decreases, segments of the Mississippi:
floodplain width…” (A floodplain is
the area of a river valley next to the i) Between Hermann, Missouri and
channel, which is built of deposited Vicksburg, Mississippi.
sediments and is covered with water ii) Between the Shoshone River at
when the river overflows its banks at Wapiti and Cody, Wyoming.
flood stage.) Write down two more d) Describe the relationship between
sentences that describe patterns or stream gradient, elevation, and
relationships in the data. stream discharge.

The Missouri River near Culbertson, Montana.

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 Chapter 4 Surface Processes

The Mississippi River near Natchez, Mississippi.

5. Obtain a copy of the data table shown determine where the gradient of your
on the next page to include in your Geo river is greatest. Note this location in
log. Use a topographic map of your area your Geo log.
to fill in rows (a) to (j) in the table for
a) Fill in rows (a) to (o) in the column
your local stream.
labeled “High-Gradient Stream” in
6. Go to the EarthComm Web site at http:// the table for this location, as you did
www.agiweb.org/education/earthcomm2/ for your local river.
to find the USGS Web site that gives
8. Use your completed data table to do
data on the discharge of rivers in the
the following:
United States.
a) Compare the width of the floodplain
a) Use the data on the Web site to record
in your local area and in the high-
the discharge (or flow), in ft3/s, the
gradient area.
drainage basin area (ft2), and stream
velocity (calculate using discharge b) Compare the stream velocity in the
and drainage area) of your local river. two areas.
Use the data from the location that is c) Compare the current discharge of
closest to your school. If your river your local stream to the maximum
is not listed, use data for the next- and minimum discharges. How
closest river. Complete rows (k) to (o) do you account for the differences
for your local stream. between the numbers?
7. Look at the state or regional (Note: You will record the data for a low-
topographic or shaded relief maps to gradient stream in the next section.)

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 Section 4 High-Gradient Streams

Comparison of Characteristics of Local and High- and Low-Gradient Streams

Characteristic Local Stream High-Gradient Stream Low-Gradient Stream

(a) Difference in elevation (ft)

between highest and lowest
points in study area

(b) Stream gradient (ft/mi)

(c) Steepness of valley walls

(steep, moderate, gentle)

(d) Channel shape (straight,

curved, meandering)

(e) Channel width (mi)

(f) Floodplain width (mi)

(g) Area of land available for

farming in valley

(h) Number of tributaries within

four miles

(i) Rapids or waterfalls present

(j) Could a large boat travel

upstream here?

(k) Drainage basin area (ft2)

(l) Current discharge (ft3/s)

(m) Current stream velocity (ft/s)

(n) Minimum discharge (ft3/s)

(o) Maximum discharge (ft3/s)

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 Chapter 4 Surface Processes

Digging Deeper
CHARACTERISTICS OF HIGH-GRADIENT STREAMS
In the Investigate, you ran a model that examined the effect that
Geo Words a stream’s high gradient has on its streamflow. You may have been
stream: a small or uncertain about the difference between a stream and a river. Geologists
large flow of water in use both words to describe a flow of water in a natural channel on Earth’s
natural channels.
surface. The word “river” is usually used for a flow in a relatively large
river: a relatively channel. The word “stream” is usually used for a flow in a relatively small
large flow of water in
a natural channel. channel. Often, however, the word “stream” is used in a general way for
all flows in natural channels, large and small. Very small streams are often
brook: a term used
for a small stream. called brooks or creeks.
creek: a term used for The gradient is the slope of a stream or river. It is expressed as the loss in
a small stream. elevation with distance downstream. High-gradient streams are usually
gradient: the slope located in the headwater areas of river systems. The headwaters are the
of a stream or river areas of the river system that are farthest away from the mouth of the
expressed as a loss
in elevation of the river. The headwaters are at the highest elevations in the river system.
stream or river with Slopes of the land surface are generally much steeper at the headwaters
distance downstream. than in the lower parts of the river system. (See Figure 1.)
headwater: the area
of the river system
The velocities of flow in high-gradient streams are high. They are
that is farthest away sometimes greater than 3 m/s (10 ft/s). However, because such streams are
from the mouth of usually in the headwaters of the river system, they have not collected much
the river. water from upstream. They also are relatively small and shallow. Streams
downcutting: erosion with high velocities and shallow depths exert very strong forces on the
of a valley by a stream bottom. The reasons for that are complicated and have to do with
stream.
the dynamics of flowing water. High-gradient streams can move very large
floodplain: the area particles on the streambed. During floods, the particles can be the size of
of a river valley
next to the channel, large boulders. In some high-gradient streams during floods, you can stand
which is built of on the bank of the stream and hear a thunderous roar. This is caused by
deposited sediments boulders colliding with one another as they are moved by the stream.
and is covered with
water when the river High-gradient streams can exert large forces on the streambed. As a result,
overflows its banks they tend to erode their valleys rapidly. Erosion of a valley by a stream is
at flood stage. called downcutting. Sometimes streams cut
straight down to form canyons with vertical
walls. However, usually the valley is in the
form of a “V” with steeply sloping sides.
Weathering produces loose material on the
valley slopes. That material then slides down
or is washed down by rainfall to the stream.
The stream carries the material downstream.
High-gradient streams cut their valleys
vertically downward very rapidly. It is too
rapid for the valleys to widen out to form
floodplains. In most high-gradient streams,
the sloping sides of the valley come down
very near the stream channel. (See Figure 2.)
Figure 1 The slope of the land at There is only a limited area of flat land
the headwaters of a river is
generally very steep.
available for farming in the valleys.

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 Section 4 High-Gradient Streams

Figure 2 Illustration of high-gradient streams in the highlands and a

low-gradient stream forming a broad valley below.

In the Investigate, you compared different points along the Mississippi

River. You noticed that high-gradient streams tend to have a relatively Geo Words
high velocity. However, they have a low stream discharge. Stream stream discharge:
discharge is the volume of water passing a point along the river in a unit the volume of water
of time. It is calculated by multiplying the cross-sectional area of the river passing a point along
the river in a unit of
channel by the velocity of the water. It is not easy to measure the cross- time.
sectional area of the river channel. Imagine finding the depths all across
the river from a bridge. Then imagine plotting these depths on a graph
to show the cross section, and then measuring the area of the cross
section. The discharge is measured in cubic feet per second (often called
“cusecs”) or in cubic meters per second (often called “cumecs”).
Stream velocity and stream discharge vary a lot over time. This can
be seen in a sample plot of stream discharge from the USGS real-time
water data Web site. (See Figure 3 on the next page.) For this stream in
the Appalachian Mountains of Maryland, the average daily discharge is
higher during the winter than the summer months. On average, greater
amounts of precipitation fell during winter. Periods of high rainfall fill
cavities in the soil. Additional rainfall on saturated slopes causes steep
rises in the graph. The peak in March was caused by the melting of large
volumes of winter snow from the upper slopes in the drainage area.
This is common over much of the colder and temperate areas of the
United States. During the summer months, several peaks coincide with
periods of thunderstorms, the greatest of which occurred after several
days of intense storms. However, unlike winter flows, the summer
base level can fall dramatically during periods of low rainfall and high
summer temperatures.

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 Chapter 4 Surface Processes

Checking Up
1. Why can high-
gradient streams
move large
sediment particles?
2. What is stream
discharge?
3. How does stream
discharge change
from high-gradient
to low-gradient
streams?
4. Why do high-
gradient streams
cause downcutting
Figure 3 Plot of stream discharge versus time for the Little
of their valleys?
Patuxent River in Savage, Maryland.
5. What causes
stream discharge to
change over time?

Think About It Again

At the beginning of this section, you looked at two illustrations of streams and
were asked the following:
• How are the two streams different?
• Could both streams be located in the same geographic area?
Record your ideas about these questions now. In your answers, draw on your
understanding of stream systems.

Reflecting on the Section and the Challenge

In this section, you used a stream table to explore how particles of sediment
were moved and deposited (erosion and deposition) along rivers that had steep
gradients. You used a topographic map to calculate the gradient (the change
in elevation with horizontal distance) of a stream near your school. You also
searched for patterns and relationships between variables used to characterize
a river along its course. Finally, you examined real-time data of streamflow
in a river that flows near your community. These explorations will help you
characterize the relationship between geology and surface change. You will
need to include this information in your Chapter Challenge.

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 Section 4 High-Gradient Streams

Understanding and Applying

1. Describe three characteristics of a high-gradient stream.
2. Is the major stream in your community a high-gradient stream? How do you know?
3. How does the elevation of your community compare to the elevation of areas around
high-gradient streams?
4. What events would cause the velocity of your river to increase? To decrease?
5. Is there a time of year when a high-gradient stream is likely to pose a hazard to
communities? Explain your answer.
6. Preparing for the Chapter Challenge
Write a short paper in which you describe the relationships between upland regions,
slopes, and the strength of erosional processes. Also, discuss some of the potential
dangers of high-gradient streams to development. Apply these ideas to the evaluation
of your Florida and Alaska Olympic Games sites.

Inquiring Further
1. Interaction between humans and rivers
Many stories and novels have been written that focus on rivers, or on the interactions
between humans and rivers, including The Adventures of Huckleberry Finn, by Mark
Twain, Siddhartha, by Herman Hesse, and A River Runs Through It, by Norman
Maclean. Write a story or essay that involves a river and members of your community.
What you write does not have to be centered on the river, but it should involve some
interaction between community residents and the river or stream.
2. Big Thompson, Colorado flood
Find information on the Big Thompson, Colorado flood of July 1976 and describe how
it is related to high-gradient streams and land use. What factors caused this flood to be
so catastrophic?

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 Chapter 4 Surface Processes

Section 5 Low-Gradient Streams

What Do You See?

Learning Outcomes Think About It

In this section, you will During the Mississippi River flood of 1993, stream gauges at
• Use models and real-time 42 stations along the river recorded their highest water levels on
streamflow data to understand record. The effects of the flood were catastrophic. Seventy-five
the characteristics of low-
towns were completely covered by water, 54,000 people had to
gradient streams.
be evacuated, and 47 people lost their lives.
• Explore how models can help
scientists interpret the natural • What happens during a flood?
world. Record your ideas about this question in your Geo log. Include a
• Identify areas likely to have sketch of the water line (the line where the water surface meets the
low-gradient streams.
riverbank) during normal flow in the river and during a flood. Be
• Describe hazards of low- prepared to discuss your responses with your small group and
gradient streams.
the class.

Investigate
In this Investigate, you will use a stream table to model how a
low-gradient stream flows and what effects this can have on the
areas surrounding the stream.
Part A: Investigating Low-Gradient Streams Using a
Stream Table
1. To model a low-gradient stream, set up a stream table as
follows. Use the photograph on the next page to help you
with your setup.
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 Section 5 Low-Gradient Streams

• Make a batch of river sediment by 3. Turn on a water source or use a beaker

mixing a small portion of silt with filled with water to create a gently
a large portion of fine sand. flowing river. Observe and record the
• Cover three-fourths of the stream changes to your stream table model.
table with a layer of the river sediment a) Which parts of the landscape are most
at least 2.5 cm thick. prone to erosion? To deposition?
• With your finger, trace a winding
b) What shape does the river
river between 0.6 cm and 1.3 cm deep
channel take?
in the sediment. Make several bends.
• Using pieces of toothpicks or small c) Describe all the areas where silt is
blocks, set up communities of being deposited. Describe all the
“buildings” along both the inside areas where sand is being deposited.
and outside of river bends. d) Observe and sketch the distributary
• Prop up the stream table about system that develops where the river
2.5 cm to create a very gentle slope. enters the “ocean.”
• Be prepared to drain, bail, or recycle e) Increase the velocity of the river
the water that accumulates at the slightly. What happens?
lower end of the stream table.
f) Increase the velocity again.
Before you begin, review all safety precautions What happens?
provided in the Investigate in Section 4
regarding the stream table setup.
g) What events might cause the velocity
of your river to increase?
2. Using additional sediment, make h) Would you expect the discharge to
landforms that you think are typical of increase when the velocity of the
areas with low-gradient streams. Refer river increases?
to a topographic map for ideas.
i) In general, which have larger
discharges: high-gradient streams
or low-gradient streams?

The stream table setup of a low-gradient stream. Pieces representing

buildings and houses are placed in the sand on the inside and outside
bends of the river.

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 Chapter 4 Surface Processes

Part B: Characteristics of
Low-Gradient Streams
1. Complete the data table you began in d) Why is this part of the river called a
Part B of the Investigate in Section 4. low-gradient stream?
a) Look at a state, regional, or United e) Compare the width of the floodplain
States map to determine where the in the low-gradient area with the
stream gradient for your river would width of the floodplain in the high-
be the gentlest. Note the location in gradient area of the previous section.
your Geo log.
f) Compare the stream velocity in the
b) Use the map to fill in rows (a) to (j) low-gradient area and the high-
in the column labeled “Low- gradient area.
Gradient Stream.”
g) Compare the area of land available
c) Use the USGS Web site (which you for farming in the low-gradient area
can find at the EarthComm Web site) and the high-gradient area. If there is
to get data on the discharge of rivers a difference, why does it exist?
in the United States to fill in rows (k)
to (o) for the low-gradient stream.

Digging Deeper
LOW-GRADIENT STREAMS
Meandering Streams
In the Investigate, you used a stream table to simulate how a low-
gradient stream flows and what can happen when that stream overflows
its banks. As you saw from where you poured the water into your stream
table “river” and where the water flowed out, there are big differences
between high-gradient and low-gradient streams. High-gradient streams
can result in downward erosion, or downcutting. This makes steep,
straight valleys with little or no floodplains. On the other hand, low-
gradient streams wear land away
both sideways and downward. This
makes wider and wider valleys. (See
the photograph in Figure 1.)
Typically, streams in the lower
areas of a river system have lower
gradients than those in higher areas.
They also have wider channels and
wider floodplains. The width of
the valleys increases as discharge
increases. This fact shows that rivers
erode the valleys that they occupy.

Figure 1 How does this stream differ

from the one shown in Figure 1 of the
previous section?

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 Section 5 Low-Gradient Streams

Low-gradient streams cut wide valleys because their channels tend to

shift sideways. Most low-gradient streams do this by meandering. A Geo Words
meandering stream is a stream with a channel that curves or loops back meandering stream: a
and forth on a wide floodplain. This is shown in Figure 2. Each curve is stream with a channel
that curves or loops
called a meander bend or meander loop. The velocity of the water is back and forth on a
greatest on the outside of the meander bend. This is where erosion tends wide floodplain.
to occur. In contrast, the velocity is lower on the inside of the bend. This meander bend: one of
is where sediment is deposited. Over time, erosion on the outside of a series of curves or
the meander bend combined with the deposition on the inside of the loops in the course of
a low-gradient, slow-
meander bend causes the river to meander farther and farther sideways. flowing river.
As a result, a wider and wider valley is cut. The flat, low-lying valley
meander scars: low
bottom surrounding the channel is called the floodplain. That is where ridges on the part of
water spreads when the river overflows its banks during floods. The the floodplain inside
floodplain is built of the sediments that the river has deposited during the meander bend
meandering, as well as sediments deposited during floods. caused by deposition
of sediment during a
flood.

Figure 2 Illustration of a meandering stream. Notice that erosion

occurs on the outside of the meander bend while deposition occurs
on the inside.

As each flood deposits some sediment on the inside of the meander

bend, a low ridge, usually no more than a meter or so high, is formed.
The area of the floodplain on the inside of the meander bend shows
a large number of these ridges, called meander scars. They reveal the
earlier positions of the meander bend.

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 Chapter 4 Surface Processes

As a meander bend grows wider, its neck usually becomes narrower as

well. Eventually, the meander bend is cut off during a flood as the water
begins to flow across the narrow neck to follow a more direct route
downstream. The more direct route is shorter and steeper than the longer
route all the way around the meander. The river abandons the former
meander bend. Soon afterward, the ends of the abandoned bend are
Geo Words plugged with river sediment. The bend becomes a curved lake, called an
oxbow lake: a oxbow lake. Later floods deposit sediment in the oxbow lake. Eventually
crescent-shaped it is filled in completely with sediment. Oxbow lakes, including those
body of standing partly or completely filled with sediment, are common features on the
water situated in the
abandoned channel
floodplains of low-gradient streams. If you are ever in an airplane flying
(oxbow) of a meander over a big meandering river (like the Mississippi or the Missouri), look out
after the stream the window and you will see the patterns of meander bends and oxbow
formed a neck cutoff lakes. (See Figure 3.) You also might be able to see meander scars, and
and the ends of the
original bend were
even the faint outlines of former oxbow lakes, now filled with sediment.
plugged up by fine
sediment.

Figure 3 Meander bends and oxbow lakes are characteristics of low-gradient

streams. Continued plugging of the channel with fine sediment will
eventually turn this meander into an oxbow lake.

Streams and the Hydrologic Cycle

The main factor that influences stream discharge is precipitation in
the drainage area of a stream. Other factors can also be important as
well. Water can be removed from a stream by loss of the water that
lies beneath Earth’s surface (groundwater). It can evaporate into the
atmosphere. Water may also be diverted from a stream for municipal
water supply or crop irrigation. Water can enter the stream from the
groundwater system. This can be from the melting of snow or glaciers,
or the release of water from reservoirs.
The flow of water in streams is closely connected to the groundwater
system. Have you ever thought about why most rivers flow throughout
the year, even during long periods when no rain falls to feed the
river? Some of the rain that falls on the land runs off directly into
streams. However, some soaks into the soil and becomes groundwater.

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 Section 5 Low-Gradient Streams

Geo Words
Groundwater flows slowly through aquifers. When the aquifer intersects aquifer: a body
the ground surface an outflow of water results. Outflow from aquifers of porous rock
or sediment that
is a major source of water for many rivers, especially during periods of is sufficiently
drought. Refer to the plot of the streamflow in Section 4. It did not rain permeable to conduct
everyday in the drainage basin of the river shown in the plot, yet water groundwater and to
continued to flow in the stream. This is mainly the result of groundwater provide an adequate
supply of water.
charging, or adding to, the stream. Groundwater that leaves an aquifer
and flows into the bed of a stream is referred to as base flow. Water base flow:
groundwater that
generally flows much more slowly through rock and sediment than it leaves an aquifer and
does over Earth’s surface. As a result, base flow can charge a stream flows into the bed of
even long after precipitation has stopped. a stream.
stage: the height of
the water surface in a
river channel, relative
to sea level, at a given
place along the river.
flood stage: the river
stage (water level)
at which a river rises
above its banks and
begins to cause a
flood.

Figure 4 Groundwater flows through the aquifer to the stream. This

prevents the stream from becoming dry during long periods of drought.

Hazards: Floods on Low-Gradient Streams

Flooding on low-gradient
streams occurs when the stream
channel cannot contain the
discharge of water that is passing
through it. The height of the
water surface in a river channel,
relative to sea level, at a given
place along the river is called
the stage of the river. During
periods of normal flow in a river,
water is confined to the channel
of the river. When the stage of
the river reaches what is called
flood stage, water overtops
the banks of the channel. The
area of a river valley that is
covered by water during a flood
is the floodplain. (See Figure 5.)
When water flows out onto the Figure 5 Deposition of fertile sediment
floodplain, it spreads out as a on floodplains provides ideal
wide and shallow flow. farming conditions.

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 Chapter 4 Surface Processes

The flow of water across a floodplain is shallower than in the channel. As

a result, the friction between the flow and the ground plays a greater role
than in the channel. The flow across the floodplain is slower than in the
river channel. The slower flow across the floodplain cannot carry as much
sediment in suspension as it did in the channel. Therefore, the floodwaters
deposit much of its sediment load (mainly sand and silt) across the
floodplain. In many areas, floodplain sediments create fertile land that
is good for farming. In areas that are not agricultural, cleaning up the
sediment left by a flood is an expensive, labor-intensive job. (See Figure 6.)

Figure 6 The flooding of the Red River of the North in Grand Forks, ND
April, 1997, caused almost two billion dollars in property damage.

It is common for the discharge in low-gradient streams to change with the

seasons. This is a result of seasonal changes in precipitation. For example,
flooding is not common in Maine during the winter. During the winter,
most precipitation is in the form of snow. The snow remains on the
ground surface. However, in the spring, warm weather causes the snow
to melt rapidly. Much of the snowmelt flows directly into streams or into
groundwater systems. These systems then feed the streams. All of the
snowmelt in the upstream parts of the drainage basin eventually drains
into the low-gradient streams in the downstream parts of the drainage
basin. This results in flooding. In such areas, the danger of flooding is
especially great during heavy rains in warm spring weather after a very
snowy winter. In contrast, during the hot summer months, precipitation
is less abundant, and more water is lost to evaporation and growing
vegetation. This reduces the risk of flooding.

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 Section 5 Low-Gradient Streams

Flooding is a natural process. It occurs as a river system develops and

evolves. Humans often try to control this process. However, efforts along
one section of a river can increase the effects of flooding along other
sections downstream. Sound land-use planning allows for the natural
development of floodplains. It helps limit property damage that could
be caused by flooding.
In many large rivers, the land area through which the river flows is
gradually subsiding relative to sea level. This causes the river to deposit
some of the sediment it carries. This helps to maintain the same elevation
of land relative to sea level. Most of this new deposition takes place in
the channel itself, and also along its banks. As sediment is deposited Geo Words
along the banks, ridges called natural levees are formed. These natural levee: a natural
levees stretch continuously along both sides of the river. With time, the or human-made
embankment built
river gets higher and higher above its floodplain. Eventually, during a along the bank of a
large flood, the river breaks out of its levees. It finds an entirely new and river to confine the
lower course across the floodplain. This is called avulsion. This results river to its channel
in a catastrophic flood on the floodplain. Also, the river may no longer and/or to protect land
from flooding.
flow through a city that was once located somewhere downstream of the
avulsion: a major
point of avulsion. change in the course
Currently, some of the lower Mississippi River flows out to the Gulf of of a river when the
river breaks out of its
Mexico along the Atchafalaya River. This is west of the main Mississippi. levees during a flood.
The U.S. Army Corps of Engineers has built an enormous structure, called
headworks: an
a headworks. It was built at the point along the Mississippi where the engineering structure
Atchafalaya branches off. Its purpose is to control how much water is built to control the
diverted from the Mississippi. flow of river water
out of a river channel
during a flood.

Checking Up
1. How does
meandering
change the pattern
of a stream
channel in a low-
gradient stream?
2. Why do low-
gradient streams
have a broad
floodplain?
3. What types of
Figure 7 Without a headworks, probably most of the Mississippi would by now be
sediment are
flowing down the Atchafalaya, leaving the city of New Orleans as a backwater city.
carried and
deposited by low-
gradient streams?
4. What causes low-
gradient streams
to flood?

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 Chapter 4 Surface Processes

Think About It Again

At the beginning of this section, you were asked the following:
• What happens during a flood?
Record your ideas about this question now. Apply your new knowledge of flow patterns
in your answer.

Reflecting on the Section and the Challenge

This section helped you to realize that streams with lower gradients and larger discharges
tend to have wider floodplains than streams with higher gradients and smaller discharges.
Large, low-gradient rivers carry large amounts of sediment into lakes and oceans as they
change the landscape and transport large volumes of water as part of Earth’s hydrosphere.
By comparing the river system in your community with both high-gradient and low-
gradient streams, you will be able to better understand the characteristics of rivers that
might affect the sites you are considering for development in Florida and Alaska.

Understanding and Applying

1. The stream gradient you measured in the investigation of high-gradient streams is

really the gradient of the valley in which the river flows. If a stream meanders on its
floodplain, is the gradient of the stream channel itself equal to, greater than, or less
than the overall gradient of the valley? How might you measure the gradient of the
stream channel, rather than the stream valley, using a topographic map?
2. Are the streams in your community generally high-gradient streams, low-gradient
streams, or somewhere in between? Explain your interpretation.
3. Because they are physical barriers to travel, streams have been used as political
boundaries throughout history. This includes boundaries between cities, counties,
states, and countries.
a) Do rivers serve as boundaries in your community? In your state?
b) On a map of the United States, identify rivers that form the boundaries between
states, between the United States and Mexico, and between the United States
and Canada.
c) How could meandering of a stream channel on its floodplain affect boundaries?
d) How would communities react to the changing of boundaries because of the
meandering of rivers?
4. Is a high-gradient stream or a low-gradient stream more likely to have a large
population center near it? Explain your answer.

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 Section 5 Low-Gradient Streams

5. Low-gradient streams have wide, flat floodplains.

a) List some advantages to locating a community on a floodplain of a river.
b) List some disadvantages to locating a community on a floodplain of a river.
c) Do you think the advantages outweigh the disadvantages, or the other way around?
6. Compare the hazards posed by low-gradient streams with the hazards posed by high-
gradient streams.
7. Is there a time of year when a low-gradient stream poses a particular hazard to
communities? Explain your answer.
8. Preparing for the Chapter Challenge
How does the capacity for erosion and deposition compare for a low-gradient stream
and a high-gradient stream? Write a short paper in which you address this question.
Consider the risks and opportunities for development by low-gradient streams in
both Florida and Alaska. How do these parts of drainage systems differ between the
two states? Find out about simple engineering practices used to reduce the risks of
developing on the floodplains of major rivers.

Inquiring Further
1. The floods of 1993, 1997, and 2001
Research the Mississippi and Missouri River floods of the summer of 1993, the Upper
Mississippi River flood in spring 2001, or the Red River flood in Grand Forks, North
Dakota and East Grand Forks, Minnesota in the spring of 1997. What happened in
cities on the floodplains? Pick a city that was affected by one of the floods and describe
the impact of the flood. Was the city prepared for floods? What did the city do once it
became clear that the river would flood? Was the city damaged? What has the city done
to prepare for future floods?

Sandbags provide added protection against rising waters during a flood.

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 Chapter Mini-Challenge

Your challenge is to find a site suitable to host the Summer

Olympic Games. You need to collect information about two
cities. One is in the state of Alaska, and one is in the
state of Florida. You will need to create a poster and
report about the suitability of each site. At this point, you
should be able to describe the surface geology of both
cities. Your Mini-Challenge is to evaluate the
suitability of the landscape of each city for Olympic
facilities. Here are some Inputs you have read about.
These should be included in your Mini-Challenge:
• What is the gradient of the land? Is the land stable
or prone to landslides?
• Are the rivers likely to flood or is the flow reliable
and stable?
• What risks are there in disturbing the ground where
the Olympic facilities will be built?
• What materials are under the site (for example, limestone,
loose sediment, river gravels, or granite)? Will these
materials support the building of the facilities and what
hazards do they present to development?
In your group, discuss the format of your evaluation and come up with a plan. Present your evaluation
to your teacher and the class for Feedback. The Mini-Challenge will help you organize your Chapter
Challenge. You will not be able to address all of the requirements at this time, but you should do your
best to fully address the topics that you have already studied.
Look back at the Goal you wrote at the beginning of the chapter. Rewrite your Goal so that you are clear
on what you will prepare for the Mini-Challenge. Review the Goal as a class to make sure you have all of
the criteria and the necessary constraints.

You have completed five sections of this chapter and read about some aspects of Earth’s
surface processes. These will be part of the Inputs phase of the Engineering Design Cycle.
Review what you have studied below to help develop your evaluation.
Section 1: You examined the unique properties of water. You found out why water is so important to
life on Earth. You also looked at the distribution of water on Earth. Then you learned about the water
cycle and saw how water moves from place to place within the Earth system.
Section 2: You explored the nature of drainage systems, interpreted topographic maps, and evaluated
important interactions between river systems, land features, and communities.
Section 3: You considered whether the slopes of land features were suitable for development and
determined how the slope of the land controls surface processes. You discovered how different Earth
materials are prone to forming unstable slopes.
Sections 4 and 5: You used streamflow data to learn about the characteristics of high- and low-
gradient streams. You calculated the gradient of streams using a topographic map, assessed possible
hazards and benefits, identified areas where these streams occur, and compared the relationship between
these streams, surface change, land use, and development.

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 In addition to these concepts, you may want to look for information on how flooding is controlled. You
should investigate flood control in both high- and low-gradient drainage systems. You may also want to
find out what engineering practices can be used to reduce the risks of building on floodplains of large
rivers or near high-gradient streams. You may wish to examine which Olympic water sport requires a
low-gradient system and which one requires a high-gradient one. Do these conditions exist in the sites
you selected?

The Process phase of the Engineering Design Cycle is when you decide what information
you have that will help meet the criteria of the Goal. At this point you need to evaluate the
information you have explored. This about what you will use to create the poster and report.
Perform a Resource Analysis. Create a list of what you have studied in the first five sections of this
chapter. For each item on your list, decide the following.
• How it will convince your audience that each site is suitable for building the Olympic facilities.
• How it will help reduce the fear of geologic hazards to the facilities during the events and afterward.
• How the landforms and the processes that form them that are present support the Olympic events.
Categorize the information you have explored. This will help you focus your energy on addressing the
parts of the challenge that you are prepared to answer at this point.
Your Resource Analysis has revealed which topics in the first five sections will be helpful for developing
your presentation. Your group might assign individuals or teams of two to work on specific parts of the
report. Then you can put all the parts together at a later time. Each person or team will now know which
chapter section or sections they can use to help him/her address their part of the presentation.
During your Resource Analysis, you can also make a list of what you still need learn to complete all parts
of the evaluation. This list will help you complete the final parts of the Chapter Challenge.

The Output of your Engineering Design Cycle for the Mini-Challenge is the evaluation of the
surface geology of both cities. Remember, everyone is working on the same Challenge. You only
need to do a good job of meeting the Goal requirements to do well.
You will present your evaluation of the site to the class. You should address the surface geology of each
city. Explain how the information you have gathered supports or does not support the development of
Olympic sport facilities. This is your design-cycle Output.

Finally, you will receive Feedback from your classmates. They will tell you what you have
done well according to the criteria from the Goal. They might also tell you some things you
can improve. To give good Feedback, it is important to consider all the criteria and
constraints. Think about how well each point addresses them. Your statements should say which parts
were satisfied and which, if any, were not. This is an objective process. It should focus on the products,
not the student scientists who produced them.
The Feedback will become an Input for your final product. You will have enough time to make
corrections and improvements. Therefore, pay attention to the valuable information your classmates
provide. Remember to correct any parts of your report that you received critical feedback on. You may
have also learned something from watching other presentations. You may want to add to your group’s
final presentation. It will be easier and faster to improve your evaluation now rather than waiting until
the chapter is finished. Remember to record all your information in a safe place. Then it will be ready to
use in the Chapter Challenge. As you complete the remaining sections, look for additional information
that will help you improve your poster and presentation.

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 Chapter 4 Surface Processes

Section 6 Sediments in Streams

What Do You See?

Learning Outcomes Think About It

In this section, you will Moving water can have amazing force. For example, rocks the
• Describe and classify sediments size of automobiles can be carried in streams during floods.
according to particle size and
shape. • What can you learn about a stream by looking at the materials
• Describe what happens to
in the streambed?
sediments composed of • How do streams change the material they carry?
different rock types as they
are transported in streams. Record your ideas about these questions in your Geo log. Be
• Identify the relationship prepared to discuss your responses with your small group and
between stream velocity the class.
and particle size.
• Identify the relationship Investigate
between transport distance
and particle size. In this Investigate, you will examine a model that shows how
sediments are formed from larger rocks. You will also explore
the differences between sediments of various sizes.
Part A: Modeling the Breakdown of Sediment
1. Obtain three or four small pieces of gypsum and three or four
small pieces of shale. Determine the total mass of the gypsum
and the total mass of the shale.
a) Record these masses.

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 Section 6 Sediments in Streams

2. You will need to be able to record a) Measure and record the longest axis.
the following measurements for each This is the a-axis.
piece of gypsum and shale: roundness,
b) Measure and record the horizontal
length (a-axis), width (b-axis), thickness
axis that is perpendicular to the
(c-axis), the ratio b/a, the ratio c/b,
a-axis. This is the b-axis.
and shape.
a) Make a table in your Geo log in c) Now measure and record the vertical
which you will display this data. axis that is perpendicular to the first
two axes. This is the c-axis.
3. Determine the roundness of each
piece according to the Roundness d) Compute and record the ratios b/a
table shown below. and c/b.
a) Record the data in your table. e) Using these ratios, plot the location
of each piece on a particle shape
4. Determine the shape of each piece,
graph with the ratio b/a on the
recording all of the data in your table.
vertical axis and the ratio c/b on the
Place each piece on a flat surface so
horizontal axis. Use the graph on the
that the longest axis is approximately
next page as a guide.
horizontal. (Refer to the following
Particle Shape Graph on the next page.)

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 Chapter 4 Surface Processes

5. Place the 6 to 8 samples in a 950-mL 7. Put the pieces back into the container,
plastic bottle that is filled halfway with add water as before, cap the bottle and
water. Cap the bottle and shake it for shake the mixture for 5 more minutes.
5 minutes.
8. Repeat Step 6.
Dry the outside of the bottle before shaking so
it is not slippery. 9. Describe what you saw each time
you emptied the container and
6. Carefully strain the water through a analyzed the pieces. Consider the
screen. Avoid spills. Place the material following questions:
that remains on the screen on a paper a) How did the mass, roundness, and
towel. Dry the rock samples and find shape change?
the total mass of the gypsum and the
shale as you did before. b) What differences did you notice
between the changes in gypsum
a) Record the mass. versus the changes in shale?
b) Determine the roundness of the c) What type of material did you collect
particles. Record this in your table. when you sieved the water?
c) Measure the a-, b-, and c-axes again.
Record each measurement. Wash your hands after each part of the
investigation.
d) Compute and record the ratios b/a
and c/b. Use these ratios to plot the
location of each piece on a new piece
of particle shape graph paper.

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 Section 6 Sediments in Streams

Part B: Analyzing Stream Sediments 4. You have grouped the sediments by

1. Obtain 5–10 pieces of coarse sediment particle size. Use your data to determine
(at least a few centimeters in diameter) the percentages of each group of
collected from a local river by sediment size. Look at the largest and
your teacher. smallest particle sizes with a hand lens.

a) Describe the characteristics of a) Can you see any differences in

the pieces. Identify the rock roundness and sphericity? Write
types, if possible. a short paragraph explaining
your findings.
2. Make a table in your Geo log in which
you will display the following data for Part D: Using a Stream Table to
each piece: roundness, length (a-axis), Observe the Beginning of Sediment
width (b-axis), thickness (c-axis), the Movement in Streams
ratio b/a, the ratio c/b, and shape. 1. Obtain two thick wooden boards as
3. Determine the roundness of each piece long as the stream table and about
using the Roundness table. 5 cm wide. Place the boards on their
edge along the center of the stream
a) Record the data in your table. table, leaving a space about 5 cm wide
4. Determine the shape of each piece, between them, to form a channel. Place
recording all of the data in your table. a wooden block 5 cm wide, 8 cm long,
Place each piece on a flat surface so and 2 cm thick between the wooden
the longest axis is approximately boards near the upstream end of the
horizontal. stream table. Refer to the photograph
to see how to arrange the board and
a) Measure and record the a-, b-, the block in the stream table.
and c-axes.
b) Compute and record the ratios b/a
and c/b.
c) Using these ratios, plot the location
of each piece on particle shape
graph paper.
Part C: Measuring Sediment Sizes
1. Obtain sediment samples from either a
local stream or your teacher. Measure
the mass of the sample.
a) Record the mass.
2. Sieve the sediment sample using a set
of sieves, or, if these are not available,
a piece of plastic window screen from a
hardware store. You have now separated
your sample into at least two groups.
3. Dry the sediment. Find the mass of the
groups and classify them by particle size
(sand, silt, and so on).
a) Record all of your data in a table.

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 Chapter 4 Surface Processes

2. Place a layer of fine sand 2 cm thick a) Record the flow velocity in your log.
between the boards. Level the bed of
5. Increase the water supply slightly, and
sand so that it is nearly flat and at the
observe the sand bed closely for any
same level as the wooden block between
sand movement. Measure the velocity
the boards.
of the flow again.
3. From a water source, run a small
a) Record the flow velocity in your log.
stream of water onto the stream table
just upstream of the wooden block. The 6. Repeat Steps 4 and 5 until you notice
water will flow across the surface of that many of the sand grains are being
the block and down the sand bed in the moved by the flow.
channel. Maintain a constant flow that
is low enough to not disturb the sand. a) Record the flow velocity for which
the sand is first moved. This is
4. Measure the velocity of the water flow called the threshold velocity for
in the channel. Do this by floating sand movement.
a tiny piece of cork on the water
surface and timing how long it takes 7. Repeat the experiment using coarse
to move down the channel. Divide sand instead of fine sand in the channel.
the downstream travel distance a) Record all your data.
(in centimeters) by the travel time
(in seconds) to obtain the velocity in Clean up all spills immediately. Wash your hands
centimeters per second. Check the sand after the investigation.
bed to make sure that no sand is being
moved by the water flow.

Digging Deeper
SEDIMENTS IN STREAMS
Size Range of Sediments
In the Investigate, you explored how sediments are formed from larger
rocks. You also looked at the sizes of different sediments. Sediments come
in a very wide range of sizes. Geologists have officially named several
ranges of sediment size. This helps them talk about sediments. (See the
table of sediment sizes below.) To geologists, the words clay, silt, sand,
and gravel mean something very definite. It is easy to measure the sizes
of sand and gravel particles. However, it is very difficult to measure the
sizes of silt particles, and especially clay particles.

Particle Size Classification of Sediments and Sedimentary Rocks

Sediment Particle Size
Boulder > 256 mm Coarse
Gravel Cobble 64–256 mm
Pebble 2–64 mm
Sand 0.062–2 mm
Silt 0.0039–0.062 mm
Mud
Clay < 0.0039 mm Fine

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 Section 6 Sediments in Streams

Sediment particles also vary greatly in their composition. Most gravel

particles are pieces of rock. In most streams and rivers, particles of sand
and silt consist mainly of the mineral quartz. Quartz is abundant at
Earth’s surface. It is very resistant to wearing away. However, depending
on the source of the sand, several other minerals may also be common
in sand sizes. Most clay-sized particles consist of minerals, called clay
minerals. These exist in the form of tiny plates or flakes.
Transportation of Sediment by Streams
Sediment can be carried by streams in several ways. This is shown in
Figure 1. Sediment can be dissolved in water and carried along invisibly
in a stream. Fine sediment particles the size of clay and silt travel mostly
while they are suspended in the water. They “ride” along with the Geo Words
stream. This material is called suspended load. The suspended sediment suspended load:
is held up above the streambed by the irregular motions of the water, material that travels
called turbulence. To get a good idea of what turbulence in a stream in a stream suspended
in the water.
looks like, watch steam or smoke coming out of a smokestack. You will
turbulence: the
be able to see the swirling masses of turbulent fluid, called eddies. irregular motion
On the other hand, very coarse, gravel-sized sediment particles travel of water.
mostly along the streambed. They move forward by sliding, rolling, and eddy: a swirling mass
bouncing. This material is called bed load. Sand is moved mostly as bed of turbulent fluid.
load when the streamflow is moderate. However, when the streamflow bed load: sediment
is very strong, sand moves as both bed load and suspended load. particles that travel
Whether a stream carries most of its sediment in suspension or as bed along the streambed,
by sliding, rolling, and
load depends both on the size of the sediment in the stream and on the bouncing.
velocity of flow in the stream.

Figure 1 Sediment transport by a stream.

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 Chapter 4 Surface Processes

The flowing water in a stream exerts forces on sediment particles resting

on the streambed. This happens in much the same way as a stream exerts
forces on you when you are standing or sitting in a shallow stream.
The sediment particles rest in little “pockets” between the particles
underneath. Therefore, a certain force is needed to move a given particle
Geo Words from its position on the streambed. For each sediment size, a certain
threshold velocity: the velocity of flow, called the threshold velocity, is needed to move some of
velocity of flow that the particles on the streambed. As you saw in Part D of the Investigate,
is needed to move
certain particles along
stronger flows are needed to move coarse sediment than are needed to
the bed of a stream. move fine sediment. This is shown in the graph in Figure 2. Below the
threshold curve, no sediment is moved. Above the threshold curve, the
flow can move at least some of the sediment. In Part D of the Investigate,
you identified two points like this on a graph. Another way of looking at
the graph is that there is a maximum size of sediment particle that can be
moved by a given velocity of flow.

Figure 2 Graph showing the relationship between stream velocity and

maximum particle size transported.

How Streams Reduce the Sizes of Sediment Particles

Sediment particles in streams can become rounded as they bounce along
the bottom of the stream and collide with other particles. The collisions chip
the edges of the particles and grind them down. In general, the higher the
flow velocity, the harder and more frequent the collisions that break down
the sediment. Smaller particles, such as sand and silt, are commonly picked
up and carried in suspension. These sediments can “sandblast” the larger
sediment particles they come in contact with. In this way, large particles
that are not in constant motion can still be worn down and rounded. Also,
powerful collisions between pieces of gravel during floods can break or split
the gravel into small pieces.

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 Section 6 Sediments in Streams

Sediment particles composed of different types of rocks or minerals

become rounded at different rates. Particles composed of softer minerals
become rounded more rapidly than those composed of harder minerals.
Limestone is composed of relatively soft calcite. It becomes rounded
more quickly than quartzite. Quartzite is composed of relatively hard
quartz. Rocks that have layering or other planes of weakness also break
down more quickly than rocks that are uniformly strong. Gneiss is a
layered rock. It may break down more rapidly than a nonlayered rock,
such as granite.
Rock and mineral particles can also be reduced in size by dissolving.
However, most of the common rocks and minerals in sediments dissolve
very slowly, if at all. Calcite is the only very common sedimentary mineral
that dissolves fairly quickly in streams.

Downstream Fining
Ordinarily, sediment particles in the upstream areas of a river system are
much coarser than the particles in the downstream areas. This is known Geo Words
as downstream fining. It can have various causes. All of the sediment downstream fining:
particles could be slowly reduced in size by abrasion and/or dissolving the decrease in
sediment size
as they travel downstream. However, most geologists think that this is
downstream in a
not the most important reason. Breakage of larger particles into smaller stream or river.
particles is probably much more important. In some streams, the coarser
sediment tends to be dropped by the stream and stored in the stream
valley. The finer particles move on downstream. This would also cause
downstream fining. In any given stream, it is usually difficult to tell
which effect is more important in causing downstream fining.

Figure 3 As you proceed downstream, you will find that the sediments carried by
the stream become finer and finer.

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 Chapter 4 Surface Processes

Stream Deposition
Sediments transported by rivers and streams are eventually deposited.
You read about the deposition of sediment on the inside bend of a
Geo Words meandering stream. You also read about deposition on floodplains. This
occurs when rivers flood. There are two other important sedimentary
alluvial fan: a wide,
sloping deposit of deposits formed by streams and rivers. They are alluvial fans and deltas.
sediment formed
An alluvial fan is a fan-shaped deposit. It forms where a stream leaves a
where a stream leaves
a mountain range. mountain range. (See Figure 4.) It occurs when the stream flows out of a
delta: a landform steep, narrow mountain valley and onto a broad, flat valley floor. When
made of sediment the stream emerges onto the valley floor, it experiences a sudden decrease
that is deposited in gradient. As a result, the velocity of the stream decreases. Therefore,
where a river flows its ability to carry sediment is also reduced. The stream deposits a large
into a body of water.
part of its load, starting with the coarsest sediments, mostly sand and
gravel, as an alluvial
fan. Drainage
continues in an
irregular radial
pattern from the
top of the fan. Finer
sediments remain
within the flow and
are carried toward
the edges. During
periods of high flows,
coarser sediments
deposited higher
on the fan may be
picked up again and
moved toward the
margin of the fan.

Figure 4 This image shows alluvial fan deposits in the

Zagros Mountains of Iran. This image was taken by the
Terra satellite as part of NASA’s Earth Observing System.

A delta is a sedimentary deposit that forms where a river flows into a

large body of water such as a lake, an ocean, or an inland sea. Deltas can
have a variety of shapes. They often have complex patterns of drainage.
(See Figure 5.) Most are triangle-shaped. When a river joins a larger body
of water, it is no longer flowing downhill. It quickly loses velocity. At this
point, the river also loses its ability to carry sediment. The heaviest particles
drop to the bottom first, forming a steeply sloping layer. Most of the fine
suspended load is carried farther out into the body of water. It eventually
settles out to form a gently sloping front. This is especially the case when
less-dense fresh water flows on the surface of denser salty water.

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 Section 6 Sediments in Streams

Deltaic deposits usually consist of silt and clay particles. As long as the
volume of sediment deposited by the river is greater than that removed
by wave erosion and currents, the delta grows outward. This allows
surface drainage to extend farther to the edge of the delta and to
continue to deposit sediment. Most of Earth’s great rivers, including
the Nile, Amazon, and Mississippi, have built massive deltas.

Checking Up
1. Compare physical
breakdown with
dissolving of
materials.
2. What would
baseball-sized
particles in
a streambed
indicate about the
maximum velocity
of the streamflow?
3. In your own words,
describe what
might happen
to a large piece
of granite as it
is transported
farther and farther
downstream. What
are the processes
that would be
acting on the
granite?
Figure 5 This image shows the Ganges River Delta in Bangladesh—
the largest delta on Earth. 4. What is the
difference between
an alluvial fan and
a delta?

Think About It Again

At the beginning of this section, you were asked the following:
• What can you learn about a stream by looking at the materials in
the streambed?
• How do streams change the material they carry?
Record your ideas about these questions now. Include what you have
learned about streamflow and sediment erosion in your answers.

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 Chapter 4 Surface Processes

Reflecting on the Section and the Challenge

In this section, you discovered that particles are changed in size and shape as they are
moved about in water. You also found that particles made out of different materials
change at different rates. You saw that a stronger flow of water is needed to move coarse
particles than is needed to move fine particles. Now you know what processes occur
in rivers. Being able to apply these concepts to the sediments you find in rivers beyond
your community will help you understand the types of flow that have helped shape the
landscape. You will need this information to complete your Chapter Challenge.

Understanding and Applying

1. From your data, what can you say about the relationship between the velocity
of a river and the size of the sediment it carries?
2. What was the likely velocity of the river from which the following sediments
were taken:
a) Silt and clay? b) Fine sand? c) Large, rounded boulders?
3. One of the political leaders in your community has suggested making a “swimming
hole” along a stream in your community. The politician proposes to dredge gravel
from some part of the stream channel to make it deep enough, then add sand to the
banks and bottom. This politician maintains that this will be a low-budget, “natural”
swimming hole. As the expert on sedimentation in your community’s streams, do you
agree with the politician? Explain your answer.
4. Preparing for the Chapter Challenge
With your group, think about the questions below.
• What geologic evidence do you need to determine if a stream has periods of
high-velocity flow?
• Could the streamflow in your Florida and Alaska cities potentially affect the
streambed and banks?
• Will the high-velocity flow affect downstream areas?

Inquiring Further
1. Cleaning up sediment
Has a stream in your community ever flooded and deposited sediments on a road,
athletic field, or parking lot? How did your community handle the cleanup? How
much did it cost? What was done with the sediment?
2. Sediment and living things
In what ways could the types of sediment in a streambed indicate the various plants
and animals that could live there? Do plants and animals that live in streams use
specific types of sediments? Would you find a different set of plants and animals
in a mud-bed stream as opposed to a gravel-bed stream?

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 Section 7 Soil and Land Use

Section 7 Soil and Land Use

What Do You See?

Soils that contain many rocks

and large boulders may be
expensive to dig out for
development.

Learning Outcomes Think About It

In this section, you will During the 1930s, severe dust storms called “black blizzards”
• Collect, study, and describe affected the midwestern United States. This period in American
local soils and develop a history has been referred to as the Dust Bowl era.
classification system for them.
• Explore how soils form, what
• In what ways is soil part of the Earth systems (geosphere,
a soil profile is, and the atmosphere, hydrosphere, biosphere, and cryosphere)?
importance of soil as a • Are all soils the same?
natural resource.
• Identify the relationship • How is soil important in your life?
between the physical Record your ideas about these questions in your Geo log. Be
characteristics of a soil and
prepared to discuss your responses with your small group
how the soil formed.
and the class.
• Establish that soil characteristics
may vary over time, and that
these variations can greatly Investigate
impact a community.
In this Investigate, you will explore the structure of soil and
• Map the location of different
how different types of soil are suited for various uses.
soils in your community.

Wear safety goggles when working with sand,

soil, or other particles. Avoid contact with eyes.
Wash hands when done.

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 Chapter 4 Surface Processes

Part A: Classifying Soil Samples

b) If possible, draw boundaries between
1. Obtain a soil sample from your different soil types.
backyard, a farm, or a relative’s house
in the country. Bring the soil to school Part B: Determining Specific
in a covered plastic container or sealed Characteristics of Soil
plastic bag. Label the container with 1. Characteristics of different soils make
your name, where the soil came from, them appropriate for different uses. You
and the kind of place where the sample can test soil for desired qualities, such as
was taken (for example, a field, hilltop, • how well it drains
riverbank, forest, and so on). Each • how well it absorbs and holds water
group will obtain a sample of each
soil available. • how well it promotes plant growth
• stability during earthquakes
2. Work in your small group to study the • strength (for example, ability to
soil samples available. support heavy structures).
a) Decide on and record a set of a) Design a test your group can perform
descriptive terms that your group on each soil sample that will identify
will use to classify all of the samples. a quality of your choosing. In your
b) Make a table in your log that lists log, describe how you will perform
the different soil samples down rows the test. Submit this description to
and your set of descriptive terms your teacher for approval.
across columns. Fill in the table, b) Predict the results you will get when
describing each sample with the you test each soil sample.
set of terms you listed.
2. After your teacher has approved
c) Develop a classification system your design, perform the test on
for your soil samples. Write the each soil sample.
name and definition for each type
of soil that you identified in your a) Display the results of your test in
classification system. tables or graphs, and present the
results to the class.
3. On a map of your community, show
the locations where each soil sample b) Take notes on the results of the other
came from. groups’ tests.
a) Label each point with the soil name c) As a class, discuss various test
your group came up with. designs and results. In your log,
summarize the results of all the tests.

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 Section 7 Soil and Land Use

Digging Deeper
SOIL
Classifying Soils
As you discovered in the Investigate, soil types can vary significantly.
Ways of classifying soil vary as well. One way to classify soils is by texture.
Texture refers to the distribution of the sizes of the particles. Most
soils are a mixture of gravel, sand, silt, and clay sizes, as well as organic
materials. Texture controls many properties of soil. It determines how fast
water will drain through it, how much water it can hold, or how much it
compacts under heavy loads. Geo Words
Soil that contains about equal parts of sand, silt, and clay is called loam. loam: in general, a
The soil texture triangle is illustrated in Figure 1. It shows how soils are fertile, permeable soil
composed of roughly
classified and named on the basis of the various percentages of grain equal portions of clay,
sizes contained. Loam is a permeable soil. Water can readily penetrate silt, and sand, and
loam. It is excellent for growing plants because it does not drain water usually containing
too rapidly or slowly and contains organic materials. organic matter.

Figure 1 Soil texture triangle. Plotting the relative percentages of clay, silt, and
sand in a soil sample allows for classification of the soil by texture.

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 Chapter 4 Surface Processes

Soil Formation
In general, soil is a thin layer of rock, mineral fragments, and decaying
organic material. It covers most of Earth’s land surface. Soil is formed by
weathering of rocks and minerals. There are two types of weathering.
They are physical and chemical. In physical weathering, rock breaks down
but its makeup stays the same. Wind, rain, running water, changes in
temperature, and sunlight are responsible for physically breaking down
rock. In chemical weathering, the actual composition of the rock changes.
The minerals in the rock react with water and dissolved oxygen and acids
and are converted into other minerals.
Biological processes are also important in forming soil. Some of the chemicals
produced by chemical weathering are important nutrients for plants. Plants
grow in the broken-down rock. They attract animals. The plants and animals
die. Their bodies decay. They undergo decomposition by bacteria and other
microorganisms. This process adds organic matter to the soil.

Figure 2 Well-rounded rocks found at a beach or in a streambed are evidence

of physical weathering.

It can take anywhere from a few hundred to several hundred thousand

years for a soil to form. The time needed to form a soil depends on
climate, bedrock type, amount of vegetation, and topography. Warm,
humid climates tend to produce soil the fastest. This is because both
chemical and physical weathering processes are very active. Different
kinds of bedrock weather at different rates, contributing soil particles at
different rates. Plants help make soil formation possible. Therefore, the
more vegetation, the faster soil tends to develop. Typically, there is little
or no soil on steep mountain slopes. This is because gravity and water
transport the sediment to lower elevations as fast as it is produced.
Valleys usually contain thick soil deposits, as do broad, flat areas.

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 Section 7 Soil and Land Use

Geo Words
soil horizon: a
layer of soil that is
distinguishable from
adjacent layers by
characteristic physical
properties, such
as structure, color,
Figure 3 Ice and snow can act to break down rocks to produce soil. What other texture, or chemical
weathering processes are at work in the photograph above? composition.

Soil Horizons
If you looked at a vertical cross section of
sediment from the surface down to a depth of
several feet, you would see various layers of
the soil. These layers of soil are what scientists
call soil horizons. (See Figure 4.) The top layer,
called the A horizon, contains more organic
matter than the other layers. This layer
provides nutrients to plants and contains
enormous numbers of insects, microbes, and
earthworms. The next layer down, called
the B horizon (or subsoil), is a transition
layer between the layers above and below.
It contains less organic material than the A
horizon. In the lowest layer, the C horizon,
partially broken-up bedrock is easily identified.
Organic material and organisms are scarce or
absent there. The thickness of the layers varies
greatly from location to location. However, Figure 4 Notice the three soil
these three layers are present in most soils. horizons in the diagram.

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 Chapter 4 Surface Processes

Soil as a Natural Resource

Soil is a vital natural resource because it allows humans to grow food
crops. Because soil takes so long to form, it should be considered a
nonrenewable resource. Unfortunately, in many places around the world,
including the United States, soil is being eroded away by wind and
running water much faster than it is being formed. Soil is lost when rain
or wind carries soil particles away from fields or construction sites that
Geo Words are left bare, without a cover of vegetation. Windbreaks (walls or rows
contour plowing: the of trees or other plants) can protect soil from wind. Contour plowing and
practice of plowing terracing can also help to reduce soil erosion. In contour plowing, soil is
soil across a slope
following contour plowed across the slope following contour lines. The rows formed help to
lines to reduce soil slow the runoff of water. In terracing, sections of the slope are leveled off,
erosion. giving the hill a step-like appearance. Another strategy is to always grow
terracing: the practice plants in unused fields. This helps to hold the soil in place. It also adds
of leveling off valuable nutrients to the soil when the plants die and decompose.
sections of a slope,
giving the hill a
stepped appearance,
to reduce soil erosion.

Checking Up
Figure 5 The Dust Bowl provides a clear example of what can happen when soil is
1. Describe three not considered in planning a community.
processes that are
involved in physical Some soils may be less suited for development than others. For example,
weathering.
soils that contain many rocks and large boulders may be expensive to
2. Draw and label dig out for development. Soils that drain poorly may require expensive
a diagram that
drainage systems to protect buildings and property from flooding.
explains the major
features of the
During earthquakes, some water-saturated sandy or muddy soils undergo
three main soil liquefaction. That is, they temporarily behave like a liquid. They therefore
horizons. cannot support structures. You may have modeled this at the beach by
3. Describe two jiggling wet sand. For a short time it flows like a liquid before becoming
methods of firm again. This happened in the 1989 Loma Prieta earthquake in
preventing soil California. Much of the damage during that earthquake was caused by
erosion. liquefaction. Many buildings that were built over old, water-saturated
4. Why are some landfill deposits collapsed. This happened because shaking caused the
soils less suited for soil below them to liquefy and flow.
development?

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 Section 7 Soil and Land Use

Think About It Again

At the beginning of this section, you were asked the following:
• In what ways is soil part of the Earth systems (geosphere, atmosphere, hydrosphere,
biosphere, and cryosphere)?
• Are all soils the same?
• How is soil important in your life?
Record your ideas about these questions now. Refer to your work on the classification
of soils and soil-forming factors in your answers.

Reflecting on the Section and the Challenge

In this section, you read that there are different kinds of soils, and that soil can be
classified and mapped on the basis of its physical properties and where it is found. You also
read that you can test soil for various properties that might be desirable for specific uses.
Soils can develop on weathered bedrock or on sediments deposited by rivers, glaciers, and
wind. Think about how your plans for development in both Florida and Alaska will affect
local soils. This will help you complete your Chapter Challenge.

Understanding and Applying

1. What are the different soil types in and around your community? For each different
type, describe the following characteristics. Organize your data in a table.
a) appearance
b) texture
c) content (kind and amount) of organic matter
d) other physical characteristics
e) location(s) where it is found
f) location(s) where it is being removed naturally or by human activity
2. Are there certain soils in your community that may be good or bad for agriculture
or for development? Use data to support your answer.
3. Have you ever noticed changes in soils as you traveled? For example, you might
notice the appearance of sandy soils as you get closer to the seashore, or the absence
of soils as you enter a region with steep topography. From a trip you have taken, or
in photographs you have seen of different regions, list some differences you may have
noticed in soils.
4. Consider one soil type you have seen on a trip or in photographs. Describe how the
characteristics of that soil can tell you something about the climate and geology of the
region where it is found.

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 Chapter 4 Surface Processes

5. Preparing for the Chapter Challenge

Find out how upland soils and lowland soils differ. What are the processes that
control their development? Apply what you have learned about slopes. What is the
relationship between soils and slopes? How does the gradient of the surface and
the rock type affect the flow of water above and through the soil and rocks? What
measures will your development include to protect against soil erosion or any other
disturbance of the soil? Be sure to examine the topography and soils for your potential
sites in Florida and Alaska.

Inquiring Further
1. Soils in your community
a) Contact a state or local soil conservation agency, the cooperative extension service
at your state university, or your state geological survey, to obtain a map of the soils
in and around your community. Describe any correlation between soil type and
current land use in your community.
b) Analyze the physical characteristics of a particular soil type or sediment type found
in your community. Questions you might answer include:
• Why is the soil a certain color in your area but a different color in an adjacent area?
• Why do deposits of sand and gravel tend to be found only at lower elevations?
• Why will some sediments or soils liquefy during an earthquake?
c) Describe a soil profile. To do this, you will need to find an area where you can
observe 1 m (about 3–4 ft) of fresh, vertically layered soil (such as a riverbank).
In your log, draw what you see in detail. Include measurements of the various soil
layers. Describe each layer as completely as you can, including observations such as
color, texture, composition, grain size, and grain shape.
d) Investigate soil erosion in your community. Write a report in which you describe
the cause(s) of the problem and state what is being done to minimize damage. Offer
your own suggestions for dealing with the problem. Include interviews with town
officials, and/or local newspaper articles, if possible.
Consult the EarthComm Web site at http://www.agiweb.org/education/earthcomm2/
for help with your research.

You can see the damage due to erosion before the Building a wall made of limestone blocks restored the
problem was corrected. area and prevented any further erosion.

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 Section 8 Glaciers and the Landscape

Section 8 Glaciers and the Landscape

What Do You See?

Soils that contain many rocks

and large boulders may be
expensive to dig out for
development.

Learning Outcomes Think About It

In this section, you will Glaciers are huge masses of ice that move very slowly across the
• Make a mathematical model land, changing the land’s shape as they move along. In Alaska,
of an imaginary glacier.
the largest glacier is the Tazlina Glacier. It is approximately
• Calculate how the glacier
40 km long. Scientists who study glaciers think about questions
would respond to hypothetical
changes in climate. like the following:
• Understand the uses and • What other materials might be in a glacier besides ice?
limitations of models in Earth
and space science. • How might the materials get into the glacier?
• Understand the mechanics of
how glaciers form and move.
• How do glaciers change the landscape?
• Discover that glaciers modify Record your ideas about these questions in your Geo log. Be
the landscape by erosion and prepared to discuss your responses with your small group
deposition.
and the class.
• Model the action of glacial
meltwater as it drains out of
a glacier. Investigate
• Establish that the movement
of glaciers can change stream In this Investigate, you will calculate the movement of a
drainage patterns. hypothetical glacier. This will help you to gain an understanding
• Model the effects of a glacier of the factors that affect the shape and movement of a glacier. You
infringing on a stream. will also examine models that show the action of glaciers as they
• Apply what you have observed move over land. Your teacher may run some or all parts of this
to determine whether glaciers
have affected your community Investigate as a demonstration for the class.
in the past.

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 Chapter 4 Surface Processes

Part A: Modeling the Behavior profiles and note that the X has moved
of a Glacier forward the same distance as was lost
1. In this part of the Investigate, as a to the head of the glacier).
glacial geologist, you are monitoring a a) How much ice is melting each year
glacier in Alaska. Assume the following from this glacier? (If the glacier
about your glacier: is at equilibrium, the volume of
• It is 100 km long, 5 km wide, and ice melted equals the distance of
200 m thick. glacier movement per year, times
• It moves at a rate of 100 m/yr. (Note: the thickness of the glacier, times
This does not mean that the glacier the width of the glacier.)
gets longer by 100 m each year, but 3. To be at equilibrium, the glacier must
rather that any one point in the glacier receive as much new ice each year as
moves forward 100 m in a year, as it loses by melting. A lot of snow that
shown in the sample profiles below.) falls on a glacier simply melts and runs
• It is at equilibrium. (Note: This means off without contributing anything to the
that it is receiving just enough snow glacier, especially in the warmer areas
to balance what it loses through near the foot of the glacier. Assume that
melting. At equilibrium, the length new ice is added only in the upper half
and thickness of the glacier remain (50 km) of the glacier.
about the same.)
a) What volume of ice is needed to
balance losses by melting?
b) What thickness (depth) of ice has
to be added each year to balance
the melting? (Remember that the
volume of ice is equal to flow
per year × depth × width.)
4. On average, 1 m of snow packs down
into about 10 cm of ice.
a) How much snow would have to fall
on the glacier each year to create
the thickness of new ice that you
calculated above?
b) Data show that there is 7.2 m of
a) How long would it take a rock that snowfall in the region in which the
falls into the ice at the head of the glacier is located. Is the amount of
glacier to reach the foot? (Remember snowfall required to keep the glacier
that the flow rate of the glacier is in balance realistic?
100 m/yr and that the rock must
travel the entire length of the glacier.) 5. Imagine that the climate in the region
of the glacier changes in such a way
2. The glacier moves at a speed of
that the winter snowfall is greater by a
100 m/yr. If no ice were melting from
factor of two (that is, it doubles) and
the glacier, it would be 100 m longer
the melting rate is less by a factor of
after one year. However, it was assumed
two (that is, it is cut in half).
that the glacier maintains a constant
size. Therefore, a volume of ice must a) How much larger will the total volume
be melting each year (see the sample of the glacier be after 100 years?

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 Section 8 Glaciers and the Landscape

b) What will be the percentage increase a) Describe the characteristics of

in the size of the glacier? (To compute the glacier.
this, subtract the original volume b) What processes might supply
of the glacier from the new volume, sediment to the surface of the glacier?
divide by the length of the time
interval in years, and multiply by c) Describe the characteristics of the
100 to convert to a percentage.) valley-floor materials.
6. Imagine that the climate in the region of d) What processes might affect the
the glacier changes in such a way that development of the valley floor?
the winter snowfall is less by a factor of 2. Think about how constructive and
two and the melting rate increases by a destructive surface processes affect the
factor of two. landscape. Predict the following:
a) How many years would it take for a) What will happen if the glacier
the glacier to disappear (that is, to advances by growing larger?
melt completely)?
b) What will happen if the glacier
Part B: Glacial Processes retreats by melting?
1. Glacial ice can grow thousands of c) Make a table with two columns
meters thick and extend tens to and two rows. Label the columns
hundreds of kilometers. Due to their “erosion” and “deposition.” Label the
size, glaciers can have a great impact rows “processes” and “landforms.”
on the landscape. You will run a model
3. You will model the movement of a
that examines the destructive and
valley glacier. Run the model by pressing
constructive effects of a valley glacier, a
the ice down into the sediments and
glacier that is confined to a valley and
slowly slide the ice forward so that it
flows from a higher elevation to a lower
advances along the valley floor.
elevation. Valley glaciers are found in
mountain landscapes. Work with your a) Record your observations under the
group to set up your model according appropriate heading in your table.
to the following diagram. Look for changes all around the
glacier, including underneath.
b) Compare your predictions to your
results. Explain any differences.
4. You will now observe what happens
when the glacier retreats by melting.
a) Make another table for recording
your observations.
b) Predict what you will observe as the
glacier retreats.
5. Run the model by letting the ice melt
and record your observations.
a) Compare your predictions to your
results. Explain any differences.
b) Discuss with your class how glaciers
change the landscape.

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 Chapter 4 Surface Processes

Part C: Modeling the Action of 6. Put the pan on a surface where water
Glacial Meltwater can drain from the pan without causing
any damage. Prop up the end of the pan
Wear goggles and a lab apron throughout this
investigation. Use the hammer with care. Clean opposite the opening with a thin strip
up spills. Wash your hands when you are done. of wood about 3 cm thick, or a
chalkboard eraser.
1. Put an even layer of cedar bedding
about 1 to 2 cm thick in the bottom of
a baking pan. Put a second pan inside
the pan with cedar bedding. Spread
an even layer of fine sand about 0.6
cm thick on the bottom of the second
baking pan. Fill the baking pan until it
is almost full of water. Put the assembly
into a freezer, and wait overnight until
the water is a solid block of ice.
Note: It will take a long time for the
water to freeze all the way to the
bottom because of the insulation of
the cedar bedding.
2. Turn the pan upside down under warm
running water until the ice block comes
loose. Set the ice block aside, and cut
down along two edges of the pan so
that one of the narrow sides of the pan
can be bent down flat, level with the
bottom of the pan.
3. Replace the ice block in the pan, and
wait until the block is at its melting
temperature. You will know when
the block has reached its melting
temperature when its surface shines
with a thin film of water.
4. Put the pan on the floor, place a
wooden block on the ice surface,
7. Spray cold water on the upper end of
and hit the board with blows from a
the ice sheet. Use just enough water so
hammer. Start very gently, and increase
that some of the water runs down the
the force of the blows until the block
surface of the ice sheet. Observe how
shows several long cracks but has not
the patterns of water flow and drainage
been completely shattered.
change with time, as some of the ice is
5. Roll three long “snakes” of modeling melted, and how the sediment at the
clay in your hands, and mold them base of the ice sheet is moved by the
along the sides of the ice sheet. flowing water.

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a) Record your observations in your log. Pack down the glacier gently (without
disturbing the stream channel) to prevent
b) Using your knowledge of the water from seeping under the ice.
properties of ice and water, account
for the behavior you observed. 5. Turn the water back on. Let it run long
enough to carve a new channel along
c) On a real glacier, what do you think the margins of the ice. Some water
happens to surface water (meltwater might seep under the ice along the old
plus rainwater)? channel. This is acceptable because, as
Part D: Using a Stream Table to you saw in Part C of the Investigate,
Model Ways that Glaciers Modify water does flow under and within
the Landscape glaciers. As long as the flow under
the ice does not completely prevent
1. To model the ways in which glaciers formation of a new channel, seepage is
modify the landscape, fill a stream table acceptable and even desirable.
with damp sand and prop up one end a) Sketch the changes that are occurring
with a think strip of wood about 3 cm on the stream table.
thick.
6. Allow the ice to melt naturally. Observe
2. Run water down the stream table long
and record the results. Complete
enough to form a well-defined channel
melting will take several hours, possibly
at least 1 cm deep. Before you run the
overnight.
model make a small channel with your
finger to guide the flow. Then, turn off a) Once the ice has completely melted,
the water in the stream table. sketch what you see in the stream
table again.
a) Sketch the river channel in your log.
b) Describe any changes in the surface
3. Make a model glacier as in Part B of the texture of the sand (besides the
Investigate by freezing a small pan of channel diversions).
water with some aquarium gravel in the
bottom. The aquarium gravel represents c) Describe any erosional features that
the sediments carried by a glacier. are formed by the meltwater from
the ice.
4. Block the channel with the model glacier,
except for a space around one side d) Where did the aquarium gravel
of the ice for a new channel to form. end up? Describe and sketch these
changes.

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 Chapter 4 Surface Processes

Geo Words Digging Deeper

glacier: a large mass
of ice on Earth’s GLACIERS
surface that flows by
deforming under its How Glaciers Form and Move
own weight.
deform: to change A glacier is a large mass of ice on Earth’s surface that flows by deforming
shape. under its own weight. To deform is to change shape. A glacier is only
regelation: a two-fold partly a large-scale version of an ice cube sliding down a sloping tabletop.
process involving the It is also like a deep puddle of honey or molasses flowing down the
melting of ice under tabletop. Many materials act like solids on short time scales but like liquids
excess pressure and
the refreezing of the on long time scales. Glass is a good everyday example. If you hit it with a
derived meltwater hammer, it shatters. If you support a long, thin glass rod horizontally by
upon the release of its two ends in a warm room and wait patiently for weeks and months,
pressure. you would find that the rod would have sagged down slightly. Similarly,
ice sheet: a large ice shatters when you hit it with a hammer. However, under high pressure,
glacier that forms on
a broad land area at deep within a glacier, it flows by deforming slowly as a plastic solid.
high latitudes where A glacier forms wherever more snow falls in winter than melts in summer,
summers are cool
enough so that not for a long period of years. As the old snow is buried by new snow, it is
all of the previous compressed by the weight of overlying snow. The crystals grow together
winter’s snow is by regelation. In this process, the greater pressure put upon lower layers
melted. causes melting. The meltwater refreezes upon the release of pressure. The
valley glacier: a air in the spaces between the crystals is gradually forced out and upward.
smaller glacier that
forms in mountainous Eventually, after several tens of meters of burial, the snow has been
areas and flows converted to solid glacial ice. After some further burial it begins to flow
down valleys to lower downslope as a glacier.
elevations.
The largest glaciers form
on broad land areas at high
latitudes where summers are
cool enough that not all of
the previous winter’s snow is
melted. Large glaciers like this,
called ice sheets, now cover
most of Greenland and
Antarctica. (See Figure 1.)
Smaller glaciers, called valley
glaciers, typically form in
mountainous areas and
move down valley to lower
elevations. (See Figure 2.)
Large valley glaciers are
common at high elevations in
Earth’s major mountain belts.
Their growth and survival
depends upon the balance
between the accumulation of
snow in winter and the melting
Figure 1 The Antarctic ice sheet is the largest
on Earth today. of ice in summer.

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 Section 8 Glaciers and the Landscape

Every glacier has an area in its

upper part, called the zone of
accumulation. This is the area
where there is a net addition of
new glacial ice year after year.
Every glacier also has an area in
its lower part, called the zone of
ablation. This is the area where
there is a net removal of glacial
ice year after year. The boundary
between the two zones is called
the snow line. (See Figure 3.)
Below the snow line, all of the
previous winter’s snow is melted
by the end of the summer and
old glacial ice is exposed to
melting. Above the snow line,
some of the previous winter’s
snow remains until the next
winter. The newly formed glacial
ice flows continuously downslope
from the zone of accumulation to
the zone of ablation. Ablation
occurs mostly by melting. Figure 2 Valley glaciers operate on much
However, where the glacier ends smaller scales than broad ice sheets.
in the ocean, large masses of ice
break away from the glacier and Geo Words
float away as icebergs. This process zone of accumulation:
the area in the upper
is called calving. part of a glacier
where there is a
net addition of new
glacial ice year
after year.
zone of ablation: the
area in the lower part
of a glacier where
there is a net removal
of glacial ice year
after year.
snow line: the
boundary between
the zone of
accumulation and the
zone of ablation.
calving: the breaking
away of a mass of ice
from a glacier.

Figure 3 Diagram of a typical glacier.

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 Chapter 4 Surface Processes

Glaciologists are scientists

who study glaciers. They try
to do “bookkeeping” of
glaciers. When accumulation
is greater than ablation for a
period of years, the volume
of the glacier increases, and
Geo Words the glacier lengthens. The
terminus: the terminus of the glacier (its
downstream end downvalley end) gradually
of a glacier.
advances downslope. When
stillstand (in a accumulation is less than
glacier): the balance
in accumulation and ablation for a period of
ablation when the years, the volume of the
volume of a glacier glacier decreases. The
is constant and the terminus retreats. Keep in
terminus stays in the
same place. mind, however, that even
internal deformation:
though the terminus is
the part of movement retreating, glacial ice is
of a glacier that is being delivered to the
caused by change terminus all the time,
of shape within Figure 4 Glaciologists at work.
the glacier.
where it finally melts. If
accumulation and ablation
basal slip: the part
of movement of are in balance, the volume of the glacier stays the same. The terminus
a glacier that is then stays in the same place. That is called a stillstand.
caused by sliding of
the glacier over the It is not too difficult to measure the speed of movement of a valley glacier.
material beneath During the summer melting season, you can plant a row of metal stakes
it, aided by a thin across the glacier. Then, set up a surveying station on the mountainside
lubricating layer next to the glacier, and survey in the locations of the stakes. A year later,
of water.
come back to resurvey the stakes. The downglacier curvature of the
new position of the row of stakes shows that the middle of the glacier
flows faster than the edges. That is the internal deformation part of the
movement. In internal deformation, the speed of the glacier at its edges
is zero, but with basal slip, the speed at the edges is greater than zero.
A glacier that is below the melting temperature at its base is frozen solid
to its bedrock base. Glaciers like that have no basal slip. (See diagram A
in Figure 5.) They are called cold-based glaciers. A glacier that is at its
melting temperature at its base has a very thin film of water, usually no
thicker than a millimeter or two. That is formed by a slow flow of heat
from the interior of Earth. The lubricating film of water allows the glacier
to slide on its bed. (See diagram B in Figure 5.) Glaciers like that are called
warm-based glaciers. (Does it strike you as strange that ice can be “warm”
as well as “cold”?) Warm-based glaciers are responsible for many geologic
processes. They can erode, transport, and deposit mineral and rock
material as they slide over their beds.

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Geo Words
tools: rock and
mineral particles that
are carried at the
base of the glacier
and that grind the
bedrock.
striations: scratches
on bed rock inscribed
by debris at the base
Figure 5 Two types of movement along the base of a glacier. of a moving glacier.

Glacial Erosion
In the Investigate, you used two models
to explore what happens when glaciers
move over land. When a glacier forms
on the surface of the geosphere, it
incorporates loose soil and sediment
into its base and moves it away. Glaciers
act like gigantic bulldozers. They scour
the surface and push rock and soil in
front of themselves as they advance.
The rock and mineral particles that are
carried at the base of the glacier are
called tools. As the glacier advances,
this material is ground together as
the ice moves. This material becomes
as fine as flour and consists mostly of
harder minerals, such as quartz and
feldspar. Clean ice is not hard enough
to affect bedrock, but the movement
of ice with rock flour acts to polish
bedrock. Sometimes, rocks in transit in
the bottom of the ice can gouge long
grooves and gashes in the bedrock called
striations. Erosion of bedrock by debris
in a glacier is called abrasion. The base
of the glacier gains new tools by taking
away blocks of the bedrock that are Figure 6 The basal load
already cut by fractures. of a glacier exposed by
a meltwater stream.

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Geo Words
plucking: a type
of glacial erosion Figure 7 Striated bedrock near Mount Rainier with grooves going from top to bottom.
by meltwater The striations were cut by moving ice and water at the base of a glacier.
penetrating, freezing,
and breaking off Meltwater at the base of a glacier sometimes penetrates fractured
pieces of bedrock
which are then
bedrock and freezes. When this occurs, bedrock can be broken apart
incorporated into the rapidly by freezing and thawing. This process is called plucking. The rock
base of the glacier. debris is then added to the load at the base and is used to polish and
cirque: a bowl-like abrade the bedrock as the glacier moves. Running water at the base of
depression formed by some glaciers also causes erosion. Water and sediment can carve channels
a glacier on the side in the ice and bedrock. Such channels can be observed flowing around
of a mountain.
obstacles on the bed of the channel.
Your model focused on the action
of glaciers on lower slopes. But,
on higher slopes, such as those in
mountainous regions, other features
develop. At higher elevation the
temperatures are cooler and there is
little or no melting of glacial ice. As a
result, glacial erosion tends to be the
dominant process.
The erosion of small round glaciers
produces interesting landforms
called cirques. These are semicircular
hollows shaped like a shallow bowl.
Cirque glaciers slide and rotate at
Figure 8 A valley glacier surrounded by the same time. This scours their bed
glacial landforms formed by erosion and and deepens the cirque. Usually, the
deposition.

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ice pulls away from its back wall, forming a large fracture or crevasse Geo Words
called a bergschrund. Here, the exposed rock suffers intense frost action bergshrund: a wide
and becomes steepened by erosion. Where cirques develop near to one and deep crevasse
where a glacier
another, distinctive mountainous landforms develop. When cirques form pulls away from
on both sides of a drainage divide, knife-edge ridges, called arêtes, its backwall.
develop. Where multiple back-to-back cirques form on mountain slopes, arête: a sharp-edged
they form mountains with many steep faces, called horns. mountainous ridge
carved by glaciers.
horn: a sharp peak
with multiple faces.
fjord: a deep
U-shaped valley
carved by a glacier
and drowned by
the sea.

Figure 9 Glacial landforms in mountain environments.

Glaciers in valleys can form extensive networks of ice. Here, large glaciers
converge with smaller tributary glaciers. Such glaciers cause extensive
erosion through abrasion and plucking. This results in the formation of
trough-shaped valleys with wide U-shaped profiles. (Remember that the
profile of a river valley is usually V-shaped.)
In lowland regions, with relatively
easy-to-erode bedrock, ice sheets can
erode out wide and deep depressions
in the bedrock. After the ice sheet
retreats, such depressions are usually
occupied by lakes. The Great Lakes,
the Finger Lakes in central New York
State (shown in Figure 10), and Lake
Champlain, are examples of large lakes
that formed in this way. Some glaciers
reach the coast, and their trough may
become submerged by the sea as the
ice retreats. This produces landforms Figure 10 The Finger Lakes were
called fjords. carved out by glaciers.

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Glacial Deposition
Geo Words Loose rock and mineral material that is carried by the glacier is called the
load (of a glacier): load of the glacier. Much of the load is frozen into the base of the glacier.
loose rock and When the glacier cannot transport part of its load, it deposits part of it by
mineral material
that is carried by plastering it onto the bedrock beneath the glacier. Sediment deposited in
the glacier. this way is called glacial till. (See Figure 11.) Till is a poorly sorted mixture
glacial till: poorly of boulders and clay-sized sediments. Sheets of till cover large areas of
sorted, unlayered North America once occupied by the Pleistocene ice sheets.
sediment carried
or deposited by
a glacier, usually
consisting of a
mixture of clay, silt,
sand, gravel, and
boulders ranging
widely in size and
shape.
moraine: a mound
or ridge of mainly
glacial till deposited
by the direct action
of glacial ice.
terminal moraine: the
outermost moraine
that marks the
farthest position of
a glacier.
push moraine: an
arc-shaped ridge of
rocky debris that is
shoved forward by an
advancing glacier.
dead ice moraine:
a broad, irregular Figure 11 Moraines of boulders and fine sediments at the terminus of the Columbia
deposit formed from Glacier, Alaska. A subglacial stream carries away the meltwater.
sediments that are
dumped when a
glacier melts. Scientists use the term moraines for landforms composed of till. When an
ice sheet is in equilibrium for a long period of time, so that its terminus
stays in the same place, high ridges of sediment, called terminal moraines,
are deposited. Terminal moraines show geologists where the farthest
advance of the ice sheet was located. Various other kinds of moraines
are formed by glaciers as well. If the terminus advances, then material
in front of the ice is bulldozed into a ridge at the front of a glacier.
This ridge is called a push moraine. If the rate of melting is greater than
the rate advance, then the glacier melts and the ice becomes thinner.
Eventually, this thin ice melts away and dumps all of it debris from its
surface to its base to form a broad, irregular deposit called a dead ice
moraine. This type of moraine often contains large chunks of ice that
are frozen into the sediments.

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Deposition also occurs along the sides of glaciers. Debris forms long ridges Geo Words
that extend along the edge of the ice. These are called lateral moraines. lateral moraine: a low
Most of the debris is deposited as material slides and falls down the side ridge of rocky debris
deposited at the side
of the glacier. As the glacier ice melts away from the lateral moraine, the
of a mountain glacier.
ridge stands alone and marks where the sides of the glacier once were.
medial moraine: a
Because lateral moraines are formed by dumping of material, their long strip of rocky
sediments are different from moraines that form at the terminus. Lateral debris formed where
moraines contain little material that has arrived from beneath the glacier. the sides of two
They also lack the fine-grained sediment formed by abrasion. Lateral glaciers converge.
moraines can grow much larger than terminal moraines because material
is constantly added to them. On the other hand, terminal moraines are
overrun and
destroyed by
advancing ice. When
two glaciers come
together, their inside
lateral moraines join
together and form a
medial moraine.
These occur as thick
bands of debris along
the center of the
new, larger glacier.
This debris protects
the ice from melting,
so medial moraines
often stand much
higher than the
surrounding ice. Figure 12 Moraines are composed mainly of glacial till.

Glacial Meltwater and its Deposits

Melting of the lower areas of glaciers in summer produces enormous
volumes of water. This water, together with rainwater from summer
storms, flows across the glacier. The water then finds its way to the base
of the glacier through fissures and holes in the ice, because water is
denser than the ice. It flows at high speeds through large tunnels at the
base of the ice and emerges at the terminus of the glacier. The meltwater
streams that flow out from the glacier carry enormous quantities of
sediment of all sizes, from clay to boulders.
As the terminus of an ice sheet retreats, much of the sand and gravel
carried by meltwater streams is deposited right at the glacier terminus.
It is often deposited in between large melting ice masses. After all of
the ice melts from the area, these deposits are left as irregular hills and
ridges. Their sizes and shapes vary greatly. In the northern parts of the
United States, these deposits are prime sources of sand and gravel for
concrete. Think about how different your life would be if there were
no sand and gravel for such an ordinary but essential building material
like concrete.

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 Chapter 4 Surface Processes

How Glaciers Alter River Systems

The Pleistocene ice sheet rearranged the courses of many rivers in North
America. (See Figure 13.) Before the Pleistocene, the river drainage system
of North America looked very different from today. The Great Lakes had
not yet formed. The Mississippi River was a smaller river with a much
smaller drainage basin. There was no Ohio River. Instead, a river system
extended across the middle of Indiana and Illinois. This system joined the
ancient Mississippi in the middle of Illinois.
There was no Missouri River. Rivers in the Northern Plains states flowed
northeast into Canada. (These rivers are now tributaries to the Missouri
River.) The headwaters of the Missouri, the Yellowstone, and other rivers
of the Northern Plains states still flow northeast. This is a remnant of this
ancient river system. By blocking rivers that were flowing northward, the
glaciers created the present Ohio and Missouri River Systems.
When glaciers blocked rivers, there were many different possible
outcomes. In some cases, small segments of existing river systems flooded
their valleys. They flowed over drainage divides and cut new valleys.
Eventually, segments of former river systems connected into a new river.
The Ohio River formed in this way. In other cases, water flowed along the
margins of the glaciers, cutting a new channel that captured all the rivers
it crossed. Meanwhile, as the ice melted, it dropped debris in the former
river channels, blocking them and often closing them up completely. This
is how the present Missouri River formed.
The glaciers retreated across the area now occupied by the Great Lakes.
As they did, they alternately blocked and exposed outlets of the lakes.
At different times, one or more of the lakes drained south through the
Mississippi. Some drained southwest across Ohio and Indiana. Others
drained across Ontario in a number of places, and down the Mohawk
Checking Up and Hudson Rivers to the Atlantic.
1. What factors
would cause a
glacier to advance
(grow)?
2. What factors
would cause a
glacier to retreat
(get smaller)?
3. How do glaciers
erode bedrock?
4. How do glaciers
deposit sediment?
5. How did the Ohio
River form?
6. How did the
Missouri River
form? Figure 13 Drainage patterns in North America before (left) and after
7. How did the Great (right) the Pleistocene ice age.
Lakes form?

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 Section 8 Glaciers and the Landscape

Think About It Again

At the beginning of this section, you were asked the following:
• What other materials might be in a glacier besides ice?
• How might the materials get into the glacier?
• How do glaciers change the landscape?
Record your ideas about these questions now. In your answers, include descriptions of how
glaciers erode bedrock and move sediment.

Reflecting on the Section and the Challenge

In this section, you learned how glaciers form and move. Whether the front edge of a
glacier advances, retreats, or remains in the same position depends on the balance between
snowfall and melting. You also simulated the effects of a valley glacier, glacial meltwater,
and a glacier blocking a stream. When glaciers move across streams, they can change
where and how rivers flow. Glaciers erode enormous volumes of bedrock. They deposit the
material beneath the glacier, at the glacier terminus, and in streams and rivers beyond the
terminus. Many communities in the United States are on rivers that were changed by the
Pleistocene ice sheets. Think about the advantages and disadvantages of glaciers for your
task in the Chapter Challenge.

Understanding and Applying

1. In Part A of the Investigate, you modeled a hypothetical glacier.

a) What assumptions did you make about the glacier?
b) In what ways would real glaciers be more complicated?
c) Are the assumptions you made realistic enough that you can draw useful conclusions
from them, or are they so simplistic that they do not reflect real glaciers?
2. How would you recognize whether a deposit of sediment on the land surface was
produced by a glacier rather than by a river? In your log, make a list of possible
criteria you would use.
3. When a glacier blocks a river, there are many things that can happen.
a) Which of the following did you observe in Part D of the Investigate? Use a sketch
to illustrate each event you observed.
• The stream is diverted permanently from its old course.
• The stream is temporarily diverted but goes back to its old channel once
the ice melts.
• The stream changes course more than once as the ice melts.
• Meltwater streams make channels that may or may not capture part
of the drainage.
b) Describe any other outcomes that you observed that are not listed.

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 Chapter 4 Surface Processes

4. Did the glacier in Part D of the Investigate leave behind a moraine? If so, describe it.
5. Find a community that is located along a river that was diverted by glaciers in
the past. How would the history of this town be different if the river had not
been diverted?
6. Pick the largest river nearest to your community, and predict what would happen
if the river becomes blocked by a glacier at various locations.
a) Would the community be flooded?
b) Would the river be diverted away from the town?
c) What would you advise your community leaders to do about it?
7. Preparing for the Chapter Challenge
When glaciers advance and retreat, they interfere with stream patterns and sometimes
change the paths of rivers. Glaciers also leave behind characteristic landforms, such
as moraines. Write a paragraph in which you describe the seasonal relationship
between glaciers and rivers. Apply these ideas to the evaluation of your Olympic
Games sites.

Inquiring Further
1. History of science
Research J. Harlan Bretz, the geologist who first proposed catastrophic flooding as
a cause of the Channeled Scablands. Describe his theory and the evidence behind it.
Why did other geologists originally discount his theory? Why did other geologists
finally embrace his theory? Use the EarthComm Web site at http://www.agiweb.org/
education/earthcomm2/ to help you with your research.
2. Glacial landforms
There are many other glacial landforms besides the ones mentioned in this section.
Research how the following glacial features form. Be sure to include your sources
and describe how you assessed their reliability.
• kames • eskers • drumlins • kettles

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 Section 9 Wind and the Landscape

Section 9 Wind and the Landscape

What Do You See?

Soils that contain many rocks

and large boulders may be
expensive to dig out for
development.

Learning Outcomes Think About It

In this section, you will Weathering breaks down surface rocks into smaller pieces that
• Model wind erosion, transport, are removed by processes of erosion. In some places, wind is very
and deposition. effective in moving sediment particles.
• Identify the locations of Earth’s
wind-dominated landscapes.
• How do particles move in flowing air?
• Explain how wind erosion • How does wind affect the landscape?
involves the interaction of
• Where on Earth do you think wind affects the landscape most?
Earth’s different spheres.
Explain your answer.
Record your ideas about these questions in your Geo log. Be
prepared to discuss your responses with your small group and
the class.

Investigate
In this Investigate, you will form a hypothesis and design your
own experiment that examines the effects of wind on loose
sediment. You will then look at the relationship between wind
speed and particle size. Next, you will examine the effects of
windblown sand on rock. Finally, you will consider how
sediment that has been carried by wind is deposited.

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 Chapter 4 Surface Processes

Part A: How Wind Moves Particles 3. After your teacher approves your
1. Following is a list of factors that affect outline, do a preliminary test of
the motion of windblown sand. With your experiment to explore its likely
your group, choose one factor to outcomes. This will help you refine
investigate. You will be investigating your plan. During this stage, develop
how that factor affects the erosion of the hypothesis you will be making.
a patch of sediment by wind. a) Record your findings.
• wind velocity 4. Draw a diagram that shows the setup
• sediment size of your experiment.
• shape of sediment patch a) Write a list of steps that you
• impacts by falling particles of will follow.
different sizes
5. After your teacher approves your steps,
• vegetation run the experiment.
• dry versus damp sediment
a) Record your observations.
a) Record the factor you chose.
6. Revisit your hypothesis.
2. Design an experiment to investigate
the affect of that factor. Consider the a) Describe how your observations
following when designing and running compare to your predictions.
your experiment: b) Explain your results.
• Look over the list of materials c) Compare your findings to other
available to you. Select the materials groups. Describe how they are
you will need. similar or how they are different.
• Develop a hypothesis and a prediction.
7. Go to the EarthComm Web site at
• Cover your workspace with a large http://www.agiweb.org/education/
sheet of white paper, to avoid earthcomm2/. Find the link that
sample loss. shows a video of sand erosion in a
• Select the best position of the fan so wind tunnel.
that it provides good airflow.
a) Describe how sand grains move in
• Identify the best position to observe the experiment.
sediments, both moving and
stationary sediments. b) Having made these new observations
of moving sand, is there anything
• Put the sediments through a sieve to
you would change about your
separate out different sized grains.
experiment? If so, what?
• Weigh sediments to determine how
much has been eroded or deposited. c) State your conclusions about
windblown sand.
• Select the number of tests you will run.
• Identify the number of factors that
are variable.
• Draw conclusions from the results of
your experiment.
a) Outline the steps of your experiment.

Wear goggles at all times for safety.

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 Section 9 Wind and the Landscape

Part B: Wind Velocity and

a) Predict what will occur when you
Moving Sediment
shake the container.
1. The size of grains moved by wind
b) Decide upon the length of the test and
depends on wind velocity. Table 1
any other refinements you need to
shows the relationship between wind
make. Record these in your Geo log.
velocity and particle size.
c) State your hypothesis.
Table 1: Relationship Between 3. Take turns vigorously shaking
Wind Velocity and Particle Size
the container.
Maximum Size of
Wind Velocity (km/h) 4. Open the container and examine
Moving Grains (mm)
0.25 16–24
the pebbles.
0.5 24–30 a) In your log, record any changes
0.75 30–35 you observe.
1.0 35–40 b) Compare your predictions to your
1.5 40–45 results. Explain any differences.
c) State your conclusions.
a) Graph the data.
Part D: Deposition by Wind
b) Describe the relationship shown
by the data. 1. In Part A, the movement of windblown
particles showed you how air moves
Part C: Abrasion by Windblown Sand across the surface. In particular, you
1. You explored how wind can pick up saw that irregular surfaces do not erode
and transport sediment. Now you will evenly, and that slopes facing the wind
examine the effects of particles carried are eroded more than slopes that are
by wind on rocky material. Your group sheltered. You are now going to look at
is going to run a model that examines how obstacles can affect wind flow and
the effects of windblown sand on rock. the movement of sand grains.
Examine a sample of small sandstone a) In nature, what might obstruct wind
or limestone pebbles. flow? Discuss your ideas with your
a) In a table, record the characteristics small group and class.
of the pebbles. Sketch them or use a 2. Lay a large sheet of paper flat on a
camera to take a few close-up photos surface. Place a fan so that its air
of the edges and faces of the pebbles. flows over the paper. Draw arrows
2. Put the pebbles and 50 g of sand in a on the paper that show the direction
small plastic container. Seal the lid and strength of the airflow you
with tape. would expect.

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 Chapter 4 Surface Processes

3. Arrange five plastic cups on the paper windblown sand. To do this, you will
to create a pattern of obstacles to the add sand directly to the flow of air
airflow over the paper. Using a different from the fan.
colored pencil, draw arrows on the sheet
a) Predict what will happen to the sand.
that show the direction and strength of
the airflow you would now expect. 9. Mark areas on the sheet where you
would expect deposition and erosion
a) Compare the two patterns of arrows.
to occur. Include any patterns of
4. Use tape to attach each cup to the paper. deposition you expect.
Attach 3-cm-long pieces of yarn to the
10. Turn on the fan.
tops of 10 toothpicks. Use modeling clay
to attach each toothpick to the sheet. 11. Supply a constant stream of sand to the
Space the skewers equally over the sheet. airflow in front of the fan. Observe how
the sand moves.
a) Make a sketch of your experiment.
12. Once all of the sand has been added
5. Turn on the fan.
and the movement of particles has
a) Record your observations. stopped, mark the observed pattern
of deposition on your sheet.
6. Turn off the fan.
13. Compare your predictions to
7. Compare your predictions to
your results.
your results.
a) Explain any differences.
a) Explain any differences.
b) Briefly describe the relationship
8. You are now going to determine how
between airflow, obstacles, and the
the pattern of airflow around obstacles
deposition of windblown sand.
affects the erosion and deposition of

Digging Deeper
WIND EROSION
Movement of Sediment by Wind
Geo Words
suspension: the
In the Investigate, you found that wind moves sediment in three different
transport of particles ways. You observed that the finest particles are lifted from the surface
within the wind and travel in moving air. This type of transport is called suspension. Some
caused by turbulence. suspended particles fall back to the surface. Depending on the amount of
saltation: the energy, these particles often bounce off the surface, or off other particles,
downstream
movement of
and back into the air. This kind of transport is called saltation. Coarse
sediment particles grains are often too heavy to move by suspension or saltation. Instead,
in a series of hops, they move forward gradually as a result of the impact of grains bouncing
jumps, and bounces against them. The impact of a high-velocity sand grain can move a particle
from the surface.
6 times its size and 200 times its own weight. This slow type of movement
surface creep: the is called surface creep. (See Figure 1 on the next page.)
slow movement of
larger grains caused
by the impact of
saltating grains.

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 Section 9 Wind and the Landscape

Figure 1 The three main ways that wind transports sediment:

suspension, saltation, and surface creep.

The way particles are captured by wind is quite complex. As wind velocity
becomes strong enough to move a particle, it begins to rock back and
forth. The wind may overcome the forces holding the particle to the
surface. At that point, the particle is suddenly lifted into the air. This
occurs because the wind creates a strong upward force under the edge
of the particle. As a result, it rises into the airflow at a steep angle. If the
wind turbulence is not strong enough to keep the particle in suspension,
it crashes to the surface. When a falling particle strikes another particle
on the surface, it transfers energy to that particle. This transfer of energy
allows the resting particle to lift off. The lift off occurs at a lower wind
velocity than would normally be needed. The falling particles bounce
back into the air. They stay in the air until they strike the surface and
other particles again. These particles may then rise into the airflow.
In this way, the velocity of airflow and the movement of particles are
important to the capture of new particles from the surface.

Factors Affecting Wind Erosion

Many factors affect wind erosion. First, as wind velocity (kinetic energy)
increases, the size of the grain that the wind can move also increases.
The graph from your experiment demonstrated this relationship. Also,
you may have observed that a patch of clay-sized grains was less likely to
move than a similar-sized patch of sand-sized grains. This may not make
sense to you. The clay is finer than sand and has less mass. However,
because the surfaces of clay particles are relatively smooth, they do not
stick up into moving air as much as those of sand. As a result, it takes a
greater velocity to move clay-sized grains than it does sand-sized grains.

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 Chapter 4 Surface Processes

Damp sediments behave in a similar way. They are usually much harder
to erode than dry sediments. Water filling the spaces between the loose
grains binds them together. Because of this cohesion, it takes a much
greater wind velocity to move damp grains than it does for dry grains
of the same size.
Another factor that affects wind erosion
is plant growth. Plants increases surface
roughness. This causes a reduction in wind
velocity. The decrease in wind velocity
causes sediment to become trapped.
Removal of vegetation has the opposite
effect. It greatly increases the chance of
wind erosion.
The shape of a sediment patch also has
an effect on erosion. Sediments packed in
ridges undergo erosion by grains blowing
from the slope that faces into the wind
and from the ridge crest. Grains that are
deposited behind the ridge and away from
Figure 2 The wind is deflected by its shelter are quickly removed. Sediments
patches of vegetation and affects that are flat and thinly spread tend to be
deposition on the downwind eroded from the downwind side. That is
side (White Sands National because there is nothing supporting them
Monument). from behind.

Wind Erosion and Abrasion

In glaciers and streams, erosion only takes place in channels. In contrast,
wind erosion can work over the entire land surface. However, there are
very few surface features that are formed just by the action of wind. The
Geo Words simplest form of erosion is the blowing away of loose material (rocks and
deflation hollow: a sediments) by wind. Sometimes this forms a depression called a deflation
surface depression hollow. In arid regions where there is little soil and vegetation to protect
formed by the
removal of fine-
the surface, finer material is removed. Bedrock and coarser material
grained sediments are left behind. These can form a surface of tightly packed angular and
by wind erosion. rounded grains called a desert pavement. (See Figure 3.)
desert pavement:
a hardened and
polished surface
of interlocking
sediments formed
by the wind.

Figure 3 The wind-polished surface of a desert pavement in Nevada. Winds and

periodic rains remove any loose sediments from the surface.

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 Section 9 Wind and the Landscape

Moving air that carries sediments has a sandblasting effect. This process is Geo Words
called abrasion. Over longer periods, abrasion can produce various small- abrasion: the wearing
scale features. These include polishing, pitting, and grooving of rocks. away of rock particles
due to their collision.
The type of feature that forms by abrasion depends on several factors.
The rock type and the direction of the wind are important factors. The
hardness, size, and shape of the transported material also affect the type
of features that are formed. In the Investigate, you observed how larger
particles in an airflow change shape. The collision of particles transported
by wind wears away sharp edges and projections. This causes particles to
become rounder in shape.

Figure 4 Notches on the Great Sphinx in Egypt are the result of

windblown sand blasting the sphinx over time.

Scientists observe the effects of

windblown sand. They place rods
made of various types of rocks in
windy environments. One study was
conducted in the Mojave Desert of
North America. In this location,
scientists recorded how the surfaces
of the rods of rock changed over a
period of 10 years. They found that
90 percent of windblown particles
travel within 65 cm of the ground
surface. They also observed the
removal of 1 mm of rock from a Figure 5 This mage from NASA’s Mars
granite boulder in just 15 years. rover shows windblown particles
in a martian desert. The amount of
This might not seem like much, roundness and angularity depends
but imagine the effects over on how far they have been
millions of years. transported.

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 Chapter 4 Surface Processes

Deposition of Moving Particles

In the Investigate, you observed how obstacles affect deposition.
Deposition of sediment occurs behind obstacles. The airflow behind
the obstacle is reduced. Therefore, the ability of air to carry sediment is
also reduced. This has been observed in the laboratory. It is also seen in
natural, windy regions.
In the Investigate, you saw that the rough and irregular surface of a patch
of sand is very good at trapping saltating particles. As the patch grows and
Geo Words becomes a mound, it starts to influence the way air and sand moves over
sand dune: a desert it. Sand dunes are hills or ridges of windblown sand. (See Figure 6.) They
or coastal landform grow because the kinetic energy of impacting grains is absorbed by loose
shaped by the wind
sand. A simple sand dune looks like a ramp that is steeper on one side than
and composed of
loose sand. the other. Sand grains saltate up the shallower side, which faces into the
wind. They then fall down the steeper face at the rear of the dune.

Figure 6 A dune field in Namibia.

Particles remain longer on the slope of the dune that is sheltered by

the wind. The rear slope gets steeper and steeper until it becomes
unstable. It then avalanches downward. In this way, the crest of the
dune moves forward and the dune advances downwind. Over time,
the rear face of the dune is buried over and over again. If you were to
cut through a dune, you would see layers where one crest after another
had avalanched down, burying the side of the dune that is shielded
from the wind.

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 Section 9 Wind and the Landscape

Figure 7 Layers at different angles reflect the buildup and avalanching of sediment.

Sand deposits have many different shapes. Ripples form when there
is an irregularity in the sand surface. Various kinds of long, narrow
dunes extend for many kilometers. They are usually oriented across
the prevailing wind direction. Some dunes are crescent-shaped, with a
horn at either end. The horns extend in the downwind direction and
taper toward their points. These dunes occur where winds blow in one
direction and the supply of sand is limited. Where winds blow in many
directions, the shapes of sand dunes reflect this condition. Star-shaped
dunes have a central peak and arms that radiate out from them.

Figure 8 Shade highlights the leeside of a dune. Figure 9 Wind ripples

on the surface of much
larger dunes.

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 Chapter 4 Surface Processes

Environments Where Wind Erosion is Dominant

Wind affects landscapes that have a steady supply of sediment and a lack
of plant cover. Such conditions are common in arid (very dry) environments.
They can also be found around the cold margins of glaciers and along
Geo Words coasts. The location of Earth’s arid environments is controlled by climate.
evapotranspiration: Deserts are common in regions where evapotranspiration exceeds
loss of water from precipitation. They often lack soil or have little soil moisture. Here, rocks
a land area through
transpiration of plants break down mostly by physical weathering. Also, the surface is usually
and evaporation from covered in loose stones, sand, and silt-sized materials. Arid environments
the soil and surface cover about 20 percent of the land surface. They include hot deserts and
water. cold deserts of middle and polar latitudes.

Figure 10 Map showing the location of arid and semiarid regions on Earth.

Figure 11 Wind-dominated environments are found along coasts and in dry, cold
environments.

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 Section 9 Wind and the Landscape

Earth’s Desert Regions

Earth’s most active wind-formed
landscapes are typically in areas
that receive less than 150 mm
of rainfall per year. Such areas
are found in the rain-starved
interiors of continents. They can
also be found in the shadow of
mountains. Here, intense wind
erosion and deposition takes
place. Erosion removes all but the
coarsest rocks and leaves bedrock
exposed. It may surprise you to
learn that only about 30 percent
of most desert areas are covered
by sand. Sand is concentrated Figure 12 A massive dust storm blows
mostly in lowland areas in great sediment over the ocean from the desert Geo Words
of Northwest Africa.
sand seas called ergs. erg: a gigantic sea
Most of Earth’s of sand with shifting
dunes.
windblown sand fields
are greater than 125 km2
in area. The largest active
sand sea on Earth is the
Rub’al Khali or Empty
Quarter (560,000 km2),
in the southern Arabian
Peninsula. Loose sands,
up to several hundred
meters thick, cover
most of the solid rock
in this region.
Where does the
sediment for Earth’s
dune fields come from?
Scientists believe that
the sediments found in
deserts originally came
from upland areas. The Figure 13 This image shows about 2500 km2 of coastal
desert in Namibia. High winds generate dunes
rock was weathered away reaching 300 m high. Checking Up
in these areas. It was 1. How do particles
carried downhill. Then it move in wind?
was deposited in alluvial 2. What is a desert
fans in lowland areas. In some tropical deserts, the source of the sand is pavement?
bedrock made up of desert sands. These sands were deposited during 3. What affect does
older geologic periods in desert environments. vegetation have
on airflow?
4. Where are Earth’s
deserts?

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 Chapter 4 Surface Processes

Think About It Again

At the beginning of this section, you were asked the following:
• How do particles move in flowing air?
• How does wind affect the landscape?
• Where on Earth do you think wind affects the landscape most? Explain your answer.
Record your ideas about these questions now. Include in your answers the different ways
wind erodes and deposits sediment.

Reflecting on the Section and the Challenge

In this section, your experiments showed how particles are transported by wind.
Understanding the patterns of erosion and deposition in windy regions is important for
understanding how the landscape changes. You have learned that in deserts and along
coastal regions, wind plays a major role. This also holds true for mountain regions with
a lot of fine-grained sediments scoured by glaciers. Think about these connections as you
work on the Chapter Challenge.

Understanding and Applying

1. Why is rainfall and moisture a factor that controls

Earth’s wind-dominated environments?
2. Explain the relationship between particle size
and wind velocity.
3. Suppose you discovered layers of rocks that
contained ancient sand dunes. What does
this evidence suggest?
4. Would more abrasion or less abrasion
occur at a higher wind velocity? What kind
of abrasion would occur at a lower wind
velocity? Explain your answer.
5. Compare wind erosion to related processes
in rivers and glaciers.
6. How do large sand dunes migrate?
7. Preparing for the Chapter Challenge
Think about how wind-driven processes
interact with other processes within a
drainage system. Start thinking about the
sources of sediment that supply particles
for wind transport, erosion, and deposition.
Consider how wind-driven processes might
affect the sites you have chosen for the
Olympic Games.

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Inquiring Further
1. Features of wind-dominated environments
There are many other landforms besides the ones mentioned in this section. Research
how the following features form. Be sure to include your sources and describe how you
assessed their reliability.
• barchan dunes
• longitudinal dunes
• yardangs
• ventifacts
2. Loess deposits
Loess is wind-deposited sediment of silt-sized grains that originate in glacial
environments. Major loess deposits are found in China, Europe, and the Midwest
of North America. Find out why these deposits are important to understanding how
landforms change, and their connection to past climates.
3. Wind erosion and deposition in your community
Explore your local area for evidence of processes driven by the wind. To find evidence
of erosion you will have to look for natural and human-made features that have been
affected by the sediment load of the wind. Think broadly about where you will find
evidence of deposition. Make a map to show the location of your field sites and take
photographs or make sketches of your findings. Use a field notebook to record your
observations and ideas.

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 Chapter 4 Surface Processes

Section 10 Coastal Processes

What Do You See?

Learning Outcomes Think About It

In this section, you will Coasts are the narrow zones where Earth’s vast oceans meet
• Model how the surfaces of the the edges of continents. Coastal regions extend for hundreds
oceans interact with winds. of thousands of kilometers. They are dynamic places where the
• Model ocean waves and their hydrosphere, atmosphere, geosphere, and biosphere interact.
interaction with coasts.
• Are all coasts the same? If not, how are they different?
• Apply ideas about balance in
systems to coastal areas. • What kinds of processes shape coastal regions?
• How can you tell which processes are doing the most work
in a coastal region?
Record your ideas about these questions in your Geo log. Be
prepared to discuss your responses with your small group and
the class.

Investigate
In this Investigate, you will explore some of the basic properties
of ocean waves. You will do this by generating waves in water
and studying their behavior. After this, you will run a model
that explores what happens to ocean waves when they meet a
shoreline. You will then explore what happens to waves as they
approach an irregular coastline with headlands and bays. Finally,
you will run a model that explores deposition along a straight
section of coast.

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Part A: Waves
a) For each of the three methods
1. Imagine the ocean on a calm day. (penny, blowing, and swasher),
a) Draw a profile of the ocean that predict what you think will happen
shows how its water moves, under to the marble and the cork.
these calm conditions, from the 8. Model waves using all three methods.
surface downward.
a) Record your observations in a table.
2. Imagine wind blowing across the ocean
surface and forming waves. 9. Compare your predictions to
your results.
a) Draw a second profile that shows
how ocean water moves under these a) Explain any differences.
windy conditions. 10. Share your findings with other groups.
3. With your group, you are going to use a) What is the main difference between
a model of ocean waves to test your the waves generated by blowing and
ideas. Begin by placing a stream table those generated by the swasher?
securely on a desk. Add 4 L of water.
Part B: Waves at the Shore
4. You are going to create waves that
move from one end of the stream table 1. You will run a model that looks at the
to the other by: effects of a shallow beach on advancing
waves. Work with your group to set up
• dropping a penny from 5 cm. your model according to the diagram.
• blowing on the surface.
• gently waving a ruler attached to
a transparency (referred to as a
“swasher”) back and forth at
the surface.
5. Practice each of these wave-
generating methods in the stream
table. Observe their outcomes closely.
Carefully observe what happens
when the waves hit the walls of
the stream table.
2. Place a stream table on a flat surface.
6. Earlier in EarthComm, you explored
Measure a distance of 20 cm from one
the behavior of seismic waves.
end of the tray. Use sand to build a
a) What connections can you make slope from this point and extending
between what you learned and about 10 cm toward the other end
your wave model? of the tray. Build a shore from the
7. To help you detect motion below the 20 cm point and extending to the
surface, place a marble on the floor of other end of the tray. Build the shore
the stream table, as close to the center with a thickness of 2.5 cm.
as possible. Place a float at the surface 3. Gradually add water to the sediment-
above the marble to help you detect free end of the tray until it covers the
motion at the surface. You can use sediments by about 1 cm. Use a ruler
a piece of cork as a float. to smooth out the profile.

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 Chapter 4 Surface Processes

colors will help you to distinguish

a) Predict what will happen as a wave
between different parts of the model.
moves from the open ocean to the
shore. Show your prediction by • Use a spoon to shape the headland
drawing the shape of the wave and bays.
from above and from the side. 2. Gradually add water to the tray until it
fills to a depth of around 3 cm. Make
4. Generate waves by moving a swasher sure that the water level is about 1 cm
through the sediment-free end of the lower than the top of the cliffs. Wait
tray. Hold the swasher at about 70° to a few minutes to allow water to seep
the base of the tray and move it slowly into the sand and then top up the water
through the water to make a single to its original height. If your sea is too
wave. Make waves one at a time and high, remove excess water with a cup
allow the water to come to rest between and keep adjusting it until the height
each wave. Do not be too vigorous. is correct.
a) In a table, record your observations 3. Assign the roles of wave maker, wave
for each wave. Once you think that counter, sketcher, and recorder to
have made enough observations, stop members of your group. The wave
making waves. maker will generate a single wave while
b) Copy the diagram of the model into the counter calls its number. The group
your log. On the diagram, draw what observes the wave and its effects.
happens to a wave as it travels from a) As you observe each wave and its
deeper water to shallower water at effects, describe what you are seeing.
the shore. The sketcher will draw how the
Part C: The Interactions of Waves With model coastline changes while the
Irregular Coasts recorder writes a description in
a table.
1. You will run a model that
explores what happens to
waves as they approach a
coastline with headlands and
bays. Work with your group to
set up your model according
to the diagram. Be sure you
complete the following:
• Fill one end of a stream
table with damp sand and
make an irregular coastline
consisting of a headland and
two bays.
• The coastline consists of
cliffs made of only one kind
of rock. Use one color of
sand to represent these cliffs.
• Build a beach in front of
the cliffs using sand of a
different color. The two

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 Section 10 Coastal Processes

4. Apply what you have previously

learned about waves to predict
the outcome of the model. Think
specifically about what happens
to the speed of a wave as it travels from
deeper water to shallower water. Think
about what happens to seismic waves as
they pass between different materials
inside Earth.
a) Apply this understanding to your
prediction. Draw diagrams that show
your predictions. Show what happens
to both the waves and the sediments
along the shore.
5. Run your model. Generate 20 to
30 waves. Make sure the waves
are consistent with each other.
a) Record your observations.
b) Compare your predictions to your
results. Explain any differences.
6. Share your findings with other groups.
a) What generalizations can you make
about the erosion of irregular coasts? 2. Gradually add water to the tray until
it fills to a depth of about 2 cm. Make
Part D: The Interactions of Waves With
sure that the water level is about 2 cm
Regular Coasts
below the top of the beach so that a
1. You will now run a model that explores strip of beach remains above the water.
deposition along a straight section Wait a few minutes to allow water to
of coast when the dominant wave seep into the sand and then top up the
direction is at an angle to the shore. water to its original height. If your sea
Work with your group to set up your is too high, remove excess water with
model according to the diagram. Be a cup and keep adjusting it until the
sure to complete the following: height is correct.
• Build a sandy shoreline along one side 3. Reassign the roles of wave maker,
of the stream table with damp sand. wave counter, sketcher, and recorder
• Use a ruler to make a profile that to different members of the group.
slopes downward into the ocean.
4. Apply what you have previously learned
• Use different colored sand to make about waves to predict the outcome
a patch that is perpendicular to the of the model.
shore and about 3–5 mm thick. This
will help you to detect movement in a) Draw diagrams that show your
this part of the model. predictions. Show what happens to
both the waves and the sediments
along the shore.

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5. Run your model. Make sure you c) Compare your predictions to your
generate waves at an angle to the shore. results. Explain any differences.
a) Record this angle. 6. Share your findings with other groups.
b) Record your observations. a) What generalizations can you make
about the erosion of regular coasts?

Digging Deeper
COASTAL EROSION AND DEPOSITION
Ocean Waves
In the Investigate, you generated waves and explored how they do work
on coastlines. At any time, the oceans have a crisscross pattern of waves
traveling on their surfaces. Ocean waves result from the friction between
winds and the ocean surface. On a windless day, the ocean surface
can appear glassy and still. However, even water has enough surface
roughness to generate friction against a moving airflow. The fact that
water is a very mobile fluid can be seen by the way the ocean surface
undulates in response to turbulent winds that pass over them.

Figure 1 This picture, taken from space, easily shows patterns of

waves traveling toward Baja, Mexico.

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 Section 10 Coastal Processes

At first you might think that waves travel at all depths throughout the
oceans. However, they are mostly a shallow feature and occur close to
the surface. As you saw in the Investigate, the windblown waves moved
the cork floating at the surface but not the marble on the bottom. In
contrast, the swasher generated deeper motion because it transferred
energy deeper into the water, moving both objects.

At a glance, it might appear that waves travel and migrate across the
surface of the oceans. Your Investigate models revealed something
different. Water within a wave is not really migrating. Instead, it is
transferring the motion of the wave form. This means that the water
remains in place after making its oscillation and there is little net
forward motion.

Figure 2 Sketches of deep and shallow water waves.

You saw how surface waves caused a smaller floating object to move
back and forth as it slowly traveled toward then away from the center
of the tub. What is happening is that small particles of water move in
a circular pattern. The diameter of each of these circular paths decreases
with depth. (See Figure 2.)

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 Chapter 4 Surface Processes

Changes in Waves at the Shore

When a wave that forms in the deep ocean reaches the shallower parts
of the shore, it changes shape. Its circular pattern becomes flatter and
elongated. Friction between the wave and the seafloor causes the lower
part of the movement to slow down. Near the surface, where the friction
is less, the wave continues forward and its peak rises. The increase in wave
height makes the wave unstable, and it topples forward up the beach
as a wall of surf called a breaker. As the breaker collapses, a sheet of
turbulent water continues forward and flows up the beach. This is known
as the swash. The surging swash has enough energy to move particles up
the beach. As the swash loses energy, the backwash retreats and flows
downslope to return to the ocean. Some of the backwash seeps into the
permeable beach material.

Figure 3 Waves change in shape and speed as they approach the shore.

Wave Action on Headlands

As a wave approaches the coast, the depth of the ocean usually
decreases. This causes the speed of the wave to decrease. When the
speed of a wave decreases, the direction it travels also changes. As a
result, the wave appears to refract, or bend. In the Investigate, you
Geo Words saw how waves bend due to the topography of the shore.
headland: a Irregular coastlines have protruding parts called headlands. They often
projection of the extend into the ocean from rounded bays called coves. Headlands are
coast into the sea.
composed of more resistant rock than bays. The topography of bays is
cove: an embayment usually deeper than that in front of headlands. As a result, waves often
on a coastline.
bend around headlands due to refraction. As the waves break in bays and

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 Section 10 Coastal Processes

Figure 4 Bays and headlands along the Pacific coast of California.

coves, energy is used for erosion and dissipated along the shore. This
means that coastal erosion is not uniform along the coast. Wave energy
is concentrated on headlands as the wave directions converge. In bays
diverging wave directions reduce wave energy. As a result, erosion is less
in bays. Because there is less energy, sediments are deposited in the bays.
The net effect of greater erosion on the headlands and deposition in the
bays is a straightening of coastlines because of wave refraction.

Figure 5 Wave energy is concentrated on headlands because waves bend as they

change speed in shallower waters near the shore.

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Waves and Sediments

There are several factors that can affect the erosion of a coast. One
factor is the supply of sediments. Another is the ability of currents
and waves to cause erosion. Both of these are important factors in the
evolution of coasts. Rivers flow from the coastal mountain ranges of
North America to the coasts. They transport 600 m3 of sediment every
day to the coasts. Powerful currents flow along the Pacific coast of
California. They are strong enough to move boulders 0.6 m in diameter.
These currents are like a super highway for sediment transport along
coasts. When sediments are moved into shallower waters, the activity
of waves becomes increasingly important.

Longshore Drift
As waves enter shallower waters at the shore, they slow down. As a result,
they are refracted and bend toward the shore. The breaking waves move
material up and across the beach. As waves retreat, material is then moved
back toward incoming waves. In your model, you saw how waves interact
with the slope of a beach to move material along the beach. Did you
notice that the material is pushed up the beach at one angle but returns
straight down the beach at a different angle? Material moving down the
beach profile behaves like all slope deposits and moves down the slope
and perpendicular to the coast. Material that is returned to the surf zone
then moves up the beach once more only to return back in the same way
as before. Sand moves down the beach in a zigzag pattern. Over time, this
Geo Words process is effective in moving large amounts of sediments from one end of
longshore drift: the beach to another. This process is called longshore drift.
process in which
sediments move
along the coast in a
zigzag pattern caused
by the swash and
backwash of waves
that move obliquely
to the shore.

Figure 6
Bending waves
and gravity are
two key factors
in generating
longshore drift
on straight
beaches.

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 Section 10 Coastal Processes

Coastal Erosion
The shapes of coastlines give evidence for the processes that form them.
Coasts that are dominated by erosion tend to be rugged and have steep
cliffs. This type of coast is common at the edge of a continental plate,
such as the Pacific coast of North America. Sea cliffs are sheer faces of
rock that meet the sea. Waves erode the bases of cliffs, and over time,
cut notches into them. When sea level falls, these notches become
stranded. These landforms indicate the former height of the sea.

Figure 7 The horizontal surface extending from the cliff in this

photograph is a wave-cut platform. It was created as waves cut
notches into the cliff and the progressive collapse of the cliff,
causing it to retreat inland.

Erosion of headlands can lead to the development of caves. When waves

break against cliffs, the impact of the water generates high pressures
that through time can weaken rocks. The roofs of enlarged caves often Geo Words
fail, resulting in the isolation of sea stacks separated from the coast. The sea stack: a small rock
evolution of coastal landforms that result from erosion are shown in the pillar island that has
been cut off from
following figures. The rate at which coasts erode is controlled by the the coast by wave
geology and oceans. Scientists have calculated that almost 90 percent erosion.
of California’s coast is retreating at an average rate of between 15 and
75 cm per year. Specific sections of the coast, such as Monterrey Bay, are
being eroded at up to 3 m per year.

Figure 8 The power of the sea is

concentrated between the high-
tide level and the low-tide level.
The overhanging notch cut at the
bottom of the cliff in this
photograph indicates the
level of high tide.

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Figure 9 Coastal erosion on either side of a headland has produced an arch from
what was once a cave.

Figure 10 The collapse of an arch leaves an isolated sea stack.

Coastal Deposition
Beaches are the most common type of deposit along coasts. Beaches are
places where sediments are continuously being moved by the action of
waves and currents. Sediments on beaches are heavily abraded. They are
mostly dominated by sand-sized grains of quartz or carbonate minerals. In
some volcanic areas, such as Iceland and Hawaii, beaches are formed from
the darker minerals of igneous rocks and consist of black sands. Some
beaches consist of pebbles, or even boulders of resistant rocks. Many
coastlines have no beach at all. Rocks cover the near-shore area. Beaches
act as barriers that protect the coast. They absorb the energy of waves
hitting the shore. The beach zone varies from about 5 m above high tide
to 10 m below low tide, depending on the shoreline. Some beaches are
stable and remain year-round, while others are seasonal.

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 Section 10 Coastal Processes

Figure 11 Iceland sits on top of the mid-Atlantic Ridge. Its black sandy beaches are
made of particles worn from basalt and other dark igneous rocks.

Deposition at the coast typically produces gentle relief where materials

are moved by waves onto the shoreline. In quieter tectonic settings, such
as the southeastern coast of North America, which trails the northwest-
moving plate, deposition is evident. Along the coast you can see barrier
spits that are deposited out from the coast by longshore drift. When a Geo Words
spit grows across a bay it is called a barrier island. It cuts off the interior barrier island: an
from the ocean. Where this happens, the inland side is called a lagoon. elongate island or
chain of islands that
A lagoon can slowly fill with sediments from inland streams. extend parallel to
the coast formed by
coastal deposition.
lagoon: a long
and narrow body
of shallow water
enclosed between
the mainland and a
barrier off the shore.

Figure 12 Taken from the space shuttle, this image shows the development
of a long barrier spit off the coast of Texas.

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Figure 13 Steep rocky cliffs on the Pacific coast as shown here contrast the low and
sandy barrier islands on most of the Atlantic coast. Both landforms tell us something
about how coastal systems work.

Emerging and Submerging Coastlines

Coastlines reflect a balance between processes in the geosphere and in
the hydrosphere. Over time, the action of the sea gradually straightens
coastlines by filling bays with sediments and eroding headlands. Features
Geo Words such as wave-cut platforms (similar to staircases) and sea cliffs are
emergent coastline: a indicators of emergent coastlines. The shape of emergent coastlines
coast that is gradually depends on the gradient of the coastal slopes. Steep slopes often produce
rising relative to the cliffs which are attacked to form headlands and bays. More gently angled
sea due to either a
fall in the sea level or coastlines are submerged to form wide and straight coastal plains.
a rise in the land.

Figure 14 The rocky shore of Acadia National Park in Maine rises from the ocean.

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 Section 10 Coastal Processes

One reason that emergent coastlines develop is because the land rises.
In some settings, the land rises because of tectonic processes that push
the crust upwards. In other places, land rises because of melting glaciers.
When glaciers cover the land, they depress the crust. Upon melting, the
crust rebounds upward.
Emergent coastlines also develop because sea level falls. Sea level can fall
because of changes in the volume of ice stored in glaciers. During glacial
periods on Earth, sea level has fallen by as much as 140 m (relative to
today). This happens as water is locked up as ice on the continents and
prevented from flowing to the oceans. Geo Words
Coastlines that are being drowned by the sea are called submergent submergent coastline:
coastlines. They also reflect the balance between the level of the sea and a coast that is slowly
being drowned by
coast. Most are formed where sea level rises as a result of the melting sea due to the land
of large glaciers that cover the continents, as happens at the end of sinking or sea level
glacial periods. Subsidence of the crust, for example due to sediment rising.
loading, will also cause the relative height of the sea to rise. Submergent
coastlines are often indicated by growth in estuaries and encroachment
of salt water upstream into parts of lowland drainage. As coasts are
submerged, remnants of former headlands become increasingly isolated
as sea stacks. Most of the eastern United States has submergent
coastlines. The Chesapeake Bay is one example.

Checking Up
1. What generates
ocean waves?
2. What pattern do
particles moving
by longshore drift
make?
3. How do emergent
and submergent
Figure 15 The ancestral Hudson River drainage system in New York coastlines differ?
has been drowned by the rising sea. 4. What are sea
stacks?

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 Chapter 4 Surface Processes

Think About It Again

At the beginning of this section, you were asked the following:
• Are all coasts the same? If not, how are they different?
• What kinds of processes shape coastal regions?
• How can you tell which processes are doing the most work in a coastal region?
Record your ideas about these questions now. Apply what you learned about how
coastlines are eroded and how sediment is deposited along coastlines.

Reflecting on the Section and the Challenge

In this section, you learned how coasts are dynamic environments. The oceans and winds
interact with the rocks and sediments of the geosphere. Coastlines are affected by the
supply of sediments from the continents. They are also affected by their shape and the
directions of waves. There are several factors you need to consider when planning new
development in coastal areas. First, you need to assess the balance between sea-level
change and uplift or subsidence. Erosion and deposition must also be taken into account.
An evaluation of the geology of coastal environments will be important as you work on
your Chapter Challenge.

Understanding and Applying

1. How do waves in the ocean form and break?

2. Why is wave energy concentrated on headlands and dispersed in bays?
3. What factors control whether beaches are dominated by erosion or deposition?
4. Why does longshore drift occur? Why is longshore drift important?
5. Describe the coastal geology in the following photographs.

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 Section 10 Coastal Processes

6. How are coastal processes connected to:

a) The rock cycle
b) The movement of lithospheric plates
c) River systems
d) Mountainous areas
7. Preparing for the Chapter Challenge
As you read in this section, waves do a lot of work on coastlines. Write a paragraph
in which you describe the features of coastlines dominated by erosion and those of
coastlines dominated by deposition. Explain how these features are formed. Also
describe the difference between an emergent and a submergent coastline. Apply these
ideas to your evaluation of your Olympic Games sites.

Inquiring Further
1. Plate tectonics and the coasts
Compare the coastal settings of the east and west coasts of North America. How do
their tectonic positions after their characteristics? What other factors have affected
each coast?
2. Changing sea level and the coasts
Almost all coasts have been affected by changes in sea level over time. Have you ever
wondered what the baseline for sea level is or how sea level is measured? Find out more
by visiting the EarthComm Web site at http://www.agiweb.org/education/earthcomm2/.
3. Coastal processes
Use an Earth imaging program on the Internet to find coasts where each of the
following processes is dominant. For each location copy the image and provide
annotations along with the name, longitude, and latitude.
• stream erosion
• stream deposition
• marine erosion
• marine deposition
• glacial erosion
• reef growth
4. Coastal hazards
On coasts where erosion works at a faster rate than deposition, engineering geologists
often intervene to stabilize coasts. Find out about coastal hazards and engineering
practices to change coastal erosion or coastal sediment transport, such as building
breakwaters and concrete barriers.

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 Chapter 4 Surface Processes

Earth/Space Science
You Learned
The Water Cycle
Water, in the form of liquid, solid, or vapor, moves through the Earth system and transforms during
its journey. Water resides in many different kinds of places, and takes many different kinds of paths.
The combination of all of these different movements is called the water cycle or the hydrologic cycle.
Each place in the Earth system where water is stored is a reservoir. The rate at which water flows
from one reservoir to another in a given time is called a flux. There is net movement of water vapor
from the oceans to the continents, and net movement of liquid (and solid) water from the continents
to the oceans.

Drainage Basins
Topographic maps provide important information about the geometry of drainage basins and river
systems. Contours can be used to determine stream gradient.
A drainage basin is the area from which all of the rain that falls eventually flows to the same final
destination, usually the ocean.
River systems consist of interconnected channels. Tributary systems consist of many smaller streams
that converge and flow into major channels known as trunk streams. A distributary system consists
of a number of small channels that branch off from the main river, often close to a delta or large
depositional feature.

Slopes
Many of Earth’s landforms are made up of slopes. Solid bedrock is stable at almost any slope angle
unless slopes are weakened. Unconsolidated materials are stable only up to a maximum slope angle,
called the angle of repose.
The process in which gravity moves material downward on a slope is called mass movement
(rockfalls, landslides, debris flows, debris avalanches, and creep).

High- and Low-Gradient Streams

High-gradient streams are usually located in the headwater areas of river systems. Their velocities
are typically high though their channels are relatively small and shallow.

High-gradient streams tend to cut downward and erode their valleys rapidly.
Streams in the lower parts of a river system typically have lower gradients, wider channels, and
wider floodplains than streams in the higher parts of river systems.
Low-gradient streams cut wide valleys because their channels tend to shift sideways. They do this by
meandering back and forth across a wide floodplain.
The flat, low-lying valley floor surrounding a river channel is called the floodplain. It is built from
sediments deposited by meandering streams and during floods.
Sediments are classified according to their diameter as clay, silt, sand, gravel, or pebbles. For a
given sediment size, a certain velocity of flow, called the threshold velocity, is needed to initiate the
movement of a particle.
Part of a stream’s load can be carried along invisibly in solution by a stream. Fine sediment particles,
of clay and silt size, travel mostly as a suspended load. The bed load consists of coarse sediment
particles that travel by sliding, rolling, and bouncing.

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 Soil
Soil is a relatively thin layer of rock, mineral fragments, and decaying organic material that covers
most of Earth’s land surface. Soil forms when weathering and biological processes break down
bedrock and organic material, such as dead plants.

Soils can be classified by texture, which refers to the distribution of the sizes of the particles. Most
soils are a mixture of gravel, sand, silt, and clay sizes, as well as organic materials. Soils often
contain layers called horizons, each with varying properties.
Glaciers
A glacier is a large mass of ice on the Earth’s surface that moves by internal deformation and by
slipping at its base. Ice sheets are the largest glaciers. They form on broad land areas at high latitudes
where summers are cool enough so that not all of the previous winter’s snow is melted. Valley
glaciers form in mountain regions both at high latitudes and at high elevations.
Glaciers scour soil and sediments from their bases to create wide U-shaped valleys. Meltwater at the
base of a glacier sometimes penetrates fractured bedrock and freezes, then later thaws. This action
can break bedrock apart rapidly. Small mountain glaciers produce semicircular hollows shaped like
a shallow bowl, called a cirque.
Till is a mixture of boulders and clay. It can be deposited on top of, within, beneath, on the side, or
in front of a glacier’s terminus. Terminal moraines are high curved ridges of sediment that mark the
maximum extent of a glacier.
Meltwater streams flow out from tunnels in glaciers. They are typically seasonal in nature and can
carry enormous quantities of sediment of all sizes.
Wind
Wind moves particles by suspension, saltation, and surface creep. Particle movement is controlled by
wind velocity, particle size, vegetation, surface cohesion, and surface roughness.
Landforms and human-made objects are eroded by the scouring action of rock particles carried by
the wind. The surfaces of rocks and monuments become pitted and etched.
Sand dunes grow because the kinetic energy of impacting grains is absorbed by loose sand. Sand
grains typically saltate up shallower slopes that face into the predominant wind direction and
avalanche down the steeper leeward slope.
Earth’s arid environments are controlled by climate. Deserts are common in regions where
evapotranspiration exceeds precipitation, and may be hot or cold.
Coastal Erosion and Deposition
Ocean waves result from the friction between winds and the ocean surface. Water within a wave
remains in place after making its oscillation and there is little net forward motion of water. Instead,
it is the wave form that moves rather than the water.
Erosion is not uniform along coasts. Contrasts in the depth between bays and headlands causes
waves to bend around headlands and preferentially break against them.
Features of coastal erosion include caves, arches, sea stacks, solution notches, and wave-cut platforms.
Beaches are the most common type of deposit along coasts. Wave action moves sand down the beach
in a zigzag pattern, a process called longshore drift.
Emergent coastlines are rising relative to the sea and often exhibit wave-cut platforms. Submergent
coastlines are slowly drowned and are indicated by the growth of estuaries.

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 Chapter 4 Surface Processes

Earth/Space Science
Chapter Challenge
You will now be completing a second cycle of you need to complete your challenge. This is
the Engineering Design Cycle as you prepare part of the Inputs phase of the Engineering
for the Chapter Challenge. The goals and Design Cycle. Your group needs to apply
criteria remain unchanged. However, your these concepts to develop your presentation.
list of Inputs has grown. You also have additional Inputs from the
Feedback you received following your Mini-
Challenge presentation.
Section 1 You examined the unique properties
of water. You found out why water is so
important to life on Earth. You also looked at
the distribution of water on Earth. Then you
learned about the water cycle and saw how
water moves from place to place within the
Earth system.
Section 2 You explored the nature of drainage
systems, interpreted topographic maps, and
evaluated important interactions between
river systems, land features, and communities.
Section 3 You considered whether the slopes
of land features were suitable for development
and determined how the slope of the land
controls surface processes. You discovered
how different Earth materials are prone to
forming unstable slopes.
Goal Sections 4 and 5 You used streamflow data
Your Challenge is to present to learn about the characteristics of high-
a poster and a report to and low-gradient streams. You calculated
compare the suitability of two sites to host the gradient of streams using a topographic
the Summer Olympic Games. One site is map, assessed possible hazards and benefits,
in Alaska and one is in Florida. You are to identified areas where these streams occur,
consider the landforms and surface processes and compared the relationship between
of each region. You should indicate any these streams, surface change, land use,
hazards that might influence the committee’s and development.
decision to select the city. Review the Goal Section 6 You explored how sediments are
as a class to make sure that you are familiar formed. You also looked at how sediments
with all the criteria and constraints. are transported by streams. You found that
the size of sediment a stream could transport
is related to the velocity of the stream. You
read about how sediments, streamflow,
and flooding affect developments along the
Inputs streambeds and banks.
You now have additional Section 7 You explored various soil types.
information to help you You learned how they are formed. Then you
address the topics you will include in your looked at the types of soil in your region,
report. You have completed all the sections their location, and the impact soil has on
of this chapter and learned about the content the community.

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 Section 8 You discovered how glaciers have • What is the relationship between soils and
affected the topography. You also explored the gradient of the land? Where did the soil
how glaciers have affected the stream drainage come from? Can it be replaced if lost due to
systems in the Unites States. the development?
Section 9 You designed an experiment to • What is the current correlation between
look at the effects of wind on loose sediment. soil types and development at your sites?
You then examined the relationship between Will that change with the building of
wind speed and particle size and the effects of these facilities?
windblown sand on rock. You also explored
how sediment that has been carried by wind • How will the plans to develop Olympic
is deposited. facilities affect the local soils?
Section 10 You explored the properties Be creative as you design and then develop
of ocean waves. You then simulated what your poster and report. This will help your
happens when ocean waves meet a shoreline. presentation be memorable. Just make sure
that every member of your group is included
and knows how he or she will be contributing
to the presentation.
Process
In the Process phase, you need
to decide what information
you have that you will use to meet the Goal. Outputs
Your goal is to decide which of the two
Presenting your poster and
regions in Alaska or Florida is most suitable
report to the class is your
for the Summer Olympic Games. Discuss
design-cycle Output. Try to create a
with your team which topics you want to
presentation that is engaging and interesting
cover in your poster and presentation to
as well as informative. Creativity is important.
convince your audience. Decide on the format
Your audience will remember presentations that
you will use. In addition to your poster,
are different from the others. Make sure that
perhaps you will show charts, graphs, and
your facts are correct and that the information
pictures to make your point. You might
you present addresses the Earth/Space Science
choose to have a panel discussion between
You Learned at the end of the chapter.
geologists, community members, politicians,
and the Olympic committee to present your
information. Another idea might be to create
a map showing a proposed layout of each Feedback
Olympic facility. The map could indicate the
Your classmates will give you
suitability of each building or development.
Feedback on the accuracy and
Your team may also decide to do a slideshow
overall appeal of your presentation based on
presentation. No matter what you choose to
the criteria of the design challenge. This
do, keep the following questions in mind.
Feedback will likely become part of your grade
• What geologic formations are required for but could also be useful for additional design
the games? Do your sites have them? revisions. No design is perfect because there is
• What are the risks of building on the land always room for optimization or improvement,
in each of your sites? Will that land be no matter how slight. From your experience
lost to other purposes, such as agriculture with the Mini-Challenge you should see how
or wildlife? you could continuously refine almost any idea.

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 Chapter 4 Surface Processes

Earth/Space Science
Systems Thinking
Revisit the Big Ideas in Surface Processes
In this chapter, you examined surface processes. Through erosion and deposition, these processes
shape and transform the bedrock of continents. The agents of these processes include streams,
wind, glaciers, slopes, and waves. Gravity plays a major role in each. In any region, some
processes are more dominant than others. Systems thinking helps you to explore the
interrelationships that cause the surface of the landscape to change.
At any given time, the landscape reflects
the balance between erosion and
deposition. Some parts of the landscape
undergo constructive, or building up,
processes. Other parts undergo
destructive, or tearing down, processes.
If the rate of erosion is greater than the
rate of deposition, there is a net lowering
of the surface. Some processes, such as
glaciers or the wind, can strip sediments
and soil from the surface to expose bare
rock. When older deposits are eroded
and buried beneath younger deposits,
unconformities are sometimes exposed Where temperatures are cold and there is an abundance
in the local geologic record. of snow, glacial erosion plays an important part in
Major surface processes are part of a shaping the surface.
particular environment. For example,
erosion and deposition by ice and meltwater take place in glacial environments. On slopes,
the mass movement of soil and rock occurs. For river (fluvial) environments, the channel, the
bed, and banks affect the surface processes that take place. Winds tend to affect the surface
everywhere. However, wind erosion is greatest on exposed surfaces. There, sediments are not
protected by vegetation. Wind-dominated environments are common in hot and cold deserts.
They also are found in coastal areas along beaches. Each environment is a system that has many
parts and processes. Each is organized in a specific way.
Looking across the surface
of Earth, you can see where
one environment ends,
another often begins. Clearly,
interconnected systems will
share some parts and processes.
For example, in very high
mountains, mass movements
transfer debris from rock walls
onto glaciers. Moving glaciers
scour the underlying bedrock.
They build up moraines of
poorly sorted sediments. In
spring, meltwater flows from
the warming ice in high-
gradient streams and transports
glacial sediments to lower parts
of the drainage basin. Sediment from high mountains are eventually deposited in the ocean.

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 Energy drives the destruction of continental rocks by erosion and their transport to the ocean. If the
energy of moving wind, water, ice, or slopes decreases, its capacity to do work also decreases. Scientists
are able to determine when there were high-energy conditions for a particular erosion process.
Surface processes are strongly affected by other major parts of the Earth system. Tectonic processes
can cause the crust to thicken and rise in some places and thin and sag in others. Erosion is
typically greater on mountain slopes. Deposition is greater in lowland basins. Climate is another
factor that controls surface processes. Colder climates favor erosion by ice. Wetter climates favor
the development of stream networks. In dry climates, the wind has a greater ability to affect how
landforms develop. Over time, regional climates undergo shifts. These can be observed by the
replacement of one process by another.

Systems Thinking Questions

1. What are the major parts involved in surface processes and landforms? Describe each
part and its location.
Thinking about the parts involved in the operation of surface processes will help you
to think about the structure of the system(s) you are examining. Describe the nature
of the parts. You might want to think about where the different parts are as well.
This will help you to understand a system’s structure even more clearly.
2. What are the major processes involved in surface processes and landforms?
Asking questions such as, “How do sediments move in streams?” or “How do
glaciers erode their beds?” helps you to figure out the operation of the system(s)
you are studying. The same method can be applied to larger or smaller systems.
You might also want to think about how one part of the system affects another.
This will help you to better understand interactions within the system.
a) Describe major ways in which matter changes through surface processes and
landforms.
Matter lies at the heart of systems. It often moves from one place to another.
It also changes sometimes between states of matter or in other physical ways.
b) Describe the role of energy in surface processes and landforms.
Energy drives systems. All systems require a source of energy for them to operate.
As systems do work, energy from the source is transformed into different kinds
of energy.
3. Over which spatial scales do surface processes and landforms operate?
Scientists like to look at different scales in the same system to seek patterns about
how things work. Think about the distribution of surface processes across a particular
region. What causes the concentration of processes to change? At a continental scale,
why are many processes interconnected? Bigger systems cover larger regions, typically
have more parts, and process more matter. They require a large and continuous source
of energy.
4. Across what time scales do surface processes operate?
Asking questions such as, “How long does it take for a meander to form?” or “What
is the lifespan of a mountain?” helps you think more closely about the rates at which
systems affect change.
5. How do surface processes affect your community?
You live on the ever-changing surface of the continents. Despite efforts to stabilize
the surface, it is mobile over long time scales. Settlements typically favor stable
landscapes, but this is not always the case. Think about the environment in which
you live and how surface processes play a role.

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 Chapter 4 Surface Processes

Earth/Space Science
Connections to Other Sciences
Slopes Physics Glaciers flow because of internal stresses
Biology Vegetation can stabilize slopes in a that develop in response to gravity. The grains
number of ways. The roots of plants help to within the ice slip past one another. Glaciers
bind the upper horizons of the soil together, also move by slipping and deforming the
which increases the slope’s strength. sediments at their bases.
Chemistry Abundant water often saturates Wind Erosion
soil cavities and reduces the amount of Biology Wind is highly effective at carrying
oxygen available for weathering compared pollen grains. Scientists have measured as
to upper slopes. Iron-bearing minerals have many as 1 million pollen grains per cubic
a reddish color in oxidizing conditions meter, close to the ground in summer. Scientists
and a green or blue color under reducing are particularly interested in the dispersal of
conditions. genetically modified pollen species because of
Physics The basic cause of mass movement the risk of cross-pollination with natural species.
is the downward pull of gravity. Gravity Chemistry Quartz sand is not the only kind
is one of four fundamental forces that act of particle transported by winds. Windblown
throughout the universe. dust containing iron is an important nutrient to
Read more about the four fundamental the surface waters of the Antarctic Ocean. Iron
forces in stimulates the growth of algae which converts
Extending the Connection atmospheric carbon dioxide into organic carbon
in the oceans, influencing the concentration of
River Discharge atmospheric carbon dioxide.
Biology In the Mekong Delta, the giant Physics Scientists have developed a Sand Particle
Mekong catfish feeds on the plentiful plants Counter that detects saltating particles when
and algae that grow on the silts deposited in they pass through a laser beam. Every time the
this high-discharge environment. beam is broken a signal is produced. This is very
Chemistry Scientists who study river systems useful for studying sandstorms.
sometimes add dyes, salts, and stable Coastal Processes
isotopes to rivers to monitor
stream behavior. Biology Marine biologists recognize distinctive
coastal zones based on the relative heights of the
Physics As water flows, it is unable to resist tides. The zone exposed only at the lowest tides
stresses and, as a result, deforms. The bed typically has the largest populations because
and banks of a stream create frictional of longer submersion times. Here, abundant
resistance to flowing water. As a result, a plants and algae are the primary producers that
stream has its greatest velocity at about support urchins, limpets, and snails. However,
7/10 of its depth. species can only tolerate direct sunlight for very
Glaciers short periods.
Biology In 1991, a 5200-year-old Chemistry Solubility plays an important
mummified male human was found role in the development of coastal landforms,
preserved in the Alps between Austria and enabling rocks like limestone to decompose and
Italy. A tiny bulge in his large intestine collapse. The development of wave-cut notches
contained einkorn wheat, meat, and in relatively insoluble granitic rocks reveals the
pollen grains from the hop hornbeam tree. importance of abrasion and hydrologic action
This provided important evidence about as well.
agricultural practices in the Neolithic period. Physics Coastal engineering practices are
Chemistry To learn about climate, scientists dependent on the application of physics. These
look at the ratios of the oxygen isotopes range from understanding the kinetics of
18
O and 16O in glacial ice. Glacial ice with shoreline sediment transport, the refraction
a relatively lower 18O content represents a of waves, to the forces acting on natural and
colder climate. human-made coastal structures.

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 Extending the Connection

THE FOUR FUNDAMENTAL FORCES

In this chapter, you investigated the role of the force of gravity as a major factor
responsible for reshaping the surface of Earth. A force is defined as a push or pull.
It is an interaction between two objects that can result in an acceleration of either
or both objects.
Scientists recognize four fundamental forces that act throughout the universe: gravity,
electromagnetic force, the strong force, and the weak force. One of science’s greatest
challenges has been to try to discover relationships among the forces. Many scientists
think that all four forces may actually be different aspects of a single force. The theory
that would explain how all forces are related is called the grand unification theory.
Gravity
The force everyone is probably familiar with is the force of gravity. Gravity is the force
of attraction (the pull) between any two objects with mass. The greater the mass, the
greater the force of attraction. You saw this force acting when you investigated the angle
of repose of materials on a slope. You observed materials sliding down a slope because
the large mass of Earth makes the force of attraction between the particles of material
and Earth very evident. Gravity is also the force that holds the Sun, moons, planets,
stars, and galaxies in their orbits. It works across tremendous distances and has an
infinite range.

Gravity is the force responsible for mass movement.

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 Chapter 4 Surface Processes

Sir Isaac Newton was one of the first to describe the law of universal gravitation. The law
of universal gravitation states that every object in the universe attracts every other object
with a force that is proportional to the product of their masses and inversely proportional
to the square of the distance between them. Recall that the gravitational force can be
described mathematically as
FG = Gm1m2
d2
where F G is the force between the objects,
G is the gravitational constant,
m1 and m2 are the masses of the objects, and
d is the distance between their centers.

Electromagnetic Force
Another fundamental force with which you may
be familiar is the electromagnetic force. You may
have observed a magnetic force act when you
placed a magnet on a refrigerator. You probably
have also experienced an electrical force when
you felt an “electric shock” when you touched
Electrical force can be a real nuisance if you
something metallic after walking across a carpet. get an unexpected “shock” when you touch a
doorknob after walking across a room.
Strong and Weak Force
The other two fundamental forces are difficult to visualize but play critical roles in the
nucleus of every atom. The electromagnetic force holds electrons in orbit around the
nucleus. But this force cannot account for what holds the particles of the nucleus together.
The strong nuclear force is the attraction between nucleons (protons and neutrons) and
holds the nucleus together, because it is a very strong force at very close range. It is
estimated to be about 100 times as strong as the electromagnetic force. However, it is a
very short-range force—at distances greater than the size of a nucleus, the force is too
small to measure.
The fourth force is called the weak force. It plays a role in the radioactive decay of unstable
atoms, particularly in the transition of a neutron to a proton. During the latter half of the
twentieth century, physicists were able to show that the electromagnetic force and the weak
force were two aspects of the same force, described as the electroweak force. The weak
force has a range of about 1/1000 of the strong force.
The following table summarizes the relative strengths and the ranges of the four
fundamental forces.
Type of Force Relative Strength Range Nature of Force
gravitational force 10–39 infinite attraction
electromagnetic force 0.0073 infinite attraction/repulsion
nuclear (strong) force 1 10–15 m attraction
–6 –18
weak force 10 10 m neither

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 Earth/Space Science
Earth/Space Science
At W
At Work
ork
How is each person’s work related to the Earth system,
and to Surface Processes?

ATMOSPHERE: BIOSPHERE: Environmental

Red Cross Worker Protection Agency (EPA)
Those who provide help and relief Ecologists
to communities during floods must EPA ecologists monitor and ensure
carefully follow the analysis of safe development of land. One of
weather data so that they are aware their goals is to make sure that
of imminent danger. They want the development of land does not
to be prepared to act immediately interfere with the preservation of
when disaster strikes. During the environment. By conducting
and after a flood, the Red Cross research on the relationship
helps organize evacuation efforts, between the landscape and
offers support to those who have ecological processes, ecologists can
lost homes, and helps to rebuild assess how land development would
communities that were damaged by affect water flow, energy, and
the effects of flooding. CRYOSPHERE: Hydroelectric nutrients in the environment.
Engineer/Planner
Glacierized drainage basins
contain vast amounts of water.
Meltwater from glaciers in
mountainous regions can be
stored behind dams and used to
generate hydroelectric power. These
projects are especially important
in poor rural regions throughout
the great mountain ranges like the
Himalayas. However, the upstream
environment is often prone to
GEOSPHERE: Captain of a rapid changes due to steep slopes
Cargo Ship and extensive weathering and HYDROSPHERE: Film Maker
erosion. Planners work closely with
Economies of scale result in the scientists to ensure that projects Many levels of government
manufacture of larger container are not impacted by unstable slopes organize efforts to work toward
ships that can carry more cargo. and catastrophic flooding. preserving balanced and
The largest ships can only navigate sustainable ecosystems in areas
in very deep channels where there such as the Everglades in South
is enough clearance for their keel. Florida. Educating the public
To accommodate these ships, many through videos and films is an
ports must dredge their channels to important part of these efforts. One
provide enough clearance. Sediments documentary about the Everglades’
are removed from the near-shore ecosystem explores how it has
environment by dredging. This can be been severely damaged due to land
done mechanically by a conveyor of development and what will need to
moving buckets or hydraulically using be done in order to restore it.
a pipeline and a giant vacuum pump.
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 Chapter 4 Surface Processes

Earth/Space Science
Practice Test
Content Review

1. When compared to the lower parts of 5. What evidence can tell you that a stream
drainage basins, we can generalize that in was once subjected to periods of very high-
the upper parts of drainage basins the velocity flow?
I. contour lines are typically spaced a) clay and silt deposits in the streambed
more closely. b) sand deposits in the streambed
II. streams have higher gradients. c) gravel deposits in the streambed
d) large, rounded boulders in
III. streams have higher discharges.
the streambed
a) I only
b) II only
6. Predict where future erosion will be
c) I and II only
greatest in a meandering stream.
d) I, II, and III
a) Erosion is greatest on the inside of the
meander bend.
2. Why would a slope of jagged particles
b) Erosion is greatest on the outside of the
achieve a steeper slope than one composed
meander bend.
of smooth, rounded particles?
c) Erosion is greatest on the bottom of
a) Jagged particles are denser. the streambed.
b) Greater friction exists between d) Very little erosion is associated with
rounded particles. meandering streams.
c) Greater friction exists between
jagged particles.
7. What was the likely velocity of the river
d) Jagged particles roll shorter distances.
from which a sample of silt and clay were
taken from the streambed?
3. Why does wave erosion focus on
a) slow
headlands and not in bays?
b) medium
a) Waves typically bend toward the c) fast
weakest parts of coasts. d) extremely fast
b) Waves typically bend toward shallower
water in bays.
8. How does the mass, roundness, and shape
c) Waves typically bend toward deeper
of a sediment particle change as it is
water in bays.
transported over a long distance?
d) Waves typically bend toward shallower
water near headlands. a) The particle will become larger, rounder,
and more spherical with more transport.
b) The particle will become smaller, more
4. Which of the following cannot be true
angular, and rod-shaped with
about an emergent coastline?
more transport.
a) Cliffs are rising relative to sea level. c) The particle will become smaller,
b) The ocean is falling relative to rounder, and more spherical with
the land. more transport.
c) Estuaries and salt water are d) The particle will not change.
encroaching inland.
d) Wave-cut platforms occur above
the highest tides.

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 9. How does the maximum particle size 13. Which glacial process has the least effect
that a stream can transport vary with on river systems?
flow velocity? a) addition of glacial meltwater to river
a) There is no correlation between the two. systems in spring
b) As the flow velocity increases, the b) erosion of slopes to form
size of the particles that can be drainage basins
transported decreases. c) scouring the bedrocks at the base
c) As the flow velocity increases, the of glaciers
size of the particles that can be d) blocking and diverting existing
transported increases. drainage networks

10. During a long period of heavy 14. Why is a patch of clay-sized particles less
thunderstorms in the upland part of a prone to wind erosion than a patch of
drainage basin, what might happen to sand-sized particles?
soils that are rich in clay? a) The minerals in sand-sized particles
I. They promote surface runoff. have less mass.
II. They become saturated and b) Clay-sized particles do not project far
waterlogged. into the airflow.
c) Clay-sized particles have greater
III. They are more prone to slide
moisture between their grains than
downslope.
sands.
a) I only d) Sand-sized particles do not project far
b) I and II only into the airflow.
c) I and III only
d) I, II, and III
15. How do sand dunes move?
a) upwind by sediment avalanching down
11. Soil development demonstrates the
the windward slope
complex interactions between the
b) upwind by sediment avalanching down
geosphere and
the leeward slope
I. the hydrosphere. c) downwind by sediment avalanching
II. the biosphere. down the windward slope
III. the atmosphere. d) downwind by sediment avalanching
IV. time. down the leeward slope
a) I only
b) I and II only
c) I, II, and III only
d) I, II, III, and IV

12. What might happen if the load of a

glacier increases?
a) The glacier system might fail.
b) The ice in a glacier will appear
very clean.
c) Abrasion by loose soil, rock, and
mineral particles will increase.
d) More incoming solar radiation will
be reflected.

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 Chapter 4 Surface Processes

Practice Test (continued)

Critical Thinking

16. “Looking at drainage basins helps us to 21. High-gradient streams have special
think about systems at different scales.” properties that enable them to cut
a) Explain what this statement means. vertically downward and not widen their
b) In what ways is your own drainage floodplains. In very high mountainous
basin an example of systems operating environments why might we see wide
at different scales? valleys that contain mountain streams
with straight narrow channels?
17. There are many different kinds of mass
movement processes. These include rock 22. Imagine a hillside that is covered by soil
avalanches, rock slides, slumps, debris and grass in a temperate region. Describe
flows, mudflows, and creep. Devise three two ways in which soil characteristics
criteria that you could use to classify might vary between the top and the
different kinds of mass movements. bottom of the slope.

18. During a period of desert expansion, the 23. Glaciers generally deposit poorly sorted
wind blows sand over a vegetated surface. sediments in their outwash areas.
The patch of vegetation becomes slowly a) Explain why this occurs.
buried by more and more sand and grows b) Why is this property useful to scientists
larger. Eventually a sand dune forms, who try to reconstruct past climates?
grows, and migrates.
a) Illustrate the concept of positive 24. A continuous coastline can have both
feedback from this scenario. You may emergent and submergent sections
expand on the physical processes. of coast.
b) Illustrate the concept of negative
a) By thinking only about the sea,
feedback from this scenario. You may
explain how this idea might
expand on the physical processes.
seem counterintuitive.
b) By thinking about both the land
19. Which is most likely to contain pollution, and the sea, explain how this idea
a high- or a low-gradient stream? Explain is acceptable.
your answer

20. Reflect on what you know about the

transport of sediments in streams.
a) Explain why streams often deposit
well-sorted sediments.
b) Describe the circumstances that might
lead to poorly sorted sediments.

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