23.3 Water Shapes the Land

23.3 Water Shapes the Land 

Key Concepts 

What is the most important 

factor influencing the 

ability of a stream to 

cause erosion? 

What features are formed 

by surface water erosion? 

What features are deposited 

by running water? 

What causes groundwater 

erosion? 

Vocabulary 

◆ deposition 

◆ saltation 

◆ flood plain 

◆ meander 

◆ oxbow lake 

◆ alluvial fan 

◆ delta 

◆ stalactite 

◆ stalagmite 

◆ sinkhole 

The Mississippi River is like an enormous convoy of dump trucks. 

Every year it carries more than 300 million tons of sediment to the ocean. 

This amount of sediment would fill a line of dump trucks wrapped 

nearly three times around Earth! This sediment has been washed away 

from the surface of the land. As mountains are made by volcanoes or 

the motions of tectonic plates, erosion begins to wear them away. 

The primary force of erosion is gravity. Gravity pulls sediment 

and water downhill. The end result of erosion is the deposition of 

sediment. Deposition is the process in which sediment is laid down in 

new locations. 

Most sediment is moved and deposited by flowing water. Flowing 

water is the major agent of erosion responsible for shaping Earth’s 

surface. Everywhere you look on land, there are features formed by 

water erosion and deposition. 

Section Resources 

Print 

• Laboratory Manual, Investigation 23B 

• Reading and Study Workbook With 

Math Support, Section 23.3 

• Transparencies, Section 23.3 

Reading Strategy 

Concept Map As you read, draw a concept 

map showing how moving water shapes the 

land. Begin with the map below. 

Water 

forms 

features 

such as 

a. ? 

by 

erosion 

deltas by b. ? 

Figure 12 Streams play an 

important role in the process of 

erosion. This stream has cut a deep 

channel in the soil. The stream 

banks collapse in mass movement. 

The soil is then carried away by 

the stream as sediment. 

Earth’s Surface 713 

Technology 

• Interactive Textbook, Section 23.3 

• Presentation Pro CD-ROM, Section 23.3 

• Go Online, Science News, Earth’s surface 

Section 23.3 

1 

FOCUS 

Objectives 

23.3.1 Explain how running water 

erodes the land. 

23.3.2 Identify features formed by 

erosion and deposition due to 

running water. 

23.3.3 Describe how caves and 

sinkholes are formed by 

groundwater erosion. 

Reading Focus 

Build Vocabulary 

Compare/Contrast Table Have 

students work in groups to make 

compare/contrast tables with the 

headings Features Formed by Erosion 

and Features Formed by Deposition. 

Ask them to sort the words from the 

vocabulary list into the appropriate 

columns. 

Reading Strategy 

a. Any of the following: V-shaped 

valleys, waterfalls, flood plains, 

meanders, oxbow lakes b. Deposition 

L2 

L2 

Earth’s Surface 713

Section 23.3 (continued) 

2 

INSTRUCT 

Running Water 

Erodes the Land 

Forming Sedimentary 

Layers 

Objective 

After completing this activity, students 

will be able to 

• describe the formation of sedimentary 

layers under water. 

Skills Focus Using Models 

Prep Time 15 minutes 

Advance Prep Sand, clay, and gravel 

can be obtained from a landscaper, 

garden supply shop, or home repair 

store. Olive jars are ideal for this lab. 

Graduated cylinders with rubber 

stoppers can be used if the stoppers 

make a watertight seal. 

Class Time 20 minutes 

Expected Outcome Gravel settles 

first, then sand, and finally clay. Some 

clay remains suspended in the water, 

making the water cloudy. 

Analyze and Conclude 

1. Gravel, sand, and clay 

2. Some clay remained suspended in the 

water, making the water cloudy. 

3. Water in a lake. It was not moving 

quickly and it contained suspended 

particles. 

4. The separation of sand and clay 

would have been less distinct. This 

would occur in a turbulent, fast-moving 

river such as one with rapids. 

Kinesthetic 

For Enrichment 

714 Chapter 23 

L2 

L3 

Use a soil-sampling tube or a section of 

pipe to collect a core sample of 

sediment from a riverbed or the bottom 

of a lake. Students can use a hand lens 

or microscope to examine the particle 

sizes in each layer and determine their 

distribution. Variation in particle size in 

these layers may reflect seasonal or 

historical changes in the speed or 

volume of the water from which the 

sediment was deposited. Students 

should wear safety goggles, lab aprons, 

and plastic gloves during this activity. 

Kinesthetic 

Forming Sedimentary Layers 

Materials 

clay; gravel; sand; small dish; tall, narrow jar with 

cover; tablespoon; clock or watch 

Procedure 

1. Crumble the clay into a fine powder over a 

small dish. 

2. Fill the jar three quarters full of water. Add one 

spoonful each of gravel, sand, and clay. 

3. Put the cover on the jar tightly and invert the 

jar several times. Then, place the jar on a flat 

surface and record the time. 

4. For 5 minutes, observe the layers of sediment 

as they pile up on the bottom of the jar. 

Record what you observe. 

Figure 13 Small grains of 

sediment are carried in 

suspension by a stream. Large 

grains move by sliding or rolling, 

and medium-sized grains move by 

saltation. Material is also carried 

in dissolved form. Predicting 

How might the speed of the 

stream affect the amount and 

size of particles it can carry? 

Suspended sediment is 

carried by flowing water. 


Running Water Erodes the Land 

Water from rain or melted snow may soak into the ground, evaporate, 

or flow over the surface as runoff. Erosion begins when runoff carries 

small particles of soil downhill. Runoff gradually forms small channels 

in the soil. These channels join together to form larger channels 

called gullies. As water flows down a hillside through gullies, the water 

can erode large quantities of soil. Gullies, in turn, flow together to form 

streams. Unlike gullies, streams flow year-round, except in dry areas 

or during droughts. 

Streams continue the process of erosion by transporting sediment, 

as shown in Figure 13. Most of the sediment in streams is carried in 

suspension, in which tiny sediment grains move along with the water. 

Larger particles of sediment slide, roll, or bounce along the bottom of 

a stream. The process of particles bouncing along a stream bottom is 

called saltation. During floods, a fast-moving river can move boulders 

the size of a small car. A large amount of sediment is also carried in 

solution. Faster streams carry more sediment, which increases abrasion. 

Dissolved sediment 

moves with flowing water. 

5. Observe the appearance of the water in the jar. 

Record your observations. 

Analyze and Conclude 

1. Observing In what order did the sediment 

layers form? 

2. Inferring Why did the water look the way it 

did after the sediment layers formed? 

3. Using Models Was the water in the jar 

similar to the water in a lake or the water in a 

fast-moving river? Explain your answer. 

4. Predicting Would the order of the sediment 

layers be different if you had stirred the water 

as the layers accumulated? Under what 

circumstances would this happen in nature? 

Direction of flow 

Large particles are pushed 

or rolled along the streambed. 

Customize for English Language Learners 

Use Flowcharts 

Have students work in groups to create flowcharts 

describing the formation of alluvial fans 

and deltas. As an extension, students could also 

Medium-sized particles 

move by saltation. 

create flowcharts for some or all of the features 

formed by water erosion, wind erosion, and 

wind deposition. Students should use their own 

words and/or drawings in the flowcharts.

Sediment 

Meander 

A stream’s ability to erode depends mainly on its speed. The 

water in a mountain stream moves quickly because it is flowing down a 

steep slope. Fast streams carry more sediment than slow streams of equal 

size. Fast streams can also carry large sediment grains. As a stream flows 

toward the sea, its slope decreases. This can make the stream move more 

slowly, causing larger sediments to settle on the stream bottom. 

Features Formed by Water Erosion 

Erosion by flowing water reshapes entire watersheds—all the land 

along and between streams and rivers. Water erosion forms 

V-shaped valleys, waterfalls, meanders, and oxbow lakes. Figure 14 

shows the features formed along the course of a river. 

V-Shaped Valleys Near a stream’s source, the stream flows fast as 

it plunges down steep slopes. As a stream erodes the rock of its 

streambed, it causes the valley’s sides to become steeper. Mass movement 

on the stream slopes causes a V-shaped valley with sharply angled 

sides to form. 

V-shaped valleys often contain rapids and waterfalls. A waterfall 

may develop where a stream crosses rock layers that differ in hardness. 

The harder layers resist erosion, forming the top of the waterfall. The 

softer rock layers downstream are worn away, leaving the cliff over 

which the waterfall tumbles. 

How do waterfalls form? 

Facts and Figures 

Great Waterfalls The world’s tallest 

waterfall is Angel Falls, Venezuela, at an 

amazing height of 979 m, almost a kilometer! 

Yosemite Falls is the tallest waterfall in the 

United States, falling an impressive 739 m. 

Waterfall 

River mouth 

V-shaped valley 

Oxbow lake 

Figure 14 As a river winds its 

way from the mountains to the 

ocean, it changes the surrounding 

landscape through erosion 

and deposition. 

Comparing and Contrasting 

Which features formed by river 

erosion typically form near a 

river’s source? 

For: Articles on Earth’s surface: 

weathering, erosion, and 

deposition 

Visit: PHSchool.com 

Web Code: cce-3233 


Science News provides students 

with current information on 

Earth’s surface: weathering, 

erosion, and deposition. 

FYI 

Though sediment is continuously moved 

by flowing streams, the occasional 

floods can increase sediment transport 

by more than 100 times. During the 

huge Mississippi River flood of 1993, the 

river level was more than 50 feet above 

normal in places, and both the stream 

velocity and sediment load increased 

dramatically. Floods are also extremely 

dangerous. More than 5 million people 

have died from flooding in China in the 

past 100 years. 

Features Formed by 

Water Erosion 

Use Visuals 

L1 

Figure 14 Explain that, as the streams 

cut down into the rock, the V-shaped 

valley slopes become steeper. When the 

valleys become very steep, waterfalls 

form or mass movement can occur, and 

rock and soil falls into the stream in the 

form of landslides or slumps. Once the 

rock and soil falls into the water, it is 

quickly washed downstream. When 

a river flows across a flat area, the 

V-shaped valley may be very broad 

and hard to recognize. The floor of the 

valley is called the floodplain. At what 

location is the river most able to carry 

large rocks? (In the mountains) What 

is the source of much of the sediment 

being deposited on the flood plain? 

(The mountains shown in the background) 

What feature will result from the 

buildup of sediment where the river 

flows into the ocean? (A delta) 

Visual 

Answer to . . . 

Figure 13 The greater the speed of a 

stream, the more kinetic energy it 

possesses and the larger the amount 

and size of particles it can carry. 

Figure 14 V-shaped valleys and 

waterfalls 

Waterfalls may form 

where a river crosses 

rock layers of different hardnesses. The 

harder layers of rock resist erosion, 

forming the top of the waterfall. The 

softer layers of rock downstream are 

eroded, creating a cliff over which the 

waterfall tumbles. 



Build Reading Literacy L1 

Visualize Refer to page 354D in 

Chapter 12, which provides the 

guidelines for visualizing. 

Instruct students to close their eyes and 

form mental pictures as you read Flood 

Plains. Read aloud to the students, 

going slowly so that they have time to 

form mental images of the processes 

you are describing. Then, tell the 

students to read the passage again by 

themselves and recreate the mental 

images as they read. Explain that 

visualizing the text as they read will be 

particularly useful throughout the next 

few pages, which detail the processes by 

which landforms are created by erosion 

and deposition. 

Intrapersonal, Visual 

A common misconception among 

students is that Earth’s features, such as 

mountains, do not change. A related 

misconception is that any changes that 

occur are sudden and catastrophic, 

resulting in the complete destruction of 

an old feature or the sudden creation of 

a new feature. The erosion of mountain 

valleys by running water is an ideal 

context in which to address this 

misconception. Explain that erosion is a 

slow, constant process that wears down 

old landforms. New landforms are 

created through erosion and deposition, 

often over thousands to millions of years. 

Verbal 

Features Formed by 

Water Deposition 

Build Science Skills 


L2 

L2 

Inferring Bring a variety of river rocks 

into class. Have students work in groups 

to make inferences about the geologic 

history of the rocks. Explain that they 

should use what they have learned 

about the formation of rocks and the 

rock cycle to describe the history of each 

rock from its formation to its erosion 

and deposition. Have students create a 

flowchart for each rock’s history. 

Logical, Kinesthetic 

Figure 15 Rivers often form 

winding meanders across their 

flood plain. An oxbow lake 

formed by the Big Sioux River 

near Westfield, Iowa, is shown. 

A 

B 

Figure 16 Alluvial fans and 

deltas form from sediment 

deposited by moving water. 

A This alluvial fan in Death Valley, 

California, formed from sediment 

deposited when a mountain 

stream reached flat land. B When 

a large river empties into the 

ocean, the deposited sediment 

often forms a delta. 



Deltas The word delta comes from the Greek 

letter delta (). The river feature received this 

name from the Greek historian Herodotus, 

who noticed that the Nile River delta had a 

shape similar to that of the triangular symbol 

for the Greek letter. 

Flood Plains Where a river or stream crosses gently sloping land, 

a flood plain forms. A flood plain is the flat area along a stream that is 

entirely covered only during times of flood. As a river flows across its 

flood plain, it deposits sediment, making the flood plain flat. Over 

time, this sediment builds up into long, low ridges called natural levees. 

These natural levees help prevent a river from spilling over its banks. 

During very large floods, however, a river may overflow its levees and 

erosion may further widen the valley. 

Where a river curves slightly, the water on the outside of the curve 

moves more rapidly than the water on the inside. Fast-moving water 

causes more erosion. Therefore, the river tends to remove soil from the 

outside of the curve. Sediment is deposited on the inside of the curve, 

where water moves more slowly. Over time, this process forms a looplike 

bend in the river called a meander. 

Sometimes during a flood, the river erodes through a narrow neck 

of land at the base of a meander and forms a new path. Sediments build 

up along the new channel, cutting the old meander off from the rest of 

the river. The result is a separate, curved lake, called an oxbow lake. 

Figure 15 shows an oxbow lake formed by the Big Sioux River. 

Features Formed by Water Deposition 

As a stream or river slows down, it begins to deposit sediment. The 

slower water cannot carry larger particles of sediment, so these particles 

fall to the bottom first. As the water slows down even more, smaller 

particles of sediment are deposited. Features deposited by flowing 

water include alluvial fans and deltas. 

As a stream flows out of the mountains and onto the plains, it slows 

down and sediment settles out. The result is a fan-shaped deposit of 

sediment on land called an alluvial fan. As shown in Figure 16, alluvial 

fans often grow into thick deposits of sediment. 

When a stream flows into a lake or an ocean, the water slows down. 

The sediment that the stream was carrying is deposited in the form of 

a delta. A delta is a mass of sediment deposited where a river enters a 

large body of water. Some deltas have a roughly triangular shape. 

However, not all deltas have a triangular 

shape. The Mississippi River, for example, has 

a birdfoot-shaped delta that extends far out 

into the Gulf of Mexico.

Groundwater Erosion 

Erosion and deposition occur below ground as well as at the 

surface. The processes of chemical weathering causes 

much groundwater erosion, including the formation of caves 

and sinkholes. Recall that carbon dioxide in the air combines 

with rainwater to form carbonic acid. As the acidic rainwater 

moves down through the ground, it reacts with some rocks and 

may become more acidic. 

Limestone easily erodes away through this process, forming 

caves, or caverns. Most caves are small, narrow passages, 

but some are hundreds of feet high and wide. Caves usually 

form when they are in the saturated zone, below the water 

table. When the water table drops, the water flows downward, 

leaving dry caves like the one in Figure 17. 

Sometimes water drips into the cavern from the rock layers 

above, carrying dissolved minerals. When this mineral-laden 

water reaches the air of the cave, some of the dissolved carbon 

dioxide escapes and the minerals are left behind. If the water drips 

from the cavern ceiling, an icicle-like formation called a stalactite 

(stuh LAK tyt) grows. If the water drips down to the floor, a pillar 

of minerals called a stalagmite (stuh LAG myt) forms. 

If erosion weakens a layer of limestone, entire portions of 

the ground can suddenly collapse. The resulting hole is called 

a sinkhole. Areas of the southern and central United States have 

many sinkholes. Sinkholes can appear suddenly, swallowing 

buildings and roads. 

Section 23.3 Assessment 

Reviewing Concepts 

1. What is the major factor that affects the 

ability of a stream to erode land? 

2. As a stream erodes the land, what 

features are likely to form in steep areas? 

What features form in more level areas? 

3. Compare and contrast deltas and 

alluvial fans. 

4. What process forms caves and sinkholes? 

5. What force provides the energy for the erosion 

caused by running water? 

Critical Thinking 

6. Applying Concepts What determines how 

much sediment flowing water can carry? 

Section 23.3 Assessment 

1. The stream’s speed 

2. V-shaped valleys and waterfalls; a flood 

plain, oxbow lakes, and meanders 

3. Deltas and alluvial fans both form when a 

river slows down or ends, depositing 

sediment. However, deltas form in water and 

alluvial fans form on land. 

4. Caves and sinkholes form by the chemical 

dissolution of underground rock by the flow of 

acidic water. If erosion weakens a layer of 

Figure 17 Carlsbad Caverns in New Mexico 

contain spectacular formations, such as the 

stalactites and stalagmites shown here. 

7. Relating Cause and Effect How does an 

oxbow lake form? 

8. Comparing and Contrasting What 

is the difference between a stalactite and 

a stalagmite? 

Describing a Process Imagine that you are 

a particle of sediment on a mountaintop. Write 

a paragraph describing your journey to the 

ocean. (Hint: Be sure to mention at least three 

steps in the transportation of sediment.) 


limestone below the ground, it may collapse 

and form a sinkhole. 

5. Gravity provides the energy for erosion 

caused by the downward flow of rivers and 

streams to the ocean. 

6. The speed that the water flows. Water can 

carry more sediment when it flows faster. 

7. An oxbow lake forms when a river erodes 

through a narrow neck of land and a meander 

gets cut off. 

8. A stalactite hangs from the ceiling of a 

cave, while a stalagmite sticks up from the 

floor of a cave. 

Groundwater Erosion 

Use Community 

Resources 

L2 

Most states have caves. Contact your 

regional USGS office or State Park 

Service to find out about caves in your 

area. Ask a park ranger or geologist to 

present a slide show to your class that 

includes pictures of caves in your region. 

If possible, arrange a field trip to a 

nearby cave. 

Visual, Kinesthetic 

3 

ASSESS 

Evaluate 

Understanding 

Have students create a flowchart that 

explains how an oxbow lake like the one 

in Figure 15 formed. 

Reteach 

Use Figure 14 to explain the features 

formed by water erosion. 

Students’ paragraphs should describe 

how a particle could be transported 

downhill by runoff from a storm. They 

should describe how the particle continues 

to be carried downhill through small 

channels of water into a gully, then into 

a small stream, a large stream, or a river. 

Depending on the size of the particle, 

they should further describe how it is 

carried in suspension, by saltation, or is 

rolled along the bottom of the riverbed 

until it reaches the ocean, where it may 

be deposited in a delta or carried out to 

the deep ocean floor. 

If your class subscribes 

to the Interactive Textbook, use it to 

review key concepts in Section 23.3. 

L2 

L1 



Should Cave Access 

Be Restricted? 

Background 

While investigating a small cave in the 

side of a limestone sinkhole, Randy Tufts 

and Gary Tenen noticed a breeze coming 

out of a crack in the rock. This indicated 

the presence of a larger cave. 

Answers 

1. Students should explain the major 

issues outlined in the text. These issues 

include: Should living caves be developed 

at all? What is the scientific value of preserving 

such caves? What are the risks 

and rewards of developing living caves? 

If such caves are developed, how can this 

best be done? 

2. Those in favor of opening living caves 

to the public argue that development 

will educate the public, create new jobs 

in the region, and protect the caves 

from potential damage by vandals. They 

assert that with proper equipment and 

safeguards, the risk of visitor damage to 

the caves is small. Those opposed to 

opening such caves to the public argue 

that each is a unique geological and 

biological laboratory. They believe that 

opening such caves would be too risky. 

Even under the best circumstances, 

they argue, the living caves would be 

damaged and will “die.” 

3. Students should clearly express their 

opinion about the possible development 

of living caves and provide supporting 

arguments for their opinion. 

4. Students should prepare a letter to 

their governor containing a series of 

specific recommendations. Sample 

recommendations might include: “Limit 

the number of people that can visit the 

cave, and use the proceeds from 

admissions to establish a scientific 

research program for the cave.” or “The 

cave should not be developed. It should 

be preserved for scientific research.” 

Have students further research 

the issues related to this topic. 


L2 

Let the Caverns Be 

A living cave undisturbed by public access provides 

scientists with a unique laboratory. Because of 

caverns’ isolation from the surface world, organisms 

found nowhere else sometimes evolve. Caverns also 

hold evidence of climate change and fossils of 

extinct animals. 

Proponents of cave preservation argue that even 

under the best circumstances, human visitors 

change a cave’s environment for the worse. They 

cite Carlsbad Caverns as a case in point. Each year, 

about 600,000 people visit Carlsbad Caverns. The 

visitors have taken bits and pieces of rock as 

souvenirs. They have disrupted the narrow range of 

temperature and humidity needed for limestone 

deposits to form. 

1. Defining the Issue In your own words, explain 

the major issues involved in preservation versus 

development of limestone caverns. 

2. Analyzing the Viewpoints What are the risks 

and benefits of opening caverns to the public? 

What is the value of preserving them solely for 

scientific research? 

3. Forming Your Opinion Should caverns like 

Kartchner Caverns be open to the public? Give 

reasons for your opinion. 



Cave Life Lechuguilla Cave, inside Carlsbad 

Caverns National Park in New Mexico, has 

been kept closed to all but scientific 

researchers since its discovery in 1986. Even 

scientific access has been limited. Only six 

expeditions are allowed per year with no more 

Should Cave Access Be Restricted? 

In a limestone cavern, it can take 300 years to add one centimeter of rock to 

a stalactite! These and other formations build up drop by drop. In a “living” 

cave, deposits form under conditions of constant temperature and high 

humidity. If these conditions change, the formation of new deposits stops, 

and the cave “dies.” 

In 1974, two explorers discovered a cavern outside Tucson, Arizona. The 

two cavers had to wriggle through a narrow, hidden tunnel to reach a 

network of magnificent caverns that stretched for several kilometers. 

Eventually, the state of Arizona decided to develop the caverns as Kartchner 

Caverns State Park. Cave experts designed special systems that allow access 

to the cave, but minimize the impact of visitors on the caverns’ fragile 

environment. Some scientists, however, are concerned that even these 

special systems will not be enough to maintain Kartchner Caverns as a 

“living” cave. Should all caverns be opened to the public? 

The Viewpoints 

Research and Decide 

Let the People See 

Proponents of opening living caves to the public 

maintain that the beauty of such caverns simply 

demands to be seen. Caverns provide an important 

recreational and educational resource. They bring 

jobs to the region where they are located. In 

addition, development may help protect caves that 

would otherwise be vulnerable to vandals. 

At Kartchner Caverns, an air lock at the entrance 

maintains the caverns’ environmental conditions. 

Blowers remove lint and dust from the visitors’ 

clothing. Walkways are designed to keep visitors 

hands away from cavern walls—skin oils disrupt the 

process by which limestone is deposited. With these 

safeguards, human impact on the cave should 

be minimal. 

4. Persuasive Writing Suppose that you have 

discovered a cavern. Write a letter to your 

governor presenting your position regarding 

whether the cavern should be opened to the 

public or preserved for research. 

For: More on this issue 

Visit: PHSchool.com 

Web code: cch-3233 

than 12 researchers on each expedition. 

Scientists have been studying microorganisms 

in Lechuguilla Cave to get an idea of what life 

on Mars might be like. Opening the cave to 

tourists would probably destroy these 

microorganisms.

23.3 Water Shapes the Land

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