Name
CHAPTER 18
Class
Date
Erosion by Wind and Waves
3 Coastal Erosion and Deposition
SECTION
KEY IDEAS
As you read this section, keep these questions in mind:
• How do changes in sea level affect coastlines?
• What are the features of a barrier island?
• How do humans affect coastal land?
What Affects Coastlines?
Coastlines are areas where land meets the ocean.
Coastlines extend from shallow water to several
kilometers inland. Many factors affect coastlines,
including changes in sea level and movement of coastal
land. Human activities also change coastlines.
How Do Absolute Sea-Level Changes Affect
Coastlines?
Absolute sea level rises or falls when the amount of
water in the ocean changes. Changes in sea level either
cover or expose coastlines.
The absolute sea level on Earth has changed over time.
During the last glacial period, some ocean water was
frozen in continental ice sheets. Over time, parts of the
ice sheets have melted. This has added more water to the
oceans. As a result, the sea level has risen about 1 mm
per year for the last 5,000 years.
In the distant future, the ice sheets could melt
completely. If this happened, the sea level would rise
more than 50 m. The oceans would cover many coastal
areas, including New York, Los Angeles, and Miami.
READING TOOLBOX
Take Notes Use two-column
notes to learn and review
concepts from this section.
Write main ideas in the left
column and detailed notes in
the right column.
READING CHECK
1. Explain Why was
absolute sea level lower
during the last glacial period?
Sea Level Change in Past 35,000 Years
0
Last glacial period
Today
Depth (m)
50
This graph shows
how sea level has
changed over the
past 35,000 years.
100
150
35
30
25
20
15
10
5
LOOKING CLOSER
2. Interpret About how
many meters has sea level
risen from 15,000 years ago
to today?
0
Thousands of years ago
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273
Erosion by Wind and Waves
Name
SECTION 3
Class
Date
Coastal Erosion and Deposition continued
Critical Thinking
3. Compare How is relative
sea level different from
absolute sea level?
How Do Relative Sea-Level Changes Affect
Coastlines?
Relative sea-level changes happen when land near the
coast changes. Changes in coastal land may result from
large-scale geologic processes or local coastal changes.
For example, movements of Earth’s crust can raise and
lower coastlines.
SUBMERGENT COASTLINES
A submergent coastline forms when sea level rises
or when land sinks. On a submergent coastline, valleys
become bays and inlets. The high land that divided the
valleys becomes headlands. The tops of tall mountains
or hills may become islands. Beaches on submergent
coastlines are short, narrow, and rocky.
New features can form along submergent coastlines.
When ocean water floods glacial valleys, fiords form.
Fiords are deep, narrow bays with steep walls. Ocean
water may also cover the mouth of a river valley to form
a wide, shallow bay. This type of bay is an estuary. In
an estuary, fresh water mixes with salt water from the
ocean.
Headlands
The features of
a submergent
coastline erode
over time as sea
level rises.
New sea
level
LOOKING CLOSER
4. Identify What is one
feature of a submergent
coastline?
Old sea level
EMERGENT COASTLINES
READING CHECK
5. Describe How does an
emergent coastline form?
An emergent coastline forms when sea level falls or when
land rises. If a steep coastline is exposed rapidly, it will
erode to form sea cliffs, narrow inlets, and bays. Wavecut terraces may also form.
A gentle slope forms when part of the continental
shelf is exposed slowly. The gentle slope forms a smooth
coastal plain. This plain has long, wide beaches. It does
not have many bays or headlands.
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274
Erosion by Wind and Waves
Name
SECTION 3
Class
Date
Coastal Erosion and Deposition continued
BARRIER ISLANDS
Sometimes sea level rises over a flat coastal plain. The
shoreline moves inland and separates dunes from the
old shoreline. These dunes form barrier islands. Barrier
islands are long, narrow ridges of sand that are parallel
to the shore. Barrier islands can be 3 to 30 km offshore.
They can be more than 100 km long. The shallow water
between the barrier island and the shoreline is a lagoon.
Barrier islands can also form from storms and waves.
Storms may separate a sand spit from the shore and form
a barrier island. Waves may pile up ridges of sand from
the sea bottom and form a barrier island.
Many natural forces affect barrier islands. Waves, currents, and winds cause barrier islands to migrate toward
the shoreline. Winds blowing toward the shore create
a line of dunes on the island. Large waves from storms
greatly erode barrier islands. Storm waves wash sand
from the ocean side to the inland side of the island. Some
barrier islands are eroding at a rate of 20 m per year.
Critical Thinking
6. Make Predictions How
would a season of heavy
storms affect a barrier island?
LOOKING CLOSER
7. Identify Circle the lagoon
in this picture.
Santa Rosa Island is a barrier island off the coast of Florida.
How Can Humans Affect Coastlines?
Humans use coastal lands for fishing, shipping, land
development, and recreation. These activities can damage
coastal areas in many ways. For example, ships and oil
wells near the shoreline may cause oil spills. Waste from
industry and coastal towns can pollute the coastline. This
pollution can harm living things, including people.
Many people want to protect coastal areas. These
people may work with the government to make rules that
protect the coastline.
Talk About It
Express a Viewpoint Do
you think it is important to
protect coastal areas? Why
or why not? Discuss your
opinions with a partner.
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275
Erosion by Wind and Waves
Name
Class
Date
Section 3 Review
SECTION VOCABULARY
barrier island a long ridge of sand or narrow
island that lies parallel to the shore
estuary an area where fresh water from rivers
mixes with salt water from the ocean; the
part of a river where the tides meet the river
current
lagoon a small body of water separated from the
sea by a low, narrow strip of land
1. Describe What are two features of a barrier island?
2. Summarize How can an increase in relative sea level affect a coastline? Give two
examples.
3. Explain How do wind and waves affect barrier islands?
4. Describe What are two ways that humans affect coastlines?
5. Predict Consequences How would coastlines change if Earth began a new glacial
period? Explain your answer.
6. Apply Concepts A scientist is studying a coastline in an area. The scientist finds
estuaries and islands in the area. Describe how these features may have formed.
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Holt McDougal Earth Science
276
Erosion by Wind and Waves