Laboratory Manual for Introductory Geology 4e

Similarly, oblique waves generate currents just offshore that parallel the shoreline.
These currents are responsible for moving large volumes of sediment and for
building distinctive elongate landforms, including well-known depositional features
such as are seen on Coney Island and Cape Cod.
17.3.4 Erosional Features
Coastal erosion produces distinctive shoreline features (FIG. 17.11) and causes coastal
landscapes to change in predictable ways. Coastal erosion is most rapid in locations
where land extends out into the ocean, called headlands, because this position allows
waves to attack the land from nearly any direction. Conversely, coastal erosion is
slowest in deep, low areas of coastal land called embayments, where wave energy is
diffused along a broad stretch of coastline.
Coastal erosion produces two types of landforms. The first type forms at the
shoreline. As waves drive loose sediment across shorelines underlain by bedrock, the
sediment abrades a flat surface, called a wave-cut bench. It then cuts into the base
of bedrock cliffs to form the second type of landform, a wave-cut notch (FIG. 17.12).
Where the coastal cliffs are made of unconsolidated sediment, the waves eat into
the cliff and pick up sediment that is added to the abrasive material. In either case,
EXERCISE 17.6
Factors in Coastal Erosion
Name:
Course:
Examine the two photographs of shorelines below.
Section:
Date:
(a) Indicate with arrows the direction in which the wind is blowing in each photo.
Two aspects of shoreline geometry influence the effectiveness of coastal erosion: (1) Is the area exposed, projecting out
into the ocean, or is it an embayment, protected by flanking headlands? (2) Is the slope of the shoreline steep, allowing
waves to crash onshore with full force, or is it gentle, causing the waves to break offshore and lose some of their energy?
(b) Compare the shoreline geometry in the two photographs above. On which shoreline would you expect coastal
erosion to be more effective? Explain.
446 CHAPTER 17 SHORELINE LANDSCAPES