COASTAL PROCESSES AND LANDFORMS - Discovering Physical Geography - page 518

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Waves and Coastal Erosion

Waves are fascinating features that often shape the coastline in
dramatic ways. Aside from witnessing these processes yourself,
the best way to visualize them is to see video of them in ac-
tion. To do so, go to the Geo Media Library and open Waves
and Coastal Erosion . The first part of this animation is a video
that demonstrates wave processes and their interaction with the

shore. Following this video is another film clip that shows coastal
erosion along the California coast in 2008. This video was filmed
during a severe storm that produced strong waves that battered
coastal bluffs. Watch how the waves crashed against the base
of the bluff and how the upper part of the cliff was destabilized in
the manner discussed in this chapter.

3. Headlands are prominent landforms that protrude into

the ocean. These landforms are eroded more vigorously
than other places along the shore because waves are
refracted around them and erode on three sides.

sometimes contained within a beach, they are usually carried
away in suspension by the longshore current. Most beach growth
occurs during the summer months in the Northern Hemisphere
when the weather is relatively calm. In winter, however, beaches
can be significantly eroded due to large waves created by strong
storms. If you happen to live on or near a beach, notice how the
shape of the beach can change between seasons.
Figure 19.21 shows how beach components are differen-
tiated on the basis of their relative position to the water. The
offshore is permanently submerged and is the zone where
waves break and the surf is most active. Moving landward, the
foreshore is the part of the beach that is influenced by the rise
and fall of the tides; that is, it is regularly exposed and sub-
merged. Separating the offshore and foreshore is a submerged
ridge called an offshore bar , which forms as a result of the
interaction between breakers and the ocean bottom in nearshore
environments, where wave velocity is relatively low. Another
noticeable feature on many coasts is a berm scarp , which is
cut at the high water line of the beach. Landward of the high
water line is the backshore , which is the relatively flat part of
the beach that is covered by water only during severe storms.

4. Marine terraces represent ancient shorelines. The land-

forms indicate either variable water levels or uplift due
to tectonic activity.

5. Other indicators of coastline recession include caves,

sea arches, and sea stacks. These erosional features
evolve in a continuum as a coastline erodes.

Depositional Coastlines
We have just seen how coastlines are shaped by erosion and
some of the diagnostic landforms that result from this process.
Now, let's turn to the coastal landforms created when sediment
is deposited in various ways and places. You were briefly in-
troduced to this concept with the formation of a pocket beach
between two eroding headlands (Figure 19.14c). Coastlines in
the process of extending outward into the water through deposi-
tion are said to be undergoing progradation .

Beaches The part of the coastal landscape people are prob-
ably most familiar with is the beach. Beaches are dynamic
places where sediment is deposited through the combination of
waves, beach drift, and wind. In some places, beaches are sup-
plied with alluvial sands derived from land far inland. The beach
is a transition between the water and the landmass and consists
of exposed, unconsolidated sediments that usually range from
sand to cobbles. Although finer silt and clay-sized particles are

Spits and Baymouth Bars As discussed earlier, one of the
ways that water moves along the coast is in association with the
longshore current (see Figure 19.11). This current is capable
of eroding a great deal of fine sediment from the foreshore and
offshore environments and transporting it down the beach. As
long as the beach continues in an uninterrupted fashion along
the shore, the current and its sediment load will flow progres-
sively down the coast because of the interaction of waves and

Progradation Outward extension of the shoreline through
deposition of sediment.

Offshore bar A small ridge on the bottom of the ocean that
separates the offshore and foreshore.

Offshore The nearshore zone that is permanently submerged
and where waves break.

Berm scarp A miniature cliff created by wave erosion that
fronts a beach berm.

Foreshore The nearshore zone that is regularly exposed
and submerged through the tidal fluctuations and movement
of surf.

Backshore The part of the beach that lies between the berm
scarp and foredune and is covered by water only during strong
storms.