1. Chapter 20: Coastal
Processes and Terrain
McKnight’s Physical Geography:
A Landscape Appreciation,
Tenth Edition, Hess

2. Coastal Processes and Terrain
• The Impact of Waves and Currents on the
Landscape
• Coastal Processes
• Coastal Landforms
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3. The Impact of Waves and
Currents on the Landscape
• Coastal processes affect
a tiny portion of Earth’s
landscape
• Waves agents of erosion
• Currents agents of
transportation and
deposition
• Beaches mark transition
between land and water
and are highly variable
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Figure 20-4

4. Coastal Processes
• Interface of three major
components of Earth’s
environment
• Highly energetic due to
constant motion of waters
• Importance of wind
• Ocean and lake formations
similar except for:
– Tidal range smaller for lakes
– Water level change differences
– Reefs only in oceanic water
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Figure 20-1

5. Coastal Processes
• Waves—transfer of energy through cyclical rising and
falling of a substance
• Most are wind generated over oceans
• Wind stress generated waves, forced waves
• Swells
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6. Coastal Processes
• Waves of oscillation and
translation
– Waves that move in a circular
or oscillatory fashion with little
forward movement, waves of
oscillation
– Wave crests and troughs
– Wavelengths and wave heights
– Wave amplitudes
– Shallow water waves influenced
by ocean floor, gain forward
progress, called waves of
translation; wave breaks
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Figure 20-2

7. Coastal Processes
• Wave refraction
– Change in wave direction as
they approach shore
– Uneven coastline and irregular
water depth
– Waves bent due to uneven
slowing of waves from irregular
water depth
– Wave action focused on
headlands, much gentler in
adjacent bay areas
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Figure 20-5

8. Coastal Processes
• Wave erosion
– Consistent pounding of small
waves results in erosion
– Large storms significantly
enhance coastal erosion
– Air forced into cracks in
coastal rocks when water
moves inland; air released as
water recedes and enhances
erosion
– Chemical action of seawater
– Notches cut in the bases of
cliffs
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Figure 20-6

9. Coastal Processes
• Tsunamis
– Waves triggered by disruptions
in ocean floor
– When fault rupture on ocean
floor generates tsunami, entire
depth of ocean above rupture
is displaced
– Inconspicuous in open ocean
with long wavelengths and low
heights
– Can travel over 400 mph
– Significant withdrawal of up to 40
meters before a significant surge
of water 9© 2011 Pearson Education, Inc.
Figure 20-8

10. Coastal Processes
• Tides
– Alterations of ocean level
from gravitational pull of Sun
and Moon
– Two high tides and two low
tides per day
– Topographic effects
generally small
– Significant agents of erosion
only in narrow bays, around
shallow seas, and in
passages between islands
10© 2011 Pearson Education, Inc.
Figure 20-9

11. Coastal Processes
• Changes in sea level and lake level
• Two primary causes of sea level changes
– Rising or sinking of landmass (tectonic change)
– Increase or decrease in amount of ocean water (eustatic
sea-level change)
– Emergent versus submergence land characteristics
• Global warming and sea-level change
– Thermal expansion of water and melting of ice caps increasing
water volume (eustatic)
– Sea level rise of up to 0.5 m by the end of the century
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12. Coastal Processes
• Ice push
– Bodies of water that freeze in winter, resulting in expansion
and subsequent contraction
– Ice pushes onto land, significantly modifying land surface,
similar to small glacial advance
– Most common in Arctic and Antarctic regions
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13. Coastal Processes
• Organic secretions
– Many aquatic animals form
calcium carbonate shells
– Animals cluster together and
form enormous masses of
reefs, platforms, and atolls
• Stream outflow
– Streams important sources
of sediment to oceans and
lakes
13© 2011 Pearson Education, Inc.
Figure 20-11

14. Coastal Processes
• Currents and coastal
sediment transport
• Longshore currents
– Water moves parallel to
shoreline (“along” shore)
– Develop just offshore and
set up by waves striking
coast at an angle
– Wind direction reflected in
longshore currents
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Figure 20-12

15. Coastal Processes
• Currents and coastal
sediment transport (cont.)
• Beach drifting
– Short distance shifting of
sand by breaking waves and
retreating water
– Zigzag pattern of particle
movement downwind and
parallel to coast
– Affects of tides on debris
movement
– Dune formation on coasts
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Figure 20-13

16. Coastal Processes
• Coastal deposition
– Results when energy of
moving water is diminished
– Maritime deposits more
ephemeral than noncoastal
deposits due to composition
and lack of vegetative cover
– Sediment budget must be in
balance to allow for deposit
to persist
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Figure 20-14

17. Coastal Landforms
• Depositional landforms
• Beaches
– Beaches relatively
homogeneous
– Mark transition between
land and ocean
– Backshore contains berms;
foreshore regularly covered
and uncovered by tides
– Offshore is zone that is
permanently submerged
17© 2011 Pearson Education, Inc.
Figure 20-15

18. Coastal Landforms
• Spits
– At mouth of a bay, sediment
moved into deeper water
– Deposit attached to land at
one end and extends to
open ocean in downcurrent
direction is a spit
– Spits that extend across a
bay, bay barriers or
baymouth bars
– Tombolos: waves converge
on each side and deposit
sand so the bar connects
to land 18© 2011 Pearson Education, Inc.
Figure 20-16

19. Coastal Landforms
• Barrier islands
– Long, narrow sand bar built up
in shallow offshore waters
– Oriented approximately parallel
to shore
– Only rise a few meters above
sea level, but some extend to
great lengths
– Lagoon formation; mudflats
– Life cycle of a lagoon
19© 2011 Pearson Education, Inc.
Figure 20-20

20. Coastal Landforms
• Human modification of
coastal sediment budgets
– Dams act as sediment traps,
allowing less sediment to
reach oceans and resulting
in shrinking beaches
– Use of groins to help impede
the downcurrent flow of
sediment
– Jetties used to keep water
moving and reduce
sediment deposits in
navigation channels
20© 2011 Pearson Education, Inc.
Figure 20-23

21. Coastal Landforms
• Shorelines of submergence
– Most oceanic coastline shows
evidence of submergence at
some time within last 15,000
years
– Ria shorelines
• Submergence results in
drowning of previous river
valleys, producing estuaries
• Coast with numerous estuaries
is called a ria shoreline
21© 2011 Pearson Education, Inc.
Figure 20-25

22. Coastal Landforms
• Shorelines of
submergence (cont.)
– Fjorded coasts
• Extensive glaciation gouges
out troughs by glaciers or ice
sheets
• Troughs far below sea level,
eventually fill with sea water
• Deep coastal indentations are
called fjords
• Create extraordinarily
irregular coastlines
22© 2011 Pearson Education, Inc.
Figure 20-26

23. Coastal Landforms
• Shorelines of emergence and
erosion
– Shoreline features raised well above
current sea level
• Wave-cut cliffs and platforms
– Constant pounding of waves at base
of landforms cuts a notch at the high
water level
– Broad erosional pattern called a
wave-cut bench or wave-cut
platform
– Most cut debris shifted just beyond
wave-cut bench to wave-built terrace
23© 2011 Pearson Education, Inc.
Figure 20-27

24. Coastal Landforms
• Marine terraces
– Wave-cut platforms uplifted
along tectonically rising
coasts
– Several instances of marine
terraces indicate several
episodes of marine terrace
formation
– Can be used to deduce
history of the water levels in
a region
24© 2011 Pearson Education, Inc.
Figure 20-28

25. Coastal Landforms
• Coral coasts
– Most continents and islands fringed with coral reefs or
another coralline structure
– Critical element is a group of anthozoan animals
– Calcium carbonate skeletons from coral polyps
– Have a blossomlike appearance similar to plants
– Have strict requirements for their survival
– Fringing reefs: those built right onto a volcano
– Barrier reefs: coral that appears to float around a volcano
– Atolls
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26. Coastal Landforms
• Distribution of coral coasts worldwide
26© 2011 Pearson Education, Inc.Figure 20-29

27. Summary
• Coastal regions make up a very small percentage of
the Earth’s landscape, but have unique structure and
processes
• The coasts are the interface between three of the
four primary spheres of the Earth
• The most energetic coastal processes are observed
by wave motions
• Tsunamis are significant dangerous waves that result
from underwater earthquakes, not from winds
• Tides play a small role in the sculpting of landforms
of coasts
27© 2011 Pearson Education, Inc.

28. Summary
• Numerous processes are involved that modify the
lake level and sea level of bodies of water
• Many other coastal processes, including ice push,
organic secretions, and stream outflow, help
structure coastal landforms
• Currents are primarily responsible for the transport of
coastal sediment
• Coastal deposition takes place in areas where ocean
water moves more slowly, and is typically ephemeral
• The most widespread coastal landform is called a
beach
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29. Summary
• Spits and barrier islands result from deposition of
sedimentary material by the longshore currents
• Lagoons result when barrier islands cut off one small
region of ocean water from the remaining ocean
• Humans have modified the structure of shorelines
through damming and the building of groins and
jetties
• Shorelines can be divided into two categories,
emergence or submergence
• Coral coasts consist of organic material and typically
surround volcanoes
29© 2011 Pearson Education, Inc.