5. Coastal Zones
• A beach is part of a coastal system, which
includes several zones defined by their
proximity to shore and the dominant
processes that occur within them.
9. Destructive Waves
• Created in storm conditions.
• Big, strong waves from powerful, consistent wind
• High wave energy from travelling over a long fetch.
• Erode the coast.
• Stronger backwash than swash.
• Short wavelength and high + steep.
10. Constructive Waves
• Calm weather + less powerful
• Deposit material, building up beaches.
• Swash is stronger than the backwash.
• Long wavelength and are low in height.
17. How is sediment transported
along a coastline ?
• Most waves move
toward the shore at
a slight angle.
• Water (swash) from
each breaking wave
is oblique.
18. Shoreline Currents
• Most waves strike
shorelines at angles
• Swash washes ashore
diagonally
• Backwash go straight
back down
• Sediments are carried
by longshore drift
19. Rip Currents
• Strong surface
currents that flow
away from the beach
• Too much water
converges at the
shore
• 2 longshore currents
meet
26. How to spot a rip channel
Head of
Rip channels Rip channel
(as seen from beach) Rip channel
(as seen from the air)
Note: a rip current is different from undertow
27. Coastal Deposition
• When the sea loses energy, it drops the
sand, rock particles and pebbles it has
been carrying.
– when the swash is stronger than the
backwash
– waves enter an area of shallow water
– waves enter a sheltered area, eg a cove
or bay.
– there is little wind
– there is a good supply of material.
28. Formation of Wave-Cut Platform
1. Weather weakens the top of the cliff.
2. The sea attacks the base of the cliff
forming a wave-cut notch.
3. The notch increases in size causing the
cliff to collapse.
4. The backwash carries the rubble towards
the sea forming a wave-cut platform.
5. The process repeats and the cliff
continues to retreat
29. Refraction of Waves
• Coastlines are rarely straight
• Waves bend when there is a change in its
speed
• What changes speed of waves?
– What causes a wave to slow down?
• Change in depth (or shallowness)
47. Depositional Landforms
• Beaches
– Constructive waves
– Larger sediments can
be carried further up
the beach during
storms
– Smallest sediments
near the water
48. Depositional Landforms
• Spit
– Longshore drift moves
material along the
coastline.
– material is deposited and
extends from mainland.
– grows and develops a
hook if wind direction
changes
– creates a sheltered area
where silt is deposited and
mud flats or salt marshes
form.
51. Types of Coastlines
• It is difficult to categorize coastlines.
• The form of a coast is a result of the
interactions of four factors:
– 1) any abrupt change in sea-level,
– 2) the amount of sediment supplied to the
coast by rivers,
– 3) the movement of that sediment upon
its arrival at the coast by oceanic processes,
and
– 4) whether tides or waves are most
effective in moving the sediment.
52. Types of Coastlines
• Emergent • Submergent
– Raised coastline – Sunken coastline
• Why? • Why?
– Drop in sea level – Rise in sea level
• Rias: flooded river
valleys
• Fjords: flooded glacial
troughs
• Estuaries: flooded river
delta
54. Types of Coastlines
• Concordant • Disconcordant
• think “Cordillera” – Alternating ridges of
– Alternating ridges of hard and soft rock
hard and soft bedrock perpendicular to
aligned parallel to coastline
coastline – Headlands and bays
– If water breaks
through a weak point
in the hard ridge, soft
rock behind erodes to
form coves
– Dalmatian Coast,
Croatia
57. Coral Reefs
•Reefs are natural structures of rock
formed by marine animals.
•Today’s reefs are largely made by
corals, but in the geological past,
have been constructed by sponges
and bizarre clams.
•Reef-building organisms build
skeletons of calcium carbonate in
the form of aragonite or calcite.
Great Barrier Reef,
Australia
58. Coral polyps
(individual coral animals)
Coral reefs are often called the “rainforests of the sea” due to the
great diversity of creatures that form them. Note that the brilliant
colours apparent in corals are from the microscopic algae in the coral
tissues (different colours absorb different wavelengths of light)
59. Conditions necessary
for reef development
•Large reefs are limited to the warm seawater areas of
the tropics.
•Calcium carbonate is easier to precipitate in warm water
than in cold water.
•Secretion of calcium carbonate is aided by microscopic
cells of algae that live in the tissues of reef builders (the
algae remove carbon dioxide from the tissues, decreasing
the acidity of the water).
60. Conditions necessary
for reef development
Reefs also tend to preferentially form in areas where:
1. Little clastic sediment occurs (such sediment
particles smother reef builders).
2. Nutrient levels are low.
3. Water is shallow
61. Reef zones
Reef builders are zoned in a reef according to their form
(encrusting forms tend to dominate the reef crest where
wave action is strongest, while more delicate branching
forms are confined to deeper water zones where water action
is more gentle)
A lagoon can develop behind a reef, where it is protected from
strong waves
62. A special kind of reef: atoll
• An atoll is a special
kind of reef that is
ring-shaped and has
a central lagoon.
63. How an Atoll Forms
• An atoll is formed first as a reef that
fringes a volcanic island.
• As the island sinks (after volcanic activity
has ceased and the crust has cooled,
becoming denser), the reef continues to
build upward, eventuallyGilligan’s Island ? as a
ending up
ring-shaped structure.
