1. COASTAL EROSION
Lesson 4

2. 2

3. Tides
• Rising and falling
of the sea level
• Cause : pull of the
moon & sun,
rotation of the
earth
• Each coastal area
receive two high
tides and two low
tides daily
3

4. The ‘shaping’ influencing factors:

5. 5

6. LESSON OBJECTIVE
• Todescribe and
explain the 4
coastal erosion
processes
6

7. Erosion Corrasion
3 COASTAL PROCESSES
Abrasion
Solution
Hydraulic action
Transport
Longshore drift
Deposition Factors:
-Supply of sediment
-Gradient of slope
-Coast position
7

8. COASTAL EROSION
More erosion Less erosion
Types of waves -Destructive waves -Constructive
(more energy) waves
(less energy)
Structure and - Numerous lines of - No cracks
composition of weakness - Hard rocks
coastal rocks - Soft rocks
Position of the - Open coast - Protected and
coast sheltered by
8
structures

9. Waves can be destructive or constructive..
1. Destructive waves:
• operate in storm conditions
• arecreated from big, strong waves when the wind is
strong and has been blowing for a long time
• occurwhen wave energy is high and the wave has
traveled for a long time
• tendto remove material from the coast and
associated with erosion
• backwash is stronger than the swash.

10. 2. Constructive waves:
• operate in calm weather
• are less powerful waves
• break on the shore and tend to deposit material,
building up beaches
• are responsible for transporting material .
• swash is stronger than the backwash.

11. Plunging Spilling

13. HYDRAULIC ACTION
• Direct impact of the waves against
the coast. Compress air and exert
pressure in the cracks of rocks (pg
92)
• Enlarges lines of weaknesses after
repeated crashes of waves
• Cavitation: water surges into
cracks, joints, faults. Results in
compressed air and builds pressure.
Water retreat releases pressure and
trapped air which breaks the rock
up. 13

14. The constant force of
waves crashing on the
shore damages it. This
is called hydraulic
action.

15. CORRASION/ABRASION
• Impact of the materials carried
by the waves scraping against
the coast
• Turbulence of the currents
produce a scouring effect
• Chiselling effect / grinding
action on the coast
• Cutting and breaking the rocks
on the coasts
15

16. ATTRITION
• Rocks rub or hit against
each other, breaks down
into small round smooth
pieces(pg 93)
• Materials from the waves
collide with materials on the
coast
• Impact causes materials to
break into smaller pieces
which becomes sand
16

17. SOLUTION/CORROSION
• Waves react chemically with
soluble minerals in the rocks
and dissolve them (pg 93)
• Corrosion of rocks by
seawater
• Wave action increases the
rate of reaction by removing
the reacted chemical solution
• Eg limestone
17

20. • Coastswhere the geology alternates
between strata (or bands) of hard rocks
and soft rocks is called a discordant
coastline.
• Discordant
coastlines will have alternating
headlands and bays.
• Concordant
coastline is where the rock
remains the same along the coastline.
• Concordant
coastlines tend to have less
bays and headlands.

21. • Alongthe coastline of the Isle of Purbeck in
Dorset (south coast of England), there are
both discordant and concordant coasts.
• Thediscordant coast has been formed into
Studland Bay (soft rock), Ballard Point (hard
rock), Swanage Bay (soft rock) and Durlston
Head (hard rock).
• AfterDurlston Head the rock remains hard.
This concordant coast has less features.

24. Coastal features Created by
erosion
Along a coastline there are often many features created by
erosion. The most common of these are:
1.Cliffs
2.Headlands and Bays
3.Caves
4.Arches
5.Stacks
6.Stumps

25. COASTAL LANDFORMS FORMED BY WAVE/MARINE EROSION:
SEA CAVES, ARCHES, STACKS AND STUMPS
(C) Sea caves, arches, stacks and stumps
1. Sea caves – a tunnel-like opening at the base of the cliff.
2. Erosional processes such as hydraulic action, abrasion and corrosion by
destructive waves act at the base of a cliff/headland along a line of weakness
in the rock to form a hole called a notch.
3. Continual erosion enlarging the notch to form a cave.
4. Prolonged wave erosion enlarges and lengthens a sea cave until it finally cuts
right through the headland and form an arch.
5. Further erosion of the arch causes it to collapse and an isolated pillar of rock
called a stack is formed.
6. The stack can be further eroded and weathered. It is finally worn down to a
stump which is covered during high tide.

26. Formation of Cave, Arch, Stack and
Stump

27. 1. Cliffs
• One of the most common features of the coastline in Britain
and around the world are cliffs.
• Cliffs are shaped through a combination of erosion and
weathering. The weather attacks the cliff top. The waves
attack the cliff foot, causing a wave-cut notch at the bottom.
• Soft rock erodes easily and creates gently sloping cliffs. Hard
rock is more resistant and erodes slowly and creates steep
cliffs.

28. Sea cliffs
A tall, steep rock face,
formed by the
undercutting
action of the sea
Seven Sisters chalk cliffs on the East Sussex coast

29. Wave-cut notches
A rock recess at the foot of a sea cliff where the energy
of waves is concentrated

30. The formation of sea cliff and wave-cut
platform

31. 2. Headlands and
bays
• Headlands are formed when the sea attacks a
section of coast consisting of alternating bands of
hard and soft rock.
• Thebands of soft rock, such as sand and clay,
erode more quickly than those of more resistant
hard rock, such as chalk.
• Thisleaves a section of land jutting out into the
sea; this is called a headland.
• Theareas where the soft rock has eroded away,
next to the headland, are called bays.

34. Headland and bay: Myrtos Bay, Kefalonia

36. Erosion can create caves, arches and stacks along a headland. Again
weathering can also help to create these landforms.
3- Caves occur when the waves force their way into
cracks in the cliff face. The water contains sand
and other materials that help to grind away at the
rock until the cracks become a cave.
4- If the cave is formed in a headland, it may
eventually break through forming an arch.
5- The arch will gradually become bigger and bigger
until it can no longer support the top of the arch.
When the arch collapses, it leaves the headland on
one side and a stack (a tall column of rock) on the
other.

38. Old cliff
line Original Land su
rface
stack
stump
Natural Wave-cut platform
Arch

39. Erosional Features

40. SUMMARY
• Describe the characteristics of 4 coastal
erosional process: CASH
• Explained how the erosional processes occur
• State the coastal erosional features and explain
how they form
40

41. Sources:
• Source: http://www.slideshare.net/shoaib1982/marine-system
by shoaib 1982
• Source: http://www.slideshare.net/esteeseetoh/coastal-proce
by estee seetoh
• hoaib1982