Coasts Revision
1. Characteristics of Destructive and Constructive Waves
Constructive waves have a greater swash than backwash whereas
destructive waves have a greater backwash than swash. Destructive
waves are higher energy waves in comparison to constructive
waves, which are low energy. Destructive waves remove sediment
from the beach whereas constructive waves build beaches.
Destructive waves break more frequently than constructive waves
as destructive waves break 13-15 times per minute whereas
constructive 5-9 times per minute. Destructive waves are higher
(than 1m) whereas constructive are (below 1m).
Erosion Processes
a) Hydraulic Action = When waves hit the coast they force
water and air into cracks in the rocks. As the water surges
it compresses the pockets of air. This continued process
weakens the joints and cracks; eventually causing the rock
to shatter.
b) Abrasion = Breaking waves throw sand and pebbles
against the cliff face with great force. These scrape away
at the cliff, eventually causing undercutting and a wave
cut notch.
c) Attrition = rocks collide against each other and became
smaller, smoother and more rounded.
d) Corrosion = A chemical reaction between rocks like
limestone and chalk and the acids in the seawater.
2. Weathering (insitu)
a) Physical Weathering
i. Freeze thaw = diurnal changes in temperature around 0
degrees. Water in cracks widened due to freezing at
night, 9% volume increase, thawing during the day
leaves crack prized open. The repeated process causes
fragments to break off.
ii. Exfoliation – heating during the day causes expansion
and cooling of cliff face at night causes contraction. This
leads to layers of rock breaking down.
b) Chemical Weathering = Rainwater has weak acids like
H2SO4, which causes acid rain, which reacts with certain
rocks like limestone, and causes the rock to dissolve and
break
c) Biological Weathering = Animals burrowing, seeds fall
into cracks and grow with their roots that force cracks in
rocks….
3. Mass Movement
, a) Landslide = Waves/sea/rain can cause the cliffs to become
saturated, if made of clay. Over time the material in the cliff
becomes weakened. Gravity causes the cliff material to slide
down. Landslides can cause rapid removal of coastal
materials.
b) Soil creep = causes slow movement of soil from coastal slopes
due to saturation of soil particles and force of gravity;
terracettes are left.
c) Slumping = rotational movement of land downward at the
coast, caused by dry weather where clay contracts and cracks
and rainwater enters the cracks making the clay saturated.
The rock gets weakened and gravity pushes it down the slope.
4. Formation of Headlands and Bays
It is caused by differential erosion (a combination of hard and soft
rock) and due to perpendicular geology. Harder rock is more
resistant therefore forms land which sticks out into the sea
(headlands). Softer rock is eroded (by hydraulic
action/abrasion/corrosion) at a quicker rate to form a bay.
5. The formation of cliffs and wave-cut platforms.
**Cliffs = Vertical and jointed and is made of chalk/limestone
Weathering weakens the top of the cliff and the sea erodes the base
of cliff via Hydraulic Action, Abrasion. This creates a wave cut notch
and overhang. Lack of support and gravity of overhang creates
pressure and causes the cliff to collapse. The backwash carries the
rubble towards the sea forming a flat wave-cut platform that
protects the coast at low tide. This steep cliff retreats over time.
6. Caves, Arch, Stack, Stump
Wave refraction causes waves to attack the side of the headland.
Joints are exploited by erosion (e.g. hydraulic action, abrasion).
Repeated erosion causes a cave, which becomes eroded through to
become an arch. Pressure on the arch and force of gravity
ultimately cause the collapse of the arch, leaving a stack. Continued
erosion and weathering will cause a stump.
7. Longshore Drift
LSD is the movement of material along the beach. It occurs in the
direction of the prevailing wind. It comprises of swash – where
waves move material up a beach in the direction of prevailing wind
(which is at an angle), and backwash – where due to gravity,
material is dragged towards the sea. Swash and backwash is
repeated leading to a zig-zag movement along beach.
8. Formation of a Beach
1. Characteristics of Destructive and Constructive Waves
Constructive waves have a greater swash than backwash whereas
destructive waves have a greater backwash than swash. Destructive
waves are higher energy waves in comparison to constructive
waves, which are low energy. Destructive waves remove sediment
from the beach whereas constructive waves build beaches.
Destructive waves break more frequently than constructive waves
as destructive waves break 13-15 times per minute whereas
constructive 5-9 times per minute. Destructive waves are higher
(than 1m) whereas constructive are (below 1m).
Erosion Processes
a) Hydraulic Action = When waves hit the coast they force
water and air into cracks in the rocks. As the water surges
it compresses the pockets of air. This continued process
weakens the joints and cracks; eventually causing the rock
to shatter.
b) Abrasion = Breaking waves throw sand and pebbles
against the cliff face with great force. These scrape away
at the cliff, eventually causing undercutting and a wave
cut notch.
c) Attrition = rocks collide against each other and became
smaller, smoother and more rounded.
d) Corrosion = A chemical reaction between rocks like
limestone and chalk and the acids in the seawater.
2. Weathering (insitu)
a) Physical Weathering
i. Freeze thaw = diurnal changes in temperature around 0
degrees. Water in cracks widened due to freezing at
night, 9% volume increase, thawing during the day
leaves crack prized open. The repeated process causes
fragments to break off.
ii. Exfoliation – heating during the day causes expansion
and cooling of cliff face at night causes contraction. This
leads to layers of rock breaking down.
b) Chemical Weathering = Rainwater has weak acids like
H2SO4, which causes acid rain, which reacts with certain
rocks like limestone, and causes the rock to dissolve and
break
c) Biological Weathering = Animals burrowing, seeds fall
into cracks and grow with their roots that force cracks in
rocks….
3. Mass Movement
, a) Landslide = Waves/sea/rain can cause the cliffs to become
saturated, if made of clay. Over time the material in the cliff
becomes weakened. Gravity causes the cliff material to slide
down. Landslides can cause rapid removal of coastal
materials.
b) Soil creep = causes slow movement of soil from coastal slopes
due to saturation of soil particles and force of gravity;
terracettes are left.
c) Slumping = rotational movement of land downward at the
coast, caused by dry weather where clay contracts and cracks
and rainwater enters the cracks making the clay saturated.
The rock gets weakened and gravity pushes it down the slope.
4. Formation of Headlands and Bays
It is caused by differential erosion (a combination of hard and soft
rock) and due to perpendicular geology. Harder rock is more
resistant therefore forms land which sticks out into the sea
(headlands). Softer rock is eroded (by hydraulic
action/abrasion/corrosion) at a quicker rate to form a bay.
5. The formation of cliffs and wave-cut platforms.
**Cliffs = Vertical and jointed and is made of chalk/limestone
Weathering weakens the top of the cliff and the sea erodes the base
of cliff via Hydraulic Action, Abrasion. This creates a wave cut notch
and overhang. Lack of support and gravity of overhang creates
pressure and causes the cliff to collapse. The backwash carries the
rubble towards the sea forming a flat wave-cut platform that
protects the coast at low tide. This steep cliff retreats over time.
6. Caves, Arch, Stack, Stump
Wave refraction causes waves to attack the side of the headland.
Joints are exploited by erosion (e.g. hydraulic action, abrasion).
Repeated erosion causes a cave, which becomes eroded through to
become an arch. Pressure on the arch and force of gravity
ultimately cause the collapse of the arch, leaving a stack. Continued
erosion and weathering will cause a stump.
7. Longshore Drift
LSD is the movement of material along the beach. It occurs in the
direction of the prevailing wind. It comprises of swash – where
waves move material up a beach in the direction of prevailing wind
(which is at an angle), and backwash – where due to gravity,
material is dragged towards the sea. Swash and backwash is
repeated leading to a zig-zag movement along beach.
8. Formation of a Beach
