Introduction to coasts.
What is a coast: A coast is a zone where the land
meets the sea.
Waves are the primary force causing erosion along
coastlines. A wave is formed by the wind blowing
across the surface of the water, creating ripples,
which then grow into waves. As waves reach the
coast the lower section slows due to friction. The
upper section topples over and breaks forward.
The size of waves depends on:
The wind speed
The length of time during which the wind blows in the
The length of sea over which the wind blows. The
greater these factors are the bigger the wave.
Constructive Waves have a number of important
i) Their swash is much stronger than their backwash,
causing the beach to be built up by the deposited
ii) They are less frequent, reaching shore between 6 and
8 times each minute.
iii) They are long waves and so roll onto the beach rather
than crashing onto it.
iv) Constructive waves create a wide, gently sloping
Destructive Waves have a number of important
i) Their backwash is much stronger than their swash,
thus allowing them to remove material from the beach.
ii) They are frequent in number, usually between 10 and
15 per minute.
iii) They are tall waves, meaning they have a greater
distance to fall when they break. This causes them to
scour out the beach material.
iv) Destructive waves create a steep narrow beach
Processors of Erosion
1. Attrition:- “Rock on rock”- Particles carried by the
waves crash against each other and are broken up into
smaller particles. 2. Corrasion (also known as
abrasion):- “Rock on cliff”- Particles carried by the waves
crash against the cliffs, eroding the cliffs. 3. Corrosion:-
“Rusting / dissolving”- Salt in the seawater slowly
dissolves the cliffs. - The material produced is carried
away by the process of solution. 4. Hydraulic Action:-
“Pressuring”- The water traps air in cracks and caves in
the rock. - This air is compressed by the incoming waves
placing great pressure on the rocks, causing them to
Long shore drift
Long shore Drift
- Material moved along the coastline by the waves.
- When waves approach the coast at an angle, carrying
material with them. This is carried up on to the beach by
- The material is then dragged out to sea by the
backwash, but this time it travels at right angles to the
beach, as it will roll down the steepest gradient (gravity)
- This movement will slowly transport material laterally
along the coast.
Long shore drift
i) Traction – the rolling of large material along the
sea floor by the waves.
ii) Saltation – the bouncing of slightly lighter material
along the sea floor.
iii) Suspension – Small particles of material carried
by the water.
iv) Solution – Material is dissolved and carried by the
Headlands and bays
Headlands and Bays
1. Orojects out into the sea
2. Is usually longer than its bredth (width)
3. Has sides which form cliffs
1. has a semi – circular shape of sea extending into
2. A wide, open entrance from the sea.
3. Land behind it that Is lower than the headlands on
Cliffs and wave cut platforms
Cliffs are formed when destructive waves attack the bottom of the
rock face between high and low water mark.
- The area under attack is eroded using the major processes of
- Points of weakness, such as faults and joints are attacked most,
and eventually a wave-cut notch is gouged out.
- The rock above overhangs the notch, and as it is cut deeper into
the rock, gravity causes the arch rock to collapse.
- The loose rocks are removed by the sea and transported along the
coast by long shore drift.
- The whole process of undercutting the cliff begins again.
- As the cliff is eroded backwards it leaves behind a wave-cut
platform, at the level of the low water mark.
- This platform is rarely eroded, as the waves energy is concentrated
on eroding the area between the high and low water mark, and not
the rock that is underneath them.
How cliffs are formed
How caves arches and stacks are
- Mainly seen on headlands.
- Waves start by attacking the main points of weakness in
the rock: the joints and faults.
- A point of weakness is increased in size until it becomes
- The waves continue to attack the cave, which finally
results in an arch being formed through the headland.
- The arch is attacked both by coastal erosion and sub-
aerial erosion and finally the roof of the arch falls into the
- This leaves behind a stack, which is then slowly eroded
down to become a stump.
How caves, arches and stacks are
How spits are created
Spits and bars
- A long, narrow ridge of sand attached at one end to the coast.
- Built up by long shore drift transporting material along the coast.
- At a bend or break (for an estuary) in the coastline the material
being carried is dropped. (move from high energy to low energy
environment) The material builds up away from the coastline.
- As the spit builds out to sea the end is affected more by the wind
and by wave currents, causing the end to curve towards the shore, to
create a hook end.
- Material often accumulates in the area of standing water that occurs
behind a spit, and this can lead to the formation of salt marshes.
- Spits can be areas where large sand dunes build up, nearer the
back of it.
If the spit extends across a bay it is called a bar.
Are mainly in the pacific ocean in shallow warn seas
Coral is made of Calcium carbonate(like limestone)
Zooaxanthallae lives inside coral and does lots of
important jobs such as absorbing CO2, releasing CO2
and making food for Polyps.
There are different types of coral such as fire coral,
plate coral, brain coral etc.
Coral reefs are important to us because they give us
protection from wave breakage, make jobs,
food(fishing) and climate change (absorb CO2)
Case study – Holderness
Eastern side of the UK
Facing the North Sea
3Km south of Hornsea
· Mostly consists of cliffs up to 30 metres high
· At the Humber estuary there is a spit called Spurn Head
· Cliffs have been retreated at a rate of about 1.2 metres a
Holderness – continued
Causes of Erosion
· Cliffs made of soft material (mainly clays and sands) that is easily
undermined by wave action
Water logging of the cliffs by rain results in slumping
Attacked by destructive waves that are blown by strong winds across
the North Sea
Processes of hydraulic action and abrasion at work
· Sand at the foot of the cliffs is constantly moving south due to
longshore drift. This means a wide beach cannot be created so the cliff
is relatively unprotected
Holderness - Continued
Effects of Erosion
· 4km stretch of land has been lost to the sea since Roman Times
· Villages, farms (e.g. Grange Farm at Great Cowden) and caravan sites lost to the sea
· Easington gas terminal is at risk of falling into the sea
· Towns including Hornsea and Withernsea are under threat
· Main roads at risk including the B1242 at Mappleton
·Wooden revetments and rock barriers have been constructed to protect Mappleton
· A series of groynes have been constructed at the cliff base to prevent the movement of
However a large rock groyne at Mapleton has increased erosion to the south to Arate of 10 metres
per year by blocking the movement of protective material
· A 1km sea wall costing £4.5 million has been built to protect Easington gas terminal
· Concrete blocks and rubble have been dumped at the cliff base as a temporary barrier to absorb
· Proposal to dump colliery waste 50km from the coast to refract waves and encourage the formation
of bays that would hold sand