Coasts Flashcards
Attrition
This is where materials carried along in the sea hit against each other causing them to get smaller and smoother. This material is used to assist in the process of abrasion.
Abrasion
This is when material carried along in the sea is hurled at cliffs by waves causing the rocks to be worn down.
Hydraulic action
This is when water and air is forced into cracks joints causing them to exert pressure and the explosive blast weakens and loosens the rock fragments causing them to break off
Corrosion
This is when weak carbonic acids as well as salts in the water can cause weathering which slowing dissolves rocks along the coast.
Salt crystallisation
When salty sea water evaporates salt can be left behind. Crystals can then grow which can force the rocks to break apart
Concordant coastline
Bands of soft and hard rock are parallel to the coastline
Disconcordant coastline
Bands of hard and soft rock are at right angles to coastline
Formation of headlands and bays
Headlands and bays form in disconcordant coastlines where bands of soft and hard rock are at right angles to the coastline.
The soft rock is eroded much quicker than harder rock as it is less resistant, by sediments such as sand and gravel in waves approaching the shore.
This happens through the process of abrasion which is when material carried in the sea is hurled at rocks by waves causing the rocks to be worn down overtime.
Hydraulic action also occurs which is when water and air is forced into cracks and joints in the rocks causing them to exert pressure and explosive blasts then weaken and loosen rock fragments causing them to break off.
Weak acid or salts in the water may also dissolve the socks through corrosion.
Hard rock is left sticking out into the sea as it is more resistant that the softer rock. These are known as headlands.
Due to the rapid erosion of the softer less resistant rock, bays form between the headlands. These are sheltered areas of water.
For example durlston head and durlston bay
Formation of cave, stack and arch
Cracks at the base of a headland within the intertidal zone become exposed through hydraulic action. This is when water and air is forced into cracks and joints in the rocks causing them to exert pressure. An explosive blast then takes place which weakens and looses the rock fragments causing them to break off. This widens the crack.
Cracks are further widened by weathering processes such as salt crystallisation which is when salty sea water evaporates and leaves alt behind. Crystals can then grow which can force the rocks to break apart.
Overtime the cracks widen and develop as wave cut notches. Further processes such as abrasion can deepen the notch to form a cave (Tilly whim caves). Abrasion is when material carried in the sea is hurled at rocks by the waves causing the rocks to be broken down overtime.
As a result of wave refraction, which distorts wave direction, destructive waves concentrate their energy on the sides of the headland which deepens the cave. Wave refraction effects all 3 sides of a headland so if 2 caves are aligned, the waves may cut through to form an arch (Durdle door).
Wave cut notches widen the base of the arch.
Vertical joints are exposed through tall breakers associated with destructive waves. Joints can also be weathered from above through carbonation in limestone. Here blowholes may form.
Overtime, the arch will become unstable and will collapse under its own weight to form a pillar of rock known as a stack (Old Harry).
Erosion will continue to take place, weakening the stack until it eventually collapse and form a stump. The broken down material often gets deposited in a bay.
Formation of a wave cut notch and platform
Wave erosion is greatest when large waves break against the foot of a cliff. This happens through the process of abrasion which is when material carried in the sea is hurled at rocks by waves causing the rocks to be worn down overtime.
With wave energy at its maximum, the waves undercut the foot of the cliff to form a wave cut notch. This may be further eroded through hydraulic action which is when water and air is forced into cracks and joints in the rocks which causes them to exert pressure. An explosive blast then takes place which weakens and loosens the rock fragments causing them to break off.
Weak acids as well as salt in the water may slowly dissolve the rocks, wearing them away, through the process of corrosion.
Over a period of time the notch enlarges until the cliff above it is left unsupported and collapses under its own weight.
As this process repeats the cliff retreats.
The gently sloping expanse of the rock marking the foot of the retreating cliff is called a wave cut platform. These are exposed at low tide and covered at high tide and usually slope at an angle of less than 5°.
For example kimmeridge ledge
Longshore drift
The prevailing wind direction makes waves wash onto the beach at an angle. This is known as smash. This transports material being carried in the sea up the beach.
The waves return to the sea at a 45° angle which is known as backwash. Material is returned to the sea due to gravity. The backwash returns at right angles to the beach.
Small material will be carried the greatest distance along the beach.
Formation of a sand spit
Explain long short drift
The coastline changes shape at a bay or river estuary but LSD (long short drift) continues out beyond it depositing sand in the calmer, shallower water where the river current and waves counteract against each other.
This repeated process causes a sand spit to start building up.
Short term changes in the wind direction can cause the spit to have a hooked end. This can happen several times leading to ‘recurved laterals’.
The force of the river brining the water down to its mouth means that the spit cannot join to the other side of the estuary.
Behind the sand spit, silt carried by the river collect. This is a low energy zone do they are not washed away by the current. Plants will eventually colonise here and a salt marsh will develop.
Formation of a sand bar
Explain longshore drift
Explain formation of a sand spit
However, a sand bar can be formed if the sand spit forms at a bay as it can reach the other side as there is no strong flow of water behind it.
This encloses a sheltered area of water known as a lagoon
For example Chesil beach
Formation of a tombolo
Explain longshore drift
Explain formation of a sand spit
A tombolo is formed when a sandspit browns out from the mainland and joins onto an island.
