attrition
coasts
material carried by the sea hit against each other causing them to get smaller and smoother
abrasion
coasts
material carried along by the sea is hurled at the cliffs causing them to be worn down
hydraulic action
coasts
water is compressed into cracks in the rocks causing them to exert pressure on the surrounding rock which weakens and loosens rock fragments causing them to break off
corrosion
coasts
weak carbonic acids as well as salts in the water can cause weathering thus slowly dissolving rocks along the coast
salt crystalisation
coasts
when salty sea water evapourates salt can be left behind, salt can then grow which can force the rocks to break apart.
factors which impact erosion rates
coasts
- rock resistance
- degree of jointing
- the angle dip of the bedding planes
- waves
- weather
concordant coastline
- rock types are parallel to the coastline
- can result in a cove forming
disconcordant coastline
- rock types perpendicular to the coastline
- can result in headlands and bays
headlands and bays
formation
- soft rock eroded faster by waves approaching shore by the processes of abrasion, hydraulic action, and corrosion
- hard rock left sticking out into sea (known as headland) as it is more resistant to erosion
- area between the headlands (known as bays) is sheltered - formed due to rapid erosion of soft rock
cave / arch / stack
formation
- cracks at the base of a headland become exposed to hydraulic action
- cracks are further widened by salt crystalisation
- over time the cracks widen and develop wave cut notches which are further deepened to form a cave through abrasion
- due to wave refraction, waves concentrate their energy on the sides of the headland which deepens the caves
- if two caves align the waves cut through to form an arch
- vertical joints in the rock are exposed to weathering from above which can produce blowholes
- further erosion widens the arch and over time the arch becomes unstable and collapses into the water to form a stack
e.g. Old Harry and Durdle Door
wave cut notch and platform
formation
- wave erosion is greatest at base of the cliff through the process of abrasion
- the wave undercuts the foot of the cliff to form a wave cut notch through the process of hydraulic action
- over a period of time the notch enlarges until the cliff is unsupported and collapses
- as this process repeats the cliff retreats
- the gently sloping expanse of rock marking the foot of the retreating cliff is known as a wave-cut platform which slopes at an angle less than 5˚
e.g. kimmeridge ledges
longshore drift
transportation
- prevailing wind makes waves wash onto the beach at an angle - swash - transporting material up the beach
- the waves return to the sea - backwash - perpendicular to the beach
- small material will be carried furthest
sand spit
formation
- prevailing wind powers longshore drift which carries material along the coastline
- due to the coastline changing shape LSD continues out beyond the headland, depositing sand in the calmer areas of water causing a sand spit to build up slowly until it appears above the water
- formation of the spit continues as long as the deposition is greater than the erosion
- short term changes in wind direction causes the end of the spit to hook round and can result in recurved laterals
- the force of the river bringing water into the sea means the spit cannot join the other side
- silts in the river collect behind the spit to form a salt marsh
e.g. poole harbour
sand bar
formation
- formation of a sand spit
- the spit grows across the gap between two headlands to form a sand bar with a lagoon behind it
e.g. chesil beach
tombolo
formation
- formation of a sand spit
- the spit grows across the gap between a headland and an island to form a tombolo
e.g. chesil beach
