Coasts Flashcards
What is the Coast?
the boundary between the land and the sea
it is a dynamic region- constantly changing
the major agent of change are waves
What is a wave?
a movement of energy
What are waves a result of?
friction caused by the wind blowing over the sea
as they approach the land they break
How does a wave ‘break’?
the bottom of the wave touches the sand and slows down due to increased friction
the top of the wave continues at the same pace becoming higher and steeper until it topples over
What does wave energy depend on?
the fetch
the strength of the wind
the length of time over which the wind has blown
What is fetch?
the distance the wind has blown over the sea
What is swash?
the push of a wave up the coast in the direction of the wind
What is backwash?
the pulling back of a wave which is always at right angles to the beach because of gravity pulling it back
What are constructive waves?
- waves with a strong swash
- have a weak backwash
- land on the coast shallowly
- are created by winds with a short fetch
- they are responsible for deposition of material on coast
- create beaches of sand or shingle
What are destructive waves?
- waves with a strong backwash
- have a weak swash
- land on the coast steeply
- are created by winds with a long fetch
- they are responsible for erosion of material away from coast
- create bare, rocky coastlines
What are the differences between constructive and destructive waves in terms of these several features: height, energy, frequency, amount of swash to backwash and the process carried out?
Constructive: H: low (less than 1 m) E: low F: low (fewer than 10 per minute) S:B: swash>backwash P: deposition
Destructive: H: high (more than 1 m) E: high F: high (more than 10 per minute) S:B: backwash>swash P: erosion
What is cliff foot erosion?
erosion caused by the sea at the base of the cliff
What are the 4 types of wave erosion?
1 hydraulic action
2 abrasion
3 attrition
4 corrosion
What is hydraulic action?
this results from the force of water hitting the cliffs, often forcing pockets of air into cracks and crevices in a cliff face
What is abrasion?
this is caused by the waves picking up stones and hurling them at the cliffs and so wearing the cliff away
What is attrition?
any material carried by waves will become rounder and smaller over time as it collides with other particles and all the sharp edges get knocked off
What is corrosion?
the dissolving of rocks and minerals by sea water
What is weathering?
the breaking down of solid rock in situ (without the rock moving)
What is physical weathering?
the disintegration of rock into smaller pieces by physical processes, without any change in the chemical composition of the rock
What are 2 examples of physical weathering and how do they work?
Salt crystal growth:
- sea water contains salt
- when spray from waves land on rocks, the water can evaporate leaving the salt behind
- the salt crystals grow, creating stresses in the rock which causes it to break down into small fragments
Freeze thaw:
- water goes into cracks and freezes
- this causes the ice to expand (by 9%)
- this weakens the rock and widens the crack until it breaks apart
What is chemical weathering?
the decomposition of rocks caused by chemical change within the rock
What is an example of chemical weathering and how does it work?
Acid rain:
- all rain is slightly acidic
- if the air is polluted, it can be very acidic
- when rain falls on the rocks, the acid in it can react with weak minerals
- this causes them to dissolve and the rock to decay
What is biological weathering?
the action of plants and animals on the land
What are 2 examples of biological weathering and how do they work?
Plant roots and Burrowing:
- the roots of vegetation can grow into cracks in a rock and split it apart
- animals (such as rabbits) also burrow into the earth
What are 3 examples of mass movement?
1 rock fall
2 slumping
3 soil creep
What is rock fall and how does it work?
- one of the most sudden forms of mass movement
- rock fall occurs when fragments of rock weathered from a cliff face fall under gravity and collect at the base
What is slumping and how does it work?
- often happens when the bottom of a cliff is eroded by waves
- this makes the slope steeper and the cliff can slide downwards in a rotational manner
- it is often triggered by saturation due to rain which lubricates the rock to move more easily
What is soil creep and how does it work?
- the freeze lifts particles of soil and rocks and when there is a thaw, the particles are set back down but not in the same place as before
- gravity always causes the rocks and soil to settle just a little further down slope than where they started from
- it is this slow movement that defines the creep
What is a wave cut platform?
an area of flat rock at the base of a cliff caused by the erosion of cliffs
How is a wave cut platform formed?
1 the waves carve wave-cut notches into cliffs at a headland and they get deeper and deeper…
2 …until one day the rock above them collapses and the sea carries the debris away…
3 …the process slowly continues non-stop, causing the cliffs to retreat, leaving a wave-cut platform behind
How are headlands and bays formed?
- the coast consists of various types of rock which are intermingles together
- these all have a different resistance to erosion
- rocks with a higher resistance to erosion (e.g. chalk and limestone), erode more slowly than those with a low resistance to erosion (e.g. clay) which causes them to create headlands where the other rock has eroded into a bay
What is an example of a bay?
Swanage Bay on the Dorset coastline
What are the 5 stages of coastal erosion?
1 crack 2 cave 3 arch 4 stack 5 stump
What is an example of an area of coastline which has gone through coastal erosion formations (CCASS)?
Old Harry Rocks,
Durdle Door,
Swanage, Dorset
Explain how the cliff formation of Old Harry Rocks was formed: (how it happens in general)
- Durdle door is made from portland limestone which is very resistant to erosion
- rocks such as clay however are not and therefore erode into a bay whereas the limestone is left as a headland
- a crack is eroded by hydraulic action and widens to form a cave
- this continues to get eroded and weathered until it erodes through to the other side, forming an arch
- soon the arch can’t support the top so it collapses leaving a stump with a smaller headland
- the waves continue to weaken the base of the limestone which makes the structure weaker until the top falls into the sea leaving a stump
What is longshore drift?
the process by which beach sediment can be transported along the coast by waves
What is longshore drift influenced by?
prevailing wind (direction wind blows from most of the time) this is due to the fact that the swash will mostly move in the direction of this wind over the year
How does longshore drift work?
- sediment is carried down the beach by the backwash and gravity
- this sediment is then carried back up the beach at an angle by the swash of the next wave
- it carries on in this zigzag and moves across the coast
What is a spit?
- a long, narrow strip of sand that extends from the land to the sea
- built up by longshore drift transporting material along the coast
How is a spit formed?
- sand and pebbles are moved along the coast by longshore drift
- when the coastline changes shape, the sand continues to be moved in the same direction
- due to weak currents, the sand is deposited and builds up
- the sand eventually extends out from the coast in a thin strip called a spit
- the end of the spit can get curved (hook) which happens due to changes in wind direction or the action of the waves
What is an example of a spit?
Spurn point/head,
East Yorkshire
What is a bar?
- formed when longshore drift blocks off a bay
- sand is moved along the coast, eventually going right across a bay to join the land at both ends
What is an example of a bar?
Slapton,
Devon
What is a tombolo?
a ridge of sand and shingle which joins an island to the mainland
What is an example of a tombolo?
Chesil beach/bank,
Dorset
What is geology?
the study of the Earth- its composition, structure and dynamic processes
What is coastal management?
the decision-making procedures governing the coastal area, which include decisions about coastal flooding and defense
Explain the case study of coastal recession in Durlston Bay, Swanage (Purbeck Heights):
- What?
- Effects?
- Coastal management?
- cliff receded by 12m 1968-1988, ended up only 25m from PH, 2000/1 severe storms and high energy waves led to a further retreat of 12m
- put properties at risk and habitats were threatened of nesting birds in the cliff (over 250 species)
- regraded cliff, installed drainage, placed rip rap (granite, 8 tonnes), built sea wall (1920s), added groynes (1930s but many replacements-wood) and beach replenishment (90,000m3 of sand dredged from studland bay and pumped onto swanage beach)
- expensive: £2.2 million spent on new coastal management adding to old
What is the prediction for rising sea levels?
rise by 1 m by 2100 due to global climate change which will put low-lying areas of coastland at risk
What are examples of areas of low-lying coastland?
Bangladesh
the Netherlands
the Maldives
eastern England (e.g. the Thames estuary)
How has London prepared for coastal flooding?
- London Thames Barrier: protects over 400,000 properties, completed 1983, used 10-15 times per year, if it was built today it would be £530 million, use is increasing due to more risk
- also plans for new flood walls and open spaces to prevent damage
- The Environment Agency creates projects to help prevent flooding: also monitor sea conditions 24 hours a day, providing forecasts, warnings and advice to their helplines
What affects coastal flooding?
tides
heavy rains
What are the flooding risks?
- drowning
- injuries caused by accidents in flowing water
- stress and strain of event and clean up - hazards
- danger of carbon monoxide fumes from indoor fuel powered appliances
What is the Coastal Embankment Project in Bangladesh?
- built many flood walls, 500 shelters (however 10,000 are needed)
- people are more knowledgeable and educated about floods and what to do
- warning systems put in place
- 1997: flood warning in Cox’s Bazaar area allowed 300,000 people to evacuate
- the roof of any building must be accessible by stairway
What are the 2 main methods of coastal management?
- Hard engineering: more intrusive methods including concrete sea walls and groynes
- Soft engineering: considered more environmentally friendly and include strategies such as managed retreat
What are groynes (how they work)?
- what type of engineering are they?
- what are the advantages and disadvantages?
- wooden, rock or concrete fences built across the beach, perpendicular to the coastline
- Hard
- A: prevent movement by longshore drift of sediment, beach can build up as natural defense against erosion which also creates an attraction for tourists
- D: look ugly, if wood then they don’t last long due to rotting, the lack of LSD affects other areas of coastline
What are sea walls (how they work)?
- what type of engineering are they?
- what are the advantages and disadvantages?
- a long concrete barrier built at the base of the cliff which can be straight or curved, curved helps reflect wave energy better
- Hard
- A: protects base of cliffs from erosion by absorbing and reflecting waves energy, land and buildings behind are protected
- D: expensive to build and cost of maintenance is high, restricts access to the beach and can look ugly, becomes damaged at the bottoms
What are revetments (how they work)?
- what type of engineering are they?
- what are the advantages and disadvantages?
- slatted wooden or concrete structures built at the base of cliffs reducing wave energy, also allowing sediment to pass through to build up beach
- Hard
- A: absorbs and spreads wave energy through slats, don’t interfere with longshore drift, cheaper than sea wall
- D: regular maintenance required, quite expensive installation cost over time as they need replacement
What are gabions (how they work)?
- what type of engineering are they?
- what are the advantages and disadvantages?
- cages filled with more resistant rock which hold up the cliff, stopping landslides and stops water getting to cliff
- Hard
- A: buried by sand and vegetation, absorbs wave energy, cheaper than other alternatives, stops slumping
- D: needs replacing, don’t last very long, not nice to look at
What are bore pipes (how they work)?
- what type of engineering are they?
- what are the advantages and disadvantages?
- pipes embedded in the cliff which drains out water preventing slumping
- Hard/Soft
- A: drainage prevents mass movement, takes water out of the cliff, hidden
- D: can get blocked by debris, water isn’t collected or re-used
What are rip rap rocks (how they work)?
- what type of engineering are they?
- what are the advantages and disadvantages?
- large boulders of water erosion-resistant rock deposited at base of cliff
- Hard
- A: absorb wave energy, protect weak cliffs behind, look quite natural
- D: can be expensive (imported from Norway), still let some wave energy through, can restrict access to beach especially for the very young and elderly
What is beach replenishment (how it works)?
- what type of engineering is it?
- what are the advantages and disadvantages?
- adding sand taken from somewhere else to the beach, often from offshore
- Soft
- A: looks completely natural, provides beach for tourists, beach absorbs wave energy protecting land and buildings behind, quite cheap
- D: sea keeps eroding it away so it needs replacing every few years
What are breakwater/offshore reefs (how they work)?
- what type of engineering are they?
- what are the advantages and disadvantages?
- rock or concrete barriers for the waves to break on
- Hard
- A: waves break on barrier, significantly reduced wave energy
- D: very expensive to build, interfere with boats and the harbour
What is managed retreat (how it works)?
- what type of engineering is it?
- what are the advantages and disadvantages?
- people and activities are gradually moved back from the vulnerable areas of coastline- sacrifice some areas to protect others
- Soft
- A: natural processes are allowed to happen, no threat to human safety
- D: compensation has to be paid, quite a lot of disruption to peoples lives and businesses
What is cliff regrading (how it works)?
- what type of engineering is it?
- what are the advantages and disadvantages?
- making the cliff face longer so that it is less steep
- Soft
- A: angle of the cliff is reduced making mass movement less likely, relatively cheap method
- D: other methods need to used at the base of the cliff to stop it from being steepened again by erosion, properties on the cliff may have to be demolished
Explain the case study at Happisburgh, Norfolk:
- North East
- shifting coastline
- 12m/40ft a year lost due to erosion and weathering (sometimes 3x amount)
- houses only worth £1 near coast
- coastal management used…
- revetments (completed 1960), groynes, offshore reef, sea wall (protecting farmland), managed retreat
26 houses already lost
MAIN CASE STUDY OF CLIFF RETREAT)
Explain the case study of Overstrand, Norfolk including causes, effects and engineering used:
Causes:
- lose glacial non-resistant rock leading to slumping
- strong waves from North Sea attack foot of cliff causing a cut notch (hydraulic action and abrasion)
- LSD takes away material from the foot of the cliff and sea wall, leaving the cliff vulnerable to slumping and landslides
- heavy rains lead to a saturation of soil/rock leading to slumping
- building on the cliff adds extra weight to the cliff, destabilising it
- walking on cliff top by many tourists causes erosion
Effects:
- a hotel and several houses fell over the edge of the cliff
- access to the beach cut off by material continually slumping onto the service road
- area becomes unsafe for tourists e.g. cliff top paths eroded away
- 1.1.1994, 100m of cliff slid over the edge
- sea defenses such as revetments are destroyed and need rebuilding
- extra money invested by the Norfolk council to stabilize the area and build new sea defenses
- Overstrand becomes an experimental area for sea defenses both hard and soft
- £1.75 MILLION SPENT
Engineering:
- Hard: sea walls, groynes, revetments, rip rap, gabions
- Soft: beach replenishment, managed retreat, cliff regrading, (tree planting)
