Coasts Flashcards
Types of erosion
- corrasion / abrasion
- hydraulic action
- cavitation
- wave quarrying
- solution / corrosion
- attrition
Definition : corrasion (abrasion)
- type of erosion
Bits of rock and sediment transported by waves that smash and grind against other rocks and cliffs becoming smoother
Definition : Hydraulic action
- type of erosion
Air in the cracks on a cliff is compressed from waves crash against it, the pressure breaks apart the rock
Definition: cavitation
- type of erosion
As waves recede from the cliff the compressed air largely expands exerting more pressure and causing rock to break
Definition: wave quarrying
- type of erosion
Energy of the waves against a cliff breaks away the rock
Definition: solution/corrosion
- type of erosion and transportation
Soluble rock (limestone or chalk) dissolved by seawater
Definition: attrition
- type of erosion
Rocks in the water smashed against each other and become smaller
Definition: suspension
- Type of transportation
Very fine material is carried in the water
Definition: saltation
- Type of transportation
Larger particles transported by the force of the water causing them to bounce along the seabed
Definition: traction
- Type of transportation
Very large particles such as boulders are pushed along the sea bed
Types of transportation
- Solution
- saltation
- traction
- suspension
How do groynes (hard engineering) work
- fences built at right angles to the coast
- trap beach material transported by longshore drift
- creates wider beaches which reduces the waves energy preventing erosion
Evaluation of groynes (hard engineering)
+ relatively cheap
+ low maintenance
Last around 10-25 years
- unnatural and can be unattractive
- only work on the part of the beach they are covering, can increase erosion in other parts of the beach
How do sea walls (hard engineering) work
- reflect waves back into the sea to prevent erosion of the coast
- can act as a barrier to prevent flooding
Evaluation of sea walls (hard engineering)
+ 30-50 years
+ effective in preventing erosion
- expensive to build and maintain
- can create a strong backwash which erodes under the wall
- can be intrusive on a beach
How does rip rap (hard engineering) work
- boulders piled up along the coast
- absorb wave energy and prevent beach erosion
Evaluation of rip rap (hard engineering)
+ fairly cheap
+ easy to maintain
- can shift in storms
- can lookout of place with local geology
- can be a danger to public with children climbing across them
How do revetments (hard engineering) work
- slanting structures built at the bottom of a cliff
- break up waves and absorb their energy which prevents cliff erosion
Evaluation of revetments (hard engineering)
+ cheap to maintain
+ effective and quick
+ last 30-50 years
- can create a strong backwash which can erode under the wall
- intrusive and unnatural
- expensive to build
How does offshore breakwater (hard engineering) work
- Concrete blocks or boulders deposited off the coast
- Force waves to break offshore
- Waves energy and erosive power are reduced before they reach the beach
Evaluation of offshore breakwaters (hard engineering)
+ Keep the beach natural
+ Last between 30 and 50 years
+ Effective in reducing erosion
- Can be damaged in storms
- Yearly maintenance and inspection required
How do gabions (hard engineering) work
- rock filled cages
- A wall is usually built at the foot of cliffs
- Absorb wave energy
Evaluation of gabions (hard engineering)
+ Cheap
+ Last between 10 and 75 years
+ Strong, stable and good for drainage
- Unnatural
- Annually inspection required
How do barrages (hard engineering) work
- A dam built to increase the depth of the water
- Controlled release of the water through turbines
- Prevents flooding and generates electricity
Evaluation of garages (hard engineering)
+ Last up to 100 years
+ Nearly 100% effective
- Very expensive
- Very man-made could possibly be an eyesore
- Can disrupt sediment flow, which may cause increased erosion elsewhere
Definition : weathering
The breakdown of rocks in situ (where it is originally found / lands on the cliff)
Definition : sub aerial processes
Land based processes which alter the shape of the coastline, combination of weathering and mass movement
Biological weathering
- break up of rocks by organic activity
- thin plant roots grow in small cracks in the cliff face
- as the plant grows the cracks widen causing rock to break off
- water running through any decaying vegetation in rocks becomes acidic causing chemical weathering
- birds and animals dig burrows into cliffs breaking off rock
Mechanical weathering
Freeze thaw : water enters the cracks in the rocks and freezes which expands the crack, process repeats until the rock eventually breaks
Salt crystallisation : when salt water evaporates it leaves behind crystals which expands over time in the cracks of the rock causes pieces to break off
Wetting and drying : rocks rich in clay expand when they are wet and contract when they are dry, this causes them to crack and break
Chemical weathering
Carbonation : carbon dioxide in the atmosphere dissolves in rainwater forming a weak carbonic acid, the acid rain reacts with rocks causing them to rock
Oxidation : reaction of oxygen with rock minerals e.g. iron reacts with o2 leaving the rock vulnerable to break
Solution : dissolving of rock minerals
Definition : mass movement
Downhill movement of material under the influence of gravity
Soil creep (mass movement)
- Movement of individual particles downhill
- extremely slow process
- cannot be seen but may be shown by a build up of particles near a tree or building
Mudflows (mass movement)
- earth and mud flowing downhill over weak bedrock
- quite rapid
Landslide (mass movement)
- block of rock moving down the side of a cliff
- triggered by earthquakes or heavy rainfall
Rockfall (mass movement)
- collapse or breaking away of rock fragments at a cliffs face
- triggered by mechanical weathering or earthquakes
- sediment at the bottom of the cliff is gradually removed by the sea
Landslip or slump (mass movement)
- movement of material on a cliff where the slide surface is curved
- occurs on weak clays or sand
Run off (mass movement)
- when overland flow occurs down a slope of cliff face small particles are moved to the coastline
Solifluction (mass movement)
- similar to soil creep but specific to cold environments
- in summer the surface layer of soil thaws out and becomes saturated
- the sodden soil and vegetation is moved slowly downhill
How does beach nourishment (soft engineering) work
Addition of sand and pebbles to a beach to make it higher protecting it from wave erosion
Evaluation of beach nourishment
+ natural beach
+ relatively cheap
+ increases tourism
- constant maintenance due to natural processes
- only lasts 2-10 years
- does not end erosion
How does cliff regrading / drainage (soft engineering) work
- reduces the angle of the cliff to stabilise it
Evaluation of cliff regrading and drainage (soft engineering)
+ can be effective where other methods don’t work e.g. On loose rock
+ cost effective
+ natural
- can dry out and lead to collapse
How does dune stabilisation (soft engineering) work
Marram grass can be planted to stabilise the dunes or areas can be fenced off
Evaluation of dune stabilisation (soft engineering)
+ natural environment
+ provides habitats
+ cheap and sustainable
- time consuming
- people may respond negatively to areas being shut off
- may need to constantly replant
How does land use management (soft engineering) work
- important for dune management
- wooden pathways may be by built to stop cyclists or the public walking on dunes
Evaluation of land use management (soft engineering)
+ can be cheap depending on size and structure
+ can fit in with the areas
- only lasts 3 to 5 years
- can destroy the land underneath
How does managed retreat (soft engineering) work
- allow low lying coastal areas to be flooded by the sea
Evaluation of managed retreat (soft engineering)
+ relatively cheap (depends on area)
+ land reverts back to original state
+ creates habitats
- agricultural land is lost
- farmers or landowners need to be compensated
