Coasts Flashcards
What are the two types of waves?
Constructive and Destructive
What are the features of a constructive wave?
Long wavelength Shallow gradient waves Strong swash Weak backwash Beach built up by deposition of material bought up in swash
What are the features of a destructive wave?
Tall waves with short wavelengths Steep gradient waves Weak swash Strong backwash that erodes beach Takes more than it leaves
Name the four types of coastal erosion
Hydraulic action
Abrasion
Attrition
Corrosion
What is hydraulic action?
The force of the water hitting the cliffs often forces pockets of air into cracks and crevices in a cliff face.
What it abrasion?
Abrasion 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 the waves will become rounder and smaller over time as it collides with other particles and all the edges get knocked off.
What is corrosion?
The dissolving of rocks and minerals by sea water.
How is a stump formed?
CRACKS form in cliff faces where less resistant rocks are eroded. The waves continue to erode the cliff and the material in the sea can turn the crack into a CAVE. If the cave is formed in a headland then it will eventually break through and become an ARCH. This will become bigger until it erodes through and becomes a STACK. Due to hydraulic action and corrosion this will eventually become a STUMP.
What is physical weathering?
The disintegration of rock into smaller pieces by physical processes without any chemical change in the rock.
E.G. salt crystal growth and freeze-thaw weathering
What is chemical weathering?
The decomposition of rocks caused by a chemical change within the rock.
E.G acid rain
What is biological weathering?
The action of plants and animals on the land
E.G. where burrowing animals and plant roots breakdown the rocks.
Name the main forms of mass movement
Rockfall and Slumping
What is rockfall
Rockfalls occur when fragments of rock weathered from a cliff face fall under gravity and collect at the base, it happens suddenly.
What is slumping?
It happens when the bottom of a cliff is eroded by waves. The slope becomes steeper and the cliff can slide downwards. Usually triggered by saturation due to rain, which lubricates the rock and makes it heavier.
Explain Salt crystal growth
The spray from sea water lands on rock, the water evaporates, leaving salt behind . The salt crystals grow and create stress on rock, causing it to break down into smaller fragments.
Give an example of where coastal erosion has occured
Old harry rocks - Dorset
Durdle door
What does fetch mean?
The distance the wind has blown over the sea.
How does fetch affect the coast?
Coasts that face a major ocean (e.g southwest coast, England) have a long fetch. This produces destructive waves with high energy. These waves can erode cliffs at rapid rates.
How is a wave cut platform formed?
> the waves carve wave cut notches into headlands
they get deeper until the rock above collapses
the sea carries the debris away
this leaves a wave cut platform
What is longshore drift?
Sediment is carried straight down the shore by backwash and gravity. It is then carried up the beach at an angle by the swash of another wave. This will continue down the beach.
Which direction is sediment carried in longshore drift?
The direction of the prevailing winds.
What is prevailing wind?
The main/strong wind on a particular area; the average direction of the wind.
How is a bar formed?
When longshore drift blocks off a bay. Sand is moved along the coast and eventually in goes across a bay joining the land on both ends.
How is a spit formed?
Longshore drift carries sediment down a coast. When the shape changes the sand continues in the same direction. There are weak currents and the sediment gets deposited. This extends out from the coast. This is called a spit.
What is a tombolo?
A ridge of sand and shingle (spit) that joins an island to the mainland.
What is a lagoon?
The stretch of water left behind when a spit travels across a bay.
What does geology mean?
The study of the Earth - it’s composition (rock types), structure and dynamic processes.
What is coastal management?
Decisions about coastal flooding and defense and about governing the coastal areas.
What happened in Durlston Bay?
Cliff recede 12 meters in 20 years (1968-1988)
Only 25 meters away from apartment block -Purbeck Heights
in 2000/01 heavy storms regraded another 12 meters. Apartment block now at severe risk
How does coastal flooding affects London?
Thames barrier protects 400,000 properties(completed in 1983)
Although Thames barrier already in place the Environment Agency proposed a new plan - Thames estuary - a new series of flood walls along the river
How does coastal flooding affect Bangladesh?
COASTAL EMBANKMENT PROJECT
Building many flood walls. 500 flood shelters. Flood warning systems put in place. New laws are in place (about tall buildings) and education about floods is being improved.
Explain an example of where coastal management is being used.
OVERSTRAND - NORFOLK
Spent 1.75 million on sea defenses
>groynes,rip-rap,revetments,sea wall,gabions
>cliff regrading,bore pipes, tree planting(absorb moisture)
What are groynes?
Wooden, rock or concrete ‘fences’ built across a beach, perpendicular to the coastline.
What are the advantages of groynes?
> prevent longshore drift
>the beach can build up as a natural defnese
What are the disadvantages of groynes?
> may look ugly
do not last - wood rots
sand is prevented from moving down the coast
What is a sea wall (and curved sea wall)?
A long concrete (curved) barrier built at the base of a cliff.
What are the advantages of a sea wall?
> protects the base of the cliff (from erosion)
land and buildings are protected
(CURVED) - can reflect wave energy
What are the disadvantages of a sea wall?
> expensive to build
maintenance cost is high
restricts access to the beach
What are revetments?
Slatted wooden or concrete structures built at the base of a cliff
What are the advantages of revetments?
> absorb and spread wave energy
>do not interfere with longshore drift
What are the disadvantages of revetments?
> regular maintenance is required
>quite expensive to install
What is hard-engineering?
Hard Engineering- man-made materials which stick out from an area e.g. offshore barrier
What is soft engineering?
Soft Engineering- using ecological methods to defend e.g. Vegetate the slope- buffers the wave, absorbs water and energy.
What are gabions?
Gabions are metal cages filled with rocks. They are stacked to form a simple wall.
What are the advantages of gabions?
> easy to use
>relatively cheap
What are the disadvantages of gabions?
> short term only - easily damaged by powerful storm waves
cages tend rust quite quickly
life span is short
What are borepipes?
Pipes put in the cliffs to help drain water and avoid slumping.
What is rip-rap (rock armor)
Large boulders of resistant rock.
What are the advantages of rip-rap?
> absorb wave energy
protect weak cliffs
look quite natural
What are the disadvantages of rip-rap?
> can be expensive
let some wave energy through
can restrict access fro the very young and elderly
What is beach replenishment?
Adding sand taken from somewhere else, often offshore.
What are the advantages of beach replenishment?
> looks natural
provides beach for tourists
absorbs wave energy
quite cheap
What are the disadvantages of beach replenishment?
> sea keeps on eroding it away
>has to be replaced every few years
What is breakwater/offshore reef?
Rock or concrete barriers built on the sea bed a short distance from the coastline.
What are the advantages of breakwater?
> waves break on the barrier before reaching coast
significantly reduces wave energy
allows a wide beach to develop
What are the disadvantages of breakwater?
> very expensive to build
>can interfere with movements of boats
What is managed retreat?
People and activities are gradually moved back from the affected areas of coast.
What are the advantages of managed retreat?
> natural processes are allowed to happen
>no threat to human safety
What are the disadvantages of managed retreat?
> compensation has to be paid
>quite a lot of disruption to people’s lives and businesses
What is cliff regrading?
Making the cliff face longer, so that it is less steep.
What are the advantages of cliff regrading?
> angle of the cliff is reduced - mass movement less likely
>relatively cheap
What are the disadvantages of cliff regrading?
> other methods needs to be used to stop it steepening
>properties may have to be demolished
