Coasts Flashcards
Why are coral reefs important?
- protect coastlines from storms & erosion
- provide jobs for local communities
- source food
- source of new medicines
What are the 3 depositional landforms?
- sand dunes
- bars
- tombolos
What are beaches made up of?
Eroded material that has been transported from elsewhere and deposited by the sea.
Which type of waves build up beaches?
Constructive
What is the cross-section of a beach called?
Beach profile
What are berms?
Shingle ridges often found towards the back of the beach.
Where is the smallest material deposited?
Near the water
Where is the larger material deposited?
At the back of the beach in times of high energy, e.g. a storm
What type of profiles do sandy beaches have?
Gently sloping
What type of profiles do shingle and pebble beaches have?
Steeper
How is a spit formed?
- Long-shore drift transports sediment to the beach in the direction of prevailing wind & back perpendicular, starting to create a spit on the corner of the beach. There is a change in the shape of the coastline.
- A salt marsh starts to occur behind the spit due to deposition & not much wave energy. Deposition keeps happening & spit grows.
- Spit continues to get longer & salt marsh gets bigger.
What is a spit?
A narrow finger of sand or shingle jutting out into the sea from land.
How does a bar form?
- Long-shore drift transports sediment to the beach in the direction of prevailing wind & back perpendicular, starting to create a spit on the corner of the beach. There is a change in the shape of the coastline.
- A salt marsh starts to occur behind the spit due to deposition & not much wave energy. Deposition keeps happening & spit grows.
- Spit continues to get longer & salt marsh gets bigger, attaching 2 headlands together.
- A lagoon forms behind the bar.
How are sand dunes formed?
- Grow when dry sand is blown off the beach in a shore ward direction
- Sand moves until it meets a slight obstruction (e.g. clump of grass) - causes sand grains to drop.
- A slight mound is created.
- Plants will colonise the land & stabilise it, allowing the mound to grow.
- Wind moves sand top the top of the pile & it continues to grow.
What does SWOP stand for?
Sand
Wind
Obstacle
Plant
What does a sand dune need to form?
- lots of sand
- consistent, shore ward wind
- vegetation to help sand accumulate
What are the different types of sand dunes?
- embryo/fore dunes
- yellow dunes
- grey dunes
- dune slacks
- mature dunes
What is an embryo/fore dune like?
- reach up to 5m
- very alkaline soil, salty & lacks humus
What is humus?
fertile soil
What are yellow dunes like?
- 5-10m high
- more favourable conditions for plant growth (more shelter & nutrients, less salt spray)
What are grey dunes like?
- 50-100m from sea
- more stable due to more diversity of plants
- much less salty, more stable conditions
- humus begins to darken surface layers, a true soil begins to form
What are dune slacks like?
- permanent/seasonal water logging & surface water exists
- depressions with strips of water - slacks
What are mature dunes like?
- found several hundred metres from shore
What plant/animal species live in embryo/fore dunes?
- marram grass grows here since its halophytic (salt tolerant)
- stabilise new dunes with networks of root systems & trap the sand
What plant/animal species live in yellow dunes?
- vegetation - greater biodiversity, marram grass still dominates
- animals - rabbits/other mammals, droppings enrich developing soil
What plant/animal species live in grey dunes?
- vegetation cover may reach 100% - marram grass less common
- rabbits & others add their droppings to help enrich developing soil
What plant/animal species live in dune slacks?
- well adapted plants to the damp, sheltered hollows e.g. creeping willow
- fresher water allows animals e.g. hatterjack toad
What plant/animal species live in mature dunes?
- soil can support shrubs & trees
- home to larger animals that need more substantial shelter e.g. red squirrel
What is deposition?
When the sea loses energy, it drops the material is has been carrying.
What factors lead to deposition?
- waves slowing down & losing energy
- shallow water
- sheltered areas e.g. bays
- little or no wind
What conditions are needed for mangroves to form?
- water above 24°C during warmer months
- at least 1250mm rainfall per year
- sheltered, calm waters e.g. river deltas
- plants are halophytic - adapted to survive in salt & fresh water
Why are mangroves important?
- coastal protection - absorbs wave energy from tropical storms & tsunamis
- many young fish species use roots as they are too tightly packed for predators
- humans use their waters for farming prawns & oysters
- they absorb large amounts of carbon dioxide & give off oxygen during photosynthesis
What are the threats to mangroves?
- sea levels rise
- developments (e.g. building hotels)
- deforestation
Where are coral reefs found?
- tropical & subtropical waters
- 30°North & South
- mainly found in the Red Sea, Indian Ocean & Great Barrier Reef
What are the 3 types of coral reefs?
Fringing reef
Barrier reef
Atoll reef
What are fringing reefs?
Coral platforms grow out to sea attached to the mainland/island. A shallow lagoon lies above them.
What are barrier reefs?
Coral grows in a shallower area away from the mainland. The water between is too deep for coral to grow so forms a lagoon. These reefs form offshore barriers along coastlines (e.g. Great Barrier Reef).
What are atoll reefs?
Develop around islands. Grow in a circle around the island. Sea level rise or subsidence of the land causes the coral to grow at the height of rising sea level to reach the light. Eventually this forms a ring of coral reefs with a lagoon replacing the island in the middle
What conditions are needed for coral reefs to grow?
- warm water (18-27°C)
- shallow water, no more than 60m deep - enables sunlight to penetrate water so coral can photosynthesise
- water must be free from sediment & clear for coral to form
- plentiful supply of oxygen in water
- calm water - if waves are too large coral can’t form
How have mangroves adapted?
- waxy leaves - keeps water from being lost
- leaves have adapted glands that secrete the salt they take in
- can survive in salt water habitats & freshwater
What is weathering?
the breakdown of material
What are the 3 types of weathering?
physical
biological
chemical
What is an example of physical weathering?
FREEZE THAW
- water collects in rock crack
- water freezes & expands forcing crack to widen
- Ice thaws, contracts & water gets deeper into cracks again
- repeated expansion & contraction causes further cracks until rock splits
What is an example of biological weathering?
- trees put down roots through joints or cracks in the cliff in order to find moisture
- as tree grows, roots gradually prize cliff apart
OR
-animals burrowing
What is an example of chemical weathering?
-rainfall is very weakly acidic
- over time it starts to dissolve minerals within some soft rocks
What is erosion?
break down & removal of material
What is abrasion/corrosion?
sediment hits cliff
What is hydraulic action?
waves hit cliffs
What is solution?
rocks dissolve
What is attrition?
sediment hits sediment
What is differential rates of erosion?
when coasts erode at different speeds
Why does differential rates of erosion happen?
- difference is strength of the waves
- how sheltered/exposed the coast is
- how hard/soft the rock is
What are discordant coasts?
alternating layers of hard & soft rock
How are wave cut platforms formed?
- sea attacks base of cliff between high & low water mark
- wave-cut notch (dent in cliff at level of high-tide) is formed by abrasion & hydraulic action
- as notch increases in size, cliff becomes unstable & collapses - leading to retreat of cliff face
- backwash carries away eroded material leaving a wave cut platform
- process repeats & cliff continues to retreat
What is an erosional landform?
a feature of the land created through erosional processes
How are stumps formed?
- joint/fault in resistant rock
- abrasion & hydraulic action widen joint to form a cave
- waves make cave larger until it cuts through headland to make an arch
- arch is eroded & roof becomes too heavy & collapses
- leaving a tall stack
- stack is eroded & collapses leaving a stump
What is the coast?
the part of the land adjoining or near the ocean
What is the crest of a wave?
top of the wave
What is the trough of a wave?
bottom of the wave
What is the wave length of a wave?
distance between 2 successive crests/troughs
What is the wave height/amplitude of a wave?
distance between the trough and a crest
What is the swash of a wave?
movement of water up the beach
What is the backwash of a wave?
movement of water down the beach
What is the wave frequency of a wave?
time between 2 crests
How is a wave formed?
- waves start out at sea & have a circular orbit
- as waves approach shore, friction slows base of the wave
- this causes the wave to become elliptical
- until the top of the wave breaks over
- the sea bed is rough & acts as a source of friction
- water swashes up the beach
- water from a previous wave returns to the sea as backwash
What factors affect wave strength?
- strength of the wind
- length of time the wind blows
- distance of sea over which the wind has blown (fetch)
- direction the wind is blowing
What are the characteristics of constructive waves?
- created in calm weather
- has a strong swash & weak backwash
- deposit material, building up the beach
- low & long
- have travelled over a short fetch
- arrive at <10 per minute
What are the characteristics of constructive waves?
- created in storm conditions
- has a weak swash & strong backwash
- erode the coast
- tall & steep
- have travelled over a long fetch
- arrive at >10 per minute
What are the types of soft engineering?
- sand dune regeneration
- beach nourishment
What are the types of hard engineering?
- groynes
- gabions
- wooden revetment
- recurved sea wall
- rock armour/rip-rap
How does sand dune regeneration work?
- plant grasses, bushes & trees to stabilise dunes & maintain their natural protection
- reservoir of sand held in planted foredunes will provide a buffer to resist storm erosion
What are the advantages of sand dune regeneration?
- helps to maintain the ecosystem of the area while offering protection
- creates new sand dunes along coast to act as a buffer between the land & the sea
- helps protect these systems that protect our coastlines & absorb storm & wave energy
What are the disadvantages of sand dune regeneration?
- time consuming to plant the marram grass & fence off areas
- less effective than hard engineering schemes
- needs regular maintenance
- shifting nature of defences
- less likely to be effective against extreme storm events
How do groynes work?
wooden/steel structures that stop LSD & build up/anchor the beach, protecting the base of the cliff
What are the advantages of groynes?
- stops LSD so encourages the build-up of the beach & effectively reduces erosion
- beaches are natural defence against erosion & an attraction for tourists
-less beach nourishment needed
What are the disadvantages of groynes?
- can increase erosion further down the coast by stopping LSD & starving areas further down the coast of sediment
- unattractive
- expensive to build & maintain
- likely to cause down drift erosion since they trap too much sediment if beach isn’t managed
How does beach nourishment work?
build up beach by replenishing beach material at base of structures to provide a natural solution to absorbing wave energy
What are the advantages of beach nourishment?
- provides natural & prettier solution
- retains natural beauty & processes of beach - recreational value of beach enhanced
What are the disadvantages of beach nourishment?
- can be expensive to keep transporting large amounts of sand
- sediment moves by LSD so will need frequent replenishment
- requires constant maintenance
- costly & time consuming
How do gabions work?
cages of boulders built into cliff face - small rocks help absorb wave energy
What are the advantages of gabions?
- effective where there is severe erosion
- cheaper than sea walls
- permeable face absorbs wave energy
- encourages upper beach stability
What are the disadvantages of gabions?
- environmentally ugly
- shorter life span than sea wall
- visually ugly
- 5-10 year lifespan leading to hazardous wire baskets along beach
- release of non-indigenous cobbles to beach
- wire affected by salt water, vandalism & abrasion by trampling
How do wooden revetments work?
break force of waves & trap beach material
What are the advantages of wooden revetments?
- much cheaper than sea wall
- effective at breaking force of wave
- 5-30 year life span
- less beach material is eroded compared to sea wall
What are the disadvantages of wooden revetments?
- less durable than sea wall - may need replacing quicker
- don’t give total protection to base of cliff
- alters beach-dune process
- environmentally ugly
How do recurved sea walls work?
the curved concrete wall deflects the power of the waves
What are the advantages of recurved sea walls?
- reflects not absorbs wave energy
- most effective way of preventing erosion
- socially reassuring
- low maintenance
What are the disadvantages of recurved sea walls?
- expensive
- may eventually collapse
- high maintenance cost
- disruption of natural beach-dune processes
How does rock armour/rip-rap work?
large boulders on the beach absorb wave energy within gaps between rocks
What are the advantages of rock armour/rip-rap?
- cheap
- use natural materials
- wave energy is dissipated very effectively through the gaps in the rocks
- allows build-up of beach
What are the disadvantages of rock armour/rip-rap?
- environmentally ugly
- can be removed by waves washing them away
- expensive to maintain & transport boulders
- ugly
- dangerous access to beach
- can alter sand dune systems permanently
Happisburgh background
- Norfolk coast, East England
- was over 250m from coast when founded in 1600s
- houses that sued to be 6m from sea now are at edge of cliff and are expected to fall in
Opportunities of Happisburgh
- tourism provides 10% jobs
- popular tourist destination - connected to London by bus
- many people live there due to its beauty & relaxing life style
- historic sites - oldest footprints outside of Africa & a wooly mammoth
- fishing for herring is a popular activity
Geology of Happisburgh
very soft rock (glacial till, clay, sand)
Sea defenses in Happisburgh
- 300m of wooden revetment was destroyed in a storm in 1990 eroding the road leading to the beach
- 2002 - 4,000 tonnes rock armour placed at base of cliff
- 2007 - 1,000 tonnes added to beach
- 2015 - 9,000 tonnes rock armour were re-aligned along base of cliff
- changes in government policy say coastal protection is no longer fundable since it would be more than the worth of the land
How are threats of the Great Barrier Reef being managed?
- land condition is being improved to reduce amount of sediment, nutrients & other pollutants transported to coral reefs
- outbreaks of crown-of-thorns starfish eat the coral only leaving white skeleton behind - Great Barrier Reef authority has a culling program where they inject them with bile salts or vinegar
- to stop reef getting smaller - coral & fragments are collected, regrown in nurseries then attatched again to the reefs
Opportunities of living on the coast
- job opportunities (fisherman/lifeguard)
- tourism
- sport (sailing/surfing/diving)
- ecosystems
- fishing
- oil & gas reserves (most oil & gas reserves are found under oceans)
- housing - many people choose to live by coasts for beauty & relaxing lifestyle
Hazards of living on the coast
- erosion - by strong storms causing rising sea levels
- sea levels rise cause flooding
- pollution from sewage discharge
- litter thrown into sea can kill animals
- tropical storms caused by rising sea levels
What is hard engineering?
involves building artificial structures, which try to control natural processes at a local scale
What is soft engineering?
doesn’t involve building artificial structures but takes more sustainable & manageable approach to managing the coast
