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2.3 Coasts (((Longshore drift (material is transported along coastline by…
2.3 Coasts
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DEPOSITION
sea loses energy, forced to deposit sediments
EROSION
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Attrition
rocks are thrown into each other,break, get smaller by waves
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Hydraulic action air trapped in crack
When a 🌊 breaks, the trapped air is compressed which weakens the cliff and causes erosion
• danger to properties on cliff top;
• people may need to evacuate;
• loss of farmland/loss of gardens;
• reduction in food production;
• roads may be damaged;
• collapse of cliffs may make beaches dangerous/rock falls can kill people;
• less tourists come;
• cost of protection measures;
• can’t get insurance for properties/unable to sell properties; etc.
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Longshore drift
- material is transported along coastline by waves
- wave approach cost at an angle 90* bc prevailing wind
- material is carried up by Swash material is dragged down by Backswash
90*↓ = shortest route
- material is moved in zigzag path
- develop in sudden change in shape of coastline
- longshore drift continues transport material in same direction rather than following coastline
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LONGSHORE DRIFT
- material is transported along coastline by waves
- wave approach cost at an angle 90* bc prevailing wind
- material is carried up by Swash
material is dragged down by Backswash
90*↓ = shortest route
- material is moved in zigzag path
- develop in sudden change in shape of coastline
- longshore drift continues transport material in same direction rather than following coastline
BAY & HEADLANDS
on discordant coastline
- alternating band of hard/week rock
- week = less resistant → erode quickly →beaches
- hard = more resistant → erode slower → headland
WAVES CUT PLATFORM 
- at hige tide
water power attack cliff bottom
→⏰ wave cut notch
- wave cut notch get bigger
→weight of rock above get bigger
→cliff cannot support its weight → fall
- process continues,cliffs retreats
→→wave cut platform
➡️ Caves occur when waves force their way into cracks in the cliff face. water contains sand/ other materials that grind away at the rock until the cracks become a cave.
Hydraulic action is the predominant process.➡️ cave eventually break through to the other side
→ arch. ➡️ arch gradually become bigger until it can't support top of arch
→ arch collapses,
- leaves headland on one side
- and a stack (a tall column of rock) on the other.
➡️ The stack attacked at the base in same way that a wave-cut notch is formed.
→weakens structure →collapse → stump.
BEACH
- coastal deposition
- impermanent features - shapes altered by waves
- gentle sloping area of land between the high/low water marks
- made up of material lying between the high/ low tide mark
- accumulation of sand between low/high tide
sources of beach material:
- Material deposited at the mouth of rivers
- Cliff erosion, provides rock fragments that build up beach
- Constructive waves have a strong swash
→ push sands /pebbles up beach
- Longshore drift carries material from elsewhere along coast
Sand Dunes
- dynamic: constantly changing.
- found behind berms
- extension of the beach.
- formed by dry sand being blown up the beach
constructive waves encourage the accumulation of sand through deposition,
prevailing onshore winds blow the sand inland.
If there is an obstacle in the way, it can block the path of the grains and trap them. As the sand grains get trapped they start to accumulate, this is the start of dune formation.
The wind then starts to affect the mound of sand by eroding sand particles from the windward side and depositing them on the leeward side. Gradually this action causes the dune to “migrate” inland, as it does so it accumulates more and more sand. A new dune may then form, called the embryo dune, which is vulnerable to sea salt spray, and erosion from destructive waves.external image moz-screenshot-10.pngsure?
conditions
plentiful amt of sandsEmbryo Dune:
- starting dunes of sand dunes
- form in the sheltered area behind the berm & strand line.
Foredunes
- Small embryo dunes join to make foredunes.
- tend to be yellow as they only have limited vegetation
so no real humus layer develops.
Yellow Dunes
- Sea couch/ marram grass begin to grow on the foredunes
→ become more stable and grow.
As the dune grows → vegetation develops a humus layer develops.
Grey Dunes:
A developing humus layers starts changing the colour of the dune from yellow to grey.Mature dunes As the humus layers grows more, the dunes can sustain more plants, flowers and even trees.Dune slack As the size of the dunes develop water can collect between the dunes. Marsh plants can grow in these wet areas.Blowout: A blowout is a depression or hole in the dune caused by the wind.Humus: Is the layer of decaying plant and animal matter that adds nutrients to the ground.Succession: The changing types of plants from basic sea couch to trees is known as succession.Water table: The line between saturated and unsaturated ground.
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Conditions
- plenty amt. of sands
- flat land
- around estuary/ on sand spit
- colonization: plant to colonise
- obstruction for sand to build around
CORAL REEFS
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FRINGING REEFS
- in gang
- develop in shallow water
- short distance from shore
BARRIER REEFS
- older
- separated from shore by lagoon
- grow further offshore to edge of continental drift
- e.g Great Barrier Reef
ATOLL REEF
- ring of reeds, often encircling island
- shallow, sandy lagoon in middle
- raised from submerging volcanic foundation
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DISTRIBUTION
- tropic/subtropical regions
- vast majority in
- Indo Pacific regions
- Atlantic regions
- tropic/subtropical regions
- SE Asia contains mangroves of greatest diversity
- inter-tidal area & estuary
- shorelines protected by ocean waves(coral reefs)
- depositional shorelines
- high salinity
- frequently flooded
coastal management
hard engineering
sea walls
A wall built on the edge of the coastline.Placed at the base of a cliff to reflect the waves energy
:check:extremely effective
:red_cross: $$$
:red_cross: high maintenance cost
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groynes
longe vertical structure places 90 to beach to trap sediments. protect from erosion
prevent longshore drift
:red_cross: erosion in further area
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soft engineering
beach management
replace beach materials
:check: natural defense
:check:attract tourist
:check:inexpesive but need constant maintenance
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managed retreat
allow area to flood and eroded naturally
encourages development of beaches, salt marcches
cheap
people need to be compensated
MIAMI
BENEFITS
PORT
- biggest port
- accounts 176,000 jobs
- annually generates $185m
REAL ESTATES
- favorable for location
- witness several estate boom
- huge demand from oversee buyers
- report along coastline
ECOSYSTEM
- unique biodiveirsty
- recreation use of coral reef
- employment
- natural defense against erosion
HARAZDS
hurricanes
- tropical monsoon climate
- hurricane season (jun-oct)
- atlantic basin near confluence w/ gulf of mexico
- extreme vulnerable for hurricanes
global warming
- increase threat of hurricane
- increasing flood
- rising sea level
"In Miami, sea-level rise is not a problem for future generations. It’s a present-day reality"
KATRINA HURRICANES
-1,800 casualties
- 3m w/o electrocoty
-crop damage $432 m
- public transport:bus
- hundred thousand are displaced
- AFFECT 90,000 miles of USA
TOT DAM of $108b
flooding of New Orleans
- category 4 storm.
- Storm surges over 6m in height.
New Orleans was one of the worst affected areas because it
lies below sea level and is protected by levees. These protect it from the Mississippi River and Lake Ponchartrain. The levee defences were unable to cope with the strength of Katrina, and water flooded into the city.
- Despite evacuation order, poorest people remained in the city.
People sought refuge in the Superdome stadium. Conditions were unhygienic, and there was a shortage of food and water. Looting was commonplace throughout the city. Tension was high and many felt vulnerable and unsafe.
1 million people were made homeless and about 1,200 people drowned in the floods.
Oil facilities were damaged and as a result petrol prices rose in the UK and USA.
Responses
Flooding caused by Hurricane Katrina in New Orleans 2005
There was much criticism of the authorities for their handling of the disaster. Although many people were evacuated, it was a slow process and the poorest and most vulnerable were left behind.
$50 billion in aid was given by the government.
The UK government sent food aid during the early stages of the recovery process.
The National Guard was mobilised to restore and maintain law and order in what became a hostile and unsafe living environment.
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