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17 Cards in this Set

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How are coasts shaped?
By waves, tides and currents.
What are waves?
The rising and falling of surface water when wind energy is transferred from wind to water.
Describe the factors of wave energy:
. wind energy
. duration of wind
. fetch (the distance of sea which the wind blows over)
Describe wave movement:
. waves move in cicular motions
. deep waters
. little energy is lost
. shallow waters (along coasts)
. friction between water and sea floor
. waves slow down
. frictional force causes the waves to rise and bend forward
. they continue to move forward and collaspe into foaming water

. swash - the forward movement of waves up the shore
. backwash - flow back to sea
What are tides?
How can they transform a coast?
Define tidal range:
. daily alternate rising and falling of waves
. caused by the gravitational pull of the Moon (and Sun)
. as the earth rotates about its axis
. coasts move over two bulges a day
. thus, there are two low and two high tides

. tidal action affects erosional and transportation processes
. places which lie in between low and high tides have more weathering/erosion
-> experience continuous wetting and drying
. places constantly submerged in seawater not so
What are currents?
eg. Longshore currents
Large-scale and persistant movements of water largely due to prevailing winds.

Longshore currents:
- parallel to shore
- waves approach shore at an oblique angle
What affects the rate of coastal erosion?
Types of waves
. destructive waves have more energy than constructive waves
. erodes the coast more than depositing materials

Structure and composition of rocks
. rocks with lines of weaknesses, cracks, joints
. eroded more quickly when hit by waves
. soft rocks (shale and clay) eroded faster than hard rocks (basalt, granite)
. rocks with mineral composition that reacts chemically with water to form solution
->weakens rocks

. coasts sheltered by man-made or natural structures
. protected from wind elements and wave action
. unlike open and unprotected coasts
Describe the four processes of coastal erosion.
Hydraulic wave action
. direct impact of waves against coast
. force of waves hitting the cliff or rocks exerts great pressure on it
. water surges into cracks in rocks
. air is compressed
. pressure exerted widen the cracks even further
. over time, constant compression by water + outward push of air enlarge cracks
. so much til it breaks

. the sandpapering effect of materials carried by waves scraping the coast
. destructive waves may lift large rocks up from the sea and hurl it towards the coast
. the strong impact eventually erodes the coast

. when rocks knock against each other
. break down into smaller pieces
. become more rounded over time

. water reacts chemically with minerals in rocks
. they dissolve to form a solution
eg. Limestone
Describe one way of coastal transportation.
One way is longshore drift
- waves approach the shore at an oblique angle
- backwash carries materials down the beach perpendicularly
-> due to pull of gravity
- materials are moved in a zig zag pattern along the beach, usually in the direction of the prevailing wind
longshore drift
What are the factors of coastal depositions?
Supply of sediments
. large amount of eroded materials
. waves have not enough energy to transport it
. deposition occurs

Position of the coast
. if it's sheltered, for example indented coasts
. less chances of destructive waves
. calm coastal conditions
. more materials deposited than eroded
. sandy beaches may form

Gradient of slope
. gentle slopes
. wave energy is spread out and decreases
-> due to friction against the shore and gravitational pull
. constructive waves deposit materials rather than erode
Explain how a wave-cut platform results from the formation of a cliff.
. crack on rock surface is eroded by hydraulic and abrasion
. enlarged into a notch
. further undercutting creates a cave
. erosion causes the cave to collapse
. process is repeated until a overhanging cliff is formed

. this cliff then collapses too overtime
. materials are deposited at the base of the cliff
. some rocks are washed away
. others are hurled by waves and erodes the base of the cliff
. erosional process repeats until the cave retreats further inland
. a gentle-sloping platform appears at the base where the cliff used to be
-> Wave-cut(shore) platform.
- usually submerged by high tide
How are headlands and bays formed?
. alternate strips of resistant hard rocks and less resistant soft rocks
. right angle to coast
. soft rocks will be eroded faster than the hard rocks, which are more resistant
. indented coasts are formed
. eroded less resistant soft rocks are called bays
. hard rocks which jut out into the sea are called headlands
What is wave refraction?
. the process whereby waves are refracted or bent
. when they approach indented shore with headlands and bays
. as waves bend, their energy is distributed unevenly along the shoreline
. waves nearer to the shore touches the sea floor first, slows down due to friction
. waves at the back continue to move towards the shore with high speed
. thus, waves approach headlands first
->wave energy is concentrated at headlands and erosion takes place
->whereas at bays, energy is spread out and deposition takes place
->overtime, indented coast will become straighter
What is a spit?
. a beach connected to the coast at just one end
. formed by longshore drift

eg. Connecticut, USA
What is a tombolo?
. a spit which joins two islands together
. formed when a spit, with one end connected to the mainland, expands until it joins a nearby island
Name the advantages and disadvantages of hard engineering methods.
. hard engineering is the construction of physical structures to defend against the erosive action of waves

. seawalls
- walls made up of concrete, built parallel to the shore
- absorb the energy of waves
- reduces erosion
- however, they do not prevent waves from undermining the base of the seawalls
- seawalls are weakened and eventually collapse

. breakwaters
- walls made of concrete, built either with one end attached to the coast or away from coast
- reduces energy of waves before they hit the shore
- creates a zone of calm water behind them
- leading to constructive waves that deposit and build up materials on the beach
- places located away from breakwaters will still be eroded

. gabions
- wire cages filled with rocks to weaken wave energy
- reduces erosion
- however, they offer short-term protection only, from 5-10years
- require proper maintenance as they corrode and may pose a danger
eg. North Norfolk, UK

. groynes
- long narrow structures built at a right angle to coasts
- prevent longshore drift from transporting materials down the beach
- tilted at 5-10 degrees such that the beach will be extended by waves
- however, materials on the downdrift side may still be eroded
eg. Eastborne, England
Name the advantages and disadvantages of soft engineering measures.
. soft engineering is the non-structural approach in reducing erosion and stabilising the beach through ecological practices and principles

. beach nourishment
- the constant replenishment of sand to the beach system
- improves beach quality and storm protection
- beach is extended
- however, it is impractical
- sand is still continuously eroded and transported away
- will have serious consequences of wildlife in the coastal environment
eg. Singapore
- large scale land reclamation has led to muddy polluted waters
- imported sand gets washed out to sea, covers coral reefs
- as a result, coral reefs are destroyed as they do not have enough sunlight to survive

. relocation of property
- "green line policy" in England
- no buildings or structure beyond a given line
- they will not be protected if they face coastal erosion
- allows nature to reclaim the beach naturally
- important due to rising sea levels by global warming
- investors will be unhappy

. planting of mangroves
- mangroves have long curved roots that prop up from the soil to trap sediments
- as they grow and expand seawards, they help to extend the coast
eg. Aceh, mangrove seedlings were planted to help the devastation caused by tsunamis.
- however, not all coasts can support mangroves
- depth of coast may become shallower, affecting coastal transportation

. growth of coral reefs
- coral reefs weaken wave energy
- even though many coral reefs are destroyed by pollution and land reclamation
- damaged reefs can be restored or conserved
- artificial reefs can be constructed
- reduce erosion
- enhance fishing opportunities