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17 Cards in this Set
- Front
- Back
- 3rd side (hint)
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How are coasts shaped?
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By waves, tides and currents.
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What are waves?
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The rising and falling of surface water when wind energy is transferred from wind to water.
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Describe the factors of wave energy:
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. wind energy
. duration of wind . fetch (the distance of sea which the wind blows over) |
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Describe wave movement:
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. 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 |
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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 |
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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 |
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What affects the rate of coastal erosion?
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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 Position . coasts sheltered by man-made or natural structures . protected from wind elements and wave action . unlike open and unprotected coasts |
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Describe the four processes of coastal erosion.
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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 Abrasion . 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 Attrition . when rocks knock against each other . break down into smaller pieces . become more rounded over time Solution . water reacts chemically with minerals in rocks . they dissolve to form a solution eg. Limestone |
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Describe one way of coastal transportation.
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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
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What are the factors of coastal depositions?
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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 |
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Explain how a wave-cut platform results from the formation of a cliff.
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. 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 |
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How are headlands and bays formed?
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. 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 |
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What is wave refraction?
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. 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 |
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What is a spit?
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. a beach connected to the coast at just one end
. formed by longshore drift eg. Connecticut, USA |
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What is a tombolo?
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. 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 |
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Name the advantages and disadvantages of hard engineering methods.
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. 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 |
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Name the advantages and disadvantages of soft engineering measures.
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. 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 |
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