Theme 2c Coasts

Question 1

What are constructive waves ?

Answer 1

• Have a low wave height & usually the beach gradient is gentle
• Waves spill forward gently creating a strong swash
• Water drains away through the beach material => weak backwash

Question 2

What are destructive waves ?

Answer 2

• Have a high wave height & the beach tends to be steep
• Wave plunges forward onto the beach => the swash is weak
• The rotation of water causes a strong backwash
  => these waves erode beaches

Question 3

What are components of waves and their descriptions ?

Answer 3

1. Swash - when a wave breaks & washes up the beach
2. Backwash - when the water drains away back into the oncoming wave

Question 4

What are the 3 factors affecting the size of waves ?

Answer 4

1. The strength of the wind
2. The length of time the wind has been blowing
3. The fetch / distance over which the wind can blow

Question 5

What are the methods of marine erosion ?

Answer 5

1. Corrasion - large waves hurl beach material at the cliff
2. Corrosion - salts and acids slowly dissolve a cliff
3. Attrition - waves cause stones to collide and disintegrate
4. Hydraulic action - force of waves enters cracks in cliff compresses air in cracks => widened cracks

Question 6

What are the methods of marine transportation ?

Answer 6

1. Suspension - Fine sediment is carried as a suspension in the water, making it look muddy/murky
2. Solution - dissolved material is carried along in solution
3. Traction - large pebbles and cobbles are rolled along the sea bed
4. Saltation - small pebbles are moved when one pebble hits another, causing it to bounce. This bouncing can set up a chain reaction

Question 7

What is a longshore drift ?

Answer 7

• When waves approach the coast at an angle, the swash moves up the beach at an angle
• Backwash, however, drains straight back down the beach.
  => Gradually move sand/stones along the beach in a zig-zag motion

Question 8

What are some coastal landforms ?

Answer 8

1. Cliffs
2. Wave-cut platforms
3. Caves
4. Arches
5. Stacks
6. Stumps
7. Bay and Headland coastlines
8. Beaches
9. Spits
10. Coastal sand dunes

Question 9

Cliff and wave-cut platforms formation

Answer 9

• Wave erosion is concentrated at the foot of the cliff so a wave-cut notch is formed
• The cliff is undercut & collapses
• Repeated collapses causes retreat of the cliff producing a platform of flat rock at the cliff foot extending out to sea

Question 10

Caves, arches, stacks and stumps formation

Answer 10

• A band of weaker rock extends through a headland
• More erosion occurs producing caves on both sides of the headland
• Continued erosion produces an arch through the headland
• Eventually, the roof is weakened & collapses forming a stack
• The stack is eroded by wave action, until it collapses, leaving a short, rocky remnant at/near waterline.

Question 11

Beaches formation

Answer 11

• In bays wave energy is dissipated creating low-energy constructive waves (strong swash & weak backwash)
• Need lots of sediment available, carried by sea
• Deposition of sediment on the coastline due to constructive waves
• Accumulation of sands & pebbles
• Builds up over time to form a beach

Question 12

Bays and headlands formation

Answer 12

• Alternating layers of hard and soft rock at right angles to the sea (discordant coastline)
• Bays are formed due to softer rock getting eroded easily
• Headlands are usually formed since they are made of resistant rock & so is eroded more difficulty

Question 13

Spits formation

Answer 13

• Spits form when the coastline changes direction; longshore drift continues to carry material in the same direction
• Sand & shingle is built up to form the spit
• The end of the spit curves round due to secondary winds push waves coming at another angle

Question 14

Sand dunes formation

Answer 14

• Form behind wide sandy beaches formed by constructive waves
• Onshore winds pick up the dry sand from above the high-water mark & carry it landward by saltation
• If they encounter an obstacle (strand line), the wind loses energy & deposits sand in the lee of the obstacle
• Eventually, a dune is formed, plants (marram grass) then grow on it & stabilize it & trap more sand
• Animal faeces & organic material develop sand to soil through progression: embryo => yellow => grey => mature dune

Question 15

Salt marsh formation

Answer 15

• Clay is deposited by the tides where there is a large tidal range
• Clay sticks together (flocculates)
• The land builds up above sea level forming mudflats
• Plants start to grow in the mud & trap more sediment
  => This forms a salt marsh which has wet depressions & drier raised grass

Question 16

Conditions needed for coral reef to grow ?

Answer 16

1. Warm WATER/ seas; temperature above 20 degrees Celsius
2. Shallow water; no more than 60 metres deep
3. Water free from sedimentation/clear for the availability of light
4. Plentiful of oxygen supply in WATER
5. Lack of strong currents
6. Plentiful supply of plankton

Question 17

What are the 3 types of reef ?

Answer 17

• Fringing reef: coral reefs grow in shallow water of the coast in tropical areas
• Barrier reef: Due to plate tectonics, the island starts to sink, the reef grows to keep up with the sinking & a lagoon develops between the reef and land
• Coral atoll: form around islands that are sinking, coral growth keep up with this and coral keeps sinking
  => eventually the island sinks below sea level form a ring of coral with a lagoon in the centre

Question 18

Groynes (hard engineering)

Answer 18

• Wooden/concrete, small walls built at right angles along the beach into the sea to stop LSD
• Advantages:
  + Protects coast behind from erosion
  + Keeps beaches for tourism
• Disadvantages:
  + Stop movement of sediment to places along the coast
  + Need to be replaced quite often

Question 19

Sea walls (hard engineering)

Answer 19

• Concrete and curved outwards to deflect the power of the waves
• Advantages:
  + Most effective in preventing both erosion and flooding (if high enough)
• Disadvantages:
  + Very expensive to build & maintain
  + Can be damaged if material in front of the wall is not maintained
  + Restrict access to the beach

Question 20

Revetments (hard engineering)

Answer 20

• Sloping wooden/concrete fence with an open plank structure; work to break force of waves
• Advantages:
  + Traps beach material behind them => defence against erosion
  + Cheaper than sea walls but not as effective
• Disadvantages:
  + Not effective in stormy conditions
  + Regular maintenance is necessary

Question 21

Rock armour (hard engineering)

Answer 21

• Large boulders are piled up to protect a stretch of coast by absorbing wave energy from base of cliffs & sea walls
• Advantages:
  + Cheap method of construction
• Disadvantages :
  + Boulders can be eroded/dislodged during heavy storms

Question 22

What are the conditions for mangroves’ location ?

Answer 22

1. Warm conditions where the sea surface is no lower than 16 degrees and air temperature at least 20 degrees
2. Tidal areas, between low-tide and high-tide marks
3. No strong waves or tidal currents
4. In brine (salty) water as other trees will grow as more dominate where there is fresh water

Question 23

Rock armour (hard engineering)

Answer 23

• Large boulders piled up to protect a stretch of coast by absorbing wave energy
• Advantages:
  + Cheap method of construction
• Disadvantages:
  + Boulders can be eroded/dislodged during heavy storms

Question 24

Gabions (hard engineering)

Answer 24

• Wire cages filled with stone, concrete, sand,… absorb wave energy
• Advantages:
  + Cheapest form of coastal defence
  + Can be stacked at the base of a sea wall/cliffs
• Disadvantages:
  + Wire cages can break => need to be securely tied down
  +Not as efficient as other coastal defences

Question 25

Offshore reef/barrier (hard engineering)

Answer 25

- Large concrete blocks, rocks & boulders are sunk offshore to alter wave direction & weaken it - Advantages: + Low maintenance + Beach material is built up behind it - Disadvantages: + Expensive to build + Can be removed in heavy storms

Question 26

Beach replenishment/nourishment (soft engineering)

Answer 26

- Replacement of sand/pebbles on eroding beaches/removed by longshore drift - Advantages: +Provide an area for recreation + Protect expensive properties in the location - Disadvantages: + One severe storm event may remove vast amounts of expensive sediments

Question 27

Cliff re-grading (soft engineering)

Answer 27

- The shape of the cliff is changed to make it more stable; usually made more gently sloping - Advantages: + Prevent slumping +Looks natural, can be covered in ecomatting => encourages wildlife - Disadvantages: +May lose some land & buildings + Not stop the sea advance by itself for long

Question 28

Sand dune stabilisation (soft engineering)

Answer 28

- Sand dunes are a natural sea defence, dissipate wave energy & protect the area behind it => Stabilised by fences & planting grasses to hold sand &rock together - Advantages: + Cheap & effective - Disadvantages: +Easily damaged by people if not maintained

Question 29

Managed retreat (soft engineering)

Answer 29

- Accepts that natural processes will always be taking place & involves moving backwards the limits of building - Advantages: + Natural & long-term solution => Allow salt marshes to form, can be flooded & absorb the energy - Disadvantages: + Farmland is lost + Require compensation for land that is lost

Question 30

Land use planning/zoning (soft engineering)

Answer 30

- Focuses on where people can build & what activities are allowed - Advantages: + Long-term safety - reduce losses + Prevents over-development of sensitive coastal ecosystems - Disadvantages: + Limit opportunities for economic coastal development + Difficult to control illegal/ informal building is some areas

Question 31

Beach re-profiling (soft engineering)

Answer 31

- The artificial re-shaping of a beach using existing beach material. - Advantages: +Replaces shingle after winter storms +Increasing profile reduces wave energy before the base of the cliffs - Disadvantages: + May have negative effects on beach habitats

Question 32

What are characteristics of coral reef

Answer 32

- Are alive, consist of living creatures (polyps, zooxanthellae) - Provides shelter for fish - Made of calcium carbonate - Very colourful (iridescent) - Fragile

Question 33

Characteristics/features of mangroves

Answer 33

- Dense thicket (Bushes/trees - Varying heights & density - Green leaves - Aerial roots - Growing in water (shallow)

Question 34

Problems caused by coastal erosion for people living along the coasts ?

Answer 34

- Damage to homes, property and settlement - Loss of farmland - Damage to roads and railways - Reduction in tourism as they fear of hazards - Damage to ports and harbours - Loss of scenery (beautiful landscape)

Question 35

Importance of mangrove swamps for people and the natural environment (benefits)

Answer 35

- Natural protection for coastline, reduces strength of waves - Reduced erosion as their roots trap sediment & soil together - Provides resources for medical use - Remove carbon dioxide from the atmosphere => reduces global warming - Wood for construction ,...

Question 36

Importance of coral reefs for people and the natural environment (benefits)

Answer 36

- Protects low-lying coasts from the impact of tropical storms - Rich fish stock to supply basic food requirements to many LICs - Provide recreational opportunities e.g scuba diving - Tourist destination, over 150 million people each year take holidays in areas with coral reefs

Question 37

Describe the process of marine deposition

Answer 37

- Waves carry sand/shingle; backwash carries it away while swash carries onto shore - When constructive wave carries sediment up beach, largest material is deposited along the upper reach of swash - Backwash loses water & energy as it travels due to sand porosity => smaller & smaller deposits - During storm, large shingle thrown above the usual high tide level => form a ridge at the top of beach called berm