Coasts gateway 1 Flashcards
1
Q
Swash vs backwash
A
- swash deposits sediments
- backwash erodes sediments
2
Q
Constructive waves (cw) vs destructive waves (dw)
- gradient and energy
- appearance of waves
- wave height and length
- type of swash and backwash
- gradient of slope
- deposits/erodes sediments
A
- cw: gentle gradient, low wave energy - dw: steep gradient, high wave energy
- cw: small, low waves - dw: tall, large waves
- cw: low wave height, long wave length - dw: high wave height, low wave length
- cw: strong swash, weak backwash - dw: weak swash, strong backwash
- cw: gentle gradient - dw: steep gradient
- cw: deposits sediments - dw: erodes sediments
3
Q
What is wave refraction and how does it affect the coast?
A
- Wave refraction is when waves changes direction as it approaches the coast while slowing down
- Wave refraction causes the coast to be uneven
- The waves approach the straight coast at an angle, refracts and breaks parallel to the coast
- At headlands, wave energy is concentrated and waves converge. The waves have a high wave height and greater erosive energy. The friction between the coast and the waves causes the waves to eventually break onto the coast
- At bays, the wave energy is spread out and waves diverge. The waves have a lower wave height and lower erosive energy. While the speed of waves at the coast slows down, the waves at other parts of the sea remain at the same speed
4
Q
What is hydraulic action?
A
- waves strike against joints in rocks
- air is trapped in joints
- air is compressed and exerts a pressure on the joints
- as air is repeatedly compressed, the joints weaken and the rocks shatter
5
Q
What is abrasion?
A
- sediments carried by waves, like pebbles and sand, are hurled against the surface of the cliffs
- the loosened sediments knock and scrape the surface of the cliffs
- this weakens and breaks down the surface of the cliff
- over time, the impact from abrasion is powerful enough to undercut a cliff
6
Q
What is attrition?
A
-rocks carried by waves knock against each other, break down into smaller pieces and become smoother and rounder
7
Q
What is solution?
A
- sea water chemically reacts with minerals in coastal rocks causes them to become weaker and eventually disintegrate
8
Q
What is longshore drift?
A
- Longshore drift is the sediment movement by beach drift and longshore current. It is the most rapid when a wave approaches a straight coast at 30 degrees
- When waves move up as swash and perpendicularly down as backwash, the zigzag movement is known as beach drift
- as waves approach the coast at an angle, it generates longshore current nearshore. The sediments move along the shore
9
Q
What affects sediment deposition?
A
- when wave energy decreases, sediments are deposited
- larger sediments like pebbles are deposited first, followed by small sediments like sand
- coasts that are sheltered from strong winds experience more constructive waves and fewer destructive waves
- fine sediments are more likely to be deposited at coasts with calm waters
- sandy beaches are common at bays that are sheltered by headlands
- coarser sediments are likely to settle at exposed bays where there is higher wave energy
10
Q
How is a cliff and shore platform formed?
A
- a cliff is a steep and near-vertical rock face
1. hydraulic action and abrasion erodes a crack
2. the crack deepens to form a notch
3. notch deepens to form a cave
4. further erosion causes the roof of the cave to collapse, forming a cliff
5. further erosion forms a overhanging cliff
6. over time, erosion causes the overhanging cliff to collapse, and its sediments are deposited at the base of the cliff. The sediments are carried away by waves then thrown back against the surface of the rock, causing abrasion and erosion. this forms a gentle sloping platform at the foot of the cliff, known as a shore platform which is submerged during high tide
11
Q
How are headlands and bays formed?
A
- alternating bands of more and less resistant rocks at 90 degrees to the sea
- less resistant rock erodes faster than more resistant rock
- bays are wide indented coasts and are formed when less resistant rock is eroded away
- the more resistant rocks from headlands which extend seaward
- at bays, waves diverge and the wave energy is spread out. These are constructive waves and deposition occurs
- at headlands, waves converge and the wave energy is concentrated. These waves are destructive waves which causes more intense erosion
12
Q
How are caves, arches and stacks formed?
A
- less resistant rock are eroded away because of hydraulic action and abrasion. Waves attack the lines of weakness at the base of headlands, undercutting it. This forms a cave hollowed out by wave energy
- caves form on either side of the headlands. The waves attack the back walls of the caves, joining them together. This forms a arch
- the arch weakens due to wind and waves attacking it at high tide.
- it collapses, forming a stack. A stack is a pillar of rock left in the sea after a arch collapses
13
Q
What are beaches and how are they formed?
A
- beaches are zones of sediment deposition from eroded cliffs, river deposits or sediments from waves
- the composition of the beach depends on the source of materials
- the size of materials changes over time due to changes in wave energy or the source of materials
- finer sediments creates a gentler gradient and coarser sediments creates a steeper gradient
- constructive waves deposit sediments and build up the beach while stronger waves erode sediments and remove materials
14
Q
How are spits and tombolos formed?
A
- a spit is a long narrow ridge of sediments with one end attached to land
- it is formed by longshore drift
- sediments are accumulated in the sea-abrupt end in the coastline-longshore drift continues in the original direction of the coastline-materials deposited in the sea after the bend accumulate in the original direction of the coastline-a narrow ridge of sediments is formed where the coastline changes direction
- a hook is formed at the end of the spit and wave refraction concentrates on that point
- a tombolo connects an offshore island to the mainland
15
Q
factors of affecting coastal erosion
6
A
- waves
- currents
- tides
- geology
- type of ecosystems
- human activities
