Coasts EQ2

Question 1

What are the characteristics of destructive waves?

Answer 1

• Deep nearshore depths- makes water motion in wave circular
• Wave frequency is 13-15 waves per minute
• Strong backwash and weak swash - removing sediment from beach

Question 2

What are the characteristics of constructive waves?

Answer 2

• Shallow nearshore depths
• Wave frequency of 6 to 8 per minute
• Motion of the water in the wave is elliptical- giving it strong forward motion
• Strong swash and weak backwash- depositing sediment on the beach

Question 3

Define these wave erosion processes- Attrition, Abrasion, Corrosion and Hydraulic action

Answer 3

Attrition- Material transported by wave broken down by hitting other sediment particles making the smaller and more round
Abrasion- Wave picks up sediment and throws against it other rocks like cliffs causing smaller fragments to break away
Corrosion- Water from waves may react with rock minerals and dissolve them- minerals then carried away in seawater
Hydraulic action- Force of water breaks apart rock- exerts pressure in cracks

Question 4

How do wave-cut notches form?

Answer 4

• At high tide, destructive waves may reach the base of the cliff
• Abrasion and hydraulic action erode the base of the cliff
• A curved wave cut notch forms along the length of the cliff- sea caves may form at weaker points along the wave cut notch

Question 5

How do wave-cut platform and cliff retreat occur?

Answer 5

• Above wave-cut notch, an overhang of unsupported rock is formed
• As the overhang is undercut, mass movement of this unsupported rock occurs and the cliff retreats
• As the cliff retreats, it leaves behind a flat or slightly sloping area of rock- wave-cut platform- weathering also contributes to the formation

Question 6

How does cave-arch-stack-stump sequence form?

Answer 6

• hydraulic action exposes cracks at the base of the cliff
• cracks furthered widened through weathering processes and form caves
• as a result of wave refraction cave is deepened until arch is formed
• overtime arch becomes unstable and collapses to form stack
• stack further eroded to form stump

Question 7

Hoe does longshore drift work?

Answer 7

• Strongest LSD occurs when waves approach beach at angle of 30 degrees
• Swash carries sediment up the beach at same angle as waves
• Backwash carries the sediment back down the beach at right angles to the shore- this moves the sediment down the beach until it meets an obstacle
• predominant wind direction determines the direction of longshore drift

Question 8

What is a sediment cell and what are the different sinks sources and transfers?

Answer 8

• A sediment cell has sources, transfers and sinks and in theory it is a closed system in dynamic equilibrium
• Sources: erosion of cliffs and land sediment transported by rivers
• Transfers: LSD, waves/currents and wind
• Sinks: Dunes, beaches, bars and offshore

Question 9

What is the difference between positive and negative feedback?

Answer 9

Negative feedback- maintain equilibrium- wave erosion causes rock falls to protect the base from further erosion

Positive feedback- increase change in the system until new equilibrium is reached - blow out in sand dune allows more sand to be eroded by the wind reducing vegetation cover

Question 10

What is a beach and how is it formed?

Answer 10

• Accumulation of sand or shingle found in foreshore and backshore zones
• Sediment deposited by constructive waves- LSD also brings beach material from erosional sources which is deposited by waves
• Destructive waves shape a beach by creating storm ridges at the backshore during high tide