2.4 - Erosion And Waves

Question 1

Factors affecting the size of waves

Answer 1

• Strength of the wind
• Duration the wind is blowing
• Water depth
• Fetch

Question 2

How do waves form and break

Answer 2

• Waves start out at sea and have a circular orbit
• As waves approach the shore friction slows the base of the wave
• Causing the orbit to become elliptical
• Until the top of the wave breaks over
• Waves break in shallow water because the crest of the wave begins to move forward much faster than the wave trough
• The trough experiences friction with the sea floor causing it to slow

Question 3

Constructive waves

Answer 3

• Low energy
• Low flat wave height (under 1m)
• Long wave length (up to 100m)
• Low wave frequency
• Strong swash that pushes sediment up the beach, but a weaker backwash that is unable to transport all particles back down so they are deposited as a berm at the top of the beach

Question 4

Destructive waves

Answer 4

• High energy
• Large wave height
• Short wave length
• High wave frequency
• Strong backwash and weak swash due to steep angle of impact
• Strong backwash erodes material from the top of the beach carrying it down the beach to the offshore zone

Question 5

How do waves influence beach morphology

Answer 5

• Destructive, high-energy waves dominate in the winter, lowering angle of beach profile and spreading shingle over the whole beach. Offshore ridges/bars formed by destructive wave erosion and subsequent deposition of sand and shingle offshore.
• In summer, constructive, low-energy waves dominate, steepening beach angle and sorting particles by size, with larger shingle particles towards back of beach. In summer, constructive waves build berm ridges, typically of gravel/shingle at high tide mark

Question 6

What is erosion

Answer 6

Erosion refers to the wearing away of the land surface and removal of materials by river and seawater, ice and wind.

Question 7

Hydraulic action

Answer 7

• this is the shear force of the waves forcing air at high pressure into cracks in the cliff over time this weakens the rock and causes the joint to widen
• High energy waves with a large wave height are the most effective at erosion through hydraulic action.
• It is also accentuated when there is no debris at the cliff foot to absorb some of the wave energy and protect the cliff base.

Question 8

Abrasion

Answer 8

• Abrasion is where a wave picks up sediment and throws these load items against a rock
• The repeated impact chips away at the rock face until small fragments break away
• High-energy destructive waves with a large wave height are most effective as they hurl load items with greater force, resulting in faster rates of erosion by abrasion

Question 9

Attrition

Answer 9

as rocks are moved around by the water, they knock into each other gradually becoming smaller and rounder

Question 10

Solution/corrosion

Answer 10

• weak acids in seawater dissolve the rock particles
• Minerals are immediately carried away by the wave in solution
• They are also vulnerable to erosion by rainwater and sea spray

Question 11

Factors affecting the rate of erosion

Answer 11

• Wave type: The size and type of waves affects the amount of hydraulic action and abrasion
• Wave size: Erosion tends to happen more during the winter due to a greater number of destructive waves
• Lithology: Weaknesses in rocks erode more quickly, more resistant rocks erode more slowly

Question 12

Wave cut notch

Answer 12

• A wave cut notch is a curved indentation of about 1-2 m high extending along the base of a cliff.
• It forms between the high and low tide marks, where destructive waves impact against the cliff.
• It’s eroded by hydraulic action and abrasion, and in some cases corrosion.

Question 13

Wave cut platform

Answer 13

• a flat rock surface exposed at low tide, extending out to sea from the base of a cliff.
• Powerful destructive waves attack the base of the cliff at high tide
• The hydraulic action and abrasion create a wave-cut notch which over time increases in size
• This is called undercutting
• Eventually, the overhang created by the undercutting collapses due to weathering and gravity
• The cliff retreats, leaving a wave cut platform that is exposed at low tide

Question 14

Crack, cave, arch, stack , stump

Answer 14

• Wave refraction concentrates wave energy onto the headland and can contribute to the formation of caves, arches, stack and stumps
• Cracks/joints in the headland are susceptible to erosion by hydraulic action
• Over time the joints widen forming a cave that is enlarged by hydraulic action and abrasion
• Eventually, erosion cuts through the headland forming an arch
• The roof of the cave will eventually collapse due to gravity and the lack of support
• This leaves a stack that will over time be eroded by weathering, abrasion, and hydraulic action to form a stump