Topic 2 - Marine processes

Question 1

What is hydraulic action?

Answer 1

• The sheer force that water exerts as it crashes against a coastline
• When a wave advances, air can be trapped and compressed, either in joints in the rock or between the breaking wave and cliff
• When the wave retreats, this continous process can weaken rocks and cracks in the cliff, causing pieces of rock to break off

Question 2

What is cavitation?

Answer 2

• Simultaneously, bubbles formed in the water may implode under the high pressure
• This generates tiny jets of water which will, over time, erode the rock

Question 3

What is wave quarrying?

Answer 3

• The action of waves breaking against unconsolidated material, such as sands and gravels
• Waves scoop out the loose material in a similar way to the action of a giant digger in a quarry on land

Question 4

What is abrasion/corrasion?

Answer 4

• When waves advance, they pick up sand and pebbles from the seabed
• When they break at the base of the cliff, the transported material is hurled at the cliff foot - chipping away at the rock and have a ‘sandpaper’ effect
• The size, shape and amount of sediment along with the type of work, determines the relative importance of this erosive process

Question 5

What is solution?

Answer 5

• Weak acids in seawater can dissolve alkaline rock, or the alkaline cement that bonds rock particles together

Question 6

What is attrition?

Answer 6

• The gradual wearing down of rock particles by impact and abrasion as pieces of rock are moved by waves, tides and currents - this makes stones rounder and smoother

Question 7

How does lithology affect coastal erosion?

Answer 7

• Tough resistant rocks, erode at very slow rates compared to weaker clay and shales

Question 8

How do waves affect coastal erosion?

Answer 8

• Wave steepness - high energy waves
• Breaking point
• Fetch
• Sea depth
• Coastal configuration - headlands attract wave refraction via reflection
• Beach presence
• Human activity

Question 9

How does geological structure affect coastal erosion?

Answer 9

• Cracks, joints, bedding planes and faults create weaknesses in a cliff that can be exploited by erosive processes
• Rocks, such as limestone, are well jointed, which means sea can penetrate along the lines of weakness, making them vunerable to erosion
• The dip of the rock is also a major factor - the steepest cliffs tend to have horizontal strata or dip inland, whereas those which dip towards the sea from gentle slopes

Question 10

How does coastal management affect coastal erosion?

Answer 10

• The presence of structures, such as groynes and sea walls, will have an impact on sediment transfer (and the build up of beaches) and the patterns of wave energy along a coastline
• In trapping sediment moved by lsd, groynes may deprive beaches further down-drift of sediment input - furthermore, sea walls may deflect wave energy elsewhere along the coast - exacerbating erosion in these locations

Question 11

What is the coastal transportation process?

Answer 11

• Transfers sediment from one store to another
• 4 major methods of transportation:
• Saltation - small stones and pebbles are bounced along the sea bed
• Traction - heavy rocks and boulders are rolled along the sea bed
• Suspension - very small particles of sand or clay that are suspended in the water
• Solution - takes place when material is dissolved in the water, it is invisible and does not color in water

Question 12

How do subaerial processes affect coastal erosion?

Answer 12

• Weathering and mass movement will weaken cliffs and create piles of debris that are easily eroded by the sea, potentially increasing erosion rates