2.1.4 Coastal Processes

Question 1

What are the six main ways that waves erode the coastline?

Answer 1

• Corrasion (abrasion)
• Hydraulic action
• Cavitation
• Wave quarrying
• Solution (corrosion)
• Attrition

Question 2

Corrasion (abrasion)

Answer 2

Bits of rock and sediment transported by the waves smash and grind against rocks and cliffs, breaking bits off and smoothing surfaces.

Question 3

Hydraulic action

Answer 3

Air in cracks in cliffs is compressed when waves crash in. The pressure exerted by the compressed air breaks off rock pieces.

Question 4

Cavitation

Answer 4

As waves recede, the compressed air expands violently, again exerting pressure on the rock and causing pieces to break off.

Question 5

Wave quarrying

Answer 5

The energy of a wave as it breaks against a cliff is enough h to detach bits of rock.

Question 6

Solution (corrosion)

Answer 6

Soluble rocks (e.g. limestone, chalk) get gradually dissolved by the seawater.

Question 7

Attrition

Answer 7

Bits of rock in the water smash against each other and break into smaller bits.

Question 8

Deposition

Answer 8

When material being transported is dropped on the coast.

Question 9

When does deposition happen?

Answer 9

When the sediment load exceeds the ability of the water or wind to carry it.

This can be because sediment loan increases (e.g. if there is a landslide), or because wind or water flow slows down (so it has less energy).

Question 10

Two types of deposition

Answer 10

• Marine deposition is when sediment carried by seawater is deposited.
• Aeolian deposition is when sediment carried by wind is deposited.

Question 11

Transportation of sediment

Answer 11

The energy provided by waves, tides and currents transports eroded material.

Question 12

Four main processes of transportation

Answer 12

• Solution
• Saltation
• Traction
• Suspension

Question 13

Solution

Answer 13

Where substances that can dissolve are carried along in the water.
For example, limestone is dissolved into water that’s slightly acidic.

Question 14

Saltation

Answer 14

Larger particles, such as pebbles or gravel, are too heavy to be carried in suspension. Instead, the force of the water causes them to bounce along the sea bed.

Question 15

Traction

Answer 15

Where very large rocks (e.g. boulders) are pushed along the sea bed by the force of the water.

Question 16

Suspension

Answer 16

Where very fine material, such as silt and clay particles, is whipped up by turbulence and carried along in the water. Most eroded material is transported this way.

Question 17

Longshore drift

Answer 17

1) Swash carried sediment (e.g. shingle, pebbles) up the beach parallel to the prevailing wind. Backwash carries sediment back down the beach, at right angles to the shoreline

2) When there’s an angle between the prevailing wind and the shoreline, a few rounds of swash and backwash move the sediment along the shoreline.

Question 18

Sub-aerial weathering

Answer 18

The gradual break down of rock by agents such as ice, salt, plant roots and acids. Weathering weakens cliffs and makes them more vulnerable to erosion.

Question 19

Types of weathering that affect coasts

Answer 19

• Chemical weathering
• Biological weathering
• Physical weathering

Question 20

Salt weathering

Answer 20

1) Salt weathering is caused by saline (salty) water.

2) This saline water enters pores or cracks in rocks at high tide.

3) As the tide goes out the rocks dry and the water evaporates, forming salt crystals. As the salt crystals form they expand, exerting pressure on the rock - this causes pieces to fall off.

Question 21

Wetting and drying

Answer 21

1) Some rocks contain clay.

2) When clay gets wet, it expands and the pressure caused by this breaks fragments off the rock.

Question 22

Freeze-thaw and weathering

Answer 22

1) Freeze-thaw weathering occurs in areas where temperatures fluctuate above and below freezing.

2) Water enters the joints and crevices in rocks.

3) If the temperature drops below 0’C, the water in the cracks freezes and expands.

4) Over time, repeated freeze-thaw action weakens the rocks and causes pieces to fall off.

Question 23

Chemical weathering

Answer 23

1) Chemical weathering is the breakdown of rock by changing its chemical composition.

2) For example, carbon dioxide in the atmosphere dissolves in rainwater, forming a weak carbonic acid. The acid reacts with rock that contains calcium carbonate, e.g. limestone, so the rocks are gradually dissolved.

Question 24

Mass movement

Answer 24

The shifting of material downhill due to gravity.

Question 25

When is mass movement likely to occur in coastal areas?

Answer 25

When cliffs are undercut by wave action – this causes an unsupported overhang, which is likely to collapse.

There are several different types of mass movement:
- Rockfall
- Landslides
- Runoff
- Mudflows
- Slumping
- Soil Creep

Question 26

What type of mass movement is the fastest, and which is the slowest?

Answer 26

In order of speed:

FASTEST
- Rockfall
- Landslides
- Runoff
- Mudflows
- Slumping
- Soil Creep

SLOWEST

Question 27

Rockfall

Answer 27

Sudden collapse or breaking away of rock fragments at cliff face.

Steep cliffs after freeze thaw or earthquakes.

Question 28

Landslides

Answer 28

A block of rock moving rapidly downhill.

Unlikely mudflow the moving block of material is intact.

Question 29

Runoff

Answer 29

When overland flow (surface runoff) occurs down a slope and small particles of sediment (e.g. sand and silt) are removed.

Question 30

Mudflows

Answer 30

Earth and mud flowing downhill usually over weak bedrock such as clay often after heavy rainfall.

Question 31

Slumping

Answer 31

It is curved rather than flat.

Occurs in weak clays and sands with permeable rock over impermeable rock.

Result in terraced appearance.

Question 32

Soil creep

Answer 32

Extremely slow movement of individual soil particles downhill.

Particles moving towards the ground surface returning to the surface due to gravity.