Deck 17a- Factors that impact on coastal recession

Question 1

What 4 physical factors impact on rates of coastal recession?

Answer 1

Waves, lithology, geological microstructures and vegetation

Question 2

How do microstructures impact on coastal morphology?

Answer 2

Microstructures form a weakness in the bedrock that erosional processes focus on meaning erosional features such as caves and cave cut are more likely to form

Question 3

What are 5 geological microstructures?

Answer 3

Bedding planes, faults, folds, joints and angle of dip

Question 4

What is a bedding plane?

Answer 4

Beds are the layers of sedimentary rocks that are distinctly different from overlying and underlying subsequent beds of different sedimentary rocks. The line between the different beds is a bedding plane.

Question 5

How do bedding planes impact on coastal morphology?

Answer 5

Bedding planes are a line of weakness for erosional processes

Question 6

What is a joint?

Answer 6

A joint is a fracture dividing rock into two sections that moved away from each other either during tectonic uplift or the contraction of sediments as they dry up.

Question 7

Which processes are joints particularly susceptible to?

Answer 7

Weathering processes such as freeze thaw weathering as the elements can impact the joints from above the waves.

Question 8

What is a fault?

Answer 8

A fault is a fracture between two blocks of rock where there has been displacement. Fault occur when rocks are subjected to high levels of stress and pressure, for example during tectonic activity.

Question 9

How do faults impact on morphology and rates of recession?

Answer 9

Faults are a line of weakness in a rock. If the rocks along a coastline are heavily faulted rates of coastal recession will be higher.

Question 10

What is a fold?

Answer 10

A fold is where the rock has bent or curved during tectonic activity.

Question 11

How do folds impact on coastal morphology and rates of recession?

Answer 11

Folds lead to a irregular occurrence of rocks and bedding planes at the surface which can lead to a variation in the amount of erosion taking place.

Question 12

What does the angle of dip refer to?

Answer 12

Dip is the angle that layers of rocks lie e.g. horizontal, vertical or dipping towards or away from the sea.

Question 13

How does the angle of dip impact on coastal morphology?

Answer 13

Depending on the dip direction and angle different layers of rock will be exposed to the sea and will lead to different rates of erosion. It is an important control on the shape of cliff profiles.

Question 14

What is a cliff profile?

Answer 14

A cliff profile is the height and angle of a cliff plus any features it includes.

Question 15

What 3 factors influence the shape of a cliff profile?

Answer 15

-The resistance to erosion of the rock (lithology)

-Weaknesses in the bedrock through geological structures

-The dip of rock strata in relation to the coastline

Question 16

What characteristics does a cliff profile with a horizontal dip have?

Answer 16

-Cliffs have a vertical or near vertical profiles

-Wave cut notches form in the weaker layers of rock as they are less resistant to erosion, particularly if they are located near the base of the cliff where the wave action is more concentrated

Question 17

What characteristics does a cliff profile with a steep sea-ward dip have?

Answer 17

-Cliff is sloped with a gentler angle

-Susceptible to land slides as the layers of rock dip towards the sea

-Layer facing the sea is vulnerable to land slides particularly if the layer beneath is weaker or along a bedding plane

-At the base of the cliffs there is often a pile of weathered material

Question 18

What characteristics does a cliff profile with a gentle sea-ward dip have?

Answer 18

-Profiles may exceed 90° producing areas of overhanging rock

-Very vulnerable to rock falls as overhangs are likely to form

-If an overhang forms then the weight of the overlying rocks will eventually lead to a collapse of the cliff

-There is often a large pile of rock debris at the base of the cliff

Question 19

What characteristics does a cliff profile with a landward dip have?

Answer 19

-Steep profiles often at angles of 70-80°

-Produce very stable cliff profiles with a smaller chance of rock falls

-It is harder to produce an overhang due to the layers dipping back towards the land

Question 20

What does lithology mean?

Answer 20

The type of rock present in an area.

Question 21

What is does mineral composition refer to?

Answer 21

The minerals which make up the rock

Question 22

What does hardness refer to? How can it be measured?

Answer 22

Hardness refer to how hard the rock is on the Mohs scale. This can be measured through the scratch test.

Question 23

Which types of rocks score highest on the Mohs scale?

Answer 23

Igneous and metamorphic rocks with a crystalline structure generally score higher, particularly those with a high concentration of quartz e.g. grantie

Question 24

What does solubility refer to?

Answer 24

Whether the rock is likely to dissolve in slightly acidic rainwater.

Question 25

Which type of rocks are more soluble?

Answer 25

Carbonate rocks that contain lots of fossils e.g. chalk/limestone

Question 26

What does permeability mean?

Answer 26

The ability of rocks to allow water to pass through them

Question 27

Which types of rocks are more permeable?

Answer 27

Sedimentary rocks such as sandstone

Question 28

How are waves created?

Answer 28

Waves are caused by the friction between wind and water, where energy is transferred from the wind to the water.

Question 29

What 3 factors impact on the strength of waves?

Answer 29

-Fetch (distance travelled over water)

-Wind speed

-Wind duration

Question 30

Why do waves break?

Answer 30

Waves are brought on shore by the wind. As the waves approach the shore friction slows the base of the wave causing the wave to steepen. This continues to happen until the wave topples over itself and surges up the beach as swash. Water from previous waves then return to the sea as backwash.

Question 31

What are the characteristics of a constructive wave?

Answer 31

Strong swash, weak backwash, low frequency (8-10 per minute), low amplitude (less that 1 metre). Associated with calmer conditions that allow for higher levels of deposition.

Question 32

What are the characteristics of a destructive wave?

Answer 32

Weak swash, strong backwash, high frequency (10-14 per minute), high amplitude (over 1 metre). Associated with stormier conditions resulting in higher levels of erosion.