Coastal Landscapes and Change

Question 1

Sediment Cells

Answer 1

Coasts are split into sections called sediment cells. They’re closed systems.

Sources - Where sediment originates.
Through flows - Movement of sediment along the shore through long shore drift.
Sinks - Locations where deposition of sediment dominates.

Under normal conditions, the coastal system operates in a state of dynamic equilibrium. This is where the input and outputs of sediment are in a constant state of change but remain in balance.

Question 2

What are feedback loops?

Answer 2

The coastal system has mechanisms which enhance changes within a system, taking it away from
dynamic equilibrium (positive feedback) or mechanisms which balances changes, taking the
system back towards equilibrium (negative feedback).

Question 3

Explain the negative feedback loop.

Answer 3

This lessens any change which has occurred within the system.

It decreases the amount of change by reducing some of the inputs, returning the system to stability.

Question 4

What is positive feedback loop?

Answer 4

This exaggerates the change making the system more unstable and taking it away from dynamic equilibrium:

People walking over sand dunes destroys vegetation causing erosion.
Eventually sand dunes are completely eroded leaving more of the beach open to erosion taking it away from dynamic equilibrium.

Question 5

Explain the littoral zone.

Answer 5

The littoral zone is the area of the coast where land is subject to wave action. It changes due to short term factors like tides, storm surges or long term factors like changes in sea level and climate change.

Question 6

What are the several sub zones within the littoral zone?

Answer 6

Back shore - Area above high tide level and only affected by exceptionally high tides.

Foreshore - This is where most wave processes occur.

Offshore - The Open sea.

Question 7

Explain Valentine’s Classification.

Answer 7

Valentine’s classification describes the range of coastlines that can occur.

An advancing coastline may be due to land emerging or deposition being the prominent process. Alternatively, a coastline may be retreating due to land submerging or erosion becoming the prominent process.

Question 8

What is Corrasion?

Answer 8

Sand and pebbles are picked up by the sea from an offshore sediment sink or temporal store and hurled again the cliffs at high tide, causing the cliffs to be eroded.

Question 9

What is abrasion?

Answer 9

Process of where sediment is moved along the shoreline, causing it be worn down over time.

Question 10

What is attrition?

Answer 10

Wave action cause rocks and pebbles to hit against each other, wearing each other down and so becoming round and eventually smaller.

Question 11

What is hydraulic action?

Answer 11

As a wave crashes onto a rock or cliff face, air is forced into cracks, joints and faults within the rock. High pressure causes cracks to force apart and widen when wave retreats and air expands. Over time this causes the rock to fracture.

Question 12

What is corrosion (solution)?

Answer 12

The mildly acidic seawater can cause alkaline rock such as limestone to be eroded and is very similar to the process of carbonation weathering.

Question 13

What is wave quarrying?

Answer 13

This is when breaking waves that hit the cliff face exert a pressure up to 30 tonnes per m^2. It’s similar to hydraulic action but acts with significantly more pressure to pull away rocks from a cliff face. The force of breaking wave hammers the rock surface, shaking and weakening it leaving it open to attack from hydraulic action and abrasion.

Question 14

When are erosion rates highest?

Answer 14

Waves are high and have a long fetch.
Waves approach the coast perpendicular to the cliff.
At high tide - Waves travel higher up the cliff so a bigger area of cliff face is able to be eroded.
Heavy rainfall occurs - Water percolates through permeable rock ,weakening cliff.
In winter - destructive waves are the largest and most destructive during winter.

Question 15

What determines vulnerability to eriosn?

Answer 15

The resistance of a rock determines it’s vulnerability to erosion.

Question 16

What determines the resistance of rock?

Answer 16

It’s influenced by various factors:

Whether rocks are clastic or crystalline - Sedimentary rocks like sandstone are clastic as they are made up of cemented sediment particles, therefore are vulnerable to erosion, whereas igneous and metamorphic rocks are made up of interlocking crystals, making them more resistant to erosion.

More cracks the more weaknesses there are in the rock and more open it is to erosional processes like Hydraulic action.

Lithology of rock.

Question 17

Give example, rate of erosion and structure of rock for the following types of rock:

Igneous
Metamorphic
Sedimentary

Answer 17

Igneous - Granite Basalt.
Very slow rate of erosion.
Interlocking crystals which allow for high resistance.

Metamorphic - Slate, Schist, Marble. Slow rate of erosion, crystal all orientated in the same direction.

Sedimentary - Limestone, Very fast, lots of fractures and bedding planes making them weak.

Question 18

What land forms can erosion create?

Answer 18

Wave Cut notches
Wave cut platforms
Cave-Arch-Stack-Stump
Retreating Cliffs
Blowhole

Question 19

How are wave-cut notch and platforms created?

Answer 19

Marine erosion attacks the base of a cliff, creating a notch of eroded material. As the notch becomes deeper sub-aerial weathering weakens the cliff. The cliff face becomes unstable and falls under its own weight through mass movement leaving behind a wave cut platform.

Question 20

Explain retreating cliffs.

Answer 20

Through the process of repeat wave-cut notches and platforms, new cliff faces are created, whilst the land retreats.

Question 21

Explain cave-arch-stacks and stumps.

Answer 21

This occurs on headlands. Marine erosion widens faults in the base of the headland, widening over time to create a cave. The cave will widen due to marine erosion and sub-aerial processes, eroding through to the other side of the headland creating an arch. The arch continues to widen until it can’t support its self and falls through mass movement leaving a stack. With marine erosion attacking the base of the stack ,eventually stack collapses and leaves a stump.

Question 22

Explain blowholes.

Answer 22

A blowhole is a combination of two features: A pot hole on a top of a cliff, created by chemical weathering, and a cave, formed by marine erosion. As the cave erodes deeper into the cliff face and the pothole deepens, they may meet. In this case, a channel is created for incoming waves to travel into and up the cliff face.

Question 23

Explain Long shore drift.

Answer 23

Waves hit the beach at an angle determined by the direction of prevailing wind.

Waves push sediment in this direction and up the beach in the swash.

Due to gravity, the wave carries sediment back down the beach in the backwash.

This moves sediment along the beach over time.

Question 24

What are the four other processes of transportation?

Answer 24

Traction - Large, heavy sediment rolls along the sea bed, being pushed by currents.

Saltation - Smaller sediment bounces along the sea bed, being pushed by currents.

Suspension - Small sediment is carried within the water column.

Solution - Dissolved material is carried within the water.

Question 25

What does the effectiveness of transportation depend on?

Answer 25

The impact of transportation depends on the severity of the angle that waves travel onto land. Swash-aligned - Wave crests approach parallel to coast so there's limited longshore drift. Sediment doesn't travel up the beach far. Drift-aligned - Waves approach at a significant angle, so longshroe drift causes the sediment to travel far up the beach.

Question 26

What determines the likelihood of deposition?

Answer 26

Deposition occurs when a wave loses energy meaning the sediment becomes too heavy to carry. Deposition tends to be a gradual and continuous processes.

Question 27

What is gravity settling?

Answer 27

The wave's energy becomes very low and so heavy rocks and boulders are deposited followed by the next heaviest sediment.

Question 28

What is flocculation?

Answer 28

Flocculation - Clay particles clump together due to chemical attraction and then sink due to their high density.

Question 29

What is a tombolo?

Answer 29

A tombolo is a bar or beach that connects the mainland to an offshore island and is formed due to wave refraction off the coast land island reducing wave velocity, leading to deposition of sediments. They may be covered at high tide if they're low lying.

Question 30

What are cuspate forelands?

Answer 30

Only occurs with triangular shaped headlands. Long shore drift along each side of the headland will create beaches where they meet and form a cuspate foreland.

Question 31

What are offshore bars?

Answer 31

A region offshore where sand is deposited, as the waves don't have enough energy to carry the sediment to shore. They can be formed as the wave breaks early, scouring the seabed and instantly deposition its sediment as loose-sediment offshore bar.

Question 32

How do sand dunes occur?

Answer 32

Sand dunes occur when prevailing winds blow sediment to the back of the beach and therefore the formation of dunes requires large quantities of sand and a large tidal range. This allows sand to dry, so it's light enough to be picked up and carried by the wind to the back of the beach. Frequent and strong offshore winds are also necessary.

Question 33

What is weathering?

Answer 33

Weathering is the breakdown of rocks over time, leading to the transfer of material into the littoral zone, where it becomes an input to sediment sells.

Question 34

What are examples of mechanical weathering?

Answer 34

● Freeze-thaw (Frost-Shattering): Water enters cracks in rocks and then the water freezes overnight during the winter. As it freezes, water expands by around 10% in volume which increases the pressure acting on a rock, causing cracks to develop. Over time these cracks grow, weakening the cliff making is more vulnerable to other processes of erosion ● Salt Crystallisation: As seawater evaporates, salt is left behind. Salt crystals will grow over time, exerting pressure on the rock, which forces the cracks to widen. Salt can also corrode ferrous (materials that contains iron) rock due to chemical reactions ● Wetting and Drying: Rocks such as clay expand when wet and then contract again when they are drying. The frequent cycles of wetting and drying at the coast can cause these rocks and cliffs to break up Chemical weathering - the breakdown of

Question 35

What are examples of chemical weathering?

Answer 35

Carbonation: Rainwater absorbs CO2 from the air to create a weak carbonic acid which then reacts with calcium carbonate in rocks to form calcium bicarbonate which can then be easily dissolved. Acid rain reacts with limestone to form calcium bicarbonate, which is then easily dissolved allowing erosion. ● Oxidation: When minerals become exposed to the air through cracks and fissures , the mineral will become oxidised which will increase its volume (contributing to mechanical weathering), causing the rock to crumble. The most common oxidation within rocks is iron minerals becoming iron oxide, turning the rock rusty orange after being exposed to the air. ● Solution: When rock minerals such as rock salt are dissolved.

Question 36

What are examples of biological weathering?

Answer 36

Plant Roots - Roots of plants growing into the cracks of rocks, which exerts pressure, eventually splitting the rocks. Research Angkor Wat for more information on this, even though it is not coastal! ● Birds - Some birds such as Puffins dig burrows into cliffs weakening them and making erosion more likely. ● Rock Boring - Many species of clams secrete chemicals that dissolve rocks and piddocks may burrow into the rock face ● Seaweed Acids - Some seaweeds contain pockets of sulphuric acid, which if hit against a rock or cliff face, the acid will dissolve some of the rock’s minerals. (e.g. Kelp) ● Decaying Vegetation - Water that flows through decaying vegetation and then over coastal areas, will be acidic, thus causing chemical weathering

Question 37

What are the two different categories of mass movent?

Answer 37

Slide and flows. For a slide, sediment keeps its same place within the whole material, simply moves downhill. However, flows, material flows down and mixes.

Question 38

Give examples of flow mass movement.

Answer 38

Soil creep - The slowest but continuous form of mass movement involving the movement of soil particles downhill. ● Solifluction - Occurs mainly in tundra areas where the land is frozen. As the top layers thaws during summer (but the lower layers still stay frozen due to permafrost) the surface layers flows over the frozen layers. ● Mudflows - An increase in the water content of soil can reduce friction, leading to earth and mud to flow over underlying bedrock.

Question 39

Give examples of slides mass movement.

Answer 39

Rock falls - Occur on sloped cliffs (over 40o ) when exposed to mechanical weathering. ● Rock slides - Water between joints and bedding planes (which are parallel to the cliff face) can reduce friction and lead to more sliding. ● Slumps - Occur when the soil is saturated with water, causing a rotation movement of soft materials (such as clay and sand) forming rotational scars and terraced cliff profiles.

Question 40

Why is coastal vegetation important?

Answer 40

▪ Roots of plants bind soil together which helps to reduce erosion. ▪ When completely submerged, plants provide a protective layer for the ground and so the ground is less easily eroded. ▪ Plants reduce the wind speed at the surface and so less wind erosion occurs. Plants grow in different coastal environments and are either halophytes or xerophytes ▪ Xerophytes – plants that are tolerant of dry conditions. ▪ Halophytes (or brackish) – plants that are tolerant of salty conditions.