Coasts EQ2 - Coastal landforms

Question 1

What are the characteristics of constructive waves?

Answer 1

• low wave height (less than 1m)
• long wave length (up to 100m)
• strong swash, weak backwash
• low frequency (8-10 waves per min)

Question 2

What are the characteristics of destructive waves?

Answer 2

• wave height of over 1m
• wavelength of around 20m
• strong backwash and weaker swash
• high frequency (10-14 per min)

Question 3

What is beach morphology?

Answer 3

The shape of a beach, including its width and slope (beach profile) and features such as berms, ridges and runnels. Also includes type of sediment

Question 4

What is fetch?

Answer 4

The uninterrupted distance across water over which a wind blows, and therefore the distance the waves have to grow in size

Question 5

What factors does wave size depend on?

Answer 5

• strength of wind
• duration wind blows for
• water depth
• wave fetch

Question 6

What are human changes that can cause beach profiles to change?

Answer 6

• construction of dams blocking sediment supply
• global warming creating more storms
• coastal management intefering with sediment supply

Question 7

What is hydraulic action and the influence of lithology on it?

Answer 7

Air trapped in cracks and fissures is compressed by the force of the waves crashing against the cliff face, causing blocks of rock to become dislodged.
Heavily jointed/fissured sedimentary rocks are therefore vulnerable

Question 8

What is abrasion and the influence of lithology on it?

Answer 8

Sediment picked up by breaking waves is thrown at the cliff face, which acts like a tool on the cliff, gradually wearing it down.
Loose sediment must be available for abrasion to be effective. Softer sedimentary rocks more vulnerable than hard igneous ones

Question 9

What is attrition and the influence of lithology on it?

Answer 9

Sediment is moved around by waves, causing collisions between particles to chip fragments off, causing sediment to become smaller and more rounded.
Softer rocks very rapidly reduced in size by attrition

Question 10

What is corrosion/solution and the influence of lithology on it?

Answer 10

Carbonate rocks (limestones) are vulnerable to solution by rainwater, spray from the sea and seawater (the rock gets dissolved).
Mainly affects limestones, vulnerable to solution by weak acids

Question 11

How does a blow hole form?

Answer 11

When a coastal cave turns upwards and breaks through the flat cliff top. Usually this is because of erosion of especially weak strata or the presence of a fault line.

Question 12

How is a wave cut platform formed?

Answer 12

1. Wave cut notch is eroded between high and low tide water marks, through erosion processes at a cliff face.
2. The notch deepens by further erosion until the overlying material collapses by mass movement due to gravity, forming a cliff.
3. The process repeats, and the position of the cliff retreats (coastal recession)
4. The rock just below low tide level is always submerged, it’s uneroded as it’s never exposed to wave impact.
5. As the overlying material is eroded, uneroded rock at low tide level is left as flat rock surface, the wave cut platform.

Question 13

Explain the cave-arch-stack-stump formation process

Answer 13

1. Weaknesses in rocks at a cliff face (joints, faults etc) are exploited by marine erosion from waves causing a sea cave to form
2. This is accentuated by wave refraction, as energy is directed at lateral erosion of the headland
3. Where a line of weakness extends right through the headland caves form on both sides. Marine erosion deepens the caves until they connect up, forming an arch.
4. Undercutting of sides of arch leads to collapse of overlying material, eroding arch wider
5. Weathering and sub aerial processes cause arch roof to collapse and this creates a stack
6. Marine erosion at the base of the stack will form a notch on all sides until the stack collapses by blockfall - forming a stump

Question 14

How is a cliff formed?

Answer 14

1. Marine erosion of land between the high tide and low tide mark by hydraulic action and abrasion forms a wave cut notch
2. The notch deepens until the overlying rock collapses by mass movement due to the force of gravity.
3. The exposed face forms a cliff.

Question 15

What factors affect sediment transportation?

Answer 15

• angle of wave attack
• process of longshore drift
• tides
• currents

Question 16

What are the 4 processes of sediment transport, and the type of sediment they transport?

Answer 16

1. traction - pebbles, boulders
2. saltation - sand sized particles
3. suspension - silt and clay particles
4. solution - chemical compounds in solution

Question 17

What is a swash aligned coast?

Answer 17

Where wave crests approach parallel to the coast, so there is limited longshore movement of sediment

Question 18

What is a drift aligned coast?

Answer 18

Where wave crests break at an angle to the coast, so there is consistent longshore drift and generation of elongated depositional features

Question 19

What is gravity settling?

Answer 19

When sediment is deposited because the energy of transporting water becomes too low to move sediment

Question 20

What is flocculation?

Answer 20

Depositional process where clay particles clump together due to electrical or chemical attraction and become large enough to sink and are no longer suspended

Question 21

What is a spit and how is it formed?

Answer 21

A sand or shingle beach ridge extending beyond a turn in the coastline
Where the coast changes direction, longshore drift continues to deposit material in a zig zag motion in the direction of the prevailing wind

Question 22

What is a tombolo and how is it formed?

Answer 22

A sand or shingle bar that attaches the coastline to an offshore island.
Formed due to wave refraction around an offshore island that creates an area of calm water and deposition between the island and the coast

Question 23

What is a barrier beach/bar and how is it formed?

Answer 23

A sand or shingle beach connecting two areas of land with a shallow water lagoon behind.
Forms when a spit extends across a bay to connect two headlands.

Question 24

What is an offshore bar/berm and how is it formed?

Answer 24

Ridges of sand or shingle running parallel to the coast in an offshore zone
Formed from sediment eroded from the coastline by destructive waves which is then dragged back by the backwash – which stops at a shallower point. Transport offshore is halted by friction with the sea bed.

Question 25

What is a cuspate foreland and how is it formed?

Answer 25

Cuspate forelands extend outwards from the shoreline in a triangular shape
Formed by accretion and progradation of sand and shingle. Waves are incident from two directions/longshore drift from two directions causes the deposition of sand in a triangle.

Question 26

What is a storm ridge and how is it formed?

Answer 26

Storm ridges consist of the largest material thrown up by the swash of strong waves in a storm – much higher than the reach of normal tides.

Question 27

What are cusps and how are they formed?

Answer 27

Cusps are semi circular depressions formed by a collection of waves reaching the same point. The curved shape causes swash to concentrate in the small bay formed in the centre, while the backwash drags material back down the middle.

Question 28

What are berms and how are they formed?

Answer 28

Berms are a series of smaller ridges on a beach formed by the deposition of sediment by spring high tides or storm waves.

Question 29

What is a hooked/recurved spit and how does it form?

Answer 29

A spit whose end is curved landward, into a bay or inlet
The seaward/distal end of the spit naturally curves landward into shallower water. The ‘hook’ may be made more pronounced by waves from a secondary direction to the prevailing wind.

Question 30

What is a sediment cell?

Answer 30

A linked system of sources, transfers and sinks of sediment along a section of coastline

Question 31

What is dynamic equilibrium and how is it reached?

Answer 31

Dynamic equilibrium is reached when inputs of sediments from the source region are balanced by the amount being deposited in sinks. It is dynamic because although it is in balance, there’s a constant movement of sediment through the sediment.

Question 32

What is negative feedback?

Answer 32

When a system returns to equilibrium following a change in the system.

Question 33

What is positive feedback?

Answer 33

When an initial change within a system brings about further change in the same direction.

Question 34

What are some examples of sources, transfers and sinks?

Answer 34

Sources - offshore bars, cliffs
Transfers - beaches, parts of dunes, salt marshes
Sinks - spits, cuspate forelands

Question 35

What is weathering?

Answer 35

The in situ breakdown of rocks by chemical, mechanical or biological agents. It does not involve any movement

Question 36

What is erosion?

Answer 36

The breakdown of rock due to the action of some external force, which then transports the eroded material to a new location

Question 37

What is mechanical weathering?

Answer 37

Rocks being broken down due to the exertion of a physical force, it does not involve any chemical change

Question 38

What is chemical weathering?

Answer 38

The interaction of rock with mineral solutions (chemicals) to change the composition of rocks.

Question 39

What is biological weathering?

Answer 39

The weakening and subsequent disintegration of rock by plants, animals and microbes

Question 40

What are some examples of mechanical, chemical and biological weathering?

Answer 40

Mechanical - freeze thaw, salt crystallisation
Chemical - carbonation, hydrolysis, oxidation
Biological - plant roots, rock boring

Question 41

What is mass movement?

Answer 41

The downslope movement of rock and soil

Question 42

What is a fall?

Answer 42

Rockfalls or blockfalls are a rapid form of mass movement where a rock fragment breaks away and either drops vertically or bounces downslope.
Initiated by mechanical weathering or marine erosion (wave cut notches, undercutting)

Question 43

What is a topple?

Answer 43

Forward rotation of rocks about a pivot point.
Where rock strata have a very steep seaward dip, undercutting by erosion will lead quickly to instability and blocks of material toppling seaward

Question 44

What is a rotational slide/slump?

Answer 44

Rock failure and movement along a curved rock plane.
Occurs in rock that is weak, unconsolidated or have complex geology. Facilitated by the presence of water (lubricates and adds weight).

Question 45

What is a flow?

Answer 45

When weak rocks such as clay or unconsolidated sands become saturated, lose their cohesion and flow downslope.

Question 46

What is a rotational scar?

Answer 46

A fresh, curved, unweathered and unvegetated rock surface on the cliff face

Question 47

What is a talus scree slope?

Answer 47

A fan shaped mound of material, formed from an accumulation of angular blockfall debris

Question 48

What is a terraced cliff profile?

Answer 48

Where the cliff profile is stepped due to lithology or fractures in the rock

Question 49

What type of rock does slumping/sliding occur in?

Answer 49

Slumping = unconsolidated sediments
Sliding = consolidated sediments