2.2. Coastal landforms of cliffed and constructive coasts

Question 1

Define cliff profiles

Answer 1

• the shape of a cliff cross-section is known as the profile
• they owe their form to geology, sub-aerial processes and wave energy along a given stretch of coastline

Question 2

What do variations in cliff profiles reflect?

Answer 2

• Rock type and resistance to erosion
• Presence of lines of weakness
• Coastal structure
• Whether cliff is active/inactive (eroded/not)

Question 3

Define composite/complex cliff

Answer 3

Cliffs composed of more than one rock type

Question 4

Define geo

Answer 4

A widened crack or inlet

Question 5

Factors influencing cliff form

Answer 5

• Sub-aerial processes of weathering and mass movement.
• Lithology and rock structure
• Isostatic (geology gravitational equilibrium between the earth’s lithosphere and asthenosphere) and eustatic (sea level changes due to an alteration in the volume of water or shape of ocean basin) changes
• Human activity

Question 6

Define bay

Answer 6

An indented area of land normally found between two headlands. Bays are usually more sheltered so there is less erosive power, meaning you often find beaches in bays.

Question 7

Define headland

Answer 7

A piece of land that sticks out into the sea

Question 8

How do bay and headlands form?

Answer 8

They are formed when you get alternate layers of hard and soft rock. The sea is able to erode the soft rock a lot quicker than the hard rock making a bay. The harder rock forms a headland.

Question 9

Process of coastal erosion

Answer 9

1. Large crack opened up by hydraulic action
2. The crack grows into a cave by hydraulic action and abrasion
3. The cave becomes bigger and breaks through the headland forming a natural arch
4. The arch will gradually become bigger until it can no longer support the top of the arch. When the arch collapses, it leaves the headland on one side and a stack (a tall column of rock) on the other.
5. The stack will be attacked at the base. This weakens the structure and it will eventually collapseto form a stump.

Question 10

Formation of wave cut platforms

Answer 10

1. High steep wave breaks at the foot of a cliff. Hydraulic action and abrasion erodes a weakness in the rock at the base of the cliff to form a wave-cut notch
2. The continual undercutting increases the size of the wave cut notch which increases the stress and tension in the cliff. The cliff eventually collapses leaving boulders at the base
3. As these processes are repeated, the cliff eventually retreats leaving a wave cut platform
4. Wavecut platform cannot exceed 0.5km in width as the waves break too far away from the cliff

Question 11

Influence of dip of strataq

Answer 11

• Strata dipping inland -> relatively stable
• Strata dipping to sea -> relatively unstable
• Impermeable layers over permeable -> stable
• Permeable layers over impermeable -> unstable

Question 12

Define shore platform

Answer 12

a rock shelf fringing the coastline between the low and high water marks

Question 13

3 types of rocky shoreline

Answer 13

• Sloping shore platform
• Sub-horizontal shore platform
• Punging cliff

Question 14

Bevelled cliff

Answer 14

• A form of composite cliff

1. Vertical cliff was formed due to marine processes in the last interglacial period (warm) when sea levels were higher than they are today
2. During the subsequent glacial phase (cold), sea levels dropped => freeze thaw affected the former sea cliff, forming a bevelled age
3. When the sea level rose again during the following warm period, there was renewed wave erosion which removes the debris and steepens the base of the cliff leaving the upper part at a lower angle

Question 15

2 types of coastline

Answer 15

• Swash aligned coasts:
  
  • are orientated parallel to the crests of the prevailing waves.
  • They are closed systems in terms of longshore drift transport and net littoral drift is 0
• Drift-aligned coasts:
  
  • are orientated obliquely to the crest of the prevailing waves.
  • The shoreline of a drift-aligned coast is primarily controlled by longshore sediment transport processes.
  • Drift-aligned coasts are open systems in terms of longshore transport. Spits, bars, tombolos are features of this coast

Question 16

Define beach

Answer 16

the accumulation of material deposited between low water mark spring tides and the highest point reached by storm waves at high water mark spring tides

Question 17

Define backshore

Answer 17

• Area of a beach extends from the limit of high water foam lines to dunes or extreme inland limit of the beach. Only affected by waves during exceptional high tides or severe storms
• Dominant in coarser shoreline
• High tidal range
• Right angles

Question 18

Define foreshore

Answer 18

• lower part of the beach where water meets the land
• Exposed at low tide
• Fulls and troughs (swales)
• Stretches of sands
• Bayhead beaches

Question 19

Define littoral deposits

Answer 19

any deposited materials in the backshore and foreshore zone. Usually coarse materials

Question 20

Define berm

Answer 20

a nearly horizontal plateau on the beach face or backshore formed by the deposition of beach material by wave action

Question 21

Factors influencing formation of beaches

Answer 21

• Size, shape and composition of materials
• Tidal range
• Wave characteristics
• Season

Question 22

Beach materials on beach formation

Answer 22

• Shingles allow rapid infiltration → less squash and backwash
  
  • Swash > backwash = deposition
• Sand produces a lower angle = less percolation
  
  • Backwash greater than on gravel beach

Question 23

Seasons on beach formation

Answer 23

• Constructive waves in summer = build up beach; destructive waves in winter change the size and shape of beach
• The winter waves erode sand off the beach and store it in offshore bars. The winter waves have enough energy to not only pick up sand as they come into shore but also transport it off of the foreshore. The largest storm generated waves also erode the face of the berm crest, reducing the width of the berm. The sand is then deposited in sandbars off-shore.
• During summer, the waves are milder. These waves have enough energy to transport sand as they come into shore. As the water flows back to the ocean, there is not enough energy to transport as much sand as the wave brought onto the forshore back off shore, resulting in a net gain of sand. This results in the gradual build up of the berm crest and the berm widens for the summer.

Question 24

Define longshore drift

Answer 24

the process by which beach material is transported along the coast by the action of waves. Waves hit the beach at am angle to the coast.This is because in many areas the prevailing wind controls the direction of the waves

Question 25

When does deposition occur?

Answer 25

If swash is greater than backwash – beaches are constructed/built up and if longshore drift is taking place then beaches are built along the shore.

Question 26

Define spit

Answer 26

A spit is a long, narrow piece of land that has one end joined to the mainland and projects out into the sea or across an estuary. It is made up of sand, sediment and shingle

Question 27

Formation of spit

Answer 27

1. Longshore drift moves sand and other sediment along the coast
2. When there is a change in the direction of the coastline( Where it opens out into an estuary) the material is deposited in the deeper waters
3. Continuous deposition builds up ridges until the ridge is built above the level of the sea and longshore drift can continue. A spit is formed (Spurn Head)
4. Material continues to move across the estuary until it reaches fast flowing waters which prevents further growth
5. In some cases the spit begins to curve round. This is caused by a change in the dominant wind direction
6. A salt marsh forms in the sheltered area behind the spit where the material carried from the river is deposited

Question 28

Define bar

Answer 28

A bar is essentially a spit that connects 2 headlands

Question 29

Formation of bars

Answer 29

1. Longshore drift moves sediments along the coast
2. When there is a change in the direction of the coastline, the material is deposited in the deeper waters
3. Continuous deposition builds up ridges until it is above sea level and longshore drift continues
4. When there is no major river flows through to the sea, the process continues forming a bar
5. Bars can also form when a sandbank develops offshore (parallel to the shore) as a result of constructive waves or winds pushing breakpoint bar material forward
6. A lagoon is formed on the landward side
7. Overtime, lagoon will become infilled by deposition

Question 30

Define tombolos

Answer 30

A ridge of material that links an island with the mainland

Question 31

Formation of tombolos

Answer 31

• Longshore drift transport beach sediment along a coastline
• There’s a sudden change in the shape of the coastline such as at a headland
• Longshore drift continues to transport material in the same direction instead of following the coastline. This transports the material out to sea
• As the strength of the drift weakens away from the coastline, sediment is deposited, forming a spit
• Sometimes a spit extends far enough out to sea to join a coastal island to mainland. When it does so, the spit is known as a tombolo.

Question 32

Define barrier islands

Answer 32

Are natural sandy breakwaters that form parallel to a flat coastline

Question 33

Formation of barrier islands

Answer 33

1. 8000 years ago the sea level was 100m or more lower. Beach ridges, or dunces, were formed along the continental shelf by waves and winds
2. The sea level rose, breaking through the ridge and flooding the low area behind it. It formed a lagoon. As a result, the former dune area became an island
3. Constant action by waves and the continuing rise in the sea level caused island to migrate landward as sand was removed from the beach and deposited inland. Its present position will change for the same reasons

Question 34

Define sand dunes

Answer 34

small ridges or hills of sand found at the top of a beach, above the usual maximum reach of the waves

Question 35

Formation of sand dunes

Answer 35

1. As the tide goes out, the sand dries out and is blown up the beach. At the top of the bach is a line of seaweed and litter called the strand line. A small embryo dune forms in the shelter behind the strand line. This dune can be easily destroyed unless colonised by plants
2. Sea couch grass colonises and help bind the sand. Once the dune grows to ovr 1m high, marram grass replaces the sea couch. A yellow dune forms at 10-20m high with a long rooted marram forming a good sand trap
3. Once the yellow dune is over 10m high, less sand builds up behind it and marram grass dies to form a thin humus layer. As soil begins to form, other plants are able to grow on the dune. This is called semi-fixed dune
4. As time goes on, the soil develops and becomes damper and richer. Lichens, mosses and flowering plants can grow on the dune

Question 36

Define salt marsh

Answer 36

are coastal wetlands that are flooded and drained by salt water brought in by the tides. They are marshy because the soil may be composed of deep mud and peat.

Question 37

Formation of salt marshes

Answer 37

1. A thin layer of mud forms over sand which is covered at each tide. The only plants are algae growing on the mud
2. More mud deposited and the first plant appear. The plants trap more mud and silt. The marsh is covered at each high tide and channels are cut as the water recedes
3. Further plants appear higher up the marsh. This accelerates mud accretion. Channels deepen as the marsh surface rises
4. More plants move into the higher zones and the mud deepens. High tides still flood the marsh but low tides are confined to the creeks, which are further eroded as the water runs off
5. The marsh is now growing slowly and the mud is very deep. Further plants colonise the higher zones. Erosion undercuts the creek banks and some collapse leaving bare salt pans