2.2. Coastal landforms of cliffed and constructive coasts Flashcards Preview

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Flashcards in 2.2. Coastal landforms of cliffed and constructive coasts Deck (37)
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1

Define cliff profiles

  • 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

2

What do variations in cliff profiles reflect?

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

3

Define composite/complex cliff

Cliffs composed of more than one rock type

4

Define geo

A widened crack or inlet

5

Factors influencing cliff form

  • 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

6

Define bay

 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.

7

Define headland

 A piece of land that sticks out into the sea

8

How do bay and headlands form?

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.

9

Process of coastal erosion

  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.

10

Formation of wave cut platforms

  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

11

Influence of dip of strataq

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

12

Define shore platform

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

13

3 types of rocky shoreline

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

14

Bevelled cliff

  • 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

15

2 types of coastline

  • 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

16

Define beach

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

17

Define backshore

  • 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

18

Define foreshore

  • lower part of the beach where water meets the land
  • Exposed at low tide

  • Fulls and troughs (swales)

  • Stretches of sands

  • Bayhead beaches

19

Define littoral deposits

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

20

Define berm

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

21

Factors influencing formation of beaches

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

22

Beach materials on beach formation

  • Shingles allow rapid infiltration → less squash and backwash

    • Swash > backwash = deposition

  • Sand produces a lower angle = less percolation

    • Backwash greater than on gravel beach

23

Seasons on beach formation

  • 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.

24

Define longshore drift

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

25

When does deposition occur?

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.

26

Define spit

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

27

Formation of spit

  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

28

Define bar

A bar is essentially a spit that connects 2 headlands

29

Formation of bars

  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

30

Define tombolos

A ridge of material that links an island with the mainland