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A-Level Geography > 3 Coastal Landforms > Flashcards

3 Coastal Landforms Flashcards

1
Q

Explain how and why the focus of erosion changes once headlands and bays form

A

Headlands become erosive environment as wave refraction concentrates wave energy on them
Caves, arches, stacks and stumps as headland slowly retreats
Sheltered bays, refraction causes energy dissipation and deposition occurs in the low-energy environment, creating beaches

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2
Q

What factors cause steep cliff profiles?

A

Resistant rocks
Horizontal strata
Basal erosion
Rockfall dominant mass movement

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3
Q

What factors cause shallower cliff profiles?

A

Less resistant rocks
Seaward-dipping strata
Sub-aerial processes cause rapid retreat of upper cliff
Sliding, slumping, mudflows

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4
Q

Describe geos

A

Very narrow inlet incised into cliffs or rocky headlands
Form when a resistant rock has a major line of weakness that is exploited by marine erosion –> hydraulic action forcing air into joints and weakening the rock strata
Erosion cuts back to create the geo, leaves the less jointed rock either side largely untouched
Sometimes initially form as tunnel-like caves at right angles to cliff line, get enlarged and roof collapse

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5
Q

Describe blowholes

A

A hole in the top of a cliff or headland, connected to the sea via a vertical and a horizontal shaft, through which sea spray may emerge in high energy conditions
In storm

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6
Q

How do blowholes form?

A
  • When a resistant rock mass contains major lines of weakness (e.g. joints, bedding planes and faults)
  • Marine erosion at the cliff base can create a deep cave under the cliff, and erosion by sea spray can then expand a vertical joint at the back of the cave to create a vertical shaft
    -Sometimes, the roof of the blowhole’s horizontally shaft may collapse and create a geo
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7
Q

Define a beach

A

Accumulation of material deposited between the lowest tide and the highest storm waves

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8
Q

Name 3 sources of beach material and the proportion of beach material that comes from each

A

Cliff erosion 5%
Offshore 5%, typically during periods of sea level rise
Rivers 90% fluvial erosion, weathering and mass movement of valley sides, and transported to the coast as suspended or bedload

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9
Q

Why do sand beaches have gentler slopes?

A

-Sand particles fine, compact when wet
-LIttle percolation of backwash in sand
-Strong backwash –> carries material back down and reduces gradient
-Material accumulates in ridges separated by troughs (runnels). May be breached by channels draining water from the beach

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10
Q

Why do shingle beaches have steeper gradients?

A

-Coarse particles have large pores between
-High percolation rates of water on the beach surface
-Weak backwash relative to swash
-Material can be transported up the beach, but less material can be transported down
-Materials accumulates on upper beach, increasing gradient

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11
Q

Define swash aligned beach

A

-Straight
-Waves approach perpendicular so little movement of material by LSD
-Closed systems –> no LSD means no movement of sediment to adjacent coastal areas

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12
Q

Define drift aligned beach

A

Waves approach at a side angle, allowing movement of sediment by LSD in an open system

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13
Q

Define storm beach

A

Ridge of coarse materials above normal high water mark, thrown up by high energy storm waves

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14
Q

Define berm

A

-series of small ridges, formed by deposition at the top of the swash at HWM

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15
Q

Define cusp

A

-Small, semi-circular depressions, often formed at the boundary of lower and upper beach
The sides of the cusp channel swash centrally, and a strong central backwash erodes material, further emphasising the semi-circular shape

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16
Q

Define runnels

A

Troughs between the ridges- may retain shallow pool of water at LWM

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17
Q

Define ridges

A

Bars of sand in the lower beach, running parallel to the shore, exposed at low tide
Formed by destructive waves transporting material from the upper beach offshore
May be breached by currents

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18
Q

How does a cycle of destructive and constructive waves create negative feedback loops for beach profile equilibrium?

A

Destructive:
Remove sediment offshore and create flatter beach profiles
Results in shallower water, more friction and a reduction in wave energy

Constructive:
Transfer sediment in the opposite direction to form steeper profiles
Produces deeper water, less friction and an increase in wave energy

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19
Q

Why can beaches be described as dynamic?

A

Profiles evolve over time, single storm event to seasonal changes
Beach systems try to reach a stable, equilibrium form with a balance between erosion and deposition

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20
Q

Define ripples

A

Tiny ridges and troughs in the lower beach, exposed at LWM and formed by orbital motion of waves

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21
Q

What can form behind spits and how?

A

Sheltered area so deposition will occur as wave energy is reduced
The silt and mud build up and salt-tolerant vegetation may colonise forming a salt marsh

22
Q

How do spits form?

A

Longshore drift occurring in one dominant direction which carries beach material to the end of the beach and then beyond into the open water
The end becomes recurved due to wave refraction and/or the presence of a secondary wind/wave direction

23
Q

Define a spit

A

Long, narrow beaches of sand or shingle that are attached to the land at one end and extend across a bay, estuary or indentation in a coastline

24
Q

How do onshore bars develop?

A

If a spit continues to grow across until it joins onto land at the other end
Forms a lagoon of brackish water
Initially thought LSD extended shingle beach at Torcross but now thought it is a ridge pushed up by rising sea levels of Flandrian Transgression

25
Q

What is the difference between particles in salt and freshwater?

A

Fresh water: Tiny clay particles carry an electrical charge and repel each other in fresh water

Saltwater: the particles are attracted to each other, combining together to form flocs, which are larger and heavier and unable to be carried in the river flow and settle out of suspension

26
Q

What does the rate of development of salt marshes depend on?

A

The rate of accumulation of sediment
Deposition of fine sediment as rivers lose energy entering the sea as well as flocculation are key factors

27
Q

What are saltpans?

A

Between the creeks, shallow depressions are often found which trap water when the tide falls

28
Q

What is the appearance and profile of a salt marsh?

A
  • Shallow gradient which slopes seawards
  • Low cliff sometimes separates the salt marsh from the unvegetated mudflats on the seaward side
  • Higher places are flooded less often but deposition rates are quite high as at high water mark, low-energy, slack water may be present for 2-3 hours
  • Greater density of vegetation trap sediment
  • Networks of small, steep-sided channels, or creeks, drain the marsh at low tide and provide routes for water to enter the salt marsh as the tide rises
29
Q

Describe the vegetation in salt marshes

A
  • Salt tolerant plant species trap sediment and gradually increase the height
  • Stems and leaves trap sediment swept in by tidal currents while the roots stabilise the sediment
  • Higher the marsh = shorter period of daily submergence and less saline conditions
  • Low marsh, on the seaward side, characterised by high salinity, turbid water and long periods of submergence
  • Few plant species can survive so diversity poor, conditions less harsh as salinity, turbidity and submergence periods all lower as you go inland
  • Greater variety of species to survive
30
Q

How do salt marshes form?

A
  • Low energy
  • Vegetated areas of deposited silts and clays
  • Twice daily inundation and exposure as tides rise and fall
31
Q

Describe a tombolo

A

Bar of sediment that connect an island
The bulldozing up of offshore sediment during the Flandrian transgression is a more likely explanation (periods of rising sea levels following the end of the Last Glacial Maximum).
During the LGM, the English Channel was a river valley covered in outwash sands and graphs - material eroded by glaciers and transported out in meltwater streams
Sea level rose –> material was pushed up in a ridge

32
Q

Define delta

A

Large areas of sediment found at the mouth of many rivers
Deltaic sediments are deposited by rivers or tidal currents
Form when rivers and tidal currents deposit sediment at a faster rate than waves and rides can remove it

33
Q

What are deltas criss-crossed by and what does this lead to?

A

A branching network of distributaries
- Overloaded with sediment, deposition forms bars and causes the channel to split into two channels with reduced energy levels so more deposition and further dividing occurs
- Channel may be lined by levees but during flood these natural embankments are breached and deposition of sediment occurs in the low-lying areas between the levees called crevasse splays

34
Q

What are the 3 distinctive components of the structures of deltas?

A

Upper delta plain - furthest inland, beyond reach of tides and made only of river deposits
Lower delta plain - intertidal zone, regularly submerged and composed of both river and marine deposits
Submerged delta plain - lies below mean low water mark, is composed mainly of marine sediments and represents the seaward growth of the delta

35
Q

Describe bird’s foot delta

A

Distributaries build out from the coast in a branching pattern, with river sediment supply exceeding the rates of removal by waves and currents

36
Q

What are crevasse splays?

A

During times of flood, levees are breached and sediment-laden water spills between the distributaries, depositing lobes of sediment there

37
Q

What is a levees?

A

Naturally-raised banks of the distributaries

38
Q

Describe arcuate delta

A

Sufficient sediment supply is available for the delta to grow seawards, but wave action is strong enough to smooth and trim its leading edge

39
Q

Describe a cuspate delta

A

A pointed extension to the coastline occurs when sediment accumulates but this is shaped by regular, gentle currents from opposite directions

40
Q

What are the 3 most common types of delta?

A

Cuspate, arcuate, bird’s foot

41
Q

Where do deltas form?

A

-Rivers entering the sea have a large sediment load
-There is a broad, shallow continental shelf to provide a platform for sediment accumulation
-There is a low energy coastline, so deposited sediment is not removed by tides or currents
-Tidal range is low

42
Q

How do steep cliff profiles form?

A
  • Destructive waves break repeatedly on relatively steeply sloping coastlines, undercutting can occur between the high and low tide levels and forms wave cut notch
  • Continued can weaken support for rock strata above, this collapses, producing a steep profile and a cliff
  • Regular removal of debris ensures cliff profile is steep and retreats inland
43
Q

What do cliff profiles depend on?

A

Geology
- horizontally bedded and landward dipping rock strata support cliffs with a steep, near vertical profile
- if rock strata inclines seaward, profile tends to follow the angle of the dipping strata

44
Q

How do shore platforms form?

A
  • As undercutting, collapse and retreat continues, the cliff becomes higher
  • At its base, a gently sloping shore platform is cut into the rock and experience abrasion
  • If rock debris is too large to be removed it will accumulate on the platform
  • Platform becomes wide and produces shallow water and small waves, even at high tide
  • Friction from platform slows down waves so break on platform rather than cliff and reduces undercutting
45
Q

What other processes apart from erosion (main) form shore platforms?

A
  • Weathering: Solution, freeze-thaw and salt crystallisation may all take place
  • Marine organisms (eg algae) can accelerate weathering when the platform is exposed at low tide. Algae release CO2 which makes sea water more acidic and increases chemical weathering
46
Q

What is the appearance of a shore platform?

A
  • Slope seawards at angles between 0-3degrees as wave erosion can occur anywhere between high and low tide levels
  • Erosion greatest at high and low tides as water levels are constant for longest –> formation of a ramp at high tide level and small cliff at low
  • Develop best if tidal range less than 4m –> if higher then erosion spread, water at high and low positions for a shorter time so platform tends to be more uniform and more steeply sloping
  • Incised with deep trenches, caused by abrasion using rockfall debris
47
Q

What are the 3 landforms that precede a stump?

A

Caves, arches, stacks and stumps

48
Q

How does a cave form?

A
  • Form on headlands (high energy) as protrude from the coast and wave refraction concentrates wave energy on them
  • Lines of weakness are exploited by marine erosion processes
  • Erosional processes cause the crack to be widened to form a cave at the base of the headland cliffs
49
Q

How does an arch and stack form?

A
  • The cave will deepen then cut right through the headland to form an arch
  • Erosion continues to undermine the arch support, subaerial weathering processes will weaken the arch roof
  • Arch roof collapse (rockfall which provides material for abrasion) leaving an isolated stack
50
Q

How does a stump form?

A
  • Further basal undercutting and subaerial weathering weakens the stack base and top
  • Collapse (rockfall) leaving a stump of rock
51
Q

What are deltas criss-crossed by and what does this lead to?

A

A branching network of distributaries
- Overloaded with sediment, deposition forms bars and causes the channel to split into two channels with reduced energy levels so more deposition and further dividing occurs
- Channel may be lined by levees but during flood these natural embankments are breached and deposition of sediment occurs in the low-lying areas between the levees called crevasse splays

52
Q

Describe bird’s foot delta

A

A-Level Geography (10 decks)

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