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Geography - B - Coastal Landscapes > Block 2 (Temporal Variations And Their Influence On Coastal Environments) > Flashcards

Block 2 (Temporal Variations And Their Influence On Coastal Environments) Flashcards

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1
Q

What are temporal variations?

A

Changes over time

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2
Q

What are tides?

A

Regular rising and falling of the sea, due to the gravitational interaction of Moon, Sun + Earth in orbit

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3
Q

How do tides form?

A
  • Water on side of Earth closest to Moon is pulled towards Moon by gravity, to create a bulge (high tide)
  • Water on side of Earth furthest from Moon has the Earth pulled away from it, to create bulge (high tide)
  • Sides perpendicular to Moon have least water, no bulge (low tides)
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4
Q

What are the two types of tide?

A
  • Semi-diurnal

- Diurnal

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5
Q

What is a semi-diurnal tide and where experiences it?

A
  • 2 high and 2 low tides across a 24hr period
  • High (6hrs), low (6hrs), high (6hrs), low (6hrs)
  • Experienced by most coastlines
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6
Q

What is a diurnal tide and where experiences it?

A
  • 1 high and 1 low tide across a 24hr period
  • High (12 hrs), low (12hrs)
  • Rarely experienced - by areas with little surrounding landmass - Antarctica
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7
Q

What is a mixed semidiurnal tide?

A
  • Semidiurnal tide (2 high 2 low over 24hrs) but the high and low tides differ in height
  • E.g one high tide (side closest to Moon) is higher than the other high
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8
Q

What is a spring tide and when does it occur?

A

When Sun, Moon + Earth are in a line, so water movement is exaggerated to produce the greatest tidal range.

  • High tides higher, low tides lower
  • (Approx 15 m above average tide)
  • Happens twice per month (Full Moon + New Moon)
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9
Q

What is a neap tide and when does it occur?

A

When Sun + Moon are perpendicular, so water movement is largely cancelled out to produce the lowest tidal range.

  • High tides lower, low tides higher
  • Happens twice per month (Half Moons)
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10
Q

What is a tidal range?

A

Difference between high + low water levels over monthly cycle

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11
Q

What areas have high tidal ranges?

A

Areas where water is largely self-contained

  • E.g. Atlantic (surrounded by landmass)
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12
Q

What areas have low tidal ranges?

A

Areas where water struggles to move in/out

-E.g. Mediterranean (has to pass in + out through narrow Gibraltar Strait)

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13
Q

What are the three types of tidal range + their definitions?

A
  • Macrotidal = >4m
  • Mesotidal = 2-4m
  • Microtidal = <2m
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14
Q

What is the Inter-Tidal Zone (ITZ)?

A

Stretch of coastline between Spring High Tide + Spring Low Tide, where coastal processes (morphology) occur

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15
Q

What are currents?

A

Steady, predictable movement of a fluid within a larger body of that fluid (e.g water movement within Sea)

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16
Q

What are the two broad classifications of currents?

A
  • Onshore currents

- Offshore currents

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17
Q

What are onshore currents?

A

Any currents flowing TOWARDS the shore

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18
Q

What are offshore currents?

A

Any currents flowing AWAY FROM the shore

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19
Q

What scale do currents occur on?

A

Local scale

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20
Q

What are the 4 specific types of currents?

A
  • Tidal currents
  • Shorenormal currents
  • Longshore currents
  • River currents
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21
Q

Describe tidal currents

A
  • Flood tide moves towards shore, entraining sediment + depositing it (onshore current)
  • Once high tide is reaches, current reverses
  • Ebb tide moves away from shore (offshore current)
    (Velocities are low at start of each flood/ebb tide, peak in middle)
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22
Q

Is a flood tide and onshore or offshore current?

A

Onshore

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23
Q

Is an ebb tide an onshore/offshore current?

A

Offshore

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24
Q

Describe shorenormal currents

A
  • Waves approach shore with crests parallel to coastline
  • Water carried straight onshore
  • Water moves along shore for short distance
  • Water moves offshore in fast (up to 1m/s), powerful RIP CURRENTS
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25
Q

Describe longshore currents

A
  • Waves approach shore at oblique angle to coastline
  • Water carried onshore at an angle
  • Water moves along shore for short distance
  • Water moves offshore in fast (up to 1m/s), powerful RIP CURRENTS
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26
Q

Are rip currents onshore/offshore?

A

Offshore

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27
Q

Describe river currents

A
  • River flow can become very energetic in estuary (e.g. after inland rain)
  • River currents pass into ITZ
  • Can cause very disturbed conditions
28
Q

What is an onshore flow?

A

Movement of any weather feature TOWARDS the shore

29
Q

What are the weather features we look at when observing onshore/offshore flows?

A
  • Hurricanes

- Sea breeze/land breeze

30
Q

Describe how hurricanes can act as onshore flows

A
  • Winds blow out of SE part of hurricane

- Winds force ocean water + precipitation shields TOWARDS coast, in a STORM SURGE

31
Q

What is a storm surge?

A

Rise in seawater levels (that can cause flooding), solely due to storm

32
Q

Describe how sea breeze can act as an onshore flow

A
  • In afternoon
  • Water cool, LAND WARMER
  • Warm air over land rises vertically
  • Cool ocean air moves onshore to fill empty space
    Creates: onshore wind, afternoon showers/storms (as warm air rises)
33
Q

What is an offshore flow?

A

Movement of any weather feature AWAY FROM shore

34
Q

Describe how hurricanes can act as offshore flows

A
  • Winds blow out of NE part of hurricane

- Wind forces ocean water + precipitation shields AWAY FROM shore

35
Q

Describe how land breeze can act as an offshore flow

A
  • In evening
  • Land cool, OCEAN WARMER
  • Warm air over ocean rises
  • Cool air over land moves offshore to fill empty space
    Creates: offshore wind, showers + storms (warm air rises)
36
Q

Case Study of onshore flow (causing storm surge) + details

A

North Sea Storm Surge - 1953
When: 31st Jan - 1st Feb 1953 (overnight)
Where was affected: E coast of England/Scotland, Netherlands, Belgium
What: High spring tide in semi-enclosed N.Sea + severe European windstorm, caused storm surge 3.35m above av + extensive flooding
What increased losses: no national warning system, at night, poor qual sea defences (after WW2)
Effects: Princess Vic ferry sank (Scot - N.Ire) (133 deaths)
307 total deaths in E(1836 in Neth)
140,000 acres land flooded in E (340,000 in Neth)
32,000 people evacuated in E (100,000 in Neth)
24,000 properties damaged in E (47,000 in Neth)
46,000 livestock killed in E (30,000 in Neth)
Responses:
UK - National ‘Storm Tide Warning Service’
- Completion of Thames Barrier (1984) to protect London from surges (plans to upgrade after 2030 - sea level rise)
Netherlands - ‘Delta Works’ (large scale protection scheme, e.g. dams, locks, barriers)

37
Q

What is a wave?

A

Disturbance of the surface of the sea/ocean, due to the transfer of energy from the wind to the surface (via friction)

38
Q

What is fetch?

A

Distance the wind blows over the sea.

  • Larger fetch gives more powerful waves
  • Largest fetch in UK = SW from S.America
39
Q

What is duration?

A

Length of time the wind lowers over the sea

- Longer time = larger, more powerful waves

40
Q

What is wave length?

A

Distance crest to crest

41
Q

What is wave height?

A

Distance crest to trough

42
Q

What is wave steepness?

A

Ratio between length + height (L:H)

43
Q

What is wave energy?

A

Length x Height squared

44
Q

What is wave power?

A

Wave energy x Wave velocity

45
Q

What is a wave period?

A

Time interactional between crests (in s)

46
Q

What is swash time?

A

Time interval between wave break + swash reaching highest point on beach
(Time waves spend pushing material up beach)

47
Q

Describe how waves form

A
  • Air blows across water surface
  • Friction causes transfer of energy between atmosphere and sea
  • Waves gain kinetic (particle movement) + GPE (wave height)
  • Individual water particles move in circular orbit within wave, so waves appear to ‘bob’
  • Diameter of circular orbit decreases as water depth increases
48
Q

Describe how waves break

A
  • Waves reach shallow water
  • Friction with seabed
  • Water particles’ orbits become elliptical (forwards movement faster than backwards)
  • Wavelength + velocity decrease
  • Wave height increases (conservation of energy)
  • Waves become very steep
  • When wave steepness reaches 1:7, orbit is broken + wave breaks
49
Q

What are the three ways that waves break?

A
  • Spilling
  • Surging
  • Plunging
50
Q

What is spilling? Where does it occur? And what type of waves spill?

A

Waves break at a distance from shore, creating lines of surf up shore

  • Seabed is GENTLY SLOPING
  • Waves are generally CONSTRUCTIVE
51
Q

What is surging? Where does it occur? And what type of waves surge?

A

Waves break (often partially) close to shore, water slides up shore

  • Seabed is STEEP
  • Neither wave specifically
52
Q

What is plunging? Where does it occur? And what type of waves plunge?

A

Waves are steep fronted, curl over and plunge vertically onto shore

  • Seabed is moderately steep, then suddenly becomes steep
  • Waves are generally DESTRUCTIVE
53
Q

What are the two types of wave?

A
  • Constructive

- Destructive

54
Q

What is a constructive wave?

A

Lower energy wave that has a stronger swash than backwash, so builds up the beach

55
Q

Where/when are constructive waves typically found?

A
  • Gently shelving beaches

- Calm, Summer conditions

56
Q

What are the properties of constructive waves?

A 
Height: low (often <1m)
Length: long (often up to 100m)
Steepness: gentle
Period: long 
Frequency: low (6-8 per min)
Breaker: often spilling 
Material movement: up beach (berm formed) 
Beach gradient: gradual 
Swash/backwash strength: swash>backwash
57
Q

What is a destructive wave?

A

High energy wave that has a stronger backwash than swash, so breaks down the beach

58
Q

Where/when are destructive waves typically found?

A
  • Suddenly shelving beaches

- Stormy/windy Winter conditions

59
Q

What are the characteristics of destructive waves?

A 
Height: high (often >1m)
Length: short (often < 20m)
Steepness: steep 
Period: short 
Frequency: high (10-14 per min)
Breaker: often plunging 
Material movement: down beach 
Beach gradient: gentle lower beach, steeper up beach (storm beach) 
Swash/backwash strength: backwash>swash
60
Q

What are the characteristics of a sandy beach?

A
  • Wide
  • Gentle gradient
  • Form in calm conditions - sand particles moved by low energy
  • Easily eroded in higher energy conditions - low percolation, small transportable particles
61
Q

What are the characteristics of a shingle beach?

A
  • Narrow
  • Steep gradient
  • Require high energy conditions to form - large particles
  • High percolation rates
62
Q

Describe sediment sorting

A
  • Largest calibre sediment deposited at back of beach
  • Smallest calibre sediment deposited closest to Sea
    Because, constructive waves only have enough energy to transport large calibre during their strong swash
63
Q

What is a strand line?

A

Non-permanent marker, made of driftwood/seaweed/non-natural material, that marks the last high tide

64
Q

What are berms?

A

Seaward-sloping ridges of sand/shingle/pebbles, deposited by tides

65
Q

Case study of how waves+tides influence geomorphology of coasts +details

A

The Gower
Location:
- S.Wales,
- Peninsula, acts as sub-cell boundary in Sediment Cell 8 (St David’s Head-The Severn)
- Swansea city
- Borders Bristol Channel (N.Atlantic)
Beaches: E.g Rhossili Bay (3 miles wide, flat)
- Waves - High energy waves form Storm Beach
- Low energy cause sediment sorting
- Tides - Tidal range impacts area exposed to geomorphology
- Strand line + berms are left
Spits: E.g Whiteford Point (across Burry Estuary)
- Waves: Cause LSD, as waves approach at oblique angle
Mudflats/saltmarshes: E.g Llanrhidian sands + llanrhidian marsh
- Waves: sheltered area causes waves to deposit mud, then colonised by halophytic veg
- Tides: Tidal range splits saltmarsh into 2 zones (mudflats - covered at normal high tide + sward zone - covered at spring high tide)
Sand dunes: E.g Oxwich Burrows (at Oxwich Bay)
- Waves: Cause LSD, providing sediment
- Tides: Also bring sediment + the larger the tidal range, the more sand dries out and can be blown to form dunes

Geography - B - Coastal Landscapes (10 decks)

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