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Physical Geography > Coasts > Flashcards

Coasts Flashcards

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1
Q

How are waves formed

A

Winds on the surface of the sea

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2
Q

Strong waves are caused by

A

Large fetch
Strong wind
Long duration of wind

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3
Q

Fetch

A

Distance that wind can blow to reach coastline

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4
Q

Energy is proportional to

A

Wavelength x wave height^2

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5
Q

Swash

A

Forward momentum of wave

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6
Q

Backwash

A

Gravity taking water back down

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7
Q

How do waves break

A

The sea bed has friction with the bottom of the wave and the crest continues to rise and moves forward causing the wave to break

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8
Q

Thermohaline circulation

A

A process driven by density differences in water due to temperature and salinity variations in the ocean.
Currents driven by thermohaline circulation occur at both deep and shallow ocean levels and move much slower than tidal or surface currents
Currents affect the Earth’s climate by driving warm water from the Equator and cold water from the poles around the Earth e.g. Gulf Stream

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9
Q

Upwelling

A

The movement of cold water from deep in the ocean towards the surface. The denser cold water replaces the warm surface water and creates nutrient rich cold ocean currents. These form part of the pattern if global currents.

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10
Q

Currents (what and causes)

A

Refers to the permanent or seasonal movement of surface water in the ocean. Measured in m/s or knots.
Caused by:
The rise and fall of the tides
Wind
Thermohaline circulation

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11
Q

Longshore current

A

Occur as most waves do not hit the coastline heads on but approach it at an angle. This generates a current running parallel to the shoreline. Also transfers sediment along the beach

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12
Q

Rip current

A

Strong currents moving away from the shoreline. They develop when seawater is piled up at the coastline by oncoming waves.

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13
Q

Tidal currents

A

Also called flood and ebb. They are the strongest near the store, and in bays and estuaries along the coast. Tidal currents change in a very regular pattern and can be predicted for future dates. In some locations, strong tidal currents can travel at speeds of 8 knots.

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14
Q

Tides

A

Tides are the periodic rise and fall in the level of the sea. They are caused by the gravitational pull of the sun and moon (moon has greater effect as its closer)
Highest monthly tidal range, or spring tide, occurs twice in a lunar month when the moon, sun and earth are in a straight line.
Twice a month, the moon and sun are positioned at 90° to to each other in relation to earth. This causes the lowest monthly tidal range, or neap tide.
Tides are created when the moon pulls water towards it, creating a high tide, and there is a compensatory bulge on the opposite side of the earth. Between the two bulges is where the tide is at its lowest.

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15
Q

Inputs to sediment cell - River discharge

A

Sediment and fine material brought to an estuary and entering the sea

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16
Q

Inputs to sediment cell -
Ocean currents moving sediment

A

These may transport material thousands of miles and upwelling currents may bring water to the surface from significant depths

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17
Q

Inputs to sediment cell -
Seabed disturbance moving sediment

A

Severe storms can destabilise material on the sea floor and move it towards the coast

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18
Q

Inputs to sediment cell -
Cliff and shore disintegration

A

The transfer of material as cliffs erode and upper bench material is removed into the active zone of coasts

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19
Q

Sediment cell

A

A length of coastline and its associated nearshore area within which the movement of coarse sediment (sand and shingle) is largely self-contained. Interruptions to the movement of sediment within one cell should not affect beaches in a neighbouring cell/

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20
Q

Key characteristics of sediment cells

A

Cells are discrete and function separately from each other
Sediment is sourced, transformed, and stored within the cell
The sediment in the sink (away from wave action and LSD) is essentially an output, as it is no longer being worked by the processes within the cell.

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21
Q

Sediment budget

A

The amount of sediment available to the cell is the sediment budget

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22
Q

How can human acitvities interfere with sediment cells

A

By disrupting the supply of sediment and therefore the sediment budget:
Groynes, jetties and harbour walls will block the movement of sediment and lend to the beach erosion further down the coast
River dams which cut down on the amount of fluvial sediment entering the coastal system

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23
Q

South Downs, Sussex sediment cell shoreline management plan (SMP)

A

The beaches are heavily defenced with rock reefs and groynes along all urban sections
Beaches composed of pebbles with sand exposed at low tide
Dominant west-east prevailing wind
Back eddy deposits sediment at Pagenham Harbour
8/22 km of cliff protected
Three beaches have been seriously depleted and artificially replenished

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24
Q

Transfers within a sediment cell

A

Longshore drift
Swash/backwash
Currents
Tides

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25
Q

Outputs of the sediment cell

A

Land - trapping sand at coastal landforms - beaches, coastal protection, beach sand mining, beach accumulation
Offshore - banks, spits, bars etc. Dredging, littoral drift out of cell

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26
Q

What are geomorphological processes

A

Study of how the Earth’s surface changes:
Erosion, weathering, deposition, mass movement, transformation

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27
Q

Weathering

A

Rocks are broken down by mechanical and chemical processes caused by the weather in situ.

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28
Q

Mass movement

A

When rocks loosened by weathering moves down slope under the influence of gravity

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29
Q

Chemical weathering

A

Chemicals in the air or dissolved rainwater breaking down rocks.
CO2 → Carbonic acid

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30
Q

Biological weathering

A

Plant roots growing into rocks or burrowing animals

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31
Q

Mechanical weathering

A

Freeze-thaw - water enters cracks and expands as it thaws

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32
Q

Rockfall

A

Occurs when rocks are broken down by freeze-thaw weathering, this loosening material is vulnerable to the elements, which can fall directly to the shore

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33
Q

Landslide

A

Landslides arise when rocks and unconsolidated material on the cliff face are saturated with water eventually the material slips down the slopes

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34
Q

Soil creep

A

Slowest type of downhill soil movement. Gravity pulls the water contained in soil downwards, which pulls the soil with it. The slope may appear rippled.

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35
Q

Mudflow

A

Occurs on very steep slopes along the coastline. Limited vegetation to bind soil together ground is saturated

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36
Q

Rotational slip/slumping

A

Heavy rain is absorbed by unconsolidated material making up the cliff. The cliff face becomes heavier and eventually it separates from the material.

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37
Q

Igneous rocks

A

Formed when magma solidifies
Very hard
2-5mm grain size
Don’t react to acids
Granite
Basalt - very small grain

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38
Q

Metamorphic rocks

A

Formed under high pressure and heat
harder than sedimentary, generally as hard or harder than igneous
Fine-grained - < 0.75mm Coarse grained 1-2mm
High melting point
Slate
Marble

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39
Q

Sedimentary rocks

A

Tend to be quite soft
Build up of sediment consolidated
Sandstone
Chalk
Limestone

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40
Q

Geology of the British Isles

A

Sedimentary rocks, mainly located in south east
Igneous rocks located in upland areas - Cairngorms, Lake District, Snowdonia, Hebrides
Metamorphic rocks found in Yorkshire and Northumberland

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41
Q

Abrasion/corrosion

A

Bits of rock and sediment transported by the waves smash and grind against rocks, breaking bits off and smoothing surfaces

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42
Q

Hydraulic action

A

Air in cracks on cliffs is compressed when waves crash in. Pressure exerted breaks off rock pieces

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43
Q

Cavitation

A

As waves recede the compressed air expands violently, again exerting pressure on the rock

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44
Q

Wave quarrying

A

Energy of a wave as it breaks against a cliff is enough to detach bits of rock

45
Q

Attrition

A

Bits of rock in the water smash into each other

46
Q

Solution

A

Soluble rocks get gradually dissolved by sea water

47
Q

Factors affecting the rate of erosion

A

Human activity
Fetch
Rock type
Coastal configuration
Destructive or constructive waves
Depth of coastline
Rock structure - cracks in rock

48
Q

Suspension

A

Floating sediment

49
Q

Solution

A

Dissolved chemicals

50
Q

Traction

A

Rolls along the bottom

51
Q

Saltation

A

Bouncing

52
Q

Deposition

A

Marine - sediment carried by seawater is deposited
Aeolian - sediment carried by wind is deposited
Deposition occurs when the flow of energy carrying the material declines

53
Q

Reasons for reductions of energy in deposition

A

Friction increases - shallow water or wind reaches land
Flow becomes turbulent if water or wind encounters an obstacle - i.e. two currents meeting
Sediment load increases
If wind drops, wave height, speed and energy will decrease

54
Q

Lithology

A

Characteristics of the rocks

55
Q

Structure

A

Layout of rock in relation to the sea

56
Q

Dip

A

Angle at which the rock faces the sea

57
Q

Impermeable

A

No water can go through them
- some igneous
- some metamorphic - marble

58
Q

Permeable

A

Water can flow through - limestone

59
Q

Porous

A

Water can be held - chalk

60
Q

Unconsolidated material

A

Loose and not cemented together

61
Q

Coastal recession

A

The retreat of coastline due to erosion, sea-level rise or submergence

62
Q

Joints

A

Fractures in rocks created without displacement

63
Q

Strata

A

Layers of sedimentary rock

64
Q

Coastal morphology

A

The shape and structure of coastal systems or subsystems

65
Q

Bedding planes

A

Natural breaks in the strata from a change in time period

66
Q

Folds

A

Geological structure that is formed by layers or beds of rock being bent or folded

67
Q

Faults

A

A fracture between two rocks with movement
e.g. slip

68
Q

Wave-cut platforms

A

When high and steep waves break at the foot of a cliff their energy is focussed on a small area at the base of the cliff, forming a wave-cut notch. Eventually, this forces the cliff to collapse.

69
Q

What factors affect a beach profile

A

Wave energy
Wave type
Sediment type (sand tends to produce gentle beaches because its small particle size mean the sand becomes compact when wet and allows little percolation - most of swash returns and material carried back down)
LSD

70
Q

Swash-aligned beaches

A

Experience very little LSD as incoming waves moved onto the beach in a parallel direction (waves hit coast head-on)

71
Q

Drift-aligned beaches

A

Considerable amounts of sediment are carried along the beach, usually where the coastline is fairly regular or the predominant wave direction is at an angle to the beach.

72
Q

Mudflats

A

Can be very extensive but are not always a permanent feature

73
Q

Salt marshes

A

Haloseres
Are more permanent ecosystems when stabilised by vegetation

74
Q

Conditions needed for mudflats and salt marshes to form

A

Found at low energy coastlines
Often found in estuaries where rivers meet the sea or in landward side of a spit
Brackish water - freshwater mixes with salt water at estuaries
Mudflats develop into saltmarshes when vegetation succession occurs

75
Q

Why does soil deepen with distance from the sea

A

The further you get away from the sea, the lesser impact wave action and tides will have on the marsh. This means there is no way for the sediment to get taken away and it builds up.

76
Q

Sand dunes

A

Aeolian depositional landforms
Accumulations of sand shaped into mounds by the wind
Harsh environment with no organic matter (soil)
Dynamic ecosystems called psammoseres
Vegetation needed to enable the dunes to mature
Constructive coastlines
Wide sandy beaches
Large tidal range
Strong winds
Lots of debris
No human intervention

77
Q

Plant succession

A

The gradual replacement of one plant community by another in an area over time in response to changes in physical environment
Primary succession - where there is no soil cover prior to the start of succession
Secondary succession - has some soil cover but the plant community has been removed - e.g. wildfire
Plagioclimax - where humans halt succession before the climax community is reached i.e. heather moorland

78
Q

Eustatic change

A

Global movement of water
Relatively quick change
In a glacial period sea levels fall as more precipitation falls as snow and forms ice sheets
In interglacial periods ice sheets begin to melt and retreat - sea levels rise.
Sea levels rise due to climate change - thermal expansion and melting of freshwater icesheets

79
Q

Isostatic change

A

Local movement of land causing a change in sea level
Relatively slow change
Ice sheets become so heavy that the land can sink in glacial periods - isostatic subsidence
Reduced weight of ice in interglacial periods causes the land to readjust and rise

80
Q

Positive water level change

A

Rise in base level - flood

81
Q

Negative water level change

A

Fall in base level - water draining off land

82
Q

How does tectonic activity cause a change in sea level

A

Tectonic activity causes 10% of sea level rise
Rising magma at a constructive plate margin/hotspots lift the overlying crust, reducing the capacity of the ocean - eustatic
When rocks cool from a molten state, they contact, this allows subsidence to occur, along mid-ocean ridges, and sea levels fall
Earthquake/tsunami can cause uplift of sea floor

83
Q

Submergent coastline

A

One which has a rising sea level, where the land is drowned (submerged) e.g. the South of England

84
Q

Emergent coastline

A

One which has a falling sea level, where the land is revealed e.g. Scotland

85
Q

Ria

A

Drowned river estuary
As sea levels rise, they flood river valleys. Leaving only high points visible
They have a long section and cross profile typical of a river valley, and usually a dendritic system of drainage
e.g.
River Fal - SW UK
Sea goes 18km to Truro and deposits sediment due to balance rejuvenation - water loses energy

86
Q

Dalmatian Coast - Croatia

A

River valleys are submerged so that only the higher land is seen - islands
The flooded valleys run parallel to the coast (rather than at right angles like rias and fjords)

87
Q

Fjord

A

Fjords are submerged glacial valleys. They have steep, cliff-like valley sides and the water is uniformly deep (often 1000m deep)
Formed when glaciers eroded below sea-level. When the ice melts the valleys flood.
Have U-shaped cross-section
Have a shallower section at the mouth called the threshold
e.g. Milford Sound Fjord

88
Q

Raised beaches

A

Emergent landform
As the land rises former wave-cut platforms and beaches were raised above the waves
e.g. Isle of Arran, West Scotland
Degraded cliffs and wave-cut platforms, old cliff line which contained arches + stacks
King’s Cave - 8m high raised beach with former notches and caves

89
Q

Relict cliffs

A

Emergent landform
Found at the back of a raised beach, a steep slope, displays evidence of former marine erosion but are now above high tide level
Also found in Isle of Arran and Western Scotland
Has a scree slope as the sea is not there to wash away rock debris

90
Q

Why are rising sea levels a worry

A

Can make sea defences ineffective
Island nations, coastal cities, and low-lying countries are threatened
Threatens countries with large coastal populations e.g. Bangladesh

91
Q

Changes in sea level are due to

A

Increases in volume of the ocean - melting of land ice
Thermal expansion
Coastal subsidence

92
Q

Impacts of climate change increasing sea levels

A

Warming seas, reduced oxygen, ocean acidification and sea-level rise are already affecting UK coasts and seas, with impacts on plankton, fish, birds and mammals
Coastal flooding is likely to get worse
Fisheries will be negatively impacted by ocean warming and historical overfishing

93
Q

How is England vulnerable to sea-level rise

A

370,000 homes are located in areas with >0.5% risk of coastal flooding - direct economic damages from coastal flooding are over £260m/year
By 2080 - 1.2 million homes may be at >0.5% risk
Lack of information about the coastal erosion from the public

94
Q

Impact of rising sea levels on freshwater

A

Impact on underground water resources
Intrusion of saltwater could contaminate freshwater sources
Water abstraction points would have to be moved further inland

95
Q

Impact of rising sea levels on environment

A

Coastal habitats threatened - wetlands/salt marshes
Ecosystems can adjust depending on how fast sea seal rises
Coastal squeeze may occur in salt marshes

96
Q
A
97
Q

Socio-economic impacts of sea levels

A

More development at risk
Insurance is more expensive in these areas - may dissuade people moving there
Mass migration may occur

98
Q

Causes of coastal flooding - subsidence

A

Low-lying coastlines are subject to natural subsidence
Weight of coastal cities can compress the ground (E.g. Venice)
Land reclaimed from the sea is subject to subsidence due to water abstraction
e.g. Bangladesh - 50 islands in delta have sunk 1.5m since 1960

99
Q

Causes of coastal flooding - height of land

A

Can suffer temporary risk from storm surges and permanent flooding from global sea level rise
e.g. Maldives - 1,200 islands, highest point is 2.3m above sea-level. Malé has a 3m sea wall protecting the city
Bangladesh - occupies Ganges-Brahmagupta delta. 60% of country is below 3m. Suffer from cyclones causing storm surges

100
Q

Causes of coastal flooding - vegetation

A

Removal of vegetation can increase risk of coastal flooding
Mangroves can act as a barrier to storm surges; vegetation absorbs wave energy, reducing wave impact and erosion and reduce distance waves travel onshore
Vegetation can also stabilise existing sediment and trap new sediment, raising the height of the land
e.g. - Bangladesh - 180km Sundarbans - largest mangrove in the world however, 71% is experiencing some removal of vegetation

101
Q

Causes of coastal flooding - global sea level rise

A

Mean global sea level increased 20cm in the 1900s - 50% of Netherlands and large areas of East Anglia Fens are below sea level and protected by coastal defences
IPCC predicts increase in 18-59cm by 2100
e.g. 50cm sea level rise would flood 77% of Maldives
e.g. 40cm sea level rise would permanently flood 11% of Bangladesh - 7.1 million displaced

102
Q

Shoreline Management Plan

A

Part of each sediment cell has an SMP aim to be technically sustainable, environmentally acceptable and economically viable, introduced in 1992

103
Q

Integrated coastal zone management

A

Considers all elements of the coastal system (land, water, people, economy)
Considers different users of the coast.
Input from regional, local, national authorities
Work with SMPs

104
Q

Differences between SMPs and ICZMs

A

ICZMs are more holistic
SMPs look at coastal defences, ICZM looks more at sustainability to a greater extent
ICZM informs the SMP

105
Q

Hold the line

A

Retain the existing coastline by maintaining current defences or building new ones where existing structures no longer provide protection

106
Q

Do nothing

A

Just monitor what is happening along some stretches of coastline as not technically, economically or environmentally viable to undertake defence work

107
Q

Retreat the line

A

Actively manage the rate and process by which the coast retreats

108
Q

Advance the line

A

Build new defences seaward of the existing line

109
Q

Coastal management

A

For a section of coastline to be protected, the cost of the scheme must be less than the value of the land, property and infrastructure saved and the scheme must have no negative ‘knock-on’ environmental effects, for example making erosion worse somewhere else

Physical Geography (5 decks)

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