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Geography - Physical > Coasts > Flashcards

Coasts Flashcards

(108 cards)

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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

Rip currents are powerful underwater currents occurring in areas close to the shoreline on some
beaches when plunging waves cause a buildup of water at the top of the beach. The backwash
is forced under the surface due to resistance from breaking waves , forming an underwater
current.

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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

Spring and neap

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

Transfers within a sediment cell

A

Longshore drift
Swash/backwash
Currents
Tides
Erosion/deposition/mass movement

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24
Q

Outputs of the sediment cell

A

Ocean currents
Rip tides
Littoral drift out of cell

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25
What are geomorphological processes
Study of how the Earth's surface changes: Erosion, weathering, deposition, mass movement, transformation
26
Weathering
Rocks are broken down by mechanical and chemical processes caused by the weather in situ.
27
Mass movement
When rocks loosened by weathering moves down slope under the influence of gravity
28
Chemical weathering
Chemicals in the air or dissolved rainwater breaking down rocks. CO2 → Carbonic acid
29
Biological weathering
Plant roots growing into rocks or burrowing animals
30
Mechanical weathering
Freeze-thaw - water enters cracks and expands as it thaws
31
Rockfall
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
32
Landslide
Landslides arise when rocks and unconsolidated material on the cliff face are saturated with water eventually the material slips down the slopes
33
Soil creep
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.
34
Mudflow
Occurs on very steep slopes along the coastline. Limited vegetation to bind soil together ground is saturated
35
Rotational slip/slumping
Slope is curved, and after slip can appear terraced Heavy rain is absorbed by unconsolidated material making up the cliff. The cliff face becomes heavier and eventually it separates from the material.
36
Igneous rocks
Formed when magma solidifies Very hard 2-5mm grain size Don't react to acids Granite Basalt - very small grain
37
Metamorphic rocks
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
38
Sedimentary rocks
Tend to be quite soft Build up of sediment consolidated Sandstone Chalk Limestone
39
Geology of the British Isles
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
40
Abrasion/corrosion
Bits of rock and sediment transported by the waves smash and grind against rocks, breaking bits off and smoothing surfaces
41
Hydraulic action
Air in cracks on cliffs is compressed when waves crash in. Pressure exerted breaks off rock pieces
42
Cavitation
As waves recede the compressed air expands violently, again exerting pressure on the rock
43
Wave quarrying
Energy of a wave as it breaks against a cliff is enough to detach bits of rock
44
Attrition
Bits of rock in the water smash into each other
45
Solution
Soluble rocks get gradually dissolved by sea water
46
Factors affecting the rate of erosion
Human activity Fetch Rock type Coastal configuration Destructive or constructive waves Depth of coastline Rock structure - cracks in rock
47
Suspension
Floating sediment
48
Solution
Dissolved chemicals
49
Traction
Rolls along the bottom
50
Saltation
Bouncing
51
Types of Deposition
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
52
Reasons for reductions of energy in deposition
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
53
Lithology
Characteristics of the rocks
54
Structure
Layout of rock in relation to the sea
55
Dip
Angle at which the rock faces the sea
56
Impermeable
No water can go through them - some igneous - some metamorphic - marble
57
Permeable
Water can flow through - limestone
58
Porous
Water can be held - chalk
59
Unconsolidated material
Loose and not cemented together
60
Coastal recession
The retreat of coastline due to erosion, sea-level rise or submergence
61
Joints
Fractures in rocks created without displacement
62
Strata
Layers of sedimentary rock
63
Coastal morphology
The shape and structure of coastal systems or subsystems
64
Bedding planes
Natural breaks in the strata from a change in time period
65
Folds
Geological structure that is formed by layers or beds of rock being bent or folded Caused by tectonic movements
66
Faults
A fracture between two rocks with movement e.g. slip
67
Wave-cut platforms
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.
68
What factors affect a beach profile
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
69
Swash-aligned beaches
Experience very little LSD as incoming waves moved onto the beach in a parallel direction (waves hit coast head-on)
70
Drift-aligned beaches
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.
71
Mudflats
Can be very extensive but are not always a permanent feature
72
Salt marshes
Haloseres Are more permanent ecosystems when stabilised by vegetation
73
Conditions needed for mudflats and salt marshes to form
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
74
Why does soil deepen with distance from the sea
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.
75
Conditions for sand dunes
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
76
Plant succession
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
77
Eustatic change
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
78
Isostatic change
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
79
Positive water level change
Rise in base level - flood
80
Negative water level change
Fall in base level - water draining off land
81
How does tectonic activity cause a change in sea level
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
82
Submergent coastline
One which has a rising sea level, where the land is drowned (submerged) e.g. the South of England
83
Emergent coastline
One which has a falling sea level, where the land is revealed e.g. Scotland
84
Ria
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
85
Dalmatian Coast - Croatia
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)
86
Fjord
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
87
Raised beaches
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
88
Relict cliffs
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
89
Why are rising sea levels a worry
Can make sea defences ineffective Island nations, coastal cities, and low-lying countries are threatened Threatens countries with large coastal populations e.g. Bangladesh
90
Changes in sea level are due to
Increases in volume of the ocean - melting of land ice Thermal expansion Coastal subsidence
91
Impacts of climate change on UK seas
Warmer waters affect marine species, especially cold-water fish like cod, and allow warm-water species to move northward, leading to disruption of food chains and fisheries Sea level around the UK has risen by ~16.5 cm since 1900 and is accelerating.
92
How is England vulnerable to sea-level rise
370,000 homes are located in areas with >0.5% risk of coastal flooding - by 2080, 1.2 million homes may be at >0.5% risk Direct economic damages from coastal flooding are over £260m/year Lack of information about the coastal erosion from the public Low-lying areas (e.g., Norfolk, East Yorkshire, Thames Estuary) are especially vulnerable.
93
Impact of rising sea levels on freshwater
Impact on underground water resources Intrusion of saltwater could contaminate freshwater sources Water abstraction points would have to be moved further inland
94
Impact of rising sea levels on ecosystems
Ecosystems can adjust depending on how fast sea seal rises Coastal squeeze may occur in salt marshes
95
Socio-economic impacts of rising sea levels
More development at risk Insurance is more expensive in these areas - may dissuade people moving there Mass migration may occur
96
Causes of coastal flooding - subsidence
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
97
Causes of coastal flooding - height of land
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
98
Causes of coastal flooding - vegetation
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
99
Causes of coastal flooding - global sea level rise
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
100
Shoreline Management Plan
Part of each sediment cell has an SMP aim to be technically sustainable, environmentally acceptable and economically viable, introduced in 1992
101
Integrated coastal zone management
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
102
Differences between SMPs and ICZMs
ICZMs are more holistic SMPs look at coastal defences, ICZM looks more at sustainability to a greater extent ICZM informs the SMP
103
Hold the line
Retain the existing coastline by maintaining current defences or building new ones where existing structures no longer provide protection
104
Do nothing
Just monitor what is happening along some stretches of coastline as not technically, economically or environmentally viable to undertake defence work
105
Managed retreat
Actively manage the rate and process by which the coast retreats
106
Advance the line
Build new defences seaward of the existing line
107
Criteria for coastline protection
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
108
Wave refraction
A process by which waves turn and lose energy around a headland or uneven coastlines. Energy is dissipated in bays leading to the formation of features associated with lower energy environments Shallower areas where the headland is curves the waves to slow down and bend in towards the headlands

Geography - Physical (15 decks)

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