Coasts Flashcards
1
Q
What is the littoral zone?
A
Dynamic zone of rapid change - the wider coastal zone where land is subject to wave action
2
Q
What are the 2 main types of coast?
A
Rocky - cliffs formed from rocks varying in height (resistant geology, high energy environment)
Coastal plains - land gradually slopes towards sea across area of deposited sediment (high sediment supply, low energy environment)
3
Q
What are the 4 areas in the littoral zone?
A
Backshore, foreshore, nearshore, offshore
4
Q
What are primary coasts?
A
Coastlines dominated by land-based processes such as deposition at the coast from rivers, or new coastal land formed from lava flows
5
Q
What are secondary coasts?
A
Coastlines dominated by marine erosion or deposition processes
6
Q
What is the difference between emergent and submergent coasts?
A
Emergent - coasts rising relative to sea level (e.g. due to tectonic uplift)
Submergent - coasts being flooded by the sea (due to rising sea levels or subsiding land)
7
Q
What is the difference between low energy and high energy coasts?
A
Low energy = sheltered, limited wave fetch, low wind speeds mean smaller waves
High energy = exposed, facing prevailing winds, long wave fetches result in powerful waves
8
Q
What is a cliff profile
A
The height and angle of a cliff face as well as its features such as wave-cut notches or changes in slope angle
9
Q
What sub-aerial processes act on cliffs?
A
weathering
mass movement
surface runoff
10
Q
What is rock erosion resistance influenced by?
A
- how reactive minerals in the rock are when exposed to chemical weathering
- whether rocks are clastic or crystalline (crystalline = more erosion resistant)
- degree to which rocks have cracks, fractures and fissures
11
Q
How are coastal plains maintained in a state of dynamic equilibrium?
A
2 balancing forces:
- deposition of sediment from rivers inland, and deposition of sediment from offshore/longshore sources
- erosion by marine action at the coast
12
Q
What is coastal accretion?
A
The deposition of sediment at the coast and the seaward growth of the coastline, creating new land
13
Q
What is dynamic equilibrium?
A
The balanced state of a system when inputs and outputs are balanced over time. By a process of feedback, the system can adjust to changes to regain equilibrium
14
Q
cliffs
What are the key elements that affect geological structure and what do they mean?
A
Jointing - division of rocks into blocks with regular shape
Dip - angle of rock strata in relation to horizontal
Faulting - weaknesses in rock layers (fractures)
Folding - crustal compression where horizontal strata are squeezed
15
Q
What are concordant and discordant coastlines?
A
Concordant - rock strata run parallel to the coastline
Discordant - different rock strata intersect the coast at a 90 degree angle
16
Q
How are headlands and bays formed at discordant coastlines?
A
Softer rock eroded faster - creating bays (differential erosion)
Wave refraction means lateral erosion occurs at headlands (cave arch stack stump), while wave energy in bays is much lower and erosion is reduced
17
Q
What is a Dalmatian coastline?
A
Where valleys/ islands run parallel to the coast - caused by high sea levels flooding the valleys between them
18
Q
What is a Haff coatsline?
A
where deposits of sand run parallel to the coastline on top of offshore bars
-> lagoons form
19
Q
What is a dip, why are they important to cliff profiles?
A
The angle the rock layer forms with the horizontal bedding plan
- rocks can dip towards land or sea
20
Q
How does the direction of the dip in a cliff impact its stability?
A
Bedding plans that tip towards SEA create gentler cliff profile
-> vulnerable to mass movement
Bedding planes that dip towards LAND create steeper profile
-> vulnerable to erosion processes
- more stable
21
Q
What are faults in cliff profiles?
A
cracks, weaknesses in the rock
- make the cliff more susceptible to erosional processes
22
Q
What are microfeatures within cliff profiles?
A
Small scale features caused by erosion or weathering
- such as notches or small caves
23
Q
What is lithology?
A
refers to physical properties of rock
- pace of coastal recession can depend of lithology
24
Q
What is igneous rock?
A
Made from cooling magma
- has a hard crystalline structure with few joints
- highly resistant to erosion
BASALT
25
What is a metamorphic rock?
Formed from intense pressure + heat on sedimentary rocks
- have a crystalline structure but they are aligned in 1 direction
-> makes them prone to folding/ faulting
Have some resistnace
SLATE
26
What is a sedimentary rock?
Formed from layers of dead animal + plant matter
- have limited resistance
- can be porus -> permeable
- can be Clastic and so have fractures that make them vulnerable to eroison
LIMESTONE
27
What is unconsolidated material?
loose rock layers that aren't cemented in one large mass
-> coastlines with this material are highly vulnerable to erosion - 10m a year
28
How does rock permeability impact coastal recession?
Impermeable rocks (clay) create greater amounts of surface runoff - which can acts with its own erosiove power
Permeable rocks allow water to pass through
- creates pore water pressure
- which weakens rock structure + enlargens joints/ faults
Permebale rocks also take in water - can lead to slumping when strata becomes too heavy
29
What is pore water pressure?
the pressure exerted by water held in permeable rocks
- weakens rock structure
30
What order of rock type is more vulnerable to costal recession of cliffs?
Less resistant at base + more resistant at top
-> experience undercutting + cliff collapse
This accelerates rate of coatsal recession
31
How does vegetation stabilise sediment?
They stabilise depositied material as their roots acts as webs to cemete the sediment together
- succession plays a large role in coatsal accreation
32
Describe dune succession
- sand dunes form sand is trapped by driftwood/ berms and is colonised by PIONEER SPECIES
- this vegetation stabilises the sand + encourages more sand to accumulate there - EMBRYO DUNE
- further plants + grasses grow - FORE DUNE
- YELLOW DUNES forms as the dune gets larger + soils begins to form
33
How do mudflats + salt marshes formed?
Form in sheltered, low-energy areas by a process called FLOCCULATION
- slit + mud deposited by river + MUDFLAT develops
- mudlfat colonised by vegetation that can survive high-salt levels + long periods of submergence
- plants trap more slit + mud as mudflats grow
- this creates an area of SALTMARSH that remains exposed for longer + longer between tides + species diveristy increases
34
What are the characteristics of constructive waves?
- low wave height (less than 1m)
- long wave length (up to 100m)
- strong swash, weak backwash
- low frequency (8-10 waves per min)
35
What are the characteristics of destructive waves?
- wave height of over 1m
- wavelength of around 20m
- strong backwash and weaker swash
- high frequency (10-14 per min)
36
What is beach morphology?
The shape of a beach, including its width and slope (beach profile)
Also includes type of sediment
37
What factors does wave size depend on?
- strength of wind
- duration wind blows for
- water depth
- wave fetch
38
What are human changes that can cause beach profiles to change?
- construction of dams blocking sediment supply
- global warming creating more storms
- coastal management intefering with sediment supply
39
What is hydraulic action and the influence of lithology on it?
Air trapped in cracks and fissures is compressed by the force of the waves crashing against the cliff face, causing blocks of rock to become dislodged.
Heavily jointed/fissured sedimentary rocks are therefore vulnerable
40
What is abrasion and the influence of lithology on it?
Sediment picked up by breaking waves is thrown at the cliff face, which acts like a tool on the cliff, gradually wearing it down.
Loose sediment must be available for abrasion to be effective.
Softer sedimentary rocks more vulnerable than hard igneous ones
41
What is attrition and the influence of lithology on it?
Sediment is moved around by waves, causing collisions between particles to chip fragments off, causing sediment to become smaller and more rounded.
Softer rocks very rapidly reduced in size by attrition
42
What is corrosion/solution and the influence of lithology on it?
Seawater gradually dissolves soluble rocks such as limestone + chalk
43
How is a wave cut platform formed?
1. Wave cut notch is eroded between high and low tide water marks, through erosion processes at a cliff face.
2. The notch deepens by further erosion until the overlying material collapses by mass movement due to gravity, forming a cliff.
3. The process repeats, and the position of the cliff retreats (coastal recession)
4. The rock just below low tide level is always submerged, it’s uneroded as it’s never exposed to wave impact.
5. As the overlying material is eroded, uneroded rock at low tide level is left as flat rock surface, the wave cut platform.
44
Explain the cave-arch-stack-stump formation proces
1. Weaknesses in rocks at a cliff face (joints, faults etc) are exploited by marine erosion from waves causing a sea cave to form
2. Where a line of weakness extends right through the headland caves form on both sides.
3. Marine erosion deepens the caves until they connect up, forming an arch.
4. Undercutting of sides of arch leads to collapse of overlying material, eroding arch wider
5. Weathering and sub aerial processes cause arch roof to collapse and this creates a stack
6. Marine erosion at the base of the stack will form a notch on all sides until the stack collapses by blockfall - forming a stump
45
How can wave refraction cause blow holes?
Wave refraction exposes both sides of a headland to erosion
sea spray can erode the top of an arch/ cave and cause a blow hole (small opening through rock)
-> normally occurs where there is a weakness
46
How is a cliff formed?
1. Marine erosion of land between the high tide and low tide mark by hydraulic action and abrasion forms a wave cut notch
2. The notch deepens until the overlying rock collapses by mass movement due to the force of gravity.
3. The exposed face forms a cliff.
47
What are the 4 processes of sediment transport, and the type of sediment they transport?
1. traction - pebbles, boulders
2. saltation - sand sized particles
3. suspension - silt and clay particles
4. solution - chemical compounds in solution
48
What are sediment cells?
Sediment cells divide the coast into seperate sections
- sediment does not move between the cells
11 sediment cells around england + wales
49
What are exmaples of inputs in sediment cells?
- erosion/ weathering of cliff face
- movement of material from offshore deposits
- rivers carrying sediment inland into coastal system
50
What are exmaples of transfers within a sediment cell?
- longshore drift moves sediment along coastline
- tidal currents
- offshore currents move sediment inland from out at sea
51
What are examples of sinks in a sediment cell
- flocculation (binding) of sediment in saltmarshes
- formation of spits + bars
- sand dunes
- beaches
52
What state are sedimemt cells described as being in?
dynamic equillibrium
53
What is a sediment budget?
the difference between amount of sediment leaving + entering a system
If more sediment enters than leaves - Positive budget
If more leaves than eneters - Negative budget
54
What is weathering?
Weakens cliffs and makes them more vulnerable to erosion + mass movement
55
What is mechanical weathering?
The breakdown of rock material without change to its chemical composition
e,g Freeze thaw
56
What is chemical weathering?
The breakdown of rock by changing its chemical composition
e.g carbonation (co2 from atmosphere dissolves in rainwater to produce carbonic acid)
Oxidation
- rocks containing iron are exposed to oxygen + iron oxide forms + crumbles rock
57
What is biological weathering?
Weathering through action of plants/ animals
58
What is mass movement?
the shifting of material downhill due to gravity
59
What is a landslide?
movement of material in a straight line down a slope
- occurs on steep slopes often after period of heavy rain
-> rain acts as lubricant to overcome friction
A landslide scar is likely to be left behind
60
What is a rotational slump?
Occurs when material slides down the slope at a curved angle
- material retains shape and slides as one mass
- usually occurs when softer permeable rock lies on top of hard, impermeable ones
61
What is blockfall?
The movement of broken blocks of material downslope
- more common on steep cliff faces with numerous joints + bedding planes
A rock topple can occur when the cliff profile has a steep dip towards sea
- can occur when waves undercut the cliff
62
What is a talus scree slope?
a steep mound of rockfall at the base of a cliff
- protects the cliff from further undercutting
63
What is a rotational scar on a cliff?
Forms after a rotational slump occurs
- its a curved mark behind the slump
- void of vegetation
64
What is a terranced cliff profile?
Can occur when multiple rotational slump occur over different time periods
- have the appearance of multiple clifftops
65
What is eustatic change?
A rise or fall in water level caused by a change in water volume - GLOBAL
66
What is isostatic change?
A local rise or fall in land level
67
How can eustatic change cause rises and falls in sea level?
During glacial periods, ice sheets form and ‘lock up’ water from the sea, causing a fall in sea level (MARINE REGRESSION)
At the end of glacial periods, melting ice sheets return water to the sea. Global temperature rise also cause thermal expansion, causing sea level rise (MARINE TRANSGRESSION)
68
How can isostatic changes cause rises and falls in land level?
Post glacial-adjustment causes isostatic rebound due to the weight of ice sheets melting off of crust - lifting the land surface out of the sea (MARINE REGRESSION)
Land can sink at coasts due to accretion of sediment and a seesaw effect causes subsidence (MARINE TRANSGRESSION)
69
What is an emergent coastline?
Parts of the littoral zone where a fall in sea level has exposed land once part of the sea bed
70
What features are found on an emergent coastline?
Raised beach
Fossil cliff
71
What is a raised beach?
A relict beach now above high tide level, usually vegetated by plant succession
72
What is a submergent coastline?
Sections of the littoral zone where sea level rise has inundated areas that were previously part of terrestial land
73
What features are found on a submergent coastline?
Rias, fjords and Dalmatian coastlines
74
What is a ria?
A drowned river valley, flooded by the sea and wider than expected (estuarine coastline)
75
What is a fjord?
Drowned glacial valley flooded by the sea
76
Why is sea level rise difficult to predict?
- uncertainties in science of relationship between climate change and melting ice
- thermal expansion depends on global temperature rise and is hard to predict
- uncertainty on when and how much ice sheets will melt
77
What are physical reasons why an areas may be at higher risk of coastal flooding?
- Low elevation areas
- Removal of vegetation results in higher risk of coastal flooding
78
What are examples of human action increasing risk of coastal recession + flooding?
- interruption of sediment cell by construction of damns
- dredging of beaches + rivers
- removal of vegetation
79
How do weathering + sub- aerial processes work toegther to influence rate of coastal recession?
- Weathering weakens rocks between high + low tide making marine erosion faster
-> increasing rate of coastal recession
80
What is a storm surge?
A short term rise in sea level caused by high winds pushing towards the coast and by low pressure from the storm
81
What factors worsen the impact of storm surges?
- if land shape funnels water into a smaller area -> will raise sea levels and increase risk of flooding
- climate change is increasing intensity + frequency
82
What are economic impacts of storm surges?
- damage to infrastructure
- saltwater may inundate freshwater bodies -> unsuitable for agricultural irrigation
- developing countries that are affected often may not have the ability to build back stronger
83
What are social impacts of storm surges?
- floodwater can contaminate drinking water
- people left homeless as floodwater damages property
- sediment may block roads + drains
- standing inland water may leave communities isolated
84
Why are the number of environmental refugees projected to increase?
- the land people live on, or earn money on is becoming submerged or may be forced to leave due to saltwater intrusion
Inhabitiants of Small Island Developing States (SIDS) may be the first to suffer
85
What is hard engineering?
Building economically costly artificial structures which deliberately alter physical processes and systems
86
What are the different coastal hard engineering strategies?
groynes
sea walls
rip rap/rock armour
revetments
offshore breakwaters
87
What are the advantages and disadvantages of hard engineering?
ADVANTAGES - reassuring to at risk people, ‘one-off’ solution that can protect coast for decades
DISADVANTAGES - high initial and maintenance costs, can be prone to failure, visually unattractive, cause issues further down the coast
88
What is soft engineering?
involves working with natural processes to reduce the effects of flooding + erosion
89
What are examples of soft engineering?
- beach nourishment
- dune stabilisation
- cliff regrading
- cliff drainage
90
What is cliff regrading?
- changes the shape of the cliff to a gentler gradient and so less susceptible to erosion
91
What is cliff drainage?
the removal of water from a cliff face by building drainage channels
-> reduces pressure within cliff face
92
What is sustainable management?
involves meeting the needs of coastal communities now without compromising the ability for future communities to meet their needs
Involves looking at the wider coastal system
93
Why can sustainable management lead to conflict?
- limiting resources may impact livelihoods
- protecting land with high economic value may make some people feel abonded
94
What is the Integrated Coastal Zone Management (ICZM)?
a strategy that considers all elements of coastal system - its a holistic view
Considers long term managment as well as short term needs
95
What are Shoreline Managment Plans (SMPs)?
The ICZM breaks the coastline into 22 smaller areas each with its own SMP
96
What are the 4 key stages in a Shoreline Managment Plans (SMP)?
- no active intervention
- strategic realingment
- hold the line
- advance the line
97
What is ' No active intervention' in a SMP?
- building no coastal defences
- any defences already in place remain there but will have limited impact long term as they are likely to be eroded
CHEAPEST
98
What is ' Strategic Realignment ' in a SMP?
involves allowing the shoreline to move naturally
- aims to cause the least damage to important areas e.g allowing farmland to flood to avoid flooding in built up area
99
What is ' Hold the Line' in a SMP?
Maintaining existing coastal defences -> position of shore line will stay the same
- often used on shorelines with high value land + with a mixture of hard + soft engineering
100
What is 'Advance the Line ' in a SMP?
Involves building new defences further out at sea than the existing line of defence
- this increases size of beach
- used on coastlines where there is likely to be reasonable levels of deposition
101
Who oversees coatsal management in the UK?
Department for Environment, Food and Rural Affairs (DEFRA)
102
What is cost-benefit analysis?
Weighs up positive and negative impacts a decision will have
- tries to weigh up social and environmental impacts against economic costs + benefits
103
What is an Environmental Impact Analysis (EIA)?
Helps to add detail to a cost-benefit analysis
Looks at the impact of construction on:
- natural processes
- particular specieis
- balance in ecosystems
- environmental quality
