Coastal Systems Flashcards
(54 cards)
1
Q
What kind of system is the coast?
A
- dynamic systems with a range of inputs, outputs, stores and flows
- works together to create distinctive landscapes
- inputs originate from outside the system (Eg. sediment carried into the coastal zone by rivers)
- outputs to other natural systems (Eg. Eroded rock material transported offshore to the ocean)
2
Q
Why are coasts important ?
A
50% of the human population lives within 150km of the sea on coastal planes
3
Q
What are inputs into the coastal system?
A
- energy - wind, waves, insolation, tides, ocean currents
- matter - sediment
4
Q
What are stores in the coastal system?
A
- beaches
- sand dunes
- cliff faces/geology
- spit (temporary)
- bars
- marram grass + other pioneer species
- tombolo
5
Q
What are flows/transfers in the coastal system?
A
- longshore drift/littoral drift
- transportation processes - solution, suspension, saltation, traction
- wind
- waves
6
Q
What are outputs in the coastal system?
A
- sediment removes beyond a local scale
- dissipation of wave energy
- accumulation of sediment above the tidal limit
7
Q
What is a sediment cell?
A
A stretch of coastline, usually bordered by 2 prominent headlands, where the movement of sediment is more or less contained
8
Q
How many sediment cells are in the UK?
Give the sediment cells of Flamborough Head and Minehead?
A
- 11 cells in the UK
- Flamborough Head = cell 2
- Minehead = cell 7
9
Q
What is the sediment budget equation?
A
Sediment budget = outputs - inputs
10
Q
What is a positive and negative sediment budget?
A
- positive: inputs>outputs - accretion creates surplus
- negative: outputs>inputs - erosion creates a deficit
11
Q
Outline the coastal system at Flamborough Head
A
- inputs - fluvial sediment from a small stream, North Atlantic storms, sediment eroded from cliffs
- outputs - deposited sediment in southern parts of the North Sea
- stores - the sea at Selwicks Bay, the coastline, the Southern North Sea, cliffs
- transfers - small stream discharging water, sediment eroded from cliffs
12
Q
what is the main sources of energy at the coast?
A
- the sea in the form of waves
- wind
- currents
- the sun
13
Q
how are waves formed?
A
- mostly by surface winds
- prevailing wind direction influences the direction of travel of the waves
- frictional drag from wind disturbs the surface and forms ripples or waves
- open sea = circular wave orbit - little horizontal movement
- closer to coast, water becomes shallower - causes horizontal movement of water as waves are driven onshore to break on the beach - waves have an eliptical orbit
14
Q
what is wind?
A
the movement of air from one place to another
15
Q
how does air pressure variation affect wind?
A
- wind moves from high pressure to low pressure (fills the gap left by low pressure rising)
- variations in atmospheric pressure reflect differences in surface heating by the sun (intense heating = low pressure)
- the greater the pressure difference (pressure gradient), the faster and stronger the wind
16
Q
how is the UKs prevailing wind direction related to Global atmospheric circulation?
A
- prevailing wind direction = SW
- air moves from subtropical high pressure belt (30 degrees N) to subpolar low pressure belt (60 degrees N)
- westerlies blow over lots of Atlantic ocean + transfer lots of energy to waves that approach the UK
17
Q
what factors affect wave energy?
A
- strength of wind - determined by pressure gradient
- duration of wind - the longer wind blows, the more powerful the waves
- fetch (distance over open water that wind blows) - longer the fetch the more powerful the waves
18
Q
how has fetch affected wave energy in the UK?
A
- longest fetch = 3000 miles from Brazil
- coincides with prevailing wind direction -
- causes high energy waves to hit the SW coast like at Cornwall
19
Q
describe the features of a constructive wave?
A
- low energy - deposition
- formed by distant weather systems over the open ocean
- wave form: low surging waves, long wavelength
- strong swash, weak backwash
- constructive - beach gains
- beach profile: short term - gentle beach profile, long term - sediment build up causes it to become steeper
20
Q
describe the features of a destructive wave?
A
- high energy - deposition
- formed by local storms
- wave form: high plunging waves , short wavelength
- weak swash, strong backwash
- destructive - beach loss
- beach profile: short term - steeper beach profile, long term - flattens out
21
Q
what is an ocean current?
A
the permanent or seasonal movement of surface/deep water in seas or oceans
22
Q
how do tides affect ocean currents?
A
- rise and fall of tides = current in the ocean
- strongest near the shore + bays and estuaries along the coast
- change with a very regular pattern - predictable
- travels at speeds of 8 kts or more
23
Q
how does the wind affect ocean currents?
A
- drives currents at or near the ocean surface
- coastal areas = local scale currents - coastal upwelling
- open ocean = global scale currents - circulate water for 1000s of miles
24
Q
how does thermohaline circulation affect ocean currents?
A
- differences in water movement due to temperature + salinity
- warmer water = higher density
- more saline water = higher density
- drives currents at both deep and shallow ocean levels
- much slower than tidal or surface currents
- drives warm water from the equator and cold water from the poles around the earth
25
key facts about the Gulf stream?
- 10000km long
- directed towards earth due to turning of the earth + west winds
- when it gets near Greenland - water becomes colder + saltier - denser so it sinks
- could come to a standstill - polar melting = less salty water - wouldn't sink as much as usual + cause the heat pump to stop working
26
what is the ocean conveyor belt?
the combination of currents the allow oceans to exchange water - aka thermohaline circulation
27
what is upwelling?
- movement of water from deep in the ocean towards the surface
- colder denser water rises to replace water warmed by the sun - nutrient rich so creates nutrient rich cold ocean currents
28
what are rip tides?
- strong localised currents on some beaches
- plunging waves cause temporary buildup of water at the top of the beach
- breaking waves = resistance - backwash forced just below the surface following undulations in beach profile
- fast offshore surge of water
29
what is wave refraction?
- essentially wave fronts are distorted when they approach an indented shoreline- the wave drags in the shallower water approaching a headland, causing it to bend
- energy is concentrated at headlands, dissipated at bays - headlands are eroded, bays are built up with sediment
30
where are high energy coastlines found in the UK?
- stretches of west coast facing atlantic ocean - waves are powerful for most of the yr - eg. Cornwall, NW Scotland, Holderness coastline
- erosion rates exceed deposition - land is lost
31
where are low energy coastlines found in the UK?
- stretches of coast where waves are less powerful/ coast is sheltered from large waves - eg. estuaries/bays of Lincolnshire and Dawlish Warren
- deposition rates exceed erosion
32
what are tides?
the periodic rise and fall in the level of the sea, caused by the gravitational pull of the sun and moon (mainly the moon), which causes bulges on 2 sides of the earth (high tide) and the area in between is low tide
33
what are spring tides?
- this happens when the sun and moon are lined up in parallel - during the full moon or new moon
- their gravitational pulls act together
- higher max high tides + lower min low tide = larger tidal range
34
what are neap tides?
- this happens when the sun and moon are perpendicular to each other - 1st/3rd quarter of the moon
- their gravitational pulls work against each other
- lower max high tide + higher min low tide = smaller tidal range
- erosion is more spatially concentrated
35
what are the main sources of sediment in the coastal system?
- rivers - most coastal sediment, esp in high rainfall envs w active river erosion. deposited in river mouths + estuaries
- cliff erosion - lots where there is lots of unconsolidated rock. eg. Holderness coast, Lincolnshire - erosion rate of 10m/yr w sand + clay cliffs
- longshore drift - sediment transported from one stretch of coastline to another
- wind - blows sand to be deposited in coastal areas. sand dunes = semi-dynamic - show accumulations of sand + potential sources
- glaciers - ice shelves calve - ice chunks break off into the sea - this deposits sediment trapped in the ice. eg. Alaska, Greenland, Antarctica
- offshore - waves tides + currents transfer sediment into littoral zone. storms surges = sediment input. eg. last glacial period
- volcanoes - volcanic ash
- biological origin - eg. shells
- waves - contribute to movement of sediment
36
how does the sediment cell operate at Christchurch Bay, Dorset?
- inputs = cliff erosion, river
- longshore drift = eastward sediment movement
- accretion/deposition at E + SE - temp stores like sand banks, spits
- River Solent reaches sea - fast flowing meets slow flowing = depostion
- no rip currents
- no outputs - closed system + no evidence of a storm event
- if Hengistbury Head eroded, the bay wouldnt be sheltered any more
37
what are sub-aerial processes?
they are coastal processes that happen at or above land - eg. weathering and mass movement
38
what is weathering?
when rocks are broken down by mechanical and chemical processes caused by the weather in situ (at or close to the ground surface)
39
what is mass movement?
a geomorphic process where soil and rock debris move down slopes under the force of gravity
40
what is mechanical/physical weathering?
the break up of rock without any chemical changes
41
what are mechanical/physical weathering processes?
- frequent cycles of wetting + drying at the coast - for rocks w lots of clay, they expand when wet + shrink when dry - causes cracks and they eventually break up - eg. shale
- salt crystallisation - salt water evaporates + leaves behind salt crystals - these grow + exert stress on the rock, causing it to break up (corrosion happens if iron is present to)
- frost shattering - aka freeze thaw weathering. water enters a crack in a rock, freezes, expands by 10% - pressure exerted on rock, causing crack to widen. this is repeated causing fragments of rock to break away and collect at the base of the cliff as scree.
- angular rock fragments are used as tools in marine erosion
- frost shattering example - 2001 - after a wet + cold Jan + Feb, lots happened in S coast of England - chalk cliffs mainly affected
42
what is biological weathering?
the breakdown of rock by organic activity
43
what are some biological weathering places?
- plant roots grow into cracks on the cliff surface - as they grow cracks widen + break up rock
- water running through decayed plants becomes acidic - more chemical weathering
- birds + animals burrow into cliffs - rabbits, puffins, sand martens
- marine organisms burrow into rock (eg. piddocks) - or they secrete acids (eg. limpets)
44
what is chemical weathering?
break down of rock where a chemical reaction is involved - involves a chemical reaction where salts may be dissolved or a clay like deposit is formed (easily eroded)
45
what are some chemical weathering processes?
- solution - dissolving of rock minerals - eg. halite (rock salt)
- oxidation - rock minerals + oxygen = rusty red powder - makes rocks more vulnerable to weathering - eg. iron
- carbonation - rainwater absorbs CO2 to form weak carbonic acid. this reacts with calcium carbonate in rocks to form calcium bicarbonate (easily dissolved). colder rainwater = more CO2 absorbed -> more carbonation in winter
46
what are the different types of mass movement?
- soil creep
- solifluction
- mudflow
- runoff
- landslide
- rockfall
- landslip/slump
47
what is soil creep?
- the slow movement of individual soil particles downhill - imperceptibly slow
- nature of movement: creep/flow
- rate of movment: very slow
- wet
48
what is solifluction?
- like soil creep but cold env specific
- soil thaws + becomes saturated on permafrost (impermeable frozen ground)
- sodden soil moves downwards with a combo of heave + flow
- nature of movement: flow
- rate of movement: very slow
- wet
49
what is a mudflow?
- earth + mud flows downhill over unconsolidated rock eg. clay - usually after heavy rain
- water trapped inside rock = higher pore water pressure = rock particles forced apart = slope failure
- pore water pressure - important in determining slope instability
- nature of movement: flow
- rate of movement: fast
- wet
50
what is runoff?
- material moves down a slope/cliff face
- small particles go down into littoral zone - sediment input
- transfers water + sediment from one flow to another
- wet/dry
51
what is a landslide?
- blockslide = blocks move down a plane on a hillside, debris slide = debris moves down
- moves parallel to the ground
- material block remains largely intact
- triggered by earthquakes/heavy rain - surface is lubricated so less friction
- eg. 1933 Holbeck Hall
- nature of movement: slide
- rate of movement: fast
- dry/wet
52
what is rockfall?
- sudden, nearly vertical movement of rock/soil - eg. an overhanging cliff
- steep/vertical cliffs
- triggered by earthquakes/freeze thaw weathering
- rocks bounce down as scree - temp store removed by waves
- nature of movement: fall
- rate of movement: fast
- dry/wet
53
what is a landslip/slump?
- slope failure which involves rotational movement of soil/rock - weak unconsolidated rock - eg. sand or soil
- more often on permeable t=rock than impermeable rock
- forms scarp
- causes curved slide appearance, multiple slumps = terraced appearance
- higher pore water pressure
- nature of movement: slide
- rate of movement: fast
- wet
54
what factors affect the nature and rate of erosion?
- waves: size + type affects rate + type of erosion on a particular stretch of coast. most erosion during winter storms (destructive waves most powerful) - eg. Dawlish 2014
- rock type (lithology): physical strength + chemistry of rock. tough + resistant (eg. granite) = very slow erosion (eg. Lands End- 10cm erosion in the past century). weaker rock (eg. clay/shale) = fast erosion (eg. Holderness coast- 120m in the last century)
- geological structure: cracks, joints, bedding planes + faults are weaknesses in rock structure - exploited by erosion. variation in geology = different rates of erosion based on rock strength
- presence/absence of a beach: presence = absorbs wave energy, reduces impact of waves on a beach. absence = ore vulnerable to wave attack so more erosion
