Coasts Flashcards
What is a system
A set of interrelated objects compromising of components (stores) and processes (links)
What are the main types of energy in coastal landscapes
Kinetic
Potential
Thermal
What are the components of an open system
Energy and matter can be transferred from neighbouring system as an input
Energy and matter can be transferred to neighbouring systems as an output
What are the inputs
Kinetic energy from wind and waves
Thermal energy from the heat of the sun
Potential energy from the position of material on slopes
Material from marine deposition, weathering, mass movement
What are the outputs
Marine and wind erosion from the beach and rock surfaces
Evaporation
What is a throughput
It consists of stores (beach, nearshore sediment) and flows (movement of sediment along a beach-LSD)
What is a sediment cell
Stretch of coastline and its associated nearshore area
Regard as a closed system but in reality it is unlikely that
How many sediment cells are in the UK and what are they defined by
11
Topography and shape of the coastline
What are the physical factors of a landscape
Wind Waves Tides Geology Currents
How do winds influence landscape
Winds drive Waves
Waves drive erosion and sediment transfer
The higher the wind speed and the longer the fetch, the larger the waves and more energy they possess
How do waves work
Potential energy above the wave crest
Kinetic energy is the motion of the water within the wave
Amount of energy in a wave formula
P=H2T
P = power is kilowatts per metre of wave front
H = wave height in metres
T = time interval between wave crests in second (wave period)
the relationship between wave height and wave energy is non-linear
Compare swell waves and storm waves
Swell waves-Long wavelength, wave period of up to 20 seconds
Storm waves-Short wavelength, greater height, shorter wave period
How do waves break
When waves moves in to shallow water (half its wavelength) there is friction between water and seafloor
wave slows down
wavelength decreases
wave steepens
What is swash
Movement of water up the beach in the same direction as waves travelling up the beach
What is backwash
Movement of water back down the beach by gravity perpendicular to the coastline down the steepest gradient
What are constructive waves
Low height, long wavelength, low frequency
Spiling waves
Strong swash
Swash is greater than backwash
Destructive waves
Greater height, shorter wavelength and higher frequency
Plunging waves
Swash of the next wave is slowed due to returning backwash
Swash is less than backwash
Beach gradient and wave type
High-energy waves (often winter months)tend to remove sediment reducing the gradient
Low-energy waves (often summer month) tend to build up the beach face, steepening the profile
Waves steepness is an important factor in this relationship
How are tides formed
Formed by the gravitational pull of the moon
Spring tides and neap tides occur twice a lunar month
Geology - Lithology
Clays - weak lithology
Basalt - resistant to erosion
Chalk - vulnerable to carbonation
What does jointing, bedding and faulting all affect
Permeability and porosity
Why is the angle of dip important for cliffs
Landward - dipping strata support cliffs within steep vertical profiles
Seaward - dipping strata support cliffs with profiles which follow the bedding plane
What are rip-currents
Caused by tidal motion or by waves breaking at right angle to the shore
Creates cusps - channelling the rip current through a narrow neck
What are terrestrial forms of sediment
Rivers are a major source of sediment inout to the coastal sediment budget
What is the origin of terrestrial sediment
Erosion carried out by
water
ice
wind
Origin of terrestrial sediments - weathering
Decay and disintegration of rock in situ
Mechanical weathering- freeze-thaw, salt crystallisation, wetting and drying
Biological - root action
Chemical weathering - carbonation
Origin of terrestrial sediments - Mass movement
Soil creep Earth flow Landslides mudflows Slumps Rockfalls Run-off
Sediment form offshore
Constructive waves, tides and currents bring sediment to the shore from offshore
Wind can blow sand from other locations
Sediment from humans
When a coastal budget is in deficit, beach nourishment is one way a sediment equilibrium can be maintained
Erosion
Abrasion - when waves armed with rock particles scour the coastline
Attrition - when rock particles collide with each other during transportation
Hydraulic action - when waves brake against a cliff face, air and water are forced into crevices. when the wave recedes the pressure is released leading to expansion of the air
Pounding - the mass of the braking wave exerts pressure on the rock causing it to weaken
Solution - dissolving minerals like magnesium carbonate minerals in coastal rock
Transportation
Solution - minerals which have been dissolved into the mass of moving water
Suspension - small particles of sand, silt and clay can be carried by currents
Saltation - series of irregular movements of material which is too heavy to be carried continuously by suspension
Traction - the largest particles are pushed along the sea floor
Deposition in coastal systems
Where the rate of sediment accumulation exceeds the rate of removal
When waves slow down immediately after braking
At the top of swash
During the backwash where water percolates in to the beach material
in low-energy environment
Cliffs and shore platforms
When destructive waves break repeatedly on relative steeply sloping coastlines
Undercutting occurs between HWM and LWM
Forming a wave cut notch
Continued undercutting weakens support of the rock strata above
This eventually collapses
Producing a step profile and a cliff
Cliff retreated parallel to the coast
Shore platforms
Often deeply directed by abrasion our to the large amount of rock debris that is dragged across the surface
Reach a maximum length of 500M
What is a Disconcordant coastline
Form due to the bands of rock with differing resistance to erosion
These bands of rocks will be perpendicular to the coastline
The width of the bay is determined by the width of the weaker rock
What is a concordant coastline
Rocks are lying parallel to the coastline
What is wave refraction
The waves is slowed down by the shallow water of the headland
The waves in the bay speed up as they are not slowed down
Waves refract around the headland
What is a geo and blowhole
Geo are narrow steep-sided inlets, weak points are eroded more rapidly by hydraulic action, they form a tunnel like cave running at right angles to the cliff line
Blowhole is when part of the roof of a tunnel like cave collapses and forms a vertical shaft that reaches the cliff top
Caves, arches, stacks and stumps
Cracks at the base of a headland become exposed through hydraulic action, the crack widens, other processes such as salt crystallisation widen it eventually becoming a wave cut notch, more weathering becomes a cave, as a result of wave refraction the waves concentrate their energy on the sides, a hole all the way through is eventually made forming an arch, over time this becomes unstable and collapses under its own weight and forms a stack, eventually due to further weathering the stack collapses forming an arch
What is a sand beach
Less than 5 degrees Small particles means it becomes compact when wet Little percolation during backwash Little energy lost to friction material is carried back down the beach Forming ridges and runnels
What is a shingle beach
Mix of pebbles and small to medium cobbles
Steeper beaches due to swash greater than backwash
What is a storm beach
At the back of the beach, Very strong swash during storm conditions may deposit larger material, forming a storm beach or a ridge
what is a berm
Small ridges that develop at the position of the mean high tide mark resulting from deposition at the top of the swash
What is a beach cusp
Cusps are semi-circular depressions, they are smaller and more temporary features by a collection of waves reaching the same point
Seasonal changes to the beach profile
High - energy destructive waves remove sediment offshore and create flatter beaches (summer)
winter is the opposite
What is a spit
Long narrow beaches of sand or shingle that are attached to the land at one end and extend across a bay, estuary or indentation on a coastline
Form as a result of LSD
The end of the spit becomes recurved
Behind the spit deposition will occur as wave energy is reduced
Silt and mud are deposited
Eventually salt tolerant plants colonise
Slat marsh develops
What is an onshore bar
Develop when a spit develops across and indentation until it joins into the land at the other end forming a brackish lagoon on the landward side
What is a tombolo
Beaches which connect the mainland to an offshore bar
Spit continued the grow seaward to join the mainland to an island
Salt marsh
Feature of low - energy environments, vegetated areas of silt and clay
Vegetation helps stabilise the sediment
The higher the marsh becomes the les saline it is
Flocculation is an important process
Shallow gradient
Delta
large areas of sediment found at the mouth of rivers
deposited by rivers and tidal action
branching network of distributaries
Overloaded with sediment, deposition in the channel occurs, this splits the channel and reduces the energy allowing further deposition, these channels are lined with levees
Cuspate delta
Appointed extension of coastline
Arcuate delta
Sufficient sediment supply is available for the delta to grow seawards
birds foot delta
Distributaries build out from the coast in a branching pattern
River sediment supply exceeding the rates of removal by waves and currents
What is eustatic change
Changes in volume of water in the global ocean stores
What is isostatic changes
Local
relative sea level changes
Isostatic changes in britain
Changes in the land
Scotland is rebounding
SE coast is sinking
Relative changes to the sea level
Scotland - sea level fall
SE coast - sea level is rising
Physical factors that can affect changes in global temperatures
Milankovitch cycles
Solar output
Atmosphere composition
Climate change and sea level
A decrease in global temperature leads to more precipitation falling in the form of snow
Eventually this snow turns to ice and so water is stored on land
As a result, there is a reduction in the amount of water in the ocean and a worldwide fall in sea level
Riss glacial period
108000 years ago
7 degrees cooler than today
Sea level was about 83 m lower than the present day
Wurm glacial period
25000 years ago
9 degrees cooler than today
sea level was 90m lowwer
Emergent landforms
Landforms are shaped by wave processes during times of high sea level
These become exposed when sea level falls
These features are often found well inland, some distance from the present coastline
Raised beaches
Are areas of former shore platforms that were left at a higher level than the present sea level
they are often found a distance inland rom the present coastline
modification on landforms
After they emerged they are no longer affected by wave action
the continued to be altered by mass movement and weathering
Rias
Submerged river valleys
The lowest part of the river course and the floodplains may be completely drowned
The sides of the valleys and the middle and upper parts of the rivers course may still be exposed
Formation of Rias
Typically underlain with alluvial deposits
These were buried in channels that were eroded by rivers the flowed down to the lowest sea levels during the Pleistocene glacial periods
During the interglacial periods, when sea level rose further deposition would have occurred as the rivers has less surplus energy for erosion
The river valleys then became infilled during the Flandrain Transgression
Fjord
Submerged glacial valleys
They have steep cliff - like, valley sides and he water is uniformly deep - reaching over 1000 m
