Coast Landscapes and Change Flashcards
How is a wave created
2B.4
created through friction between the wind surface, transferring energy from the wind into the water
what is a wave
2B.4A
transfer of energy from one water particle to its neighbour with individual water
what is wave height
2B.4A
vertical distance from the peak to trough
how is wave height determined
2B.4A
energy transfer from the wind and water depth
what is wave length
2B.4A
horizontal distance from crest to crest
what is wave frequency
2B.4A
number of waves passing a particular point over given period of time
waves in a open sea
2B.4A
- waves are simply energy moving through water
- water itself only moves up and down not horizontal
- there is some obital water particle motion within the wave but no net forward water particle motion
what does wave size depend on
2B.4A
wave fetch -
wave depth
strength of wind
duration of wind blows
how does a wave break
2B.4A
waves reaching shore reach a wave depth 1/2 their wavelength the internal orbital motion of water within the wave touches the sea bed
Wave particle is distorted due to friction between the sea bed, this slows down the wave
- wave depth decreases further, wave velocity slows wavelength shortens and wave height increases.
- wave crest begins to moe forwards much faster than the wave trough
- wave crest outruns the trough and wave topples forwards
wave breaks in the nearshore zone and water flows up the beach as swash
wave losses energy and gravity pulls the water back down the beach as backwash
Constructive Waves
2B.4A
low energy waves low flat wave height long wavelength low wave frequency (6-9 per minute) strong swash - pushes sediment up the beach but weaker backwash can't transport all particles back - backwash into beach material
Destructive Waves
2B.4A
high energy waves
large wave height
short wavelength
high wave frequency
strong backwash weak swash due to steep angle of impact = energy directed downwards and backwards
strong backwash erodes material from top of beach
what is beach morphology
2B.4A
shape of the beach
what is a beach sediment profile
2B.4A
pattern of distribution of different sized or shaped deposited material
how do constructive waves effect beach morphology
2B.4A
net movement of sediment up the beach steeping the beach profile
Produce berms at the point where swash reaches high tide line
swash carries sediment of all sizes up the beach but weaker backwash can only transport smaller particles down the beach = larger heavier shingle at back of beach and sand closer to ocean -> backwash flows down beach loses energy through friction = sediment further sorted = fine sands closest to sea - coarser sands deposited in middle of beach
what is a berm
2B.4A
ridge of material across the bridge
how do destructive waves effect beach morphology
2B.4A
- beach gradient reduced due to weak swash and powerful backwash which produces sediment down the beach
- some sediment thrown forwards by strong waves
- large pebble sized sediment dragged down the beach by backwash to form wide ridge of material below
- friction could cause backwash to down some sediment on middle or lower beach = deposited size sediment decreasing towards sea
Decadal Variation - Beach Morpholgy
2B.4A
Climate change is expected to produce more extreme
weather events in the uk
winter profiles may be present for longer time over course of year
more frequent powerful destructive waves reduce beach size = high tides to reach inland = rate of erosion increase
Monthly Variation - Beach Morphology
2B.4A
Highest tide occurs every 2 months at spring tide - two very low high. tides
As months progress from spring down to neap tides - lower high tides produce series of berms at lower and lower points down the beach
Berms destroyed as material pushed further up beach - once a neap tide passes and moves towards next spring tide
Daily Variation
2B.4A
Destructive waves from storms in summer reshape beach
Constructive waves = calm conditions in winter
Wind Drops = destructive waves -> constructive waves
Storm beaches = result from high energy deposition of sediment from sever storms
what does energy transferred from the wind depend on
2B.4A
wind strength
wind fetch
uninterrupted distance upon water over which wind blows over
wind duration
how are sea waves produced
2B.4A
winds currently blowing in local area - vary in height and direction
what happens when the wind drops
2B.4A
wave energy continues to be transfers across ocean in the form of swell waves
Swell Waves
2B.4A
absorb smaller sea waves and gain energy and height as they travel
travel long distances before they lose energy
produce waves at coast even with no wind
can form periodically larger waves amongst smaller
Name the 4 erosion processes
Hydraulic Action
Corossion
Abrasion
Attrition
Effect of Erosion
Boudle clay of the Holderness coast retreated by 120cm in last 100 years
Granite of Lands End in Cornwall has retreated by only 10cm in last 100 years
How the 4 erosions are influences by wave type, size and lithology
Most effective during storms events with large destructive waves
Coastlines of soft sediment experience little erosion under normal conditions
Most erosion in UK in winter high energy storms
what does hydraulic action do and where it occurs
force of water itself breaks up rock
occurs through direct impact of the water itself
Hydraulic Action and Destructive waves
plunging destuctive waves can exert a force of 50KG
sufficer tor break off material from unconsolidated material - boulder clay
Process of Hydraulic Acton
force of breaking waves compresses air into crack \
wave energy exhausted, the compressed air explodes outwards = fractures in rocks
over time small fragments of rock break away or main rock is weak enough too all
Hydraulic action is igneous rock
hydraulic action attacking its cooling joints only effective wave erosion process
What is abrasion
wave picks up sediment - throws load item against the rock - repeated impact chips away at the rock face until small fragments break away
When is abrasion most effective
high energy destructive waves with large wave height hurf load items with greater force = faster rates of erosion by abrasion
what rock erode quickly from abrasion
soft sedimentary rock such as chalk mudstones and clays. Unconsolidated material - boulder clay
What is Corrosion
Water dissolves rock minerals, minerals carried away by wave in solution - vulernable to erosion by rainwater and sea spray
Most effective waves of Corrosion
Constructive
Slow with long wave length (longer the better) prolongs the contact of rock with water
what rocks erode quickly from Corrosion
Carbnate rocks like limestones (chalk, jurassic limestone)
what is attrition
material transported by wave edged through collision with other low items.
how does attrition break down sediment
into smaller sized particles and repeated cousin blunts any of the sharp edges
where does attrition occur
in foreshore and nearshore zones, where sediment is moved by swash and backwash
what rocks erode quickly from attrition
soft rocks - chalk and clay
how is a wave cut notch formed
2.4BC
between hide tide and low tide marks - destructive waves impact against the cliffs
how is wave cut notch eroded
hydraulic action and arbasion, sometimes corrosion
wave cut notch example
Kimmeridge bay
what is a wave cut platform
flat rock surface exposed at low tide - extends from the sea and base of cliff
Formatio of Wave cut platform
- abrasion and hydraulic action erode between high and low tide, which forms notch at the base
- notch depends by further erosion until material collapses due to gravity, forming a cliff
- Process is repeated - until coastal recession
- rock below low tide is always submerged, never exposed to wave impact
- overlying material eroded , uneroded rock left flat = wave cut platform
wave cut platform extra info
slope seaward at 4 degrees
rock pools created by weathering attacking weaknesses at low tide
platform rarely extend more. than hundred metres
Cliffs - Coastal landscapes produced by erosion
Formation of a cliff
steep slopes usually unvegetated
hydraulic action dn abrasion forms a wave cut notch
notch deepens until rock collapses due to force of gravity
exposed face forms a cliff
Cave -> Arch -> Stack -> Stump sequence
- joints and faults or dipping bedding planes in rocks are eroded rapidly (hydraulic action)( forms a sea cave)
- wave refraction concentrates energy on the sides of the headland, producing destructive waves with large wave height
- A line of weakness extends right through the headland caves form on both sides
marine erosion = cave deepens until they connect up = complete tunnel through the headland and forming an arch
Hydraulic action and abrasion forms wave cut. notches from attacking the side of the arch
mass movement = undercutting of the sides and widening of the arch
Weathering attack the arch roof = roof the arch collapses = leaving seaward end of the headland detached = called a stack
Marine erosion at base stack forms notch on all sides until stack collapses
remnants of the stack base from stump, small projection of rock exposed only low tide
what does cliff slope angle depend on
the rip of the rock strata
Horizontal, vertical or landward dip produces steep cliffs
Seaward dip produces a shallower slope angle - can be produced when lithology is unconsolidated
what is traction, and examples
where large, heavy load items are rolled along the sea bed
Boulders and cobbles and pebbles
what is saltation, and examples
lighter sediment bounces along, sand particles are usually transported this way. Sand can be saltated by wind as well as waves - dry windy day there can be a layer of salivating sand 2-10cm above this beach
what is suspension and examples
very light sediment is carried aloft within body of water or air
Silt or Clay particles
Suspended clay particles give sea cloudy, muddy brown colour on soft rock coasts - Holderness
Solution
sediment is carried dissolved within the water
Direction of the Wave Attack
Main determinant of the direction of the sediment transport
Wind is blowing directly onshore the incoming swash transport the material direction up the beach 90 degrees to the coastline
backwash then transport perpendicularly back down to the beach so its original starting position
Sediment is moved up and down the beach, but there is no lateral
What is longshore drift
net lateral transport of material along the coastline when waves approach the coast at an angle
Process of Longshore drift
swash transports sediment up the beach
Gradational backwash then transport sediment back down the beach 90 coastline
Sediment particle rests some distance along the beach due to no net lateral movement
Particles moves in zig zag along the beach with the wave
what wave angle produces strongest Longshore drift
30 to the coastline, on most coastline their is dominant prevailing wind = over time dominant direction of wind
what is current
flow of water in particular direction and can transport sediment in the nearshore and offshore zones
what is current driven by
winds, initiated by differences in water density temperature or salinity
global thermohaline - Currents
global thermohaline circulation connects four ocean and takes 5000 years for one complete circuit
What is a rip current
currents on the beach transport sediment few metres out to sea for a few hours when the wind is blowing directly onshore with the right strength
Tides
Incoming and ebbing tide can create tidal currents in the nearshore and offshore zones that transport sediment
prevailing wind
most common direction
domaint wind
strongest wind direction
where is the dominant wind in the UK
North East
UK south coast wind
wind from the south west is both dominant and prevaling
what is tidal range
distance between high tide and low tide
what does a large tidal range produce
strong tidal current - may create tidal bore which produces wave that can transport sediment
2B.5B
Depositon
occurs when waves no longer have energy to transport its material
Why could waves lose energy 2B.5B
wind is dropping, removing an energy source
resistance by obstruction - groyne or headland
dissipation of energy through refraction
Friction from extended transport across shallow angled nearshore an foreshore zone
Two ways deposition occurs 2B.5B
gravity settling when energy transporting water becomes to low to move sediment. Large sediment is deposited first followed by smaller
Pebbles -> Sand -> silt
Flocculation is important for small particles - clay, so small that they will suspend in water = clay particles clump together through chemical attrition and become large enough to sink
how are beaches produced 2B.5B
material deposited by constructive waves - swash carries material up beach but backwash only has enough energy to transport material back down = remainder deposited
What are bay-head beaches 2B.5B
curved beaches found at the back of bay
where are bay head beaches common 2B.5B
swash aligned coastlines, wave refraction disperses wave energy around bay perimeter
how are bay head beaches formed 2B.5B
waves break at 90 degrees to shoreline, move sediment into bay and beach forms
wave refraction erosion is concentrated at headlands and bay is an area of deposition
what are spits 2B.5B
linear ridges of sand or shingle beach, connected to land at one end
how do spits form 2B.5B
drift aligned coastlines, coastlines changes direction by more than 30 degrees. bay or river mouth
how are the lengths of spits determined 2B.5B
existence of secondary currents causing erosion, either the flow of river or wave action which limits length
Process of Spits 2B.5B
energy from longshore drift is dispersed, wave refracts and currents spreads leading to deposition on sea bed.
Sediment is deposited txobreak surface extending the each into the sea as spit
process continues until equilibrium is reached at the distal end of the spit, between deposition and erosion by waves or the existing river currents
Hooked and Recurved spits 2B.5B
end of the spit is curved landwards into a bay or inlet
Hook or a recurve may form at the end of the spit
Why do recurve spits happen 2B.5B
Wave refraction round the distal end transports and deposits sediment for a short distance in the landward direction
Wind and wave front are an opposing angle to the prevailing wind = short periods of longshore driftrs in landward direction
strong tidal current
Double spits 2B.5B
twon spits extend out in opposite directions from both sides of the bay towards the middle
how do double spits form 2B.5B
Longshore drift is operating in different directions on opposite bays
rising sea levels drive ridges of material onshore from the offshore zone
Barrier beach driven across a bay forms a bar - strong existing river current may breach the bar and form a double spit
Poole Harbour 2B.5B
main longshore drift is SW - NE driven round Studland Bay by prevailing wind producing spit from the south,
HoweverWave refraction produces wave fronts from NW-SW along coastline towards north spit of Poole = north spit
Breakpoint Bars (Offshore Bars) 2B.5B
Ridges of sand or shingle running parcel to the coast in an offshore zone
how do breakpoint bars form 2B.5B
sediment eroded by destructive waves and carried seawards by backwash, sediment deposited at boundary offshore and nearshore zone, where orbit of water particles cases to reach seabed
what tide can expose breakpoint bars 2B.5B
Neap Tide
what are breakpoint bars used for 2B.5B
construct wind farms - Scroby Sands Norfolk
Source of sand for beach nourishment
Shingle dredging for construction material
Bars 2B.5B
linear ridges of sand extending across a bay connected to land on both sides, traps body of seawater behind it forming. a lagoon
two ways bays form 2B.5B
rising sea level = constructive waves to drive sediment onshore to coastlines (9KM Barrier beach across Start Bay in Devon - Slapton Ley lagoon behind it
Drift aligned coastlines, Longshore drift extends two spit across the entire with of the bay
Tombolos 2B.5B
linear ridges of sand and shingle connecting offshore island to the coastlines of the mainland
ways tombolos form 2B.5B
drift aligned coastlines, Longshore drift builds spit out from land until it contacts with offshore island
Wave refraction around both sides of the island on swash aligned coast
examples of tombolos 2B.5B
St Ninain on Shetland Islands
Tombolo connecting Portland Oil to Dorset
Cupsate Forelands 2B.5B
low lying traingular shaped headlands extending our from shoreline, formed from deposited sediment
how do cupstate forelands form 2B.5B
Longshore drift currents from opposing directions converge at the boundary of two sediment cells
Sediment is deposited out into the sea by both currents creating triangular shaped area of deposited material
example of cuspate foreland 2B.5B
Dungeness in Kent, extends 11km south east, where main west east longshore drift meets north south longshore currents produced by swell waves travelling down North Sea into English channel
why are depositional landforms unstable 2B.5B
made of unconsolidated material
dynamic as they loose material transported by waves, tides, currents and wind
why can plants stables unconsolidated material 2B.5B
roots hold sediment together
leaves/stems slow water and wind flow reducing erosion and encouraging further deposition
what is plant succession 2B.5B
binds the loose sediment together and encourages further deposition
factors of swash aligned coastline 2B.5B
- directly faces prevailing wind
- wave fronts approach it aligned parallel to coast
- swash aligned beaches exhibit well defined berms
drift aligned coastline factors 2B.5B
aligned at an angle to the prevailing wind
- wave fronts approach coast at angle = transport from Longshore drift
Exhibit sorting sediment with smaller, rounded sediment due to more frequent movement leads to greater rounding attriton
drift aligned beaches 2B.5B
part of sediment cell
they’re dynamic as material moved in constant motion due to Longshore drift
- linear beaches along drift aligned coastline
- need consent input of sediment from river mouth or coastal erosion
2B.5C
Sediment Cell explanation
concept (sources, transfers and sinks) is important in understanding the coast as a system with both positive and negative feedback, example of dynamic equilibrium
what is a sediment cell
(littoral cell) linked system of sources, transfers and sinks of sediment along a section of coastline
Example of sediment cell
Flanbourough Head - source Region
Holdernes Coast - transfer zone
Spurn Head - sink region
how does a sediment operate
closed system with no inputs or outputs sediment from the cell, system contains inputs and transfers and outputs
what are inputs
sources are places where sediment is generated, cliffs or eroding sand dunes. some sources are offshore bars and river systems are an important source if sediment for the coast
examples of sediment inputs
cliff erosion onshore currents river transport wind blown subaerial proceses marine organisms
what are transfers
places where sediment is moving alongshore through Longshore drift and offshore currents (drift aligned) beaches and parts of dunes and salt marshes perform this function
examples of sediment transfers
longshore drift swash backwash tidal currents sea/ocean currents wind (onshore, offshore,along shore)
outputs
sinks are location where the dominant process is deposition and depositional landforms are created including spits and offshore bars
outputs/sinks examples
backshore deposiitonal landforms - Sand Dunes
Foreshore depositional landforms - Beaches
Nearshore Deposiitonal Landforms - Bars
Offshore Depositional Landforms - Barrier Island
Why are sediment cells dynamic
sediment is constantly generated in source region transported through the transfer regions and deposited in the sink regions
how is dynamic equilibrium reached
inputs of sediment from the source region is balanced by the amount deposited in sinks
dynamic equilibrium and changing
climate change creating more frequent storm or erosion of the cliff line to a more resistant rock type
System equilibrium may be interrupted (during storm event) tend to return to balance on average over time due to negative feedback
Seasonal Change - storms strong wind during winter) change dynamic equilibrium
how does coastal management reduce sediment supply
sea walls preventing cliff erosion
management in transport may reduce or halt sediment supply eg gryones trapping sediment to encourage beach out building
What is negative feedback
when the change produced creates effects that operate to reduce or work against the original change
Examples of negative feedback
when erosion leads to blockfall mass movement. Collapsed debris act as a barrier protecting the cliff base, slowing or preventing erosion for a period of time
Major erosion of sand dunes could lead to excessive deposition offshore, creating an offshore bar = reduces energy = dunes time to recover
What is positive feedback
changed produces an effect that operates to increase the original change
example of positive feedback
wind erosion of a dune section high velocity storms may removing stabilising vegetation = further wind erosion now occurs later low velocity wind conditions = depletion dune sand increase
2B.6A
what is weathering
breakdown of rock on the earths surface
Weathering Infomation
Weathering and mass movement are subaerial processes
Weathering attacks the back shore and foreshore parts of the littoral zone
Weathering creates rock fragments that form sediment
Most active in the source zone of the sediment cell
What is Mechanical weathering
application of force to physically fragment rock into smaller pieces called clasts. Break downs rock by exertion of physical force = no chemical change
Examples of Mechanical Weathering
Freeze Thaw
Wetting and Drying
Salt Crystal Growth
Process of Freeze Thaw
water seeps into cracks in rocks
water freezes, expands in volume, exerting tensional force that widens rock
thawing allows more water to enter crack, process repeats cracks forced open
cabble, boulder sized fragments loosened off
water in pores may freeze, prising off individual rock grains and producing sand sized fragments
rock with cracks are vulnerable to it. high on cliffs away from sea spray
freezing uncommon In uk coast
Process of Salt Crystal Growth
common on coast as sea is salty
breaking force less than freeze thaw
fractured rocks are vulnerable to it
effect is greater in hot and dry climate, promoting evaportation of salt crystal
attacks foreshore zone and back shore zone that’s reached by destructive wave spray
Process of Wetting and Drying
Rock containing clay mineral such as clay and shales
High tide minerals on the roc surface are soaked with sea water and expand in volume
low tie minerals dry and shrink
repeated cycles expansion and contraction eventually cause the rock to fragment and crumble
What is chemical weathering
chemical reactions attack individual minerals in the rock breaking bonds and producing new chemical compounds
Examples of Chemical Weathering
Carbonation
Hydrolysis
Oxidation
Process of Carbonation
Attacks calcium carbonate in limestone, other carbonate rocks and sedimentary rocks with calcite sediment
Rainwater mixed with carbon dioxide from the air to form weak carbonic acid
Acidic rain mixed with calcium carbonate to form soluble calcium bicarbonate solution
Rock disappears as new minerals dissolve into solution
Sediment left from limestone is clay particles that had formed impurities in original rock
Calcite sediment is weathered previously cemented clasts are released to form sediment
Process of Hydrolysis
Breakdown of minerals to form new clay minerals, plus materials in solution due to effect of water and dissolved carbon dioxide
what rocks are vulnerable to hydrolysis
igneous and metamorphic rocks as their contain feldspar and silicate minerals
Oxidation Process
addition of oxygen to minerals in iron compounds produces iron oxide and increases volume contributing to mechanical breakdown
what rocks are vulnerable to oxidation
sandsone slitstones and shales
when is oxidation effectivee
seawater or water with impurities than pure water
What is Biological Weathring
break down of rock in situ by living or once living organisms, often speeds up mechanical or chemical weathering through actions of plants bacteria or animals
Examples of Biological Weathering
Treet Rot Weathering
Rock Boring
Seaweed Acid
What is seaweed acid
kelp contains pockets of sulphuric acid
cell breaks sulphuric acid arracks rock minerals like calcium carbonate leading to chemical reaction similar to carbonation
Process of Rock Boring
Piddocks drill depression into soft rocks by rotating their shell equipped with sharp edges
Piddocks live in circular depressions, filter feeding whilst protected from high energy waves
Attack soft rock like clay and shales, vulnerable rocks ar sedimentary rocks = limestones.
Where does Tree Root weathering occur
back shore zone away from reach of spray from destructive waves
Process of Tree Root weathering
seeds fall into rock cracks, Evan germinate, nourished from rainwater
plant grows roots expand = rock widneing
tree roots exert sufficient tensional force to widen rocks
fragments break away as cobble or boulder sized sediment
How does weathering increase rate of recession
weakens rock making them vulnerable to mass movement and cliff retreat
Weathering and the climate
rates of weathering are slow
hot, wet, climate, igneous rocks weathers at 1-2mm every 1000 years
hot wet climate encourages chemical and biological weathering
carbonation increases in winter as calcium bicarbonate is more soluble in cold conditions
when are rocks eroded more rapidly? With example
in the foreshore zone between high and low tide
by marine erosion hydraulic action
Vulernable wave cutch notch forms and deepens more rapidly in weathered rocks, leading to faster recession and undercutting and mass movement collapse
2B.B6
What is mass movement
downslope movement of rock and soil under force of gravity
when does mass movement occur
downslope gravitational force exceeds the resisting forces of friction and internal rock cohesion
Type of mass movement depends upon lithology
unconsolidated material (boulder clay) - slumping consolidated rock (limestone, granite) - sliding
How is rockfall initatied - weathering
mechanical weathering
freeze thaw
salt crystal growth
how is rockfall intimated
erosion
marine erosion
hydraulic action
abrasion
undercutting cliff creating wave cut notch = notch removed supporting material that supplied resistive force holding up rock
Cliff prone to block fall have..
steep, near vertical drip of stata
often also in earthquake prone area
geological structure with many joints faults or bedding planes
how quick is blockfall
rapid, few seconds
BlockFall case study
April 2013
Large Blockfall in St Oswald Bay on South Dorset Coast
80m section of Chalk detached overnight
what is rotational slumping
involves rock failure and movement along a curved rock plane
where does rotational slumping occur
weak rocks
unconsolidated material - boulder clay sands and gravels
permeable rock strata overlie impermeable beds
how is slumping faciliatated
presence of water = adds weight = increasing gradational force as well s lubricating it reducing friction
Example of rotational slumping
Christchurch Bay
Unconsolidated sand overlie clay
Slumping process
funnelling water into permeable sand in dry weather sand cracks
water pressure form lines of weakness in the sand
water goes into lower sand as unable to percolate in impermale clay, water pressure lubrcating the bedding plane which makes sand move
weight of water adds to downslope force = wave erosion created notch at the cliff foot removing support
how is landslide made
marine erosion of a cliff foot undercutting blocks weakened by jointing
how is landslides encouraged
rainstorms = lubricating the slip plane reducing resistance
when do landslides occur
consolidated rocks with joints or bedding planes sloping seawards
ways to classify mass movement
speed of movement
water content
type of sediment
when do flows occur
uncolsidated rocks fine grained sediment (clays) mixi with large volumes of water
where are flows common
weak rocks such a clay or unconsolidated rocks - become saturated low their cohesion and flow downslope
how is saturation contributed to = flow
heavy rainfall with high waves and tides
types of flows
earthflows, mud flows
earth flows more viscous than mudflows and contain larger sediment
earth flows and environment
cold environment - solifluction occur in unfrozen layer between permafrost and tundra vegetation turf
how can mass movement be classified
type of sediment
water content
speed of movement
what distinctive landforms can be created by mass movement
rotational scars, talus scree slopes, terraced cliff profiles
what is a rotational scar
fresh, curved, unweathered and unvegetated rock surface on the cliff face
what does a detached slope section form
beach or terraced cliff profile
what can undercutting of cliffs result in, and how are they undeructted
wave cut notches.
this can lead to large falls of talus scree slopes are their base
how is a talus scree slope formed
angular blockfall debris accumulates at the cliff foot
