Coasts - EQ2 - How do characteristic coastal landforms contribute of coastal landscapes? Flashcards
What is the cause of waves
friction between wind & the sea surface
Describe the process of wave formation
1.
- wind moves across the surface of the water
- causing frictional drag
- which creates small ripples & waves
- this leads to a circular orbital motion of water particles in the ocean
Describe the process of wave formation
2. ….this leads to a circular orbital motion of water particles in the ocean….
- as the seabed becomes shallower towards the coastline, the orbit of the water particles becomes more elipitical, leading to horizontal movement of waves
Describe the process of wave formation
3. ….the orbit of the water particles becomes more elipitical, leading to horizontal movement of waves so…..
- wave height increases
- wave length & wave velocity both decrease
Describe the process of wave formation
4. …wave height increases, wave length & wave velocity both decrease….
- this causes water to back up from behind the wave, until the wave breaks (collapses) & surges up the beach
Name 4 factors affecting wave size
- Time of wind blowing
- Strength of the wind
- water depth
- Fetch - distance of open water over which the wind blows
Why are waves generally larger in the South West (e.g Cornwall)
- dominant & prevailing winds come from the South West direction
- this wind is sustained over a greater distance,
- which transfers kinetic energy from wind to wave,
- growing the waves size & strength
Why does Cornwall have such large waves
- Larger fetch from Florida to Cornwall:
- they are 4000 km apart
- and as there are no land masses between them,
- the Waves from the Atlantic Ocean aren’t slowed down before they react the Cornish coast
Name 2 wind types
Prevailing
Dominant
Define Prevailing Wind
the most frequent type of wind in an area - affecting weather patterns & soil erosion
Define Dominant Wind
Strongest winds in an area at a given time
Define Crest
the highest point the wave rises to
Define Wavelength
distance from one wave crest to another
Define Trough
the lowest point the wave sinks to
Define wave height
the distance between the trough and crest
How do waves form
- From the transfer of energy from the wind to the sea surface
- which causes friction
- & the water begins to move in a circular motion
The amount of energy a wave gains depends on…
- wind speed
- time the wind has been blowing for
- distance the wind has been blowing for (fetch)
Friction with the seabed _____ the wave at the base, but the top of the wave doesn’t ________________
slows
slow down
Friction with the seabed slows the wave at the base, but the top of the wave doesn’t slow down, therefore….
the top becomes higher & steeper until it breaks
Define swash
The wave moving up the beach
Define backwash
the water slowing back down to the sea, which is due to gravity
What are Constructive Waves associated with
Linked to low energy coasts and deposition
Fetch of Constructive Waves
short fetch
wave form of Constructive Waves
low surging waves - long wavelength
wave break of Constructive Waves
strong swash, weak backwash
beach gain/ loss with Constructive Waves
gain
frequency of destructive Waves
High frequency - 11-16 per minute
Constructive Waves have ______ wavelength in proportion to height
low
What are Destructive Waves associated with
linked to high energy & storm weather which leads to erosion
Fetch of Destructive Waves
long fetch
Wave form of Destructive Waves
high plunging waves - short wavelength
Wave break of destructive waves
weak swash, strong backwash
beach gain/ loss with destructive Waves
loss
frequency of constructive Waves
Low frequency - 6-9 per minute
Destructive waves have ______ wavelength in proportion to height
high
Define beach morphology
- The shape of a beach including:
- its width and shape (the beach profile)
- features (e.g. berms, ridges and runnels)
- sediment type (shingle, mud & sand)
- found at different locations on the beach
Name the 3 temporal factors affecting beach morphology
daily
seasonal
long-term
Describe the temporal factor (daily) affecting beach morphology
Over a day, as a storm passes & destructive waves change to constructive ones as the wind drops
Describe the temporal factor (seasonal) affecting beach morphology
between summer & winter
Describe the temporal factor (long-term) affecting beach morphology
- where there are changes to the climate
- e.g if climate change resulted in the UK climate becoming on average stormier then destructive waves & winter beach profiles would become more common
There are summer & winter beach profiles for each beach due to variations in…
wind & wave energy between seasons
Regardless of direction, wind speed is ________ in the winter because of the increased temperature differences between the poles and the equator
greater
Why is wind speed greater in the winter
Regardless of direction, because of the increased temperature differences between the poles and the equator
How does air movement result in a change in wind speed
- Air movement leads to uneven heating,
- so the difference between the temperature of the poles & equator increases
- and so does the pressure differences,
- resulting in a change in wind speed
Characteristics of a summer beach profile
elevation and width
- gentler summer waves deposit sand from offshore bars onto the beach
- ultimately widening it & increasing its elevation
Characteristics of a summer beach profile
waves
constructive waves which build up berm ridges
Characteristics of a summer beach profile
sands
finer & medium grain sands are predominant
Characteristics of a summer beach profile
Vegetation
dune plants are green, lots of vegetation
Characteristics of a winter beach profile
width
- stronger winter waves, with more energy
- pick up those particles deposited in the summer
- and carry them back offshore in bars,
- thus narrowing the beach
Characteristics of a winter beach profile
waves
offshore ridges / bars are formed by destructive wave erosion
Characteristics of a winter beach profile
sands
the sand composition will be much coarser
Characteristics of a winter beach profile
vegetation
the plants go dormant, while only the roots remain alive
Material found on a beach ______ in size and type as you move further away from the shoreline
varies
The smallest material is deposited near_____
the water
the largest material is found nearer to_______
the cliffs at the back of the beach
Large material is deposited at the back of the beach in times of…
high energy e.g during a storm
Define Hydraulic Action
- water is forced into cracks in the rock
- this compresses air
- when the wave retreats, the compressed air blasts out
- which forces rocks apart
Define Corrosion (solution)
- mildly acidic seawater can cause alkaline rock such as limestone to be dissolved & eroded in a chemical reaction
Define Abrasion
- caused by the waves picking up sand & pebbles
- hurling them at the cliffs with force
- wearing the cliffs away
Define Attrition
any material carried by the waves will become rounder & smaller over time as it collides with other sediment
How are wave cut notches formed
1. waves
At high tide, destructive waves may reach the base of the cliff
How are wave cut notches formed
2. erosion
the processes of abrasion & hydraulic action erode the rock at the cliff base
How are wave cut notches formed
3. forms
a wave cut notch forms along the length of the cliff
Sea caves may form at ……….. points along the wave cut notch line
weaker
How are wave cut platforms formed
1. wave cut notch
Above the wave-cut notch, an overhang of unsupported rock is formed
How are wave cut platforms formed
2. recession
- as the overhang is undercut,
- mass movement of the unsupported rock occurs
- & the cliff retreats (recession), which is variable according to the lithology
How are wave cut platforms formed
3. post cliff retreat
- as the cliff retreats,
- it leaves behind a flat or slightly sloping area of rock
- between the high & low tide levels:
- a wave cut platform
……………. also contributes to the formation of some wave-cut platforms
weathering
How are cliffs eroded
constant wave action & erosion against the base of the cliff ensures that it maintains its steep profile as it retreats inland
Rock angle of steeper cliffs
rock strata are vertical, horizontal or have almost vertical joints
Rock angle of gentler cliffs
where rock dips towards or away from the sea
How are headland & bays formed
they form on discordant coastlines, where waves erode the softer rock faster than harder rock
How are bay-head beaches formed
- bays have a semi-circular shape once eroded,
- and the waves entering a bay dissipate & lose energy,
- and hence deposit a bay-head beach
The Cave, Arch, Stack, Stump Sequence
1. weaknesses
- the erosion of rocks like limestone & chalk tend to be exploited at any lines of weakness e.g joints, faults & cracks
The Cave, Arch, Stack, Stump Sequence
2. Caves
If the joints & faults are eroded by hydraulic action & abrasion, this can then creates caves
The Cave, Arch, Stack, Stump Sequence
3. Blowholes
If the overlying rock then collapses, a blowhole will develop as the cave opens up at ground level
During high tides, seawater can be ……… …… of these blowholes with considerable force
blown out
The Cave, Arch, Stack, Stump Sequence
4. Arch
- If 2 caves on either side of a headland join up,
- or a single cave is eroded through a headland,
- an arch is formed
- the gap is then further enlarged by erosion & weathering - becoming wider at the base
The Cave, Arch, Stack, Stump Sequence
5. Stack
Eventually, the top of the arch will become unstable & collapse, leaving an isolated pilar of rock called a stack
The Cave, Arch, Stack, Stump Sequence
6. Stump
- The stack itself will continue to be eroded by the sea
- As it collapses & is eroded further,
- it may only appear above the surface at low tide,
- and is now known as a stump
Wave move sediments up and down via
LSD
Tides and currents
Name the 4 methods of transportation
traction
saltation
suspension
solution
define traction
large, heavy pebbles are rolled along the seabed
define saltation
pebbles are bounced along the sea bed
define suspension
lighter sediment is suspended (carried) within the water
define solution
the transport of dissolved chemicals
LSD
1. the strongest LSD occurs when waves approach the coast at an angle of ____ to the beach
30 degrees
LSD
2. the forward movement of each wave, the ______, moves beach sediments…..
swash
up the beach at the same angle as the waves approach
LSD
3. the _______of each wave then carries the sediment……
- backwash
- back down the beach at right angles to the shore under the influence of gravity
LSD
4. In this way, sediments slowly moves in small ________ steps along the beach until they reach a…… or a……..
- zigzag
- natural obstacle, such as a bay or an estuary,
- or an artificial barrier such as groynes
LSD
5. The __________ will determine the LSD direction at any section of the coast
dominant wind
LSD
Name an example of LSD along the UK coastline
- Along the South Coast of England
- LSD is west to east because the dominant waves come from the Atlantic Ocean
What are tides
Changes in the water levels of seas & oceans
What causes tides
the gravitational pull of the moon & to a lesser extent the sun
The UK coastline experiences ___high & low ______ in the oceans a day
2
bulges
Define tidal range
the relative difference between high & low tides
What does a high tidal range create
relatively powerful tidal currents, as tides rise & fall
Where can tidal currents become particularly strong and fast
in estuaries and narrow channels
tidal currents become particularly strong and fast, in estuaries and narrow channels meaning they are important in…..
transporting sediment
Name 6 depositional landforms
Beaches
Cuspate Forelands
Offshore bars
Spits (recurved & double)
Barrier beaches (bars)
Tombolos
What is a depositional landform
occurs along the coast when waves no longer have enough energy to transport sediment
What is a beach
a common coastal depositional landform
Beaches
___________ creates these low energy environments
Wave refraction
Beaches are made of ____________ or _______ depending on…
- Beaches are made of rounded sand or shingle depending on factors like the nature of the sediment and the power of the waves
What are the 2 types of beaches
Drift Aligned
Swash Aligned
How are swash aligned beaches built
By constructive waves
How are drift aligned beaches made
LSD - transports sediment down the coast keeping beaches relatively narrow
What is a Cuspate Foreland
A low lying roughly triangular shaped headland
How are cuspate forelands formed
- When significant longshore drift comes from opposite directions along a coast,
- so that pebbles & sand are deposited across a bay from both directions,
- forming a spit
Where can the largest Cuspate Foreland in Europe be found
Dungeness in Kent
What is an offshore bar
- A long ridge of sand or pebbles,
- formed a short distance out to sea,
- in shallow water
- where destructive waves break before reaching the beach
How is an offshore bar formed
- Destructive waves erode sand from the beach
- with their strong backwash
- & deposit it on offshore bars
What does an offshore bar look like at high tide
The offshore bar is below the sea
A line of breathers reveals its location as waves break on it
What does an offshore bar look like at low tide
A beach parallel to the coast can be seen, which is an offshore bar
What is a spit
- a long narrow depositional feature,
- made of sand or shingle,
- which extends from the road into the sea
Where do spits form
- On drift-aligned beaches,
- when there is a dominant main LSD direction,
- plenty of sediments from mass movement & erosion,
- & a gap in the coastline such as an estuary or bay
How are spits formed
- sand or shingle is moved along the coast by LSD,
- but if the coastline suddenly changes direction,
- sediment will be carried for a short way in the same direction until they are deposited on the seabed
- overtime, so much sediment is deposited that a narrow strip of land (a spit) forms across a bay or estuary
What prevents a spit from extending across the estuary mouth
the outward flow of the river associated with the estuary
How do salt marshes develop once spits are formed
- the shelter provided by the spit
- means that sediment is deposited behind it to form mudflats,
- on which a salt marsh may develop
- & be colonised by salt tolerant plants
What is a tombolo
a narrow low ridge of sand & pebbles connecting an island to the mainland
How do tombolos form
- After longshore drift carries sediment across a gap between the mainland and an island,
- where the waves lose their energy,
- so a tombolo builds up
What is a barrier beach (bar)
a beach that connects two areas of land with a lagoon forming behind
In what conditions will a barrier beach form
- a plentiful supply of sand or shingle
- shallow nearshore or offshore areas
- waves with enough energy to move the sand or shingle
- a rising sea level to push the sediment towards the shore
How do barrier beaches form
- When rising sea levels cause constructive waves
- to drive a ridge of sediment onshore to coastlines
- with a gently sloping shallow sea bed (a barrier beach)
Example of a Tombolo
St. Ninian’s in the Shetland Islands
Where are barrier beaches common
Along Dutch coastlines
What are subaerial processes
- A combination of weathering & mass movement processes
- that alter the shape of the coastline,
- distinct from marine erosion, transport & depositional processes
Define weathering
- The breakdown of rocks in situ or near the Earth’s surface,
- exploiting weaknesses in rocks over a long timescale
What does weathering produce
Loose sediments that can be moved by gravity or removed by erosion (wind, rivers, waves or ice)
What are the 3 types of weathering
Chemical
Mechanical
Biological
Where does weathering operate
Between the low-tide level & the cliffs or land of the backshore
Define chemical weathering
- The erosion or disintegration of rocks
- caused by chemical reactions, chiefly with water & substance’s dissolved in it,
- rather than by mechanical processes
Define mechanical erosion
- Any of the various weathering processes that cause physical disintegration of exposed rock
- without any change in the chemical composition of the rock,
- such as collision between rock surfaces
Define biological weathering
- The weakening & subsequent disintegration of rock by plants, animals & microbes
- growing plant roots can exert stress or pressure on the rock
- although the process is physical, the pressure is exerted by a biological process (growing roots)
What type of weathering is freezethaw
mechanical
where does freeze thaw occur
on coasts in a climate where the temperature changes daily above & below zero
describe the process of freezethaw
water seeps into joints & cracks in the rock, & when it freezes & expands, it exerts pressure & forcing the rocks apart
what are the effects of freeze thaw
angular rock fragments
what type of weathering is salt crystallisation
mechanical
what is salt crystallisation
when waves break or splash cliffs on coastal rocks, the water evaporates, leaving behind sodium & magnesium
What is the effects of salt crystallisation
Angular rock fragments are loosened and fall to create scree slopes at the base of the cliff or rock faces crumble away
What type of weathering is oxidation
Chemical
Describe what is meant by oxidation
- Oxygen combines with iron-based minerals in a rock
- causing a chemical breakdown of the minerals,
- as shown by a red-orange rusty colour on a rock face
What is the effects of oxidation
The rock minerals will no longer be bonded together and so the rock will crumble, making erosion easier
What type of weathering is seaweed acids
Biological
Describe what seaweed acids is
Some seaweed (eg kelp) cells contain pockets of sulphuric acid, so when these cells break in contact with rock, the acid will dissolve some rock minerals
What is the effects of seaweed acids
Rock minerals will no longer be bonded together and so parts of a rock will crumble, and these become points of greater erosion
What type of weathering is boring molluscs
Biological
Describe what boring molluscs are
- Many marine molluscs live on coastal rocks, scraping away at the rock surface to get food or boring a hole in the rock to make a home
- One example is the Piddock, which has a shell with serrated cutting edges.
What are the effects of boring molluscs
- Pebbles and rocks with holes bored into them are more easily moved around by the waves.
- The holes also provide weak points for other weathering processes to act.
What is mass movement
Downslope movement of rocks, sand, glacial till or soil
What causes mass movement
- By gravity once a slope has become unstable
- & it is common at the coasts due to the constant undercutting of the cliffs
The _____ content also determines the type of mass movement
Water
How does water content determine the type of mass movement
The sheer weight of rainwater and weak geology will lead to cliff collapse
What are the 6 mass movement types
Soil Creep
Solifluction
Mud flows
Rock falls
Landslides
Slump/ rotational slip
Soil creep is the ______ form of mass movement & is almost a ______ process
Slowest
Continuous
Where does soil creep occur
On very gentle slopes because of the way soil particles repeatedly expand & contract in wet & dry periods
How can soil creep be identified
By terracettes
Solifluction’s movement averages between…
5cm & 1m per annum
How does solifluction occur
- when the top layer of soil thaws in the summer,
- but the layer below remains frozen as permafrost
- the surface layer becomes saturated and flows over the frozen subsoil & rock
Where does solifluction occur
Occurs mainly in tundra areas, where the ground is frozen
What is a mud flow
- An increase in the amount of water can reduce friction
- causing earth & mud to flow over underlying bedrock
- typically, a torrential rainfall or very rapid snow melt run off is the initiating factor
What is the difference between a slide & a flow
Is that in a slide the material remains intact wheras in a flow, material is jumbled up
How can you identify a mud flows
A lobe ( material at the bottom )
Where do rock falls occur
- On slopes over 40 degrees
- Most likely to occur when strong joined and steep rock faces/cliffs are exposed to mechanical weathering
What is a rock fall
The material once broken down from the source by mechanical weathering, either bounces or falls vertically
What is a block fall
Similar to rock falls
A large block of rock falls away from the cliff as a single piece, due to the jointing of the rock
How can rock falls be identified
By scree/ talus
Where can landslides occur
Rocks that are jointed or have bedding planes are susceptible to landslides
How do landslides occur
An increase in the amount of water can reduce friction - causing sliding
In a landslide, slabs of rock can slide over underlying rocks along a slide or slip plane
Where do slumps/rotational slips occur
In saturated (raining) conditions on moderate to steep slopes
When do slumps/ rotational slips occur
Common when softer materials overlie more resistant or impermeable rock
What is the difference between sliding and slumping
There is a rotational movement in slumping
How can slumps be identified
Rotational scars
What does repeated slumping create
A terrace cliff profile
