Coasts Flashcards
Mechanical weathering
breakdown of rock without changing its chemical composition
Salt weathering
main type of weathering that affects coasts
1) sea water gets into cracks in the rock
2) when the water evaporates - salt crystals form
as the crystals form they expand - puts pressure on the rocks
2) repeated evaporation of saltwater and the forming of salt crystals widens cracks and causes rock to break up
Chemical weathering
breakdown of rock by changing its chemical composition
Carbonation weathering
type of chemical weathering that happens in warm and wet conditions
1) seawater and rainwater have carbon dioxide dissolved in them - makes them weak carbonic acids
2) carbonic acid reacts with rock that contains calcium carbonate such as Carboniferous limestone - so rocks are dissolved by rainwater
Biological weathering
breakdown of rocks by living things
plant roots break down rocks by growing into cracks on their surface and pushing them apart
Mass movement
shifting of rocks and loose material down a slope e.g. a cliff
happens when the force of gravity acting on a slope is greater than the force supporting it
causes coasts to retreat rapidly
more likely to happen when the material is full of water - acts as lubricant and makes material heavier
3 processes of erosion
Hydraulic power
Abrasion
Attrition
Hydraulic power
waves crash against rock and compress the air in the cracks
this puts pressure on the rocks
repeated compression widens the cracks and makes rock break off
Abrasion
eroded particles in the water scrape and rub against rock - removing small pieces
Attrition
eroded particles in the water smash into each other and break into smaller fragments
their edges also get rounded off as they rub together
More resistant rocks
Hard rocks like limestone and chalk are more resistant
takes longer for them to be eroded and weathered by physical processes
Less resistant rocks
Softer rocks like clay and sandstone are less resistant
eroded and weathered more quickly
Joints and faults
cracks and weaknesses in the rock
rocks with lots of joints and faults erode faster
Discordant coastlines
coastlines made up of alternating bands of hard and soft rock that are at a right angle to the coast
Concordant coastlines
coastlines that are made up of alternating bands of hard and soft rock that are parallel to the coast
erosional land forms like bays and headlands are more common on…
Discordant coastlines
because bands of rock are being eroded at different rates
Fewer erosional land forms occur on…
Concordant coastlines
because they are eroded at the same rate along the coast
What increases the rate of salt weathering?
Warmer temperatures - water evaporates more quickly
Impact of storms on UK coastlines
Storms are very frequent in many parts of the UK especially in winter
strong winds create high energy destructive waves which increase erosion of the cliffs
intense rainfall can cause cliffs to become saturated - makes mass movement more likely
What are the prevailing winds in the UK?
Warm south westerlies - bring storm from the Atlantic Ocean
south coast is exposed to these
Destructive waves
1) waves that carry out erosional processes
2) high, steep, have high frequency (10-14 waves per minute)
3) backwash is more powerful than swash - so material is removed from the coast
4) storms increase the erosional power of destructive waves - can lead to increased rates of coastal retreat
Backwash
the movement of the water back down the beach
Swash
the movement of the water up the beach
How does a wave-cut notch form?
Waves cause erosion at the foot of the cliff through abrasion and hydraulic action which causes a wave-cut notch to form as the cliff is undercut
how does a wave-cut platform form?
once a wave-cut notch is formed the rocks above the notch becomes unstable and eventually collapses
repeated collapsing results in the cliff retreating
a wave-cut platform is the platform that’s left behind as the cliff retreats
How are Headlands and Bays formed?
1) Headlands and bays form where there are alternating bands of resistant and less resistant rock along a coast - discordant coastline
2) less resistant rock - eroded quickly and this forms bays
bays have gentle slopes
3) resistant rock - eroded more slowly and its left jutting out forming a headland
headlands have steep sides
How does a cave form?
waves crash into the headlands and enlarge the cracks - mainly by hydraulic power and abrasion
repeated erosion and enlargement of the cracks causes a cave to form
How does an arch form?
continued erosion (hydraulic power and abrasion) deepens the cave until it breaks through the headland which forms an arch such as Durdle Door in Dorset
How does a stack form?
Continual erosion wears away rock supporting an arch until it eventually collapses
Further weathering and erosion leaves smaller flatter versions of stacks called stumps
Longshore drift
1) waves follow the direction of the prevailing winds
2) they usually hit the coast at an oblique angle
3) swash carries material up the beach in the same direction as the wave
4) backwash then carries material down the beach at right angles back towards the sea
5) over time material zigzags along the coast
Constructive waves
waves that deposit more material than they erode
low, long, have low frequency (6-8 waves per minute)
swash is powerful and carries material up the coast
backwash is weaker and doesn’t take a lot of material backdown the coast
deposit material such as sand and shingle along coast to form beaches
Deposition
when material being carries by seawater is dropped on the coast
occurs when water carrying sediment slows down so it isn’t moving fast enough to carry so much sediment
Spits
form a sharp bend in the coastline
longshore drift transports sand and shingle past the bend and deposits it in the sea
strong winds and waves can curve the ends of the spit - recurved end
sheltered area behind the spit is protected from waves - material accumulates in this area so plants can grow
over time sheltered area can become - mud flat, salt marsh
Bars
formed when spit joins two headlands together
the bar cuts off the bay between the headlands from the sea
means lagoon can form behind the bar
Why is agricultural land often left unprotected?
has low economic value
How does farming affect stability of cliffs?
Vegetation helps to bind the soil together and stabilise clifftops
clearing vegetation from grazing land to make room for crops can expose the soil and underlying rock - vulnerable to weathering by rain and wind
Effects of draining Marshland
reclaimed and drained for agricultural use
reduces the natural flood barrier that marshland provides
Positive effect of development on coastline
coasts with lots of settlement may have more coastal defences - people want ti protect their homes/businesses
land is better protected against erosion
Negative effect of development on coastline
change in the transportation and deposition of material along the coast
building on coastal lowlands - restricts sediment supply to beaches which makes them narrower
narrower beaches don’t protect the coast as well - land is more venerable to erosion
Effects of coastal quarries
exposed large areas of rock making them more venerable to chemical weathering and erosion
Effect of construction industry on the coast
gravel is extracted from beaches for use in construction industry - for making concrete
removed material from coast and increased rick of erosion. as there is less material to protect cliffs
Industrial growth at ports has led to increased pressure to build on salt marshes
why is this and what is the effect of this?
salt marshes provide flat land and sheltered water - ideal for ports and industry but also natural flood barriers
building on them makes lands more vulnerable to erosion
What 2 things are making coastal flooding more likely?
Rising sea levels
Increased frequency of storm
Rising sea levels
1) pose a threat to low-lying and coastal areas
2) causes higher tides - flood coastal areas more frequently
3) higher tides could also remove larger amounts of material from beaches - lead to increase erosion of cliff as there is less material to protect them from the sea
4) expose more of the coastline to erosion - beaches become narrower as the sea will be able to move further inland
Storm frequency
1) climate change is causing storms to be more frequent
2) storms gives the sea more erosional power -
hard rock areas - more vulnerable to erosion
soft rock areas - erode more quickly
3) sea will have more energy to transport materials - high energy waves can’t move material greater distances - leads to some areas with lack of material
these areas are vulnerable to erosion and flooding
Threats of coastal flooding to people
1) low-lying coastal areas could become permanently flooded - impossible to inhabit
2) coastal industries may shut - damage to equipment and buildings
3) risk of damage to infrastructure
4) fewer tourists - businesses relying on tourism may close leading to loss of livelihood
Threats of coastal flooding to the environment
1) damage to ecosystems
sea water has high salt content - increased salt levels due to coastal flooding can damage or kill organisms in an ecosystem
can also affect agricultural land - reduces soil fertility
2) force of floodwater can uproot trees and plants and standing floodwater drowns trees and plants
Hard engineering
man-made structures built to control the flow of the sea and reduce flooding and erosion
examples of hard engineering defences: sea walls, groynes
Soft engineering
Schemes set up using knowledge of the sea and its process to reduce the effects of flooding and erosion
examples of soft engineering defences: Beach replenishment, slope stabilisation
Sea walls
a wall made out of land material like concrete that reflects waves back to sea
benefits - prevents erosion of the coast and acts as a barrier to prevent flooding
costs - creates strong backwash which erodes under the wall and is expensive to build and maintain
Groynes
wooden or stone fences that are built at right angles to the coast
they trap material transported by longshore drift
benefits - create wider beaches which slow the waves - gives greater protection from flooding and erosion
fairly cheap defences
costs - starve beaches father down the coast of sand - makes them narrower
narrower beaches don’t protect the coast as well leading to greater erosion and floods
Beach r - gives greater protection from flooding and erosion eplenishment
sand and shingle from lower parts of the beach or else where are added too the upper parts of the beaches
benefits - creates wider beaches which slow the waves - gives greater protection from flooding and erosion
costs - taking material from sea bed can kill organisms like sponges and corals
very expensive defence and has to be repeated
Slope stabilisation
slopes are reinforced by inserting concrete nails into the ground and covering the slope with metal netting
benefits - prevents mass movement by increasing slopes strength
costs - very expensive and sometimes difficult to install
Strategic realignment
removing an existing defence and allowing the land behind it to flood
benefits - overtime land will become marshland - creating new habitats
flooding and erosion reduced behind the marshland
costs - people may disagree over what land is allowed to flood
for example - flooding farmland would affect farmers livelihoods
What is Integrated Coastal Zone Management
an approach that aims to protect the coast while taking everyones interests into account
