Coasts Flashcards
Backshore
area above high tide level and only affected by exceptionally high tides
Littoral zone
and what it consists of
The littoral zone is the area of the coast where land is subject to wave action. The littoral zone consists of the backshore , foreshore and offshore
Foreshore
Land where the most processes occur
Offshore
the open sea
High energy coastlines
where the rate of errosion exceeds the rate of deposition
Low energy coastlines
where the rate of deposition exceeds the rate of errosion
How can coasts be classified
- geology
- level of energy
- balance between erosion and deposition
- changed in sea levels
Resistant rock coastlines
- igneous rocks
- older compacted sedimentry rock
- metamorphic rock
Costal plain landscapes
consists of much younger weaker sedimentry rock
Lithology
Structure of the rock
Concordant coastlines
This is where rock strata runs parallel to the coastline and the rock type varies but usually consists of bands of more resistant and less resistant rock
What can concordant coastlines lead to the formation of
- Dalmatian coasts
- Haff coasts
Discordant coastlines
This is where rock strata runs parallel to the coast
What can discordant coastlines lead to the formation of
Headlands and bays
Headlands and bays
defenition and process
Headlands jut out into the sea while bays lie between them.
* As headlands and bays occur at disocrdant coastlines where strata runs perpendicular to the coastline less resistant rock such as chalk and limestone is erroded quicker than the more resistant rock hence forming headlands and bays where the headlands are the more resistant rock.
Dalmatian coast
Tectonic acticity causes syncline and anticlines to form , as this feature is submegent due to eustatic sea level rise when water floods the synclines this causes the anticlines to stand out of the water.
Haff coasts
Large bays are crossed by spits creating extenive lagoons
How does vegitation help stabalise costal sediment
- Roots of plants bind soil toegether which helps reduce errosion
- When completely submerged plants provide a protective layer fo the ground so that it is less easily erroded
- Plants reduce wind speed so less wind errosion occurs
Xerophytes
plants that are tolerent to dry conditions
Brackish plants
plants that are tolerent of salty conditions
Plant succession
Plant succession is a long term change in a plant community in an area.
* On coasts where there is a supply of sediment and deposition occurs , pioneer plants begin to grow in bare mud and sand.
* Due to the saltyness of the area only certain plants can grow here
* As more deposition occurs vegitation dies realising nutrients into the sand
* This reduces the saltyness of the sand
* Other plants can therefore grow here
Maram grass
example of an pioneer plant
- tough and flexible can therefore cope when being blasted with sand
- adapted to reduce water loss through transpiration
- roots can gro up to three metres deep and can tolerate temperatures of up to 60 degrews
Dune succession
Constructive waves
and effect on beach profile
- low surging waves
- strong swash weak backwash
- Builds up the beach with a more gentle beach profile
Destructive waves
and effect on beach profile
- Higher wave height
- Weak swash strong backwash
- steeper beach profile in the short tun
Errosional processes
4
- Abrasion
- Attrition
- Hydraulic action
- Corrosion
Abrasion
Stones and sediment are pricked up by the waves and wear away at the cliff/headland
Attrition
Rocks are moved around by waves and as they knock into one another or due to processes such as abrasion the rocks gradually becomes smaller and rounder
Hydraulic action
Due to shear force of the waves which forces air at high pressure into cracks within the cliffface overtime this weakesn the rock and makes the joint to widen
Corrosion
weak acid within the seawater dissolves rock particles
How are errosional processes influenced by wave type
- most errosion occurs during winter as waves are more destructive
- destructive waves - more abrasion and attrition
- the more resistant the rock is the less prone it is to errosion
Wave cut platform
Process
- occurs at high energy coastlines
- hydraulic action and abrasion are the main errosional processes causing the formation of a wave cut platform
- powerful destructive waves attack the cliff face at high tides
- hydraulic action and abrasion over time create a wave cut notch which over time increases in size
- this is known as undercutting
- over time the overhang created by undercutting collapses due to weathering and the force of gravity
- The cliff retreats and reveals a wave cut platform at low tides
Cave , arch , stack , stump
sequence
This occurs at headlands where the rock is hard and errosion is slow
1. Joints in the headland are succesptible to erroision due to hydraulic action
2. Over time the join is widened which forms a cave
3. The cave is enlarged due to hydraulic action and abrasion
4. As the cave grows in size it eventually breaks through the headland to form a natural arch
5. The arch is erroded and collapses which can be due to both costal errosion and sub areial proccesses
6. This forms a stack which is eventually erroded to a stump due to abrasion , attrition and hydraulic action
Longshore drift
process
Longshore drift is the main process of deposition and transportation along the coast
* Due to prevaling winds , waves approach the beach at an angle which is similar to the that of the wind
* As the waves break swash carriers material up the beach at the same angle
* The backwash carriest the material down the beach at a 90 degree angle to
* Therefore this process repeats and sediment is moved along the beach in a zig zag pattern
Spit
formation
A spit is an extended stretch of sand or shingle that extends out to the sea from the shore
* Sediment is transported along the coast normally most often due to longshore drift
* When the coastlines change direction there is not enough energy in the water to carry the sediment hence it is deposited
* The build up of sediment normally into an estuary form a spit
* There are often curved ends or hooks at the end of the spit due to second prevailing winds
bar
where sediment meets either an island or the opposite side of a headland respectivley
Lagoon
A lagoon is where a small body of water is cut off from the sea
* a lagoon may form behind a bar or tombolo
* Lagoons do not last forever and may fill up with sediment to form new land
Tombolo
a tombolo is when a spit joins a mainland to an island
e.g Chesil beach in dorset
Salt marsh
Behind barrier beaches and spits the are is very sheltered and lots of deposition occurs as tidal and river current meet
* Leads to formation of salt marshes
* As sediment accumulates
* Pioneer plants such as halopytes like eelgrasss begin to colinise
* This traps more sediment and slow tidal flow
* As more sediment accumulates the surface becomes drier
* Other plants such as sea asters start to colinise there
Sediment cells inputs
- more brought by rivers
- cliff errosion
- where coastlines are retreating there is a large inout of sediment to the coastal zone
- wind - sand dunes
sediment cells
overview
- area along the coastline where the movement of sediment is largely self contained
- closed system
sediment budget
balance between the inputs and outputs of the sediment in a system
* should be in dynamic equilibrium
* human and natural change like climate chage can disturb this equilibrium
Weathering
Breakdown of rock in situ
* Mechanical
* Biological
* Chemical
Mechanical weathering
When rock breaks down with no physical changes
* Freeze thaw weathering
1. Water from rain collects in a crack in a rock
2. When the temperatures drop in the evening and overnight the water freezes expanding the crack
3. The water melts and gets deeper into the crack
* Salt crystillisation
1. Water from the sea gets into cracks in the rock
2. Due to energy from the sun the water evaporates leaving salt crystas behind within cracks in the rock
3. Salt crytals break over time and exert pressure on the rock casuing it to break down
Biological weathering
Rock breaks down due to organic activity
* Roots from plants enter cracks in the rock under the soil
* as the roots grow when the plant does the cracks get larger
* more stress on the rock
* breaks down
* nesting birds and small burrowing animals
Chemical weathering
Rocks break down due to chemical reaction - rock changes
* acid rain - carbonation - limestone
* oxidation - iron in rock
* soloution
Mass movement
The downhill movement of material under the influence of gravity
* Throughflow and runoff caused by heavy precipitation can make cliffs more unstable and make mass movement more likely
Eustatic
when global sea levels rise or fall
Isostatic
when land rises or falls relative to the sea level
* isostatic change is local
Causes of eustatic change
- Thermohailine expansion
- rising temp melt water from water in the cryosphere such as glaciers and ice caps
- Tectonic activity - sea floor spreading - ocean basin increases
Causes of isostatic change
- post glacial adjustment - lowers sea level as land is rising as due to the decreases weight from glaciers
- also known as isostatic adjument , recovery
- Ash and lava from volcanoes is increasing height
energent coastlines
lanforms that exist due to a reduction in sea level
* occurs during isostatic recovery
* examples are rasied beaches and fossil cliffs
raised beach
- beaches which are above high tide level
- flat and covered by sand/pebbles
- seen on the Scotish Island of Mull
Fossil cliff
- steep slope at the back of a raised beach
- wave cut notches , caves and arches may be evident
Submergent coastline
- Landforms that exist due to a rise in sea level
- Happens where coastlines are flooded
- normally due to eustatic change
- examples are rias and fjords and a dalmation coast
Ria
- when costal areas flood
- the lower part of a river can also be flooded
Rias have a : - V shaped cross setion
- a eustarine coastline
- most common costal landform
Fjord
- this is when glacial valleys are flooded
- fjords are deeper and more inland than rias
- orgiannly a flat bottom u shaped valley due to powerful glaciers
- reltively straight profile
- may be deeper than some nearby seas
Human impacts on costal recession
**Dredging **
* this is the removal of sediment from sea or oceans
* impacts the amout of sediment on the coast
**Dams **
* construction of dams traps sediment behind the dams walls
*starves the coast of sediment
* River embro has a 93% reduction in sediment downstream due to construction of dams
**Beaches decrease in size **
destructive waves have more impact
Wind direction and fetch
imoact on rates of recession
- wind can be onshore or offshore
- when wind direction , onshore and the direction of the largest fetch , large destructive waves are formed
Onshore
Wind is blowing over the sea towards the land
Offshore
wind is blowing from the land towards rhe sea
* calmer conditions
Factors increasing flood risk
*** height of land **
* low lying areas are more vulnerable to rising sea levels
* **degree of subsidence **
* when subsidence occurs the land is lower and more vulnerbale to flooding
* building settlements increase the risk of susidence
* clearling land for agriculture decreases the risk of subsidence
* vegitation removal
* vegitation helps to trap sediment which increases the land height
* reduces the impact of waves and errosion as it absorbs energy
Physical factors increasing recession
**Wind direction and fetch **
* Onshore waves normally have the largest fetch and the most destructive waves
**Tides **
* Rates of recession are greatest during high tide as water and waves can reach the back shore
* high tides occur twice a day
* twice a month the sun, moon and earth are in allignment increasing the gravity pull
Seasons
* winter recession is higher as there are more destructive waves in winter
*
**storms **
* high energy destructive waves
*
*
Climate change and flood risk
- global sea level rise
- increased frequency and magnitude of storms
Storm surges
Events that can lead to severe costal flooding with dramatic short - term impacts
* Warmer ocean temperatures combined with higher sea levels are predicted to make storms and tropical cyclones more frequent and more severe
Tropical cyclones
- area of very low pressure
- heavy rains and strong winds
Hard engineering
Construction of man made structures designed to absorb the energy of the waves
* grones
* sea wall
* rip rap
* revetments
Gryones
These are structures built at right angles to the shore to trap sediment that is being transported by longshore drift
PROS
1. not as expensive as other hard enginnering
2. builds up beach which improves tourist potential
CONS
1. can cause sediment starvation further along the coast
2. unattractive
3. lots of maintaince
Sea walls
Walls with a curved or stepped face that absorb or reflect wave energy
Pros
* Highly effective
* can have tourisim benefits as walkways are created
Cons
* Very expenive to build and maintain
* £6000 per metre
* ugly and intrusive to the landscape
Rip rap
Large concrete/granite bolders at the foot of a cliff. The spaces between bloulders catch waves and cause them to loose energy
PROS
* Cheaper than sea walls
* Used for fishing
CONS
* Dangerous when people are on them
* Rocks from elsehwere are intrusive to local geology
Revetments
A sloped or ramp like structure that breaks up wave energy
Pros
* Cost effective comapred to other hard engineering strtagies
**Cons **
* needs lots of maintence
* unatural looking
* slopes are dangerous
Soft engineering
Works with natural processes and material to absorb the energy of waves
* beach nourishment
* cliff regrading and drainage
* dune stabilisation
* marsh creation
Beach nourishment
Adding sand or shingle to a beach to widen it creating more surface area to absorb wave energy
Pros
* looks natural
* bigger beaches are good for tourisim
* relativley inexpensive
Cons
* material is constantly subject to errosion and longshore drift
* dredging the seabed can have impacts to local ecosystems
* expensive 20million per km
Cliff regrading and drainage
Reducing the cliff angle to stablise the slope. Re vegetated to reduce surface errosion. Drainage of water also reduces the risk of the cliff against mass movement
Pros
* cost effective compared to other stratagies £1 million per km
Cons
* can look unnatural as cliff is flatter
* distruptive during construction
* effectivley retreating the cliff
* dried out cliffs can cause it to collapse
Dune stabilisation
Planting species like Marram grass so that the roots bind to the dunes. The dunes absorb wave energy and protect the land behind
Pros
* Cheap and sustainable
* Creates habitats for wildlife
* maintains a natural enviroment
Cons
* People may walk on the dunes and damage them
* Planting is time consuming
Marsh creation
This is a form of do nothing managed retreat where land is allowed to be flooded by the sea creating a a salt marsh which absorbs wave energy and also creates a buffer to rising sea level and protects higher value land.
Pros
* Cheap option
* Creates important and unique wildlife habitats
*Cons
* agricultural land is lost
Sustainable management
Managing the wider costal zone in terms of people and there economic livlihoods.
* Adaptation to erosion and flood risk
* education of local communities
* supporting livelihoods dependent on the costal zone such as fishing
* moniitoring of costal changes
* ICZM is based on the idea of sustainable costal management
ICZM
integrated costal zone management
UK
The shoreline plans in the UK are a form of ICZM
* they recognise that the sediment cells interact with one another and that canages in one part of a coast impact other area such as terminal gryone syndrome
* ICZM involves a range of stakeholders involved in the use of managament of the coast aims to
1. create sustainable and economic activities
2. protect the costal enviroment
3. manage flood and costal eroion risk
4. reslove any conflics that may occur
Winners vs loosers costal management
Winner
* property and businesses are protected
* enviroment is conserved
* farmland is protcted
Loosers
* people have to relocate
* homes and businees are lost
* farmland is lost
* habitats are destroyed
