Coastal Envronments Flashcards
Hydraulic action
Waves hit cliffs and force air into cracks causing the rock to break apart
Abrasion
Waves pick up pebbles and hurl them against the cliff
Solution
The dissolving CaCO3 rocks like limestone or chalk by the sea
Attrition
Pebbles carried by the waves collide with each other and become smaller and more rounded over time
Deposition
Occurs when waves lose energy/material carried is too large to transport with the amount of energy the wave has
Mechanical weathering
Breaks down rocks by processes such as freeze-thaw, salt crystal growth and wetting and during of clay rich rocks
Biological weathering
It is when rocks are broken down by plant roots, burrowing animals and nesting birds
Chemical weathering
It is when rocks are broken down by carbonation, oxidation, and acid rain. Usually impacts CaCO3 rock
Slumping
Waves erode the cliff base and cause instability. Rain water permeates through the rock saturating it, until it becomes in stable and slumps along bedding planes. Leads to a stepped appearance to the cliff
Sliding
Weathering loosens the rock, which slides down off bedding planes. Leads to landslides and mudslides
Geology
Rock type like granite, chalk and etc
Lithology
Characteristics of the rock eg relative hardness, permeability etc
Discordant coastline
Rock outcrops are at 90 degrees to the sea. Leads to headlands and bays where there are bands of soft and hard rock interspersed with each other
Concordat geology
Rock outcrops are parallel to sea. Creates straighter coastlines. Though can create coves, like Lulworth Cove, Dorset
Bedding planes
In cliffs determine how susceptible the cliff is to collapse
How does vegetation influence the coastline
-biological weathering
-can create sand dunes via encourage deposition, and then stabilise them
-can protect and preserve coastal landforms by buffering and reducing wave energy(mangroves
Influence of wave refraction by bays and headlands
-waves approach parallel to the coastline as a whole
-as the sea shallows, on approach to the coast the waves refract to mirror the individual shape of the coastline
-this leads to energy being concentrated on headlands(due to converging waves). Despite this, headlands remain sticking out to sea more than bays due to their relatively harder lithology
Formation of cliff/cliff retreat
-erosion is concentrated at the base of the cliff between the low tide and high tide mark in the wave attack zone through hydraulic action and abrasion
-the creates a wave cut notch
-the cliff above is undercut, is therefore unsupported and collapses due to gravity
-this creates a wave cut platform
-over time, this repeats and the cliff retreats inland
Longshore drift
-waves approach the coast at an angle because of the direction of the prevailing wind
-the slash will carry the material towards a and on to the beach at an angle
-the backswash then flows back to the sea, directly down the slope of the beach due to gravity
-the process repeats itself along the coast in zigzag moments
How does sea level influence the coast by
-coastal flooding is caused by rising sea level
-fjords form when glacial landscape are flooded - rias from flooded areas
-retreating sea level due to land uplift creating landforms such as relict cliffs and raised beaches
-saltwater incursion - loss of groundwater causes sea water in coastal region to be drawn into permeable rock
How do people influence the coast
-settlements
-fishing
-trade
-tourism
What are beaches
They are areas where there is an accumulation of sand and shingle, caused by deposition. They often form in bays, where the coast is sheltered from high energy, erosion all waves, or where long horse drift provides a large supply of material
How does a spit form
-sudden change in coastline shape or direction
-longshore drift has momentum and so continue to transport and deposited material at sea, following the original direction of longshore drift
-over time, sediment builds up creating a sandy ridge outcrop (a spit) on the coast
-salt marshes form behind spits as these water are low energy and stagnant. Rivers often deposited their sediment too, growing the spit
-spits often become curbed due to secondary prevailing wind or the impact of cross-currents/storm
What are cuspate forelands
-triangular shapes accumulations of sand and shingle
-develop due to LSD from two directions
-collision of two LSD directions encourages deposition and creation of the foreland )Dungeness, Kent)
Where are corals found
30 degrees N and S of the equator in the tropics
Factors needed for corals
-sea surface temperatures of 23-25 degrees Celsius
-<25m deep water(as sunlight needed)
-salinity
-clean water, with not too much sediment that would otherwise clog feeding structures
-moderate wave action
What % of the ocean floor do corals cover
1%
What % of marine biodiversity is contained within coral reefs
25%
What are corals composed of
Coral polyps(animals that have a symbiotic relationship ship with zooxanthellae(algae)
What services do coral reefs provide to ecosystems
-regulating, provisioning, supporting and cultural
Biotic factors of the GBR
-coral
-algae
-fish
-sharks
-turtles;es
-plankton
Abiotic factors of the GBR
-temperature
-water flow
-salinity level
-pH of seawater
-light level
-nutrient availability
Nutrient cycling in a coral reef
- Nutrient source - Sea water. Corals filter nutrients out of seawater
- Biomass - coral, algae, seaweed, sigh, crustaceans and invertebrate species
- Litter - dead coral, fish, invertebrates, seaweed etc. Moved around by tides and ocean currents
How are reefs threatened
-tourism
-industrilisation
-agriculture and deforestation
Where are mangroves found
-32 degrees north to south of the equator
-sheltered, intertidal areas that receive high annual rainfall
Factors needed for mangroves to survive
-a average temperature of the coldest month higher than 20 degrees C
-a fine-grained substrate or sediment(like sand and soil)
-the shores must be free os strong wave action and tidal current
-salt water
Benefits of mangrove
-traps silt to create new land
-provides timber for building materials
-provides protection from storms, storm surges and tsunamis
Why are mangrove forest threatened by industrialisation, agriculture, tourism and deforestation
-timber for fuel and building material
-aquaculture
-land reclamation for tourist hotels and other amenities
-diversion of fresh water
-farming requires application of herbicides to prepare for cultivation
Where are sand dunes found
Worldwide at the interface between land and sea
Limiting factors of sand dunes
-wide beach and large quantities of sand
-onshore prevailing wind(from the sea to the shore)
-an obstacle such as marram grass, driftwood to encourage deposition
Name the sand dunes from youngest to oldest
Embryo dunes, foredunes, yellow dunes, grey/mature dunes
Where do dune slacks form
In between dune crests
What is plant succession on the dunes called
Psammosere succession
What do mature dunes have that is different to embryo dunes
More humus and more acidic pH due to the absence of seashells
How are sand dunes threatened by tourism and recreation
-recreation such as trail biking and hours riding. Gold courses and caravan sites
Where are salt marshes found
In intertidal zones, separating permanently flooded mudflats and dry, inland, areas above the high tide mark
-usually in sheltered areas of coastline such as estuaries and bays, and usually behind spits
What do salt marshes adapt to
-either adapted to saltwater(if in bays) or brackish water(if in estuaries)
How are mudflats colonised by vegetation over time
-they are colonised by vegetation over time, until the most stable climax community vegetation of Carr woodland is achieved at the back of a salt marsh)this is permanently waterlogged
How are salt marshes threatened by industrialisation, agriculture and tourism
-reclamation to create farmland and sites for industrial and port developments
-industrial pollution from ports, power stations and oil refineries
-agricultural pollution from fertilisers such as marinas and other recreational facilities
Solution(movement)
When minerals in rocks like chalk and limestone are dissolved in seawater and then carried in solution. The load is not visible
Suspension
Small particles such as silts and clays are suspended in the flow of the water
Saltation
Where small pieces of shingle or large grains are bounced along the sea bed
Traction
Where pebbles are larger materials are rolled along the sea bed
Bar formation
- Sudden change in coastline direction
- Longshore drift has momentum and so continues to transport and deposit material at sea
- Over time sediment builds up creating a sandy ridge outcrop
4.spit grows across a bay joining up two headlands
Tombolo
When a spit connected the mainland coast to an island or wave refraction around an island causes sediment to buildup
Causes of coastal flooding
- Storm surges
- Tsunamis
- Climate change
Storm surge cause from air pressure
-High tide and low air pressure, raising the height of the high-tide further. Strong onshore winds then push the raised sea towards the coast and are capable of breaching coastal defences
Storm surge caused by hurricanes
-hurricanes cause low pressure and the sea bulges upwards is then pushes on shore
-much bigger and has more energy than normal storm surges
3 types of sea level rise due to climate change
- Isostatic readjustment - rise of land masses that were depressed by the huge weight of ice sheets during the last ice age
- Eustatic change - sea level changes due to an alteration in the volume of water in the oceans - caused by melting land
- Thermal expansion, causing it to expand
How are tsunamis formed
-Generated by earthquakes that occur underwater
-can also be formed by massive volcanic eruptions or meteor strikes
Prevention methods for coastal flooding
- Flood defence construction in high risk areas
- Building emergency centres where people will be safe from flooding
- Removing housing and human activities from high risk areas
- Designing new buildings to cope with low levels of flooding(silts)
- Installing advance warning systems for possible flooding
- Education of local people on what to do when warning systems are activated
Use Historical records in prediction
Looking back at historical records and identify areas that have been frequently flooded to define high risk areas
Forecasting in prediction
-relying on accurate forecasting on hazard events
-should predict when and where a flood event will occur and its scale, strength etc
Where do coastal management work within
Coastal cells
Coastal cell
-Self contained stretch of coastline
-closed system as sediment is not usually transferred from one to the other
Options for shoreline managements
- Hold the line
- Managed retreat
- No active intervention
- Advance the line
Hold the line
Intervene against coastal erosion with hard or soft engineering to prevent any further shoreline retreat
Managed retreat
Realignment of the coast to a predetermined line some distance further inland from the current position of the coast
No active intervention meaning
-Permit natural systems to modify the coastline as they are currently operating
-usually means allowing erosion and cliffs retreat to continue
Advance the line meaning
Extend the coast into what is currently the sea
Factors affecting which option is designated for section of the coast
- The rate of coastal change
- The economic value of land
- Value of agricultural land/habitats of value
- Cost of intervention strategies
Hard engineering
Building or creating something which will interfere with coastal processes- usually to reduce the power of breaking waves against cliffs
Soft engineering
-Working with the natural processes of sea and sand in a more environmentally sustainable way
-using natural processes to bring about an intended effect
Groynes
-narrow structures built at right angles to the coastline
-aim to slow down longshore drift and trap sediment
-can be made of timber, concrete or rock
Advantages of groynes
-More beach material to dissipate wave energy which slows down cliff erosion
-cheap in comparison to other hard engineering
Disadvantages of groynes
-beaches further along the coast are starved of beach material due to their effect on longshore drift
-alters the usage of the beach
(Recurved) sea walls
-concrete walls that are placed at the foot of a cliff to prevent erosion
-can be curved to reflect the energy back into the sea
Advantages of sea walls
-Effective at protecting the base of the cliff
-sea walls usually have promenades so people can walk along them
Disadvantages of sea walls
-waves are still powerful and can break down and erode the sea wall
-expensive
Rip raps
-Large boulders placed at the foot at a cliff or on a slope
-break the waves and absorb their energy
Advantages of rip raps
-Cheaper than a sea wall and easy to maintain
-can be used for fishing
Disadvantages of rip raps
-Look different to the local geology, as the rock has been imported from other areas
-the rocks are expensive to transport
Gabions
Steel wire baskets filled with rock and built into an eroding cliff to improve stability
Advantages of gabions
-Cheap
-Fairly effective
Disadvantages of gabions
Unattractive - can leave rusting metal wire on the beach
-cannot withstand strong waves
Revetments
Wooden slatted barrier constructed towards the rear of beaches to protect the base of cliffs
Advantages of revetments
-Less beach material is eroded compared to a sea wall
-cheaper and less intrusive than a sea wall
Disadvantages of revetments
-short life span
-unsuitable where wave energy is high
Offshore reef
Enormous concrete and natural blocks are sunk offshore to alter the wave direction
Advantages of offshore reef
-The waves break further offshore so reduce erosive power
-allow the build up of sand
Disadvantages of offshore reefs
-may be reduced by heavy storms
-difficult to install
-can be high cost depending on installation issues
Beach nourishment
-beaches are built up by pumping sand onto the beach
-the source of the material is usually from offshore dredging
Advantages of beach nourishment
Retains the natural appearance of the beach
Disadvantages of beach nourishment
-Offshore dredging of sand and shingle increases erosion in other areas and effects ecosystems
-can be expensive - large storms means replenishments need to be done regularly
Cliff regrading
Making the cliff face longer so that it is less steep
Advantages of cliff regrading
-Cheap
-natural, encourages wildlife back into the area
Disadvantages of cliff regrading
-not effective on its own - need other defences at the base of the cliff
-some homes on the cliff may need to be demolished
Mangrove rehabilitation/revegetation
Ability to absorb the power of the waves particularly during ‘freak’ events
Advantages of mangrove rehabilitation
-Provides a habitat for numerous
-popular with bird watchers and wildlife enthusiasts
-low costs and naturally occurring
Disadvantages of mangrove rehabilitation
-can restrict access to beaches
-take up large areas of land which could be developed for tourism
Managed retreat in soft engineering
-The controlled flooding of low-lying coastal areas
Advantages of managed retreat
-Cheap option compared to paying for sea defences
-creates a salt marsh which can provide habitats for wildlife and a natural defence against erosion and flooding
-salt marshes are diverse ecosystems supporting many species
Disadvantages of managed retreat
-Land is lost as it is reclaimed by the sea
-landowners need to be compensated
