Coasts Flashcards
How is the strata arranged at a concordant coastline?
Parallel to the coastline
What causes weaknesses at concordamt coastlines?
Tectonic forces
What is the case study for dicordant coastlines?
Lolworth cove
What do concordant coastlines form?
Small beaches and coves
How is the strata arrganed in a discordant coastline?
At an angle to the beach
What is the case study for discordant coastlines?
Bantry Bay, SW Ireland
What is the resistant strata at discordant coastlines made of?
Devonian old red sandstone
What is the weaker strata at discordant coastlines made of?
Carboniferous limestone
What wave action happens at discordant coastlines?
Wave refraction
How long ago was the devension ice age?
10,000 years ago
What was the time period after the devension?
The Holocene
What happened in the Holocene?
Ice sheets melted
What do the melting glaciers in the Holocene deposit?
Sediment
Where does the sediment land in front of the glaciers melting?
Outwash plain
What type of coastline is a Haff?
Concordant
How does a lagoon form?
Unconsolidated sediment builds up ——> forms an offshore bar ——-> traps water behind it
What type of a coastline is a Dalamtian?
Concordant
At Dalmatian coastlines, what do tectonic plates do to each other?
They move towards each other casuing folding to form causing sink lines and anticlines
How is horizontal dip made?
Compaction and cementation
Are the bedding planes exposed at horizontal dip?
Yes
What forms at horizontal dip?
Wave cut platform and caves
What happens to rock along a fold?
Weaknesses are exploited causing stretching and faults to occur
What angle do bedding planes at a high angle seaward dip lie?
Greater than 45°
What forms at a high angle seaward dip?
Scree of sediment (slopes)
What angle do bedding planes at a low angle seaward dip lie at?
Less than 45°
What forms at a low angle seaward dip?
Scree slopes
What is evident at a low angle seaward dip?
Cliff collapse shown by rockfall
At the south Dorset coastline what is the resistant strata made of?
Portland Limestone
At the south dorset coastline what is the weak strata made of?
Portland Limestone and Wealden clay
What wave action breaks through a fault/ joint at a concordant coastline?
Hydraulic action
How does strata erode when a concordant coastline resistant layer is broken through?
Laterally
At discordant coastlines, what causes strata to be less resistant?
Lithology and structure
What are the three causes of high angle degree of indentation of Bantry Bay?
Prevailing wind direction/ fetch, presence of a fault or sea level rise
How does a Haff coastline form?
Deposition of unconsolidated sediment parallel to the coastline
What is the case study of horizontal dip?
Glamorgan Heritage coastline
What is the uppermost strata attacked by with high angle seaward dip?
Sub-aerial processes
What is the case study for low angle seaward dip?
Button Hive, south Dorset
What angle do low angle seaward dip produce?
70-80°
What has unconsolidated sediment not done to form a solid rock layer? (3)
Compression, compaction and lithifaction
What is the function of leaves on a beach?
Reduce wind velocity and decrease erosion
What do the roots of a plant on a beach do?
Bind the sediment together
What adaptation will sand dunes need to have to survive?
Able to withstand dry conditions
What adaptation will salt marshes need to have to survive?
Able to withstand salty, moist conditions
How is sedimentary rock formed?
Deposition of sediment on sea bed and adds weight causing compaction
What kind of structure is sedimentary rock?
Clastic
How is igneous rock formed?
Magma cools to form a solid rock, forms interlocking crystals
Which is more resistant: igneous rock or sedimentary?
Igneous
What kind of strucutre does igneous rock have?
Crystalline
What happens when a wave hits a fracture?
It wodens as air is trapped inside and it expands in size and causes rockfall
What can lithology refer to?
Rock class and mineral composition
What reactive minerals are in limestone?
Calvite
What pH does weak carbonic acid have?
5.6
What type of process wears away limestone (calcium carbonate rock)?
Solution
What is produced with via surface run off in sedimentary rcoks?
Distinctive grooves and runnels
What are the recession rates of sedimentary rocks?
0.5-10cm a year
Is sedimentary rock easily faulted and jointed?
Yes
Why does wave refraction occur at headlands?
When the waves hit shallower water the length is 1/2 the height as the internal orbital motion touches the floor
What does friction do towards the wave in wave action?
Distorts the wave from circular to elliptical cashing the wave to turn inwards
What can wave action create?
Cave, arch, stack or stump
What height are constructive waves?
Below 1m
What makes a wave constructive?
The fact that it has enough energy to push sediment up the beach
How do constructive waves create a gently sloping beach profile?
The backswash loses energy and so less sediment is being deposited towards the top of the wave
What is the wave length of a destructive wave?
20m
What other factors can influence wave action and marine erosion?
Seasons
How is a wave-cut notch formed?
A curve is made from the wave compressing air into the fracture causing it to explode and waves to cut away
What factors contribute to a speeding erosion?
High wind, large fetch, storm surges and seasons
What is longshore drift?
Net transport of material along the coastline
What causes drift aligned feature to occur?
Prevaling wind at an angle to the beach
What ° is the strongest longshore droft movement?
30°
What 3 types of wave action are used in a swash aligned feature?
Traction, saltation and suspension
What angle does a wave approach at a swash aligned feature?
90°
What coastal landform forms at a swash aligned feature?
Bay-head beaches
What is a example of a negative feedback loop?
Wave erosion causing blockfall —-> creates an overhang —-> rockfall
What do negative feedback loops do to wave energy?
Decrease it by breaking up the waves which leads to reduced impact on a cliff
What does a negative feedback loop do to the coastal sediment cell?
Slows the rate of sediment enerting the cell reducing the size of the landform
What is an example of a positive feedback loop?
The removal of plants in a sand dune environment ——> marram grass —-> slows down wind direction so increases rate of erosion
What is the case study for delta subsidence?
Ganges Brahmaputra Delta
What causes delta subusdence?
Fluvial deposition of sediment —-> depostis on river mouth ——> weight increases causing crustal sag —-> increases sea levels
What is thermal expansion?
Water molecules gain energy and the space between the particles increases leading to sea level rise
What is thermal contraction?
Drop in global temperatures so space between molecules decreases so reduction in volume of water
What is rotational slumping?
Warm weather dries out layer, rain water funnes into sand layer, percolation begins, water travels along clay layer, lubricates it so it slips
What is mass movement?
The downhill movement of material due to the force of gravity
What is the case study for mass movement?
Christchurch Bay in Barton on Sea
What is a RIa?
A flooded valley
What 2 time ages cuase eustatic sea level change?
Devensian, Holocene
How many metres lower were sea levels in the devension?
120m
What causes eustatic sea level change?
Water melting from the cryosphere increasing size of the molecules
When a river meets the sea, what happens to energy of the sediment?
It deacreses depsoting sediment on the delta
What landform is caused by sea level rise?
A fjord
What is a fjord?
A flooded glacial valley
How many islands have subsided in the Ganges Brahmaputra Delta
50
What does dredging do to the sediment cell?
Starves the sediment
What happens when there is starvation of sediment after dredging?
Erosion continues at the same rate
What is the case study for human intervention for dredging?
Hall sands
how many tonnes of sediment were removed in hall sands?
1,600
when was the storm that removal hall sands?
1917
How do dams affect the sediment being transported to a coastline?
They reduce it causing starvation of sediment
What year was the Aswan high dam?
1960
what was the reduction of discharge in the Aswan High Dam?
35 billion m3/2 to 10 billion m3/2
what was the volume of sediment reduced to at the Aswan high dam?
130 million tonnes to 15 million tonnes
what are the levels of erosion at the Aswan high dam?
20-25 m/year to 200m/year
What happens with the starvation of sediment at a dam?
It increase the rate further downstream
How do groynes affect recession rates?
They will increase it further downstream
What is an example of human intervention that caused increased erosion?
Groynes
What is the highest point above sea level in the Maldives?
2.3m
What type of sea level is at the Maldives?
Eustatic
If sea level rise was 50cm in the Maldives what % of land would be lost?
70%
What industry will be felt if the Maldives lost land?
Tourism
What is an example of isostatic sea level change?
Delta subsidence
What risk increases with delta subsidence?
Flood risk
What is the role of planting mangroves?
Stabilises the sediment with root systems to decrease erosion
What is the cause study for removing mangroves?
Bangladesh
What is the length of the mangroves removed in Bangladesh?
100m
What does 1mb decrease in air pressure do to sea level?
Rise by 1cm (locally)
What is a case study for a developing country?
Bangladesh storm sidir 2007
What catagory cyclone was the storm sidir in Bangladesh in 2007?
4
What % of land in Bangladesh is 3m above sea level?
60%
What were the deaths of the Bangladesh storm sidir?
15,000
What is the case study for a developed country?
Storm Xavier 2013 UK
What was the storm surge of the developed country of the UK?
3m
How many people were evacuated in the 2013 storm Xavier?
18,000
What stopped the flooding of the Thames in 2013 Storm Xavier?
Flood barriers
What are hard engineering strategies?
Disrupt natural processes using man-made structures
What is a case study for groynes?
Holderness
What are the cost of groynes per metre?
£150
What do groynes do?
Prevent longshore drift encourage deposition as it reduces the energy of transporting water
What is a negative of groynes?
It starves the sediment in the sediment cell
What is the case study for sea walls?
Holderness
What is the cost of sea walls per metre?
£3,000-10,000
What is a sea wall?
A wall made out of hard material that reflects waves back into the sea
What is a negative of sea walls?
They are expensive to build and not economically viable
What is a case study for rock armour?
Holderness
What is rock armour?
Piles of large boulders placed at a foot of the cliff
What is a negative for rock armour?
They disrupt the coastal sediment cell
What is offshore breakwater?
Large rocks in the sea to break the wave to reduce energy
What are revetments?
Interlocking stone structures to absorb wave energy
What are the cost of revetments per metre?
£500-3,000
What are soft engineering strategies?
Working with natural processes
What is beach nourishment?
The addition of large quantities of sand to the beach system
What is a positive of beach nourishment?
It is a more economically viable option
What is a case study for beach nourishment?
Hallsands
What if cliff stabilisation?
Drainage pipes to channel groundwater to reduce rotational slumping
What is a negative of cliff stabilisation?
It is expenisve
What is dune stabilisation?
Planting marram grass to prevent erosion to grow the dune
What is a negative of dune stabilisation?
Could be trampled, overgrown and removed by storms
What is sustainable coastal management?
Meeting the needs of the people without impacting the ability of future generations
What is considered with sustainable coastal management?
Responsibility, economic viability, negative unintended consequences
What is a stakeholder?
Someone with vested interest in the coast
What are 4 actions for a shoreline management plans?
No intervention, hold the line, managed realignment (retreat) , advance the line
