Coasts Flashcards
What is a concordant coastline?
Different rock strata with varying resistance to erosion are aligned parallel to the coastline
What is the case study for concordant coastlines and what type of strata does it have?
South Dorset Coastline, resistant Portland limestone and weak Wealden clay
What coastal feature forms from a concordant coastline and what is the case study for this feature?
Coves, Lulworth Cove
How do coves form?
At points where Portland limestone is weaker due to the presence of joints, hydraulic action/abrasion break through resistant layer and rapidly erode weaker strata behind it
What is a discordant coastline?
Different rock strata with varying resistance to erosion are aligned at an angle to the coastline
What coastal features form from a discordant coastline and what is the case study for these features?
Headlands and bays, Bantry Bay - weak carboniferous limestone and Devonian Old Red sandstone
What are the 2 alternative concordant coastlines?
Dalmatian and Haff
What is the case study for a Dalmatian coastline?
Croatia - tectonic forces from collision of African and Eurasian plates compressed carboniferous limestone and created synclines and anticlines, synclines flooded by sea level rise at the end of Devensian period
What is the case study for a Haff coastline?
Neman Haff
What is the case study for horizontal dip influencing cliff profile?
Glamorgan Heritage coastline - sedimentary rocks deposited horizontally and are tilted by tectonic forces
What coastal features usually form from a horizontal dip?
Notches, wave-cut platforms
What are the 2 types of rock?
Sedimentary and igneous
What can sedimentary rock be classed as and what processes took place to make them this way over many years?
Clastic, cementation and compaction
What reactive mineral in sedimentary rock does acid rain react with and what pH is acid rain (weak carbonic acid)?
Calcite, pH 5.6
What are the 3 types of weathering?
Chemical, mechanical, biological
What coastal features does chemical weathering produce?
Grooves and runnels
By what % does water expand by when it freezes in a crack (mechanical/freeze-thaw weathering)?
9%
Which process other than weathering is clastic rock susceptible to?
Hydraulic action
How do plant stems/leaves increase sediment accumulation (plant succession)?
Reduce velocity of wind and water carrying sediment which leads to deposition
What are embryo dunes colonised by and give an example?
Xerophytic pioneer species e.g. sea rocket
What do xerophytic pioneer species allow to grow and what does the plant create?
Marram grass, yellow dune
What does marram grass add to the sand when it dies, what type of dune does it create, and what type of plant grows here?
Hummus, grey dune, gorse
What is an example of a halophytic pioneer species and what do they do in salt marshes?
Blue-green algae, binds mud and sediment and adds organic matter
When mud is covered for less time by the tide, what species can grow at a salt marsh?
Halophytic glasswort and then sea lavendar
What can happen after a salt marsh eventually rises above tide level?
Rain washes salt from the soil so non-halophytic plants can grow
How does wave amplitude increase?
- Internal orbital motion of wave comes into contact with sea floor at depth of 1/2 the wavelength
- Front of wave slows down, allowing back of wave to catch up
- Wave amplitude increases
What do constructive waves have and what sediment profile do they form?
Strong swash and weak backwash, graduated sediment profile
What do destructive waves have and what sediment profile do they form?
Weak swash and strong backwash, mixed sediment profile
What 8 things influence the likeliness of a wave to erode a coastline?
- Windspeed
- Fetch
- Wind direction
- Sea level rise
- Angle at which wave is attacking
- Storms
- Seasons
- Tides
What marine process occurs around headlands?
Wave refraction
What 4 coastal features can from from the erosion of a headland and what is the case study?
Caves, arches, stacks, stumps, Old Harry Rocks
Which process forms a spit?
Longshore drift
What is the case study for spit formation?
Spurn Head, Holderness
At what angle does backwash drag sediment backwards after it has been pushed to the shore by prevailing winds?
90°
Where does wave energy dissipate as it transports sediment down the coast?
When it reaches deeper water e.g. river mouth
How does a spit form once wave energy has dissipated?
Sediment particles deposited on sea bed via gravity settling, once enough settled particles break the surface a spit forms
Where is wave energy focused when forming a bayhead beach and where does it dissipate to?
Focused on the headlands, dissipates into the bay due to wave refraction
How is a bayhead beach built up?
Constructive, lower-energy waves deposit sediment
Which coastal feature can be both swash-aligned and drift-aligned?
Tombolo
What is the case study for tombolo formation?
St. Ninian’s Isle
How does a drift-aligned tombolo form?
Longshore drift builds a spit out from land until it connects with an offshore island
How does a swash-aligned tombolo form?
Wave refraction around both sides of offshore island causes a collision of wave fronts on the landward side which produces a zone of calm water where deposition occurs between the island and coast
Which process is a negative feedback loop?
Rockfall - forms rock armour at the base of the cliff which dissipates wave energy
Which process is a positive feedback loop?
Storm causes erosion of a sand dune - vegetation removed so the sand dune isn’t stabilised and continues to be further eroded
How does salt crystallisation increase recession rates?
Seawater penetrates cracks in rock at high tide and evaporates at low tide, leaving NaCl crystals which grow and exert tensional force on the crack, widening it and leading to the granular disintegration of rock
What is the application for the seed of a plant falling into a crack and being germinated, causing biological weathering?
E.g. sea milkwort
What is the case study for rockfall (mass movement)?
April 2020 Jurassic coast of Dorset
How many metres of cliff weighing how many tonnes fell at the Jurassic coast?
300m, 4,000 tonnes
What is the case study for rotational slumping (mass movement)?
Christchurch Bay
What starts off rotational slumping?
Dry weather cracks soil so water funnels down into permeable sands
What does water funneling into permeable sands do?
Increases pore water pressure along lines of percolation
Where does water accumulate after pore water pressure increases along lines of percolation and where does it then percolate to?
Lower sands, percolates into clay
What does the percolation of water into clay do to bedding planes and what does it then encourage?
Lubricates bedding planes along clay-sand boundary, encourages movement of sand
What combined with downslope gravitational force causes slumping?
Weight of water
What type of coastline does marine regression form?
Emergent
How much did sea levels drop by during the Devensian period?
120m
Where did water move to during the Devensian glacial period?
Hydrosphere to cryosphere
What is thermal contraction?
Less space between water molecules as they have less energy so further reduction in volume of sea water
How can marine transgression also create an emergent coastline?
Weight of overlaying ice caused crustal sag but then ice melted during Holocene so reduction in downward pressure on land and land rebounds over many years
What is the process called when marine transgression creates an emergent coastline?
Post-glacial isostatic readjustment
What type of coastline does marine transgression form?
Submergent
What is thermal expansion?
More space between water molecules as they have more energy so further increase in volume of sea water
In which time period did glaciers melt and water moved from the cryosphere to hydrosphere?
Holocene
What is the case study for ria formation?
Bantry Bay
What is a ria?
Flooded river valley
How is a ria formed?
- Fault in carboniferous limestone allowed rapid vertical fluvial erosion by rivers to occur
- Produced a deep river valley below sea level
- Sea level rise during Holocene flooded it
What is the case study for fjord formation?
Oslo Fjord
What is a fjord?
Flooded glacial valley
How is a fjord formed?
- During Devensian, glaciers caused vertical and lateral erosion of river valleys, creating wide U-shaped valleys
- Terminal moraine carried by glaciers deposited at coastlines
- As ice sheets thaw, U-shaped valley is flooded and terminal moraine forms lip at entrance to fjord
Summary: What are the 3 ways marine transgression can create a submergent coastline?
- Global temp. rise during Holocene so water returned to hydrosphere
- Delta subsidence
- Thermal expansion
Summary: What are the 2 ways marine regression can create an emergent coastline?
- Global temp. drop during Devensian so water locked in cryosphere
- Thermal contraction
Summary: What is the 1 way marine transgression can create an emergent coastline?
Post-glacial isostatic readjustment
What is the case study for post-glacial isostatic readjustment and at what rate has land been rebounding since the Devensian period?
Scotland, 1.5mm/year
How does delta subsidence occur?
More fluvial deposition of sediment from rivers occurs so coastal acretion and over time weight of overlaying sediment causes crustal sag so local sea level rise
Which area is affected by delta subsidence and how much have land levels dropped since 1960?
Ganges Brahmaputra Delta, 1.5m since 1960
How do dams lead to increased recession rates?
Causes a reduction in discharge of sediment-carrying river water flowing to the coastline so decreased inputs of sediment
What is the case study for dams increasing recession rates?
Aswan Dam
How does dredging increase recession rates?
Removes sediment from source region of coastal sediment cell so reduced sediment inputs so beach is starved of sediment so reduced area of beach to dissipate wave energy
What is the case study for dredging, how many tonnes of offshore sand was removed, and what was the sand used for?
Hallsands, 1500 tonnes, used to build a naval dockyard
What year did a storm hit Hallsands and what did it destroy?
1917, destroyed Hallsands village
Which area has dominant wind from the North, how long is its fetch, and what is its recession rate?
North Norfolk, 1600km, 8m/year
Why does stronger wind and longer fetch increase recession rates?
Waves generated due to friction between wind and surface of water so high energy wind = high energy transfer to waves
By what % does a 100m belt of mangrove forest reduce wave height?
40% - can also use for soft engineering strategy PAD
What % of the Sundarbans area in Bangladesh is experiencing some form of mangrove removal and what rate are some parts eroding at?
71%, 200m/year
What is the highest point of land at the Maldives?
2.3m
What % of land area would the Maldives lose if sea level was to rise 50cm by 2100?
77%
What % of the Maldives’ GDP is based around tourism and how far from the coastline are many major tourist resorts?
70%, 100m
At what rate does delta subsidence occur at the Ganges Brahmaputra Delta?
5mm/year
What % of Bangladesh is less than 5m above sea level?
60%
How does flooding in Bangladesh affect crop yield?
Increases soil salinity so decreased crop yield
What are storm surges and how do they increase sea level?
Temporary rises in local sea level when a depression/storm reaches the coast, low air pressure allows ocean surface to dome upward and generates strong winds
What is the case study for storm surges increasing flood risk in developing countries?
Storm Sidr hit Bangladesh
What was the height of the storm surge and how many hectares of agricultural land was destroyed in Bangladesh after Storm Sidr 2007?
6m, 600,000 hectares
What is the case study for storm surges increasing flood risk in developed countries?
Storm Xavier hit East Anglia
What was the height of the storm surge and how many homes were flooded in East Anglia after Storm Xavier 2013?
3m, 1,400 homes flooded
What is the linked evaluation for sea walls being an effective coastal management strategy?
Aren’t appealing to tourists, expensive to implement
What are groynes and how do they reduce coastal recession?
Long timber structures aligned 90° to the coastline - trap sediment from longshore drift to build up the beach
What is the rate of recession now at Holderness after groynes were added and reduced it?
2m/year
What is the linked evaluation for groynes being effective?
Cause sediment starvation further along the coast (conflict)
What has rate of recession at Cowden, Holderness increased to since the addition of groynes?
4m/year (conflict)
How does rock armour decrease recession rates at the base of a cliff?
Larger, igneous rocks so more resistant to erosion and dissipate wave energy
Where was rock armour used and how much?
Holderness, 130,000 tonnes
Where was beach nourishment used?
Lincshore 2013
What is the linked evaluation for beach nourishment?
Very expensive - £2 million per km of beach
What % of Britain’s gas does Easington gas terminal produce and how far away is it from the cliff edge?
25%, 25m
What are the 4 policies of coastal management?
- No active intervention
- Hold the line
- Managed realignment
- Advance the line
What is cost benefit analysis and what is the case study for it?
Determines whether a protection scheme is economically viable, Happisburgh
How long is the fetch from Norway that causes Happisburgh to suffer from frequent high energy destructive waves?
1600km
What is the management plan for Happisburgh?
Short term no active intervention, long term managed realignment
Why will no active intervention and managed realignment be used at Happisburgh?
If hard engineering strategies were used, it would become a promontory which blocks longshore drift and causes sediment starvation
What is a cost and benefit of the management strategy used at Happisburgh?
Cost: Loss of grade 1 listed building St. Mary’s Church (conflict)
Benefit: 45ha of farmland saved
What is an environmental impact assessment and what is the case study for it?
Determines how management strategies will impact flows of sediment, marine ecosystems, and noise pollution, Blackwater Estuary
Why are hard engineering strategies at Blackwater Estuary no longer sustainable?
Sea level rise so salt marshes are being eroded, removing natural protection (positive feedback loop)
How many hectares of managed realignment was used at Blackwater Estuary and what was a benefit?
4000ha, new salt marshes formed so water quality in estuary improved due to reed beds
