2. Coasts Flashcards
What is the littoral zone and what are the zones
It is a dynamic zone of rapid change
Backshore - usually above the influence of waves
Foreshore - inter-tidal or surf zone
Nearshore - breaker zone
Offshore - beyond the influence of waves
Classifying coasts - long term criteria
Geology - can create cliffs or plains depending on resistance and the angle of the coastline
Energy level - higher energy waves with longer fetches create more erosion all landforms / lower energy waves create depositional landforms
Sea level change - produce submerging/emergent coastlines
Classifying coasts - short term
Formation processes - waves/tides/storm surges lead to erosion creating landforms and primary coasts, secondary coasts are produced by waves
Balance between deposition and erosion
Coastal landscapes - What are cliffed/rocky coasts and where are they found
What - vertical cliffs, wave cut platforms formed due to high energy destructive waves eroding and undercutting resistant rock
Where - north and west of the Tees-Exe line, hard lithology, high energy waves
Coastal landscapes - what are sandy coasts and where are they found
What - sand dunes from vegetation which stabilises the coast and prevents erosion
Where - south and east of Tees Exe line, soft lithology, low energy waves
Coastal landscapes - what are estuarine coasts and where are they found
What - form salt marshes meaning there is a gradual transition from land to sea
Where - south and east of Tees-Exe line, soft lithology, low energy waves, at river mouths
What is geological structure
The arrangement of rock
What are the scales of geological structure
Macro - large stretches of coastline and their rock bands
Meso - smaller scale stretches of cliff and their layers/lithology
Micro - one cliff profile and its features
What are concordant coastlines
Rock strata is parallel to coastline
How do coves form
Coastline - concordant
1. Faults and joints in hard rock (eg limestone) allow erosion by destructive waves especially in winter
2. Once the waves reach the softer rock (sands and clay) erosion occurs at a faster rate
3. Once the waves reach a second layer of hard rock erosion occurs outwards and energy begins to dissipate
Example - Lulworth Cove, Dorset
How to Dalmatian coasts form
Coastline - concordant
1. Tectonic activity folded limestone layers creating ridges and valleys parallel to the coast
2. At the end of the ice age sea level rose and drowned the valleys creating a submergent coastline
3. The ridges remain as islands parallel to the coast
Example - Croatian Dalmatian coast
How do haff coasts form
Coastline - concordant
1. Long sediment ridges (sand/mud) topped by sand dunes
2. The build up of sand dunes creates haffs/lagoons parallel to the coast
3. They form in low energy environments due to deposition by onshore winds and low energy constructive waves
What is a discordant coastline
Rock strata is perpendicular to the coast
How do headlands and bays form
Coastline - discordant
1. Softer rock is quickly eroded by wave action forming headlands and bays between rock strata
2. Wave energy becomes concentrated on the headland causing the wave to refract and dissipate in the shallower water
3. The low energy environment allows deposition of sand in the bay forming a beach
What is a dip
When the rock strata is angled seaward or landward
What are joints and faults
Cracks in the rock produced by tectonic processes
What are folds
Deformities in the rock due to tectonics
How does geological structure impact erosion
Landward dip and horizontal bedding planes are the most stable
Seaward dip and joints increases recession rates
What is lithology
The physical characteristics of the rock
What are characteristics of igneous
- most resistant
- Crystalline structure (interlocking) so well connected and impermeable, few joints
- create rocky coastlines with steep profiles
- erosion rates 0.1-0.3cm/year
- eg granite
- lands end Cornwall
What are the characteristics of metamorphic rock
- well connected and impermeable
- folded/faulted
- create rocky coastlines and steep profiles
- 0.5-1.0cm/year
- eg marble, slate, schist
- St Ives, cornwall
What are the characteristics of resistant sedimentary
- clastic (made of cemented sediment particles)
- limestone is formed in strata layers, permeable due to joints
- chalk is porous (air spaces between particles) so permeable
- create steep cliffs, headlands, wave cut platforms
- limestone erodes 1-2cm/year
- chalk erodes 1-100cm/year
- Purbeck, Dorset (old harry)
What are characteristics of less resistant sedimentary
- layers of permeable rock so water removes cement between particles
- high pore water pressure reduces stability
- erosion rate 10-100cm/year
- eg sandstone
- Walton on Naze
What are characteristics of unconsolidated rock
- not cemented by pressure
- create steep/slumped coastlines due to land/mudslides
- erosion rate 100-1000cm/year
- eg boulder clay
- Holderness, Yorkshire
What is differential erosion
Different sections of a cliff eroding at different rates due to horizontal rock strata
This creates complex cliff profiles
What are xerophytes and halophytes
Xerophytes are plants adapted to survive in very dry conditions
Halophytes are plants adapted to live in saltwater
How does maram grass stabilise sandy coastlines through dune successional development
- metres-long roots catch sand being blown around as they are strong and flexible, also maximise water absorption and provide nutrients to the sand
- roots bind sand making it less permeable therefore reducing tidal erosion
- pioneer species so the nutrients they provide allows more species to grow and further stabilise the coast
How does glasswort stabilise estuarine coasts through successional development
- strong roots trap mud/silt/sand to stop it being washed away (tidal erosion)
- roots slow water allowing more deposition
- it adds dead organic matter to create soil making it less vulnerable to erosion
What is plant succession
- changing structure of a plant community over time after a bare surface is colonised by a pioneer species
- low energy environment
How do sand dunes form
- sand dries out and is blown by onshore winds, it accumulates and forms embryo dunes
- pioneer species (maram grass) colonise the dune
- a foredune develops when more sand is trapped
- soil develops, forming a yellow dune, this has more agreeable conditions for plants
- maram grass provides dead organic matter to the dune, improving conditions
- dune slacks develop between dunes, usually waterlogged
- furthest inland the climax community forms, dune is fully stabilised and there is high biodiversity
How do salt marshes form
- low energy environments in estuaries are given fine muds and silts by the river, the tide brings other sediments
- flocculation of tiny sediment particles occurs, algae colonises this area
- vegetation traps sediment and builds the marsh’s height allowing other species to grow
- sediment becomes more stable and less salty
- soil develops further inland and climax community is established
Destructive waves
Strong backwash
Scours beach
Causes cliff retreat
High wave height
Plunging breaker
High energy
Long fetch
Constructive waves
Strong swash
Weak bachwash
Builds up beach
Low wave height
Spilling breaker
Low energy
Short fetch
Long term influence of waves (seasonal) on beach morphology
Summer - large sand dunes, berm, constructive waves
Winter - some dune erosion, lots of berm erosion, destructive waves, bar formation
Short term influences of waves on beach profiles
Shoreline is exposed to erosion so pebbles are smaller and smoother
Large sedimentary at back of beach is from mass movement not waves
Only the strongest swash waves deposit sediment at the back as destructive waves lose energy due to percolation
Erosion processes
Hydraulic action - water gets in cracks forcing the air to compress and break the rock
Abrasion - sand paper effect, rub together
Attrition - rocks are thrown together
Solution - rocks are dissolved by acids in the water
Formation of erosional coastal landforms - wave cut platform
- Wave action focuses on base of cliff
- Notch is eroded by hydraulic action and abrasion
- Unsupported rock collapses and cliff retreats
- Rock underneath the notch remains forming a platform
Formation of erosional coastal landforms - cliffs
Marine erosion dominated - steep face due to undercutting and collapse
Sub-aerial dominated - permeable rock, forms curved profile and a lower angle face, accumulates debris
Formation of erosional coastal landforms - cave, arch, stack, stump sequence
- Headlands protrudes and wave energy is concentrated here
- Wave refraction happens
- Hydraulic action forces water to compress in air pockets (cavitation)
- Crack erodes into a cave and then arch
- Unsupported ceiling collapses leaving a stack
- The stack is undercut causing it to collapse, leaving a stump
Sedimentary transportation types
Traction - boulders rolled along seabed
Saltation - small rocks bounce along seabed
Solution - sedimentary is dissolved by weak acids in sea water
Suspension - very small sediment particles float in the water
Waves, tides, current, rivers, wind
Process of longshore drift
- prevailing winds from the SW push sediment up the beach in the swash at the same angle
- it comes down the beach, perpendicular to the coast, due to gravity in the backwash
- this repeats from west to east, eroding rocks into smaller, round pebbles
Formation of depositional landforms - beaches
Drift aligned beaches - sediment is moved by LSD creating wide beaches with uneven sediment
Swash aligned beaches - beach is even because swash and backwash are perpendicular
Formation of depositional landforms - recurved spit
- Sediment is moved by LSD and this continues when coast direction changes (eg river mouth)
- Waves lose energy in the slacker water behind the headland
- Largest sediment is deposited first as it is heavier (gravity settling)
- As deposition continues a split forms and flocculations helps to settles fine clay
- The spit grows into a recurved spit
- In the slack water a salt marsh may develop
Formation of depositional landforms - double spit
- LSD happens in different directions on opposite sides of the bay
- Wave refraction produces wave fronts which generate a spit
- Rising sea levels drive material onshore
- Barrier beaches driven across a bay form a bar
- River currents breach the bar forming a double spit
Eg Poole Harbour, Studland Bay
Formation of depositional landforms - offshore bars
- Large erosion events (winter storms) scour the beach which changes beach morphology
- Extra sediment is deposited vertically offshore in a temporary bar
- LSD can add to them or change their shape
Formation of depositional landforms - barrier beaches
- A ridge of sediment is deposited further down the beach
- Sea levels rise which floods the land between and creates a lagoon and elongated islands running parallel to the coast
- As levels rise further they migrate inland providing protection to the coast in storms
Eg USA Eastern Seaboard
Formation of depositional landforms - bars
LSD continues along the entrance to a cove creating a bar which separates the sea from a lagoon
Formation of depositional landforms - tombolos
- on drift aligned coastlines they form when LSD builds a spit which connects the mainland to an offshore island
Eg Isle of Portland - on swash aligned coastlines wave refraction Ono both sides of the island create a collision of wave fronts which cancel each other out, producing a zone of still water where deposition occurs
Eg St Ninian’s tomoblo, Shetland Islands
Formation of depositional landforms - cuspate forelands
- After a double spit forms, LSD from opposing directions converge at the boundary of sediment cells
- Sediment is deposited into the sea by both currents creating a triangle shaped area of deposited material
Eg Dungeness, Kent
What are sediment cells
- an area of coastline that acts like a closed system (no energy change)
- there are sources (erosion), transfers and sinks (deposition) in each cell
- there are 11 cells in the UK, split into lengths of relatively self contained coastlines which are separated by natural boundaries
- sub cells are managed at a local level by a shoreline management plan (SMP)
What is positive feedback
When a change enhances a processes, creating a new equilibrium
Eg when a sand dune is eroded in a storm it becomes more vulnerable to further erosion as it is less stable
What is negative feedback
When a change reduces a process, returning it to its original equilibrium
Eg cliff collapse (West Bay, Dorset) causes a build up f sediment which protects the cliff from further erosion
What is the sediment budget
Calculation which shows sediment change
Helps SMP decide on coastal management techniques
What is weathering and how is it different to erosion
Weathering - the process of breaking down rock in situ
Different to erosion because it doesn’t include its removal
Types of mechanical weathering - freeze thaw
- water in cracks freezes and expands, exerting pressure on the rock causing it to loosen and break
- Requires temp to fluctuate around 0 degrees
- creates angular rock at cliff base called scree
Types of mechanical weathering - salt crystalllisation
- Salt spray/waves make the cliff wet with seawater which evaporates
- salt left in cracks crystallises, exerting pressure on the cracks which loosens and breaks rock
- happens mostly in hot climate to limestone and sandstone/chalk
- creates scree
Types of mechanical weathering - wetting and drying
- rocks rich in clay expand when wet and contract when dry causing them to break
- this creates cracks in the cliff making it vulnerable to slumping
Types of chemical weathering - carbonation
- limestone dissolves when it reacts with weak carbonic acid in rainwater
- cracks widen making the cliff more vulnerable to mass movement
Types of chemical weathering - oxidation
- oxygen combines with iron based minerals in a rock causing them to rust
- this causes crumbling of the life as sections are no longer bonded together
Types of biological weathering - plant roots
- tree and plant roots growing into cracks slowly widen them causes them to break apart
- can cause rock falls
Types of biological weathering - rock boring
- clams and molluscs dig into rocks to make homes which can secrete acids in the rock
- sedimentary rocks in the intertidal zone are vulnerable
- holes/weaknesses are easily eroded or weathered
Types of biological weathering - seaweed acids
- some seaweed species like kelp contain pockets of sulphuric acid that burst and dissolve rock
- leads to crumbling as sections are no longer bonded together
Types of mass movement - blockfall
- blocks are dislodged by weathering/erosion and collapse due to undercutting
- this creates talus scree slope
Eg St Oswald’s Bay, Dorset
Types of mass movement - landslides
- low angle seaward dip prevents falls
- slide planes exist between strata which material slides down
- leaves debris at cliff base
Eg Pembrokeshire coastline, south Wales
Types of mass movement - rotational slumping
- rock is infiltrated by rain water until an impermeable layer is reached
- bedding plane dips seaward and rock slumps down
- leaves scars and terraced cliff profiles
What is eustatic sea level change?
Sea level change relative to land
Ice melts (ice caps and glaciers) due to thermal expansion
Global climate (glacial and interglacial periods)
What is isostatic sea level change
Land changes relative to sea level locally
The amount of ice on the land in the last ice age will cause it to sink or rise
What is accretion (isostatic SLC)
Deposition of sediment in a river estuary/delta can weigh down the crust and cause subsidence (sinking)
What is a submergent coastline
Produced by eustatic SLC or isostatic downwarping
Eg Land’s End is submerging by 4mm/year
What landforms are on submergent coastlines
Rías - a flooded river valley (V shaped), eg Falmouth, Cornwall
Fjord - flooded glaciated valley (U shaped), eg Sognafjord, Norway
Dalmatian coasts - due to tectonics, ridges in land are submerged in water eg Croatia
What is an emergent coastline?
A coastline produced by isostatic rebound
eg Scandinavia is uplifted by 2cm a year
What landforms are on an emergent coastline
Raised beaches - beach above high tide line consisting of multiple layers from various stages of uplift, eg Isle of Arran (5m above sea level)
Fossil cliff - near vertical slope formed by marine processes that is now inland, eg fossil cliff - Vik, south Iceland
Why is contemporary sea level change room global warming/tectonics a risk to some coastlines
SLC isn’t even globally
Areas most at risk are the Gulf Coast, USA; Bangladeshi; China; the Netherlands
What are local factors increasing flood risks
Low lying
Degree of subsidence
Vegetation removal (eg mangroves or dunes)
How does global sea level rise cause risk to the Maldives
They are islands in the Indian Ocean only 1-2.3m above sea level
There is unusual topography that causes major land loss form small SLC (50cm rise would cause 77% of land to be lost)
How do the maladives respond to SLC
3m sea wall around Malé
Hulhamalé is an artificial island made by coral and dredging which is a metre higher than Malé above sea level
How do storm surges cause coastal flooding
Low pressure/storm conditions create a bulge which is pushed landward by the wind
This is enhanced by high tides or funnelling effect
Coastal flooding due to storm surge - typhoon Haiyan, Philippines 2013 (category 5 cyclone)
Causes
- 7m storm surge
- Enhanced by low lying conditions and destruction of mangroves
Impacts
- flooding 1km inland - 90% of the city flooded
- 4 million displaced
- over 40 damaged ports
Coastal flooding due to storm surge - Bangladesh (1970)
Causes
- 10m storm surge
- enhanced by low lying conditions (1-3m above sea level), funnelling and deforestation of mangroves
Impacts
- increase in malnutrition and disease
- 500,000 deaths
- $90million lost
Coastal flooding due to climate change
Can cause SLC and increased storm magnitude/frequency
Coastal flooding due to SLC - Maldives
Cause
- SLC enhanced by unusual topography and ad low lying conditions
Impacts
- spent $32million USD on Hulhumalé
Coastal flooding due to SLC - Kiribati, Pacific Ocean
Causes
- SLC
- enhanced by being low lying (3m above sea level)
Impacts
- risk of flooding to increase 200x between 2000 and 2080
- government consider moving population to islands in Fiji (environmental refugees)
Why is the threat of climate change on coastal flooding uncertain
Unclear how fast ice caps will melt
Projections vary depending on temperature increase
How physical factors (wind direction) cause coastal recession
Prevailing wind produces largest wave
Most erosion in Cornwall when wind is from SW and in Norfolk when its from N
Larger fetch increases erosion
How physical factors (tides) cause coastal recession
Extreme high tides (spring tides) are when sun and moon align so gravitational pull is strongest - weakest are called (neap tides)
Higher tides reach backshore and erode land faster
How physical factors (weather systems) cause coastal recession
Anticyclones (high pressure) bring calmer waves / less erosion
Depressions bring larger waves due to air rising and mixing quicker with rapid winds - intensified by global warming
How physical factors (geology) cause coastal recession
More stable geoglogical structure erodes slower
Softer rock erodes faster
How human factors (dredging) influence coastal recession
Removes benthic species and increases suspended sediment levels
Increased deposition can offset isostatic downwarping
It can also alter sea currents leading to larger waves
How human factors (coastal management) influence coastal recession
Do nothing - no investment in coastal defences
Strategic realignment - removal of hard engineering for more sustainable and natural techniques including protection/management/restoration of ecosystems eg Abbots hall farm
Hold the line - trying to stop further coastal retreat by involving both hard and soft engineering eg Minehead Sea Palling
Advance the line - reclaiming the land and building out into sea by involving drainage/engineering eg Netherlands
How humans influence coastal recession in the Nile Delta
- used fro resorts, tourism, port infrastructure, agriculture and settlements
- SLR caused salt intrusion into the delta meaning more floods, alongside more erosion of offshore bars
- the Aswan Dam caused a massive imbalance in the sediment cell
- it traps sediment behind it meaning the delta is getting smaller
- Erosion rates exceed sediment supply
Impacts of coastal recession - Holderness Coast, Yorkshire
Why
- boulder clay is easily weathered and eroded (1.8m a year)
Economic
- settlements rely on tourism which will diminish if erosion continues at current rate
- farms devaluing
- gas terminal close to sea may have to close
Social
- no investment to local communities
- young people move away due to no jobs
What are hard engineering approaches
Built structures that work against nature
What are hard engineering approaches - groynes
Wooden/rock structured along beach perpendicular to the coast
They trap sediment moved by LSD, making the beach larger, enhancing recreational value
Cons: wood goes mouldy/needs replacing, can cause sediment starvation down coast
What are hard engineering approaches - sea walls
Concrete barrier recurved to reflect waves and wave energy - can be stepped to dissipate energy
Gives confidence and the tops can be used as promenades
Long lasting
Cons: ugly, technical to build, expensive
What are hard engineering approaches - rip rap
Large boulders along the coastline
Large SA absorbs wave energy
Holds back mass movement
Cons: expensive, can be scoured by backwash
What are hard engineering approaches - revetments
Wooden/rock ramps lining the coast
Absorb wave energy
air spaces allow backwash to drain whilst trapping sediment
Cons: requires lots of maintenance, don’t cope with strong storms
What are hard engineering approaches - offshore breakwaters
Granite rock boulders dropped in shallow waters parallel to the coast
Absorb and dissipate waves before reaching foreshore
Creates sheltered areas for recreation/boats/deposition (tombolo effect)
Cons: expensive, ugly, may need further engineering
What are soft engineering approaches
Make use of natural systems to manage coastal processes
What are soft engineering approaches - beach nourishment
Sand dredged from the seabed and then pumped to beach to replenish effects of LSD/destructive waves
Beach is reprofiled to original shape and absorbs wave energy
Cons: time consuming, causes sediment starvation elsewhere, expensive
What are soft engineering approaches - cliff regrading
Engineers calculate stable angle for the rock and cut cliff back to meet this
Cons: expensive, cliff still retreats into valuable land
What are soft engineering approaches - cliff drainage
Pipes are inserted into cliffs to remove water that has percolated through reducing saturation and risk of slumping
Cons: ugly, weaken cliff, difficult to insert
What are soft engineering approaches - dune stabilisation
Geotextile netting reduces erosion but still allows water through
Planting vegetation encourages sand deposition to build up the dune
Cons: only effective if public access is controlled, can be damaged in storms
Sustainable management - Holderness UK
What
- 2 groynes in Mappleton
- nearly 5km sea wall in Bridlington
Sustainability
- no - reduces tourism as its ugly leading to economic losses
Conflict
- unnatural - opposed by environmental groups
- groynes cause more erosion down coast
Sustainable management - Maldives
What
- Hulhumalé
- 3m sea wall
- Japanese government fund mangroves nurseries
Sustainability
- mangroves lessen impacts of flooding and trap carbon
- wont benefit whole population
Conflict
- priorities Malé/tourism over fishing and farming communities
Sustainable management - Namibia (spec named)
What
- use intergrated coastal zone management (ICZM) ad holistic approaches
- Henties Bay (tourist spot) uses beach nourishment and dune restoration
- Walvis Bay (port) uses sea walls and raised infrastructure
-Skeleton coast (empty coast of shipwrecks) uses dune stabilisation/restoration
Sustainability
- yes - each areas has the appropriate management to accommodate the areas economic, environmental and social value
Conflict
- communities in Walvis bay are relocated
Sustainable management - Happisburgh, Norfolk (spec named)
What
- £2-6million sea wall
- £1-3.6million rip rap
- £0.1-1.5million groynes
Sustainability
- protects local jobs and farmland along with £4-7million worth of property
Conflict
- coastal managers argue whole SMP needs to be considered so the village isn’t worth defending as cost would only just equal the value what is saved
- locals have attachments and want to protect their homes
Sustainable management - Chittagong, Bangladesh (spec named)
What
- infrastructure on platforms above expected sea level
- embankments 60cm above flood level
Sustainability
- would alleviate poverty by 10%
- could be disruptive to people and wildlife
Conflict
- Asian Development Bank (ADB) support Climate Change Resilient Infrastructure Project
- 200 people would be relocated
