coastal systems and landscapes Flashcards
what kind of system is the coastal system?
an open system
positive feedback
when the effects of an action are amplified by changes in the inputs/ outputs/ processes
negative feedback
when the effects of an action are nullified by the changes to the inputs/ outputs/ processes
feedbacks in the coastal system
- coastal management increasing erosion elsewhere
- mass movement decreasing cliff for erosion
flows/transfers in the coastal system
- erosion
- LSD
- mass movement
stores and components of the coastal system
- beaches
- sand dunes
- spits
- bars
- wave cut platforms
outputs in the coastal system
- ocean current
- riptides
- evaporation
inputs in the coastal systems
- wind
- precipitation
- fluvial sediment (sediment flown from rivers to the sea)
dynamic equilibrium
a system in dynamic equilibrium has inputs and outputs of energy and matter that balance
what can dynamic equilibrium be affected by?
- supply of sand
- energy of waves
- sea level changes
- location of the shoreline
landforms
individual features which are created by coastal processes e.g. stacks and spits
landscapes
the entire area of sea, coastline and immediate and behind the sea front. within the landscape are characteristic landscape.
constructive wave
- strong swash
- weak backwash
- low wave, long wavelength
- add material to the coastline
- formed by distant weather systems e.g. right out in the Atlantic
destructive wave
- weak swash
- strong backwash
- tall wave, shorter wavelength
- formed commonly during winter forms
- removes material from coastline
- caused by local weather systems
tides
tides are the periodic rise and fall in the level of the sea caused by gravitational pull of the sun and the moon
neap tides
occurs when the moon is in the first or third quarter when the sun, earth and moon form a right angle. the sun at high tide coincides with the solar low tide and they partly cancel out giving an overall small tide
spring tide
just after every full moon and new moon when the sun, moon and earth are in line. lunar and solar tides line up and reinforce each other, making a bigger total tide
features of high energy coastlines
- destructive waves
- rocky coastlines
- many examples in Cornwall
- in the UK often Atlantic facing
- erosion exceeds deposition
- contains cliffs and headlands
features of low energy coastlines
- constructive waves
- sandy as estuarine
- less powerful waves
- sheltered areas e.g. bags
- deposition excess erosion
- beaches and spits are found here
what are the main sources of sediment in the coastal system?
- rivers, carried by solution, saltation, suspension and traction. deposited mainly in river mouths and estuaries where there is less energy.
- cliff erosion
- offshore sediment (from the sea)
- wind e.g. blows sand from dunes into the sea from the back of beaches
sediment cell
a sediment cell is a stretch of coastline within which sediment movement is more or less contained
how many sediment cells are there in the UK?
11
transfers within the coastal system
- longshore drift
- tide currents
stores within the coastal system
- beaches
- sand dunes
- offshore bars/ banks
in theory what should a sediment cell look like?
in theory a sediment cell should be in a state of dynamic equilibrium between inputs via deposition and outputs due to erosion
example of a sediment cell
flamborough head is an 8 mile long sediment cell found in Yorkshire. it stretches from Filey and bridlington bays.
land’s end to portland bill sediment cell 6 where start bay is located.
name the geomorphological processes
- weathering
- mass movement
- erosion
- transportation
- deposition
- runoff
categorise the geomorphological processes into marine processes and sub-ariel processes
marine:
- LSD
- erosion
- deposition
sub-ariel:
- weathering
- mass movement
- runoff
types of erosion
- hydraulic action- As a wave crashes onto a rock or cliff face, air is forced into cracks, joints and faults within the rock. high pressure forces to widen. sheer force of water
- abrasion- This is the process where sediment is moved along the shoreline, causing it to be worn down over time.
- attrition- Wave action cause rocks and pebbles to hit against each other, wearing each other down and so becoming round and eventually smaller
- solution- mildly acidic seawater can cause alkaline rock such as limestone to be eroded
- corrasion- land and pebbles hurtled against cliffs
factors affecting erosion
- rock type
- rock faults e.g fissures
- waves
- beach defences e.g. groynes cause erosion in other parts of the beach
rock types and how fast do they erode?
- sedimentary - fast e..g limestone (0.5-10cm/year)
- metamorphic- slow e.g. slate, schist, marble
- igneous- e.g granite, basalt
what is longshore drift?
- waves hit the beach at an angle determined by the prevailing wind. push material onto the beach by the swash
- backwash perpendicular to the shoreline taking material from the backwash
- this continues causing material to move along the shoreline.
deposition
Deposition occurs when sediment becomes too heavy for the water to carry, or if the wave loses energy. Deposition tends to be a gradual and continuous process, so a wave won’t release all its sediment at the same time.
weathering
Weathering is the breakdown of rocks over time, leading to the transfer of material into the littoral zone, where it becomes an input to sediment cells.
mechanical weathering
the breakdown of rocks due to exertion of physical forces without any chemical changes taking place
chemical weathering
The breakdown of rocks through chemical reactions
biological weathering
The breakdown of rocks by organic activity
types of mechanical weathering
- Freeze-thaw (Frost-Shattering): Water enters cracks in rocks and then the water freezes overnight during the winter. As it freezes, water expands by around 10% in volume which increases the pressure acting on a rock, causing cracks to develop. over time becomes more vulnerable to erosion
- Salt Crystallisation: As seawater evaporates, salt is left behind. Salt crystals will grow over time, exerting pressure on the rock, which forces the cracks to widen.
- Wetting and Drying: Rocks such as clay expand when wet and then contract again when they are drying. The frequent cycles of wetting and drying at the coast can cause these rocks and cliffs to break up
types of chemical weathering
- carbonation: Rainwater absorbs CO2 from the air to create a weak carbonic acid which then reacts with calcium carbonate in rocks to form calcium bicarbonate which can then be easily dissolved. Acid rain reacts with limestone to form calcium bicarbonate, which
is then easily dissolved allowing erosion - Oxidation: When minerals become exposed to the air through cracks and fissures, the mineral will become oxidised which will increase its volume, causing rock to crumble. most common is iron oxide
- Solution: When rock minerals such as rock salt are dissolved
types of biological weathering
- Plant Roots - Roots of plants growing into the cracks of rocks, which exerts pressure, eventually splitting the rocks.
- Birds - Some birds such as Puffins dig burrows into cliffs weakening them and making erosion more likely
- Rock Boring - Many species of clams secrete chemicals that dissolve rocks and piddocks may burrow into the rock face
- Seaweed Acids - Some seaweeds contain pockets of sulphuric acid, which if hit against a rock or cliff face, the acid will dissolve some of the rock’s minerals. (e.g. Kelp)
- Decaying Vegetation - Water that flows through decaying vegetation and then over coastal areas, will be acidic, thus causing chemical weathering
mass movement
Mass movement is the movement of material down a slope under the influence of gravity.
4 types of mass movement
- soil creep
- flows
- slides
- falls
different types of mass movement
- soil creep
- solifluction
- mudflows
- rockfall
- landslide
- landslump
- runoff
soil creep
The slowest but most continuous form of mass movement involving the movement of soil particles downhill. Particles rise and fall due to wetting and freezing and in a similar way to longshore drift, this causes the soil to move down the slope.
solifluction
Occurs mainly in tundra areas where the land is frozen (periglacial environments). As the top layers thaw during summer (but the lower layers still stay frozen due to permafrost) the surface layers flow over the frozen layers. Forms solifluction lobes
mudflows
An increase in the water content of soil can reduce friction, leading to earth and mud to flow over underlying bedrock, or slippery materials such as clay. Water can get trapped within the rock increasing pore water pressure, which forces rock particles apart and therefore weakens the slope. Pore Water Pressure (PWP) is an important energy source for determining slope stability and refers to the pressure of groundwater held within soil or rock. Mudflows represent a serious threat to life as they can be very fast flowing.
rockfall
Occurs on sloped cliffs (over 40o ) when exposed to mechanical weathering, though mostly occurs on vertical cliff faces and can be triggered by earthquakes. It leads to scree (rock fragments) building up at the base of the slope. Scree is a temporal store which acts as an input to the coastal zone.
landslide
Heavy rainfall leads to water between joints and bedding planes in cliffs (which are parallel to the cliff face) which can reduce friction and lead to a landslide. It occurs when a block of intact rock moves down the cliff face very quickly along a flat slope. Can be very dangerous.
landslip or slump
Contrary to a landslide, the slope is curved, so often occur in weak and unconsolidated clay and sands areas. A build up in pore water pressure leads to the land to collapse under its own weight. This can create a scarred/terraced appearance to the cliff face.
runoff
Runoff is an example of a link between the water cycle and the coastal system, as the water in the form of overland flow may erode the clifface and coastal area or pick up sediment, that then enters the littoral zone, when it is transported in the water via suspension. It may also be responsible for increasing pollution in coastal areas if it picks up waste or excess chemicals.
4 methods of transportation
- solution - particles dissolved in water
- saltation - smaller rocks bounced along the seabed
- suspension - smaller particles carried in river flow
- traction - large particles/ rocks rolled along the seabed
concordant coastline
layers of alternating hard and soft rock are parallel to the coastline. e.g. south purebeck
discordant coastline
layers of alternating hard and soft rock are perpendicular to the coastline e.g. east purebeck
how do wave cut platforms form?
- erosion creates faults/ cracks in clifface
- over time this crack gets eroded and becomes wider forming a wave cut notch
- this wave cut notch gets larger and wider over time and eventually the top above the wave cut notch becomes unsupported
- this unsupported over hanging rock eventually collapses causing a wave cut platform which is covered at high tide
- this processes repeats itself causing headlands to retreat however finally stops when the waves can no longer reach the cliff therefore the platform has directly acted to decrease the rate of future erosion.
- this can be seen as a negative feedback loop
example of a wave cut platform
Taman selera, sarawak, malaysia.
- 4m wide
- next to Miri river east Malaysia
coastal landforms of deposition
- beaches
- spits
- offshore bars
- salt marsh
- tombolo
beaches
A beach is a depositional landform that stretches from roughly the low tide to the high tide line and is created when sediment is deposited near the coastline when waves lose their energy. It is one of the most important stores in the coastal system. Beach accretion occurs when the beach is being built up by constructive waves, usually during the summer months. Beach excavation occurs in winter when destructive waves remove sediment from the beach.
what is a swash-aligned beach?
Wave crests approach perpendicular to coast so there is limited longshore drift. Sediment doesn’t travel far along the beach. Wave refraction may reduce the speed of high energy waves, leading to the formation of a shingle beach with larger sediment
what is a drift-aligned beach?
Waves approach at a significant angle, so longshore drift causes the sediment to travel far along the beach, which may lead to the formation of a spit at the end of a beach. Generally larger sediment is found at the start of the beach and weathered sediment moves further down the beach through longshore drift, becoming smaller as it does, so the end of the beach is likely to contain smaller sediment
how do spits form?
- change in direction of the coastline means that longshore drift continues to carry material out into the sea in the same direction as it has been moving along the coastline previously
- due to low energy material is deposited
- saltmarshes form in the sheltered area behind the spit
- Another change in wind direction or wave direction can cause the end of the spit to curve (known as a recurved end).
barrier beach/ bar/ lagoon
A barrier beach occurs when a beach or spit extends across a bay to join two headlands. This traps water behind it leading to the formation of a brackish lagoon which is separated from the sea.
tombolo
A tombolo is a bar or beach that connects the mainland to an offshore island and is formed due to wave refraction off the coastal island reducing wave velocity, leading to deposition of sediments. They may be covered at high tide if they are low lying.
offshore bars
An offshore region where sand is deposited, as the waves don’t have enough energy to carry the sediment to shore. They can be formed when the wave breaks early, instantly depositing its sediment as a loose-sediment offshore bar. Waves may pick up sediment from an offshore bar, which then provides an important sediment input into the coastal zone.
formation of sand dunes (not officially a depositional landform due to needing wind to form)
- sand accumulates on the beach from LSD
- at low tide, the sand dries out allowing the prevailing winds to move the loose sand up the beach
- large inter tidal zone for sand to be dry
- sand transported by saltation
- debris on beach traps sand (called a strand line)
- grass allowed to grown such as Lyme grass and marram grass which stabilises dunes.
types of dunes from youngest to oldest
- embryo dune- mostly made up of exposed sand. few metres tall, Lyme grass first to colonise and stabilise. sand starts to accumulate around a small obstacle (driftwood, wooden peg, ridge of shingle)
- a few metres taller. marram grass stabilises. more resilient to flooding/ storms.
- Yellow Dunes – As more sand accumulates and the dune growns, vegetation may develop on the upper and back dune surfaces, which stabilises the dune. The tallest of the dune succession
- Grey Dunes – Sand develops into soil with lots of moisture and nutrients, as vegetation dies, enabling more varied plant growth. fixed and stable.
- Dune slack- The water table rises closer to the surface, or water is trapped between hollows between dunes during storms, allowing the development of moisture-loving plants (e.g. willow grass).
- dune health/ mature dune- Sandy soils develop as there is a greater nutrients content, allowing for less brackish plants to thrive. Trees will also grow (willow, birch, oak trees) with the coastal woodland becoming a natural windbreak to the mainland behind.
- climax vegetation- reaches a stage of ecological equilibrium approximate to the climate experienced there.
mudflats
created by the deposition of fine silts and clays in the sheltered, low energy coastal environments such as estuaries.
salt marsh
a salt marsh is an area of coastal grassland that is regularly flooded by seawater.
difference between mudflats and saltmarshes
there is a major difference in height. salt marshes are higher as more sediment is built up. mudflats are regularly flooded at high tide.
how do mudflats and saltmarshes form?
- Deposition occurs in river estuaries because when the flow of water from the river meets with the incoming tides and waves from the sea, water flow virtually cease, so the water can no longer carry its sediment in suspension.
- They may also occur in sheltered areas such as behind a spit or other areas where there are no strong tides or currents to prevent sediment deposition and accumulation.
- As most of the sediment is small, this leads to a build up of mud, which over time builds up until it is above the water level.
- deposition occurs due to flocculation
- Pioneer plants colonise this area, leading to more sediment becoming trapped. This colonises the transition zone between high and low tide.
- A meadow is formed as sections of the salt marsh rise above the high tide level, leading to the climatic climax of the vegetation succession when trees begin to colonise the area.
pioneer species
first species to colonise a new habitat
flocculation
particles carried by a river join together on contact with the salt in the sea water.
halophytes
a pioneer plant species that is tolerant to salt and periodic soaking into the sea. e.g. glasswort and sea bite.
eustatic sea level change
a global change in sea level resulting from a fall or rise in the level of the sea itself
isostatic sea level change
local changes in sea level resulting from the land rising and falling relative to the sea. it can increase or decrease. this doesn’t directly cause sea levels to rise.
what is eustatic change influenced by?
- thermal expansion
- land ice melt (melting of glaciers and ice sheets)
- tectonic movements- alter the shape of the land and volume of ocean basins. e.g. sea floor spreading increases the volume of the basin and so decreases the sea level.
thermal expansion
volume of water increases as it gets warmer
how has isostatic change affected the UK?
- last glaciation period 10,000 years ago.
- north areas of UK were under an ice sheet which was several km thick sat on the land
- put pressure on the land slowly forcing it down
- ice melts very slowly so the land continues to rise as its does not have a heavy mass pushing it down.
- the change in land is isostatic change
- the NORTH of the UK is RISING, whereas the south is SINKING.
how does the greenhouse effect work?
as greenhouse gas concentration increases, these GHGs absorb outgoing long-wave radiation, so that less is lost to space. as their concentration increases more energy is trapped and the planet warms up.
submergence
something that goes over water, causing land to sink and go below sea. Landforms of submergence occur when the sea level rises or the coastline sinks in relation to the sea. Where the land has been raised in relation to the coastline.
emergence
it appears or sides up. water push up the land
landforms of emergence
- raised beaches
- marine platforms/ terraces
- relic/ fossil cliffs
landforms of submergence
- rias
- fjords
- Dalmatian coastlines
raised beaches formation (emergent)
formed when the fall in sea level leaves beaches above the high tide mark. over time, beach sediment becomes vegetated and develops into soil. e.g. Scottish islands
marine platform formation (emergent)
wide, rock base of eroded cliffs that extends as cliff retreat. forms at inter tidal zones between high and low tides in the area of maximum wave impact. infant of relic cliffs above active wave action. wave cut platform that has been uplifted by tectonic movement. water pushes up as it is emergent.
e.g.
relict cliffs (emergent)
the steep cliffs found above raised beaches which are no longer eroded by the sea and slowly get covered by vegetation. may wave cut notches/ caves. e.g. isle of Arran. 5m above sea level at coast of drumadoon.
rias formation (submergent)
this is a drowned river valley.e.g. Milford haven in south Wales. as sea level rise they flood the river valleys, leaving only the high land visible. rias have a gentle long and cross profile. they are wide at the mouth and become narrower and shallower the further inland they reach
fjords formation
fjords are similar to rias but they are a drowned glacial valley rather than river valley. relatively steep and narrow with steep sides. shallow mouth due to a raised bit of ground called the threshold formed by deposition of material by the glacier. e.g. the Sognefjord, Norway.
Dalmatian coastlines formation
in areas where valleys lie parallel to the coast, an increase in sea level can form a Dalmatian coastline. valleys are flooded, leaving islands parallel to the coastline. named after dalmation coast in Croatia. e.g. east shores of Adriatic Sea, southern Croatia.
2 causes of sea level change
- subsistence to the coastline
- increase in water volume in the ocean
subsistence
coastal areas sinking. often this is due to excess groundwater extraction. has the effect of making sea level relatively higher.
water volume
changes due to either thermal expansion (water expanding as it gets warmer causing the volume to increase) OR addition of extra water from land stores during ice melt.
when was the quaternary period
the last 2.5 million years
key impacts of sea level rise
- 1-4 ft rise in one persons lifetime
- salt water mixes with groundwater
- earth’s ocean absorbs 90% of heat from global warming
- when ocean water heats up it releases CO2 which warms the atmosphere.
- if all ice sheets melt 72m of global sea level rise will occur
- if the antarctic ice sheet melts 65m of sea level rise
effects of sea level rise on the coastal system
- increased erosion rates specifically softer rocks
- increased storm activity
- increased land loss due to erosion
- increased flooding because coast is eroded- sediment input insole areas of cliffs will protect.
4 methods of coastal management
- hold the line - maintain existing coastal defences
- advance the line- build new defences further out to sea than existing defences
- do nothing- build no defences, deal with flooding as it happens
- managed retreat- allow shoreline to move but managed so it causes as least damage possible e.g. flooding farmland rather than towns.
methods of soft engineering
- beach nourishment
- beach profiling
- coastal realignment/ managed retreat
- land use management
- dune regeneration
- do nothing
methods of hard engineering
- sea walls
- revetment
- gabions
- groynes
- breakwaters
- tidal barrage
- offshore bars
- offshore reef
- rip rap/ rock armour
barrage
a barrage is a type of low-head, diversion dam which consists of a number of large gates that can be opened or closed to control the amount of water passing through
offshore reef
a partly submerged rock barrier, designed to break up the waves before they reach the coastline
revetment
sloping wooden or concrete structures placed at the foot of a cliff or at the top of a beach. they break up the waves energy
how is the coastline managed in the UK?
cannot actively protect the coastline as there is so much with a limited budget. therefore government have assessed all of the UK’s coastline and created 22 shoreline management plans.
- mainly no intervention however there is a hold the line approach in the East Midlands and the south east of the UK. advance the line approach only in the south east coastline.
how much coastline does the UK have?
12, 429km
SMP
shoreline management plan. created in 1992
ICZM
integrated coastal zone management. created 1992
what is the purpose of SMPs and ICZMs?
to avoid undesired affects on adjacent areas of the coastline. it does this by looking holistically at an area of coastline. most often a sediment cell.
how are SMPs better than hard or soft engineering?
- thinking about how it will change over time
- thinking into the future
- no risk to habitats
- regulations must be complied with
- historical monuments not damaged
- circumstances can always change so its important to continue the review
- policies are long term and are well thought out
aims of SMPs
- assess the risk associated with coastal erosion
- address risks in a sustainable way
- ensure management plans comply with nature conservation
- promote long term project management
aims of ICZMS
aims to focus on the most economically valuable yet ecologically sensitive places on earth. they work with multiple stakeholders to manage the cost. they consider all elements of the costal system:
- water
- land
- people
- the economy
CASE STUDY- COASTAL ENVIRONMENTS AT A LOCAL SCALE: Slapton Sands
- where is slapton sands?
Slapton Sands is located in Start Bay in the south hams district in Devon.
it is a 5km stretch of shingle barrier beach extending from limpet rocks in the south to ship hill rock at strete gate.
characteristics of slapton sands
- shingle barrier beach 5km long
- wider in the north at strete gate and narrower towards torcross. also becomes less tall from 7.5m above sea level to 4.9m
- bay is in an exposed position and faces south eas, meaning the influence of incoming waves on sediment cells and transport is large.
what processes are occurring at slapton sands?
- deposition- bars, beaches
- LSD- creation of bar beach across the bay
- erosion- headlands (start point, Combe point)
- transportation- beaches
why does slapton sands need protecting?
- during winter months of 2000-01 a series of storms occurred damaging the A379 (min road linking slapton to kings bridge (nearest town)
- storm lasted 4 days and damaged the beach profile
- 48 properties at torcross that need protecting, worth millions
- slapton ley considered a site of specific scientific interest and would be a great loss if damaged
what is being done to protect slapton sands?
- maintaining the sea wall at torcross to provide defence for homes
- maintenance is being done on the 23m concrete sea wall along the edge of the slipway
- maintaining 700m of rock revetment at torcross
- beach recycling has been implemented
CASE STUDY: COASTAL RISK AND OPPERTUNITY IN ODISHA
- where is Odisha?
Odisha is a state located in eastern India on the east coast. it borders the Bay of Bengal, the largest bay on earth.
ecological characteristics of Odisha
- wide range of coastal and marine flora and fauna, as well as 1435km^2 of mangrove forest.
- chillina lake, salt lagoon which well known for housing bird life.
- temporary store in the water cycle
how many km^2 are the mangroves in Odisha?
1435km^2
characteristics of sediment and landscape in Odisha
- coastline is depositional
- Asia’s largest internal salt water lagoon
- significant sediment source
- 6 major deltas known as the ‘gift of 6 rivers’
- deposition at deltas in the north, erosion in southern parts of Odisha.
3 main coastal environments in Odisha
- chillika lake
- mahanadi delta
- bhitarkanika mangrove
how much of Odisha’s coastline is dynamic? (always changing)
85.6%
risks in Odisha
- vulnerable to tropical storms
- tsunamis
- wildfire risks
- sea defences shift issues to other areas making it worse
- tourism perhaps could destroy natural landscapes
rewards in Odisha
- wide variety of coastal fauna including mangroves, estuaries, salt marshes, sand dunes and lagoons
- large stocks of fish and Marine mammals for fishing
- abundant seaweeds
- huge area potential for tidal and wave power
- 35% of coastal stretch laden with sediment and minerals and heavy metal deposits.
- important clay and limestone resources
- opportunities for offshore oil
- many locals employed in fishing and tourism
- chillika lake- over 150 species of bird
cyclone phailin
- location
- dates
- losses
- deaths
- max windspeeds
- category
- Gopalpur, Odisha coast, India
- 4th-14th October 2013
- $70,000, 500,000Ha of agricultural crops
- 44 deaths
- windspeeds: 215km/h
- category 5
when did Phailin make landfall?
October 12th 2013, 9pm local time
track of cyclone Phailin
tracked north north west
why was the planting of mangroves necessary for Odisha?
- large loss in recent times due to the development of fisheries and other economic demands
- width of mangroves has decreased from 5km to 1km over 50 years
- during phailin, areas with mangroves less than 3km wide had a higher death rate, this will only worsen as storms worsen
