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.