COASTS PT.1 Flashcards
closed system
when things move around inside a system but there’s no inputs or outputs.
open system
has an input and output so can get bigger or smaller
dynamic equilibrium
when a system constantly changes over time and self regulates
equilibrium
when a system’s inputs and outputs are equal eg/ a beach
a sediment cell is an example of a…
closed system
how many sediment cells are there in england and wales
11
what is there no loss of in sediment cells?
no longshore loss of sediment
what r the boundaries of sediment cells determined by?
the topography and shape of the coastline
if the input>output in a sediment budget what happens?
1-more material is added to cell than is removed
2-there’s a positive budget or surplus of sediment on beach
3-so shoreline builds towards sea
if output>input in a sediment budget what happens?
1- more material is removed than added
2-there’s a negative budget or deficit in sediment supply
3- so shoreline retreats landward
what’s the inputs onto a beach?
-cliff erosion
-rivers
-off-shore
-beach replenishment
-LSD
what r the outputs of a beach?
-LSD
-offshore
-dredging
what’s geothermal energy responsible for?
tectonic activity and causes an uplift
what does solar energy power?
hydrological cycle which transfers water from land to coastal systems.
what’s solar energy responsible for?
atmospheric processes such as wind
what does GPE cause?
tides by the pull of the sun and moon
where’s potential energy from
unbroken waves and material on cliff
where’s kinetic energy from?
broken waves and wind
where’s GPE from
sediment on cliffs
where’s thermal energy from?
sun
what’s a sandy beach?
quick to respond to changes in energy
what’s a rocky coastline?
an energy change lasting a few hours will make no difference to the coastline
what’s positive feedback?
reinforces a change
found when humans have affected a system
what is negative feedback?
reduces a change
-resits a change and brings it back to original shape
how are waves formed?
when wind blows over water it creates frictional drag which produces movement in upper parts of water
-water particles move in circular orbit as waves ripple, when water becomes shallower this change to an elliptical shape and the wavelength and velocity decrease and height increases
where r swell waves formed?
in open oceans and can travel huge distances
have a long wavelength
characteristics of constructive waves?
-lower energy level
-long wavelength
-low in height
-strong swash
-weak backwash as it soaks into beach
characteristics of destructive waves?
-short wavelength
-high in height
-little swash
-strong backwash which interferes with swash of next wave
-higher energy levels
what r tides controlled by?
the gravitational pull of the moon
when do spring tides occur ?
when earth, sun and moon align
when do neap tides occur?
when the sun and moon are at right angles
when is tidal range at the lowest?
when the sun and moon are at right angles
when r seas exceptionally high?
when spring tides coenside with on-shore gale
leads to flooding
what can change the input of sediment in a cell?
human activity
what is sediment budget decreases?
then waves will move less sediment and erode areas
what if sediment budget increases in a cell?
more deposition occurs
what is longshore drift?
prevailing wind direction of SW means waves break on to the beach obliquely at an angle of around 45 degrees. The swash moves beach material along the beach and the backwash, under gravity, pulls the material back down the beach at right angles to the coastline. Over time this creates a net shift of material along the coast.
what are the three types of sediment supply?
-offshore supply
-terrestrial supply
-human supply
what is offshore supply?
-constructive waves bring sediment to shore from from offshore locations and deposits it which adds to the sediment budget
-wind blows sediment from other locations
-tides and current being sediment to shore
what it human supply?
-if sediment budget is in deficit beach nourishment can maintain equalibrium
-used to preserve and protect coastlines
-sediment brought by lorry and spread by bulldozers
-sand and water can be pumped onshore by pipeline from offshore
-wind, waves and LSD remove sediment
-sediment gained-sediment lost=sediment budget in surplus deficit or equilibrium
what is terrestrial supply?
-rivers are major sources of sediment input into coastal budget
-sediment delivery can be intermittent mostly occurring during floods
-origin of sediment is erosion of inland areas
-70% from cliff erosion on high energy coastlines
-LSD can supply sediment from one coastal area by moving it along the coast
what is physical weathering
no chemical altering of the rock and it produces smaller fragment’s of the same rock
what is freeze thaw weathering
water enters cracks or joints and expands by 10% when it freezes
-in combines spaces this exerts pressure on the rock causing it to split
what is pressure release?
when overlying rocks are removed by weathering and erosion
-underlying rock expands and fractures parallel to the surface
what’s thermal expansion ?
-rock expands when heated and contracts when cooled
-when exposed to constant temp changes the outer layers may crack and flake off
what is salt crystallisation ?
-solutions of salt can seep into pore spaces in porous rocks
-salts precipitate and form crystals
-creates stress and causes it to disintegrate
what is wetting and drying?
-clay rich rocks expand when wet and contract when dry resulting in cracks which r vulnerable to freeze thaw and salt crystallisation
what is chemical weathering
chemical reactions between moisture and minerals in rocks
-rate of reaction increases with heat
what’s oxidation?
-minerals in rocks react with 02 either in air or water
-iron minerals in rocks turn to rust which weakens the rock and causes it to crack
what’s carbonation
-rainwater combines with dissolved CO2 from the atmosphere to produce weak carbonic acid
-dissolves the rock
what is solution?
-some salts are soluble in water and other ions are only soluble in very acidic waters
-the process where minerals dissolve =solution
what is hydrolysis?
-chemical reaction between rock minerals and water
-silicates combine with water producing secondary minerals
what is hydration ?
-water molecules added to rock minerals create new minerals
-causes surface flaking and some minerals expand 0.5% during chemical change as they absorb H2O
what is biological weathering ?
consists of physical actions such as growth of plant roots or chemical processes such as chelation by organic acids
what do tree roots do?
-grow into cracks or joints in rocks and exert outward pressure
-when trees topple they can exert leverage on rocks and soil from their roots and bring them to the surface and expose them to more weathering
-borrowing animals on cliffs
what are organic acids?
-produced during decomposition of plant and animal litter which causes soil water to become more acidic and react with minerals in a process called chelation
-blue green algae produces a shiny film of iron and manganese oxides on rocks
-molluscs secrete acids which produce small surface hollows in rocks on in shore platforms
what’s abrasion?
when waves armed with rock particles scour the coastline
-rock rubbing against rock
what’s attrition?
-occurs when rock particles transported by wave action collide with each other and get warn away
what’s hydraulic action?
-occurs when waves break against cliff face and air and water get trapped in cracks and become compressed
-as wave recedes pressure is released and air and water suddenly expand and the crack is widened
what’s pounding?
-when mass of breaking wave exerts pressure on the rock causing it to weaken
what’s transportation?
waves, tides and currents can move material shoreward
what’s solution(transportation)
-minerals that have been dissolved into moving water
-will remain in water until it’s evaporated
what’s suspension?
-small particles of sand, silt and clay can be carried by currents
-larger particles are carried like this in storms
what is saltation?
-material that is too heavy to be carried continuously in suspension are picked up and carried for short distances then dropped in turbulent flow
what is traction?
-largest particles in load may be pushed along sea floor by force of flow
what’s mass movement?
-occurs when forces acting on slope material exceed forces trying to keep material on slope and fall down
what’s rockfall?
on cliffs of 40* or more, especially if a cliff face is bare , rocks may become detached from the slope by physical weathering
-fall of foot of cliff from gravity
what are slides?
downslope movement of discrete blocks of rock down a flat/linear slip plane, maintaining contact with the cliff surface throughout.
-The discrete blocks are released by mechanical weathering of well jointed rocks
what are slumps?
-common in weak rocks such as clay which also becomes heavier when wet
-adds to downslope force
-when material moves down a slope
how to bays and headlands form
-typically form adjacent to each other due to the presence of bands of rock of differing resistance to erosion
-bays are formed when the rock outscrops lie perpendicular to the coastline and the weaker rocks are eroded more rapidly to form bays whilst the more resistant rock remain between bays as headlands
what’s refraction
when a wave approaches an irregularly shaped coastline and they develop a configuration increasingly parallel to the coastline these occurs on coastlines with bays and headlands
how does refraction work?
-as waves approach the coastline they are slowed by friction in the shallow water off the headland
-at the same time the part of the wave crest in deeper water moves faster as there’s no friction
-this means waves bend and refract around headlands and orthogonal d converge
-wave energy is focused on the headland and erosion is concentrated there
what happens as waves break on the side of headlands
-if waves come in at an angle there is longshore movement of eroded material into bays adding to beach sediment supply
how do cliffs form
-Waves attack the base of the newly exposed rock faces. By hydraulic action and abrasion, and the other processes of coast erosion,
-the base of the cliff is undercut to form a wave-cut notch. The rock face above sees the effects of wave action and begins to overhang.
-the size of the overhang increases until the weight of the rock above can no longer be supported and a section of the cliff collapses.
-Active marine erosion begins again at the base of the cliff after the waves have removed the loose rock, leading to further collapses
-cliff retreats
what are the three profiles of cliffs
-horizontally bedded strata (undercutting leads to rockfall and cliff retreats inland and parallel to the coast)
-seaward dipping strata (undercutting removes basal support and rock is loosened by weathering along bedding planes )
-landward dipping strata(rock loosened by weathering, angle is lowered by weathering and mass movement )
how are wave cut platforms formed?
1-The sea attacks the base of the cliff between the high and low water mark.
2-A wave-cut notch is formed by erosional processes such as abrasion and hydraulic action - this is a dent in the cliff usually at the level of high tide.
3-As the notch increases in size, the cliff becomes unstable and collapses, leading to the retreat of the cliff face.
4-The backwash carries away the eroded material, leaving a wave-cut platform.
5-The process repeats. The cliff continues to retreat.
how are geos formed?
A geo is formed by the action of waves eroding the lower portion of a cliff. A depression or sea cave may form. The cliff face above the cave can erode and collapse over a period of time, creating a geo or extending the geo deeper into the cliff.
-due to hydraulic action and abrasion
what’s an example of a geo
-huntsman’s leap in pembrokeshire
-35m deep
-eroded along a large joint in carboniferous limestone
how are caves formed
-any points of weakness are exposed to erosional processes as energy is concentrated on the sides of headlands
-lines of weakness are caused by hydraulic action and crystallisation
-wave attack is concentrated between high and low tide levels
how are arches formed
-by undercutting the cave, rock is weakened by freeze thaw weathering and wave cut notches widens the arch
how to stacks form
-continued erosion widens the arch and weakens its support
-the arch collapses due to weathering like biological and chemical
-weakened by sub aerial processes and the arch leaves isolated stack separated from the headland
how do stumps form
-further erosion at the base of the stack causes it to collapse further leaving a stump
what does beach material consist of and where does that come from?
-Consists of sand, pebbles and cobbles
– 5% comes from cliff erosion
– 5% comes from offshore
– 90% comes from rivers
what are the features of a sand beach?
A gentle gradient of less than five as particles are small and allow percolation during backwash, so material carried back down. The beach is not trapped at the top which results in ridges and runnels that are parallel.
what is the features of a pebble beach?
steeper gradient as swash is stronger than backwash rapid percolation due to large airspaces material is deposited at top of each
what is a storm beach/Ridge?
It’s formed as storm, waves, hurl, pebbles and cobbles to the back of the beach
what is a berm?
Small ridges at the mean high tide mark
what are cusps and how are they enlarged?
Small semi circular, depressions formed by collection of waves, reaching the same point where swash strength equals backwash strength
-The sides produce a strong backwash that drugs more material down the beach which enlarges the depression
what do high energy destructive waves do?
Remove sediment offshore and create flatter beach profiles and more friction so decreases wave energy
what do low energy, constructive waves do?
For steep profiles, so deeper water and less friction, which increases wave energy energy
what are the two ways on shoe bars conform?
-They can develop, if a spit continues to grow across an indentation in the coastline into the drawings onto land, which forms a lagoon of brackish water
-they can form when material is rolled on shore after sea levels rise in the interglacial period called the flangian transgression
what was the sea level rise called 10,000 years ago
The Flangian transgression
what is an example of a on shore bar
-Slapped and sands in Devon
-100 m wide and 5K in length
-Doesn’t appear to have a dominant direction of longshore drift on the east facing coastline
-Mainly composed of shingle
-Goes from Torcross in south and strete in north
-formed by onshore movement of sediment during the past glacial sea level rise that ended 6000 years ago
what is found behind a bar?
A lagoon of brackish water, which has more salinity than freshwater but less than sea water
what is a tombolo? and how’s it formed
A beach that connects the mainland to an offshore island. It’s often formed from spits that grow Seawood until they reach or join an island. or from sediment rolling on shore in the flangian transgression
-it’s also formed when waves refract around the island, causing annul waves lose energy, depositing the sediment to form a Tombolo
place specific detail of Tombolos
-chesil, near weymouth, dorset
-Most likely caused was on shore, movement of sediment
-At the east end of Portland, the Ridge of shingle is 13 m high and composed of Flint pebbles
-At Western end near Burton Bradstock, the ridge is 7 m high and composed of smaller pea size shingle
-ridge is 30 km
If longshore drift was responsible, it would be expected sediment further east would be smaller, so more likely, ensure migration originally produced a uniform distribution of sediment sizes
what are deltas?
Large areas of sediment found at the mouth of many rivers
when do deltas form?
When rivers and tile currents deposit sediment at a faster rate, then waves and tides can remove it
Where do deltas typically form?
-where Rivers entering the sea are carrying large sediment loads
-a broad continental shelf margin exits at Rivermouth to provide a platform for sediment accumulation
-Low energy environments in coastal areas
-Where tidal ranges are low
what do the structural deltas consist of?
-upper delta plain (which is the furthest inland beyond tidal reach, made up of river deposits)
-The lower Delta plain(tidal zone, regularly submerged, and composed of river and Marine deposits)
-The submerged Delta plain (lies below watermark, and composed of marine sediment and represents seaward growth of Delta)
what our deltas crisscrossed by?
Networks of distributaries
what happens in distributaries in deltas?
Deposition occurs and forms bars which causes the channel to split into and create two channels with lower energy levels, so more deposition and dividing occurs
What may your channels be lined by in delta?
channels may be lined by levees so in times of flood, they are breached and deposition of loads of sediment take place in low lying areas between levees crevasse splays
what are the three types of deltas
-arcuate deltas
-Birds foot Delta
-cuspate delta
characteristics of a birds foot delta?
distributaries build out from the coast in a branching pattern with river sediment supply, exceeding the rates of removal by waves and currents
characteristics of a cuspate delta
A pointed extension to coastline, which occurs when sediment accumulates and is shaped by regular gentle currents from opposite directions
Characteristics of a arcuate delta
sufficient sediment supply is available for delta to grow seaward, but wave action is strong enough to smooth and trim it’s leading edge
what does development of saltmarshes depend on?
The rate of accumulation of sediment
-Common rates equal 10 cm per year
when does deposition of sediment occur in saltmarshes?
As rivers lose energy, when approaching the sea
what occurs in saltmarshes?
Flocculation, when tiny clay particles carry an electric charge and repel each other in freshwater in saltwater, they are attracted to each other So they combined to form flocks, which cannot be carried in river flows, so settle out of suspension
what are salt marshes a feature of?
Features of low energy environments, such as estuaries and landward side of spits
how many hectares does the UK have of saltmarshes?
UK has 45,500 ha, mainly in the east and north-west England
what are saltmarshes?
Vegetated areas of deposited silts and clays
what are saltmarshes subject to?
Inundation and exposure as tides, rise and full twice a day
what do salt tolerant plants species do?
Help trap sediment and increase the height of the marsh they act as baffles and trap sediment swept in by title currents whilst roots stabilise the sediment
what are examples of plants found in the upper marsh of a salt marsh?
-Sea plantain
-sea lavender
-sea aster
-sea blight grass
-rushes and reeds
what is a salt pan in salt marshes?
A depression that trapped water as the tide falls
What two things does geology consist of?
Lithology and structure
what is lithology?
Describes physical and chemical composition of rocks
One example of a rock with weak lithogy
clay has a weak lithology with a little resistance to erosion, weathering and mass movement due to its bonds between particles being weak
what is structure in geology?
Concerns, the properties of individual rock type, such as jointing, bedding and footing. It also includes the permeability of rock.
what is an example of a porous rock
Chalk, which has tiny airspaces called paw, which separate the mineral particles, these paws can absorb and store water this is called primary permeability and these joints are enlarged by solution
what types of currents can influence coastal landscape systems?
Offshore and near shore currents
what are rip current?
They transport coastal sediment, and they caused by tidal motions or waves breaking out right angles to the shore
what happens when rip currents form?
They modify the shore profile by creating cps, which help perpetuate the rip current channelling flow through an narrow neck
what are ocean currents generated by?
Earths rotation, and by convection
what are ocean currents?
They are rip currents on a much larger scale. They are set in motion by movement of winds across surface waters.
what do you warm ocean currents transfer?
Heat energy from low latitudes towards the poles
What do you cold oceans transfer?
Cold water from Polar regions to the equator
why don’t currents affect coastal landscape systems?
they don’t affect the geomorphic processes, but transfer of heat energy affects air temperatures, and therefore sub aerial processes are affected
