A-Level Geography Coasts

coast

the part of the land near the sea, the edge of the land

coastline

an open system, with inputs, outputs and processes

flow/transfer

movement of energy or mass between stores

input

addition of matter/energy into a system

output

loss of matter/energy out of the system

system

a set of interrelated components working together to achieve a specific function

inputs to the coast

marine, geological, people, atmospheric

processes at the coast

deposition, erosion, weathering

outputs at the coast

land forms of erosion, land forms of deposition

open system

matter + energy can be transferred from the system into the surrounding environment

importance of coasts

50% of world’s pop lives on coastal plains

landscape

consists of a constantly changing assemblage of erosional + depositional land forms, they are a result of continuous change in elements of the coastal system

landform

a natural feature of the Earth’s surface

wave dominated land forms

shore platforms, cliffs, beaches, spits, tomobolos, deltas

wave and tide dominated landforms

mud flats, sand flats, salt marshes, mangroves, deltas

tide and wind dominated land forms

sand dunes

what does wave energy depend on?

speed of wind (faster, bigger wave), time of wind (longer length of time of wind, bigger wave), distance of wind (longer fetch, bigger wave)

wave height

height difference between a wave crest and neighbouring trough

wave length

distance between successive crests

wave frequency

time for one wave to travel the distance of one wavelength, or the time between one create and the following passing a fixed point

how do waves work?

as air moves over the water, frictional drag disturbs the surface and forms ripples or waves. in the open water, waves have a circular orbit. as the waves approach the coast, the seabed gets higher. friction between the sea bed and the bottom of the wave causes the orbit to become elliptical. the wave will eventually break and the swash moves up the water and backwash returns to the sea.

explain how friction affects a wave (4 marks)

waves in the deep ocean/sea move in a circular motion as the wind transfers energy into the waves. as the wave approaches the coast, the sea bed rises and the friction begins to slow down the water particles, making the motion elliptical. the closer to the coast the wave gets, the more elliptical the motion becomes as the friction increases. the wave then breaks as the water is moving faster on top of the wave than on the bottom, and the swash moves up the coastline.

describe wave refraction

most waves usually arrive at angle to the shoreline, this angles approach of a wave toward the shore can change direction of wave travel. one end of the wave feels the bottom of the sea floor and slows down, while the rest of the wave continues at its deep-water speed. as more + more water comes into contact with the sea floor, more of the wave slows down. as the wave slows down progressively along its length, the wave crest changes direction and becomes more parallel to the shoreline.

describe a negative feedback loop in coasts

sediment is eroded from the beach during a storm. sediment is deposited offshore forming an offshore bar. waves now forced to break before reaching the beach, dissipating their energy, and further reducing erosion when they reach the beach. when storm calms, normal wave conditions rework sediments from the offshore bear back into the beach to reach dynamic equilibrium.

describe a positive feedback loop in coasts

global temp rises. increased oceanic temps. dissolved co2 released by warmer ocean. more co2 in the atmosphere, leading to increase in global temps.

what are the characteristics of constructive waves?

low waves with long wavelength (up to 100m). break gently, with a low frequency (6-8 per min) have strong swash which carries material up the beach. weak backwash, which doesn’t take material away. material is moved up the beach leading to the formation of ridges (berms). allows material t be deposited along the coastline leading to the formation of spits, tombolos and bars. create a wide, gently sloping beach. sometimes seem not to break at all but just run up the beach losing energy as they do. if not many waves, each wave will be able to complete its swash and backwash without interference from the next wave coming up the beach.

what are the characteristics of destructive waves?

high in proportion to wavelength. high frequency (10-14 per min). rapidly steepen as they approach the beach and plunge down when breaking. strong backwash, weak swash, so rocks, pebbles and sand carried back out to sea. erode the coastline. commonly associated with steeper beach profiles + help form features e.g. wave cut platforms, headlands, bays, arches, stacks, caves + stumps.

describe wave refraction on irregular coastlines

as each wave nears the coast, it drags in the shallow water. this causes the wave to become higher and steeper with a shorter wavelength. that part of the wave in deeper water moves forward faster, causing the wave to bend. the overall effect is that the wave energy becomes concentrated on the headland, causing greater erosion which leads to the development of features such as cliffs, caves and arches. where the waves diverge, they lose power and drop their sediment forming beaches.

as waves approach a bay, they diverge and there is a reduction in energy resulting in deposition. at a headland, the waves refract around the headland and the wave direction converge resulting in the concentration of energy on the headland and its subsequent erosion.

what are examples of physical weathering?

freeze-thaw, salt crystallisation, wetting + drying

physical weathering

involves the break up of rocks without any chemical changes taking place

what are examples of chemical weathering?

carbonation, oxidation, solution

chemical weathering

involves a chemical reaction where salts may be dissolved or a clay-like deposit may result which is easily eroded

what are examples of biological weathering?

roots in rock, birds in burrows

biological weathering

the breakdown of rocks by organic actvitiy

freeze-thaw weathering

occurs when water enters a crack or joint in the rock, and then freezes in cold weather. when water freezes, it expands in volume by 10%. this expansion exerts pressure on the rock, which forces the crack to widen. this process repeats making the crack wider and deeper, as fragments of rock collect at the base of the cliff as scree.

salt crystallisation

when water evaporates, it leaves behind salt crystals. these can grow overtime and exert stresses on the rock causing it to break up. salt can also erode rock particularly if it contains traces of iron.

wetting + drying

rock alternates between being wet and dry. rock rich in clay expand when they get wet and contact as they dry up, causing them to crack and break up.

carbonation

coastlines composed of chalk or limestone (calcium carbonate) react with acid rain (carbonic acid) to form calcium biocarbonate which is easily dissolved. the cooler the temp of rainwater, the more co2 is absorbed, so carbonation is more effective in winter.

oxidation

the reaction of rock minerals with oxygen, e.g. iron, to form a rusty red powder leaving rocks more vulnerable to weathering

solution

the dissolving of rock minerals, such as halite (rock salt)

roots in rock

thin plant roots grow into small cracks in a cliff face, and the crack widens as the root grows, breaking up the rock

birds in burrows

birds, e.g. puffins, and animals, e.g. rabbits, dig burrows into cliffs, breaking away the rock

what are examples of errosional processes?

hydraulic action, cavitation, corrasion, abrasion, quarrying, solution, attrition

hydraulic action

air can be trapped and compressed in joints in the rock as a wave advances. when the wave retreats, the compressed air expands, causing a mini explosion/release of pressure. this continuous process puts pressure on the joints and crack in the cliff, causing pieces of rock to break off

cavitation

bubbles formed in the water may implode under the high pressure, generating tiny jets of water which will, overtime, erode the rock

corrasion

when a wave breaks at the base of the cliff, the transported material (sand + pebbles) is hurled at the cliff face, chipping away the rock.

abrasion

involves a sandpapering effect as sediment is dragged up and down or across the shoreline, eroding and smoothing rock surfaces.

quarrying

the action of waves scooping out loose material from the cliff base, e.g. sand and gravels

solution/corrosion

weak acids in seawater can dissolve alkaline rock (such as chalk or limestone)

attrition

the gradual wearing down of rock particles by impact and abrasion as the pieces of rock are moved by waves, tides and currents. this process gradually makes stones rounder and smoother.

mass movement

the movement of consolidated material (solid rock) and unconsolidated material (clay and soil) due to gravity.

what are examples of mass movement?

rockfall, landslides, runoff, mudflows, slumping/landslips, soil creep

rockfall

involves sudden collapse or breaking away of individual rock fragments (or a block of rock) at a cliff face, most commonly associated with steep or vertical cliffs

landslide

involves a block of rock moving very rapidly downhill along a planar surface, often a bedding plane that is roughly parallel to the ground surface. the moving black of material remains largely intact.

runoff

when overland flow occurs down a slope or cliff face, small particles are moved downslope to enter the littoral zone, potentially forming an input into the sediment cell.

mudflows

involves earth and mud flowing downhill, usually over unconsolidated or weak bedrock such as clay, often after heavy rainfall

slumping/landslips

commonly occur in weak and unconsolidated clay and sand, often when permeable rock overlies impermeable rock, which causes a build-up of pore water pressure.

soil creep

an extremely slow form of movement of individual soil particles downhill. often involves particles rising towards gorund suface due to wetting or freezing and then returning vertically to the surface in response to gravity, as the soil dries out or thaws.

what are examples of methods of transportation?

traction, saltation, suspension, solution, longshore drift

traction

the rolling of course sediment along the sea bed that is too heavy to be picked up and carried by the sea

saltation

sediment bounced along the seabed, light enough to be picked up or dislodged but too heavy to remain within the flow of the water

suspension

smaller, lighter sediment picked up and carried within the flow of the water.

solution

chemicals dissolved in the water, transported and precipitated elsewhere

longshore drift

most waves approach the beach at an angle, generally from the same direction as the prevailing wind. as the wave advances, material is carried up the beach at a 45 degree angle, the backwash the pulls material down the beach at right angles to the shore due to gravity. this creates a zigzag movement of sediment up and down the beach, transporting sediment along the coastline.

when does deposition occur?

once the energy flow that is moving material declines, then deposition is likely to occur. energy flows decline due to: waves starting to slow down and lose energy, shallow water, sheltered areas, e.g. bays, and little or no wind

what are examples of landforms of deposition?

beaches, spits, bars, mudflats, sand dunes, offshore bars

storm surge

the pushing of water against a coastline to abnormally high levels, usually a combination of extreme low pressure and high tides

ocean current

large scale movements of water in the oceans

tidal range

the vertical difference in height of sea level between high and low tide

spring tide

tides that occur twice a month when the sun and moon align on the same side of the Earth

neap tide

tides that occur twice a month when the sun and moon are at right angles to the Earth

what causes tides?

the gravitational pull of the moon and sun. the moon pulls water towards it, creating high tide, and there is a compensatory bulge on the opposite side of the earth, created by the earth itself pulling away from the water on the opposite side. in the areas of the world between the 2 bulges, the tide is at its lowest.

tides

the periodic rise and fall in seal level

how does a spring tide form?

twice in a lunar month, when the moon, sun and earth are in a straight line, the tide raising force is the strongest, producing the highest monthly tidal range.

how does a neap tide form?

twice in a lunar month, the moon and sun are at right angles to each other in relation to the earth, producing the lowest monthly tidal range.

where is tidal range greatest?

where an ocean is funnelled into a constricted channel and the water is forced to rise as it is contained e.g. in the English channel

what is the significance of tides?

the movement of tides can generate ocean currents that influence the direction and scale of coastal sediment movement. when high tides are combined with a low pressure system, an extremely high storm surge can be generated, which leads to flooding along coastal areas. the regular movement of the tides can be used to generate renewable energy, e.g. Swansea Bay, Wales is an area that utilises this energy to generate power.

what causes ocean currents?

tides, wind, thermohaline circulation

tidal currents

tides create currents in the oceans which are strongest near the shores + in bays and estuaries along the coast, these are called tidal currents. tidal currents change in a very popular pattern and can be predicted for future dates.

how does wind create currents?

wind drives currents that are near to or at the surface of the ocean. near coastal area, winds tend to drive currents on a localised scale and can result in coastal upwelling. in the open ocean, on a global scale, winds drive currents that circulate water for thousands of miles throughout ocean basins.

thermohaline circulation

a process driven by density differences in water due to temperature and salinity variations in different parts of the ocean. currents driven by thermohaline circulation occur at both deep and shallow ocean levels and move much slower than tidal or surface currents.

how do currents affect the earth’s climate?

currents drive warm water from the equator and cold water from the poles around the earth via the great ocean conveyor belt

how do currents affect us?

current measurements are important to shipping, commercial fishing, recreational boating and safety. by using predicted, real-time and short term forecasted currents, people can safely dock and undock ships and navigate safely through coastal waters. search and rescue personnel can use real-time and predicted current patterns to determine whether water may carry a missing person or floating objects. geographic information systems (GIS) programs are used to assist in search and rescue efforts (these programs know last known position of lost person/item, predicted and real time current and weather data, and drift patterns to estimate the location of the person or item.

sediment cell

stretch of a coastline, unusually bordered by 2 prominent headlands, where the movement of sediment is more or less contained

inputs of a sediment cell

primary derived from the river, coastal erosion and offshore sources (bars and banks)

transfers within a sediement cell

involves littoral drift (longshore) together with onshore and offshore processes, such as rip currents

stores in a sediment cell

includes beaches, sand dunes, and offshore deposits (banks + bars)

outputs of a sediment cell

material within the cell tat may be swept out to sea to act as an output from the system. this may occur as a result of a severe storm event.

sediment budget

for a beach to exist, sediment has had to come from somewhere, and the combination of a wave, current and tide action ensures this. balance between sediment being added to and removed from the coastal system (systems within each sediment cell)

positive sediment budget

more material is added than removed, accretion/surplus of sediment. shoreline builds out towards the sea (gets bigger)

negative sediment budget

more material is removed than added, deficit of sediment. shoreline retreats (gets smaller)

rivers as a sediment source

sediment that is transported in rivers often accounts for the vast majority of coastal sediment, especially in high rainfall environments where active river erosion occurs. this sediment is deposited in river mouths and estuaries where it will be reworked by waves, tides and currents

cliff erosion as a sediment source

cliff erosion is important as a source in areas of relatively soft or unconsolidated rocks. e.g. the cliffs of the Holderness coast comprise of sand and clay, and rates of erosion can be as high as 10m a year.

longshore drift as a sediment source

sediment is transported from one stretch of coastline (as an output) to another stretch of coastline (as an input)

wind as a sediment source

in glacial or hot arid environments, wind-blown sand can be deposited in coastal regions, e.g. can be seen through sand dunes

glaciers as a sediment source

in areas such as Alaska, Greenland and Antarctica, ice shelves calve (chunks of ice breaking off a glacier/ice sheet) into the sea, depositing sediment trapped within the ice.

offshore as a sediment source

sediment from offshore can be transferred into the coastal (littoral) zone by waves, tides and currents. E.g. in the UK sea levels rose at end of last glacial period, resulting in a considerable amount of coarse sediment being bulldozed onto the south coast of England to form land forms such as barrier beaches. storm surges associated with tropical cyclones and tsunami waves can also be responsible for inputs of sediment from offshore into the coastal system

backshore

the area between the high water mark and the landward limit of marine activity. changes normally take place here only during storm activity

foreshore

the area lying between the high water mark and the low water mark. this is the most important zone for marine processes in times that are not influenced by storm activity.

inshore

the area between the low water mark and the point where waves cease to have any influence on the land beneath them