- Created by: malonemily
- Created on: 08-12-17 11:47
earth's major subsystems
atmosphere: the air that surrounds th earth, made up of gases and water vapour.
lithosphere: the rigid outer part of the earth: the crust and upper mantle.
hydrosphere: a discontinuous layer if water at or near the earth's surface. it includes all liquid and frozen surface waters, groundwater held in soil and rock, and atmospheric water vapour.
biosphere: the total sum of all living matter, the biological component of the earth's systems.
how might each subsystem link? e.g living matter in the oceans links the biosphere and the hydrosphere.
coasts as natural systems
a systems approach is a model used to help explain coastal environments.
systems can be described in three ways:
- ISOLATED: there is no input or output of energy or matter.
- CLOSED: there is input, transfer and output of energy, but not of matter (or mass).
- OPEN: most environmental systems are open, there are inputs and outputs of both energy and matter.
matter= any physical substance.
e.g closed system: a domestic central heating system
e.g an open system: domestic water supply
- closed system: a system in which the amount of matter remains constant, but energy can be transferred as an ouput, input or flow.
- open system: a system in which energy and matter can be transferred in, through and out (beyond the boundary of the system).
- input: energy and/or matter entering the system.
- output: energy and/or matter leaving a system.
- store/ component: a section of a system in which matter can remain, be added or removed from.
- flow/ transfer: movement between stores/ components in a system.
- boundary: the edge of a particular system.
- dynamic equilibrium: is when the inputs and outputs in a system are balanced and the stores stay the same.
- feedback occurs when a system changes because of an outside influence. this will upset the dynamic equilibrium, or state of balance, and affect other components in the system. outside influence affects dynamic equilibrium.
- negative feedback is when a system acts by lessing the original effect, ultimatley reversing it.
negative feedback is when a systems acts by lessening the effect of the original change, reversing it.
positive feedback is when a change within a system causes a further, or snowball effect, continuing, or even accelerating the original change, amplifies the original effect.
negative feedback in coastal environments
where storms remove sediment from a beach, it might get deposited offshore, making waves break earlier, erosion is reduced, and under calmer conditions the sediment may be returned to the beach, highlighting negative feedback and dynamic equilibrium.
coasts as natural systems
Inputs within the coastal zone:
- wave energy
- geological structure
- human activity, including climate change
Transfers within the coastal zone:
- processes of wave erosion
- mass movement
- hard/soft engineering
Outputs within the coastal zone:
- landforms of erosion
- landforms of deposition
- coastal defence
factors influencing coastal landforms
marine factors: waves, winds, tides, salt spray and currents.
subaerial factors: temperatures, weather (rain, snow, frost, winds, sun).
human factors: pollution, conservation management, buildings, recreation.
tectonics: coastal uplift, volcanic activity.
geomorhpic factors: rivers, glaciers, mass movement.
geology: structure and lithology (rock type).
biotic factors: impact of vegetation, coral reefs etc.
climatic factors: winds (generate waves and currents), weather (affects weathering of cliffs, sources of beach material), climate change, glaciation (changes in sea level eustatic/ isostatic).
how might each factor influence coastal landforms?
systems and processes
what is wind?
within the atmosphere, areas of high and low pressure form. in a low pressure area, the air is rising, which draws air in from higher pressure areas. this movement of air from higher to lower air pressure areas is wind.
prevailing wind is the direction from which wind most commonnly blows.
prevailing wind in the UK comes from the South West.
how are waves formed?
As air moves across the water, frictional drag disturbs the surface and forms ripples or waves. In open sea theres an orbital motion of water particles.
1. the water becomes shallower and the circular orbit of the water particles changes to an elliptical shape.
2. the wavelength (distance between crest of the two waves) and the velocity both decrease, and the wave height increases- causing the water to back up from behind and rise to a point where it starts to break.
3. the water rushes up the beach as swash and flows back as backwash.
what will affect the amount of energy provided by the wind?
- strength of the wind
- duration of the wind- longer the wind blows, the more powerful the waves
- fetch: distance of open water over which the wind blows.
how are waves formed? diagram
wave key terms:
- wave crest: the highest point of the wave
- wave trough: the lowest point of a wave
- wave height: the height difference between a wave crest and a neighbouring trough
- wave length or amplitude: the distance between crests
- wave period: the number of waves per minute
- wave frequency: the time in seconds between two succesfive crests or troughs
- swash: the rush of water up the beach after a wave breaks
- backwash: the action of water receding back down the beach towards the sea
- swell waves: waves in open water, characterised by longwavelengths and reduced height. they can reach up to 15m high and can travel huge distances.
- storm waves: waves generated local winds which travel only short distances. (waves closer to the coast)
constructive waves diagram
destructive waves diagram
constructive/ destructive characteristics
constructive: (swell or surging waves)
- distant weather systems generate these waves in open ocean
- low swinging waves, long wavelength
- strong swash, weak backwash
- beach gain
- associated with gebtle beach profile, over time builds up beach making it steeper
- low frequency (6-8 waves per minute)
- long wave period
destructive: (storm or plunging waves)
- local storms cause these waves
- high, plunging waves with short wavelength
- weak swash, strong backwash
- beach loss
- short wave length
- high frequency (10-14 per minute)
- steeper beach profile, will flatten beach over time. short wave period
effects of waves on coastlines
the alternating action of constructive and destructive waves on a beach, diagram:
this is an example of negative feedback.
zones of a coastline diagram
when each wave approaches the coastline, it drags in shallower water which meets the headland, increasing the wave height and steepness and shortens the wave length (destructive waves). the part of the wave in deeper water moves faster, causing the waves to bend. wave energy becomes concentrated on the headland causing greater erosion, the low energy waves spill into the bay causing deposition.
tides are caused by the gravitational pull of the moon and sun.
tides are long-period waves that appear to move through the oceans due to the gravitational forces exerted by the moon and the sun. their apparent movement towards the coast creates a rise of the sea surface, though due to earth's rotation it is the coast rolling into a deeper bulge of ocean that creates the effect.
high tide: where the sea surface rises to it's highest point.
tidal range: the difference between the high and low tide.
coastal areas experience two high and low tides every lunar day (24 hours and 50 minutes)
where a section of the earth towards the moon, then a high tide will occur as gravity pulls the ocean towards the moon. additionally, on the opposite side of the earth (facing away from the moon) will also have a high tide. this is because of inertia and centrifugal force, as gravitational pull is weaker here, the ocean bulges out as a result. the areas at a 90 degree angle to the moon will experience low tide. as earth spins, the rotation causes tides to cycle around the planet.
tides increase the rate of coastal erosion. where tidal range is low e.g the Mediterranean, wave energy is less and many cliff faces are unaffected by marine processes. in other places, such as the UK, tidal range is greater, leading to increased erosion and creates more landforms such as wave cut notches and platforms.
spring tides are when the moon, sun and the earth are in a straight line, producing the strongest tide-raising force, leading to the highest monthly tidal range (happens once a lunar month).
neap tides are lower than normal tides, they occur when the sun and the moon are at right angles to the earth, so gravitational pull from both has a reduced impact.
macro tidal: more than 4m
meso tidal: 2 to 4m
micro tidal: less than 2m
formation of a storm surge:
- occur when meterological conditions give rise to strong winds which produce much higher water levels than high tides.
- depressions (intense low pressure weather systems) produce low pressure conditons that can raise sea levels.
- strong winds drive waves ahead of the storm, pushing the sea water against the coastline. this causes water to 'pile up' against the coast
- high tides then intensify the effect.
Cromer, Norfolk UK , north coast is likely to be affected by storm surges.
how do tides affect coastal environments?
e.g tidal ranges determine the upper and lower limits of erosion and deposition and the amount of time each day that the litoral zone is exposed and open to sub-aerial weathering. e.g the Mediterranean has a low tidal range, this restricts wave action to a narrow width in the coastal zone.
ocean currents are located at both the ocean surface (surface currents) and in deep water below 300 metres (deep currents). they move both horizontally and vertically and occur at both local and global scales. the ocean is an interconnected system powered by the forces of wind, tides, Coriolis force, the sun, and water density differences. the topography and shape of ocean basins and nearby land also influences ocean currents. these forces and physical characteristics of both land and ocean affects the size, shape, speed, and direction of ocean currents.
surface ocean currents are typically wind driven, resulting in both horizontal and vertical water movement. horizontal surface currents that are local and typically short term include rip currents, longshore currents, and tidal currents. in upwelling currents, vertical water movement and mixing brings cold water towards the surface while pulling warmer, less dense water downward, where it condenses and sinks. this creates a cycle of upwelling and downwelling.
Deep ocean currents are density driven, and differ from surface currents as they are slower moving.
the global conveyor belt includes both surface and deep ocean currents that circulate the globe in a 1000 year cycle. the global conveyor belt is the result of two processes:
- warm surface currents carrying less dense water away from the equator towards the poles
- cold deep ocean currents carrying denser water away from the poles toward the equator.
the ocean's global circulation system plays a key role in distributing heat, regulating weather and climate, and cycling nutrients and gases around the earth.
the role of ocean currents in the coastal zone
longshore currents (littoral drift)
occur as most waves approach at an angle to the shoreline, this generates a current running parallel to the shoreline. this not only moves water along the surf zone but also transports sediment parallel to the shoreline.
are strong currents moving away from the shoreline. they develop when seawater is piled up along the coastline by incoming waves. initially the current may run parallel to the coast before flowing out through the breaker zone, possibly at a headland or where the coast changes direction.
the movement of cold water from deep in the ocean towards the surface. the more dense cold water replaces the warmer surface water and creates nutrient rich cold ocean currents. these currents form part of the pattern pf global ocean circulation currents.
high and low energy coastlines
wind and waves: coastlines where strong, steady prevailing winds create high energy waves.
dominant coastal processes: the rate of erosion is greater than the rate of deposition.
typical landforms: typical landforms include headlands, cliffs and wave-cut platforms.
high energy coastlines are the exposed Atlantic coasts of northern Europe and North America, including the north Cornish coast in south west England.
high and low energy coastlines
wind and waves: coastlines where wave energy is low
dominant coastal processes: the rate of deposition often exceeds the rate of erosion of sediment.
typical lanforms: beaches and spits.
examples: many estuaries, inlets and sheltered bays e.g the Baltic Sea
sediment sources, cells and budgets
what is sediment?
sediment is any naturally occuring material that has been broken down by the processes of erosion and weathering and has then been transported and subsequently deposited by the action of ice, wind and water.
inputs (source of sediment): cliff erosion, fluvial sediment, erosion of depositional features (beaches, dunes), beach recharge, offshore bars and sediment, erosion of wave cut platforms.
transfers (transportation): longshore drift (movement of material caused by approach of swash at an angle to the shore, and perpendicular backwash down the steepest beach gradient which moves the material laterally downdrift, aided by wave refraction.), currents, saltation (transportation of sand along the shore by the wind).
stores (sinks): sinks/ permanent storage (estuary, submarine canyon, offshore bar/ bank, dredging), subsinks and temporary stores (sedimentary features (beaches, dunes, spits, bar)
how is sediment added to coastal systems
- rivers: sediment with transported by river erosion, it is deposited in by river mouths and estuaries where it reworked by waves tides and currents.
- cliff erosion: less resistant rock (sand, clay) like Holderness in Lincolnshire, can erode at 10m per year. Tough igenous granites (resistant rocks) in Cornwall erodes much slower.
- longshore drift: sediment is transported from one stretch of coastline (as an output) to another stretch of coastline (as an input).
- wind: in glacial or hot arid environments, wind-blown sand can be deposited in coastal regions. sand dunes are semi-dynamic features at the coast represent both accumulations and sinks of sand.
- glaciers: in places such as Alaska, Antractica, ice shelves (chunks of ice breaking off a glacier or ice sheet) calve into the sea, depositing sediment trapped within the ice.
- offshore: transferred by waves, tides and currents, also storm surges associated with tropical cyclones and tsunami waves can also be responsible for inputs of sediment into the coastal system.
sediment cells are areas along the coastline and in the nearshore area where the movement of material is largely self-contained. they can be considered as a closed coastal sub-system. they are often determined by the topography and shape of the coastline which directs the movement of the sediment within the cell. this is what makes them closed systems: sediment is largely recycled within them rather than having significant inputs or outputs. the boundaries of sediment cells tend to be headlands and peninsulas which act as natural barriers to stop the further movement of the sediment.
despite that most sediment remains within the cell, changes in wind direction and movements of ocean currents can affect some of the sediment under high-energy conditions and cause some sediment to move offshore into long-term ocean floor stores of sediment. within each sediment cell, there can be smaller sub cells.
a sediment budget is the balance between changes in the volume of sediment held within the system and the volume of sediment entering or leaving the system.
- a positive budget is where there are more inputs than outputs.
- a negative budget is when there are more outputs than inputs.
the budget can alter according to the following factors:
- input changes: the volume of fluvial material being deposited into the coastal system and the impact that human intervention can have on that, e.g damming a river. coastal defences can impact on the outputs too with reduced cliff face erosion taking place. sea level rise may add more sediment with increased coastal erosion.
- output changes: human intervention, such as removing large amounts of sand from an area for industrial or coastal protection use. also, sea level rise can increase the liklihood of changing ocean currents and material being removed from sediment cells.
positive budget (surplus) of sediment > more material is added to the cell than is removed- a net accretion of material > shoreline builds towards the sea.
negative budget (deficit) of sediment > more material is removed from the cell than added > shoreline retreats landward.
geomorphology is the study of landforms, their processes, form and sediments at the surface of the earth. they can be divied into marine processes and sub-aerial processes.
marine processes: operate upon a coastline and are connected with the sea, such as waves, tides and longshore drift.
sub-aerial processes: includes processes that slowly (usually) breakdown the coastline, weaken the underlying rocks and allow sudden movements or erosion to happen more easily. material is broken down, remaining in or near its original position.
key processes: weathering, mass movement, run-off, marine erosion, marine transportation, marine and aeolian deposition.
key geomorphic processes
- weathering: the breakdown and/ or decay of rock at or near the earth's surface creating regolith that remains in situ until moved by erosional processes. weathering can be mechanical, biological or chemical. encourages mass movement
- mass movement: the movement of material downhill under the influence of gravity, but may also be assisted by rainfall. coastal retreat, changes shape of coastline..
- runoff: all the water that enters a river channel and eventually flows out of the drainage basin. erodes, adds sediment
- marine erosion: wearing away of the earth's surface by the sea: waves, tides and longshore drift. arches, stacks coastline retreat (how quick depends on geology)
- marine transportation: the processes that move the material from the site where erosion took place to the site of deposition by the sea (waves etc). spits bars tombolos
- marine and aeolian deposition: occurs when velocity (energy) of waves decreases until it can no longer transport the grains it is carrying. deposition forms beaches.
weathering: mechanical/ physical
there are three main types of weathering that operate in coastal environments. weathering is the breakdown of rock near or at the earth's surface.
physical weathering: processes that occur at coasts depending on the climate.
freeze-thawing: where temperatures fluctuate above and below frezing. water from rivers or rainfall enters cracks in the rock and freezes as temperatures remain below 0 degrees. as it freezes water expands and puts pressure on the rock. as the process repeats and continues, cracks widen and rock breaks off.
salt crystallisation: when salt water evaporates, it leaves salt crystals behind. these can grow over time and exert stresses into the rock, just as ice does, causing it to break up. salt can also corrode rock, if it contains traces of iron especially.
wetting and drying: frequent cycles of wetting and drying are common on the coast. rocks rich in clay (e.g shale) expand when they get wet and contract as they dry. this can cause them to crack and break up.
includes processed that lead to the breakdown of rocks by the action of vegetation and coastal organisms.
plants: thin plant roots grow into small cracks in the cliff face, cracks widen as roots grow, which breaks up the rock.
water: water running through decaying vegetation becomes acidic, which leads to increased chemical weathering.
birds and animals: birds (puffins and sand martins) and animals (rabbits) dig burrows into cliffs.
marine organisms: also capable of burrowing into rocks (e.g piddocks) or of secreting acids (e.g limpots).
occurs when rocks are exposed to the air and moisture so chemical processes can break down the rocks.
- carbonation: occurs when CO2 dissolved in rainwater makes a weak carbonic acid (H2C03). this reacts with the calcium carbonate (CaC03) in rocks like limestone and chalk to create calcium bicarbonate. which then dissolves easilt in water. carbonation is more effetcive in locations with cooler temperatures as this increases the amount of carbon dioxide that is dissovled in the water.
- oxidation: causes rock to disintergrate when the oxygen, dissolved in water reacts with some rock materials, forming oxides and hydroxides. it especially effects ferrous, iron-rich rocks, and is evident by a brownish yellow staining of the rock surface.
- solution/ hydrolysis: is where midly acidic water reacts or combines with materials in the rock to create clays and idssolvable salts; this itself degrades the rock, but both are likely to be weaker than the parent rock, this making it susceptible for further degradation.
- acid rain: other gases from fossil fuels mix with rainwater making it mildly acidic. the presence of sulphur dioxide and nitric oxides can create rainwater, with weak sulphuric and nitric acids. this acid rain can react with various minerals in different rocks weakening them.
mass movement (with diagrams)
soil creep: slow form of movement of individual soil particles downhill. this precise mechanism of movement often involves particles rising toward the ground surface due to wetting or freezing then returning vertically to the surface in response to gravity as soil dries or thaws.
mudflows: a mudflow involves earth and mud flowing downhill, usually over unconsolidated or weak bedrock like clay, often after heavy rainfall. water gets trapped in the rock, increasing pore water pressure, forcing rock particles apart and leading to slope failure. mudflows are often sudden and fast-flowing so can be a significant natural hazard.
mass movement (with diagrams)
landslide: a block of rock moving very rapidly downhill along a planar surface (side plane), roughly parallel to the surface. they are triggered by earthquakes or very heavy rainfall, when the slip surface becomes lubricated and friction is reduced. landslides are rapid. moving material doesn't mix and stays largely intact.
rockfall: a rockfall is sudden collapse or breaking away of individual rock fragments at a cliff face. mostly associated with steep or vertical cliffs, with resistant rock.
mass movement (with diagrams)
landslip or slump (rotational slumping): slide surface is curved rather than flat. landslips occur in weak and unconsolidated clays and sands, often when permeable rock overlies impermeable rock. sharp break of slope and the formation of a scar. multiple landslips can result in a terraced appearance on the cliff face.
described as rotational slumping because it slopes downward at a curved angle rather than sliding across.
the draining away of water from the surface of an area of land.
explain the importance of runoff in shaping coastal environments through mass movement:
- hydraulic action: the force of the water as it crashes against the coastline.
- wave quarrying (cavitation): when a wave advances, air can be trapped and compressed, either in joints on the rock or between breaking of wave and cliff, causing rock to break off. bubbles formed in the water may implode under high pressure, generating jets of water that erode the rock, this is cavitation). the action of waves breaking agaisnt unconsolidated material such as sands and gravels. waves scoop out the loose material in a similar way to the action of a giant digger in a quarry on land.
- abrasion/corrAsion: a) sediment is dragged up and down the shoreline, eroding and smoothing rocky surfaces. c) when waves advance, they pick up sand and pebbles from the seabed, a temporary store or sediment sink. when they break at the base of the foot of the cliff, chipping away the rock.
- solution (corrOsion): weak acids in seawater can disolve alkaline rock (chalk or limestone) or thr alkaline cement that bonds rock particles together.
- attrition: the gradual wearing down of rock particles by impact and abrasion, as the pices of rock are moved by the waves, tides and currents. this process gradually makes stones rounder and smoother.
suspension: small particles of sand and silt are carried along by moving water. picked up mainly through turbulence that exists in water.
solution: dissolved materials are transported within the mass of moving water.
traction: large stones and boulders are rolled and slid along the seabed and beach by moving sea water, this happens in high energy environments.
saltation: small stones bounce along the seabed and beach by moving seawater. this happens in high energy environments.
longshore drift diagram
weathering and erosion in coastal environments
- geology: the physical structure of the earth (rock types)
- structure: is defined by the way the rocks are disposed or geologically arranged.
- lithology: is the make-up of each individual rock type.
- 1. hardness of rock type as a result of heating and compression during their formation, as a general rule igneous and metamorphic rocks are ahrder and therefore more resistant to erosion, forming many high cliffs in north west britain. contrastingly, many rocks forming the south and east of britain are soft, unconsolidated sands and clays of teritary age, as well as deposits of glacial bouder clay and gravels. other factors being equal, these rocks are easily eroded.
- 2. permeability occurs as a result of the incidence of pores (e.g open textured sandstone), or as a result of fissures, cracks and joints (chalk and limestone). as any surface water seeps through the cliffs, in increases resistance to subaerial processes so adding strength to some relatively soft rocks. this explains why chalk invariably forms relatively high, near vertical cliffs, and supports arches and stacks. where permeable rocks such as chalk are underlain by impermeable clays (eg Folkestone where the chalk is underlain by gault clays) a zone of lubrication occurs which can lead to cambering and extensive mass movement.
weathering and erosion in coastal environments
3. physical make-up of rocks the amount of joints, bedding planes and faults, has an impact on rates of weathering (both freeze-thaw and chemical). where joints and bedding planes occur at a high density this weakens the rokc and makes it subject to increased subaerial and marine erosion.
4. chemical composition some rocks such as quartzite or some sandstones, are made almost completely from silica which is chemically inactive. the very low rate of chemical weathering makes rocks more resistant. other rocks are prone to rapid chemical weathering because of their chemical composition. iron compounds oxidise in some sandstones.these 'rotted' zones increase vulnerability to both subaerial and marine erosion. the chemical decomposition of limestone by carbonation happens rapidly under the influence of saltwater, leading to accelerated disintergration of some wave cut platforms. the impact of salt water causes rocks like basalt to weather 14X faster than under freshwater conditions. therefore, certain aspects of lithology and structure combine to make neighbouring rocks more or less subject to weatherig and erosion and therefore they erode ar faster or slower rates relative to eachother. this process of differential erosion (rocks eroding at different speeds) is the key to understanding coastal erosional landforms.
cliff profiles and geological structure
coastal morphology is related not only to the underlying geology, or rock type, but also its lithology (geological structure). lithology means any of the following characteristics:
- strata: layers of rock
- bedding planes: horizontal. natural breaks in the strata, caused by gaps in time during periods of rock formation.
- joints: vertical fractures caused either by contraction as sediments dry out, or by earth movement during uplift,
- folds: formed by pressure during tectonic activity, which makes rocks buckle and crumple (e.g Lulworth crumple)
- faults: formed when the stress or pressure to which a rock is subjected, exceeds its internal strength (causing it to fracture). the faults then slip or move along fault planes
- dip: refers to the angle at which rock strata lie (horizontally, vertically, dipping towards the sea, or dipping inland).
cliff profiles and geological structure
the relief- or height or slope of land- is also affected by geology and geological structure. there is a direct relationship between rock type, lithology and cliff profiles. as illustrated in diagrams: (p42 book1)
rock types + characteristics
- not permeable
- can be jointed
- very resistant (slow erosion rates)
- found in SW england. produces steep rugged cliffs.
- permeable (due to joints and bedding planes)
- highly jointed
- medium resistance. (chemical weathering concentrates on joints and bedding planes. joints also vulnerable to hydraulic action).
- steep cliffs, white in appearance. large no. of fossils found within strata.
rock types + characteristics
- permeable (porous spaces in the rock hold water)
- medium/ high resistance to weathering and slumping
- tall steep cliffs. vulnerable to rock falls if another rock present, e.g Seven Sisters, Brighton where flint makes chalk unstable.
- allow percolation of water and other fluids. are porous.
- jointed (strata are often evident as they differ in colours)
- resistance varies based on type of sand that composes them. generally medium resistance.
- composed of sand grains
rock types + characteristics
- highly impermeable
- not jointed
- very low resistance (vulnerable to erosion).
- slip planes are often created where a porous/ permeable rock overlies clay- causing rotational slumping. creates features like bays.
sand and gravel
- permeable (sand and gravel are not bonded together so plenty of space for water to be held)
- not jointed but gaps are present
- low resistance, vulnerable to marine erosion and weathering
- composition and characteristics will depend on the amount of sand and gravel. will create unstable cliffs prone to mass movement.
factors affecting rates of erosion
waves: constructive vs destructive/wave refraction/storms= stronger waves
rock type: harder rock erodes slower (igneous+ metamorphic) /sedimentary erodes easier
geological structure: faults and joints cause rocks to erode much faster, cracks and bedding planes create weaknesses in cliffs.
presence of absence of beach: beach protects cliff face by absorbing wave energy.
sub-aerial: weathering and mass movement wil weaken cliffs and create piles of debris that will be eroded easily by the sea, potentially increasing the rate of erosion.
coastal management: seawall prevents erosion/ groynes cause erosion further along the shore/ has an impact on sediment transfer and patterns of wave energy.
concordant/ discordant coastlines
concordant: where the rock bands run parallel to the coastline.
features: coves, wide bays, e.g lulworth cove or dalmatian coast, croatia
discordant: where the rock bands run perpendicular to the coastline.
features: headlands, bays, microfeatures
south Purbeck coastline
- geology and lithology of the coast.
- angle of dip of coastline infront of the headland
- nature of waves approaching the coast
- direction and strength of the prevailing winds
- differential rates of erosion of the different rocks
- wave refraction
- erosion of the headland
- deposition in the bay
- features of the resulting landscape: headland and bay
- erosional and depositional features in headland and bay
headlands and bays
develop where there are alternating bands of hard and soft rocks. the softer rocks are eroded more rapidly creating indentations along the coastline (bays), with the more resistant harder rocks remaining as headlands.
formation of headland and bays diagram:
cliffs and wave cut platforms
- a gently sloping platform of rock stretching out from the cliff to the sea (with an angle of less than 5 degrees)
- the platform looks smooth from a distance, but is deeply cut into by the action of abrasion
- as the platform grows, it causes waves to break further out at sea, which dissipates wave energy and reduces rate of erosion, and limits growth of wave cut platform to about 500m from the cliff out to sea.
- waves focus erosion between the igh and low tide level (via abrasion and hydraulic action)
- leads to formation of a wave cut notch at foot of the cliff
- as the wave cut notch grows, cliff is undercut, until the unsupported rock above collapses.
- the debris now protects the foot of the cliff from further erosion, until it is broken down (via abrasion and attrition) and carried away
- as cliff retreats inland the gently sloping platform of rock is left behind.
e.g Kimmeridge Bay, Dorset UK
diagrams formation of wave-cut platform
cliff profile features
cave, arches, stacks and stumps.
- Caves occur when waves force their way into cracks in the cliff face. The water contains sand and other materials that grind away at the rock until the cracks become a cave. Hydraulic action is the predominant process.
- If the cave is formed in a headland, it may eventually break through to the other side forming an arch.
- The arch will gradually become bigger until it can no longer support the top of the arch. When the arch collapses, it leaves the headland on one side and a stack (a tall column of rock) on the other.
- The stack will be attacked at the base in the same way that a wave-cut notch is formed. This weakens the structure and it will eventually collapse to form a stump.
- One of the best examples in Britain is Old Harry Rocks, a stack found off a headland in the Isle of Purbeck.
geo and blowholes
formed as sea caves grow landwards and upwards into vertical shafts and expose themselves towards the surface, which can result in blasts of water from the top of the blowhole if the geometry of the cave and blowhole and state of the weather are appropriate.
formed by the action of the waves (hydraulic action) eroding the lower face of the 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.
geo and blowholes diagram
- material from erosion of cliffs and from rivers is transported along the coastline by longshore drift.
- the strong swash of a constructive wave deposits the largest material at the top of the beach.
- the upper beach starts to build up, the backwash becomes weaker because a greater proportion of the water drains away by percolation, rather than running down the beach and carrying sediment.
- the weak swash of a destructive wave deposits material at the base of the beach. it can't advance further up the beach because it is destroyed by the backwash from the previous breaking wave.
- over time the beach builds up through these processes and is shaped through different factors.
inputs: wave energy, sediments processes: transportation, deposition output: coastal landform, beach
factors affecting beach profile:
- wave energy (affected by winds): high energy waves tend to produce shingle beaches, sandy beaches are found in low energy environments.
- wave type: destructuve waves cause more material to move back down the beach because of stronger backwash, forming a shallower beach profile. constructive waves cause more material to be deposited up the beach because swash is stronger, forming a steeper beach profile.
types of beach:
- swash-aligned beaches: fromed in low energy environments (e.g bays). they are shaped by waves travelling parallel to the shoreline. they can be made of sand or shingle depending on wave energy.
- drift-aligned beaches: formed by waves approaching the shore at an angle, longshore drift moves sediment along the beach often forming spits. sediment can be graded along this beach with finer and smaller shingle particles being carried further up the beach and become increasingly rounded.
Spits are created by deposition. A spit is an extended stretch of beach material that projects out to sea and is joined to the mainland at one end.
Spits are formed where the prevailing wind blows at an angle to the coastline, resulting in longshore drift. An example of a spit is Spurn Head, found along the Holderness coast in Humberside.
- Longshore drift moves material along the coastline.
- A spit forms when the material is deposited.
- Over time, the spit grows and develops a hook if wind direction changes further out.
- Waves cannot get past a spit, which creates a sheltered area where silt is deposited and mud flats or salt marshes form.
inputs: sediment, prevailing winds processes: longshore drift, swash and backwash outputs: spit
e.g Spurn Head UK. Sandy Hook Spit, New Jersey USA
- Compound spits exhibit a number of recurved ‘spurs’ along their length as each recurvature represents a ‘break in coast orientation’ and the development of a new extension of the main spit under conditions of consistent longshore drift.
- usually have a number of recurved ridges, or minor spits along their landward side, possibly marking the position where they terminated in the past.
tombolos (with diagrams)
a tombolo is a beach (or ridge of sand and shingle) that has formed between a small island and the mainland. deposition occurs where waves lose their energy and the tombolo beings to build up. e.g ST. Ninians in the Shetland Islands. as material accumulates it becomes more permanent, as is well above water at high tide.
- inputs: type of wave (constructive), wave refraction, direction of prevailing winds
- processes: longshore drift, formation of spit
- outputs: tombolo, spit
bars (with diagram)
offshore bars are submerged ridges of sand or coarse sediment created by waves offshore from the coast. destructive waves erode sand from the beach with their strong backwash and deposit it offshore. offshore bars act as both sediment sinks and potentially sediment input stores. they can abosrb wave energy thereby reducing the impacts of waves on the coastline, e.g Cles Islands, Spain.
inputs: destructive waves, direction of longshore drift, direction of prevailing winds. processes: longshore drift, formation of spit. outputs: bar, lagoon
barrier islands (diagram)
barrier islands are long offshore deposits of sand that run parallel to the coastline, they are separated from the mainland by a shallow bay or lagoon and are often found in chains. e.g Gulf of Mexico. barrier islands are common in areas with low tidal ranges, where the offshore coastline is gently sloping.
inputs: prevailing wind, type of wave, lagoon or bay, processes: longshore drift, formation of spit and bar, erosion. outputs: barrier island.
sand dunes are dynamic (always changing). inputs required for sand dunes to form are:
- plentiful supply of sand and large tidal range
- strong onshore winds to transport sand particles through saltation.
- an obstacle to trap the sand e.g a plant, seaweed or driftwood.
vegetation is key for sand dune development to begin.
- pioneer species: the first plants that colonise an area, usually with special adaptations.
- climatic climax community: the vegetation that would evolve in a climatic region if the seval progression is not interrupted by human acitvity, tectonic processes etc.
- psammosere: vegetation succession that originated in a coastal area.
- saltation: rocks and sand that is moved in a series of leaps across a river or sea bed.
UK Camber Sands, or Dune du Pilot
sand dune succession
- bare sand
- salty (alkaline), lack of organic matter and water, windy
- pioneer species invade, colonise and trap sand moving via saltation.
- embyro dunes form
- plants die
- organic material is added to sand and water improves retention
- soil conditions improve
- more plant species can grow (not pioneers)
- higher species diversity (moisture loving plants develop in dune slacks)
- trees/ scrub can now be supported
- climax community
estuarine mudflat/ saltmarsh environments
- are low lying areas of the shore that are submerged at high tide and are composed of salt and clay.
- found in estuaries where rivers meet the sea or on the landward side if a spit.
- develop when sea water flows in the river mouth with each high tide and out with each low tide
- flocculation: indivual clay particles aggregate together to form larger, heavier particles that can sink to the bed.
over time mudlfats can become a saltmarsh, with a clear vegetation succession (halosere).
four elements necessary for a saltmarsh:
- a stable area of sediment covered by the tide for a short time
- a supply of suitable sediment available
- low water velocities for some of the sediment to be deposited
- a supply of seeds for the sediment the established of vegetation cover.
formation of salt marshes
- The formation begins as tidal flats gain elevation relative to sea level by sediment accretion, and so the rate and duration of tidal flooding decreases so that vegetation can colonize on the exposed surface.
- The arrival of pioneer species such as seeds or rhizome portions are combined with the development of suitable conditions for their establishment in the process of colonisation.
- When rivers and streams arrive at the low gradient of the tidal flats, the discharge rate reduces and suspended sediment settles onto the tidal flat surface, helped by the backwater effect of the rising tide.
- Mats of algae can fix silt and clay sized sediment particles to their sticky sheaths on contact which can also increase the erosion resistance of the sediments. This assists the process of sediment accretion to allow colonising species to grow. These species keep sediment washed in from the rising tide around their stems and leaves and form low muddy mounds.
- Once vegetation is established on depositional terraces further sediment trapping and accretion can allow rapid upward growth of the marsh surface such that there is rapid decrease in the depth and duration of tidal flooding. As a result, competitive species that prefer higher elevations relative to sea level can inhabit the area and often a succession of plant communities develops.
e.g UK Keyhaven marsh, or Pontine marshes, Italy
zones of a salt marsh:
eustatic, isostatic and tectonic sea level change
major changes in sea-level over 10,000 years:
glacio-eustacy caused sea level change in the Plaistocene. ice sheets we 3x wat they are today, a large amount of water was stored in them and so less in the oceans. sea levels dropped by 100-150m, exposing most continental shelves as dry land. a geological period called Holocene (6000-10,000) years ago sea levels rose very quickly, flooding the North sea and the English channel, breaking the link between england and ireland and flooded mnay rivers, valleys, forming the indednted coastline of southwest england and and ireland called rias.
eustatic change: global
- when the sea level itself rises or falls
- causes of falling: precipitation fall as snow, forming ice sheets that store water held in the oceans. sea levels fall.
- causes of rising: temperatures rise at the end of glacial periods (interglacial period) ice sheets begin to melt and retreat, stored water then flows into the rivers and the sea, sea levels rise.
eustatic, isostatic and tectonic sea level change
isostatic change: (local)
- when the land rises or falls, relative to sea.
- causes of rising: ice melts at the end of glacial period, reduced weight of ice causes land to readjust and rise, isostatic recovery.
- causes of falling: enormous weight of the ice makes the land sink, isostatic subsidence.
Isostatic change in the UK:
- (in the north) ice melt is causing isostatic rise, as a result of isostatic recovery
- ice/ glacier melt causes sea levels to rise and land to rise isostatically
- (in the south) isostatic sink, rivers pour water into Thames Estuary and English Channel, weight of sediment causes crust to sink and relative sea levels to rise, all sea levels rise because of global warming.
- sea levels rise eustatically
sea level change diagrams
emergent and submergent coastlines
submergent features: (because of sea level rise)
e.g Rias, Fjords, Dalmation coasts
Rias (diagram) UK Kingsbridge, Rhode Island Narrangasett Bay
a river valley that’s been flooded by the eustatic rise in sea level. like a typical river valley but they have even more water in them. The cross section of a ria is really similar to the one you’d find for a river in the lower course.the floodplain of the river also gets flooded, altering the cross profile of a ria ever so slightly so that it includes the floodplain.
emergent and submergent coastlines
Fjords (diagram) e.g Western Scottish Fjords, Millford Sound NZ
steeper and deeper variants of riases that are relatively narrow for their size. They have a u-shaped cross profile and are often found in particularly icy sections of the world. they’re flooded glacial valleys.fjords are really deep however they have a shallow mouth (known as a threshold) as this is where the glacier deposited its load.
emergent and submergent coastlines
dalmation coasts e.g Dalmation coast in Croatia, coastline of soutern Chile
mountain chains that have been submerged by water leaving mountain tips like islands because of sea level change. mountains run parallel or concordant to the coastline. coastal submergence produces long, narrow inlets with a chain of islands parallel to the coast. typically names dalmation coasts or pacific coasts as this type of coastline is typical in both areas.
emergent and submergent coastlines
emergent features: (sea level drop)
e.g raised beaches and marine platforms
- a marine platform is rock (an old wate cut platform, when sea level was higher), an erosional feature
- a raised beach is formed of marine sediments deposited when the sea level was higher, a depositional feature.
raised beaches are former wave cut platforms and their beaches which are at a higher level than the present sea level. there can be old cliff lines with old cliff lines and wave-cut notches, sea caves, arches and stacks.
where a greater expanse of gently sloping formerly submerged alnd has been exposed by uplift or lowering of sea levels, known as a mrine platform. a marine platform is now exposed and is part of a gently sloping continental shelf, whose gradient is now continued for some distance both offshore and in land, whereas a raised beach is not.
raised beaches and marine platforms diagram:
climatic change on coasts
- sea levels stabilised about 3000 years ago, since then they have changed very little since very recently
- from late 19th century to late 20th century sea levels rose globally by 1.7mm per year
- but between 1993-2010 it has increased to 3.2mm per year
- IPCC estimates that by 2100, sea levels could rise by between 30cm and 1m from current levels,though there will be slight variation from place to place.
changes in sea level are due to to:
- changes in volume of the oceans
- tectonic movement (subsidence or recovery)
causes of the oceans volume increasing:
- thermal expansion of water due to heating
- melting of freshwater icem such as Greenland and Antarctic ice sheets and mountain glaciers.
Kiribati, Pacific Ocean, consists of 33 islands, very low lying sand and mangrove, mostly a metre or less above sea level.
- rising sea levels are contaminating groundwater sources affecting the ability to grow crops
- land in Fiji will be used in the immediate future for agriculture and fish- farming projects, to guarantee food security.
- people from Kiribati could potentially move to Fiji
- Government has launched a 'migrate with dignity' policy to allow to apply for jobs in neighbouring countries such as New Zealand.
- if islands are submerged, kiribatis populations will become environmental refugees (people forced to migrate as a result of changes in the environment).
human intervention in coastal landscapes:
coastal management has 2 aims:
- provide defence against, and mitigate the impacts of flooding
- provide protection against, and mitigate the impatcs of coastal erosion.
hard engineering strategies
- sea walls £6000/m, stone or concrete walls at foot of a cliff or top of beach, curved face to refect waves back into the sea. + prevention of erosion, have a promenade for people to walk across. - reflect wave energy rather than absorbing it. can be intrusive and unnatural looking. expensive to maintain and build.
- revetments £4500/m, sloping wooden conrete or rock structures placed at top of a beach, break up waves energy. + not expensive - intrusive and unnatrual looking, high levels of maintenance.
- rock armour £100,000-£300,000/ 100m, large rocks placed at the foot of a cliff, or top of a beach. it forms a permeable barrier to the sea- breaks up waves allows some water to pass through.+relatively cheap and easy to construct and maintain. often used for recreation- fishing, sunbathing. - very intrusive, rocks usually arent local and can lok out of place with local geology. can be dangerous for people.
- groynes £5000- £10,000 each. timber or rock structures built at right angles to the coast. they trap sediment being moved along the coast by longshore srfit, builds up the beach. + work with natural processes to build up the beach, increases tourist potential, protects land behind, not too expensive. - starves beaches further along the coast of fresh sediment, increased erosion, interupts longshore drift, unnatural and unattractive.
hard engineering strategies
- cliff face strategies:
- fixing: pins rocks layers together
- regrading: lowers the cliff angle to make it more stable
- drainage: removal of water prevents landslides and slumping.
- +effective approach, effective on clay or loose rock, cost effective. - technically difficult, retreat of cliffline uses up land, drained cliffs an dry out, leading to rock falls.
- offshore reef
soft engineering strategies
- beach nourishment & redistribution: £300,000/100m the addition of sand or pebbles to an existing beach to make it higher or wider. the sediment is usually dredged form the nearby seabed. + cheap and easy to maintain. it looks natural and blends with existing beach, it increases tourist potential by creating a bigger beach. - needs constant maintenance because of natural processes erosion and longshore drift.
- dune regeneration: £200, £2000/ 100m, marram grass can be planted to stabilise dunes. areas can be forced to keep people off newly planted dunes. + maintains a natural coastal environment, provides important wildlife habitats, cheap and sustainable.- time consuming to plant marram grass. people may respond negatively to being kept off certain areas.
- marsh creation: variable cost, a form of manages retreat, by allowing low-lying coastal areas to be flooded by the sea. the land then becomes a salt marsh. + relatively cheap (land reverts to its original state before management). creates a natural buffer to powerful waves. creates an important wildlife habitat. - agricultural land is lost, farmers or landowners need to be compensated.
soft engineering strategies
- cliff regrading and draining: variable cost, cliff regrading reduces the angle of the cliff to stabilise it. drainage removes water to prevent landslides and slumping. + can be effective on day or loose rock where other methods will not work. drainage is cost effective. regrading effectively causes the cliff to retreat. drained cliffs can dry out and lead to collapse (rocks falls).
soft engineering Pevensy Bay
pevensey bay, east sussex
- groynes in Eastbourne starve Pevensey Bay
- major storms
- sea level rise
- coastal flooding
management solutions: beach nourishment, shingle barrier extending 9km between Eastbourne and Bexhill.
impacts effctiveness/ defences currently protect:
- 10,000 properties
- recreattional and commercial sites
- A259 coast road and railway line from Hastings to Portsmouth
- 2 nature reserves, an SSSI wetland site, livestock and arable farms
soft engineering Pevensy Bay
beach maintenance strategies in Pevensey Bay:
- recharge- natural movement of sediment from west to east
- recycling of sediment and redistribution from areas with accumulation of sediment to places with less
- bypassing- trucks used to transfer sediment shingle to the west, (bypasing the harbour).
- beach surveys
shoreline management plans
a shoreline management plan is a plan/ intergrated system created to avoid piecemeal approaches to shoreline management.
there are 22 SMPs around the coast of England and Wales
key aims and features of SMPs:
- plan for short, medium and long term
- address risks in a sustainable way
- promote long term management policies for the 22nd century
- aim to be technically sustainable, environmentally accepted and economically viable.
- provide a foundation for future research and the development of new coastal management
- ensure management plans comply with international and national nature conservation and biodiversity legislation.
- incorporate a 'route map' to allow descision makers to make changes to short and medium term plans to ensure a long term sustainability is maintained.
- provide an assessment of the risk associated with the evolution of coast
- provide the policy agenda for coastal defence management planning.
key options for management
hold the line: retain the existing coastline by maintaining current defences defences or building new ones where existing structures no longer provide sufficient protection.
managed retreat: actively manage the rate and process by which the coast retreats.
advance the line: build new defences seaward of the existing line.
no active intervention: on some coastlines it is not economically or environmentally viable to undertake defence works, the value of the built environment does not exceed the cost of coastal defences.
the factors that determine which of the four options are designated for a section of the coast depends on:
- the rate of coastal change (threatened loss of land as well as sea level rise)
- the economic value of land uses put at risk by coastal change (homes, businesses, infrastructure)
- the value of agricultural land at risk, along with habitats of value
- the cost of intervention strategies
integrated coastal zone management
ICZM: originated from the UN Earth Summit of Rio de Janeiro in 1992.
why is it needed?
- coastal zones are some of the most ecologically productive areas in the world.
- natural assets of coasts have for millenia made them popular for settlements, tourist destinations, business centres, ports.
- around 200 million people live near Europe's coastline.
why is concentrating on people and economic activity putting pressure on coastal environments:
- biodiversity loss
- habitat destruction
- conflict between stake holders
- overcrowding in some locations
what issues are coastal environments facing in the future?
- vulnerable to climate change and natural hazards
- sea level rise
- extreme weather events
- lives of people in coastal communities are changing because of these issues.
who are the stakeholders, who have impact on coastal management?
- local council
- EA (environmental agency)
- local people
- organisations (e.g National Trust)
- holiday companies, hotels etc.