Coastal Landscapes Flashcards
Define erosion
The wearing away and / or removal of rock and other material by a moving force.
What are the 4 types of erosion?
Abrasion
Attrition
Hydraulic action
Solution
Define abrasion
When the waves armed with rock particles scour the coastline and rock is thrown against rock.
Define attrition
Rock particles transported by wave action collide with each other and with coastal rocks, progressively wearing away. Become smoother and rounder, eventually becoming sand.
Define hydraulic action
Waves break against a cliff face, and air and water trapped in joints becomes compressed. Pressure is released and air and water expand, widening the crack.
Define solution
Dissolving minerals in coastal rock. Usually limited as pH of water is around 7-8. Not acidic enough.
Define transportation
Movement of material by the kinetic energy of a medium, such as water, wind or ice.
Name the 4 types of transportation
Traction
Saltation
Suspension
Solution
Define traction
Large boulders and particles pushed along the seabed. These roll continually.
Define saltation
Irregular movement of material which is too heavy to be carried continuously. Bounce along the surface.
Define suspension
Fine material like sand, silt and clay can be carried by currents. Gives a murky appearance.
Define longshore drift
Movement of sediment by waves and currents along a coastline.
Define deposition
The laying down of sediment transported by rivers, waves and glaciers, as energy levels decline, and become more laminar.
Define weathering
The in situ breakdown of rocks at the Earth’s surface by physical, chemical and biological processes.
Define physical weathering
Break up of rock in the place where it lies by mechanical processes. The minerals in the rocks are not changed. The rock itself breaks up, often along lines of weaknesses such as joints.
Define chemical weathering
Break up of rock in the place where it lies by chemical processes. Composition of rock is changed.
Define biological weathering
Breakdown of rock by plants and animals.
Explain salt crystallisation
Physical
Water is slightly saline and when this evaporates salt crystals are left. As these become larger, the rock breaks up.
Explain freeze-thaw
Physical
Temperatures drop below freezing, water trapped in cracks in the rock freezes, causing the rock to crack further, due to ice expanding by 10%. Thawing releases pressure. Many times causes rock to break off.
Explain thermal expansion
Rock expands when heated and contract when cooled. Outer layers warm faster and cool down faster than inner layers, internal stress caused, leading to outer layer to peel off.
Explain pressure release
Physical
Many rocks formed under immense pressure so when exposed to the atmosphere, the slight decrease in pressure causes the rock to expand. This leads to cracks, weakening the rock.
Explain hydration
Chemical
Hydrogen in water reacts with minerals in the rock. Hydrogen ions in water replace cations in the mineral decomposing the rock.
Explain oxidation
Chemical
Rocks exposed to the oxygen in the air or water. E.g. rusting. Rocks will crumble more easily.
Explain solution
Chemical
Dissolving of certain minerals in water. Rate of solution is dependent on acidity.
Explain carbonation
Rainwater and carbon dioxide mix to form carbonic acid. The weak acid reacts with minerals in the rock, in particular limestone, and dissolves it. Deepens and widens the joints, making the rock weaker
Explain hydrolysis
Chemical
Breakdown of rock by acidic water to produce clay and soluble salts.
Explain organic acids
Biological
Areas with limited vegetation cover, rain removes soft, fine material from between large boulders. Humid acid released from the decomposition of vegetation speeds up this process.
Explain burrowing
Biological
Animals burrow into the rocks, breaking them apart. Seaweed attaches itself to rocks and the swaying causes the rocks on the seabed to break apart.
Explain tree roots
Biological
Tree roots follow joints in rocks. This widens the the joints and weakens the rock so it shatters.
Describe and explain the process of forming cliff and shore platforms
Vertical cliffs due to resistant rock with horizontal strata.
Upper sections are weakened by weathering, such as freeze-thaw, carbonation oxidation etc.
Erosion along the base creates an undercut, or a wave cut notch, through marine erosion.
Cliff face is unsupported and so collapses as rock fall.
Fallen material becomes smaller due to attrition, and is removed by destructive waves acting on the beach.
A shore platform is exposed, as fallen material is taken out to sea in the backwash.
The platform is flat (0-3degrees) and very wide. Creates increased friction so waves break on the platform not cliff base, so cliff erosion slows down.
The uneven surface is modified over time as the area is exposed for longer at low tide, so more weathering.
May develop a ramp at the high water mark and a cliff at the low water mark, due to a small tidal range so greater erosion happens at the HWM or LWM for longer.
Describe and explain the formation of goes and blowholes
There is a line of weakness in resistant rock, determined by the rock structure and the presence of vertical joints e.g. limestone.
The rock erodes to create a tunnel cave into the cliff, e.g hydraulic action, pounding or solution.
A vertical joint in the cave roof collapses, due to further weathering and erosion, leaving it unsupported.
This creates a geo vertical chimney (blowhole) e.g. Trevone, Cornwall (25m deep).
Erosion and weathering of the cave roof continues at the inlet.
The cave roof collapses entirely and rock fall may occur.
A narrow, steep inlet is created (geo) e.g. Huntsmans Leap, Pembrokeshire (35m deep)
Describe and explain how headlands and bays form
Along a discordant coastline.
The less resistant rock is eroded through processes such as hydraulic action, abrasion etc. This leaves a bay.
The more resistant rock is eroded slowly, leaving a headland to form.
E.g. Swanage Bay.
What other process helps in the formation of headlands and bays?
Wave refraction
What is wave refraction?
Waves approach the shore at an oblique angle.
The section of the wave in the shallower part of the water decelerates due to friction.
The wave that is in the deeper part of the water moves forward at a consistent velocity.
Wave refracts so that its orientation is more parallel to the shape of the coastline.
Describe and explain the formation of cave, arch, stack and stump
Vertical cliffs - strata of more and less resistant rock.
Erosion at the base e.g. hydraulic action, abrasion etc.
Creates a crack in the rock, which enlarges to create a cave, through continued erosion and pressure release.
Same process occurs on the opposite side of the headland.
Cave erodes backwards, meets and forms and arch, when eroded all the way though e.g .Durdle Door, Dorset.
Arch becomes higher and wider, from further sub-aerial processes.
Arch collapses to leave a stack, under gravity and the roof being unsupported.
Erosion at the base of the stack e.g HA, abrasion, attrition, solution.
Stack collapses to form a stump e.g. Old Harry Rocks, Jurassic Coast, Dorset.
Define the coast
The zone where the sea interacts with the land.
What are the 3 main components of a coastal system?
Inputs, stores, outputs.
Name some energy inputs
Solar, wind, waves, currents, tides.
Name some sediment inputs
Artificial sediment, geology, offshore marine material
Name some erosional landforms (stores)
Headlands and bays Wave cut platforms Geos and blowholes Cave, arch, stack and stump Cliffs
Name some depositional landforms (stores)
Beaches On-shore bars Spits Tombolos Sand dunes Estuaries Salt marsh
Name some coastal ouputs
Sediment removed by aeolian and marine erosion
Evaporation
Dredging /sand mining
Offshore bars
Define kinetic energy
The capacity to do work as a result of motion
Define potential energy
The capacity to do work that a body posses by virtue of its position and that its potentially transferable into another form of energy
Define thermal energy
The capacity to do work as a result of heat
Define solar energy and an example
Powers the hydrological cycle, transferring water from land to coastal zone e.g. atmospheric processes winds=waves
Define gravitational energy and example
Gravitational pull of the sun and moon creates tides. Gravity is key for downward movement of sediment e.g. mass movement
Define geothermal energy and example
Tectonic activity =uplift e.g. convection currents
Describe the process of changes in the coastal landscape in terms of inputs and flows of energy
1) the sun creates solar/thermal energy
2) thermal energy affects the global climate by…
3) warms part of the earth’s surface so that hot air rises
4) results in low and high pressure areas forming and air moves between the two areas as wind
5) wind blowing over the oceans as kincetic energy creates waves
6) waves possess potential energy (in its position above the wave trough) and kinetic energy (due to motion of water in waves)
7) as the wave breaks potetial energy is transferred to kinetic energy which moves the wave up the beach as the swash
8) when the wave has no more kinetic energy the swash stops travelling up the beach
9) gravitational potential energy draws water back down the beach as the backwash
Describe the changes in energy that occur during a cliff fall
1) erosion and weathering occurs weakening cliff face. More susceptible to gravitational energy
2) the waves which have potential and kinetic energy continually erode cliff face in the swash
3) backwash occurs removing sediment from the cliffs when the waves have no more kinetic energy
4) gravitational energy causes the cliff to eventually collapse due to the pressure and weight from higher up, causing cliff fall iin mass movement e.g. rock fall
What is equlibrium in terms of the coast?
Steady state where inputs equal output, so the beach or coastline remains the same - unchanged.
This can lead to dynamic equilibrium if the position of equlibrium is disturbed and the system readjust to reach equlibrium.
What is positive feedback?
Leading to durther changes on the coastline
What is negative feedback?
Reduces the effect of the change
Give one way in which sediment can flow through a coastal system using a river as an example
Sediment is carried in a river
River energy decreases at the river mouth so sediment is deposited
Sediment stored in an estuary
High energy waves erode sediment and transport out to sea
Sediment moved to an offshore bar
Describe how sediment initally located on a cliff face may be moved through the coastal system
High energy waves erode sediment and transport it out to sea
Energy decreases so sediment is deposited
Sediment stored in an offshore bar
Sediment is carried in a river
Sediment stored in an estuary
What is a sediment cell?
Stretch of coatsline and nearshore usually bordered by 2 prominent headlands, where the movement of sediment is mostly self-contained. 11 in the UK with smaller subcells within a sediment cell
How can sediment cells be viewed as a closed system?
Sediment is not transferred between two cells
Stroed as beaches, sand dunes, estuaries and nearshore zone
Trasnfers by longshore drift
Inputs and outputs restricted to energy - solar, wind, waves, tides, and graviational potential
Boundaries are determined by the shape and topography of the coastline - prevents the transfer of sediment to adjacent cells.
How can sediment cells be viewed as an open system?
Sediment transferred between cells
Wind and tidal currents transfer sediment
Sourced from fluvial and marine deposition, weathering and mass movement of cliffs
E.g. littoral drift divides - net movement of sediment output causing erosional processes and landforms - eroding of beaches and cliffs
Occur without any change in shape of coastline - wave conditions caused a change in drift direction e.g. Sheringham, Norfolk. Sediment moved outwards.
What is the result of sediment cells being both an open and closed system?
Causes dymanic equilibrium to be reached, due to the process of both positive and negative feedback combined
Describe terrestrial inputs of sediment
1) fluvial deposits = river more laminar near mouth causing sediment to be deposited - 80% - mostly during floods
2) marine eroison = enhanced by geology of rock - unconsolidated or less resistant e.g. Holderness, Lincolnshire vs igneous rock of Cornwall
3) longshore drift = from output to input using the swach and backwash + energy
4) weathering and mass movement
5) aeolian processes = wind-blown sand can be deposited in coastal regions e.g. hot, arid environments. Sand dunes show accumulations (sinks) and potential sources.
Describe offshore sediment input
Causes marine deposition e.g. sediment from offshore transferred to coastal zones by waves, tides and currents. Barrier beaches like Start Bay, Devon and Chesil Beach, Dorset. Tropical cyclones and tsunami’s can also cause inputs of sediment into the coastal system
Describe humn inputs of sediment
Beach nourishment - maintains sediment level on beaches and coatsal areas. Protect coastal locations from the energy of waves. Maintains sediment equilibrium by providing negative feedback to counter the removal of sediment in positive feedback.
Give an example of an arch formation
Durdle door, Dorset
Give an example of a stack formation
Dun Briste, Ireland
Define prevailing wind
The dominant wind source e.g. south-west in the UK
Define fetch
The distance of open water in one direction from a coastline, over which the wind can blow
How does wind create waves?
1) wind blows over the water’s surface
2) the wind creates frictional drag
3) kinetic energy transferred from the wind to waves
4) water particles move in an elliptical motion as waves pass
5) this causes movement in the upper surface of the water, seen as a wave
What term is used to describe any process involving wind?
Aeolian
How can wind affect the coastline?
1) Erosion = wind is able to pick up and carry sediment (e.g. sand on a beach). The sand can then be ‘thrown’ at other landscape features causing erosion through abrasion.
2) Transportation = wind picks up sediment and then carries it to a new location. E.g. sand on a wide, flat beach is blown inland to form sand dunes.
What does the prevailing wind determine?
The direction of the swash moving up a beach during longshore drift
How are the fetch and wave height linked?
The higher the fetch, the greater the wave height e.g. a fetch of 7000km causes a height of 30m waves from the Dominican Republic to Cornwall
What is wind duration?
The longer the wind blows for, the greater the wave energy, because more energy can be transferred as kinetic energy into the waves. The shorter the wind duration, the less energy transferred, so the lower the wave energy.
Define the wave crest
Top/peak of the wave
Define wave trough
Base/bottom of the wave
Define wave height
Vertical distance between wave crest and wave trough
Define wavelength
Horizontal distance between two consecutive crests
Define wave base
Deep water unaffected by the movement of waves
Define stillwater level
The horizontal level of water through the middle of the wave
Define ocean depth
Distance from the stillwater levelto the ocean bottom
Define potential energy of a wave
The highest point in the wave above the wave trough
Difference between wave frequency and wave period
Wave frequncey is the number of waves per minute
Wave period is the time between crests
Equation for calulating wave energy
Power(kW/m) = height^2 (m) x time (secs)
Describe constructive waves
Strong swash, weak backwash
Long wavelength (low amplitude as well)
Low frequency (6-8 per min)
Normally break as spilling waves
More deposition of sediment as lower energy (laminar)
Form a steep beach overtime and a berm forms from deposition
Describe destructive waves
Weak swash, strong backwash
Short wavelength (large amplitude)
High frequency (12-14 per min)
Removal of sediment from the coastline offshore
Occur durig winter months when more storms
Often plunging waves
Results in formation of beach cliffs and wave cut notch. Flatter beaches.
Describe a spilling wave
Form on gently sloping sea beds. Waves are steep and break some distance forom the shore. White foam forms at the wave crest as it breaks and becomes a line of low level surf as the wave approaches the shore.
Describe plunging waves
Form on steeply sloping sea bed. Waves are fairly steep and tend to curl over and drop vertically down onto the beach as they break.
Describe surging waves
Low level waves breaking ont oa steeply sloping sea bed. The waves tend to slide forward without really breaking fully.
What causes tides?
The gravittational attraction of the moon and the sun to the oceans
What are spring tides?
The moon and sun are in allignment witht he earth. This causes the highest high tide and lowest low tide.
What are neap tides?
The moon and sun allign at a right angle /perpendicular to the earth, causing the lowest high tide and highest low tide
Define tidal range
Difference in water level between high and low water mark
How does tidal range affect coastal processes?
Erosion of coastline, particulary at high tide with destructive waves.
Weathering e.g. salt crystallisation particulalry at low tide on wave cut platforms
Deposition at low tide
Transportation at high tide
Why do high tides vary between different locations?
The moon orbits the earth, at the same time as the earth rotating on its axis. The difference in time between certain points on the rotation means tides can be slightly different. The shape of the coastline also influences the height of the tide. Steeper coastline means shorter tidal range, whilst a flatter coastline allows for a longer tidal range due to reduced friction.
Define semi-diurnal rides
2 high tides and 2 low tides (approx. 24hrs)
Define diurnal tides
1 high tide and 1 low tide (approx. 24hrs) e.g. Antarctica
Define current
Identifiable flow in a water body
How do tidal currents affect erosion and deposition processes in estuaries?
Sediment is entrained and carried inland due to flooding, during a flood tide = rising tide
Once high tide has been reached the current reverses and the ebb tide comes into effect = falling tide
What is a longshore current? How do these affect shorelines?
Waves breaking offshore at an angle, causing water to move along the coastline. This causes sediment to be transported along the coastline, which will be deposited further along. High velocity with a steep beach profile, and the wave breaks at an angle - more destructive
3 main types of rock
Igneous
Sedimentary
Metamorphic
Example of igneous rock
Granite
Example of sedimentary rock
Chalk or sandstone
Example of metamorphic rock
Slate
Define lithology
Physical and chemical composition of rocks which affect their resistance to erosion and the types of liffs that they form
Igneous rocks
Rock that have solidified from the molten /partiallly molten material
Metamorphic rock
Rocks that result fromt he complete recyrstallisation in the solid state under temp. +pressure
These erode the slowest due to being dense and having interlocking crystals
Form high, vertical cliffs 500m high
Clay, glacial deposits, mudstones (sedimentary rocks)
Erode quicker:
Unconsolidated material so bonds weaker between particles and easily broken
Can’t form steep slopes so cliffs no more than 50m
Chalk (sedimentary rocks)
Soft rock but resistant to erosion - form steep, high cliffs especially if:
Horizontal bedding planes
Well compressed/fewer joints so a stronger structure
Limestone (sedimentary rock)
Clear vertical (joints) and horizontal (bedding planes) cracks in the rock
Cracks weakened by the weathering/erosion
Strong bonds within the rock, so can form steep, high cliffs
