Coasts Flashcards
What is input?
Material or energy moving into the system from the outisde
What is output?
Material or energy moving from the system to the outside
What is energy?
Power or driving force
What are stores/ components?
The individual elements or part of a system
What are flows/transfers?
The link or relationships between the components
What is positive feedback?
Where a flow/transfer leads to increase or growth
What is negative feedback?
Where a flow/transfer leads to decrease or decline
What is dynamic equilibrium?
This represents a state of balance within a constantly changing system
Give an example of input
Precipitation, wind
Give an example of an output
Ocean currents, rip tides, sediment transfer, evaporation
Give an example of energy
Energy associated with flowing water, the effects of gravity on cliffs and moving air
Give an example of stores/components
Beach,sand dunes, nearshore sediment
Give an example of flows/transfers
Wind-blown sand, mass movement processes, long shore drift
Give an example of positive feedback
Coastal management can lead to an increase in erosion somewhere along the coast. Groynes trap sediment, depriving areas further down- drift of beach replenishment and this can exacerbate erosion.
Give an example of negative feedback
When the rate of weathering and mass movement exceeds the rate of cliff-foot erosion and a scree slope is formed. Over time this apron of material extends up the cliff face protecting the cliff face from sub aerial processes. Leading to a reduction in the effectiveness of weathering and mass movement.
Give an example of dynamic equilibrium
Constructive waves build up a beach making it steeper. This encourages the formation of destructive waves that plunge rather than surge. Redistribution of sediment offshore by destructive waves reduces the beach gradient which in turn encourages the waves to become more destructive. This is a state of constant dynamic equilibrium between the type of wave and the angle of the beach.
What factors affect wave energy?
- The strength of the wind (determined by the pressure gradient)
- The duration of the wind (the longer the wind blows, the more powerful waves will become)
- The fetch (the distance of open water over which the wind blows. The longer the fetch, the more powerful the waves)
How are waves formed?
As air moves across the water, frictional drag disturbs the surface and forms ripples or waves. In the open sea there is little horizontal movement of water. Instead there is an orbital motion of the water particles. Close to the coast, horizontal movement of water does occur as waves are driven onshore to break of the beach
Compare destructive and constructive waves
Costructive
-Distant weather systems generage these waves in the open ocean
-Low surging waves with a long wavelength
-Strong swash, weak backwash
-Beach gain
-Associated with a gentle beach profile
Destructie
-Local storms are responsible for these waves
-High, plunging waves, with a short wavelength
-Beach loss
-Usually associated with a steeper beach profile
What are tides?
Changes in the water level of seas and oceans caused by the gravitational pull of the moon and a to a lesser extent, the sun.
What is tidal range?
The coastline experiences two high and two low tides in. The relative difference in height between these tides is tidal range.
What are rip currents?
Strong localised underwater currents that occur in some beaches, posing a considerable danger to swimmers and surfers. They are commonly formed when a series of plunging waves cause a temporary build up of water at the top of a beach. Met with resistance from the breaking waves, water returning down the beach (the backwash) is forced down below the surface following troughs and small undulations in the beach profile.
Where are rocky coasts generally found?
-in the UK where do these tend to be?
In high energy environments
- stretches of the Atlantic-facing coast e.g Cornwall
- where the rate of erosion exceeds the rate of depositon
Give 3 examples of erosional landforms that are found in high energy environments
- headlands
- cliffs
- wave cut platforms
What is indicative of a low energy coast?
-in the Uk where do these tend to be?
Sandy and estuarine coasts
- stretches of the coast where the waves are less powerful, or where the waves are sheltered from large waves (e.g bays of Lincolnshire)
- where the rate of deposition exceeds the rate of erosion
Give 3 examples of erosional landforms that are found in low energy environments
- beaches
- spits
- coastal plains
What does wave refraction cause?
Energy to be concentrated on headlands and dissipated at bays
What erosive features may wave refraction cause?
At headlands -cliffs -stacks In bays -depositional features- beaches
How can negative feedback be seen in wave refraction?
Variations in rock strength lead to the formation of headlands and bays
This causes wave refraction which in turn encourages erosion of the headlands and deposition in the bays-working against the erosion of the softer rock that formed the bay originally
-if conditions remained stable for a long period of time a state of equilibrium would be reached where the shape of the coastline remains static due to a balance between the potential erodibility of the rocks and the effect of wave refraction.
Give 6 sources of sediment
- rivers (this will be deposited in river mouths and estuaries where it will be reworked by waves, tides and currents)
- cliff erosion
- longshore drift (sediment is transported from one stretch of coastline (as an output) to another stretch of coastline (as an input)
- wind (wind-blown sand can be deposited in coastal regions). Sand dunes are semi-dynamic features at the coast that represent both accumulations (sinks) of sand and potential sources
- glaciers (in Alaska ice shelves carve depositing sediment trapped within the ice )
- offshore (storm surges can be responsible for input of sediment into the coastal system)
What is a sediment cell?
A stretch of coastline, usually bordered by two prominent headlands, where the movement of sediment is more or less contained
What are the inputs of a sediment cell?
These are derived from the river, coastal erosion and offshore sources such as banks or bars
What are the the transfers of a sediment cell?
These involve longshore (littoral) drift together with onshore and offshore processes such as rip currents
What are the stores of sediment cells?
These include the beach, sand dunes and offshore deposits (bands and bars)
What would you consider a state of dynamic equilibrium?
-how could this balance be upset?
Where erosion and deposition are balanced?
- a surge in river discharge following floods introducing vast amount of sediment into the system
- an extreme storm may erode transport and transfer sediment out of the system
What is weathering?
The breakdown or disintegration of rock in situ
What is mechanical (physical )weathering?
The breakup of rocks without any chemical changes taking place
What are the different types of mechanical (physical weathering)?
- Freeze thaw weathering (chalk is the main rock affected)
- Salt crystallisation (when salt water evaporates, it leaves salt crystals behind. These can grow over time and exert stresses in the rocks. Salt can also corrode rock, particularly if it contains traces of iron
- wetting and drying (rocks such as clay expand when they get wet and contract as they dry. This can cause then to crack and break up)
What is biological weathering?
The breakdown of rocks by organic activity.
How can biological weathering take place on the coast?
- thin plants roots grow into small cracks in a cliff face. These cracks widen as the roots grow which breaks up the rock
- water running through decaying vegetation becomes acidic, which leads to increased chemical weathering
- birds (e.g puffins and sand martins and animals (rabbits) dig burrows into cliffs
- marine organisms are also capable of burrowing into rocks (piddocks) or of secreting aids (e.g limpets)
What is chemical weathering?
Involves a chemical reaction where salts may be dissolved or a clay-like deposit may result which is then easily eroded.
What are the three types of chemical weathering?
- Carbonation (rainwater absorbs carbon dioxide from the air to form a weak carbonic acid. The reacts with calcium carbonate in rocks, such as limestone and chalk, to form calcium bicarbonate which is easily dissolved. The cooler the temperature of the rainwater the more carbon dioxide is absorbed. So carbonation is more effective in winter
- Oxidation (the reaction of rock minerals with oxygen e.g iron forms a rusty red power
- Solution (the dissolving of rock minerals such as rock mi eras, such as halite (rock salt)
What is mass movement?
The downhill movement of material under the influence of gravity
Give an example of mass movement
Feb 2014- the Jurassic coast near Lyme regis in Dorset was affected by a number of dramatic landslips, damaging holiday chalets. The exposed stretch of the coastline is constantly being reshaped.
What are the four main types of mass movement?
- creep
- flow
- slide
- fall
What is soil creep?
- an extremely slow form of movement of individual soil particles downhill
- often involves particles rising towards the ground surface due to wetting or freezing and then returning veritically to the surface in response to gravity as the soil dries out or thaws. This zig zag movement is similar to the of longshore drift
What is landslide
- a block of rock moving very rapidly downhill along a planar surface, often a bedding plane that is roughly parallel to the ground surface. Unlike a mudflow where the moving material becomes mixed, the moving block of material in landslide remains largely intact
- frequently triggered by earthquakes or very heavy rainfall when the slip surface becomes lubricated and friction is reduced.
- tend to be a considerable threat to people and property.
What is a mudflow?
A mudflow involves earth and mud flowing downhill, usually over unconsolidated or weak bedrock such as clay, often after heavy rainfall. Water gets trapped within the rock, increasing pore water pressure, which forces rock particles apart and leads to slope failure. Pore water pressure is a form of energy within the slope system and is an extremely important factor in determining slope instability. Mudflows are often sudden and fast flowing
What is rockfall?
A rockfall involves the sudden collapse or breaking away of individual rock fragments at a cliff face. Often triggered by mechanical weathering or an earthquake. Once broken away from the source the rocks fall or bounce down the slope to form scree at the foot of a slope. Scree often forms a temporary store within the coastal system, with material gradually being moved and transported elsewhere by the store. The scree forms an impute to the sediment cell
What is 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 to the sediment cell. Runoff transfers both water and sediment. Toxic chemicals can contaminate storm water and cause threats to coastal ecosystems
What is solifluction?
Specific to cold periglacial environments
In the summer the surface layer of soil thaws out and becomes extremely saturated because it lies on top of impermeable frozen ground. Known as the active layer, this sodden soil with its blanket of vegetation slowly moves downhill by a combination of heave and flow. Solifluction characteristically formed features called solifluction lobes.
What is landslip of slump?
- Its slide surface is curved rather than flat
- commonly occur in weak and unconsolidated clays and sands often when permeable rock overlies impermeable rock which causes a build up of poe water pressure.
Describe hydraulic action
When a wave advances air can be trapped and compressed. When the wave retreats the compressed air expands. This continuous process can weaken joints and cracks in the cliff, causing pieces of rock to break off. Simultaneously, bubbles formed in the water may implode under high pressure. This generates tiny jets of water which will over time will erode the rock. This process is specifically termed cavitation.
Describe wave quarrying
The action of waves breaking against 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 the quarry on land
Describe corrasion
When waves advance they pick up sand and pebbles from the seabed, a temporary store. When they break at the base of a cliff, the transported material is hurled at the base of a cliff, the transported material is hurled at the cliff foot-chipping away at the rock.
Describe solution (corrosion)
Weak acids in seawater can dissolve alkaline rock (e.g chalk) or the alkaline cement that bonds rock particles together. This is solution
What is 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.
What are the two factors affecting coastal erosion?
-waves
most erosion happens during winter storms (e.g dawlish in 2014 when destructive waves are at their largest)
-rock type (lithology)
physical strength and chemistry. Tough and resistant rocks such as granite erode at slower rates compared to weaker clays and shales.
-Geological structure
e.g cracks joints
-Presence of absence of a beach
beaches absorb wave energy and reduce the impact of waves on a cliff
-subaerial processes
weathering and mass movement will weaken cliffs
-coastal management
e.g groynes
What is traction?
The rolling of coarse sediment along the saa bed that is too heavy to be picked up and carried by the sea
What is 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
What is suspension?
Smaller, lighter sediment picked up and carried within the flow of water
What is solution?
Dissolved load- chemicals dissolved in the water, transported and precipitated elsewhere.Plays an important role in the carbon cycle, transferring and redepositing carbon in the oceans.
What are the characteristics of swash aligned beach?
Tend to form in low energy environments such as bays that are affected by waves roughly parallel to the shore
What are the characteristics of a drift aligned beach?
Form where the waves approach the coast at an angle.. Longshore drift moves sediment along the beach, often cumulating in the shape of a spit, a sediment sink or store. Sediment may be graded along a drift aligned beach. Finer shingle particles are likely to be carried further by longshore drift and and also to become increasingly rounded as they move.
What is a spit?
A long narrow feature made of and or shingle, that extends from the land into the sea. Spits form on drift aligned beaches. Sand or shingle is moved along the coast by longshore drift, but if the coastline suddenly changes direction, sediment begins to build up across the estuary mouth and a spit will form. . The end of the spit will also begin to curve round as wave refraction carries material round into the more sheltered water behind the spit. A ‘compound spit’ occurs where the transport processes are variable over time which produces a series of ‘barbs along the spit’
What is a tombolo?
A beach that has formed between a small island and the mainland. Deposition occurs where waves lose their lose their energy and the tombolo begins to build up. Tombolo’s may be covered at high tide
What is an offshore bar?
Submerged ridges of sand or course 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 sediment input stores. They can absorb wave energy thereby reducing the impacts of waves on the coastline.
Where do steep cliffs tend to occur?
- where the rock is strong and resistant to erosion, such as most igneous and metamorphous rocks
- sedimentary rocks that are dipping steeply or even vertically tend to produce steep and dramatic cliffs, as with the absence of a beach and exposed orientation with a long fetch and high energy waves that encourage erosion and undercutting by the sea
Where do gentle cliffs tend to occur?
- weak or unconsolidated rocks that are prone to slumping
- rocks that are dipping towards the sea also tend to have low-angle cliffs
- a sheltered location with low energy waves and a short fetch will result in subaerial debris building up at the foot if a cliff, reducing its overall angle
- a wide beach will absorb wave energy preventing significant undercutting and steepening
What does the rate of retreat on a cliff depend on?
-the balance of marine factors:
e.g *wave energy
*fetch
*presence of a beach
-terrestrial factors such as sub-aerial processes:
*rock strength
*geology
The most rapidly retreating retreating beaches seem to be composed of very weak rock such as the glacial till cliffs of the Holderness coast
