Coasts (non landforms)
Systems
System make up
Inputs
Fluvial sediment, energy from etc
Ouputs
Erosion
Throughputs (flows/transfers)
Longshore drift
Stores
Beaches and areas of sediment accumaltion
Equilibruim
When inputs and outputs in a system are equal the system is in equalibruim.
When the inputs and outputs are disrupted the system works to restore equiblruim. -- Dynamic equilbruim
Closed and open systems
Closed sytem --> energy can enter and leave, but matter can't.
Open system --> energy and matter can leave and enter.
Sediment cells
Closed system
However some sediment can cross into over cells under the right conditions.
11 around the coast of England.
Factors infleuncing coastal landscapes:
Winds
Creates waves by blowing over the seas anc creating frication on the sea. Higher the wave speed and longer the fetch the greater the energy of waves.
Fetch -- how far the wind blows across the sea
Aeolian processes can transport material and edrode themselves, however these are weak.
Waves
Wave anatomy
Crest -- highest point of the wave
Trough -- lowest point of the wave
Wave length -- distence between either: two crests or two troughs
Wave hieght -- distence between crest and trough of the wave
Waves breaking
Waves begining to break when the water becomes more shallow. Water mollecules begin to drag on the seafloor this slows down the speed of the bottom of the wave (deepest part of the wave slows down more then the top). The wave steepens as the crest advances ahead of the base until the water depth is less then 1.3*wave height. This causes the wave to topple and break.
There are three ways waves break
Spilling
Plunging
Surging
Steep waves break on a gentle slope, this causes the waves to gentle spill forwards.
Moderatly steep waves breaking onto steep beaches, this causes the water to plunge verticlly downwards as the crest curls over.
Low angle waves breaking on steep beaches, this causes the wave to slide forward and this can mean the wave deosn't break.
Swash and backwash
Swash is the movement of water and energy up the beach, as this looses energy it will deposit material.
Backwash is the movement of water backdown the beach (driven by gravity), a strong backwash will lead to the erosion of beach.
Types of waves
Constructive
Low frequency
Low wave height
Long wavelength
Usually spilling waves
Stong swash and weak backwash
Destructive
High wave height
Shorter wave lengths
Higher frequency
Usually plunging waves
Strong swash and strong backwash
Tides
Tidal range -- difference between high tide and low tide -- where most wave action and sub-arial processes occur.
Types of tides
Neap tides -- higher tidal range (sun and moon aligned).
Spring tides -- lower tidal range (sun and moon pulling in different directions).
Geology
Made up of two different factors
Lithology
Structure
Physical and chemical composition of the rocks.
These are the properties of individual rock types, ie: jointing, bedding and faulting.
Weak lithology = easier to erode
Stronger lithology = harder to erode
These normally make up headlands.
These normally make up bays.
Structure also defines the two types of coast
Concordant -- rocks run parrel to the coast.
Discordant -- rocks lie at a right angle to the coast.
Strata (the angle of the rocks)
Horrizontal and landward dripping strata support steep cliffs.
Currents
Terrestrial
Offshore
Human
Rip currents play an important role in moving sediment around, as well as creating cusps on sand beaches.
Ocean currents
Warm ocean currents move warm water to the poles (North Atlantic Drift).
Cold ocean currents move cold water to the equator.
Ocean currents transfer heat energy which can infleunce sub-arial processes.
Fluvial sediment is the biggest provider of sediment to coastal system (providing 80% of sediment).
Wave erosion also acts to provide a large amount of sediment to coasts, in some areas with weak cliffs wave erosion (eroding cliffs) can provide 70% of the sediment.
Longshore drift can move sediment about, from one coastal area to another.
Construtive waves bring sediment to the shore from offshore locations. Wind also moves sediment from other areas such as exposed spits and bars (this sediment is very fine those).
Humans can add sediment to areas so as to prevent the erosion of beaches (beach replenishment), this sediment can either come from offshore sources that are pumped onto the beach or brought in from land.
Geomorphic processes
Weathering
This is the breakdown of rock in situ through either physical or chemical actions.
Physical
Freeze thraw
Pressure release
Thermal expansion
Salt crystalisations
Chemical
This occurs when the chemical compostition of the rock is changed by the weathering process.
This is where rock is broken down through physical processes and where no changes to the chemical structure occurs.
Oxidation
Carbonation
Solution
Hydrolysis
Hydration
Biological
This can contian componets of both physical and chemical processes
Tree roots -- physical
Organic acids -- chemical
Mass movement
This is where the force trying to make material on a slope move is greater then the forces trying to stop it move.
In a coastal system mass movement mainly impacts cliffs. This can lead to the transfer of rocks and regolith (unconsilidated rocks on the surface) to the shore below.
Main processes:
Rock fall
Slides/slumps
Rocks become detached from a cliff face and then fall of the cliff (if it is at a degree of 40o or greater).
This is the movement of material downwards along a fualt or beding plane.
Slumps are rotional slides and are caused by material getting heavier when it is wet .
Wave processes
Erosion
Transportation
Depostion
Solution
Abrasion
Attrition
Hydraulic action
Pounding
Solution
Suspenion
Traction
Saltration
This is where material is droped by waves when they lose energy and are unable to cary the sediment. Heavier material is droped first as it requires the most energy to carry.
Fluvial
Erosion
Fluvial erosion in the upper regions of the river provides 80% of the coasts sediment budget.
Transportation
Fluvial sediment is transported down stream until it reaches the oceans.
Depostition
As rivers enter the sea they deposit material as they lose energy, this is because they are following into either static seas, or seas going in the opposite direction to the river.
Aolian
Erosion
Wind does do some erosion, but it is limited as the energy required to move sediment is higher then a lot of winds have.
Transportation
Wind can use all the transportation methods execpt sollution, however winds can only move very small particles (the largest they can move is 2mm in diameter).
Depostion
This occurs when the wind speeds drop, this is caused mainly by frication. Deposition occurs mostly in land as there is greater frication.
Human activitity in coastal landscapes
Humans can have intentional infleunces on the coastal system, where we activly try and change the coastal system.
Or we can have unintentional impacts on the coastal landscapes through actions not designed to damage them.
The most common interaction humans have with coasts to to mitigate processes such as wave erosion. This can be done through multiple prevention techniques:
Groynes -- These are stone or wooden barriers that are placed along the beach to prevent longshore drift from moving sediment around. They can however deprive areas along the coast of sediment by preventing the movement.
Beach replenishment -- This is a process of adding sediment to a beach so as to off set the impact of erosion.
Sea walls -- These are physical strutures that are built to prevent the waves from eroding the land behind them.
Rip raps -- These are layers of rubble in front of a coast to prevent erosion of the coasts, they are very similar to sea walls.
Gabion -- These are mesh boxes flled with rocks that are meant to reduce the energy of waves.
Above are hard engineering and Bellow is soft engineering
Planting Maram grass -- This is a type of grass that can be used help bind the sand together, this means that it is hard for the sand to be eroded.
Humans use of coastal landscapes can have an impact on the sediemnt budget by either removing sediment through sand dredging, damming rivers to prevent sediment flow or polluting seas with oceanic trade.
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