Summary
Summary OCR AS/Alevel geography: coastal ;landscapes full notes
- Module
- Coastal landscapes
- Institution
- OCR
OCR AS/Alevel geography: coastal ;landscapes full notes
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1.1 How can coastal landscapes be viewed as systemsThe components of open systems
- Coastal landscapes are considered open systems because energy and matter can be transferred to and
from neighbouring systems
- Coastal landscapes have inputs, outputs and processes
- Inputs are what enter the system and are separated into energy (waves, wind, tides, sun, currents) and
sediment (o shore deposits, uvial deposits, estuaries)
- Outputs are what is transferred to a neighbouring system (evaporation)
- Processes are what store the energy (coastal landforms) and what transports the inputs (coastal
processes)
System feedback in coastal landscapes
- When a system’s inputs and outputs are equal a state of equilibrium exists within it
- When the system is disturbed the system will undergo dynamic equilibrium
- This is where the system produces its own response to the disturbance in order to restore equilibrium
(negative feedback)
Negative feedback
- Acts to lessen the e ects of the original change and ultimately reverse it
Positive feedback
- When the change causes a snowball e ect that continues or accelerates the original change
Sediment cells
- Sediment cells are where sediment is moved repeatedly within a distinctive area
- Both erosion/weathering and deposition is present within each cell
- The boundaries of sediment cells tend to be headlands and peninsulas which act as natural barriers to
stop further movement of the sediment
- Sediment cells are closed systems
- However, they are not truly closed systems as ne particles may move between systems due to
variations in wind and tidal currents
Sediment budgets
- Each sediment cell has a sediment budget
- Sediment budget refers to the balance between sediment added to and removed from the coastal system
Positive budget
- More inputs than outputs to the system
- There will be more deposition so the coastline builds up
Negative budget
- More outputs than inputs to the system
- More sediment is removed so the coastline recedes
Physical factors which in uence coastal landscape systems
Winds (aeolian processes)
- The source energy for coastal erosion and sediment transportation is wave action
- Wave energy is generated by the frictional drag of winds moving across the ocean surface
- The higher the winder speed and the longer the fetch, the larger the waves will be and the more energy
they posses
- When the winds blow at oblique angles towards the coast the waves they generate will also be at an
online angle which will cause longshore drift
- These aeolian processes are able to carry out erosion, transportation and deposition
Waves
Wave anatomy
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,- Crest: highest point of the wave
- Trough: the lowest point of the wave
- Wave height: vertical distance between the crest and the trough
- Wavelength: the horizontal distance between two adjacent crests or troughs
Breaking waves
- Swash- the movement of water up a beach, driven by the transfer of energy when the wave breaks
- Backwash: the movement of water down the beach, driven by gravity and it always occurs perpendicular
to the coastline
Constructive waves
- The waves break spilling forwards
- Have long wavelengths
- Due to the long wavelength, the backwash returns to the sea before the next wave breaks
- The next swash movement isn't interrupted so the energy is retained
- This means energy exceeds the backwash energy so the material is deposited rather than removed
- Form gently sloping beaches
- Have low wave heights (less than 1m)
- Have lower wave frequencies and break about 6-9 times per minute
Destructive waves
- Waves break by plunging forward
- This means there is little forward transfer of energy to move sediment up the beach
- Forms steep beaches
- Friction from the steep beach slows thee swash so it docent travel far before it returns to the sea as
backwash
- The backwash energy exceeds the swatch energy so the material is removed rather than deposited
- Shorter wavelengths
- Due to this, the next swash is slowed
- Have high wave heights (more than 1m)
- Have higher frequencies and break 14 or more times per minute
Tides
- Tides are the periodic rise and fall in the sea level
- Tides are caused by the gravitational attraction of the moon and sun on the oceans
- Outward bulging in oceans closest to the moon creates high tides
- During this water is drained from areas between the bulges which causes low tides
- When the sun and the moon are aligned there is a combined gravitational force creating a big bulge that
forms spring tides
- Spring Tides are what create high (high tides) and low (low tides) creating a large tidal range
- When the sun and the moon are not in line the gravitational forces interfere with each other meaning the
gravitational pull is weaker creating neap tides
- Neap tides have a small bulge and a smaller tidal range
- The tidal range in uences where wave action and subaerial processes occur
Geology
Lithology
- Describes the physical and chemical composition
- Basalt, chalk and limestone are made of dense interlocking crystals that are more resistant to erosion and
weathering
- They are more likely to form prominent coastal landforms such as cli s and headland
- Soft rocks such as clay have weak bonds between their particles making them less resident to
geomorphic processes and mass movement
- Chalk and limestone are vulnerable to chemical weathering as they predominately contain calcium
carbonate, which is soluble in weak acids
Structure
- Refers to the properties of individual rock types
- It includes jointing, faulting, bedding and the permeability of rocks
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, - Porous rocks such as chalk have tiny pores that separate the mineral particles
- These pores absorb and store water (primary permeability) which can crystallise or freeze leading to the
rock being weathered
- Limestone is also permeable as it has many joints (secondary permeability) which are enlarged easily be
solutions
- Rock outputs that run parallel to the coast produce concordant coastlines
- Rock outputs that lie at right angles to the coast produce discordant coastlines
Types of rock
Igneous rock
- Formed by the cooling and solidi cation of magma
- They are resident to erosion as they contain interlocking crystals and have very few joints
- They are impermeable
- Igneous coasts erode at less than 0.1 cm per year
Metamorphic rock
- Are formed through the process of metamorphism where sedimentary and igneous rocks are altered in
structure and composition as they are exposed to extreme pressure and heat forming larger crystals (re-
crystallise)
- They are impermeable
- Are resistant to erosion due to the heat and pressure they underwent
- However, they may exhibit crystals that are only printed in one direction which causes weakness
- Metamorphic coasts experience erosion rates of 0.1-0.3m per year
Sedimentary rock
- Formed by the cementation or compaction of layered accumulation of mineral particles from weathering
and erosion of preexisting rock
- They are porous due to the air spaces formed as they were compressed
- They are more clastic so they are less resistant to erosion
- Erosion varies from 0.5-10cm per year
- Older sedimentary rock is more resistant to erosion
Currents
Rip currents
- On a local scale
- Are strong o shore ows and occur when breaking waves push water up the beach
- Rip currents form when the backwash can’t ow back out to the sea easily
- The returning backwash moves through the point where lower section waves have broken
- This creates a strong backwash
- Rip currents modify the beach by creating cusps that penetrate the current and take material out to sea
Ocean currents
- On a larger scale
- They are generated by the earth’s rotation and by convention
- Warm ocean currents transfer heat while cold ocean currents do the opposite
- The current a ects the strength of geomorphic processes
- The transfer of heat engird impacts air temperatures and therefore subaerial processes
Where does coastal sediment come from
Terrestrial
River erosion
- Inputs sediment into the coastal sediment budget
- Especially signi cant for coasts with a steep dragnet where rivers directly deposit their sediment coast
- Sediment delivery occurs mostly during oods
- In some locations, 90% of coastal sediment comes from rivers
- The origin of this sediment is the erosion and weathering of inland areas by water, wind and ice, as well
as mass movement
Wave erosion
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