Coastal landscapes Flashcards
A system
A set of interrelated objects comprising components and processes that are connected together to form a working unit.
Coastal landscapes
They store and transfer energy (kinetic, potential and thermal ) on time scales.
Open system ~ energy and matter can be
transferred from neighbouring systems as an input and transferred to neighbouring systems as an output.
Has 4 components:
- inputs
- stores
- flows
- outputs
input examples
- kinetic energy from wind and waves
- thermal energy from the heat of the sun
- potential energy from the position of material on slopes
- weathering and mass movement from cliffs
- material from marine deposition
A process
Consists of stores and flows.
store e.g ~beach sediment accumulation
flows e.g ~ movement of sediment along a beach by longshore drift.
output examples
- marine erosion
- wind erosion
- evaporation
Equilibrium & dynamic equilibrium
Equilibrium ~ the inputs and outputs of a system are equal.
If this is disturbed , the system produces its own response to this to self regulate. This is known as dynamic equilibrium and is an example of negative feedback.
sediment cells
A stretch of coastline within which the movement of sediment , sand and shingle is largely self contained.
A closed system ~ however not completely due to variations in wind direction and tidal currents , causing sediment to be transferred.
Boundaries ~ determined by the topography and shape of the coastline.
The only inputs into the cell come from the erosion of the land or sea bed.
- There are also many sub -cells of a smaller scale existing within the major cells.
5 physical factors influencing coastal landscape
- wind
-waves
-tides
-geology
-currents - these vary in terms of their spatial (from place to place) and their temporal (over time)
-they can be interrelated and influence each other.
wind
- wave action is the source of energy for coastal erosion and sediment transport.
- Generated by the frictional drag of winds moving across the ocean surface.
- The higher the wind speed , the larger the fetch, the larger the waves and the more energy they possess.
ONSHORE WINDS ~ drive waves towards the coast.
OBLIQUE WINDS ~ cause waves to move obliquely, generating longshore drift.
Fetch ~ the distance over which wind travels over open water
oblique
Neither parallel nor at right angles to a specified or implied line ; slanting.
longshore drift
A geological process that moves sediment along a coastline in a zig zag pattern.
Generated by waves approaching obliquely due to wind blowing at an oblique angle.
wave development and breaking
- a wave enters shallow water
- friction with the sea bed increases
- the wave slows down as it drags along the bottom
- the wavelength decreases, and successive waves begin to bunch up.
- the wave increases in height
- eventually , the wave plunges and breaks onto shoreline.
wave components
Crest ~ the highest part of a wave.
Wave height ~ vertical distance between the crest and the trough.
Wavelength ~ horizontal distance between two adjacent troughs or crests.
Trough ~ lowest part of a wave.
wave frequency
&
wave period
wave frequency ~ the number of wave crests passing a point each second.
wave period ~ the time required for the wave crest at one point to reach the second point.
Formula to determine the amount of energy in a wave in deep water
P=H2T
P ~ power (Kw per metre of wave front)
H ~ height (metres)
T ~ time interval (between wave crests in seconds)
constructive wave
- low wave height
- long wavelength, therefore a low frequency.
- strong swash and a weak backwash
- This is because the backwash returns to the sea before the next wave , meaning the next swash is uninterrupted and retains its energy.
- leads to the build up of beach material to form depositional landforms
- waves spread a long way up the gently sloping beach
destructive wave
- steep wave front
- short wavelength , therefore a high frequency.
- weak swash and a strong backwash
- leads to the removal of beach material to form erosional landforms
- wave does not travel far up the steep beach as energy is directed downwards.
swash
- the movement of water up a beach
- movement is driven by the transfer of energy that occurs when the wave breaks
- the speed of the swash decreases as it travels further up the beach due to friction and the uphill gradient of the beach.
back wash
- the movement of water down a beach
- movement is driven by gravity and always occurs perpendicular to the coastline.
Beach gradient and wave type
These have and important and complex relationship.
HIGH ENERGY WAVES ~ remove material from the top of the beach to the offshore zone, reducing the beach gradient.
LOW ENERGY WAVES ~ build up the beach face , steepening the profile.
This is due to :
- wave steepness
- angle of waves
- sediment particle size
Tides
The periodic rise and fall of the sea surface , produced by the gravitational pull of the moon and sun.
- The moon pulls water towards it
- This creates a high tide
- There is a compensating bulge on the opposite side of the earth.
-At locations between the two bulges there is a low tide.
-As the moon orbits the earth the high tide follows it.
When do the highest and lowest tidal ranges occur
HIGHEST TIDES ~
- occur when the moon , Earth and sun are aligned and so the gravitational pull is the strongest.
- This causes spring tides with a high tidal range
LOWEST TIDES ~
- When the moon and sun are at right angles to each other the gravitational pull is weak.
-Causes neap tide with a low tidal range
Tidal range
The vertical difference in height between high tide and low tide.
Influences:
- where wave action occurs
- weathering processes
- impact of processes between tides ( e.g scouring)
Enclosed sea ~ tidal ranges are low so wave action is restricted to a narrow area of land.
Funnelled coast ~ tidal range can be as high as 14 metres.
Geology
Refers to the lithology and structure of the coast line.
Lithology
- Describes the chemical and physical structure of rocks.
- This will impact physical processes such as weathering , mass movement and erosion.
CLAY ~ weak rock which will erode faster.
BASALT ~ MADE of dense interlocking crystals , meaning it is highly resistant and more likely to form prominent coastal features.
CHALK & LIMESTONE ~ susceptible to chemical weathering due to their calcium carbonate content which is soluble in weak acids.
Structure
- Refers to features of jointing, faulting and bedding planes in rocks and also to their permeability.
Affects the shape of the coastline :
CONCORDANT ~ rocks lie parallel to the coastline.
DISCORDANT ~ rocks lie at right angles to the coastline.
Affects the dip of rocks towards the coastline :
LANDWARD dipping rock layers ~ steep cliffs.
SEAWARD dipping rock layers ~ cliffs follow the angle of the dip.
Rip currents
Narrow currents in the surf zone that move quickly away from shore (up to 5mph).
- play an important role in the transport of coastal sediment.
- caused by TIDAL MOTION or by waves breaking at RIGHT ANGLES to the shore.
- A cellular circulation is generated by differing wave heights parallel to the shore.
- water from the top of breaking waves with a large height travels further up the shore and returns returns through the adjacent area where the lower height waves have broken.
3.once rip currents are forms , they modify the shore profile by creating CUSPS ( a point of transition ) which hep perpetuate (sustain) the rip current, channelling flow through a narrow neck.
Ocean currents
- the global pattern of ocean currents is generated by the earths rotation and the currents are set in motion by the wind.
- WARM ocean currents ~ transfer heat from low latitudes (equator) to high latitudes (polar regions).
- COLD ocean currents ~ transfer heat from high latitudes to low latitudes.
- Affects air temperature , therefore SUB-AERIAL PROCESSES.
sub-aerial process ~ collective term for weathering and mass movement processes.
Sediment budget
The balance between the input and removal of sediment.
Total input - total output
Requires the identification of sediment sources and sinks.
Positive budget:
- more material added than removed
- shoreline builds to the sea (advances)
Negative budget:
- more material removed than added
- shoreline recedes landward.
Sources of sediment
- rivers/ streams
-estuaries
-wave erosion
-cliff erosion
-longshore drift
-erosion of inland areas by water , wind , ice , mass movement and weathering.
how humans use beach nourishment to maintain sediment equilibrium.
- sediment brought by a lorry and dumped on the beach before being spread out by bulldozers (machine).
- sand and water can be pumped onshore by pipeline from offshore sources, low bunds hold the mixture in place while the water drains away and leaves the sediment behind.
Low energy coasts
- low wave energy
- deposition is greater than erosion
Landforms formed:
- beaches
-spits
Examples:
- sheltered bays
- estuaries
- inlets
High energy coasts
- high energy waves
- strong and steady prevailing wind
- erosion is greater than deposition
Landforms formed :
- headlands
- wave-cut platforms
- cliffs
Examples:
- Atlantic coasts
- Cornish coasts
