Coasts as a system
Inputs,outputs, energy, stores/components, flows/transfers,positive/negative feedback,dynamic equilibrium
Inputs
Material or energy moving into the system from the outside
Examples
Precipitation
Wind
Output
Material or energy moving from the system to the outside
Example
Ocean currents
Rip tides
Sediment transfer
Evapouration
Energy
Power or driving force
Examples
Energy associated with flowing water
The effects of gravity on cliffs
Moving air
Stores/components
The individual elements or parts of a system
Examples
Beach
Sand Dunes
Nearshore sediment
Positive feedback
Where a flow/transfer leads to increase or growth
Coastal management can inadvertently lead to an increase in erosion elsewhere along the coast. Groynes trap sediment, depriving areas further down-drift of beach replenishment and this can exacerbate erosion. Seawalls can have the same effect by transferring high energy waves elsewhere along the coast
Negative feedback
Where a flow leads to decrease or decline
When the rate of weathering and mass movement exceeds the rate of cliff-foot erosion a scree slope is formed. Over time, this apron of material extends up the cliff face protecting the cliff face for sub aerial processes. This leads to a reduction in the effectiveness of weathering and mass movement
Dynamic equilibrium
This represents a state of balance within a constantly changing system
Coastal land forms and Landscapes
The concepts of Landforrm and landscapes and how related landforms combine to form characteristic landscapes
Landscape
The coastal landscape is the "big picture". It refers to the whole coastline that is being viewed and includes the coast and countryside linked to it. It is the broader picture and is made up different features including landforms
E.G - The Jurassic Coast
Different land forms combine to give unique coastal landscapes
Landforms
A landform is an individual component of the coastal landscape. They are a distinct part of the wider coastal landscape but must be viewed individually
E.g A stack
Helps form the landscape
Waves
The formation of waves and their size and shape is a result of the exchange of energy wind blowing over the sea. The longer the wind blows for, and greater the distance it blows over, the larger the waves that result and the greater their energy
The extent to which the shape of a beach or coast can be altered depends largely on the action of waves upon it. Waves can be gentle and infrequent or larger, more frequent and more powerful
Other factors include
Wave strenght
Time Wind blows for
Distance (fetch)
Key Terms
Wave fetch- The distance of open water over which a wave had passed. Maximum fetch is the distance from one coastline to the next landmass, it often coincides with prevailing wind direction
Wave crest-Highest point of a wave
Wave trough-Lowest point of the wave
Wave height- Distance between trough and crest(Amplitude)
Wave length-Distance between one crest/trough and the next
Swash- Water movement up a beach
Backwash-Water movement down a beach
Wave Refraction
It is very rare for waves to approach a regular uniform coastline, as most have a variety of bays, beaches and headlans
Because of these features, the depth of water around the coast varies and as a wave approaches a coast its progress is modified due to friction from the seabed,halting the motion of waves.
As waves approach a coast they are refracted so that their energy is concentrated around the headlands but reduced around bays. Waves then tend to approach the coastline parallel to it, and their energy decreases as water depth increases
Constructive waves
Long wavelength
low amplitude
Strong swash pushes sediment up the beach
Weak backwash
Strong Swash
Net impact - gain
Net process - deposition
Destructive waves-
Short wave length
Steep wave faces and high wave height
Backwash is very strong and drags material back down the beach
Backwash = strong
Swash = weak
Net process - erosion
Net impact - coastal loss
Tides
Causes
Gravitational pull of sun +moon
Moon = bigger influence
Moon impact varies every day - this is because the moon spins on a axis
Moon pulls water towards it creating high tides and there is a compensatory bulge on the other side of the earth - results in " high tides and 2 low tides
Spring Tides
1) as the moon orbits the earth the tide follows it. Twice in a lunar month when the sun-moon and earth are in a straight line, the tide raising force is the strongest
Produces the highest monthly tidal range
Neap tides
Twice a month the sun and moon are positioned at 90˚ to each other in relation to the earth
This alignment gives the month tidal range, or neap high tide
Tidal Range
This is the height between the low and high tide
Severn estuary = highest
Significant factor in the development of a coastline
Mediterranean Sea Tidal ranges are low
Restricts wave action to a narrow width of the coastal zone.
UK - ranges are high --> gives a wide zone of attack, resulting in the formation of wave cut platforms
Currents
movement of energy in water
Often follow a circular pattern
Move in similar patterns either side of the equator
Clockwise = northern hemisphere, Anit-clockwise = Southern hemisphere
Sediment Cells
Types of sediment
Clastic
Biogenic
Non-cohesive sediment
Cohesive sediment
Sources
Rivers
Cliffs - erosion
Longshore drift
Tides, waves, currents
Biogenic - marine organisms providing sediment such as skeletons
Run-off - saturated cliffs have surface water that runs off and brings sediment to the coast
What are sediment cells
movement of sand and shingle in the nearshore zone by longshore drift has been found to occur in discrete, functionally separate sediment cells
11 cells around UK coastline
Smaller sub cells idenified
Self-contained
Natural processes
Sub-arieal Weathering
Erosion
Mass movement- This is the movement of large areas of material downslope under the force of gravity (Cliff Collapsing)
Freeze-Thaw/mechanical-
Chemical-
Biological-
Abrasion-Sediment chipping away
Corrosion -
Transportation
Attrition-
Hydraulic Action - The sheer force of the waves
Suspension-
Solution-
Traction-Rolling of large sediment
Saltation -
Sediment budgets-
The material contained in a sediment cell can be viewed in the form of a budget
It has gains and losses
Sediment Gain-cliff erosion, river deposition, tidal deposition
Sediment loss- deposition in sediment sinks (stores) such as bars, spits, dunes or human dredging
Said to be in a state of dynamic equilibrium
Upsetting the balance- storms, flooding, human engineering
1) This is also called physical weathering/ freeze thaw weathering or frost shattering
2) It is the direct result of atmospheric - rainfall and temperature
3)It is common in the areas with a high diurnal temperature range
Diurnal- between day and night/hottest and coldest points
1) This involved the action of chemicals in weather conditions (acid rain) dissolving certain rock types over time. The decomposition is a result of chemical change
Oxidation
Hydration
Hydrolysis
Carbonation-one to refer to limestone and chalk
This is the result of organic agents
For example - tree roots growing into and widening a crack in rocks or the action of burrowing animals physically enlarging joints in weak rocks
Some Sea Creatures like piddocks actually drill into rocks leaving them pitted with holes
Salts within the seawater slowly dissolve carbon based rocks
Links with solution
Larger Sediments collide
Links with traction
Links to attrition
Slightly smaller sediment is flipped in the swash
Sediment held in the water - fine sediment -sandy
Links with Abrasion
Sediment that has been dissolved
Links with solution
Long shore Drift- The movement of sediment along a beach due to swash and backwash
Falls- rapid movement of material on vertical/steep slopes over 40 degrees
Slides- A type of mass movement where large areas of coastal rock and soil slide downwards from the cliff
Slump-Very similar to a slide only it usually involves a smaller distance of movement that is on curved axis
A rotational movement
Earth/mud flows- Saturated soil moving under its own weight on slopes 5-10 degrees
Soil creep-Very slow (1cm per year) movement of material due to raindrop impact, saturation and freeze-thaw expansion
Deposition