Coasts Flashcards
What makes up a coastal system
- Inputs
- Sores and components
- Flows / transfers
- Outputs
Fetch
The distance a wave has travelled
What does larger fetch mean
The waves can be acted upon by the wind for a longer time so gain more energy
Inputs
Wind, precipitation, sediment
Flows/transfers
LSD, mass movement, erosion
Stores and components
Beaches, headlands, bays, sand dunes
Outputs
Evaporation, ocean currents, rip tides
What might dictate sediment in cell
- Weather = storms
- Humans = coastal defence
UK sediment cells
11 major cells which are subdivided into sub cells local to an area
Subcells
Generally bordered by 2 large headlands or deep water
Dynamic equilibrium
An ever changing state but in balance
Causes of tides
Gravitational pull of the sun and moon
Wave formation
Waves form when winds blowing across the water’s surface transfer their energy to the Water
What happens to sediment in the direction of prevailing wind
Gets smaller and rounder due to LSD and attrition
High energy coast
- Rough landscape
- Little deposited material
- High erosion
Low energy coasts
- Smooth coastline
- Calm waves
- Sheltered areas
Constructive waves
Add material to the coastline with strong swash
Destructive waves
Remove material with strong backwash with high erosion
Why are sediment cells considered closed systems
- Sediment exclusively moves between the stores retained by the two headlands
- Sediment created through the erosion of cliffs
Why is the coastal orientation key to determining coastal characteristics
Winds prevailing direction and magnitude
Coastal weathering
- Biological
- Chemical
- Mechanical
Sediment cell example
Flanborough head
Biological weathering 2
- Plant roots growing into cracks
- Animals burrow into weak points
Mechanical weathering 3
- Freeze thaw
- Salt crystallisation
- Wetting and drying
Freeze thaw erosion
Water enters a fault, freezes and then expands repeatedly
Crystallisation erosion
Can grow within cracks and expand
Wetting and drying erosion
Rock wetting of certain rocks make them expand and shrink
Positive feedback
Feedback that speeds up processes
Negative feedback
Feedback that slows processes
Mass movement
Downhill movement of sediment under gravity adding sediment
Geomorphical processes
- Erosion
- Transportation
- Deposition
Factors that affect erosion 4
- pH
- Geology
- Human presence
- Wind speed/direction
Transportation methods 4
- Traction
- Suspension
- Saltation
- Solution
Traction
Large boulders rolled along seabed
Saltation
Pebble sized particles bounced along seabed
Suspension
Small particles carried along water
Abrasion
Eroded material thrown against the rock
Attrition
Rocks carried are thrown against each other, smoothing them
Solution
Soluble materials dissolved in water
Factors affecting transportation
- Strength of waves
- Size of sediment
Wave cut platform
Flat area of rocks extending from base of cliff
Long shore drift alternative name
Littoral drift
Effect of wave cut platform
Waves have further to travel in shallow water and so break earlier, dissipating energy
Formation of wave cut platform
- Waves produce a wave cut notch on a cliff
- As cliff is undercut it collapses and gradually retreats
- Leaving behind a platform made from the base of the cliff
Bedding planes
Flat surfaces along which rocks tend to separate or break
Cliff profiles are influenced by
Geology and tectonic movement dips
Vertical bedding planes
When rock below is eroded it is on the same plane which means the whole plane stumps
Horizontal bedding planes
Rock above not affected by erosion below
Where can’t wave cut platforms be formed
- Soft rock
- Steep bedding planes
Causes for weaknesses in cliff
- Rock band orientation
- Bedding plane
- Layering of sediment
Salt marsh formation
The area behind a spit will become a salt marsh due to low energy
Formation of a spit
- LSD continues in direction of prevailing wind until coastline changes
- Sediment is taken out to sea until it looses energy and deposits, building up over time
- Hooks round due to secondary wind direction
Depositional landforms
- Beaches
- Spits
- Tombolos
- Offshore bars
Tombolo
Spit that connects an island to the mainland
What causes the hook on a spit
- Wave refraction curves sediment
- Second dominant wind direction
Wave refraction
The bending of waves due to reduction in velocity so they move nearly parallel to the shoreline
Neep tide
Sun and moon fight against each other, pulling in opposite planes, spreading water evenly
Spring tide
Sun and moon pull in the same plane, highest tides
Sand dune
Accumulation of mounds of sand blown by the wind (aeolian)
Stack formation 4
- Weakness in headland
- Carves out cave, punching through, forming an arch
- Erosion attacks base, weathering attacks roof, roof cannot hold itself up and collapses
- Forming a stack until it topples and leaves behind a stump
Tidal range
Difference in height between the high and low tide lines
Tidal range influences on processes
Dictates how long a process can act on a cliff face, small range focuses on the same area for longer
Sand dune formation
- Sediment accumulates on beach with large tidal range to dry
- At low tide, wind carries sand by creep or suspension
- And obstacle that causes the sand to lose momentum and settle, forming an embryo
Pioneer species
First species to populate an area
Flocculation
Particles come out of suspension and lump to form something larger
Halophytes
Salt tolerant plants
Conditions for mudflats 4
- Sheltered low energy environment
- large tidal range
- Supply of sediment
- Prevailing wind
Succession of salt marshes
- Pioneer plants first move
- Builds up land allowing other plants to move in
- makes area an extension of land
Isostatic change
A LOCAL rise or fall in land level causing RELATIVE sea level change
Eustatic change
An ACTUAL change in sea level
Emergent landforms
Raised beaches, abandoned cliffs, marine terraces
Submergent landforms
Rias, fjords
Effects of climate change on coastline 4
- Major infrastructure nearby
- Disrupt fresh water supplies
- Damage environments
- Urban environments at risk
What is a sediment cell
Areas that encompass the intertidal and nearshore moment of sediment
Sediment cell advantages
Allows for a sediment budget to be established to understand coastal changes
Sediment cell disadvantages
Fine sediment is not confined by boundaries and so model is not entirely closed
Swash aligned beach 3
- Smooth curved beach
- Waves aligned with beach
- Likely a closed sediment cell
What is a swash aligned beach
- The deposited sediment moves up and down the beach
- Shaped by waves arriving parallel to the shore
Drift aligned beach 4
- Angle of beach based on prevailing wind
- Backwash at 90°
- Material is moved and becomes smaller over time
- Sediment moves to another beach
What is a drift aligned beach
Drift aligned beaches are produced where waves break at an angle to the the coast
Wave quarrying
Waves breaking against cliffs traps air which compresses it into gaps which creates explosive effect
Sea level rise facts
- only 2/3 of ice sheets have potential to melt
- can cause 72 meters of sea level rise
Offshore bar formation
- Destructive waves remove sediment parallel from the beach and form the offshore bar
- constructive do the opposite
Sources of energy
- wind
- waves
- currents
- tides
Why do areas receive variable wave energy
- Direction of prevailing wind
- Larger fetch
- Wind circulation (Gulf Stream)
Sources of sediment
- river estuaries
- cliff erosion
- offshore sediment
- wind
Factors that affect rate of erosion 5
- geology
- wind
- pH
- landscapes
- coastal defences
Required conditions for mudflats 5
- Sheltered low energy environment
- Larger inter tidal range
- Dominant wind direction
- sediment supply
- Occasional flooding
Threats to salt marshes 3
- SLR
- Wave energy increase
- Higher rates of flooding
What is the difference between weathering and erosion
- Weathering = land based
- Erosion = water
Weathering and processes
- Land based processes above water line
- Weathering
- Mass movement
Erosional processes 5
- Hydraulic action
- Abrasion
- Attrition
- Solution
- Wave quarrying
Causes for joints in bedding planes
- Igneous rock cooling
- Compression/stretching sedimentary
Joint
Fractures in rocks created without displacement increasing erosion rates by creating cracks
