Coastal systems and landscapes Flashcards
How is the coast a natural system?
Inputs of energy and sediment
Components of erosional landforms and landscapes
Components of depositional landforms and landscapes
Outputs of energy, sediment removal, sediment above tidal limit
What are the coastal zones?
- Offshore
- Nearshore
- Foreshore
- Backshore
Where is the offshore?
Beyond the point where waves have impact on the seabed
Where is the nearshore?
Between LWM and area where waves cease to have influence on seabed
Where is the foreshore?
Between HWM and LWM
Where is the Backshore?
Above HWM up to landward limit of marine activity
What are the zones in the foreshore?
- Swash zone
- Breaker zone
- Surf zone
What happens in the swash zone?
Turbulent water rushes up the beach as swash
What happens in the breaker zone?
Waves approaching begin to break
What happens in the surf zone?
Between waves breaking and moving up the beach as swash
What are the sources of energy?
- Waves
- Winds
- Tides
- Wave refraction
- Currents
How are waves sources of energy?
Frictional drag of wind
What are the two types of waves?
- Constructive
- Destructive
What are the features of a construction wave?
- Low height
- Low frequency (6-8/min)
- Swash more powerful than backwash
- Beaches built up, gentle beaches
What are the features of destructive waves?
- High heights
- High frequency (10-14/min)
- Backwash stronger than swash
- Sediment removed, steeper beaches
What is the energy of winds dependent on?
- Strength
- Duration
- Fetch
How are tides a source of energy?
Gravitational pull of the moon and to a lesser extent the sun
How is a spring tide created?
When the sun and moon are aligned (every 14 days)
How is a neap created?
When the sun and moon are at right angles
How often do High and Low tides occur?
Every 12h and 25min
What is wave refraction?
When energy of wave become concentrated on headlands and dissipated at bays, since waves in shallow water slow down due to friction with sea bed
What are the different types of currents?
- Longshore drift
- Rip currents
- Upwelling
What is a rip current?
Move away from the coastline at, for example, a headland
What is upwelling?
Cold water making its way to the surface
What is a sediment cell?
A stretch of coastline, usually bordered by two headlands, where the movement of sediment if largely contained
How many sediment cells are there in England and Wales?
11
What is there within sediment cells?
Inputs (sources)
Transfers and stores (sinks)
What is the sediment budget?
The amount of sediment that is available and tries to be in dynamic equilibrium
How can the sediment budget be upset?
By a storm or sudden increase in discharge or by human activity
eg groynes
What are geomorphological processes?
Processes involved in the change of landforms
What are examples of geomorphological processes?
- Erosion
- Transportation
- Deposition
- Weathering
What are the coastal processes of erosion?
- Wave quarrying
- Attrition
- Solution
- Hydraulic action
- Abrasion
What is wave quarrying?
Cavitation which traps aire causing huge pressure, which is released when wave withdraws
What is attrition?
Material being carried by the sea hit against each other becoming smaller, rounder and smoother
What is solution?
Rocks, normally limestone or other rocks containing carbon, are dissolved, through this is normally by rainfall
What is hydraulic action?
Sheer force of the water puts pressure on the rocks and forces them apart
What is abrasion?
Material is used by the waves
eg Shingle which is thrown at the cliff
What are the coastal processes of transportation?
- Saltation
- Traction
- Solution
- Suspension
- Longshore drift
What is saltation?
sediment bounces along the bed of the sea and dislodges other particles
What is traction?
bedload rolls along the sea bed
What is solution?
minerals are dissolved and are carried in the water
What is suspension?
particles are carried along in the water
What is longshore drift?
swash comes in at an angle due to prevailing wind direction, backwash straight back down due to gravity, moves material in a zig zag along the coastline
What are the coastal processes of deposition?
- Where marine energy is lost
- Aeolin - carried/deposited by the wind
When is marine energy lost?
- The wave slows down after breaking
- Where accumulation is quicker than removal
- Where the coastline changes direction
- Just before backwash
What is Aeolin?
Wind is often onshore during the day due to temperature differences
Sand is entrained (picked-up) and then moves through
Surface creep - rolls
Saltation - bounces
What are sub-aerial processes?
These are land-based and consist of weathering and mass movement
What are the different types of weathering?
- Mechanical
- Chemical
- Biological
What are the different types of mechanical weathering?
- Freeze-thaw
- Salt crystalisation
- Wetting and drying
- Exfoliation
What is freeze-thaw weathering?
water into cracks, expands 10%, puts pressure on rocks until they crack and break. The shattered, angular fragments are found at the base as scree (talus)
What is salt crystalisation?
salt crystals are deposited in cracks and accumulate under drier conditions, over time it applies pressure to the rocks and they crack.
What is wetting and drying?
Common on the coastline, in the inter-tidal zone, with clay and shale which expands when wet and contracts when dry. This produces cracks which are then vulnerable.
What is exfoliation?
Rock under considerable heat will expand and then cooled by the sea causing rapid contraction. This repeated process causes the outer layer to crack and peel off - onion-skin weathering
What are the different types of chemical weathering?
- Carbonation
- Oxidation
What is carbonation?
Sea and rain absorb carbon dioxide forming carbonic acid which then dissolves the calcium carbonate in rocks such as limestone or chalk into calcium bicarbonate, especially in cracks and joints.
What is oxidation?
Rocks containing iron (ferrous) compounds experience this when turned into a ferric state (rusting) when oxygen and water are available, leading to disintegration.
What are the different types of biological weathering?
Growing plant roots widen cracks, in windy conditions these can widen. On the coastline the Piddock drills holes in rocks, puffins excavate nests and seaweed can move in storm conditions weakening rock
What is mass movement?
A sub-aerial process, involving the downhill movement of material under the influence of gravity
What are the different types of mass movement?
- Soil creep
- Rotational slumping
- Rock falls
- Landslides
- Mudflows
- Runoff
What is soil creep?
very slow movement (1cm/yr), dislodged by raindrops or wave splash and freeze/thaw or wetting/drying
What is rotational slumping?
Heavy rain infiltrates unconsolidated soil e.g. glacial till (East coast), impermeable soil traps water adding weight, undercutting causes collapse on slip plane
What is rock falls?
physical weathering, weaknesses exposed and can’t support
What is landslides?
significant section, unconsolidated shales & sandstones, usually been lubricated
What is mudflows?
excessive amounts of rainfall, infiltration can’t take place, fine particles of mud
What is runoff?
intense rainfall, impermeable surface, transports fine material
What are the landforms of erosion?
- Caves, arches and stacks
- Cliffs and wave cut platforms
- Headlands and Bays