Coast must know 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 Swash Zone Breaker zone Surf zone
Offshore:
Beyond the point where waves have impact on seabed
Nearshore:
Between low water mark and area where waves cease to have influence on seabed
Foreshore:
Between High water mark and Low water mark.
Backshore:
above high water mark up to landward limit of marine activity
Swash zone:
Turbulent water rushes up the beach as the swash
Breaker zone:
Waves approaching begin to break
Surf Zone
between waves breaking and moving up the beach as swash
What are the sources of energy?
Waves Winds Tides Wave refraction Currents
What are the 2 types of wave?
Constructive
Destructive
What are the characteristics of constructive waves?
Low height, Frequency (6-8/min), energy. Swash more powerful than backwash, Beach is built up Gentle beaches
What are the characteristics of destructive waves?
High heights,
Frequency (10/14/min), energy. Backwash stronger than swash
Sediment removed
Steeper beaches
What does the energy of wind depend on?
strength
duration
fetch
What are tides?
What are the 2 types?
Gravitational pull of the moon and to a lesser extent the sun,
Creating spring tides (every 14 days)
When aligned and neap (every 14 days) at right angles.
High (and low) tides occur 12 hours and 25 mins apart.
What do tides vary due to?
Morphology of sea bed, Proximity of land masses Coriolis force
What is Wave refraction?
Energy of wave becomes concentrated on headlands and dissipated at bays
Since waves in shallow water slow down due to friction with sea bed.
What are the 3 differnt types of current?
Longshore currents -
Rip currents -
Upwelling
What are Longshore currents?
The process of Longshore drift
What are rip currents?
move away from the coastline at for example a headland
What is upwelling?
cold water makes it’s way to the surface
What is a sediment cell?
How many are there is England and Wales?
Sediment cell is a stretch of coastline, usually bordered by two headlands, where the movement of sediment is largely contained.
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What happens within a sediment cell?
Within the cell there are inputs (sources), transfers and stores (sinks).
What is a sediment budget?
What can upset this?
The sediment budget is the amount of sediment that is available and tries to be in dynamic equilibrium.
Can be upset by a storm or sudden increase in discharge or by human activity e.g. groynes
What are the geomorphological processes?
Processes involved in the change of landforms 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 air 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?
Solution - rocks, normally limestone or other rocks containing carbon, are dissolved, though this is normally by rainfall and is therefore not technically erosion but….
What is Hydraulic Action?
Hydraulic action - sheer force of the water puts pressure on the rocks and forces them apart
What is Abrasion?
Abrasion - material is used by the waves e.g. shingle which is thrown at the cliff
What are the coastal processes of transportation?
Saltation - Traction - Solution - Suspension - Longshore drift -
Saltation
Saltation - sediment bounces along the bed of the sea and dislodges other particles
Traction
Traction - bedload rolls along the sea bed
Solution
Solution - minerals are dissolved and are carried in the water
Suspension
Suspension - particles are carried along in the water
Longshore Drift
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/desposited by the wind
Where 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?
carried/desposited by the wind
Wind is often onshore during the day due to temperature differences
What is the process of sand being picked up my the wind called?
What processes does it move though?
entrainment
Surface creep - rolls
Saltation - bounces
What are sub-aerial processes?
These are land-based and consist of weathering and mass movement
What are the 3 different types of weathering?
Mechanical (physical)
Chemical
Biological
What are the different types of Mechanical weathering?
Freeze-thaw -
Salt crystallisation -
Wetting and drying -
Exfoliation -
What is Freeze-thaw?
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 crytallisation?
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 2 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 is 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 6 types of mass movement?
Soil creep - Rotational slumping - Rock falls - Landslides - Mudflows - Runoff -
What is Soil creep -
Soil creep - very slow movement (1cm/yr), dislodged by raindrops or wave splash and freeze/thaw or wetting/drying
What is Rotational slumping -
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 are Rock falls -
Rock falls - physical weathering, weaknesses exposed and can’t support
What are Landslides -
Landslides - significant section, unconsolidated shales & sandstones, usually been lubricated
What are Mudflows -
Mudflows - excessive amounts of rainfall, infiltration can’t take place, fine particles of mud
What is Runoff -
Runoff - intense rainfall, impermeable surface, transports fine materia
What are the landforms of erosion, include examples?
Individual components of the landscape
Caves, arches stacks - Old Harry, Swanage, or The Needles or the 12 Apostles on Great Ocean Road
Cliffs and wave cut platforms - Watchet, West Somerset, Kimmeridge Bay
Headlands and Bays - Swanage Bay
What are the landforms of coastal deposition, include examples?
Beaches
Simple and compound spits - Sandbanks, Hurst Castle, Spurn Point
Tombolos - Chesil Beach joining Isle of Portland
Offshore bars - Hordle Cliff
Barrier islands - Fire Island, Long Island - New York.
Bar/barrier beach - Slapton Sands
Sand dunes - Ainsdale, Braunton Burrows, Oxwich
Saltmarsh/mudflats - Keyhaven Marshes (Hurst Castle)
What are the factors and processes in the origin and development of cliffs and wave cut platforms?
- Waves attack base of cliff, via abrasion and hydraulic action
- Creates a wave-cut notch which is undercut, becomes unstable and collapses
- Notch migrates inland and cliff retreats leaving a gently sloping wave-cut platform, exposed at low tide.
- Wave cut platform smoothed via abrasion and solution
- Most less than 0.5km
What is a Discordant coastline?
Give an example?
geology at right angles e.g. Purbeck, Dorset
What is a concordant coastline?
Give an example?
geology runs parallel to coast e.g. South Dorset, and Dalmation Coast
What are the factors and processes in the origin and development of cliff profile features to include caves, arches and stacks?
Lithology
Structure
Geomorphology
What is Lithology?
- the physical properties of a rock such as its resistance to erosion - the rock type.
What is Structure?
What do the differnt angles of rock lead to?
whether the rocks run parallel or perpendicular, joints and bedding planes
Horizontal - produce steep cliffs
Dip towards the sea - less stable, joints exposed
Dip towards the land - more stable
What is Geomorphology?
the shape of the coastline e.g. refraction
What type of beach does shingle produce?
What is the material like?
shingle produces steeper beaches due to less powerful backwash
Material more angular, larger, more varied towards top of beach - due to cliff falls, less attrition, storms move material up the beach
What is a Swash-aligned beach?
no drift, bays, waves parallel
What is a Drift-aligned beach?
drift, waves oblique, regular coastline
What is a berm?
ridges runing parallel marking high tide marks
What is a Cusp?
embayments caused by save dividing around horns
What are Ridges & Runnels?
spreading of the waves energy across the beach creates these
How do Spits form?
What forms behind them?
LSD, coastline changes direction, deposition occurs and conginues in direction of LSD, change in wind direction causes recurved end, also via wave refraction,
mudflats and slat marshes behind, flow of water out of estuary stops spit reachign the other side
What does a Bar/Barrier beach form?
Develops in same way to a spit but where flow of water from river is less powerful and therefore joins to headland on th either side, creating a lagoon
What is a Tombolo?
Where a spit connects to an an island
What is an offshore bar?
ridge of material running parallel to the coastline, caused by desgtrctive waves with strong backwash
What is a Barrier island?
similar to offshore bars but always exposed, created after the last ice age left behind material
What is Plant succession?
- where plants gradually make an area more hospitable for other plants which then take over
What do you need for a sand dune to form?
arge supply of sand, therefore large tidal range, exposed to wind to dry & entrain
What are the 5 types of dune?
Embryo dune, fore dune, yellow dune, grey dune, mature dune
How does a Sand dune form?
Sand accumulates against an object e.g. driftwood
Behind the barrier wind drops so more sand is deposited and pioneer plants able to tolerate harsh conditions colonise e.g. sea rocket
Marram grass, with long tap roots to get water, colonise dunes making them more stable
Decaying plants add humus to the soil which allows other plants to colonise.
Soil developed which allows a range of different plants to colonise and eventually trees to develop as the climax vegetation
What harsh conditions do sand dunes need to cope with?
(salt water, inundation, dry, lack of nutrients, windy)
Give an example of a pioneer plant.
Sea Rocket
What do mudflats/salt marsh need to form?
estuaries, low wave/river energy, sheltered areas, low lying and flat, behind spits which create a Halosere.
what is a mudflat?
deposition of fine silts and clays
How does a Saltmarsh form?
Mud is deposited close to high-tide line, dropping out of the water by flocculation - tiny individual particles of clay stick together which enables them to sink
Pioneer plants such as eelgrass and spartina colonise the transition zone between high and low tide. These plants can tolerate inundation by salty water and they also help to trap deposits of mud.
The mud level rises above high tide and lower saltmarsh develops with a wider range of plants that no longer need to be so well adapted to salty conditions.
Soil conditions improve and the vegetation succession continues to form a meadow.
Shrubs and trees will colonise the area as the succession reaches its climatic climax.
What is it called when tiny individual particles of clay stick together which enables them to sink?
flocculation
What is flocculation
tiny individual particles of clay stick together which enables them to sink
What are the pioneer plants in the formation of salt marshes?
eelgrass and spartina
What was the sea level like 20,000 years ago?
120m below current level
What was sea level like between 10,000 to 7,000 years ago?
50m below current level
What is Eustatic?
a global change in sea level as a result of change in input and stores e.g. input of snow stored as ice which decreases ocean store & melting of ice decreases store of ice and increases flow to oceans.
What is Isostatic?
a local change in sea level caused by land weighed down by weight of ice (isostatic subsidence), once ice melts land rebounds (isostatic recovery) - acts like a sea-saw
How has tectonics effected sea level change?
Give an example
Magnitude
Sea bed ride Subsidence
Changes in level of the land and/or sea bed as a result of tectonic activity
e.g Nea Zealand in 2016 after 7.8 earthquake, seabed rose by 0.5-2m along a 20km stretch of South Island, however areas on North Island coastline is subsiding by 5mm a year.
How much sea level change is Thermal expansion responsible for?
50%
