Coasts Flashcards
Littoral zone
The wider coastal zone including adjacent land areas and shallow parts of the sea just offshore
Primary coasts
Dominated by land based processes such as deposition from rivers or new land from lava flows
Secondary coasts
Dominated by marine erosion or deposition processes from the sea
Emergent coasts
Where the coasts are rising relative to sea level eg due to tectonic uplift
Submergent coasts
Where coasts are being flooded by the sea either due to rising sea levels or subsiding land
Low energy coastlines
Sheltered coasts with limited fetch and low wind speeds resulting in small waves
High energy coastlines
Exposed coasts facing prevailing winds with long wave fetches resulting in powerful waves
Cliff profile
The height and angle of a cliff face as well as it’s features such as wave cut notches or changes in slope angle
Dynamic equilibrium
The balanced state of a system when inputs and outputs balance over time
Short term factors showing the littoral zone is constantly changing
Individual waves
Daily tides
Seasonal storms
Long term factors showing the littoral zone is constantly changing
Changes to sea level
Climate change
3 features of a marine erosion dominated cliff
Steep face
Active undercutting
Limited cliff base debris
3 features of a sub-aerial process dominated cliff
Curved slope profile
Lower angle face
Accumulated debris
Faults
Major fractures that have moved rocks from their original positions
Formed when the pressure to which a rock is subjected exceeds its internal strength causing it to fracture
Deformation
Folds and dips caused by tectonic activity
Strata
Different layers with bedding planes
Joints
Fractures caused either by contraction as sediments dry out or by earth movements during uplift
Concordant coastline
Rock strata run parallel to the coastline
Discordant coastline
Different rock strata run at right angles to the coastline
Bands of more and less resistant rock
Headlands and bays
Deposition
The laying down of sediment carried by wind or water
Coastal erosion
The process in which cliffs are worn away and transported by the sea
Traction
Large materials such as boulders are rolled along the sea bed
As they are heavy so waves don’t have enough energy to carry them
Saltation
Pebbles or small stones are lifted by the sea but dropped when energy is lost.
As a result pebbles are bounced along sea bed
Suspension
Smaller particles such as sand float in the sea
Solution
Particles such as clay are dissolved in the sea and constantly move with water
Abrasion
Material is hurled against the cliff by waves wearing away at it
Attrition
A pieces of material knock each other they get smaller smoother and more rounded
Hydraulic action
Where waves crash into base of cliff forcing air into cracks. This exerts a pressure, cracks grow until rock detatches
Solution (erosion)
Soluble particles dissolved by acids in sea water
Lithology
The characteristics of the rock including the type, whether it’s permeable or impermeable, how porous it is
Isle of Purbeck, Jurassic coast
Resistant Portland limestone lies parallel to the coast
At points where this limestone is weaker erosion causes small coves eg Lulworth cove
Igneous rock erosion rate
Very slow
Interlocking crystals make rock strong and resistant
Few joints and therefore limited areas of weakness to exploit
Metamorphic rock erosion rate
slow
Crystallised sedimentary rock
Some folds and fractures to exploit
Sedimentary erosion rate
Moderate to fast
If cement between layers is weak then it will be weak
Younger rocks are weaker
Permeability (lithology)
The ability of water to pass through the rock.
Related to its previousness and porosity.
Pervious rocks
Eg limestone
Joints and bedding planes that water can flow through
How can groundwater flow weaken rocks
Flows through rocks layers removing binding cement
Carbonation
Acidic rainwater slowly dissolved the calcium carbonate in the limestone or chalk creating calcium bicarbonate which is taken away in solution
Hydrolysis
Water combines with minerals like granite and the chemical reaction creates salts and clay
Eg in Devon it has created Kaolin (porcelain china clay)
Freeze thaw
Water goes into cracks and freezes
This expands and breaks the rock
Horizontal bedding plane
1)Erosional processes
2)Main mass movement type
Undercutting by wave action can lead to development of wave cut notches and platforms
Main mass movement=rock fall
Sloping bedding plane (towards sea)
1)Weathering
2)Sub aerial processes
Large slabs of rock loosened by weathering slide off easily along bedding planes.
Sub aerial processes have a greater influence than marine processes leading to shelling cliffs
Sloping bedding plane (away from sea)
Rocks loosened by weathering and wave action are difficult to dislodge
Slope profile lowered by mass movement and weathering
Cliff face is rugged and uneven
Marram grass
Helps stabilise the unconsolidated sediment of the dunes and encourages other plants to grow there as well so helping plant succession
Ways vegetation helps stabilise unconsolidated sediment
1)roots of plants bind sediment particles together so harder to erode
2)When submerged plants provide protective layer sonnet exposed to moving water
3)Protect sediment from wind erosion by reducing wind speed due to friction
What does geological structure of rock include
Strata
Bedding planes
Joints
Folds
Faults
Dip of the strata
Joints
Vertical cracks
Bedding planes
Horizontal cracks
Dip of the strata
Angle at which rock strata lie
Concordant
Bands of more resistant and less resistant rock parallel to coast
Discordant
Bands of more resistant and less resistant rock perpendicular to coast
Halophyte
Tolerate salt water around roots, tolerate being submerged in water or salt spray from the sea.
Xerophyte
Tolerate very dry conditions, like on sand dunes where sandy soil has very little water due to drainage
What factors affect size of wave
Fetch: stretch of ocean over which wind blows
Longer fetch -> larger wave
Wind speed
Duration of wind
Rockfall
Occur when there is erosion at the base of cliffs creating overhang
Rock type must be resistant. As unconsolidated cliffs slump too quickly to allow overhangs to form.
Rock fragments fall due to gravity
Slumping
Occurs in weak unconsolidated cliffs
These cliffs have little strength and are vulnerable to slip planes developing
Rainwater enters cliff increasing weight of soil and lubricating slip plane
Material slides along slip plane
How are wave cut platforms formed
Horizontal bedding planes
Wave cut notch forms due to hydraulic action and abrasion
Notch increases in size
Wave cut platform forms when rockfall happens
Longshore drift
Swash deposits material on the beach at 45 degrees
Backwash pulls material off beach at 90 degrees
This repeats moving sediment along the coastline
How do spits form
-Sand or shingle beach ridge extending beyond a turn in the coastline
-Longshore drift current spreads out and loses energy leading to deposition
-Length of spit is determined by existence of secondary currents causing erosion
-Flow of river or wave action limits its length
Detailed example of a spit
Spurn Head, Holderness coast
3.5 miles long
Grows 10cm a year
Recurved spits
-A spit whose end is curved landward into a bay/inlet
-Seaward end curved landward into shallower water
-“Hook” may be made more pronounced by waves from a secondary direction to prevailing wind
Example of a recurved spit
East Head West Wittering
Tombolos
Sand/shingle bar that connects coastline to offshore island
How are tombolos formed
-Spit/bar grows due to LSD joining island
-Formed due to wave refraction around island around island
-Area of calm water created
-Opposing Longshore currents may play a role
Example of a tombolo
Chesil beach Dorset
-Swash aligned
-Faces SW
How are beaches formed
Occur in littoral zone between low and high tide
Constructive waves with strong Swash and weak backwash allow a net increase of material
Longshore drift moves material along shoreline
Barrier beaches
-Sand or shingle beach connects 2 areas of land with a shallow water lagoon behind
-Occurs when a spit grows so long that it extends across a bay closing it off
Examples of barrier beaches
Many are found along Eastern Seaboard of the USA
Scapton, Devon
Offshore bars
-Raised area of seabed that is found offshore
-Form adjacent to coastline
-Formed in areas with high levels of sediment and shallow water
-Form when sediment is transported on and off a beach
Cuspate forelands
Roughly triangular shaped features extending out from shoreline
One hypothesis is due to growth of 2 spits from opposing longshore drift directions
Yellow dunes
Mobile dunes
Marram grass/Lyme grass/Sandcouch
Grey dunes
Less salt tolerant plants
Sea buckthorn, Dewberry
More organic matter and humus in soil
Fixed grey dunes
hawthorn
Oaks
Maple
Ash
Climax species
Dynamic equilibrium
The balance of all the factors affecting the coastal system. If there is a change to one factor the system will respond and there will be consequent changes
Sources of Flamborough head sediment cell
-Deposition from river Humber
-Rockfall from cliffs
-Soft boulder clay
-Chalk from Flamborough head
Transfers in Flamborough Head sediment cell
Longshore drift along Bridlington bay
-going southwards
-large waves from north east
-Increased erosion
How is the Flamborough Head sediment cell being disrupted?
-Mappleton village intense erosion
-2m a year
-£2000000 spent on rock groynes and revetments
-Due to this there has been more erosion further south
-No beach to protect cliffs so sea reaches base of cliffs causing erosion
Isostatic change
A LOCAL rise or fall in LAND level
Eustatic change
Rise or fall in WATER LEVEL.
This is a GLOBAL change.
Post glacial isostatic adjustment
Refers to uplift of land following removal of the weight of ice sheets
How do sea levels change day to day?
-High/low tides alter local sea level every few hours
-Atmospheric air pressure influenced sea level (low pressure=slight rise)
-Winds can push water towards coast
How much have sea levels risen by since last glacial period (ice age)
120m
Eustatic fall in sea level
During glacial periods when ice sheets form on land in high latitudes, water evaporated from the sea is locked up on land as ice to sea levels fall.
Isostatic fall
Weight of ice sheets causes earths coast to sag. When they melt the island surface slowly rebounds upward over 1000s of years. This lifts land out of sea
Eustatic rise in sea level
At end of glacial period melting ice sheets return water to sea causing level to rise globally
Isostatic rise
Lands can sink due to deposition of sediment (accretion)
Raised beach + example
Old abrasion platform which has been lifted out of the sphere of wave activity
Developed when sea was at that level and then the sea level changed during the ice age
Fife Scotland
Fossil cliff + example
Ayreshire Scotland 10m high
Land can be stressed downwards from post glacial adjustments, subsidence and accretion
Rias + example
Drowned river valley
Caused by sea level rise flooding
Kingsbridge estuary Devon 500 to 1000m wide creeks
Fjords + example
Deeper than adjacent sea
Submerged lip at seaward end
Post glacial isostatic adjustment slowly raises land out of sea
Barrier islands + example
Offshore sediment bars.
Formed as lines of coastal sand dunes. Dunes are not eroded so become islands
Florida USA
Dalmation coasts + example
Concordant coasts where sea has flooded landscape brewing long bays and parallel hilly islands
Croatia
What effect does past and present tectonic activity have on sea level change?
Example
-Can lead to subsidence causing land to sink
-Oceanic plates sink
Turakirea head NZ shoreline has raised several metres by major earthquakes
Eccentricity cycle
Earths orbit
Obliquity cycle
Earths tilt
Precession
A gradual change or wobble of earths axis
Human reasons for spatial variations along the coast
-Coastal defences can cause starvation of sediment further south.
-Groynes interrupt longshore drift
Example: Hornsea
Hornsea groynes caused sediment starvation is mappleton so increased erosion
Physical reasons for spatial variations along coast
Example
-Variations in cliff height
-Variations in rock resistance
-Mass movement susceptibility
-Debris from previous erosion
Example
Flamborough head shelters area south of it reducing impact of waves
Also has resistant chalk
Ords
Deep hollows on the beach running parallel to the cliff at the base
What influence do ords have
-Concentrate erosion in particular locations
-By allowing waves to directly attack the cliff with little energy dissipation
Skipsea: Economic impacts of sea level rise
-10 caravan patches a year lost
-Property values declining
-No compensation for homeowners
-Loss of tourism revenue
Social impacts of sea level rise in Skipsea
-Displacement of residents
-Stress over lost caravans/homes
What’s needed for a storm surge to happen?
-Area of low pressure
-Strong winds around it
-High tides around the coast
What physical factors make Bangladesh prone to flooding?
-Low lying. 0 to 3m above sea level
-Delta funnel shape
-Deforestation of coastal mangroves
-Floodplains of 3 major rivers incl Ganges
Cyclone Sidr
-Heavy rain
-223 km/h winds
-$1.7 billion
-Contaminated drinking water
-Electricity and comms knocked out
-10000 deaths
Economic costs of coastal recession
-Housing eg 24 homes at risk Skipsea
-Businesses
-Loss of tourism
-Infrastructure
Social costs of coastal recession
-Impacts on health eg stress
-Relocation separates people
-Loss of livelihood
-Loss of amenity areas eg beaches
What is ICZM
Integrated coastal zone management
Entire coastal zone is managed.
Ecosystems, resources, human activity
Recognises importance of zone to livelihoods
Involves all stakeholders
Policy options of shoreline management plans
No active intervention
Managed realignment
Hold the line
Advance the line
Example of a good ICZM
Blackwater Estuary Essex
Wildlife trust bought Abbots Hall Farm for market price
Paths and waterways for measure
5 breaches created in sea wall to form salt marshes
Impacts of storm Xaver North Sea in England
100 000 homes lost power
Severe flooding Hull, Skegness, Whitby, Rhyl
2500 coastal homes flooded
-15 deaths
Physical factors North Sea storm xaver
Sea gets shallower and narrower towards south
Increases height of storm surge
