Coasts Flashcards
Longshore Currents
These occur as most waves do not hurt the coastline ‘head on’ but approach at an angle to the shoreline. This generates a flow of water (current) running parallel to the shoreline. This also transports sediment parallel to the shoreline.
Constructive Waves
- Strong swash
- Long wavelength (up to 100m)
- Depositional waves
- Energy concentrated on movement up the beach
- Low frequency (8-10 per m)
- Low height (less than 1m)
- Caused by local offshore storms
- Low levels of infiltration
- Swell or spilling waves
Destructive Waves
- Strong backwash
- Short wavelength (less than 20m)
- Erosional waves
- Energy concentrated close to the breaking zone to scar seabed
- High frequency (10-12 a min)
- High height (over 1m)
- Caused by swell from distant storms
- High levels of infiltration
- Surfing, surging or plunge waves
Coastal Sand Dunes
Accumulations of sand shapes into mounds by the wind. Dunes are subject to different forms and sizes based on interaction with the wind.
Rip Currents
Strong currents moving away from the shoreline. They develop when sea water is piled up along the coastline by incoming waves. Current runs parallel to the coast before the break zone.
Deposition
Material that is being held or transported is laid down.
How do Sand Dunes Develop?
- Embryo dunes develop where wind speeds slow and sand is deposited beyond the beach
- Drought and salt-tolerant plants colonise the sand which stabilises the dune and more sand, less wind velocity
- Foredunes develop with more sand and plants
- Humus layer changes the dune from yellow to grey
- Dunes inland become fixed
- Dune slacks may develop, higher moisture
- A dune heath may develop inland
Freeze Thaw
Rainwater penetrates joints in exposed rock and if night temperatures drop below freezing, the resulting conversion to ice expands and exerts pressure within the rock, enlarging the fissure/crack.
Plants
The roots of surface plants on cliff tops can create and expand tiny cracks. Subsurface seaweed attached to rocks can weaken and detach them as it sways in the currents of storm conditions.
Types of Sea Level Rise that caused Climate Change
- Thermal expansion
- Added water from melting land ice
Why don’t we protect the whole coastline from the effects of erosion?
- Uneconomical
- Would cause environmental damage
- As the coast is a system what is eroded one place may provide important inputs elsewhere
Hard Engineering Techniques
- Revetments
- Gabions
- Groynes
- Concrete tetrapods
- Rock armour (rip rap)
- Off-shore reef/breakwaters
- Sea wall
- Barrage
Soft Engineering Techniques
- Beach nourishment
- Dune regeneration/stabilisation
- Beach re-profiling
- Cliff re-grading and drainage
- Managed retreat
- Managed realignment
Landslides
A significant section of the cliffs becomes detached and slides down. They usually affect less consolidated geology, such as boulder clays or weathered shales and sandstones.
Where do mudflats develop?
- On sheltered shorelines that are not exposed to powerful waves/tides and where deposition occurs
- On estuaries where the flow of water is weak
- Where both the river and sea are carrying large loads of fine sediments
Weathering
The disintegration of rock in situ
Mechanical, chemical, biological, freeze-thaw, exfoliation, wetting and drying, crystallisation, carbonation, oxidation, hydration, hydrolysis, plants, animals
Dynamic Equilibrium
A state of equilibrium where environmental conditions fluctuate around an average that is gradually changing itself, a state of balance between inputs and outputs.
Change in equilibrium = Change in inputs/outputs
Positive Feedback
A response to a system change that enhances the change leading to a new state of equilibrium. It aids change and creates a new equilibrium.
Negative Feedback
A response to a system change that aids recovery of the original state of equilibrium. It opposes change, it stabilises the coastal morphology and mountains a dynamic equilibrium.
Human intervention into natural processes at the coast is most often designed to…
- Manage the shape and profile characteristics of the coastline
- Reduces the rate of erosion
- Limit the likelihood of coastal flooding
- Protect valuable land
Aerolian Processes
Entrainment, transportation and deposition by the wind.
Sediment Budget
The balance between the sediment being added to and removed from the coastal system.
Hard Engineering and Soft Engineering
Hard Engineering: strategies that are designed to intercept and impede natural marine and coastal processes.
Soft Engineering: low-incursion, sustainable coastal protection strategies that work with nature to manage the coast.
Isostatic Change
Change in height of land surface relative to the sea level. Operates at a more localised scale. The weight of ice sheets can lower the land’s surface by depressing the crust into the viscous mantle
When ice sheets melt, the land can bounce back up.
Eustatic Change
The change of sea level relative to the land. The change is global in scale. Global sea levels can be thought as a system that depends on relative rates of inputs and outputs.
Falls due to freezing.
Tidal Range
The vertical difference in height between consecutive high and low waters over a tidal cycle.
Sub-aerial Processes
Includes processes at the base of the atmosphere that slowly breakdown the coastline, weaken the underlying rocks and allow sudden movements or erosion to happen more easily - weathering, mass movement and run-off.
Pioneer Species
The first plant species to colonise an area. It is well adapted to living in harsh environments.
Why do tides occur?
Tides are caused by slight variations in gravitational attraction between the Earth and the moon and the Sun in geometric relationship with locations on the Earth’s surface.
Mudflats
Low-lying areas of the shore that are covered at high tide and when uncovered at low tide a stretch of muddy land composed of silt and clay are left.
What makes a Wave Form?
1) Circular orbit in open water
2) Friction slows down base of the wave
3) Wave becomes more elliptical in movement
4) Top of wave moves faster. Becomes increasingly elliptical
5) Wave begins to break
6) Water rushes up the beach as swash
7) Water from previous wave returns as backwash
Carbonation
Coastlines composed of chalk or limestone may be dissolved by acidic rainwater or seawater. The rain/sea absorbs carbon dioxide from the atmosphere, creating a weak carbonic acid. This can convert solid calcium carbonate to soluble calcium bicarbonate and the rock dissolves.
Swell and Sea
Swell: waves formed by distance storms that travel a long distance.
Sea: waves formed by local winds and travel only short distances.
Soil Creep
The gradual movement downhill of individual particles due to gravity. Raindrops or wave splash may dislodge a particle, and it is most likely to take a downwards trajectory due to the influence of gravity.
Barrier Beaches
An elongated bank of deposited sand or shingle lying parallel to the coastline and not submerged by incoming tides. Where the bank is high enough to allow sand dunes to develop it is known as a barrier island.
They tend to develop where the coast has relatively high energy waves, small tidal range, gentle gradients offshore and plentiful supply of sediment.
Rockfall
Arch roofs, stacks and cliff faces collapse as a weakness becomes unsupportable.
Headlands and Bays
- Discordant coastlines
- Alternating bands of hard and soft rock
- Less resistant soft rock gets eroded quicker
- Headlands left sticking out and eventually collapse as they’re unsupported as vulnerable
- Bays form from rapid erosion from soft rock
The methods of Transportation
Traction: rolls along seabed
Saltation: bounce along seabed
Suspension: carried along seabed
Solution: dissolved
Longshore Drift
At an angle from the angled prevailing winds. Therefore swash is at an angle and the backwash comes down from the force of gravity. The process repeats itself and transports sediment across the coastline.
Wave Quarrying
When high energy, tall waves hit the cliff face they have the power to enlarge joints and remove large chunks of rock in one go through vibration. This occurs due to the intense force of these waves.
Solution/Corrosion
When sea water dissolves certain types of rocks. In the UK, chalk and limestone cliffs are prone to this type of erosion.
Attrition
When rocks that the sea is carrying knock against each other. They break apart to become smaller and more rounded.
Abrasion/Corrasion
When pebbles grind along a rock platform, much like sandpaper. Overtime, the rock becomes smooth.
Hydraulic Action
The sheer power of the waves as they smash against the cliff. Air becomes trapped in the cracks in the rock and causes the rock to break apart.
Run-off
Water is running off the land.
E.g. a stream across a bay or over a cliff
Transportation
Material is removed from one location to another
Traction, saltation, suspension, solution
Submergent Coastlines
- Develop as a result of eustatic sea level rise or isostatic descent
- Rias, fjords, dalmation coasts
Erosion
Degradation of rock and its removal to expose a fresh rock face.
Hydraulic action, abrasion, attrition, solution, wave quarrying
Marine Processes
Operate along the coastline and are connected with the sea, such as waves, tides and longshore drift: erosion, transportation and deposition.
Exfoliation
Dry rock in the sun may absorb considerable heat, then be cooled rapidly by contact with the much cooler sea. Repeated expansion and contraction may lead to the outer layers of rock fracturing.
Tidal Surge
A coastal fixed or tsunami-like phenomenon of rising water commonly associated with low pressure weather systems, such as cyclones. It is measured as the rise in water level above the normal tidal level and does not include waves.
Animals
Surface animals may excavate nesting burrows in cliff faces. Subsurface marine creatures such as the piddock drill holes in rock and limpets create a home indentation on their base rock to which they return after grazing.
Geomorphological Processes
Natural mechanisms that result in the modification of the surficial materials and landforms at the Earth’s surface.
Vegetation Succession
A sequence of vegetation species colonising an changing an environment.
Crystallisation
The high salt content of seawater can lead to the growth of salt crystals within rock under drier conditions. These can exert pressure within small joints and, overtime, cause the rock to lose integrity.
How do mudflats form?
- Low energy environment and shelter from winds and waves
- Large inout of sediment
- Coastal accretion reduces flooding and allows plants to grow
- Glasswort, cordgrass (pioneer species) grow
- More plants colonise marsh, red fescue
- Deepen, only highest tides
- Sea lavender
- Halosere
Tombolo
When a spit extends from a shore and reaches an offshore island.
E.g. Onesil Beach, Dorset
Beach Morphology
The shape and make-up of the beach
Dependent on several factors:
- Wave type
- Energy
- Sediment type
- Sea bed morphology
Where does sediment come from?
- Rocks on land
- Volcanoes
- Streams or rivers flowing into seas
- Estuaries
- Cliff erosion
- Offshore banks
- Material from biological origin, shell fragments, coral fragments
Bar
When a spit extends across a bay and rejoins the coast on the opposite shore, completely confining salt water behind it in a lagoon.
Some bars form by onshore migration if material deposited offshore as sea levels rose after the last ice age. E.g. Slapton Ley, Devon
Oxidation
Rocks containing iron compounds experience oxidation of the iron into a ferric state (or ‘rusting’) when oxygen and water are readily available from air or sea. This can lead to disintegration.
Offshore Bar
Where a ridge of beach material that remains semi-submerged accumulates seaward of the breaker zone then it is called an offshore bar. They form from sediment eroded by destructive waves and carried seawards by backwash.
Hydration
Makes rocks more susceptible to further chemical weathering, although involves addition of water to minerals in the rock. This causes the rock to expand, creating stress, which can itself cause the rock to disintegrate. The process weakens the rock and can create cracks or widen joints allowing further chemical weathering to occur.
Sediment Cells
A length of coastline within which the movement of coarse sediment is largely self-contained. They are separated from other areas by well-defined boundaries, such as headlands and stretches of deep water.
Wetting and Drying
Rock in the intertidal zone may alternate between being wet and being dry. Some rocks expand when they are wet and contract dry, and this can contribute to tiny cracks developing and the rock fragmenting.
Mudflows
Fine particles of mud flow down the face of cliffs, often heavily saturated by persisted rainfall which adds to its bulk and makes it a more liquid consistency.
Emergent Coastline
- Can be caused as a result of eustatic fall in sea level or isostatic rise or a combination of both
- Raised beaches, relict cliffs
Rotational Slip/Slumping
A succession of rational landslips in which the cliff face collapses in distinct stages. Heavy rain may lubricate a curved slip plane and undercutting at the cliff base by wave action results in a slippage of material down towards the beach. It often occurs on cliffs composed of glacial deposits.
Psammosere
A succession beginning in a sandy environment.
Upwelling
The movement of cold water from deep in the ocean towards the surface. The more dense cold water and creates nutrients rich cold ocean currents. These currents form parts of the pattern of global ocean circulation currents.
Factors affecting Wave Energy
- Wind speed (the higher the wind speed the greater the energy)
- Fetch (the longer the fetch the greater the energy)
- Solar energy
- Length of time the wind has been blowing
- Variability of wind direction (prevailing winds generate more high energy waves than conditions where the wind direction is constantly shifting)
- Pressure gradients (low pressure will generate stronger winds and more high energy waves)
Hydrolysis
Where mildly acidic water reacts or combines with minerals in the rock to create clays and dissolvable salts; this itself degrades the rock, but both are likely to be weaker than the parent rock, this making it more susceptible to further degradation.
Mass Movement
The movement of consolidate material (solid rock) or unconsolidated material (clay and soil) due to gravity.
Rockfall, landslides, mudflows, soil creep, rotational slip/slumping
Factors affecting the Rate of Erosion
- Wave steepness and breaking point
- Fetch
- Sea depth
- Coastal configuration e.g. convergent energy at headlands
- Beach
- Human activity
- Geology
Difference between High and Low Energy Coastlines
Higher-energy destructive waves during the stormier winter months as there is low pressure and more storms.
Constructive lower-energy waves are during the calmer summer months.
Marine Deposition
The sea deposits its loads when it looses energy or there is an increase in the amount of eroded material.
