Coasts Flashcards
What type of a system is a coastline?
Open system
Example of an input into a coastal environment:
Wind, precipitation, waves, pollution, river flow
Example of an output of a coastal environment:
Ocean currents, rip tides, evaporation, sediment transfer (via longshore drift)
Example of a store in a coastal environment:
Beach, sand dunes, spits, bars, caves, salt marshes etc…
Example of a flow/transfer in terms of coastal environments:
- Wind blowing sand
- Longshore drift
- Mass movement processes
- Weathering
- Erosion
What are the 3 types of weathering?
- Mechanical/Physical
- Biological
- Chemical
What are examples of geomorphological processes?
- Weathering
- Mass movement
- Erosion
- Transportation
- Deposition
What are the main types of erosion?
- Hydraulic action
- Wave quarrying
- Corrasion
- Abrasion
- Cavitation
- Solution/corrosion
- Attrition
Define dynamic equilibrium (in terms of coasts)
A state of balance within a constantly changing coastal system.
What factors affect wave energy?
- Strength of the wind
- Duration of the wind
- Fetch (distance of open water over which the wind blows)
Key characteristics of constructive waves, inc:
- Formation
- Wavelength
- Frequency
- Swash/backwash characteristics
- Wave characteristics
- Effect on beach
- Formed by distant weather systems in the open ocean.
- Long wavelength
- 6 to 9 per minute
- Strong swash, weak backwash.
- Low waves which surge up the beach.
- Gentle beach profile
Key characteristics of destructive waves, inc:
- Formation
- Wavelength
- Frequency
- Swash/backwash characteristics
- Wave characteristics
- Effect on beach
- Localised storm events.
- Short wavelength
- 11 to 16 per minute
- Weak swash, strong backwash.
- High waves which plunge onto the beach.
- Steep beach profile
What type of wave is more common in the summer?
Constructive
Key characteristics of high energy coastlines:
- More powerful, destructive waves (large fetch).
- Rocky headlands.
- Rate of erosion exceeds rate of deposition.
Key characteristics of low energy coastlines:
- Less powerful, constructive waves.
- Sheltered, fairly sandy areas (with low fetch).
- Landforms of deposition.
- Rate of deposition exceeds rate of erosion.
What is wave refraction?
The process by which waves turn and lose energy around a headland; the wave energy is focused around a headland, causing erosive features here.
The waves then dissipate in bays, forming beaches.
What is corrasion?
Sand/pebbles hurled against cliffs by waves.
What is abrasion?
Rocks hurled against cliffs by waves.
What is attrition?
The smoothing and reducing of angular rock fragments into pebbles, shingle and eventually sand particles.
What is corrosion/solution?
When mildly acidic saltwater causes alkaline rock (e.g. chalk and limestone) to erode.
What is hydraulic action?
Waves break against a cliff face and water forces itself into cracks - compressing the air inside.
What is cavitation?
The opening of cavities within cliffs
What is chemical weathering?
When rain and/or seawater containing chemicals react with the chemical compounds in the rock, altering its structure.
What is mechanical/physical weathering?
The breakdown of rocks due to exertion of physical forces (without chemical changes taking place).
What is biological weathering?
Organic activity breaking down rocks; typically through living organisms such as plants and animals.
Examples of mechanical weathering:
- Freeze-thaw weathering
- Salt crystallisation
What is freeze-thaw weathering?
A type of mechanical weathering whereby water enters cracks in a cliff and freezes overnight, expanding in volume, growing cracks in the cliff and making it more vulnerable to other erosional processes.
What is salt crystallisation?
A type of mechanical weathering whereby seawater evaporates, leaving salt crystals to grow over time, widening cracks in the cliff and making it more vulnerable to other erosional processes.
Examples of chemical weathering:
- Carbonation
- Oxidation
- Solution
What is carbonation?
Carbon dioxide in moisture in the air reacts with carbonate minerals in rock, creating carbonic acid.
What is oxidation?
Reaction of minerals in rock with atmospheric oxygen. Iron compounds begin to rust and crumble.
Examples of biological weathering:
- Plant roots
- Birds
What are the 3 main types of rock?
- Igneous
- Metamorphic
- Sedimentary
What is the definition of erosion?
The breakdown and subsequent removal and transportation of material.
What is the definition of mass movement?
The movement of consolidated material (solid rock) and unconsolidated material (clay and soil) due to gravity.
What are the 4 key types of transportation?
- Traction
- Saltation
- Suspension
- Solution
What is traction?
When large particles like boulders are pushed along the sea bed by the force of the water.
What is saltation?
Pebble sized particles are bounced along the sea bed by the force of water.
What is suspension?
Small particles like silt and clay are carried along in the water without touching the sea bed.
What is solution?
Soluble materials dissolve in the water and are carried along.
What type of rock erodes the slowest (and at what rate)?
Igneous
- Less than 0.1cm/year
What type of rock erodes the fastest (and at what rate)?
Sedimentary
- 0.5 to 10cm/year
How do waves form?
- Wind moving across surface causes frictional drag, resulting in a circular motion of water.
- As the seabed gets shallower, the wavelength shortens and velocity decreases, but the wave height increases.
- This causes water to back up from behind the wave until the wave breaks.
What are the main sources of sediment?
- Rivers
- Cliff erosion
- Longshore drift
- Wind
- Glaciers (melting)
- Waves, tides and currents (offshore)
What is a sediment cell?
A stretch of coastline, usually bordered by two headlands, where the movement of sediment is more or less contained.
What is the difference between erosion and weathering?
Weathering breaks down rocks in-situ (without displacing them), whilst erosion displaces the rocks.
What are the 5 main types of mass movement?
- Is the ground wet or dry when they occur?
- Mudflow - Wet
- Runoff - Wet
- Landslide - Dry or wet
- Rockfall - Dry
- Soil creep - Wet
What is a concordant coastline?
A coast where layers of differing rock types run parallel to the coast. Results in the formation of coves.
What is a discordant coastline?
A coast where layers of differing rock types run at right angles to the coast (perpendicular). Results in the formation of headlands and bays.
How does a wave-cut notch form?
When waves erode a cliff, the erosion concentrates on the high tide line. Hydraulic action and corrasion create the wave-cut notch through this.
How does a wave-cut platform form?
As a wave-cut notch becomes deeper, the cliff face becomes unstable and collapses, leaving behind a platform which builds up over time, creating a wave-cut platform.
When are wave-cut platforms usually exposed?
At low tide.
Example of a negative feedback loop at a coastline:
A negative feedback loop can develop when a wide wave-cut platform dissipates the energy of waves before it can reach the cliff. This slows erosion of the cliff and therefore the rates of retreat slows.
What is a tombolo?
A bar or beach that connects the mainland to an offshore island.
How are tombolos formed?
When wave refraction off the offshore island reduces wave velocity, leading to deposition of sediment on either side.
What is longshore drift also known as?
Littoral drift
What does SMP stand for?
Shoreline Management Plan
What does ICZM stand for?
Integrated Coastal Zone Management
What are the 2 different beach types?
- Swash aligned
- Drift aligned
What is a swash aligned beach?
Waves approach parallel to the shore. Wave refraction can reduce the wave speed resulting in a beach with larger sediment.
What is a drift aligned beach?
Waves approach at an angle, resulting in longshore drift moving sediment along the beach, potentially forming a spit. The end of the beach will have smaller sediment because it will become smoother the more it moves.
Order of coastal zones from ocean to land:
- Offshore
- Nearshore
- Foreshore
- Backshore
What coastal zone lies between the high tide and low tide mark?
Foreshore
What is the nearshore zone also known as?
Breaker zone
How deep is the nearshore/breaker zone?
5-10m
What is located in the backshore zone?
Storm beach
What is the foreshore zone also known as?
Surf zone
What is the offshore zone beyond the influence of?
Waves
What zone is the maximum spring tide located?
Backshore
What zone are sand ridges and runnels found?
Foreshore
What zone are berms found?
Backshore
What is a spit?
A long, narrow depositional landform made of sand/shingle which extends from the land to the sea on a drift aligned beach.
Examples of depositional landforms:
Beach
Spit
Tombolo
Barrier beach/bar
Sand dunes
Estuarine mudflats
Saltmarshes
Examples of erosional landforms:
Headland
Cove
Cave
Arch
Stack
Stump
Wave-cut Platform
Blowhole
What is a barrier beach/bar?
A beach or spit that extends across a bay to join two headlands. This forms a lagoon behind it.
What are offshore bars and how do they form.
An offshore region where sand is deposited as the waves don’t have enough energy to carry the sediment to shore.
What can offshore bars reduce?
Erosion of the mainland
How do spits form?
- Sand/shingle is moved along the beach via longshore drift, until the coastline changes in direction (e.g. due to a river estuary)
- Sediment begins to build up across the mouth, forming a spit.
What is a blowhole?
A hole in the top of an arch due to wind/wave erosion causing it to collapse.
What is a recurved tip?
When the end of the spit begins to curve around due to wave refraction carrying sediment to more sheltered water behind the spit.
What are berms?
A series of small ridges that form near the high tide mark, as a result of constructive wave swash deposition.
What are sand ridges and runnels?
A series of ridges and troughs running parallel to the coast near the low water mark, as a result of deposition during backwash.
Order of sand dune stages from shoreline to inland:
- Embryo dune
- Fore dune
- Yellow dune
- Grey dune
- Mature dune
What can estuarine mudflats develop into?
Saltmarshes
How do estuarine mudflats form?
Develop in estuaries when water flow virtually ceases due to the meeting of river water and tides, leading to heavy deposition. Most of the deposition consists of mud.
How do saltmarshes form?
- Mud is deposited via flocculation.
- Pioneer plants (e.g. cordgrass) that can tolerate inundation and salty water (halophytes) colonise the transition zone between low and hide tide, trapping mud.
- Mud levels rise above high tide, allowing other vegetation to grow.
- Soil conditions improve to allow meadows to form.
- Climactic climax/climax vegetation is reached with shrubs and trees growing.
What are saltmarshes?
Areas of flat, silty sediments that accumulate around estuaries or lagoons.
When are saltmarshes covered?
High tide
When are saltmarshes exposed?
Low tide
What plants can tolerate salty conditions?
Halophytes
What plants can survive in extreme conditions?
Xerophytes
What conditions are needed for sand dunes to form?
- Large quantities of sand onshore.
- Large tidal range, allowing sand to dry and be picked up by wind.
- Dominant onshore winds to blow the sand to the back of the beach.
How do sand dunes initially develop?
When sand is trapped by debris towards the back of the beach, and vegetation helps to stabilise this sand.
Examples of pioneer species in sand dunes:
- Sea rocket
- Couch grass
Where is marram grass typically found?
Fore dunes
How is marram grass well adapted to its environment?
Has long tap roots to seek water, which also stabilise the grass.
Define eustatic change:
When the sea level itself rises or falls.
Define isostatic change:
When the land rises or falls, relative to the sea.
Does eustatic change occur globally or locally?
Globally
Does isostatic change occur globally or locally?
Locally
How does eustatic change occur?
- In cold, glacial periods, water is stored as snow and ice sheets, lowering sea levels.
- As temperatures rise, ice and snow melts, flowing into rivers and seas, raising sea levels.
How does isostatic change occur?
- During glacial periods, the weight of ice sheets (several kilometres thick), makes the land sink (isostatic subsidence).
- As temperatures rise, the ice sheets melt and the land readjusts and rises (isostatic recovery/rebound).
Define isostatic subsidence:
Land sinks due to weight of ice sheets.
Define isostatic recovery/rebound:
Land rises after ice sheets melt, relieving the weight.
What is an emergent coastline?
When a fall in sea level exposes land previously covered by the sea.
What is a submergent coastline?
When a rise in sea level floods the coast.
What type of coastline are raised beaches found?
Emergent coastline
What landforms develop at a submergent coastline?
- Rias
- Fjords
How do rias form?
When valleys in a dissected upland area are flooded.
Where region in England are rias common?
South-west England (e.g. Devon)
What are fjords?
Long, steep sided, U-shaped valleys which have been flooded.
Where are rias deepest?
At the mouth
Where are fjords deepest?
Inland (in the middle)
What countries are fjords common?
- Norway
- Chile
- New Zealand
What are Dalmation coasts?
Distinctive submergent coasts which have formed due to the flooding of valleys and ridges which were running parallel to the coast, creating offshore islands.
What are Dalmation coasts also known as?
Pacific Coasts
Example of a country with dalmation coasts:
- Croatia
- Chile
What does CBA stand for?
Cost-Benefit Analysis
Examples of hard engineering techniques:
- Groynes
- Sea walls
- Rip rap (rock armour)
- Revetments
- Offshore breakwater
Examples of soft engineering techniques:
- Beach nourishment
- Cliff regrading
- Dune stabilisation
What does SSSI stand for?
Sites of Special Scientific Interest
What are revetments?
Sloping wooden, concrete or rock structures designed to break up wave energy.
Groynes advantages:
- Not too expensive (£5000 to £10000 each)
- Builds up the beach
Groynes disadvantages:
- Visually unappealing
- Increases erosion further along the coast by restricting longshore drift.
Offshore breakwater advantages:
- Effective at breaking wave energy.
Offshore breakwater disadvantages:
- Visually unappealing
- Potential navigation hazard.
Sea walls advantages:
Effective protection against erosion.
- Tourism benefits (acts as a promenade).
Sea walls disadvantages:
- Wave energy reflected, not absorbed, increasing erosion elsewhere.
- Expensive to construct and maintain (£6000/metre).
Revetments advantages:
- Relatively cheap (£4500/metre).
Revetments disadvantages:
- Visually unappealing.
- Require constant maintenance.
Rock armour advantages:
- Relatively cheap and easy to construct and maintain (£1000 to £3000/metre).
Rock armour disadvantages:
- Dangerous if climbed upon.
- Rocks used aren’t local and can therefore look out of place with the local geology.
How many sediment cells are there in England and Wales?
11
What are the 4 options considered in a SMP?
- Hold the line
- Advance the line
- Managed retreat/strategic realignment
- No active intervention
Beach nourishment advantages:
- Relatively cheap (£3000/metre)
- Easy to maintain
- Tourism benefits
- Looks natural
Beach nourishment disadvantages:
- Could damage local ecosystems.
- Requires constant maintenance due to longshore drift.
Dune stabilisation advantages:
- Cheap (£2 to £20/metre)
- Creates an important wildlife habitat.
Dune stabilisation disadvantages:
- Time consuming (to plant the marram grass).
Cliff regrading advantages:
- Cost effective.
- Can be effective on clay or loose rock where other methods will not work.
Cliff regrading disadvantages:
- Causes the cliff to retreat.
What is the purpose of an ICZM?
To establish sustainable levels of economic/social activity, resolve environmental, social and economic challenges, and protect the coastal environment.
- Provides a more holistic overview of the coast.
