Coasts Flashcards
What is a coast?
Where land meets the sea
What is a coastline?
the edge of the land marked though the high water mark on a low lying coast or the foot of steep sloped coasts
What is a shore?
Area between lowest and highest tide points
How often do tides occur? What is tidal range? How do tides affect waves and costal features?
Tides are twice a day (vary)
Difference between high and low tide = tidal range
-> Tide controls how waves work
-> Action of waves and currents contribute to coastal features
What are waves?
marine processes that erode, transport and deposit materials
Transfer of energy from wind blowing over the sea (result of friction)
Water doesn’t more -> energy is transferred
What affects the size of a wave?
Velocity of wind
Fetch (distance of water wind blows over (same direction as wind))
Time duration of wind (24 hours for full potential)
How do waves break onto the beach?
Wave approaches coast (shallower waters -> friction with sea bed -> wave leans forward -> breaks
What is the movement of the water on the beach called?
Swash -> up the beach
Backswash -> down the beach
What are the two types of waves ?
Constructive -> builds up beaches
Destructive -> erodes the beach
What are the characteristics of constructive waves?
Strong swash, weak backwash
Long wavelength (100+ m)
Low frequency (6-8/min)
Low energy
Low height (less than 1 m)
What are the characteristics of a destructive wave?
Weak swash, strong backwash
Short wavelength (20+ m)
High frequency (10-12/min)
High energy
High height (more than 1 meter)
What is marine erosion?
The process when marine processes (sea levels rise, strong wave action, coastal flooding) wears down the coast
What are the 4 processes in marine erosion?
Hydraulic action
Attrition
Corrosion/solution
Abrasion/corrasion
What is hydraulic action?
The force of the wave compressing air in the cracks of a cliff/rock
What is attrition?
Rocks and boulders are carried by the wave and bump into each other (smaller and smoother -> form shingles and sand)
What is corrosion/solution?
Slightly acidic and salty sea water gradually dissolves certain costal rocks
What is abrasion/corrasion?
Large waves pick up and throw rocks at the coast
What is marine transportation?
Movement of material in the sea and along the coast
Materials arrive from:
Erosion
Long shore drift
Constructive waves
Rivers
What are the 4 processes in marine transportation (+ definition)?
Traction: heavy material dragged along sea floor
Saltation: smaller material bounced along sea floor
Suspension: fine material held in water
Solution: dissolved material is carried in the water
How does long shore drift occur?
Prevailing wind makes waves approach at an angle -> wave breaks + swash carries material onto the beach (same angle as wave)-> swash dissipates and backswash carries material down perpendicular to the beach (gravity)
Creates zig-zag movement -> material transported down the coast
What is marine deposition?
When material is transported and dropped off by constructive waves
How is sediment sorted on the beach?
Largest material -> furthest from the sea -> swash deposits heaviest material first
Backwash lose energy/water as it moves back down because of sand porosity -> deposition of sediment gets finer and finer
Sorted by wave deposition
What is a beach berm and how is it formed?
If a destructive waveform due to a storm, then a large shingle is thrown above the usual high tide level to form a ridge at the top of the beach called a berm
How are cliff and wave cut platforms formed?
Many cliffs have wave cut notch (indent in foot of cliff)
Abrasion, corrosion and hydraulic action push the notch back
Cliff becomes unstable and collapse
Backwash carries the eroded material, and leaves a wave cut platform
What is coastal retreat?
As the cliff is eroded and retreated, this is referred to as costal retreat
How are caves, arches, stacks and stumps formed?
Cliff -> resistant rock
Erosion at weak points (crack, faults) and widens the weak points
Weakness widens -> cave
If located at a headland and erodes further (cuts through the platform)-> arches
Base of arch -> wider but thinner -> roof of arch collapse -> stack
Stack is undercut and collapses -> stump
CASS
How are bays and headlands formed?
Found in areas with alternating resistant and soft rocks, perpendicular to waves
Less resistant rock eroded back -> bay (inlet of sea where land curves inward, usually with a beach)
More resistant rock -> left protruding -> headland
What are some features of headland?
Cliffs along all sides of the
Projects into the sea
Longer than it is wide
Resistant rock
What are some features of bays?
Wide open entrance
Roughly semicircular shape
Land is lower than headlands
Many beach (sheltered area -> good for deposition)
How are beaches formed?
Beaches -> best natural defense
Tide and current move sediment and debris -> changes the beach (erodes and builds up)
Formed in sheltered areas
Constructive waves
Usually formed in the summers (calmer weather)
What are the features of well sorted and poorly sorted beaches?
Well sorted:
Uniform sediment and size
Low energy conditions
Sandy/muddy beaches
Poorly sorted:
Variety of sediment and size
High energy conditions or extreme weather
How are spits formed?
Extended stretches of sand or shingle that extends out to sea from the shore
Occur at change in coastline or mouth of river
May have hooked end (if wind direction changes)
Area behind spit -> sheltered (salt marshes or mud flats)
Sediment transported by long shore drift -> coastline change have shallow shelter area for deposition of sediment -> more friction more deposition -> spit builds to sea level and extends
How are bars formed?
Spit grows across a bay -> bar is the bit of sand created
How are lagoons formed?
When a bar goes fully across a headland, a small body of water is isolated from the sea -> lagoon
May fill with sediment to form land
What is a tombolo?
When a spit joins an island to the mainland
What is a barrier island?
Like a bar, but both ends are open
What are sand dunes?
Dynamic environment -> changes quickly
Sandy beaches backed by sand dunes
Winds + transport move dried and exposed sand -> sand trapped by obstacles -> Dune slowly moves inland
How are sand dunes formed?
Wind blown sand deposited against obstruction (pebbles or driftwood) -> more sand particles caught and dune grows -> ridges colonized and fixed by vegetation (succession)
What do pioneer species in sand dunes have to deal with with?
Salinity
Lack of moisture (sand drains quick)
Wind
Temporary submergence in sand
Rising sea levels
What are the different stages of sand dune formation?
Embryo dunes:
Sand is trapped and deposition starts
Pioneer: Lyme grass and sea couch grass
Alkaline and little soil
Max 1m tall
Fore dunes:
Embryo dune brings protection against winds
Organic matter -> hospitable for plants
Species: Marram grass -> stabilises the dune (roots)
Max 5m tall
Yellow dune:
Initially yellow but darken (organic material)
Marram grass dominates -> other flowering plants and insects in slacks
20% exposed
Max 8m tall
Gray dunes:
More stable -> less than 10% exposed
Good biodiversity
Shrubs and bushes appear
Soil acidity and water content increase
8-10m tall
Mature dunes:
Most old and stable
Soil -> can support many varieties
Final stage of succession
What is succession?
The change in an ecosystem, over time, of the species that occupies it
What is a dune slack?
Low lying areas in a dune system -> seasonal flooding and nutrients levels are low
Where can salt marshes form?
Aren’t temp dependent
Intertidal ecosystem
Flat with many channels
Costal areas that are sheltered
Tidal waters flow gently and deposits sediment
Brackish (salty and fresh) water
What are the features of a salt marsh?
non-woody, salt tolerant plants
Begin as tidal mud flats then gain height with sediment
Tidal flooding ensured that the soil never dries out (daily floods)
Pioneer species of halophyte plants Dead plants add nutrients and sediment to the soil
How are coral reefs formed?
Build up and compression of skeletons of lime secreting marine animals -> polyps
Living coral polyps -> outer and upper parts
Skeletons (hard masses) -> formed when one generation dies and next grows on top -> cause of direction of coral growth
Need a solid surface to start
Parallel to coast
Sensitive -> need certain conditions
What conditions are needed for coral reefs to form?
within 30°N and 30°S latitudes
Temperature (min 18°C, but ideally 22-25°C)
Light (need to photosynthesis for algae (zooxanthellae) that live in the tissue)
Water depth (less than 25m (light), clear and clean water)
Salinity (33-42% salty water)
Wave action (provide oxygen)
Cannot be exposed to air
What are the 3 types of coral reefs?
Fringing (ex: coral coast of Fiji):
Low and borrow bands of coral
Parallel to coast around a land mass
Covered by narrow and shallow lagoon at high tide
Outer slopes -> steep into sea
Barrier (ex: Great Barrier Reef):
500m-multiple km
Separated from coast by by deep lagoons
Atolls (Maldives Suvadiva):
Narrow ring shaped reef
Encircles lagoon
Channels -> connects lagoon to sea
Why are mangroves the most successful ecosystem on earth?
Warm tropical areas, but is highly adaptable to changing conditions
What are some facts about mangroves?
Originated from Southeast Asia
Mainly found in warm tropical waters and coastal swaps within 30° N and S
Intertidal zones of the coast
What are some characteristics of mangroves?
Range in size from small shrubs to 60m
Tangled roots form a dense thicket
75-80% humidity
1500-3000mm rainfall
Ideal temp-27 degree
Filtration system to keep salt out
Snorkel like root -> easier to get air
Prop roots -> trunks kept upright in soft sediment
Colonises new land
Fruit and seedling -> travel very far
What are some opportunites presented by coast?
Development (houses, shops, hotels, roads, school, restaurants, etc.)
Nature reserves
Swimming and sports
Industry
Dishing and aquaculture
Tourism
Agriculture
Ports and harbors
What are some human induced hazards of coast?
Urbanisation and transport
Change in land use, disposal of sediments and waste, congestion
Loss of habitat, pollution, health risk, etc.
Industry
Land use change, power stations, extraction of natural resources
Loss of habitats, pollution, costal erosion, decreased fresh water, etc.
Agriculture
Land reclamation, fertiliser/pesticide use, livestock density
Loss of habitat, pollution, etc.
Fisheries and aquaculture
Ports and harbors, fishing gear, shrimp/fish farming
Overfishing, impact of other species, pollution, invasive species
Tourism and recreation
Development, congestion, pollution, waste disposal, water activities
Loss of habitat, disturbance of migration patterns, pollution, health risk
What are some nature induced hazards to coast (tropical storms)?
Tropical storm
Hurricanes, typhoons, cyclones, tsunamis
Destruction of infrastructure
Heavy rainfall and storm surges
Loss of ecosystem, habitats, etc
Ship wrecks
Losss of power and communication
Millions of dollars in damage
Reduce risks:
Sea walls and artificial levees
Evacuation plan
Tracking and warning systems
Good and strong Infrastructure
Supplies and shelter
What are some nature induced hazards to coast (changing sea levels)?
Rising sea levels -> Ria and fjords
Falling sea levels -> emergent coastlines
Poses danger for low lying coasts and islands
What are some nature induced hazards to coast (erosion)?
Geology shapes the coastline
Erosion:
Less resistant rock -> faster erosion
Long shore drift and destructive waves move sand and expose base of cliff -> coastal erosion
Coastal management can cause erosion further down
Other factors speed rate of erosion
What are some methods of costal erosion (soft engineering)?
Natural processes
Less expensive and preserves looks
Sustainable, but not as effective
Beach replenishment
Fencing, hedging, replacing vegetation
Cliff regrading
Managed retreat
What are some methods of costal erosion (hard engineering)?
Sea defenses
Expensive to maintain and build
Used when thing protected has great economic benefit
Sea wall
Groynes
Rip rap
Revêtements
Gabions
Offshore barriers
How can prediction help prepare for a flood?
Past records
Modern tech -> satellite, monitoring system, weather stations, etc.
Indicates possible strength and scale of damage can be predicted
What are some methods of prevention for coastal flooding?
Flood defenses
Emergency centers
Early warning systems
Education
Planning
Designing buildings to withstand flooding
Buffer zones
What are the four shoreline management plans?
Hold the line
Long term and high cost
Build and maintain costal defenses
Hard engineering + soft engineering support
Advance the line
Build new defenses to extend the shoreline
Land reclamation
Both types of engineering
Managed realignment
Coastline moves naturally
Process monitored and directed
Soft engineering + hard engineering support
Do nothing
Controversial and cheap
Allow erosion and retreat
How do governments decide what type of engineering is best?
Economic value of resources
Cultural value of land
Community pressure
Social and historical communities
