Coasts Flashcards
What is a coastline?
Where the land meets the sea
What is the size of a wave determined by?
- Strength of the wind
- Length of the fetch
- How long the wind blows for
What causes waves to form?
Friction between the wind and sea causes the orbit to become elliptical rather than circular
Name the properties of a destructive wave
- High wave height
- Short wave length
- Powerful backswash, weak swash
Name the properties of a constructive wave
- Low wave height
- Long wave length
- Weak backswash, powerful swash
What are tides caused by?
Gravitational pull of the moon and sun
Define the tidal range (intertidal zone)
The difference between high and low tide
When do Spring tides occur?
When the moon and sun are aligned
What do Spring tides cause?
Very high and very low tides
When do neap tides occur?
When the moon and sun are at right angles to each other
What do neap rides cause?
Lower high and higher low tides
Define weathering
The break up of rock in situ
Define abrasion using the coastline terminology
Rocks being thrown into cliffs and break the cliff a little at a time
Define solution using the coastline terminology
The slightly acidic sea water dissolving the cliff
Define hydraulic action using the coastline terminology
He sea water forces air into cracks in the cliff which causes them to get larger
Define attrition using the coastline terminology
Rocks being thrown up into each other by the waves, breaking them apart
Name two types of physical weathering
- Freeze thaw
- Exfoliation
Name 2 types of chemical weathering
- Carbonation
- Oxidation
How does temperature have an affect on chemical weathering?
Hot temperatures increase the rate of weathering
How does geology change the rate of weathering?
- Rocks with already existing cracks will weather more easily
- Hard rock will weather slower than a soft rock
-Limestone weathers faster from carbonation due to its high CaCO3 levels
How do humans affect the rate of weathering?
- Chemicals added by us increase CW
- Introducing animals increases CW
- Insulating rocks reduces temperature,variation decreasing PW
- Deforestation reduces BW
What is the aspect of land?
It’s orientation in relation to the sun
How does the aspect of a piece of land affect its rate of weathering?
IF slopes are facing the sun:
-increased vegetation, increased BW
IF NOT facing the sun:
-Increased CW AND PW
How does the relief of land affect the rate of weathering?
Steep slopes cause:
- Increased PW due to increased surface runoff
- Reduced chemical weathering, lack of stationary water
Flat surfaces cause
-Increased rate of CW
How does vegetation affect the rate of weathering?
- vegetated areas have a higher rate of BW
- Some mosses contain acids that can cause CW
What is the rate of coastal erosion determined by?
- Wave size
- Type/profile of beach
- Supply of beach material by LSD
- Vegetation cover
- Local hydrology
- Rate of removal of debris from cliffs
- Cliff material
How does the wave size affect the rate of coastal erosion?
The longer the fetch of the wave the greater the erosive energy of the wave
How does the profile size affect the rate of coastal erosion?
Beaches dissipate energy
The higher the beach the lower the energy in the wave
How does the supply of beach material from LSD affect the rate of coastal erosion?
A consistent supply of beach material slows down erosion
How does vegetation affect the rate of coastal erosion?
Cliffs with vegetation cover tend to be more resistant to recession as roots help Bing and reinforce cliff material
How does the local hydrology affect the rate of coastal erosion?
A large amount of surface run off and infiltration can increase the rate of cliff recession
How does the rate at which debris is remove from the foot of cliffs affect the rate of coastal erosion?
If material formed at the foot of the cliff is rapidly transported away, the cliffs are exposed to erosion
How does the cliff material affect the rate of coastal erosion?
Soft Boulder clay cliffs recede faster than cliffs formed of hard rock such as chalk
Define a wave cut notch
A hole at the bottom of a cliff created by erosion
Define a wave cut platform
A rock platform which is left behind as the cliff retreates
Define cliff recession
The cliff starts to recede due to the erosion and weathering, causing cliffs to collapse
Explain rock pools at a cliff
This is where rocks have fallen to create holes in the wave cut platform
Define a headland
An area of hard rock which is eroded less than the soft areas, creating an outcrop of the hard rock
Define a Bay
An area of soft rock which is eroded more than the more resistant areas, resulting in an indent in the coastline
Describe a concordant coastline
Bands of soft and hard rock which run parallel to the coastline
Describe a discordant coastline
Bands of soft and hard rock which run at
right angle to the coastline
Describe the formation of a bay on a discordant coastline using rock examples
- Less resistant clay is eroded and weathered quickly
- Sub aerial and marine processes causes a quick rate of recession
- In a discordant coastline it will be flanked by headlands
- An indent is made, which is then shielded by headlands
What happens at a concordant headline in relation to bays and headlands?
Less headlands and bays form
Describe the formation of a headland on a discordant coastline using rock examples
- The more resistant limestone is eroded and weathered slowly, due to the lesser amount of weaknesses in the rock
- Eventually the headland juts out as the softer rocks besides it retreats at a much faster rate
- The headland then is more susceptible to erosion, as waves are concentrated there , protecting the bays
What is the order of features which are created at a headland?
- Lines of weakness
- Cave
- Arch
- Stack
- Stump
What creates wave refraction?
When waves reach the shallow water they bend as the wave has increased friction with the sand
What does wave refraction cause?
More erosion at the headland
Less erosion at bays
Define long shore drift (LSD)
This is the process of waves moving material along a coastline
Define swash
The waves breaking and travelling up the beach carrying load. The swash travels in the direction of the prevailing wind
Define backswash
The waves returning to the sea with load. Waves will take the shortest route back to the sea (gravity)
Define prevailing wind
The direction that wind normally hits a coastline
Define groynes
Wooden or concrete fences placed out into the sea to stop LSD occurring
Define sea currents
The movement of water caused by differences in temperature, changes in wind or tides.
Currents can be very strong and can carry large amounts of material
Define saltation in the context of the coast
Wind transports sand and small stones across a beach. The process is the bouncing sand and material.
Explain long shore drift
- Occurs when the direction of the prevailing wind causes the swash to transport material at an angle
- The backswash takes the material at right angle to the coast
- The sediment is moved down the coast in the direction of the prevailing wind
- This will continue until there is a change in the coastline or groynes are found
Define a spit
A long thin stretch of sand connected to mainline
Define a bar
A spit that connects two headlands or runs across a bay
Define a tombolo
A spit that joins the mainland to an island
Define a lagoon
A salt water lake that develops behind a bar or spit
Define an island
A small body of land found in oceans and seas
Explain spit formation
- LSD takes the sediment down the coast until a change in the shape of the coastline and drop in of wave energy
- Wave energy is changed by conflicting currents, deposition occurs
- Deposition occurs at a faster rate than it can be eroded
- A ridge of sediment is built up, which is the spit
- Recurved laterals are result of temporary changes in wind and wave direction. This creates a hook shape to the spit
- A salt marsh is created in the slow moving water on the landward side behind the spit
How does a spit become permanent?
Sand dunes form on the spit and vegetation will stabilize it
How can a bar form?
- A spit develops across a bay
- A sandbank would develop offshore, parallel to the shore, and is moved towards the coastline by the wave and wind joins the mainland
Give an example of a bar
Slapton Sands
Give an example of a tombolo
Chesil beach connects the mainland to the Isle of Portland
Where are salt marshes usually found?
Areas of stagnant water, behind bars, spits and tombolos
What are the three conditions required for salt marsh development?
- Sheltered from strong tidal waters
- Large amount of sediment
- Low gradient and shallow
Why does deposition exceed erosion at salt marshes?
As there is low energy at the salt marsh
What does deposition eventually lead to the development of at salt marshes?
Mudbanks
Define an halophyte
A plant that grows in waters of high salinity
When mud banks are exposed at low tide what is able to grow on them?
Halophytic vegetation
Give two examples of a halophyte
Cordgrass
Glasswort
What is the rate at which a salt marsh can grow upwards each year?
0.001 cm to 10 cm
What is the sward zone?
A flat piece of land that very rarely floods on a salt marsh
What is the maximum amount of time in the sward zone can survive under sea water?
4 hours
What are the three threats to salt marshes?
Pollution
Land Claims
Grazing
Why does pollution threaten salt marshes?
Can lead to algae growth which causes problems
Why do land claims threaten salt marshes?
People take salt marsh land for building or farming, completely destroying it
Why does grazing threaten salt marshes?
Animals eat the plants, loss in biodiversity. Therefore less attractive for birds
What is the backshore?
The area of the beach which is above the normal high tide level
What is the foreshore?
The area of beach in between normal high and low tide
What is the backshore?
The area of beach below the normal low tide
What can a beach shape be changed by?
Every time the tide comes in and goes out
What type of beach has a steeper gradient than a sandy beaches?
Shingle beaches
Define a beach
Accumulation of sand between lowest and highest spring tides.
What can a sand be made out of?
Sand, shingle, pebbles
Define a strand line
Material that is deposited by the sea at the furthest point above the high tide
Define a berm
A ridge that forms at the top of the beach. It is the highest section of beach and is basically sand collected on the strand line
What is a sand dune?
Small ridges of collected sand which forms from sand collecting around an obstruction
Why are sand dunes a dynamic system?
As the mobile sand on the top is always moving and being transported mainly by the wind
What is the meaning of a xerophyte?
Plants which have adapted to a dry environment
What is a pioneer plant?
First plants to colonize embryo dunes
As the sand dunes get further away from the sea what happens to the acidity and organic matter content?
The acidity increases (pH decreases) and the organic matter increases as the dunes get further away from the sea
What are the three mobile dunes?
- Embryo dunes
- Fore dune
- Yellow dune
What are the two fixed dunes?
- Grey dune
- Mature dune
What are the characteristics of the embryo dune?
Nearest to the sea
pH7 and 0.1% Organic Matter
What are the characteristics of the fore dune and the yellow dune?
2nd and 3rd nearest to the sea
pH6.5 and 0.23% Organic Matter
What are the characteristics of the grey dune?
2nd last dune
pH6-5 and 1.0% Organic Matter
What are the characteristics of the dune slack?
Depression in the dune somtimes with water
pH4-5 and 8.5% Organic Matter
What are the characteristics of the Mature dune?
Furthest away dune
pH4 and 12.1% Organic Matter
Define coral
A limestone rock which is made up of timing marine organisms called coral polyps
Define a polyp
An individual sedimentary type of animal from characterized by a more or less fixed base with a free end and mouth and tentecles
Define a fringing reef
Coral platforms growing out into the sea, attached to the mainland. A shallow lagoon lies above them
Define a barrier reef
Coral grows in a shallower area away form the mainland.
Define an atoll
Start as fringing reefs which grow around the island. The rising sea level causes the coral to grow upwards to get more light, eventually forming a ring around an island.
What happens to an island after an atoll forms?
The island slowly sinks as the sea levels continue to rise, and the atoll stays in place of the island
What does coral require to grow?
- Seawater temp. of 23-25C
- Clear water
- Not too deep water (less than 50m)
How can unclear water prevent coral from growing?
Silt reduces light, inhibiting photosynthesis used by symbiotic algae
Silt may also clog the mouths of corals, prevents feeding
How does deep water prevent coral from growing?
Light for photosynthesis would be reduced as it gets deeper
Where do coral reefs occur ?
Within 30° of the equator - temperature
Just off the coast of a land mass - water depth
Not near to largely industrial countries - water clarity
What are the four parts of a coral?
Tentacles
Gullet
Gut cavity
Mouth
Why does a barrier reef form?
The island sinks into the crust, much further away form the shore
What separates a fringing reef and a barrier reef?
A large lagoon separates them
Describe a mangrove swamp
An area of salt-tolerant trees and bushes that grow in coastal areas of tropical and subtropical reigons
List four examples of places where mangroves are found
- East coast of Africa
- Madagascar
- Mexico
- Indonesia
How are the roots of mangroves adapted?
- Cone roots rise vertically from the ground
- Pores when the root is in the air can absorb oxygen (lenticel)
- Long knobbly roots, further reach
Why do mangroves grow near to the mouth of a river?
Shallow water-shorter and more stable for roots
Large amounts of sediment for roots to grow into
How do mangroves protect the coastline?
- Roots dissipate wave energy before the shoreline
- Trapped sediment increases land from river deposition
What are the four conditions required for a mangrove forest to develop?
Warm water temperature
A river estuary
Soft, muddy substrate (sand material)
Low tide action
Why do mangroves need a warm water temperature to develop?
Good for bacteria, they have adapted to warm temperatures
Why do mangroves need a river estuary to develop?
Low strength waves to enable growth and limit erosion. Also large amount of sediment is needed
Why do mangroves need a soft/muddy substrate to develop?
High bacteria concentration, great food for ecosystem and nutrients for plants. Mangroves need to take roots in it
Why do mangroves need low tide action to develop?
Sediment can build up and mangroves will not be strongly eroded
What are the three approaches to protecting the coast?
- Hard engineering
- Soft engineering
- Managed retreat
Give examples of hard engineering
- Groynes
- Sea wall
- Rip rap
- Gabions
- Revetment
- Off shore breakwater
Explain managed retreat
Allowing part of the coastline to be eroded
How does an estuary form?
A lowland area which was formally flooded in an ice age is flooded because of rising sea levels
What are the stages which lead to erosion at the coastline? (Holderness Coast)
- Soft boulder clay cliffs become saturated with rain water and loses its strength
- The cliff is too steep and falls either as a block f material or a slurry slide
- Cliff failure reduces the angles and prevents further erosion but..
- Large waves from the NE remove the debris by LSD
What is the crest of a wave?
The highest point of a wave
What is the trough of a wave?
The lowest point in between two waves crests
What is the wave length?
Length between two wave crests
What is the wave frequency?
The number of waves passing a point every minute
Define erosion
The wearing away of rock in situ
What is biological weathering?
When a plant or tree’s roots grow into and enlarge the cracks in a rock
How does vegetation cover affect the rate of coastal erosion?
Decreases erosion as roots bind and reinforce the cliff material
What things are required for a cyclone to form?
At least 60m deep water
Greater than 27C water
Trade winds
Large expanse of water
How are cyclones formed?
- Warm air rises to create low pressure
- Trade winds cause the storm to spin
- Warm air drawn up and cold sucked down
- This increases in speed to cause a cyclone
What causes the trade winds to curve?
Coriolis effect
What is the eye of the cyclone?
Center of the cyclone with calm winds surrounding a spinning vortex of high winds/rain
