Coastal Processes Flashcards
What is the coastline?
A line on a map that signifies the position of:
- the mean high water mark on a lowland coast
- the foot of a cliff on a steep coast.
What is the shore?
The area between the lowest tide level and the highest point reached by storm waves.
What causes freak waves?
- Movement of the seabed during earthquakes.
- Large ships passing too quickly near the coast.
What is wave refraction?
- Occurs when coastlines are not straight (i.e. waves not approaching at 90º angle).
- As waves reach shallow water, their frequency stays the same but their velocity decreases, causing a change in wavelength and direction.
- Waves refract around the headland and disperse into the bay.
- This means that the energy of a wave is most concentrated when it hits the headland.
What causes normal waves?
Friction between the wind and the surface of the sea.
What factors influence the size of the wave?
- Wind speed
- Length of time the wind blows in the same direction
- The fetch of the wave
What factors influence the velocity of a wave?
- Fetch
- Wind
- Depth of water
How does a wave move? [Use a diagram if necessary]
- Each wave particle moves in a vertical circle to form the wave.
- The wave particles themselves don’t move with the waves - only the shape and energy of the wave changes.
Why and how do waves break? [Use a diagram if necessary.]
- When the wave approaches the shore, water particles can no longer move in a circular motion.
- This is because the bottom of the wave is slowed by friction more than the top.
- This causes the wave to topple as the bottom slows.
- Water is forced to rush up the beach.
What are the differences between destructive and constructive waves?
Destructive
Constructive
Effect
Erosion
Deposition
Swash
Weak
Strong
Backwash
Strong
Weak
Fetch
Long
Short
Anatomy
Steep
Low
Frequency
Frequent
Less frequent
Constructive waves often form in closed bays, while destructive waves are found in exposed areas.
What is shingle?
Rounded beach material of intermediate size between boulders and sand.
How would the effects of attrition be increased?
- Longer time period over which material is moved by waves
- Greater distance “ “
What is longshore drift?
Movement of sediment along a beach.
Why is a smaller beach a problem for local authorities?
- Less attractive to tourists, so income and investment is lost.
- Less protection from erosion.
What is a curved spit indicative of? [Use a diagram if necessary.]
- Material is moved in two directions.
- Thus, there are conflicting prevailing and onshore winds.
What is the direction of longshore drift caused by?
- Direction of prevailing wind
- Direction of dominant (strongest) wind
How is sediment deposited on a beach?
- Strong swash of a construcive wave carries sediment.
- Largest material is deposited at the top of a beach.
- A storm can throw larger material even further up the beach to form a ridge.
- Smallest material deposited down the beach as the wave progressively loses water (because the beach is porous) and therefore energy - which weakens the backwash.
How does a wave cut platform form? [Use a diagram if necessary.]
- Waves attack the base of a cliff, forming a wave-cut notch.
- Cliff becomes unsupported and collapses.
- Wave cut platform is the area of retreated cliff below the high tide level.
- Fallen rock helps to builds this wave cut platform.
How do headlands and bays form?
- Coast is discordant - bands of hard and soft rock at right angles to the sea.
- Bands are eroded at different rates - soft = more, hard = less.
- Creates:
- A headland, which projects out into the sea.
- A bay, which retreats into the land.
How do caves, arches stacks and stumps form?
- Oblique waves (at an angle) are refracted as they enter shallow water.
- This causes them to turn and erode the headland at all angles.
- This means that a line of weakness (e.g. a bedding plane, NOT just ‘soft rock’) quickly develops into a cave.
- Cave eroded into an arch (back is eroded through the headland).
- Arch is eroded. Roof becomes heavy and collapses to form a stack.
- Stack collapses into a stump due to erosion.
Where do spits and bars form?
- Spits and bars form in straight coasts - not bays.
- Form where the coast changes direction e.g. meets an estuary or bay.
What is a spit?
- A long, narrow ridge made of sand or shingle, with one end attached to the land and the other ending in open water.
What is a bar? (Use a diagram if necessary)
- A spit that extends across a bay.
- Contains a lagoon in the middle.
What is a lagoon?
- An area of water dammed by a bar.
- Contains salt water at first but will be replaced with fresh water as a river enters it.
- River will continue to deposit its load and eventually the lagoon will dry up to form a marsh.
How does a salt marsh form?
- Water behind a spit is sheltered and low energy, meaning that sediment is deposited.
- Mud brought in when tide rises sinks into water because it is sheltered.
- Mud flat accumulates.
- Salt tolerant plants grow.
- Plants slow water further and encourage more deposition.
- Roots of salt-tolerant plants traps more mud and holds it in place.
What are the features of a salt marsh?
- Flat land
- Covered with water at high tide
- Has tidal channels at low tide
- Sheltered behind the spit
Why are salt marshes important?
What are mangrove swamps?
- Salt marshes that form in tropical areas.
Why are mangrove swamps important?
- Slow down water and make it lose energy, thus acting as a barrier against flooding.
- Roots stabilise the coast against erosion.
- Grow up to a tall height, protecting the coast from hurricanes.
- An important habitat - nursery for fish and shellfish.
- Carbon sink.
- Source of firewood.
- Absorb inorganic nutrients from farmland and prevents them from being deposited in the sea.
How do sand dunes form?
- Sand is carried in wind via suspension.
- Sand deposited against an obstacle e.g. plant, dead animal, stone etc. due to friction.
- Size of obstacle increases and more deposition occurs.
- Salt-tolerant plants grow.
- Wind picks up sand from seaward face and deposits it on leeward side.
- Embryo dunes develop and form a line (fore dune), parallel to the sea.
- Dunes grow in size away from the shore.
- Grey dune forms as a humus (soil layer) develops from a nutrient cycle.
- Dune becomes a fixed dune with most trees but fewest plants (due to shade from tree and bigger roots).
What are slacks?
- Long, marshy depressions.
- Have strips of water in between.
- Contain water and salt tolerant species.
What is a blow-out, and how does it form?
- A depession cutting through the dune.
- Formed as marram grass is trampled, dies and a dune cannot support itself any more.
How do you protect sand dunes?
- Fence them off.
- Provide broadwalks.
What is the importance of coasts?
- Tourism - swimming, sunbathing
- Sport - sailing, windsurfing, surfing, boating, diving
- Fishing
- Ecosystems
- Protection from coastal erosion
- Industry - located there because it is easier to export
- Oil and gas reserves
What are the hazards coasts face?
- Coastal erosion
- Tropical storms
- Oil spills
- Pollution from river discharge especially from farms
- Litter
- Overfishing
- Rising sea levels due to global warming
- Privatisation limiting access
What is a tombolo?
- Where a spit joins an island with the mainland.
What causes sea currents?
- Differences in temperature…
- Which cause a movement of water.
What is the significance of currents?
- Transport large amounts of material.
- Often extremely strong.
How do you manage coastal erosion (hard engineering)?
Defence
Description
Advantages
Disadvantages
Rip Rap
Boulders placed at the foot of cliffs. Absorb the wave energy and protect the cliffs behind.
Effective
Looks Ugly
Reduce access to beach
Expensive
Gabion
Large boulders are placed in cages.
Quick to install
Effective
Looks ugly
Reduces access to beach
Expensive
Sea Wall
Made out of concrete. Absorb wave energy and often recurved to diffract the waves back.
Effective
Look ugly
Expensive
Reduce access to beach
Breakwater
Often found at estuaries or ports. Designed to absorb wave energy.
Effective
Expensive
Disrupt shipping
Disturb animals
Revetments
Sea walls built out of wood and placed at the foot of cliffs. Absorb wave energy.
Pretty
Need replacing regularly
Do not absorb large waves
How do you manage coastal erosion (soft engineering)?
Defence
Description
Dune Stabilisation
Plant vegetation on the berm of the beach or the dunes. This makes dunes more stable and reduces the moisture content.
Cliff Regrading
Cliffs are made less steep – this prevents undercutting by reducing the angle of the cliff, and thus reduces the chance that the cliff collapses.
Beach Nourishment
Add more sand to the beach, so that energy is absorbed. Take sand from the sea bed or dunes inland.
Beach Drainage
Saturated cliffs are more likely to collapse. Reducing excess water reduces the stress on the cliff.
Managed Retreat
Allow the sea to take low value land. Unpopular because it takes up land and also changes ecosystems inland by adding salinity.
What is the water table?
The line between saturated and unsaturated ground.
What is a succession?
The changing types of vegetation from sea couch to tree.
What is a salt marsh?
A low energy, intertidal ecosystem that forms in the sheltered area behind a spit.
