Theme 2 - 2.3 - Coasts Flashcards
Define abrasion (or corrasion).
Rocks been thrown into the cliffs by waves and breaking off bits of the cliff.
Define hydraulic action.
This is when sea water and air get trapped in cracks. The increasing pressure of the water and air cause the rocks to crack.
Define solution (or corrosion).
The removal of chemical ions, which causes rock to dissolve.
Define attrition.
When rocks in the sea hit against each other, wearing themselves down.
Define fringing reef.
A reef that grow outwards around an island.
Define barrier reef.
A reef that is separated from the coast by a deep channel.
Define atoll.
A circular reef enclosing a shallow lagoon.
Define weathering.
The breakdown of rocks in situ (in place).
Define erosion.
The breakdown and removal of rock, involving the movement of the material by water, ice or wind.
What are the three main categories of weathering?
- Chemical
- Biological
- Physical/Mechanical
Define chemical weathering.
The break down of rocks caused by a change in their chemical make-up.
Define biological weathering.
Biological weathering is when flora and fauna break down the rock - E.g. growing roots systems or burrowing animals
(Biological weathering is sometimes included within physical weathering)
Define physical weathering.
The break down of rock caused by physical processes with no change in the rock’s chemical make up.
Name some marine processes which occur in coastal zones.
- Wave action from constructive and destructive waves
- Wind action
- Mass movement and weathering
- River and ice actions
What are marine processes?
Processes operating at a coastline that are connected with the sea, such as waves, tides and long shore drift.
What are the features of destructive waves?
- Short wavelength
- High height (>1m)
- High frequency (10-12/min)
- Backwash is stronger than swash
What are the features of constructive waves?
- Long wavelength
- Low height (<1m)
- Low frequency (6-8/min)
- Swash is stronger than backwash
What are the 4 processes of transportation?
- Traction - Dragging particles along sea floor
- Saltation - Smaller particles are bounced along
- Suspension - Fine particles are held up
- Solution - Sediment is dissolved
What are some reasons why deposition happens?
- Decrease in wave energy or velocity
- Large supply of material
- Irregular, indented coastline
How are waves formed?
Friction from the atmosphere (wind) causes a circular orbit in the water, which creates waves.
What causes waves to break?
The friction at the bottom of the waves slows the bottom down, meaning the top travels faster and causes the wave to eventually break.
What factors affect the size of waves?
- Fetch size
- Wind speed
- Wind duration
Which waves have more energy, constructive or destructive?
Destructive
What is the swash?
The pushing of a wave up the beach.
What is the backwash?
The pulling of a wave back down the beach.
What does constructive mean?
When a wave deposits more sediment than it takes away, helping to build a beach up.
What does destructive mean?
When a wave deposits less sediment than it takes away, destroying a beach.
What are plunging breakers?
Breaking waves whose crest curls over and collapses suddenly.
What are surging breakers?
Breaking waves whose crest remains relatively unbroken as waves slide up and down the beach.
What is wave refraction?
When waves approach an area of irregular coastline, the shallowness of the water near some features increases friction and causes the waves to bend so that they’re perpendicular to the coastline. This usually concentrates energy on the flanks of headland and disperses the waves in bays.
What does incomplete refraction result in?
Long shore drift
What is longshore drift?
The process by which sediment is moved along a coastline.
Describe longshore drift.
- Waves approach the beach at an angle due to the prevailing wind
- The swash deposits material at that angle
- The backwash drags material back to the sea at right angles to the beach (due to gravity)
- The process repeats and sediment moves down the coastline
When do headlands and bays form?
When rocks are of different strengths.
How do headlands and bays form?
- Sections of soft rock are eroded quickly, whereas hard rock does not erode so easily
- This creates headlands of hard rock, between which there are bays of soft rock
How do cliffs, wave-cut notches and wave-cut platforms form?
- Maximum erosion of a cliff occurs at the foot of the cliff
- This creates a wave-cut notch
- Eventually, the rock overhanging this collapses
- This leaves a steep side, which is called a cliff
- The process repeats and this leaves a wave-cut platform beneath the wave level
What is a wave-cut notch?
An indentation in at the bottom of a cliff caused by erosion.
What is a wave-cut platform?
A long section of rock under the water surface left behind by a cliff which has been eroded.
Describe the formation of caves, arches and stacks.
- A weakness, such as a fault line, in some headland can be eroded to form a cave
- Eventually, the cave erodes the entire wave through the headland, creating an arch
- When this is widened enough the arch can collapse to leave a stack
- Finally, this stack collapses to leave behind a stump
Describe the formation of a spit and salt marsh.
- Longshore drift moves sediment along a coastline
- When the coastline suddenly changes direction and the water is shallow and shelter, sediment can be deposited and builds up
- This eventually results in a spit
- A hooked end may form due to a change in wind direction
- In the shelters area behind the spit, a salt marsh can form
Where is wave energy concentrated?
On headland - due to refraction.
What is a bay-head beach?
A beach that forms at the head (inner most part) of the bay. It does not extent to the headland, because erosion is too strong.