The Coastal Zone Flashcards
Describe how waves are formed and what happens when the reach the coastline.
The wind blows across the open ocean creating ripples. These ripples act as small sails to catch more wind and become bigger swells. As the swells approach the land the sea becomes shallower and the bottom of the wave slows due to friction whilst the top carries on to form a crest. The crest topples forming a breaking wave.
Define swash.
The movements of a wave up the beach.
Define backwash.
The movement of a wave down the beach back into the ocean.
What is fetch and what does it affect?
Fetch is the distance the wind blows over the sea. The height and type of wave is affected by the fetch. A bigger fetch means a bigger wave.
Describe the features of a destructive wave.
Created by a large fetch. Big, strong waves with high energy. Erodes the coastlinge as backwash is stronger than swash. 14 waves per minute.
High wave in proportion to lenght and tall breaker - breaks downwards with great force.
Describe the features of constructive waves.
Created by a short fetch. Small, gentle with low energy. Deposits sediment as swash is stronger than backwash. 7 waves per minute.
Low wave in proportion to length.
Define ‘erosion’.
Erosion is the wearing down of rock by moving forces. It ususally occurs at the base of cliffs and by waves.
Define ‘weathering’.
Weathering is the wearing down of rock ‘in situ’ by its environment. Sub aerial forces (like rain, air, and temperature) act on cliffs to break them down.
Define ‘mass movement’.
Mass movement is the movement of rock downhill due to gravity.
Describe chemical weathering.
Chemical weathering is the wearing away of rock by natural chemicals in the air. It creates small potholes in the rock and is often caused by acid rain.
Describe biological weathering.
Biological weathering is caused by grass, moss, and lichens which grown on the cliff. The roots create small cracks. When the plants die chelic acid is also produced.
Describe mechanical weathering.
Mechanical weathering (freeze-thaw) is caused when water is trapped in cracks in the rock, freezes, exapands, and enlarges the cracks. This leaders to large cracks and angular fragments of rock.
Which types of rock are affected most by which types of weathering?
Porous rock is affected most by mechanical weathering due to the larger already existing holes/pores. The more porous and soft a rock is, the more it will be affected by mechanical weathering.
Harder rock tends to be affected by chemical weathering more.
How many different types of mass movement are there and what are they?
4 types.
- Rockfall
- Landslide
- Mudflow
- Rotational Slip
Decribe rockfall.
Fragments of rock break away from the cliff due to mechanical weathering.
Describe a landslide.
Blocks of rock slide downhill.
Describe mudflow.
Saturated soil and weak rocks flows down a slope.
Describe roational slip.
Also known as soil creep. The slow, steady movement of top soil downhill due to gravity.
How many types of erosion are there and what are they?
4 types.
- Hyrdaulic action
- Abrasion
- Attrition
- Corrosion/solution
Describe hydraulic action.
Erosio of cliffs caused by the force of water and air in the waves colliding with the cliffs.
Describe abrasion.
Erosion of cliffs as waves throw particles of rock against them.
Describe attrition.
Erosion of material carried in the waves. It is smoothed over as it bumps into other material.
Describe corrosion/solution.
Erosion of cliffs by salts and acid in sea water. Salts + acid are able to disolve soft rocks like chalk and limestone.
How many processes of transportation are there and what are they?
4 processes.
- Soltion
- Suspension
- Saltation
- Traction
Describe the process of Longshore Drift
- Swash approaches in the direction of the prevailing wing.
- Backwash does down the beach at 90° due to gravity.
- Sediment is moved down the beach in a zig-zag motion. This is longshore drift.
Describe how headlands and bays are formed.
- Waves atack the base of the cliff through abrasion and hydraulic action.
- Harder, more resistant rock takes longer to erode and retreat. This leaves a headland protruding into the sea.
- Softer, less resistant rock takes less time erode and retreats quickly. This creates a bay.
- The headland then provides shelter so in the bay deposition occurs and a beach is formed.
Describe cliff retreat and how wave-cut notches and wave-cut platforms are formed.
- Abrasion and hydraulic action erode the base of cliff.
- Over time the remainder of the cliff will remain unaffected and will be undercut. This formes a wave-cut notch.
- Eventually, the cliff will become unstable and will collapse. Further cliff retreat will create a wave-cut platform.
REMEMBER: A wave-cut notch will only form between the high and low tide marks. It is often darker in colour because it is saturated with sea water.
Describe the formation of cracks, caves, arches, stacks, and stumps.
- The waves erode the cliff through hydraulic action and abrasion to form cracks (faults) in the headland.
- The waves continue to erode the crack until the rock begins to fall away and forms a cave.
- The waves continue to erode through the headland to form an arch.
- The arch becomes unsupported and collapses to form a stack.
- Furter hydraulic action and abrasion cause the stack to topple over and form a stump.
Describe the formation of spits.
- Longshore drift transports sediment down the coast in the direction of the prevailing wind.
- A change in the shape of the land (caused by an estuary) means longshore drift begins to deposit sediment out away from the coast.
- A long tongue of sediment builds up, this is a spit. The end is curved by a secondary wind.
- Salt marshes develop in the sheltered area behind the spit. (e.g Keyhaven Marshes behind the Hurst Castle spit).
Describe the formation of bars.
Bars form where a spit grows across two headlands, enclosing an area of water known as a lagoon.
Describe the formation of tombolos.
Tombolos form where a spit grows away from a headland and links it to an offshore island.
(As opposed to an onshore island…?)
Describe the process of post glacial rebound.
- The north of the UK was once covered in heavy snow.
- Because we are an island we act a bit like a seesaw. As the north sank under the weigh of the snow, the south rose.
- The north is now rebounding back, so the south is beginning to sink.
