Coasts part 2
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Define: mass movement
the downhill movement of rock and soil in response to the force of gravity
define: hydraulic action
The sheer power of the waves on the cliff which compresses air into gaps in the rock face and weakens rocks over time
Rocks and boulders being hurled against the side of the cliff causing it to weaken and break
Rocks hitting against each other and becoming smaller and smoother
Chemicals in water dissolve rock, influenced by sea temperatures
Name the factors that affect the rate of erosion (4)
- Wave steepness
- Fetch of wave
- Depth of sea
- Presence of a beach
- Human intervention
- discordant/Concordent coastline
- Strength of rock
What is longshore drift?
- The zig-zag net movement of material along the coast
- Waves approach coast at an angle (usually following the direction of the prevailing wind), pushing material up the beach by the swash
- Water is dragged back at a right angle to the beach
The rapid movement of detached slabs of rock down a slide plane
Individual rock fragments falling off a cliff face, often due to freeze thaw
Define: rotational slip
Common coastal landslips in weak rocks
Saturated soil flows downhill, often triggered by heavy rain
Define: soil creep
Very slow downhill movement of individual rock particles
What is solifluction?
the gradual movement of wet soil or other material down a slope, especially where the land has permafrost
A piece of land usually formed of resistant rock that juts out into the sea, usually accompanied by a bay
Explain the formation of headlands and bays
- Rocks of different geological structure are found along a discordant coastline
- The less resistant rocks (such as limestone) are eroded at a faster rate than the more resistant rocks (such as granite) by processes of hydraulic action and abrasion. The more resistant rock is left jutting out into the sea, forming a headland. Wave refraction during calmer weather deposits sediment into the gaps of the rocks, which then forms bays.
What are wave cut platforms?
The remains of the base of the cliff visible at low tide.
Explain the formation of wave cut platforms
An exposed cliff face with vertical bedding planes is attacked by processes of erosion, such as hydraulic action, abrasion and to a less extent attrition. Over time the intertidal zone is eroded laterally to form a wave-cut notch. This leaves rock overhanging it, which over time will be unable to support itself and collapse. This leaves a wave-cut platform which is visible at low tide
What is a geo?
a long, narrow, steep-sided cleft formed by erosion in coastal cliffs.
a stretch of deposited sediment at the coast which is liable to change as a result of waves and human interference. Acts as a natural buffer zone and coastal defence between the land and the sea
Put the following terms into order: Nearshore, Off shore, back shore, foreshore. (start with the one closest to the cliff)
- Off Shore
Are beaches sediment stores?
What inputs are there for a beach? (4)
- Cliff erosion
- Mass movement
- Constructive waves
- Longshore drift
What outputs are there for a beach? (3)
- Longshore drift
- Destructive waves
What is meant by the morphology of a beach?
The shape of the profile of the beach
Do larger sediment particles create a shallow or steep beach profile?
Steeper, as they are too heavy for the sea to carry and are instead deposited upwards
Do smaller sediment particles, such as sand, create a shallow or steep beach profile? Why?
shallow because the sand becomes compact when wet, which restricts percolation and material is carried down
Describe the characteristics of a berm and explain their formation
- A berm is a ridge of material at high tide mark
- Constructive waves deposit material at highest point of tidal range.
- As tides move from spring to neap, successive ridges of sediment left untouched by decreasing tides
Describe the characteristics of runnels and explain their formation
- Runnels are channels on the beach which can be 1m deep and many meters wide. they usually form in areas with a large tidal range and at the low tide mark.
- As the tide drops on shallow, sandy beaches the backwash (unable to percolate) erodes material and cuts a channel as it returns to the sea.
Describe the characteristics of a cusp and explain their formation
- Cusps are semicircular shaped depressions which form where there are small irregularities in the upper reaches of the beach, developed by the swash.
- Strong swash and backwash deposit material on the rim of the cusp.
Describe the characteristics of a shingle beach and explain their formation
- Consists of larger material
- steep profile
- water percolates through the shingle
- backwash is weaker thus less material is moved down beach
Describe the characteristics of a sand beach and explain its formation
- Smaller sized particles create a shallow profile
- Sand becomes compact when wet which prevents percolation, results in swash returning as backwash
- little energy lost
- Allows the formation of runnels and berms
What is a spit?
A ridge of sediment attached to the land at one end that extends out into the sea at the other. The tip of the spit is liable to recurving due to changing wind and wave directions
How are spits formed?
Spits form where the coastline changes direction suddenly. Longshore drift works along the coast and loses energy at the point of change resulting in deposition of material. Over time this material builds up and extends, forming a spit. The tip of the spit curves around as waves refract around it, shaping it.
What are bars and how are they formed? (give example)
A bar is a spit that has joined one part of the mainland to another, trapping an area behind it which is then known as a lagoon.
eg. Slapton Sands, Devon
What are tombolos?
A spit that joins an island to the mainland.
Describe the characteristics of a salt marsh and explain their formation
- Saltmarshes are intertidal mudflats of stagnant water, exposed at low tide.
- The form in sheltered areas along the coast, such as behind a spit, plants begin to colonise the area and make the salt marsh difficult to erode once it is established
Describe the characteristics of a blowhole and explain its formation
- A blowhole is a hole at the inland end of a cave.
- Formed when a cave move inland, making the roof of it weak. Waves in the cave can be reflected upwards further weakening the roof. As well as this, sub-aerial weathering weakens the roof from above and eventually it will collapse or water will break through.
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