Coastal environments Flashcards
Fetch
Length of time and distance over open water that the wind has blown to create a wave
Features of constructive waves
- Long wavelength
- Shallow gradient waves
- Strong swash
- Weak backwash
- Deposition of material
Features of destructive waves
- Steep gradient waves
- Tall waves with short wavelength
- Weak swash
- Strong backwash
- Erosion of material
Hydraulic action
Waves hit cliffs and force air into cracks
Abrasion
Waves pick up pebbles and hurl them against the cliff
Solution
The dissolving of soft rocks by the sea
Attrition
Pebbles carried by waves collide with each other and become smaller and more rounded over time
Deposition
Occurs when waves lose energy/material carried is too large to transport with the amount of energy the wave has
Longshore drift
- Wave swash approaches beach at an angle (the same direction as the prevailing wind)
- Backwash is at a 90-degree angle due to gravity
- Process repeats, moving sediment along the beach
- Smaller material is transported further as it requires less energy
Solution
When minerals in rocks like chalk and limestone are dissolved in seawater and carried within. The load is not visible
Suspension
Small particles such as silts and clay are in the flow of the water
Saltation
Where small pieces of shingles or large sand grains are bounced along the sea bed
Traction
Where pebbles and larger material are rolled along the sea bed
Weathering
The breaking down of rocks and other materials in situ
Mechanical weathering
Processes such as freeze-thaw, salt crystal growth, and wetting and drying of clay rich rocks
Biological weathering
When rocks are broken down by things such as plant roots, burrowing animals and nesting birds
Chemical weathering
Processes such as carbonation, oxidation and acid rain
Slumping
Waves erode the cliff base and cause instability. Rainwater permeates through the rock, saturating it, until it becomes unstable and slumps along bedding planes. Leads to a stepped appearance to the cliff
Sliding
Weathering loosens rock, which slides down off bedding planes. Leads to landslides and mudslides
Geology
Rock type e.g. granite or chalk
Lithology
Characteristics of the rock e.g. relative hardness and permeability
Discordant geology
Rock outcrops are at 90 degrees to the sea, leading to headlands and bays where there are bands of soft and hard rock interspersed within each other
Concordant geology
Rock outcrops are parallel to the sea, creating straight coastline, though it can create coves
How does vegetation influence the coast?
- Biological weathering
- Can create sand dunes via encouraging deposition, and then stabilise them
- Can protect and preserve coastal landforms by buffering and reducing wave energy e.g. mangroves
How does sea level influence the coast?
- Flooding, a huge issue associated with rising sea level, especially considering many urban areas are situated on the coast
- Saltwater incursion
- Creation of landforms (different depending on whether sea levels are rising or falling - remember this is different in different parts of the world)
How do people influence the coast?
- Settlements
- Fishing
- Trade
- Tourism
What is the influence of wave refraction?
Waves approach parallel to coastline. As sea shallows, waves refract. This causes energy to concentrate on headlands (due to converging waves) more than bays (due to diverging waves). Despite this headlands remain sticking out due to their harder lithology
How do cliffs and and wave cut platforms form?
- Erosion is concentrated at the base of the cliff between the low tide and high tide mark in the wave attack zone.
- This creates a wave cut notch.
- The cliff above is undercut, is therefore unsupported and collapses due to gravity.
- This creates a wave cut platform.
- Over time, this repeats and the cliff retreats inland.
How are caves formed?
Cliff surfaces are naturally made up of layers of rock called bedding planes and the joints between them are more susceptible to erosion. Joints are eroded and quickly expand, turning into larger cracks or fractures. Continued erosion through hydraulic action and abrasion will see these cracks expand
How are arches formed?
When two caves back into one another, across a headland
How are stacks formed?
Weathering processing, particularly freeze-thaw, weaken the roof of the arch until it eventually collapses leaving behind an isolated column
How are stumps formed?
A stack continues to be impacted by weathering and erosion, until it can no longer be seen at high tide
How are beaches formed?
Often form in bays, where the coast is sheltered from high-energy, erosional waves or where longshore drift provides a large supply of material
Beaches
Areas where there is an accumulation of sand and shingle caused by deposition
Spits
Long narrow beaches of sand or shingle, attached to the land at one end
Bars
Long, narrow beaches of sand or shingle across bays or estuaries
How are spits formed?
- Sudden change in coastline shape/direction
- Longshore drift has momentum and so continues to transport and deposit material at sea, following its original direction
- Over time sediment builds up creating a sandy ridge outcrop
How are tombolos formed?
When a spit connects the mainland coast to an island or wave refraction around an island cause sediment to build up
What is the distribution of coral reefs?
Between 30oN and S of the equator between the tropics