Coastal Physical Processes Flashcards
How do waves form
- formed by wind blowing across the surface of the sea creating friction
- friction creates energy which make small ripples (circular movements)
= develop into waves - wave energy depends on strength of wind, length of time over which wind has blown and the fetch
- as water gets shallower seabed interrupts circular motion of water
= make waves more elliptical
= causes crest of wave to rise and collapse onto beach - water rushes up (swash) and water flows towards sea (backwash)
Features of constructive waves
- very little energy
- strong swash
- weak backwash
= deposit a lot of sediment - small wave height
Describe process of freeze thaw weathering
- happens when temp alternates above and below 0C
- water enters rock that has cracks
- when water freezes it expands
= puts pressure on the rock - when water thaws it contracts
= releases pressure on the rock - repeated freezing and thawing widens cracks and causes rock to break up
Describe process of carbonation
- happens in warm and wet conditions
- rainwater has co2 dissolved in it
= makes it a weak carbonic acid - carbonic acid reacts with rock that contains calcium carbonate eg limestone
= rocks are dissolved by rainwater
Describe process of mass movement
- rain saturates permeable rock above impermeable rock making it heavy
- waves or a river will erode the base of the slope
= making it unstable - eventually weight of permeable rock above impermeable rock weakens and collapses
- debris at base of cliff is then removed and transported by waves or river
How do waves break
- waves start out at sea
- as waves approach shore friction slows the base
- causes orbit to become elliptical
- until top of wave breaks over
How do headlands form
- form along discordant coastlines where there are alternate bands of hard and soft rock
- weathering and erosion both reduce height of softer bands of rock
= cause then to retreat backwards quicker - hydraulic action and abrasion erode the base of the cliffs
= cause mass movements and retreat - happens to headlands but more slowly
= they’re left sticking out into sea - sand starts to be deposited in the sheltered bat
How do stacks form
- resistant rock that makes up headlands often has weaknesses like cracks
- waves crash into headlands and enlarge the cracks
- repeated erosion and enlargement of cracks cause cave to form
- continued erosion depends cave until it breaks through headland to form an arch
- erosion continues to wear away at rock supporting arch until it collapses
= forms a stack
= an isolating rock that’s separate from the headland
Process of wave cut platforms
- waves cause most erosion at the foot of a cliff
= forming a wave cut notch which is enlarged over time - repeated erosion causes rock above notch to become unstable and collapse
- collapsed material is washed away and new wave cut notch starts to form
- after repeated collapse cliff retreats
= leaving a wave cut platform
Processes of spits
• A spit is a sand or shingle beach that is joined to the land but projects out into the sea.
• Longshore drift transports sand along the coast. Direction of prevailing wind determines direction of LSD.
• Spits form where the coastline suddenly changes shape. Sand or shingle starts to build up in the sheltered side of the headland. This will continue to build up.
• Finer material is carried out into the deeper water of the estuary and is deposited as the water loses its capacity to transport it any further.
• A spit will continue to grow until the water becomes too deep or until material is removed faster than it is deposited.
Process of bars
- forms when a spit joint 2 headlands together
- bay between headlands gets cut off from sea
- means lagoon can form behind it
- offshore bars can form of coast has a gentle slope
- friction with sea bed causes waves to slow down and deposit sediment offshore
= create a bar that isn’t connected to the coast
Process of freeze thaw
- water enters cracks in rocks and freezes water overnight
- as it freezes water expands
= increases pressure acting on rock
= cause cracks to develop - over time cracks grow
= weaken the cliff making it more vulnerable to other processes of erosion
Process of biological weathering
Plant roots grow through cracks in the rocks
Slowly erode areas of the coast
What does mass movement depend on
Angle of slope/cliff
Rock type
Saturation of ground from previous rain or flooding
Describe rock falls
Occur on sloped cliffs when rock becomes exposed to mechanical weathering
