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Coasts - Coggle Diagram
Coasts
Erosion
Hydraulic action - this is the sheer power of the waves as they smash against the cliff. Air becomes trapped in the cracks in the rock and causes the rock to break apart.
Abrasion - this is when pebbles grind along a rock platform, much like sandpaper. Over time the rock becomes smooth.
Attrition - this is when rocks that the sea is carrying knock against each other. They break apart to become smaller and more rounded.
Solution - this is when sea water dissolves certain types of rocks. In the UK, chalk and limestone cliffs are prone to this type of erosion.
Transportation
Solution - when minerals in rocks like chalk and limestone are dissolved in sea water and then carried in solution. The load is not visible.
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Waves
Constructive -
- Strong swash and weak backwash
- The strong swash brings sediments to build up the beach
- The backwash is not strong enough to remove the sediment
- The waves are low and further apart
Destructive -
- Weak swash and strong backwash
- The strong backwash removes sediment from the beach
- The waves are steep and close together
Backwash is the water that flows back in to the sea after the swash has occurred which is when the water rushes up towards the land.
Weathering
Freeze-thaw weathering -
- Water enters cracks in the rock.
- When temperatures drop, the water freezes and expands
causing the crack to widen.
- The ice melts and water makes its way deeper into the
cracks.
- The process repeats itself until the rock splits entirely.
Biological weathering -
- Plant roots can get into small cracks in the rock.
- As the roots grow, the cracks become larger.
- This causes small pieces of rock to break away.
Chemical Weathering -
Rainwater and seawater can be a weak acid. If a coastline is made up of rocks such as limestone or chalk, over time they can become dissolved by the acid in the water.
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Spits + Bars
Spit
- Sediment is carried by longshore drift.
- When there is a change in the shape of the coastline, deposition occurs. A long thin ridge of material is deposited. This is the spit.
- A hooked end can form if there is a change in wind direction.
- Waves cannot get past a spit, therefore the water behind a spit is very sheltered. Silts are deposited here to form salt marshes or mud flats.
Bars
- Longshore drift occurs
- It makes a hole and the water makes its way into it to fill it up.
- Then after time a bar of deposition closes off the lagoon of water so it becomes detached from the sea/
Mass Movement
Rockfall - Bits of rock fall off the cliff face, usually due to freeze-thaw weathering.
Mudflow - Saturated soil (soil filled with water) flows down a slope.
Landslide - Large blocks of rock slide downhill.
Rotational Slip - Saturated soil slumps down a curved surface.
Headlands and Bays
Bands of soft rock such as clay and sand are weaker therefore they can be eroded quickly. This process forms bays. A bay is an inlet of the sea where the land curves inwards, usually with a beach. Hard rock such as chalk is more resistant to the processes of erosion. When the softer rock is eroded inwards, the hard rock sticks out into the sea, forming a headland.
Wave-Cut Platforms
- The sea attacks the base of the cliff between the high and low water mark.
- A wave-cut notch is formed by erosional processes such as abrasion and hydraulic action - this is a dent in the cliff usually at the level of high tide.
- As the notch increases in size, the cliff becomes unstable and collapses, leading to the retreat of the cliff face.
- The backwash carries away the eroded material, leaving a wave-cut platform.
- The process repeats. The cliff continues to retreat.
Caves, Arches, Stacks and Stumps
- Cracks are widened in the headland through the erosional processes of hydraulic action and abrasion.
- As the waves continue to grind away at the crack, it begins to open up to form a cave.
- The cave becomes larger and eventually breaks through the headland to form an arch.
- The base of the arch continually becomes wider through further erosion, until its roof becomes too heavy and collapses into the sea.
- This leaves a stack (an isolated column of rock). The stack is undercut at the base until it collapses to form a stump.
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