Coastal processes

Caves, Arches, Stacks and Stumps

A fault (crack) is formed in the headland due to hydraulic action and abrasion. 

These faults further deepen from both sides forming a cave. 

The cave erodes further from both sides and eventually erodes through, forming an arch.

The base of an arch is eroded away due to undercutting making the roof collapse; leaving a stack.

Waves erode the base of a stack making it collapse which finally leaves a stump

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Coastal Retreat - Slumping

Heavy rain on headlands makes the clay unstable.

Waves form an indent at the base of the headland, a wave-cut notch.

Continued erosion enlarges the notch and the portion above to overhang.

The portion becomes unstable as it has no support underneath and eventually collapses.

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Coastal Erosion

1. Hydraulic Action

Water is forced into cracks, this compresses the air in the cracks, causing the rock to crumble.

2. Corrosion

Rock dissolved over time by acidic sea water (lightly acidic).

3. Abrasion

Loose rocks are thrown against cliffs by waves. This wears the cliff away and chips and bits of sediment fall off.

4. Attrition

Loose sediment constantly collides with other loose sediment and gradually gets worn into smaller rounded sediment.

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Coastal Transportation

1. Traction

Rocks roll over the seabed by currents and are broken down into pieces.

2. Saltation

Rocks are thrown around on the seabed, and therefore crash against each other.

3. Suspension

Fine light material is carried around by the water body 

4. Solution

Minerals are dissolved into the water, a chemical change.

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Weathering - Freeze thaw

1. Freeze thaw

Occurs in permeable/porous rocks

Water enters cracks in rocks.

This water freezes and expands in time, causing the cracks to widen

Gradually the ice melts and water seeps in deeper. 

The process repeats until the rock splits

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Weathering - Exfoliation

2. Exfoliation

Rocks in hot environments expand in the daytime due to extensive heat.

At night, these rocks cool down and contract again.

As the process repeats, the surface layer begins to flake and fall off.

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Weathering - Chemical

3. Chemical Weathering

Rainwater and seawater can be a weak acid.

A coastline consisting of pf rocks such as chalk or limestone can dissolve over time due to the slight acidity of the water.

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