3.2.1 Coastal Processes

Erosion

Coastal Erosion

How do our coastlines erode material?

Hydraulic Action

• The power of the waves as they smash onto the cliff.
• Trapped air is forced into cracks and holes in the rocks, eventually forcing the rock to break apart.

Abrasion

• Fragments of rock, pebbles, and sand are picked up by the waves and hurled at the base of the cliffs.
• These fragments act like sandpaper, eroding the base of the cliff.

Attrition

• Rock fragments moving underwater rub against one another, knocking fragments off.
• This process happens continually and wears the rocks down.

Solution

• Rocks can be eroded through chemical action.
• Sea water dissolves certain types of rocks, such as chalk and limestone, in the UK.

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Weathering

COASTS – Weathering

Freeze-Thaw Weathering

Occurs when rocks are porous (contain holes) or permeable (allow water to pass through).

1. Water enters cracks in the rock.
2. When temperatures drop, the water freezes and expands, causing the crack to widen.
3. The ice melts and water makes its way deeper into the cracks.
4. The process repeats itself until the rock splits entirely.

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.

Biological Weathering

Plants and animals can also have an effect on rocks.

5. Roots burrow down, weakening the structure of the rock until it breaks away.
6. Plant roots can get into small cracks in the rock.
7. As the roots grow, the cracks become larger.
8. This causes small pieces of rock to break away.

Transportation

Suspension

• Particles are carried suspended within the water.

Solution

• Rock is transported as dissolved chemicals, often from chalk and limestone cliffs.

Traction

• Large pebbles are rolled along the seabed by the currents.

Saltation

• Turbulence and currents lift up pebbles, which then bounce along the sea bed.

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Types of Waves

Constructive Waves

• Low waves that surge up the beach and spill with a powerful swash.
• Carry large amounts of sand and pebbles, constructing the beach.
• They have traveled a very long way (Large fetch).

Constructive Waves

Destructive Waves

• Formed by local storms close to the coastline.
• Take beach material away, eroding the beach.
• Steep, plunging waves, close together with a stronger backwash than swash.
• Effective at removing sand and pebbles from the beach.

Destructive Waves

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Mass Movement

Effects

• Causes coasts to rapidly retreat.
• More likely to happen when the material is full of water, acting as a lubricant and making the material heavier.

Types

• Rockfalls: Bits of rock fall off the cliff face, usually due to freeze-thaw weathering.
• Slumps: Saturated soil slumps down a curved surface.
• Landslides: Large blocks of rock slide downhill.
• Mudslide: Saturated soil flows down a slope.