Coasts

Movement of water

Wave Types

• Some waves build up beach material [constructive waves] whilst others drag sand and pebbles down the beach [destructive waves].

Wave Processes

• Waves erode or wear away the coast and transport the eroded material along the coastline - a process called longshore drift. Eventually the material will be deposited on a beach or will form a larger feature. Erosion works in four ways:

Wave Erosion

• Erosion works in four ways:

• Hydraulic action - this results from the force of the water hitting the cliffs.

• Corrasion - this is caused by the waves picking up stones and hurling them at the cliffs.

• Attrition - any material carried by the waves will become rounder and smaller over time.

• Corrosion [solution] - the dissolving of rocks by sea water.

Erosion

• The nature of a coastline is often determined by its geology. Some coastlines are very dramatic, with tall, vertical cliffs whilst others are low-lying or marshy. Some coastlines are straight for miles and miles whilst others are indented with many headlands and bays.Long, fairly straight coastlines result where the rocks are very similar or just one type. If there are many rock-types and they vary in their resistance to erosion, then headlands and bays will form.

Headlands and Bays

Caves, arches, stacks

• As waves approach a bay, they loose energy because of the reduced depth of the sea.

• The energy is diverted towards the headland where cliff are surrounded by deeper water.

• This process of deflection of wave energy around and towards the headland is called wave refraction.

Caves, arches, stacks

• Lines of weakness in the headland are attacked.

• Fissures open under the influence of hydraulic action and corrosion forming inlets and caves.

• If caves occurs on both sides of the headland, then erosion will run right through until the walls of the cave may open to form an arch.

Caves, arches, stacks

• As erosion continues, the arch will collapse leaving behind a stack.

• A stack is a pillar of rock which lies in direct line with the cliff.

Caves, arches, stacks

Cliff and Wave-cut-platform

• Many areas have cliffed coastlines. The nature of the cliff again depends on the geology of the rocks. Hard, resistant rocks form tall cliffs with a jagged upper section and a smoothed wave-cut notch at the base. If the rocks have many joints(vertical cracks) then erosion will be greater at some points and a cave may form. As the waves erode back into the cliff, the upper section becomes unstable and eventually collapses. In time the material from the cliff will be eroded into smaller and smaller pieces to form new beach material.

Cliff and Wave cut notch

Cliff, notch and wave-cut platform

• Soft rocks are less resistant than hard rocks and so are more susceptible to wave erosion.

• Cliffs are steep near vertical slopes that rise abruptly from the sea.

• Hydraulic action and abrasion causes undercutting.

• As erosion continues, a notch is cut into the base of the cliff.

Cliff, notch and wave-cut platform

• A cave develops creating an overhanging cliff.• As weathering and erosion continues, the

overlying section weakens and topples.• Wave erosion removes the loose material which

is used in further erosion.• Materials in suspension scour the base and the

cliff recedes.• The effect of wave on the cliff decreases.• A platform replaces the retreating cliff.

Cliff, notch and wave-cut platform

• Wave action continues its scouring and cutting action on the platform creating a feature called a wave-cut platform.

• The platform is visible at low tide and covered at high tide.

Transportation

• Waves transport material along the coast.

• These materials may come directly from the coastline or may come from other locations.

• The swash of waves carries the materials obliquely up the beach and deposited.

• The backwash drags the material back down the shore at right angles.

Transportation

• By this process, materials are transported up and down the beach, and also sideways.

• This is known as longshore drift and is responsible for the development of most coastal features of deposition.

• Longshore drift: the movement of materials along the coastline by the action of breaking waves which generally approach the shoreline at an angle.

Longshore Drift

Depositional FeaturesBeaches

Spits

Tombolos

Bars

Beaches

• The beach is a very common depositional feature. It is formed from the continuous accumulation of sand, silt, shingle and pebbles. The material is deposited along the coast and longshore drift distributes the material. Material that make up beaches are derived from erosion of the land by both rivers and the sea

Beaches

Spit

• A spit is formed when a large accumulation of material forms a narrow strip of land that juts out into the sea but is connected to the mainland at one end. Where a river carries large amounts of material into a bay, waves moving obliquely will transport the material in a diagonal direction along the beach by the process of longshore drift.

Spit

Please see the following website for additional information

• http://www.scool.co.uk/alevel/geography/coastal-processes/coastal-deposition.html

Tombolo

• The spit may continue to grow, until it joins onto an island or the mainland, and becomes a tombolo.

Tombolo

Bars

• A bar is a narrow strip of sand and shingle formed by longshore drift but not connected to the mainland. Most bars are exposed during low tide.

Bar