What is the primary difference between abrasion and attrition?

Abrasion involves sediment being used as a tool to erode the coastline (rock-on-cliff), whereas attrition involves sediment particles colliding with each other (rock-on-rock) to become smaller and rounder.

How do concordant and discordant coastlines differ in their formation of landforms?

Concordant coasts have rock types running parallel to the shore, often forming coves, while discordant coasts have rock types at right angles to the shore, leading to the formation of headlands and bays through differential erosion.

Compare the swash and backwash of a destructive wave.

A destructive wave has a weak swash but a very powerful backwash. This imbalance means more material is removed from the beach than is deposited, leading to net erosion.

What is a common misconception regarding the direction of backwash in longshore drift?

Students often think backwash returns at an angle. In reality, backwash always returns perpendicular ($90^{\circ}$) to the shoreline because it is pulled directly by gravity down the steepest slope.

Why is it incorrect to say that hydraulic action is just 'water hitting rocks'?

Hydraulic action specifically refers to the compression of air inside cracks. The erosion is caused by the pressure of the trapped air and its explosive release, not just the weight of the water itself.

What error is made when identifying the 'prevailing wind' in a coastal diagram?

Students often confuse the prevailing wind with the direction of the waves. While the wind generates the waves, the waves may refract as they enter shallow water, but the initial angle of approach is set by the prevailing wind.

Define 'Fetch' and explain its importance.

Fetch is the maximum distance of open water over which wind blows to create waves. A larger fetch allows waves to gain more energy, resulting in more powerful erosional forces at the coast.

What is a 'Wave-cut Notch'?

A wave-cut notch is a hollow eroded into the base of a cliff between the high and low tide marks. It represents the point of maximum marine attack where abrasion and hydraulic action undermine the cliff.

Define 'Longshore Drift'.

Longshore drift is the process by which beach material is transported along the coast in a zig-zag motion due to waves approaching at an angle and returning perpendicular to the shore.

Why does deposition occur in a spit?

Deposition occurs because the coastline changes direction, causing the longshore drift to lose energy as it enters deeper or more sheltered water, leading to the 'dropping' of sediment.

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Marine processes and the coast

Marine Processes and the Coast

Summary

Coastal landscapes are dynamic environments shaped by the continuous interaction of marine processes, including erosion, transportation, and deposition. These processes are primarily driven by wave energy, which is influenced by wind strength, duration, and fetch, resulting in distinct landforms that evolve over geological and human timescales.

1. Definition & Core Concepts

Marine processes refer to the physical actions of the sea that shape the coastline, categorized into erosion, transportation, and deposition. These processes are powered by wave energy, which is generated by the friction of wind blowing over the water's surface.
The fetch is the distance of open water over which the wind has blown; a longer fetch typically results in more powerful, higher-energy waves. When a wave reaches the shore, the movement of water up the beach is called the swash, while the movement of water back down toward the sea is the backwash.
Coastal morphology is also influenced by sub-aerial processes, such as weathering and mass movement, which weaken cliffs from above, making them more susceptible to marine attack at the base.

2. Marine Erosion Processes

Hydraulic Action: This occurs when waves trap and compress air into cracks in a cliff face. As the wave retreats, the sudden release of pressure causes the rock to shatter over time through a process of explosive expansion.
Abrasion (Corrasion): This involves the 'sandpapering' effect where waves fling pebbles and sand against the cliff base. This mechanical scraping is highly effective at carving out wave-cut notches and undermining cliff structures.
Attrition: Unlike other forms of erosion that target the coastline, attrition occurs when rocks and pebbles carried by the sea collide with each other. This process rounds and smooths the sediment, eventually breaking it down into smaller fragments like sand.
Solution (Corrosion): This is a chemical process where weak acids in seawater dissolve certain rock types, such as limestone or chalk. It is most effective in areas where the water is warmer or more acidic.

3. Transportation and Longshore Drift

Diagram showing the zig-zag movement of longshore drift, with swash at an angle and backwash perpendicular to the shore.

4. Key Distinctions: Wave Types

5. Exam Strategy & Tips