Coastal Landforms 🌊

Welcome, students! In this lesson, you will learn how coastlines are shaped by the sea, waves, sediment, and sometimes humans. Coastal landforms are the physical features found at the edge of land and sea, and they are among the most visible results of marine processes. By the end of this lesson, you should be able to explain how different landforms form, use the correct geography vocabulary, and connect these ideas to the wider IB Geography SL topic of Oceans and Coastal Margins.

Learning objectives

• Explain the main ideas and terminology behind coastal landforms.
• Apply IB Geography SL reasoning to explain how landforms are created and changed.
• Connect coastal landforms to the broader theme of oceans and coastal margins.
• Use real examples and evidence to support explanations.

1. What are coastal landforms? 🌍

Coastal landforms are features created by the interaction of marine processes and the land. The coast is not a fixed boundary. It changes over time because of waves, tides, currents, sediment movement, weathering, and erosion. Some coasts are rocky and steep, while others are sandy and flat. These differences depend on rock type, wave energy, sea level, and human activity.

The two main groups of coastal landforms are:

• Erosional landforms: created when the sea removes rock and sediment.
• Depositional landforms: created when material carried by water is dropped in a new location.

The coast is shaped by three main processes:

• Erosion: wearing away of rock by hydraulic action, abrasion, attrition, and solution.
• Transportation: movement of sediment by waves, currents, and longshore drift.
• Deposition: dropping of sediment when energy decreases.

A useful IB idea is that coastal landforms are the result of a balance between destructive processes and constructive processes. If wave energy is high, erosion is often stronger. If wave energy is lower, deposition may dominate.

2. Erosional landforms: how waves shape rocky coasts 🪨

Erosional landforms often form on discordant coasts, where bands of hard and soft rock run at right angles to the coastline. Softer rock erodes faster, leaving more resistant features behind. A classic sequence is: crack, cave, arch, stack, and stump.

Headlands and bays

When a coastline has alternating bands of hard and soft rock, waves erode the softer rock more quickly. This forms bays, while the harder rock stands out as headlands. Because wave energy is concentrated on headlands, they continue to be eroded by processes such as abrasion and hydraulic action.

For example, on parts of the Dorset coast in the UK, softer clays and sands have eroded faster than harder chalk and limestone, creating a coastline with bays and headlands.

Cliffs and wave-cut platforms

A cliff is a steep rock face formed when waves undercut the base of a coast. Over time, the rock above becomes unstable and collapses. This process repeats, causing the cliff to retreat inland.

At the base of the cliff, a gently sloping rocky surface may remain called a wave-cut platform. This feature forms as waves erode the base of the cliff and material is removed. The platform is often exposed at low tide.

A simple sequence helps explain formation:

1. Waves erode the foot of the cliff.
2. A wave-cut notch forms.
3. The cliff becomes unstable and collapses.
4. The cliff retreats.
5. A wave-cut platform is left behind.

Caves, arches, stacks, and stumps

These are some of the most famous coastal landforms.

• Cave: formed when waves exploit a crack or weakness in a headland.
• Arch: formed when caves on opposite sides of a headland join through erosion.
• Stack: formed when the roof of an arch collapses, leaving an isolated pillar of rock.
• Stump: formed when a stack is eroded further and becomes shorter than the surrounding waves at high tide.

These features show how coastlines can change dramatically over time. A well-known example is the Old Man of Hoy in Scotland, a sea stack formed by erosion in a high-energy marine environment.

3. Processes behind erosion and weathering 🌬️

To understand coastal landforms well, students, you need to know the processes that create them.

Erosion processes

• Hydraulic action: waves force water and air into cracks, increasing pressure and widening the crack.
• Abrasion: waves throw sand and pebbles against rock, grinding it away.
• Attrition: rock fragments collide and become smaller, rounder, and smoother.
• Solution: acidic seawater dissolves certain types of rock such as limestone.

Weathering and mass movement

Coastal landforms are not shaped by waves alone. Weathering weakens rock in place, and mass movement moves material downhill under gravity.

• Freeze-thaw weathering can widen cracks in rock.
• Salt weathering can weaken cliffs in coastal areas.
• Rockfalls, slumps, and slides can occur when cliffs become unstable.

These processes often work together. For example, weathering may weaken a cliff, wave erosion undercuts it, and then mass movement causes collapse.

4. Depositional landforms: when the sea builds land 🏖️

Depositional landforms form where sediment is dropped because the water has lost energy. This often happens in sheltered areas, such as bays, estuaries, or behind offshore features.

Beaches

A beach is a deposit of sand, shingle, or pebbles along the shoreline. Beaches form when material is moved by waves and deposited where wave energy is lower.

The size and shape of a beach depend on:

• Sediment supply
• Wave energy
• Coastal shape
• Tidal range
• Human management

A constructive wave has a stronger swash than backwash, so it deposits material on the shore. This is common on many beach environments. In contrast, destructive waves have stronger backwash and can remove sediment.

Spits

A spit is a long, narrow ridge of sand or shingle that extends out from the coast into the sea or across an estuary. It forms through longshore drift, which moves sediment along the coast in a zigzag pattern.

A spit may curve at the end if wind or wave direction changes. This hooked end is common in real examples such as Spurn Head in England.

Bars and lagoons

If a spit grows across a bay and joins two headlands, it becomes a bar. This can trap water behind it and create a lagoon.

These depositional features show that coastlines are dynamic. They may change as sediment supply, sea level, and wave direction change.

Tombolos

A tombolo is a narrow ridge of sand or shingle that links an island to the mainland. It forms when waves refract around an island, causing deposition in the sheltered area between the island and the coast. An example is Chesil Beach in southern England, which is often used in geography to discuss coastal deposition, although its formation is complex and related to longshore drift and changing sea conditions.

5. How coastal landforms connect to the wider topic of oceans and coastal margins 🌐

Coastal landforms are not isolated facts to memorize. They are part of a bigger system called the coastal margin, the zone where land and sea interact. In IB Geography, this matters because coastlines are influenced by energy transfers, sediment budgets, sea-level change, and human management.

Key connections

• Wave energy controls whether erosion or deposition dominates.
• Sediment cells move material along stretches of coast, affecting landform development.
• Sea-level change can flood coastlines or expose new areas to erosion.
• Human actions such as groynes, sea walls, and dredging can interrupt natural coastal processes.

For example, groynes trap sediment moving by longshore drift, which may build up a beach on one side but increase erosion downdrift. This shows how people can change the balance that creates coastal landforms.

In exam answers, students, it is important not just to name a landform but to explain the process sequence and the conditions needed for it to form. Strong answers often include:

• Correct terminology
• A clear process chain
• A named example
• A link to coastal system ideas

Conclusion ✅

Coastal landforms are created by the interaction of erosion, transportation, deposition, weathering, and mass movement. Rocky coasts develop erosional landforms such as cliffs, wave-cut platforms, arches, stacks, and stumps, while lower-energy environments often produce depositional landforms such as beaches, spits, bars, tombolos, and lagoons. These features are important because they show how coastal margins are constantly changing. Understanding them helps you explain how ocean energy and sediment movement shape the edge of the continent, which is central to the IB Geography SL theme of Oceans and Coastal Margins.

Study Notes

• Coastal landforms are features shaped by the interaction of marine processes and the land.
• The main coastal processes are erosion, transportation, and deposition.
• Erosional landforms are common on high-energy rocky coasts.
• A sequence of crack → cave → arch → stack → stump explains one common erosion pattern.
• Cliffs retreat when waves undercut the base and mass movement causes collapse.
• Wave-cut platforms are left behind as cliffs move inland.
• Depositional landforms form where wave energy decreases and sediment is dropped.
• Constructive waves build beaches because swash is stronger than backwash.
• Longshore drift moves sediment along the coast and helps create spits and tombolos.
• Bars can close off bays and create lagoons.
• Coastal landforms are part of the wider coastal system, influenced by sea level, sediment supply, wave energy, and human activity.
• Use named examples, accurate vocabulary, and clear process explanations in IB Geography answers.