2.3 Coasts (Enhanced Detail Notes)

These notes provide a comprehensive and highly detailed exploration of coastal processes, the landforms they create, coastal ecosystems, and the relationship between humans and coastlines, fully aligned with the Cambridge IGCSE Geography syllabus.

1. The Work of the Sea and Wind

Waves are the primary agents of change at the coast. Their energy is derived from the wind. Key factors influencing wave energy are the fetch (the distance of open water the wind blows over), wind speed, and wind duration.

• Constructive Waves: These are less powerful waves that build up the coast through deposition. They are characterised by a strong swash (the movement of water and sediment up the beach) and a weak backwash (the return flow of water and sediment down the beach). This imbalance leads to a net gain of sediment. They are typically low in height, have a long wavelength, and a low frequency (6-8 waves per minute).
• Destructive Waves: These are powerful waves that erode the coast. They have a strong backwash and a weaker swash, leading to a net loss of sediment from the beach. They are high, have a steep wave front, a short wavelength, and a high frequency (12-14 waves per minute). They often occur during storms when the fetch and wind speed are great.

Coastal Processes

1. A) Erosion (The wearing away and removal of material)

1. Hydraulic Action: The sheer power of waves crashing against cliffs. The force of the water compresses air within cracks and faults in the rock. As the wave recedes, the pressure is released explosively, causing the crack to shatter and widen over time. This is particularly effective during storms.
2. Abrasion (Corrasion): The ‘sandpaper’ or ‘scouring’ effect. Waves pick up and hurl sediment (sand, shingle, boulders) against the cliff face. This grinds and chisels the rock away. It is the most effective form of marine erosion.
3. Attrition: The process where rocks and pebbles being transported by the sea collide with each other. They break into smaller pieces and become smoother and more rounded over time. This process does not erode the coastline itself, but the material involved in erosion.
4. Solution (Corrosion): The chemical process where seawater (which is mildly acidic) and its salts react with minerals in the rock, causing them to dissolve. This is most effective on rocks like chalk and limestone.

1. B) Transportation (The movement of eroded material) The sea transports sediment in four ways:

1. Traction: Large boulders and pebbles are rolled along the seabed by the force of the water.
2. Saltation: Smaller pebbles and stones are bounced along the seabed.
3. Suspension: Fine, light material like sand and silt is carried along within the water column.
4. Solution: Dissolved minerals are transported within the mass of moving water.

• Longshore Drift: This is the primary process of sediment transport along the coastline, acting like a river of sand.
  1. The direction of the prevailing wind causes waves to approach the coast at an angle.
  2. The swash carries sediment up the beach at this angle.
  3. The backwash then carries the sediment straight back down the beach at a 90° angle, under the influence of gravity.
  4. This continuous zig-zag movement gradually transports vast quantities of material along the coast.

1. C) Deposition (The dropping of eroded material) Deposition occurs when the sea loses energy and can no longer transport its load. This happens when:

• Waves enter a sheltered area, such as a bay or the area behind a spit.
• Waves enter shallow water.
• There is a large supply of sediment.

2. Landforms of Coastal Erosion

Erosional landforms are most common on high-energy, exposed coastlines.

Headlands and Bays These form on discordant coastlines, where bands of hard rock (e.g., chalk, limestone) and soft rock (e.g., clay, sand) are perpendicular to the coast.

1. The less resistant soft rock is eroded much faster by processes like hydraulic action and abrasion. This forms wide inlets called bays.
2. Bays are sheltered, low-energy environments, so deposition occurs, often forming sandy beaches.
3. The more resistant hard rock is eroded much more slowly and is left jutting out into the sea as a headland. Headlands are exposed and become the focus of erosion.

On a concordant coastline, the bands of rock are parallel to the coast. Erosion is slower, but can create coves where a weakness in the hard outer rock is exploited.

Sequence of Headland Erosion: Cliffs, Caves, Arches, Stacks, and Stumps

1. Cliffs & Wave-Cut Notch: Waves attack the base of the headland, concentrating their energy between the high and low tide marks. A wave-cut notch is formed at the base of the cliff through abrasion and hydraulic action.
2. The undercutting of the notch leaves the rock above unsupported. Eventually, it collapses under gravity. This process repeats, causing the cliff to retreat inland.
3. Wave-Cut Platform: As the cliff retreats, it leaves behind a gently sloping, solid rock platform at its base, called a wave-cut platform. This is often exposed at low tide and covered by the sea at high tide.
4. Caves: Headlands often have lines of weakness, such as faults or joints. These are eroded more rapidly than the surrounding rock, forming caves.
5. Arches: Where a cave erodes through to the other side of a headland, or where two caves on opposite sides of a headland meet, a natural arch is formed. Example: Durdle Door, Dorset, UK.
6. Stacks: The arch is widened by erosion and weakened by weathering on its roof (e.g., chemical weathering, freeze-thaw). Eventually, the roof collapses, leaving a tall, isolated pillar of rock detached from the headland, known as a stack. Example: Old Harry, Dorset, UK.
7. Stumps: The stack is undercut by erosion at its base and will eventually collapse, leaving a much smaller, often tide-covered, piece of rock called a stump.