Coastal Landscapes: Processes (SQA National 5 Geography): Revision Note

Specification checklist

This page covers what you need to know from the SQA National 5 geography specification to answer questions on:

• The identification and formation of the following landscape features:

  • Cliffs, caves and arches, stacks, headlands and bays, spits and sand bars

The processes of coastal erosion

• Destructive waves are responsible for the majority of erosion that happens along a coast

• There are four types of erosion:

  • Hydraulic action

  • Abrasion

  • Attrition

  • Solution

Hydraulic Action

• This is the sheer force of waves crashing against the shore and cliffs.

• The power of the waves forces air into cracks, compresses it and breaks the rock apart as the pressure is released

Abrasion/Corrasion

• Rocks and pebbles carried in the waves wear away the coastline as they are thrown against it (the sandpaper effect)

Corrosion/Solution

•  When chemicals in the seawater dissolve minerals in the rocks, causing them to break up.

 Attrition

• When rocks and pebbles carried by the waves smash into each other

Formation of coastal erosion features

Cave and arch formation

•  The waves attack a line of weakness, such as a fault line, in the headland

•  Erosion, such as hydraulic action, widens the gaps/cracks

•  Over time, hydraulic action enlarges the crack and it develops into a sea cave (e.g. Tilly Whim caves)

• As the cave becomes larger, abrasion wears away the back and sides of the cave (the sandpaper effect)

• Further erosion of the cave, from opposite sides of the headland, cuts through the rock to form an arch (e.g. Durdle Door)

Stack formation

• The base of the arch is attacked by the waves and gets wider, so the top of the arch collapses 

• This leaves behind a freestanding piece of rock called a stack, which is separate from the headland (e.g. Old Harry)

Cliff formation

• Cliffs usually form where there is harder, more resistant rock, such as limestone and chalk

• Wave erosion is strongest where large waves break against the base of the cliff

• A wave-cut notch will be formed as the cliff is undercut by the erosive power of the waves, through the processes of hydraulic action, solution (corrosion) and abrasion (corrasion)

• Eventually, the cliff above the notch becomes unsupported and collapses into the sea

• The cliff retreats and leaves behind a gentle sloping shelf of rock, a wave-cut platform, which is visible at low tide

Formation of headlands and bays

• Headlands and bays are found in areas where there are bands of alternating hard and soft rock, which meet the coast at right angles (for example, sandstone, a hard rock, and clay, a soft rock)

• Headlands and bays are formed by differential erosion

  • The softer, less resistant rock erodes backwards more quickly, forming bays

  • When formed, the bays then become sheltered by the headlands, and erosion slows down.

  • The harder rock erodes more slowly, forming headlands which are left sticking out as rocky outcrops.

• The headlands are then vulnerable to erosion as the wave's energy is concentrated here

Process of coastal transportation

There are three parts of coastal transportation, which result in the formation of many coastal landforms:

1. Swash and backwash – movement up and down a beach

2. Longshore Drift – movement along a coastline

Longshore Drift

• Every time a wave breaks, the swash washes sand up the beach at an angle, in the direction of the prevailing wind

• The water then washes straight back down the slope of the beach, perpendicular to the coastline, taking sand with it

• Over time, sand is moved along the beach

  • This process is called longshore drift.

• On many coasts, longshore drift is in one direction, e.g. on the south coast of England, where the prevailing wind and the maximum fetch are both from the south – west, there is a dominant movement of beach materials eastwards

Coastal deposition features

Formation of spits

• Sand spits are long, narrow ridges of sand or shingle which form where the coastline changes direction

• Longshore drift transports sand along the coastline and deposits it in a shallow or sheltered area

• The deposited sand builds up over time until it is above sea level

• This deposition continues until the beach extends into the sea to form a spit

• Sand spits can also develop a hooked or curved end due to a change in prevailing wind/wave direction

Formation of sand bars

• Sand bars are long, narrow ridges of sand or shingle which join one headland to another

• When the spit forms across a bay, it reaches another headland forming the bar