Coastal landforms of erosion

How a coast erodes depends on its rocks:

• Hard rocks, such as chalk, limestone and granite, resist erosion and form high cliffs and headlands.
• Soft rocks, such as clay and sand, erode quickly and form lower, gentler coasts and bays.

The geological structure, the way the bands of rock lie, matters too:

• On a discordant coast, bands of hard and soft rock meet the coast at right angles. The sea erodes them at different rates, making headlands and bays.
• On a concordant coast, the bands run parallel to the coast, so it stays straighter.

Cracks, called joints and faults, are lines of weakness that the sea erodes first.

On a discordant coast:

1. The sea erodes the bands of soft rock quickly, by hydraulic power and abrasion, wearing them back into bays.
2. The bands of hard rock erode more slowly and are left sticking out into the sea as headlands.
3. Once formed, the headlands take the full force of the waves, while waves spread out and lose energy in the bays.
4. With calmer water, the bays collect beaches, while the headlands keep being eroded, into caves, arches and stacks.

1. Destructive waves attack the foot of the cliff, between high and low tide, by hydraulic power and abrasion.
2. This cuts a wave-cut notch.
3. The notch grows deeper, and the cliff above is left overhanging.
4. The overhang becomes too heavy and collapses, and the cliff retreats inland.
5. Again and again, the cliff retreats, leaving a gently sloping, rocky wave-cut platform, visible at low tide.

1. The sea erodes a crack or joint in a headland, by hydraulic power and abrasion.
2. The crack widens into a cave.
3. The cave is eroded right through the headland, making an arch.
4. The bottom of the arch is eroded and its roof is weathered, until the roof collapses, leaving a pillar of rock: a stack.
5. The stack is eroded at its base until it collapses into a short stump, covered at high tide.