Home / Learning / Science Topics / Landforms / Rugged Coasts / Coastal Erosion

Coastal Erosion

Punakaiki / Pancake Rocks are a classic. Image: Julian Thomson.

Punakaiki / Pancake Rocks are a classic. Image: Julian Thomson.

There are many spectacular examples of coastal erosion by the sea and the weather around New Zealand.

Coastal erosion is caused mainly by wave action in the surf zone, along with tides and currents. As waves are mostly an effect of wind, it is the top five or ten metres of the sea that is the most turbulent. This means that most coastal erosion occurs at or just below water level. The waves rush into the cliffs, undercutting them and giving rise to a great variety of features such as caves, blowholes, arches and stacks. The end result is a smoothed horizontal area of rock called a wave-cut (or shore) platform. Sometimes coastal uplift due to tectonic movements can lift these platforms out of reach of the sea to create a raised shore platform or marine terrace.

Headlands of relatively hard, resistant rocks form sea cliffs which stand out relative to bays where more easily eroded material has been eroded away.

Erosion of the coast also affects human structures, such as roads, buildings and other infrastructure. With rising sea levels this is likely to be an increasing problem worldwide.

Beach houses damaged by erosion at Haumoana in the Hawkes Bay. Image: Julian Thomson.

Beach houses damaged by erosion at Haumoana in the Hawkes Bay. Image: Julian Thomson.