Coastal erosion occurs when waves eat away at the land causing the shoreline to retreat. The sand and gravel stripped from a beach or cliff can be carried away by ocean currents. They can then be deposited out at sea or on another beach, causing it to build up – a process known as accretion.
A rising sea can speed up erosion along some parts of the coastline and trigger it in others.
Erosion (and accretion) around much of the coastline of New Zealand is a natural process that has been happening for thousands of years. As the sea rises, cycles of erosion and accretion on beaches will change. The net effect of a higher sea will generally be increased erosion because the high-energy waves that strip sediment will reach further up shores.