How do sea arches form along rocky coasts?

Sea arches are spectacular erosional landforms that develop along rocky coasts primarily due to varying rates of erosion caused by the differing resistance of bedrock.12

As waves strike the shore, they exert hydraulic pressure and utilize the abrasive action of sand and pebbles to wear away the rock. When a section of the coastline contains rock that is less resistant to these forces, it erodes more quickly than the surrounding material, eventually carving out an arcuate or rectangular opening that can extend below the water level.21

These features are part of the ongoing evolution of erosional coasts. Over time, continued wave action may cause the arch to collapse, leaving behind an isolated sea stack on a wave-cut platform. Eventually, further erosion will remove the stack entirely, leaving only the platform at the base of the retreating coastal cliff.13