In stormy weather, powerful waves hurl loose rocks at the shore, undercutting cliffs. While soft rocks are worn back to form bays, hard often survive as headlands in which waves then hollow out caves. If the roof of a cave collapses, a ‘blow hole’ is formed in the ground above. When waves break in the cave, clouds of spray burst through these holes.
Caves on opposite sides of headlands often meet to form arches. When arches collapse, a rocky island, or stack, is left behind, but this, too, will eventually be removed by the relentless waves.