Along The Great Ocean Road, Vic. Australia - dpb photos

Coastal Sea Stack

The formation process usually begins when the sea attacks small cracks in a headland and opens them. The cracks then gradually get larger and turn into a small cave. When the cave wears through the headland, an arch forms. Further erosion causes the arch to collapse, leaving the pillar of hard rock standing away from the coast—the stack. Eventually, erosion will cause the stack to collapse, leaving a stump. This stump usually forms a small rock island, low enough for a high tide to submerge.

erosionsea stackstackcollapsearchGreat Ocean RoadVictoria AustraliaTwelve Apostlesheadland