Durdle Door

Durdle Door is a natural limestone arch on the Jurassic Coast of Dorset, southern England, formed where a resistant band of Portland limestone, tilted nearly vertical by ancient tectonic folding, runs out into the English Channel. Wave action attacking the narrow limestone ridge from both sides gradually breached a weakness near its seaward end, first carving a cave and then enlarging it into a full archway spanning the ridge, a formation process comparable to that of a headland arch, while continued erosion means the arch will eventually collapse to leave an isolated sea stack, as has already happened to nearby formations along the same coastline. Its name is thought to derive from an old English word meaning "door" or "gate," and the surrounding coastline is part of the Jurassic Coast UNESCO World Heritage Site for its exceptional record of geological time.