It is technically a continuous barrier beach, though at its western end it tapers to a point less than 100 metres in width which is occasionally breached at high tide.

The sea level at that time was 130 meters lower than today, and the coast was up to 50 km east of its present-day position; the Canterbury plains were twice their present width.

Ten thousand years ago the Canterbury coastline was approaching the area presently occupied by Lake Ellesmere / Te Waihora.

Powerful southerly waves in the Canterbury Bight rapidly eroded these weakly-resistant sands and gravels, and transported them northwards by longshore drift.

The barrier is of considerable ecological significance and is home to the majority of the surviving specimens of shrubby tororaro (Muehlenbeckia astonii) – a nationally endangered endemic plant.