Then, as now, the coast was made of unconsolidated sands and gravels from the fans of major rivers such as the Rakaia and Waimakariri. Powerful southerly waves in the Canterbury Bight rapidly eroded these weakly-resistant sands and gravels, and transported them northwards by longshore drift.
In both present and historical settings, the coast is made of unconsolidated sands and gravels from river fans such as the Rakaia and Waimakariri. Powerful southerly waves in the Canterbury Bight rapidly erode these weak materials, and transport them northward via longshore drift.