Story: Coastal erosion

As the sea has risen over the last 10,000 years it has flooded former river valleys. The Marlborough Sounds, at the northern tip of the South Island, are drowned river valleys. The land here is slowly sinking into the sea, so few beaches have formed. The waters are sheltered, with small waves eroding the coast at a much lower rate than at the outer shores, which face the exposed waters of Cook Strait.