Remains of a former ocean floor

These limestone boulders characterize the landscape of Castle Hill Basin, located in the foothills of New Zealand’s Southern Alps. Where do these massive, sometime castle-high blocks come from? 25 million years ago, the Pacific Plate collided with the Australian plate during the Kaikoura orogeny, giving birth not only to the Southern Alps but also lifting up thick limestone beds formed in shallow ocean water. Once the limestone was exposed to the atmosphere, weathering and erosion quickly ate it away and today only the scattered boulders of Castle Hill remain, serving not only as last witnesses to a former ocean floor but also as popular rock climbing spots.