Moeraki Boulders are the number one tourist stop on the North Otago Pacific Coast.
You will notice the signpost on State Highway 1, roughly halfway between Moeraki and Hampden. The main access is through the Visitor Centre, which includes a tourist shop and cafe. Or you can park a bit further south and walk about 500 metres north along Moeraki Beach to the Boulders. The best time to visit is as the tide goes out, as many boulders are below the high tide mark.
The Moeraki Boulders are a natural form of concrete created by cementation near the surface of the Paleocene sea floor millions of years ago. The concretion effect is due to calcites that bind the mud particles together. Over time, the concretions built up in size; this process occurred before the pressure compressed the surrounding mud into stone. The boulders typically took four to five and a half million years to grow; the largest are about two metres in diameter.
Mud accumulated above them and eventually uplifted to form the cliffs above the beach. As the softer stone of the cliff erodes, the harder concretions become exposed. Look closely; you will see netting-style cracks in the boulders, called septaria. They gradually filled with brown and yellow calcites and other minerals, and you see the colourful effects of this within the heavily eroded boulder remains.
Although the Moeraki Boulders are famous, concretions, though not as round, can be seen further south on Katiki Beach (although they are not as spherical). At Whitecliffs in the Manawatū, concretions have been exposed by the erosive effects of the Rangitīkei River, and similar boulders can be seen near Koutu Point on the Hokianga Harbour.
Māori refer to the boulders as Kaihinaki. One of the original waka, Arai-te-uru, was wrecked at nearby Shag Point, and the legend is that the boulders are kumara that washed ashore. In this story, the waka’s fishing nets neatly explain the netting-styled septaria in the boulders.
