How were the Moeraki Boulders formed?

The Moeraki Boulders are concretions — masses of minerals that crystallised around a central nucleus (often a fossil or shell fragment) within marine mudstone on the seafloor. The process took millions of years: mineral-rich water slowly deposited calcite around the nucleus, growing the boulders layer by layer. The mudstone containing them formed around 60 million years ago; the boulders formed within this sediment over subsequent millions of years. Coastal erosion has gradually exposed them from the cliff face and left them on the beach.

How big are the Moeraki Boulders?

The largest Moeraki Boulders reach up to about 2 metres in diameter, though most are somewhat smaller. They are among the largest concretions of their type known. Many are cracked and hollowed as the internal structure has eroded after the outer shell was exposed to weather and wave action.

What is the Māori explanation for the Moeraki Boulders?

In Māori tradition, the boulders are the remains of eel baskets, gourds, and kumara washed ashore from the great canoe Āraiteuru, which ran aground on the reef at Shag Point nearby. The crew members became the Moeraki hills; the food stores and cargo became the boulders. The legend ties the boulders into a wider narrative about the Polynesian settlement of Otago that includes several local geographic features.

Where are the Moeraki Boulders and how do you get there?

The boulders are at Koekohe Beach, around 40km north of Oamaru on State Highway 1. There is a car park and short walkway to the beach. Entry to the beach has a small fee managed by local operators. The boulders are about 75km south of Dunedin — a convenient stop on a South Island road trip between Christchurch and Queenstown or Dunedin.

Moeraki Boulders: The Giant Spheres on New Zealand's Otago Coast

On Koekohe Beach near the South Island town of Moeraki, large spherical boulders sit in the surf zone as if placed by hand. Some are intact; others have cracked open to reveal a hollow honeycomb interior. The largest approach 2 metres in diameter. They have been forming inside marine sediment on the seafloor for millions of years and are gradually being exposed as the coastal cliffs above them erode. The result is one of the more genuinely strange beaches in New Zealand — and one that has attracted scientific study, Māori legend, and an enormous volume of photographs.

The Geology

Concretions: formed from the inside out

~60 million years of geology Calcite-cemented mudstone

The Moeraki Boulders are a type of geological formation called a concretion. They grew within marine mudstone on the ancient seafloor, around 60 million years ago, by the gradual accumulation of calcite minerals around a central nucleus — often a fossil fragment, shell, or bone. Mineral-rich water moving through the sediment deposited calcite slowly, layer by layer, eventually producing near-perfect spheres. The process took millions of years.

The surrounding mudstone cliff — the Moeraki Formation — has been eroding over millennia, releasing the harder concretions onto the beach. New boulders continue to emerge from the cliff face as erosion progresses, while older ones already on the beach crack and break down. It is a geological process in visible slow motion.

The Māori story of Āraiteuru

Ngāi Tahu tradition

In Māori tradition, the boulders are the eel baskets, gourds, and kūmara (sweet potato) that washed ashore from the great canoe Āraiteuru when it was wrecked on the reef at Shag Point (Matakaea) nearby. The crew members who survived the wreck became the hills around Moeraki; those who drowned became the reef. The boulders mark the location where the canoe's cargo was scattered along the coast. The legend connects the Moeraki Boulders to a broader set of South Island geographical features that Māori whakapapa (genealogy) explains as the remains of the Āraiteuru voyage.

Visiting the Boulders

Koekohe Beach: what to expect

40 km north of Oamaru Small entry fee

The boulders are accessible via a short walkway from the car park on State Highway 1. The beach itself is not particularly large — the main cluster of boulders sits within a short walk. You can walk among and around the boulders freely; some people climb on them. The boulders are best photographed at low tide, when the largest ones are fully above water and the sand around them is clean. At high tide, some boulders sit in surf and are harder to reach.

Early morning is the best time for photography — soft light, low crowds, and a chance of mist over the water. By mid-morning on a fine day in peak season, the beach has significantly more visitors. The cliff face above the beach shows new boulders in various stages of emergence — the erosion is gradual but visible if you look for it.

Road trip context: Moeraki sits on State Highway 1, making it a natural stop between Christchurch and Dunedin (about 75km north of Dunedin). Combine with Oamaru — New Zealand's Victorian heritage town and home to a wild little blue penguin colony — for a half-day Otago coast circuit.

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