Like a giant dinosaur nest from Jurassic Park, huge, spherical stones called the Moeraki Boulders lie on the Koekohe Beach on New Zealand’s North Otago coast. Some of the boulders remain partially encased by the sea shore and only peek out at onlookers, while others have completely revealed their beautiful shapes and patterned surface lines or colorful hollow cores. This magnificent display of nature reflects the incredible historic mysteries of the Otago coast that have spawned legends and scientific intrigue.
Maori legend provides an explanation for the origin of the Moeraki Boulders. One version of the story tells that long ago, the Kähui Tipua people sailed out on an expedition to the mythical land of Hawaiiki in their double-hulled waka, or canoe, called the Arai Te Uru. Their goal was to find and bring back kumara sweet potato plants to grow back home. A storm engulfed the Arai Te Uru during the return journey and the hulled voyager wrecked off the Otago Coast at a place called Shag Point. The hull of the canoe became a reef near the Waihemo River Mouth. Baskets and gourds that had carried food and water also washed ashore, preserving the cargo for all time as the great boulders along New Zealand’s Moeraki beach on South Island. (New Zealand Department of Conservation).
How Were the Moeraki Boulders Formed?
These natural wonders began forming about 60 million years ago as concretions that developed when calcite crystallized around organic material in the mudstone. The resulting nodules hardened. Subsequently, surface imperfections allowed a chemical process to dehydrate the nodule cores. This process caused cracks and permitted yellow or brown calcite, quartz, or dolomite crystal deposits to invade the cracks. This has caused a beautiful basket-like appearance on many of the boulders. Geologic activity pushed the mudstone out of the sea, thus creating the cliffs along the beach behind the boulders. Today, the beach is artfully arrayed with the spherical concretions, preserved because of calcification that resisted the erosion of the surrounding mudstone.
Early Documentation of the Boulders
Maori ancestors occupied the vicinity of the Otago Coast for hundreds of years, beginning around the 13th century CE. However, documentation of the boulders did not take place until European involvement. Hence, it wasn’t until around 1814 during the War of the Shirt that the world learned of the boulders. Stability in the area came subsequently after the establishment of the Otago whaling station by the Weller brothers in 1836. The Wellers also involved themselves heavily with merchant-based trading as well.
Walter Mantell was a politician and scientist of geology and paleontology. As part of his work, he documented the Moeraki Boulders in a seaside sketch dated to 1848. In it, Mantell showed the presence of a greater number of beach stones at that time. Just two years later, colonists in 1850 began presenting the area as a tourist attraction through reports and articles.
The University of Auckland Library has copied pages of Gideon Mantell’s (Walter Mantell’s father) book from 1850, Notice of the Remains of the Dinornis and other Birds…, which includes the following excerpt on the Moeraki Boulders by Walter Mantell:
“Midway between the Bluff and Moeraki, the clay contains layers of septaria [Moeraki Boulders], varying from one to five feet and more in diameter. Hundreds of these nodules, which had been washed out of the undermined clay cliffs by the encroachment of the sea, were scattered along the beach, as represented in the sketch, fig. 5. Some were subglobular,
[Quote continues…] 1850.] MANTELL ON THE GEOLOGY OF NEW ZEALAND.
others spherical; many were entire, whilst others were broken, and glittering with yellow and brown crystals of calcareous spar.”
The Moeraki Boulders are ever changing. As such, their geologic history comprises a saga of decay. The very organic matter that served as the nuclei of these boulders absorbed water percolating through ancient cracks in the surface calcite. Those “clean” cracks would refill with newer calcite or dolomite, and the process would repeat. However, in the last 170 years, the ocean with its dissolving waters is slowly eroding the Moeraki Boulders. As a result, no one is able to give these stone marvels of nature any kind of lifetime estimate. However, a glimpse of this natural phenomenon may be an impossibility in the future.
Caring for the Natural Treasure
Maori have always strived to remain connected with nature and to preserve its resources. Thus, the Moeraki fishing village cares for its stone-dotted beach. They also maintain a yellow-eyed penguin reserve and oversee a seal sanctuary. Today, a viewing platform overlooks the Moeraki Boulders. From that vantage point, visitors may see just beyond the beach stones to observe Hector’s dolphins cavorting in the sea, oblivious to the legendary splendors lying on the beach.