On the Southeast coast of New Zealand’s South Island lies perhaps some of the most visited boulders in the world. It might seem strange that people would travel far and wide to look at some boulders, but these Moerkai boulders are rather special. Ranging in size from around half a meter to just over two meters in diameter, these boulders are nearly perfectly spherical.

These boulders have are a thing of beauty - and of Maori legend. Over 1000 years ago, the legend goes, a large sailing canoe the Arai-te-uru became shipwrecked at the nearby Shag Point during a storm. The canoe itself turned to stone, it’s hull creating a reef that extends out to sea from Shag Point. Nearby, a rocky promontory is the petrified body of her commander. As for the boulders themselves, these are the petrified remains of the canoe’s eel baskets, calabashes (gourds), and kumaras (sweet potatoes), and fishing nets.

Of course, being near-perfect spherical boulders, they have also attracted the a few conspiracy theories. The most common - they are eggs left behind by aliens. But science has it’s own story to tell too. The boulders are actually mudstone with a good dose of calcite, created during the Paleocene around 66 to 56 million years ago on what was then the sea floor. The largest of the boulders would have taken somewhere between 4 to 6 million years to grow. As they did, they were slowly buried by mud accumulating above them. When sea levels dropped, the boulders remained hidden from view - until erosion of what is now the shoreline exposed them.

The Sea Shorts series offers tiny glimpses into all things ocean and coastal. Read more Sea Shorts and other stories here.