at Koekohe beach
round Moeraki boulders
huddle in the sand
On the Otago coast we visit the astonishing and beautiful Moeraki Boulders.
They look like giant grey turtles resting on the sand.
Our geologist guide explains that the large boulders are septarian concretions that took 4 to 5.5 million years to grow on the Paleocene sea floor as mud, silt and clay were cemented together with calcite into spheres as large as 3 meters (10 feet). Large cracks called septaria that formed in the boulders were filled in my brown and yellow cacite, dolomite and quartz. Eons later, erosion of the mudstone exposed the boulders, leaving them high but not quite dry on the beach.
I have seen similar boulders at Rock City in Ottawa County, Kansas, although the American cousins are much bigger, 3-6 meters (10-20 feet), and formed from sandstone on what was then a coastal plain. I wonder if one of these will fit in my backpack.
The Māori, the first humans to behold these marvelous boulders, have a different explanation for their origin. Their legend tells of a large sailing canoe, an Arai-te-uru, which wrecked on the rocks. The boulders are the eel baskets, calabashes and kumara (sweet potatoes) that washed ashore. The nearby rocky shoals and promontory are the petrified hull of the canoe and the body of the canoe captain.
I have my own theory about how these septarian concretions came to be. They were built out of concrete by gnomes, each one taking 70 years to construct, and were abandoned when the beach became a tourist attraction.