NZ – Moeraki Boulders | A Leaf on the Wind

– MARCH 25, 2015

After some time with real people (aka the Hughes farm crew), we jumped back onto the road for our southern route journey. Roughly 4 days will take us through Dunedin, the Catlins, Bluff, Te Anau and a return visit to Queenstown. However first we are stopping at the natural phenomenon named the Moeraki Boulders.

The Moeraki boulders are spherical rocks – concretions – that reach over 1 meter across. They started to form about 55 million years ago, when mud/pebbles/shells were deposited on a quiet sea floor and were gradually buried. In places, lime was deposited slowly and evenly around a shell or pebble, to form a hard, cemented, spherical concretion. While still buried, some concretions split and became infilled by walls of yellow crystals of lime. As the region was uplifted in recent geological times, the sea eroded nearby cliffs of mudstone to free the boulders from their encasing softer rock.

Jill beside a Moeraki Boulder

Moeraki Boulders

The spherical boulders on the beach did not originate from bedrock in the way boulders normally do, as mentioned above they are concretions. This concretion process is similar to the way pearls are formed around a particle in an oyster. The boulders here are built up from a mineral called calcite. When they are exposed to the weathering effect of the sea they lose their outer layers, and this leaves hard veins of crystallised calcite standing out in relief. As the weathering progresses the veins control the break-up of the boulder into small polygonal pieces.

Moeraki Boulders

Everything on New Zealand has a Maori legend attached to it. The story of the Moeraki bulders is linked to Araiteuru, an enormous Waka Atua, a canoe of the Gods. The traditions tell of this great canoe journeying from Tai Te Whenua across the Great Ocean of Kiwa, the Pacific Ocean. The jouney was long, and the Waka became waterlogged and foundered at Matakaea, 12 km south of this location. The reef at the mouth of the Shag river is the petrified hull of the Waka, and a prominent rock near the reef is said to be the perfied body of Hipo, the navigator. The coastal region is named after Araiteuru after the canoe. The crew and cargo of the wrecked Waka were thrown into the sea and washed up on the shore, and the cargo can be seen strewn along the beaches north of Matakaea. The large boulders here are considered the gourds and calabashes bound with flax which held water for the voyage.

Moeraki Boulders

The image below displays the various components of the Moeraki Boulders. The dark outer layer is the densely cemented rim. The layers as you proceed inward show the early brown calcite, then the late yellow calcite, then the loosely cemented core, then the void in the middle. This example also shows both concentric and radial cracks.