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Creation 36(4):20–21, October 2014

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Moeraki Boulders: giant marbles of New Zealand



Scattered over a beach on the South Island of New Zealand, dozens of huge spherical boulders look like the remains of a monster game of marbles. The grey stone balls are a fascinating tourist attraction about 70 km north of Dunedin near Moeraki (pronounced ‘moi-ra-kee’), a small town on the Otago Coast. Some boulders stand alone but most sit in clusters with the waves splashing over them at high tide. Many others lie broken into segments on the sand.1

The boulders are spectacular examples of concretions, which form in a deposit of mud or sand when minerals from the groundwater cement some of the sediment into rock. As you walk down the steep bluff to the beach you can see some enormous boulders still embedded in the mudstone and others being exposed as the ocean waves erode the loose embankment. They will eventually fall onto the beach.

The larger stones stand taller than a man, more than 2 metres (6.5 feet) in diameter, and weigh around 10 tonnes. Most are spherical but some are slightly squashed.

Although dramatic, the boulders are by no means unique. In New Zealand you can find similar ones called Katiki Boulders on a beach just 12 km south, and others on the North Island along the shore of Hokianga Harbour. Similar concretion boulders are found in a deposit called the Kimmeridge Clay in cliffs along the Wessex Coast of England; on the shore of Lake Huron near Kettle Point, Ontario; within sandstone outcrops in central Wyoming and northeast Utah; and at Rock City in Kansas, to mention a few.

Outside, the shell of each Moeraki boulder is hard, cemented by a mineral called calcite. Inside, the boulders are not so well cemented, and are eroded by the waves after they break apart. The spherical shape suggests that the calcite mineral precipitated from the groundwater as the concentration of the solution moved outwards in concentric shells from a central point.2 This indicates the surrounding mud was fully deposited before the boulders began to form.

Cracks, filled with calcite, cover the surface of the boulders, dividing it into segments like a soccer ball. These cracks radiate outward from the core of the boulder, becoming thinner toward their tips.

The Moeraki Boulders formed within a thick deposit of mud, silt and clay called the Moeraki Formation. Tourist information says the boulders were “exposed by erosion of sedimentary rocks laid down from 65 to 13 million years ago. They are formed by the gradual precipitation of calcite in mudstone over 4 million years.”3 We will see below that there is another explanation.

People could be excused for imagining that the dates quoted were carefully measured with a scientific instrument, but that is not the case. The conventional dating relies on multiple assumptions about past conditions, and the validity of the result depends on the validity of the assumptions. The most basic assumption behind the dating is that the worldwide catastrophe of Noah’s Flood never happened.

The ‘date’ of 65 million years for the mud deposit was decided by the type of tiny fossils found in it.4 The 4 million year ‘date’ for the boulders to harden was calculated from hypotheses about how they formed.5 The fact is that sediment can cement into hard rock within days.6

Creation geologists conclude that the boulders formed as a consequence of Noah’s Flood. The mud sediments were deposited rapidly in the second half of the catastrophe, some 4,500 years ago. Based on the geographical location, it is considered that the mud was deposited after the floodwaters had entirely covered all the earth and as the floodwaters had begun to fall.

It took more than seven months for the floodwaters to completely recede into the oceans and the land to become dry (Genesis 8), during which time sediments were deposited at the continental edges. The mud would have been deposited quickly, within a period of days or weeks. The large size of the boulders suggests the thick mud was deposited rapidly and that the water in the mud was full of minerals.7

Recent experiments have shown that mud can be deposited rapidly, even from flowing water.8

After the sediment was deposited, the minerals in the groundwater precipitated and cemented the boulders. It may have taken weeks for the mineral cement to precipitate, but the process could have continued after the Flood ended.

After reading the official commentary that the boulders formed over millions of years, visitors would not realize that they were given a biased view about what happened. Visitors need to know that features like the Moeraki Boulders can be accurately interpreted through the lens of biblical history. Not only would this connect the world of tourism to the true history of mankind but it would help people understand their place in it.

Posted on homepage: 11 January 2016

References and notes

  1. Moeraki Boulders Facts, moerakiboulders.com/facts/ (Accessed 28.4.14). Return to text
  2. These are known as Liesegang rings, and are common when chemical solutions undergo precipitation reactions. Return to text
  3. Moeraki Boulders, NZ Department of Conservation, doc.govt.nz/parks-and-recreation/places-to-visit/otago/coastal-otago/moeraki-boulders/ Return to text
  4. Skeletons’ of single-celled organisms called foraminifera (pronounced for am’ in if’ ara). Return to text
  5. Boles, J.R., Landis, C.A. and Dale, P., The Moeraki Boulders; anatomy of some septarian concretions, Journal of Sedimentary Research 55(3):398–406, May 1985. Return to text
  6. For example, see: Walker, T., Rapid rock: unexpected application for hard-rock recipe, Creation 24(2):38–39, 2002; creation.com/rapid-rock. Return to text
  7. Astin, T.R., Septarian crack formation in carbonate concretions from shales and mudstones, Clay Minerals 21:617–631, 1986. Return to text
  8. Walker, T., Mud experiments overturn long-held geological beliefs, J. Creation 22(2):14–15, 2008; creation.com/mud-experiments. Return to text

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