Moeraki Boulders

Inland Empire

The Moereki Boulders are scattered across a stretch of coastline of New Zealand’s South Island. This popular tourist stop is located along Route 1 between Dunedin and Christchurch on the islands southeastern shoreline (65km from Dunedin). The boulders are large, spherical, sedimentary concretions of marine sediment (mud-clay-silt) that accumulated on the sea floor ~60 million years ago (dated from fossil records). The concretions formed by the cementation of soft clay rich marine muds around a harder solid nucleus (shell-skeletal matter), as more material precipitated around the core, the concretions progressively grew outwards over time. Calcite (CaCO3) gradually precipitated around the nuclei resulting in spherical nodules. This process is estimated to have taken ~120,000 years for small concretions (<0.5m) and ~4 million years for larger concretions (>2m). The variability in size of the boulders, is thus attributed to age with a higher % of growth and accumulated material over time.


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