Environment Geological origins
The Norfolk Island group is situated on the Norfolk Ridge, an elongated submarine rise which extends from New Zealand to New Caledonia.
There are no other emergent outcrops in the group, with the closest land being New Caledonia (approximately 800 kilometres to the northwest).
Norfolk and Phillip Islands have similar geology, both being almost completely volcanic in origin. The sporadic volcanic activity which built the Islands extended over a period of roughly 700,000 years, beginning about 3 million years ago. The sea has since eroded Norfolk Island to about one-third of its original size and formed a coastline of high cliffs.
The volcanic activity generated four distinct rock formations, consisting of fine to medium grained olivine basalts and tuffs (layered volcanic ash). These are the Ball Bay Basalts (the oldest dating to about 3 million years ago), the Duncombe Bay Basalts (2.66-2.69 million years), the Cascade Basalts (2.4 million years) and the Steeles Point Basalts (2.33-2.39 million years).
Nepean Island and part of Norfolk Island near Kingston consists of coarse marine calcareous rock (sand, coral and shell fragments cemented with lime) of late Pleistocene origin. The rock was in part deposited by on-shore winds during a period of low sea level. It was this rock which was quarried for the convict buildings at Kingston.
Courtesy of Department of Environment & Natural Resources
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