The other islands of Aotearoa: an unexplored history

In the article ‘Geology of New Zealand’s Sub-Antarctic Islands’ published in the New Zealand Journal of Geology and Geophysics, researchers James M. Scott and Ian M. Turnbull of the University of Otago explore geological information, maps and hypotheses for each island. 

The islands of Aotearoa New Zealand are the small, exposed areas of the world’s 8th continent, Zealandia. Other than the two main islands, Aotearoa New Zealand is made up of the Chatham Islands, Stewart Island, some Kermadec Islands, and five uninhabited Sub-Antarctic Islands. The Sub-Antarctic Islands are the only exposed areas of the Campbell Plateau, a large oceanic plateau that originated in the Gondwanan break-up. The island groups are made up of the Bounty Islands/Moutere Hauriri, Antipodes Islands/Moutere Mahue, Campbell Island/Motu Ihupuku, Snares Islands/Tini Heke and the Auckland Islands/Motu Maha, all of which are United Nations Educational Scientific and Cultural Organisation (UNESCO) World Heritage areas.

The islands are considered World Heritage areas due to their diversity of flora and fauna, particularly the endemic seabirds and marine animals. The islands also have a history of whaling, sealing, and farming. However, permanent living stations on the islands have been abandoned due to isolation, poor agriculture, and because successful arrival to the islands is weather-, swell- and tide-dependent.

The Bounty Islands/Moutere Hauriri are the least hospitable of the Sub-Antarctic Islands. They are made up of multiple islets all less than one kilometre in width, with no fresh water and very little vegetation. These islets were first discovered in 1788 and had a large fur seal population that was decimated by sealers in the 1800s.

The Antipodes Islands/Moutere Mahue are a set of islands on the eastern side of Zealandia. The first geological notes recognising the islands to be volcanic date back to 1868. Both pyroclastic rocks (rocks of primary volcanic material) and basaltic lava are found on these islands. However, due to extensive erosion, it is hard to place individual eruption centres.

The Campbell Island/Motu Ihupuku is the farthest south and the geologically best-known island group. It was discovered in 1810 and promptly became an active site for sealing and whaling. It has the oldest exposed metasedimentary rocks from the Early Paleozoic era. Overlaying these rocks are sedimentary basin rocks and then deposits from the Campbell Island volcano.

Although Snares Islands/Tini Heke were not discovered by Europeans until 1791, they had long been known by local Māori. Snare Granite is the most common rock on this cluster of islands. It is a pale-coloured granite that is largely covered by a blanket of peat reaching eight metres in thickness. This peat layer may have started growing as early as the beginning of the Holocene era.

Auckland Islands/Motu Maha are the largest of the Sub-Antarctic Islands; however, despite Māori settlements in the 13th century and a heavy European presence due to whaling stations, the islands have not been formally geologically surveyed. In the explorations that have happened, Musgrave Granite, sedimentary rock formations and lava flows from volcanos in both the northern and southern parts of these islands have been found.

The five Aotearoa New Zealand Sub-Antarctic Island groups show a wide variety of rock, types, ages and geological processes. While many of these processes have been studied, researchers believe there are still many good geological questions to be answered, specifically on the formation of the island groups and the climatic records preserved on them.