Solander Island – an extinct volcano
In February 2010, geologists from GNS Science and Macquarie University in Sydney spent 6 days on the inhospitable Solander Island, 40km south of the Fiordland coast. The team collected rock samples, made observations and updated a geological map of the island.
Solander Islands
Little Solander Island is in the foreground with Solander Island in the background. The islands are eroded remnants of an extinct volcano and the only volcano in the Pacific Ring of Fire that is south of Mount Ruapehu.
Dating rock samples
The team was only the third party of geologists to ever visit the island, with previous visits in 1958 and 1973. The geologists on this trip made some interesting discoveries. While they had known from the first visit some 60 years ago that Solander Island (Te Niho a Kewa) is the eroded remnant of an extinct volcano, they had thought that it last erupted about 2 million years ago. However, recent radiometric dating of Solander rock samples has shown them to be between 150,000 and 400,000 years old, making the volcano not so old after all.
However, Solander Island (along with Little Solander Island) is still classed as an extinct volcano because of the long interval since its last eruption. Apart from abundant protected albatrosses, penguins and seals, it is uninhabited and is subject to the Department of Conservation’s strict Subantarctic Island access control and quarantine procedures. The islands form a specially protected part of the Fiordland National Park.
Getting access to Solander Island and staying there for 6 days wasn’t easy. The geologists flew to and from the island by helicopter from Invercargill Airport. Once on the island, there is little flat land, so finding a place to camp was a challenge. There was also no freshwater so the group had to be fully self-sufficient.
Significance of the Solander volcano
Party leader Dr Nick Mortimer of GNS Science says the eruptive history, growth, longevity and alteration of the Solander volcano will be compared with that of the mainly submarine volcanoes near the Kermadec Islands, north-east of New Zealand (another team of GNS Science geologists is currently researching New Zealand's northern offshore volcanoes).
Dr Mortimer says the island is actually only the tip of a much larger submerged volcano about the size of Mt Taranaki and that it was remarkable that so little was known about the geology of an island that is visible from mainland New Zealand.
Geologically, it’s unique. It’s the only volcano in the Pacific Ring of Fire that is south of Mount Ruapehu. It’s a very substantial volcanic structure. It would have been spectacular to see it erupt from mainland New Zealand.
Dr Nick Mortimer
The eruption history of the island has raised the possibility that there is volcanic ash from Solander scattered across the Southland plains that is contributing to the soil fertility of the area.
The field expedition will be followed by at least 3 years of laboratory work on the new rock samples. This will include radiometric dating and geochemical analysis.
This will enable geologists to establish the exact age of the volcano, how explosive it was when it erupted and how it is related to the Fiordland tectonic plate boundary.
Activity idea
In relation to this news article, your students may like to do this activity, Identifying volcanic rocks, in which they watch a video describing the different types of volcanic rock and then match the chemical composition and type of volcanic eruption each rock is associated with.
