Where is Tuhua?

Tuhua also known as Mayor Island is a peralkaline volcano situated 26 km north of Tauranga, Bay of Plenty, New Zealand. It is of Quaternary age and compromises peralkaline rhyolitic rocks (commendites and pantellerites). The North Island hosts many other (recently) active volcanoes, some of which are displayed below.

The oldest rocks on Tuhua are dated at about 120 ka. On the island one may find both spectacular obsidian flows as well as tens of meter thick pumice deposits that display the explosive nature of this volcano. Peralkaline rhyolitic magmas are not too common on our planet. However, there are some other locations such as Pantelleria in the Mediterranean and the East African Rift where such magmas were generated.

The volcanic evolution of Tuhua is associated with three caldera collapses (see below the geological map; modified from Houghton et al. 1992) each of which generated thick pyroclastic deposits. The main caldera depression nowadays lies almost below sea level. An 8000 years old obsidian flow is beautifully exposed at the eastern part of the island. It drapes both the inner and outer caldera walls and is interpreted to represent a spatter-fed lava flow.

My work on Tuhua involved the investigation of the thermal history of this flow. Click here for a PDF of the resulting paper published in Bulletin of Volcanology .

The remote island of Tuhua offers amazing tracks for hiking, an incredible variety of bird species and beautiful beaches to relax on. The island is in tribal hands and currently uninhabited. Unfortunately, public access is currently prohibited.

Tuhua underwater

The island allows you to experience splendid underwater wildlife: a huge variety of fish (beautiful Blue Moki, Maomao, big schools of Kawahi), kelp and monster crayfish. A marine reserve off the north coast of the island, offers great opportunity both for snorkelers and the ambitious scuba diver. Occasionally, you may crash into a Mako shark and Great Whites were reported just around the corner (thankfully not too often, as I was told). If you need information about diving around Tuhua feel free to contact me. There are a number of professional diving operators in Tauranga offering week-end trips as well as the Tauranga Dive Club.

Obsidian

Most importantly the island is the destination to study obsidian flows both onshore and underwater. The obsidian outcrops along the coastline are breathtaking.

Have a look at these pictures.

Obsidian was prized by early Maori for cutting and scraping tools and weapons and has been found at Maori occupation sites as far afield as Tiwai Pt in the south to the Kermadec islands in the north. The name Tuhua has a double significance: it applies to the locality itself and also to its black obsidian, which when chipped reveals its true dark greenish colour. Such a valuable resource meant the island was permanently occupied despite scarcity of water and lack of land suitable for cultivation.

Getting to the island

may sometimes be quite difficult, since it is definitely off the beaten track of NZ's tourism. If the island is open to public access (which will hopefully be the case in the near future) catch a big game fishing boat off Tauranga on the weekend and let yourself be dropped off on the island. Whether or not access is possible may be checked by contacting the

Department of Conservation at the Tauranga Area Office 253 Chadwick Road West Greerton PO Box 9003 Tauranga, New Zealand ph: (07) 578 7677; Fax: (07) 578 1634.

Sampling on Tuhua is prohibited since the island is tribal land and hence privately owned. In addition, the obsidian is sacred to the Maoris.

This document maintained by jgottsmann@ija.csic.es.
Material Copyright © 2005 Jo Gottsmann