14 Jun 2012

Hangi experiment tests Earth's magnetic field

6:31 am on 14 June 2012

A group of scientists are digging to the bottom of a hangi pit to find out why the Earth's magnetic field has changed over the centuries - which is important to navigation.

Scientists, archaeologists and Te Kawa a Maui, the School of Maori Studies at Victoria University, have teamed up in a unique project to investigate changes in the Earth's magnetic field through the magnetisation of ancient hangi stones.

All rocks, including those favoured by Maori for hangi stones in the earth oven, contain small amounts of magnetic minerals such as magnetite.

A senior lecturer in physics and geo-physics Gillian Turner says she hopes some volcanic stones from the Mohaka River will point them in the right direction.

Dr Turner says she wants to find out what the magnetic field has done in the past.

She says they only have direct measurements for the past 150 years, but the hangi style of cooking has been around in New Zealand since the early Polynesian ancestors of Maori arrived here more than 700 years ago.

Dr Turner says the recent experiment in Waiwhetu in Lower Hutt is being used to see if the hangi stones will record today's magnetic field.

She says that by careful measurement of the magnetisation of a hangi stone they will be able to retrieve both the direction and the strength of the magnetic field in which it is cooled.

The experiment will also help the scientists to understand the processes deep within the core of Earth that generate the magnetic field.

Dr Turner says after their recent experiment in Wellington, ultimately they hope to go around the rest of New Zealand sampling hangi sites dating back over the last 600 years - which is when the real data will come out.

Hangi magnetism is part of a wider Marsden-funded project titled Unlocking the secrets of the geodynamo: the Southwest Pacific key.