Hangi feast of magnetic field data

WHITE HOT: A modern hangi pit shows just how hot they can get.
WHITE HOT: A modern hangi pit shows just how hot they can get.

Ancient stones used in hangi have become a valuable tool for scientists learning about the Earth’s magnetic field.

Researchers from across the world have met up for a conference in the US this week for earth scientists to share their work, said the BBC.

A Victoria University scientist, Dr Gillian Turner, spoke about her project to investigate how the Earth’s magnetic field has changed over the last 10,000 years.

Turner said the Northern Hemisphere already has a lot of data about the Earth’s magnetic data from rocks, but the southern hemisphere is another story.

"The southwest Pacific is the gap, and in order to complete global models, we're rather desperate for good, high-resolved data from our part of the world," she told BBC News.

Usually, Turner would look at old pottery sites in other parts of the world – but because Maori were the first settlers to New Zealand 800 years ago, she found hangi was an alternative.

The traditional Maori technique of cooking involves a pit in the ground with very hot stones placed at the bottom. They were then covered with baskets of food and layers of fern soaked in water. It would then be topped with soil and left to cook for hours.

Scientists think the process generates so much heat the magnetic minerals in the stones will realign with the current field direction.

"The Maori legend is that the stones achieve white hot heat," said Turner.

"Red hot is about 700 degrees and so white hot would be a good deal more than that, but by putting some thermocouples in the stones we were able to show they got as high as 1100 degrees Celsius, which of itself is quite surprising.

‘‘At that temperature, rock-forming minerals start to become plastic if not melt.”

She said Maori used volcanic boulders because they did not crack and shatter in the fire.

Now, her team is scouring the country to find uncovered hangi ovens, which Turner expected would give information dating back to the 1200s.