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Kawatiri, Westport - Day 9

27 February 2008

Work continued today with the excavation teams removing Layer 2 to define any features in Layer 3.

Features already defined in Layer 3 were today half sectioned to provide an understanding of their fill . These included fire features which were found to contain charred bone and a dense concentration of charcoal confirming their use as cooking purposes.

The Kawatiri site is a relatively large and well preserved site containing excellent information on the spatial distribution of archaeological material. Nevertheless, determining where to dig in a site like this can be a very difficult and expensive task.

Results of fluxgate gradiometer survey of the Kawatiri site. Note dark circles which often indicate a fire feature. Image: Otago University

As mentioned in yesterday's report, in 2007 a fluxgate gradiometer (see glossary) was used to map magnetic variations in the soil. This has allowed us to develop a more accurate and detailed understanding of spatial features within the site. The excavation areas that have been chosen this year are based on the results of the fluxgate gradiometer. So far the features found have been in very close correlation to the spatial data, reinforcing the value of the fluxgate gradiometer.

A fluxgate gradiometer works by measuring disturbances in the earth's magnetic field. At Kawatiri, it was set up so that its depth-range was approximately 1.4 metres - ideal for these site conditions. The fluxgate gradiometer works on a large scale and identifies variations in the soil that could represent archaeological features, such as cooking areas or other types of prehistoric activity.

Test pit dug using the results of the fluxgate gradiometer. This fire feature was subsequently found. Photo: Otago University

Its output is a map, as shown in the figure above. But to fully understand what the patterns on the map mean it is important to test the results using small test pit excavations. We carried out the mapping and testing last year and as a result of that were able to locate this year's excavation areas in positions where we considered them most likely to produce the types of information we were interested in gaining.

As the map shows, at the Kawatiri site, the areas of high magnetic disturbance are found to run in a band approximately 40 metres east-west and 80 metres north-south. This band probably represents scatters of coming fires and food processing areas. The bright white spots on the map reflect metal deposits, probably resulting from farm activities over the last century or so. The dark circles have nearly always proved to be fire features, often an oven (a haangi or umu).

Acknowledgment: to Ben Shaw for his description of the workings of the fluxgate gradiometer.

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GLOSSARY   Archaeological terminology Like any profession, archaeology comes with its own "language". This glossary helps with less familiar terms, particularly those used on this site. >> Read more

For questions about the Kawatiri excavation, contact archaeology@historic.org.nz