Investigation of Maori archaeological site occupation patterns using geophysical techniques

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White, P.A.; Broadbent, M. 1993 Investigation of Maori archaeological site occupation patterns using geophysical techniques. Wairakei: Institute of Geological & Nuclear Sciences Ltd.. Institute of Geological & Nuclear Sciences science report 92/06. 2 v. (45; 119 p.)

Abstract: Magnetic and galvanic electrical resistivity measurements have been made at the site of the former Kaiapohia Pa, near Christchurch. Tha pa was built mostly on sand dunes in what was formerly a swampy area. it's main defensive blockade was breached by fire prior to destruction of it's buildings in 1831. The site has been used for pastoral farming in recent years. Few rocks of both significant size and magnetisation are likely to naturally occur at shallow depth within the thick unconsolidated sediments beneath the site. An Overhauser-effect proton magnetometer and gradiometer was used to measure the vertical gradient of the earth's magnetic field averaged between 0.5 and 2.0 m above the ground. The final maps show anomalies which are apparently sytematically grouped. Some anomolies are associated with geographic features, such as part of the stockade rampart, whilst others occur over flat ground. Many anomolies appear to define rectangular patterns or lineations, some of which may mark former building sites, including that of the meeting house. Many of the detected magnetic anomolies are suspected to be associated with thermal remanent magnetisation resulting from activities of man. A square configuration of electrodes, the square having a side length 0.5 metres, has been used to measure apparent resistivities over a 300 square meter area centrally situated within the area magnetically surveyed. These experiments indicated that buried objects having the dimensions of individual post holes would be near the limit of detectability of the field procedures adopted at the pa. Maps are presented which show either an orientationally averaged apparent resistivity for each measurement location or a ratio which gives information about the orientational dependence of apparent resistivity at the location. Both magnetic and electrical methods have detected cultural features of the pa site that were previously unsuspected, and the information they have provided will allow future investigations of the site, whether they involve geophysical measurements or excavations, to be better focused than they would otherwise have been. Magnetic and resistivity methods, being non-destructive, are likely to prove useful at other Maori pas constructed on coastal sediments or alluvium.