Imaging indigenous sacred sites: A tale of clay, silt, and sand

Abstract

When studying indigenous sites, especially sacred sites such as burials, the needs and wishes of the indigenous people are paramount; the site integrity must be respected, and the site must be left intact and undisturbed. Noninvasive, nondestructive geophysical imaging is well suited to such investigations, but suspicion within indigenous communities because of past transgressions is a barrier to widespread use; skepticism is not uncommon, but we have always managed to convince skeptics. We have developed an overview of results from 10 Māori (the indigenous peoples of New Zealand) sites in the South Island of New Zealand: one historic burial site, six modern burial sites that also had historical use, one historic battle site, one prehistoric site that may have been a burial site, and one prehistoric site used for food storage that was tapu (sacred). Our approach was to let them ask us to delineate areas of importance, for example, old burial sites. There are, naturally, processes and protocols, cultural and technical, that we followed. The sites comprised a range of lithologies and soil types: one site where clay soil overlays limestone, five sites where loess (airborne silt) overlays basalt, one set of inland silty soil sites, one site on peat soils overlying sandy gravels, and two sites in coastal sands. The geophysical responses of the sites cluster into three groups: Horizontal loop electromagnetic (HLEM) and magnetic field methods worked well for the clay soil site, and once the effects of the conductive clay response were removed by filtering, ground-penetrating radar (GPR) worked well. HLEM and magnetic results were good to equivocal on the silty and peaty sites, whereas GPR excelled at delineating anomalous features, particularly burials, which yielded clear characteristic diffraction responses. Finally, results for coastal sand sites were disappointing. Such sites appear to be too dynamic to yield useful results.