Geochemistry and Technology of Basaltic Glass Artefacts from an Embedded Source and Two High-altitude Base Camps in the Mauna Kea Adze Quarry Complex, Hawai‘i

Abstract

Located at the base of an escarpment at ~3720 m elevation, in the Mauna Kea Adze Quarry Complex, Hawai‘i Island, is a small outcrop of basaltic glass that was utilised by adze makers for at least several hundred years as a source of toolstone for the manufacture of small, expedient flake tools. A test excavation of this previously unknown source/quarry was undertaken in 1976 to obtain a sample of artefacts to compare with what appeared to be lithologically identical basaltic glass cores and flakes from excavations at two nearby rockshelters used by adze makers as base camps. Comprehensive geochemical analyses of a small sample of flakes from the source and base camps confirm that all but one of the rockshelter artefacts are local basaltic glass and that the manufacture and use of basaltic glass tools was therefore an activity embedded in the adze quarry ‘industry’. The one anomalous sample, which was selected for analysis because of its unusually vitreous appearance, is a trachytic glass flake sourced to Pu‘u Wa‘awa‘a, a volcanic cone located ~40 km west of the Mauna Kea Adze Quarry and source of the best quality and most used volcanic glass on Hawai‘i Island. The provenance of the Pu‘u Wa‘awa‘a flake suggests that it was an offering or gift and not part of some down-the-line exchange network, as often assumed in the case of volcanic glass artefacts found in coastal habitation sites. Although there is no conclusive evidence that any of the Mauna Kea basaltic glass was exported, it is a possibilty that needs to be considered in future studies of volcanic glass distribution patterns, which appear to have been far more complicated than previously thought. To characterise sources/quarries and to provide robust matches of artefacts to sources, we advocate using comprehensive geochemical techniques and reporting the data in full—not just mid-Z elements and select oxide values.