Late-Holocene Volcanics on Tutuila Island, American Samoa: an Archaeological Perspective on Their Chronological and Spatial Distribution

Abstract

Data on 28 radiocarbon dates and volcanic stratigraphy from 23 archaeological excavations located on the Leone Volcanics to understand the temporal and spatial distribution of late-Holocene eruptive events on Tutuila Island, American Samoa. Some of the underlying lava flows of the Leone Volcanics are at least 2000 years old. A distinctive reddish ash stratum is the most recent clearly identifiable eruptive event, dating to ~AD 650-750. Other possible interpretations from the data reviewed in this report are that: 1) lithified-ash strata are generally thickest near the seaward craters, suggesting that they are the source of the deposits; 2) for all of the excavation locations reported here, where both grey and reddish-ash strata are present, the reddish ash is always above the grey ash. It is inferred that the volcanic event(s) that generated the reddish ash occurred later than those that produced the grey ash; 3) locations with black pyroclastics are closer to the inland craters, suggesting that they are source of this material; 4) at Locations 12 and 16 the black pyroclastics are below the reddish-ash layer, while at Locations 5 and 7 the black pyroclastics are above the reddish-ash layer, suggesting that at least two eruptive events were responsible for producing the black pyroclastics, at least one before the reddish-ash-producing event(s) and at least one after; 5) if it is correct that the black pyroclastics are from the inland crater and the reddish ash from the seaward craters, then having black pyroclastics both above and below the reddish ash suggests that both seaward and inland craters were active more-or-less contemporaneously; 6) if the soils overlaying the reddish ash are derived from volcanic ash, and if the ash source is the seaward craters, then these craters were the last to erupt – perhaps as recently as AD 1300.