VSF 2010 Report - Nabo

Figure 1. Total Alkali-Silica (TAS) plot of Vatnsfjörður data and Hekla 1693.
The composition of the tephra layers found at the archaeological site were compared
to proximal geochemistry from known eruptions. The eruptions that the tephra was compared
to was based on prior information about placement of the layers within the stratigraphy of the
site as well as information about which eruptions carried ash material over the Vestfirðir
region. Therefore the possible eruptions were narrowed down to a particular age range based
on position in the stratigraphy relative to the archaeology (roughly AD 1200 – 1800). Likely
eruptions from those dates that would have dispersed ash across the area were determined
using isopach maps to the eruptions of Hekla 1693, 1766, and Katla 1721. Hekla 1104 was
also included in the analysis as it occurred close to the time period and the ash fall was
widely dispersed (Haflidason, Eiriksson, & van Kreveld, 2000). By geochemical bi-plots,
Figure 2 shows that the Hekla 1693 eruption has the same glass chemistry as these distal
tephra and suggests these layers were associated with the eruption. Dugmore et al. published
the geochemistry of Hekla 1693 after collecting proximal tephra samples during an
investigation of Þjórsárdalur (Dugmore et al. 2007: 6). These results agree with
Sigurgeirsson’s findings for similar visible tephra layers at the Vatnsfjörður site (2006).
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