VSF 2010 Report - Nabo

Changes in Charcoal and Seaweed Content
There was a tacit assumption made when this study began, that the amount of charcoal
present in the samples was likely to decrease over time, with larger amounts present in the
Viking and Early Medieval layers than in later contexts. There has been a long-running
bias in Icelandic archaeology towards the idea that Birch woodland in Iceland was reduced
to very low measures soon after landnám. This has been hinted at in historical sources (e.g.
Íslendingabók, ÍF I) and backed up by palynological evidence from certain parts of the
country (e.g. Hallsdóttir 1987), although numerous other studies both of historical records
and of pollen cores from around the country suggest that this was not the case everywhere
(e.g. Vésteinnsson & Simpson 2004; Church et al 2007; Lawson et al 2007). However,
when studying the results of the charcoal quantification, both in the graphs Figures 2 and 3
and in Table 1, it is clear to see that the amount of charcoal present peaks in the middle of
the column, between about 40-80 cm from the base of the column. In the absence of any
clear trend, and with the knowledge that even in the early layers of this column that large
amount of firewood and charcoal were being used for industrial and domestic purposes in
the nearby Viking Age area of the site (Mooney 2009), it would be unwise to suggest any
temporal correlation to changes in charcoal quantity found in these contexts.
The variation in charcoal quantities is much more likely to result from changing use
of the area. Samples to , which contain by far the largest quantities of
charcoal, seem likely to represent an intensification of midden activity in the area. These
layers are capped by the Hekla 1693 tephra layer, and also by a layer of turf collapse
[10407]. Small layers of this tephra are also present within [10407], indicating either that
the building was built of turves containing the tephra, or that the tephra fall occurred
during the collapse of the structure. The latter would appear to be the more convincing
explanation, as the H1693 tephra is present immediately adjacent to this deposit, but not
underlying or overlying it (Figure 1). In any case, this gives a clear terminus ante quem
date of 1693 for the charcoal-rich midden deposits. If the ashfall did occur during the
collapse phase of the unidentified structure, it is possible that these midden deposits were
directly connected to this building. The ‘burnt’ deposits [10409] and [10411], which
contained the greatest charcoal concentrations in the column, probably represent deposits
from cleaning out hearths, while other contexts with less charcoal are most likely related to
other domestic activities. Unfortunately no finds were recovered from these deposits which
would give any indication of their source.
Interestingly, the quantity of charred seaweed contained in the samples does not
show any correlation with the quantity of charcoal recovered (Figure 3). For example,
sample , from the turf collapse layer [10407], shows the third highest charcoal
measurement from the column, but contains relatively little charred seaweed. On the other
hand, samples and , from the midden deposits, contain large amounts of
charred seaweed but relatively little charcoal in comparison. It has been suggested that
seaweed was used as a fuel in Viking Age and Medieval Iceland (e.g. Vésteinnsson &
Simpson 2004), however a brief experimental burning carried out at Vatnsfjörður during
the 2009 field season by the author, Garðar Guðmundsson (FSÍ) and Nicolás Sepúlveda
(University of Iceland) showed that dried Ascophyllum nodosum seaweed, which is most
commonly found charred at Vatnsfjörður, actually served to damp a strong fire, and would
not carry a flame on its own. The fact that relatively large quantities of seaweed were
found outside of charcoal rich contexts lends weight to the idea that seaweed ash was used
for an industrial purpose, for example as a flux in iron smelting or in making lye for dyeing
wool (c.f. Mooney 2009; Birch, this volume). The hypothesis that seaweed was used in
smelting has also recently been bolstered by the discovery of large pits full of charred
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