Jökull - 01.01.2005, Blaðsíða 78

Kate T. Smith and Hreinn Haraldsson
Table 1: Radiocarbon dates used in discussion, including two new dates from Smith (2004). Calibrated dates
are calculated at two sigmas (94.5% probability). Dates in brackets are less probable. See Figure 1 for locations
of sites. – Kolefnisaldursgreiningar sem fram koma í greininni, þ.á.m. tvær nýjar frá Smith (2004). Leiðréttur
aldur er reiknaður með tveim sigma (94,5% líkindi). Aldur í svigum er ólíklegri. Sjá staðsetningu sýnatöku á
1. mynd.
Location Sample type 14C yr BP Cal BP Cal AD Lab Code References
Teigsaurar Plant remains from silty
sediment layer
1485±65 1520–1290 430–660 U-2807 Haraldsson
(1981;36)
Hólmar, Land-
eyjar
Peat 1350±65 1390–1130
(1110–1090)
560-820
(840–860)
U-4298 Haraldsson
(1981;36)
Drumbabót Buried birch tree bark
(AMS)
1230±35 1270–1060 680–890 AA-48027 New date
from Smith
(2004)
SILK YN
tephra, Sól-
heimajökull
foreland
Subsamples of a 1cm
thick peat layer between
SILk YN and overlaying
La tephra
1660±12 1575–1525
(1605–1580)
375–425
(345–370)
Weighted
mean of
19 dates
from GU-
7070 to
GU-7096
Dugmore et al.
(2000)
Layer H tephra,
Lambafells-
heiði, S. Eyja-fjallajökull
Peat 1540±50 1540–1330 410–620 GU-10383 New date from
Smith (2004)
RESULTS
Drumbabót trees and flood sedimentology
In the summer of 2000 the authors reinvestigated the
Drumbabót site as part of a wider project chroni-
cling the flood history of theMarkarfljót valley (Smith
2004).
These trees can still be found extruding through
the sandur surface at the site of Drumbabót (around
63◦N 42’ 43”, 019◦W 06’ 57”, Figure 1). Today some
of these trees have snapped due to exposure to the el-
ements and now stand between 20 and 60 cm above
the sand surface. Others several metres long lie hor-
izontally within and top of the sands. The trees are
very well preserved birch trees (betula penchula) and
their trunks have diameters of up to 25 cm where they
are entombed in situ by the sands, most of them lean-
ing slightly to the west or south-west (Figure 2). They
show no sign of damage or scouring and are coated
in a fine layer of pale silt between their bark and the
surrounding sands. Roots up to 5 cm in diameter are
found within a grey silt deposit and underlying grav-
els. This silt layer includes casts of woodland-floor
vegetation, some of which are briefly exposed on the
surface but are quickly eroded away by the action of
the wind. The story behind the demise of these trees
is an important puzzle and is the main focus of this
paper. They are also important due to their large size
compared to present-day Icelandic birch woods, upon
which we will briefly touch, and their use as a den-
drochronological resource for dating other wood re-
mains in Iceland, as discussed by Eggertsson et al
(2004).
Bark from one tree has been dated using AMS ra-
diocarbon dating to 1230±35 14C yr BP (AA48027,
Smith 2004, calibrates to 1270–1060 cal BP). It is
considered likely that the sampled tree died some time
during the centuries shortly before the eruption of the
Landnám tephra, the deposition of which has been
dated from correlations to the GRIP Greenland ice
core to 871±2 AD (Grönvold et al. 1995). The diam-
eter of the tree (∼23 cm) and rough counting of the
tree rings indicates that is was 60–80 years old when
it died.
78 JÖKULL No. 55