Jökull - 01.12.1981, Page 29

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Thickness in cm
2-0- Isopach in cm
Figure 5. Distribution of Sn-3.
J. Mynd. Útbreiðsla Sn-3 á Snœfellsnesi.
some reason or another, the layer has not been
found west of Ólafsvík. Its thickness at Ólafs-
vík is still 19.5 cm and thus the layer should be
expected to be found further west. A minor
irregularity is present and is seen in the 1.0 cm
isopach which has a more easterly trend than
the others. This could be explained either as
being caused by local weather conditions i. e.
topographic effect on low altitude wind, or as
being an indication of a changing wind direc-
tion during the course of the eruption. Similar
irregularities were observed for the other two
layers and this point will be discussed further
later.
The maximum grain size is about 6 cm close
t0 the volcano but there the average grain size
is about 1—2 cm. The layer is light-coloured,
consisting of frothy pumice and ash, usually
well sorted, but dark glass fragments of a
similar size are common.
Sn-2
The middle layer, Sn-2, is found at depths
of 15—120 cm. The layer is found east of the
volcano and was traced as far as Alftafjördur.
On the other hand it does not exist in situ west
of the volcano and seems to have similar dis-
tribution pattern as Sn-1. Sn-2 was identified
in profile 43 west of the volcano but there the
layer is vvithout doubt water-transported be-
cause the grains are rounded. It is suggested
that the tephra was transported by meltwater
burst from the ice-cap. The axis of maximum
thickness is not easily defined but appears to
be between north and northeast (Fig. 4).
Considerable deviation is observed from the
main trend in that the 5.0, 2.5 and 1.0 cm
isopachs have a trend close to N75°E.
The layer is light-coloured and consists of
frothy pumice and ash. The grain size is close
to 1 — 2 cm at Ólafsvik but drops to 0.2 cm or
JÖKULL 31. ÁR 27
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