Náttúrufræðingurinn - 1987, Blaðsíða 65

Iceland observed very fine-grained ash
on the grass.
The wind direction and the position of
the ship suggest that the ashfall was
caused by a volcanic eruption within the
Vatnajökull glacier in southeastern Ice-
land. It is suggested that the eruption
was in the Grímsvötn volcano, which has
erupted frequently during the last three
centuries at least. The jökulhlaup which
occurred in the Skeiðará River in the
middle of June, 1816, strongly supports
the idea that an eruption indeed took
place in the Grímsvötn volcano.
Usually jökulhlaups in the Skeiðará
River accompany eruptions in the
Grímsvötn volcano within a few days,
but exceptions are known. The Gríms-
vötn eruption in 1933 was not accompa-
nied by a jökulhlaup (Haukur Jóhannes-
son 1983). No changes were observed in
the Skeiðará River during the eruption
in May/June 1983 (Karl Grönvold and
Haukur Jóhannesson 1984), but there
was a minor jökulhlaup in early Decem-
ber that same year.
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