Jökull - 01.12.1965, Page 3

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JOKULL
Á R S R I T
J Ö KLARAN NSÓKNAFÉLAGS ÍSLANDS
III 15. ÁR REYKJAVÍK 1965
SIGURDUR THORARI NSSON :
Changes of the Water-Firn Level in the Grímsvötn
Caldera 1954—1965
INTRODUCTION.
Since 1953 the Iceland Glaciological Society
has sent expeditions to Vatnajökull every spring
and somatimes in the autumn too. Most of
these expeditions have had on their programme
to study changes in the Grímsvötn area, both
the sudden ones caused by jökulhlaups and the
slower ones going on between them. Measure-
ments of the accumulation and ablation within
the Grímsvötn area have also been on the pro-
gramme. Seismic soundings and gravimetric mea-
surements have been carried out within the
area.
In the last issue of Jökull it was mentioned
that a paper summing up the results of the
research work within the Grímsvötn area would
be published in the next issue. Owing to vari-
ous circumstances but mainly because of the
Surtsey eruption not yet having come to an
end, I have not found time to write the com-
prehensive Grímsvötn paper I liad intended to
write so that I have had to restrict this paper
to the measurements of the changes in lieight
of the water- and firn-level in the Grímsvötn
caldera and a preliminary discussion of these
changes in light of the results of seismic sound-
ings carried out in the Grímsvötn area.
MAPPING OF THE GRÍMSVÖTN AREA.
During the Grímsvötn expedition in June
1958 (cf. Thorarinsson 1958, pp. 1—4) the geo-
decist Baldur Jóhannesson carried out triangula-
tions in the Grímsvötn area in order to work
out a map of the area. This map is published
here for the first time (Fig. 1). The reason why
it was not published earlier was that there rose
some doubt as to the length of tlie base line
used for the triangulation, a doubt which later
mapping proved to be groundless. In the
meantime a new triangulation was carried out
in the Grímsvötn area in June 1960 by Gunnar
Þorbergsson, civil engineer, and liis map was
LAHBSSíihASAFN
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Í3LAKSS
JÖKULL 109