Jökull - 01.12.1990, Qupperneq 137

ISOTOPIC COMPOSITION
The deuterium content of groundwater has been
used to construct a country-wide and detailed system
°f groundwater currents (Árnason, 1976). This was a
bold idea and a magnificient work but of course it has
its flaws, as most innovations. The primary one is that
it was based on a single parameter and could hardly
be checked against other types of hydrogeological in-
formation, which at that time were only available in a
rudimentary form. An other one is that seasonal varia-
tions make representative sampling of ”local“ ground-
water difficult, especially in view of the state of the
hydrogeological knowledge at that time. A third one
ls that the size of the scope of the work does not allow
for a very exact interpretations of details. Fourth, the
omission of altitudinal corrections in areas that were
not sampled may have led to grave errors in interpre-
tations, and so on.
Nevertheless, the deuterium presents an indepen-
dent parameter, which most probably is not very sen-
sitive to geological conditions, so that it is in any case
very promising, even if it is not decisive, single and
alone. The knowledge on groundwater, accumulated
m the meantime, permits now a counterchecking in
the evaluation of the sampling and the interpretation
°f the data. A thorough and scrutinous review of the
deuterium mapping, inclusive renewed sampling, is
now not only a promising possibility but even an ur-
gent necessity. In that expectation a further, detailed
consideration of the hydrogeological interpretations
°f the deuterium analysis will here be allowed to rest.
Árnason’s (1976) results for the various glacier - fed
groundwater basins will be referred to in the further
discussion as occasion arises.
The general conditions of the glacial groundwater
will here not be dealt with any further in details. In
the following some local and regional problems will be
briefly considered, to elucidate the possibilities and or
difficulties in assessing the glacial groundwater factor.
SOME LOCAL AND REGIONAL
ASPECTS
The groundwater basins, which are dealt with, are
the following: The basins surrounding the glacier
Figure 16. The Langjökull groundwater basins.
Explanations: 1) Boundaries of the groundwater basins
system. 2) Majorspring areas. 3) Inferredgroundwater
currents. — Grunnvatnskeifi umhverfis Langjökul.
Skýringar: 1) Mörk grunnvatnssvœðis Langjökuls.
2) Helstu lindasvœði. 3) Aœtlaðir grunnvatnsstraum-
ar.
Langjökull, the Hofsafrétt basins north of Hofsjökull,
the Ódáðahraun basins north of westem Vatnajökull,
the Tungnaár basins southwest of western Vatnajökull
and the Mælifellssandur basins.
JÖKULL, No. 40, 1990 133