Rit (Vísindafélag Íslendinga) - 01.06.1976, Page 137

15. 7.2 Geysir area.
Samples collected in the Geysir high-temperature area (samples
No. 22-28) have ðD-values ranging from — 82.6%0 to — 89.2%0, with
a mean ðD = — 85.5%0. The hase temperature in this area is not
known hut the silicate content of the water, assuming equilibrium
with quartz, indicates that this temperature might be as high as
230°C (Amórsson 1973). Thus the corrected mean ðD-value for this
area could he as low as ðD = — 91.5%0. The deuterium map shows
that the nearest present-day precipitation with the same ðD-value
is found in the northem part of the Langjökull glacier.
15. 73 Hreppar and SkeiS.
The sampling points Hlemmiskeið, Reykjadalur and Skipholt
(samples No. 29, 30 and 31), located in the districts Hreppar and
Skeið, lie close to a NE-SW line, which is almost parallel to the
main tectonic lines in this area. All these sources have a similar
deuterium content with a mean ðD = — 81.6%0, which suggests that
these sources receive water from the same deep ground water flow.
Assuming NE-SW flow direction for this groundwater, the possible
recharge area for this water could be the lava field Kjalhraun south
of Hveravellir. Precipitation with similar ðD is, however, also found
in the central part of Langjökull.
The water in the Flúðir area (samples No. 32-35) has consider-
ably higher ðD-values in spite of the fact that this area lies on the
same line and between the above-mentioned sources. The same is
tme of the sampling point Brautarholt (sample No. 36). The mean
values are ðD = — 73.9%0 and ðD = — 78.1%0 for the Flúðir area
and Brautarholt respectively. There are two possible explanations
for this. Either the deep groundwater becomes mixed with a more
local near-surface water as it flows to the surface, or the water at
Flúðir is a separate groundwater system with a different recharge
area. Which of these two explanations is the true one cannot be
decided from the available data.
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