Rit (Vísindafélag Íslendinga) - 01.06.1976, Page 144

lating water at Vindheimar thus might well be derived from the
same groundwater system that feeds the drill holes at Nesjavellir.
15. 9 The Reykjanes peninsula.
On the Reykjanes peninsula three geothermal areas, Krísuvik,
Svartsengi and Reykjanes, have been studied. The peninsula, which
is the landward extension of the Reykjanes Ridge, is mainly built
up by basaltic layers. The surface of the peninsula is covered with
post-glacial lavas and hyaloclastic rocks and there are numerous
open fissures and faults indicating strong activity of tectonic forces.
The lavas are interbedded with thick sand- and gravel-layers and
these formations are very permeable down to a depth of at least
200 m. The ocean water therefore can easily penetrate the peninsula.
15. 9.1 Krísuvík.
Several wells have been drilled in the Krísuvík area, and samples
from three of them have been collected for deuterium analysis. For
location of these wells see Fig. 36, samples No. 77-79. Table 12
gives the mean ðD-values of these wells, together with their Cl-
and Na+ content and the base temperature. When necessary, the
8D-values have been corrected for deuterium enrichment due to eva-
poration.
The water from the two wells H-5 (sample No. 79) and H-14
(sample No. 78) has a similar ðD-value, with mean ðD = — 51%0.
The well H-6 (sample No. 77), on the other hand, discharges
water with a somewhat higher deuterium content ðD = — 47%0. The
Cl“ content of the water also increases from H-5 to H-6. Since the
peninsula is very permeable, it is not unreasonable to assume that
the “fresh” thermal water can mix with sea water to some extent.
Thus the higher ðD-value in the well H—6 is explained by such mix-
ing. Mixing of the water in H-5 with 6% seawater would result in
water with the same ðD-value and Cl“ content as that found in H—6.
The ðD-value of the thermal water in Krísuvík is about the same
as obtained for present-day precipitation around Krísuvík and on
the inner part of the Reykjanes peninsula. The thermal water at
Krísuvík therefore is believed to be almost entirely of local origin.
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