Rit (Vísindafélag Íslendinga) - 01.06.1976, Blaðsíða 136

shallow marine sediments of variahle thickness were deposited in
some places. North-east lying faults are frequently ohserved in the
area. Some of the thermal springs are obviously located on faults
and dykes but a linear distribution along the faults is not very
obvious (Arnórsson 1970 a). One of the geothermal areas, the
Geysir area, has been classified as a high-temperature area, other
areas are low-temperature areas.
Numerous samples have been collected from hot springs and drill
holes at various places in the areas and their deuterium content
measured. The sampling points are shown in Fig. 32. The numbers
given for the points refer to Table IV in the Appendix. The 8D-
values shown in Fig. 32 are mean values obtained for the respective
sampling point.
15. 7.1 RauSukambar in Þjórsárdal.
The hot spring Rauðukambar (sample No. 21), located farthest
to the east in the area, has a very low 8D = — 93.6%0. When con-
sidering the deuterium map, the nearest areas with such precipita-
tion are found in the central parts of the Hofsjökull glacier and in
the northern part of Langjökull glacier. This means that if the
water emerging from the hot spring Rauðukambar is derived from
precipitation deposited under climatic conditions similar to those of
today, the recharge area of the thermal water lies either in central
Hofsjökull or northern Langjökull, from where it has flowed
underground for a distance of up to 90 km, without any appreci-
able mixing with other groundwater on its way. Assuming that
the water was deposited in periods when the mean 8D-value of the
precipitation was approximately 5%0 lower than today, i.e. in the
period from 1920 and several thousand years back in time, this
would extend the possible recharge area, but the recharge area
would still be the Hofsjökull or the northern Langjökull. The fact
that the thermal water at Rauðukambar has flowed underground
for a such a long distance without appreciable infiltration of other
groundwaters supports the opinion that deep groundwater systems
are rather isolated from near-surface groundwater systems.
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