Rit (Vísindafélag Íslendinga) - 01.06.1976, Side 115

sample No. 2). The mean 5D = — 55%0 shows that this water is
not derived from local precipitation but originates farther inland.
According to the deuterium map, this water has flowed from in-
land for a distance of approximately 30 km on the average.
Consequently the cold groundwater flow in the Reykjanes penin-
sula, as proposed from deuterium measurements in the above dis-
cussed drill holes, can be indicated by the arrows shown in Fig. 27,
where the arrows are extended to the approximate mean recharge
area.
14. 3 Hraunfossar.
Hraunfossar are several large springs which emerge from under
a lava field on the northern hank of the river Hvítá. For the loca-
tion of Hraunfossar see Fig. 27, sample No. 3. The local precipita-
tion at Hraunfossar has 8D = — 66%0. Hraunfossar with 8D =
— 84%0 are therefore 18%0 lower in 8D than the local precipitation
and approximately 4%0 lower than the water of the river Hvítá mea-
sured at the same place (sample No. 4), and in the river Norðlinga-
fljót measured approximately 10 km north-east of Hraunfossar
(sample No. 5).
The river Norðlingafljót comes from an area north-west of the
glacier Langjökull and runs along and over the same lava field,
from which Hraunfossar emerge, and joins Hvítá 10 km north-
east of the springs. Samples collected from the river Norðlingafljót
at three places farther upstream (samples No. 6, 7 and 8) show
a 8D-value similar to that in Hraunfossar.
The obvious explanation of the origin of the Hraunfossar springs,
therefore, is that they receive water from approximately the same
recharge area as feeds the uppermost part of the river Norðlinga-
fljót, i.e. the region north-west of Langjökull. The results indicate
that we under the lava-hed have a water course which is to some
extent isolated from the river flowing on top of it. Possibly there
is a leakage from the uppermost part of the river through the
lava-bed.
The cold spring at Húsafell (sample No. 9), with 8D = — 81.8%0,
emerging from under the same lava field approximately 8 km
riorth-east of Hraunfossar, also seems to originate in the same re-
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