Rit (Vísindafélag Íslendinga) - 01.06.1976, Síða 116

charge area as the river Norðlingafljót. On the other hand, the
water in two springs at Kalmanstunga (sample No. 10 and 11),
with ðD = — 74.5%0 and ðD = — 76.3%0 respectively, seems to be of
local origin.
The main flow pattern of the Hraunfossar water as inferred from
deuterium measurements is indicated by an arrow in Fig. 27.
14. 4 Þingvellir — Langjökull drainage area.
The geographical location of the Þingvellir — Langjökull drain-
age area is shown in Fig. 27. The sampling points, together with
the obtained ðD-results are shown in Fig. 28.
Since large parts of the area north of lake Þingvallavatn and
south of the Langjökull glacier are covered by lava fields with no
visible water flowing at the surface, the total drainage area has
not been well known until recently. In order to study the extent
of the drainage area and the flow pattern of the cold groundwater,
several samples from cold springs and rivers have been collected
and their ðD-value measured.
The river Sog (sample No. 14) is the outlet of lake Þingvallavatn
and has a mean ðD = — 65.5%0, which should represent the mean
value of the total recharge area. According to the deuterium map
the local precipitation on the lake is approximately ðD = — 60%o.
Two samples, öxará (No. 15), with ðD = — 60.5%0, and Flosagjá
(No. 16), with ðD = — 65.4%0, located on the northem shore of
the lake, have a ðD-value similar to local groundwater in the moun-
tains north and north-west of the lake. Two cold springs, at Miðfell
(No. 19), with ðD = — 64.0%o, and at Sog (No. 20), with ðD =
— 65.5%0, located on the south-east shore, have a ðD-value similar
to the precipitation in the mountains north-east of the lake. Two
cold springs, Vellankatla (No. 18), with ðD = — 71.9%0, and Vatns-
kot (No. 17), with ðD = — 71.4%0, located at the north-eastern end
of the lake between the above mentioned springs have, on the other
hand, ðD-values the same as the present-day precipitation on the
southernmost part of the glacier Langjökull.
The cold springs Vellankatla and Vatnskot therefore confirm the
belief that the lake receives some glacial water from Langjökull.
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