Rit (Vísindafélag Íslendinga) - 01.06.1976, Side 120

area Dyngjufjöll, there is practically no surface water in the entire
area between Vatnajökull and lake Mývatn, but numerous springs
are found to emerge from under the edge of the lava field.
In order to explore the cold groundwater movements in this area,
samples have been collected from many of these springs and mea-
sured for their deuterium content.
The data obtained generally agree with the idea that the drain-
age area can be extended far into the glacier Vatnajökull. The ðD-
values both at the westem and the eastern border lines of the
southemmost part of Ódáðahraun are similar to those in the pre-
sent-day precipitation on the northem part of Vatnajökull. In hoth
cases, the ðD-values then increase somewhat towards the north as
a result of mixing with groundwater derived from precipitation in
the lava field itself. According to the deuterium map, the ðD-value of
the precipitation increases as one travels through the lava field to-
wards the north. The precipitation deposited on the lava goes al-
most entirely into the ground and mixes with the groundwater
flow coming from the glacier. The proposed flow pattems shown
by arrows in Fig. 29 are based on the obtained deuterimn results.
The main groundwater divides, shown as lines of open circles, are
again based on hydrogeological studies carried out by Sigbjamar-
son (personal communication). The agreement between the deu-
terium studies and the hydrogeological studies is obviously very
good.
The pattern obtained of the groundwater flow in the area is only
a very crude one and many more studies are needed before a de-
tailed groundwater map of this area can be drawn. The picture
shows, however, some interesting general features.
The groundwater flow from Vatnajökull is separated into two
main streams by the mountains Dyngjufjöll. The westem main
stream originates in the westem part of central Vatnajökull. It flows
through the lava-bed west of the mountains Dyngjufjöll and can
be followed northwards for a distance of approximately 85 km to
the lake Svartárvatn. The eastem main stream originates in the
central Vatnajökull and flows in direction north-east of Dyngjufjöll
and along the river Jökulsá. This groundwater stream can be traced
over a distance of approximately 150 km northwards.
Between these two main streams there is a central drainage area,
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