Rit (Vísindafélag Íslendinga) - 01.06.1976, Page 82

7. THE DEUTERIUM MAP
As already discussed, mean 8D-value of precipitation can only
be established by repeated measurements over a long period of time.
Such a study covering sufficient number of localities would be
very time-consuming and difficult to carry out, since most of the
interior of the country is unpopulated and there are very few
meteorological stations at which precipitation could be sampled
regularly. In the previous chapter, however, it has been shown that
relatively accurate values for the distribution of the mean SD-values
of the precipitation throughout the country can be obtained by much
simpler methods.
The deuterium map presented in Fig. 20 is based on measure-
ments carried out at the 65 7 sampling points for local groundwater,
24 points where winter precipitation has been measured on glaciers
and at the three meteorological stations Rjúpnahæð, Hveravellir
and Vegatunga. All these places are shown on Fig. 19.
Fig. 19 shows that some districts are adequately covered by
sampling points, in other districts the points are much fewer and
in some districts there are no sampling points. The lack of sampling
points in some districts can be due to two reasons.
In some districts there are no water sources available which can
be classified as local in origin. An example of this is the Ódáða-
hraun area north of the glacier Vatnajökull. This area is covered
by postglacial lava with no visible water flowing on the surface
and geological circumstances make it impossible to predict whether
cold springs at the periphery of the lava field originate in the lava
field or in the glacier Vatnajökull.
Other districts are relatively inaccessible by landvehicles and
consequently a sampling program would have been very time-
consmning or expensive. An example of such an area is the high
basaltic plateau of Vestfirðir in Northwest Iceland. Samples of
78