Jökull - 01.12.1990, Page 143

Figure 20. Groundwater systems and hydrogeology of
Odáðahraun. Explanations: 1) Central volcano with a
caldera. 2) Geothermal high temperature field
3) Fissure zone. 4) Major spring areas. 5) Inferred
groundwater currents. — Grunnvatnskerfi
1 Odáðahrauni. Skýringar: 1) Megineldstöð með kötlu
( öskju “).2) Háhitasvœði. 3) Sprungurein. 4) Helstu
Hndasvœði. 5) Áœtlaðir grunnvatnsstraumar.
VODJK 965 FS
90.06.0245 ÓD
Figure 21. Chloride in precipitation and groundwater
from the Odáðahraun region. (Values from Gíslason,
1985). — Klóríðinnihald í úrkomu og grunnvatni í
Odáðahrauni og nágrenni. (Gildifrá Sigurði R. Gísla-
syni, 1985).
tion during summer (Fig. 21), which is not surprising
in view of the high ratio of snow and the strong evapo-
transpiration in this area (Einarsson, 1972). In NEA’s
precipitation series (see above) the chloride contents
appeared to be generally about three times as high in
winter as in summer (Sigurðsson, 1985b).
The cold springwater in the upper reaches of
Skjálfandafljót, in Suðurárbotnar and on the south
bank of Svartárbotnar has a chloride content of 1.6
ppm. Values of 1-2 ppm could be expected from ex-
trapolation of the groundwater data in the foreland of
the glacier itself and also on its lower parts. Similar
chloride values are found in the mountain area E of
the Kverkfjöll fissure zone, where a glacial origin is
much less likely. A glacial origin is thus indeed not
necessary to explain these low values, but the high dis-
charge of the constantly flowing springs on the upper
reaches of Jökulsá á Fjöllum (near to 50 m3/s, Orku-
stofnun, Vatnamælingar, NEA’s Hydrological Survey,
JÖKULL, No. 40, 1990 139