Jökull - 01.12.1990, Page 124

groundwater can in some way be distinguished from
the groundwater originating in the glacier free areas,
quantitatively and qualitatively. In the following some
aspects of such a consideration are briefly reviewed.
To the author’s knowledge, no explicit and com-
prehensive study has previously been undertaken
on this subject. Sigbjamarson (1972) mapped the
glacially fed Tungnaá basin, which was a pioneer work
in hydrogeological- hydrological mapping in Iceland.
Gíslason’s (1985) treatise on the Odáðahraun basin
is similarily a pioneer work in hydrochemical map-
ping of a glacier- fed basin. Ámason (1976) discussed
the great, glacier-fed groundwater basins in Iceland
on the basis of his deuterium mapping. The present
author has been working for the last ten years on the
groundwater basins in the Icelandic highlands, includ-
ing hydrogeological mapping, systematic sampling of
groundwaterforchemical analyses andvariousassess-
ment studies. The present article is primarily the prod-
uct of these efforts.
Figure 1. Presumed mean an-
nual precipitation in Iceland
and the mean discharge of
the major rivers (not accu-
rate). (Sigurðsson and Sig-
bjarnarson 1985). Explana-
tions: 1) Mean discharge in
m3/s. 2) Precipitation >
3200 mm/year. 3) Precipita-
tion 1600 - 3200 mm/year.
4) Precipitation 800 - 1600
mm/year. 5) Precipitation <
800 mm/year. —Áœtluð
meðalársúrkoma á Islandi
og meðalrennsli helstufall-
vatna. Skýringar: 1) Meðal-
rennsli í m3ls. 2) Urkoma >
3.200 mmlyear. 3) Úrkoma
1.600 -3.200 mm/ári. 4) Úr-
koma 800 -1.600 mm/ári.
5) Úrkoma < 800 mm/ári.
THE HYDROGEOLOGICAL SITUATION
OF THE GLACIERS
The rock formations of Iceland have different
hydrological properties, dependent on age, origin
and geological history. The most simple classifi-
cation is in permeable, young formations (mostly
Late Quaternary to Recent, corresponding to the
Brunhes magnetic epoch) on the one hand and
impermeable-semipermeable, old formations (mostly
Tertiary and Early Quatemary) on the otherhand. (Sig-
urðsson, 1976; Hjartarson et al., 1980; Sigurðsson
and Sigbjamarson 1985; Sigurðsson, and Ingimarsson
1990/1987).
The rocks in the permeable formations have a very
wide range of permeability and storage qualities, fis-
sure swarms create regionally a strong anisotropy in
the permeability and various geological structures di-
rect the groundwater currents towards spring areas.
The groundwater ratio in the runoff from the differ-
ent glaciers can therefore be very different. Most of
the glaciers cover a part of a number of groundwa-
120 JÖKULL, No. 40, 1990