Jökull - 01.12.1990, Side 123

Groundwater from glacial areas in Iceland
FREYSTEINN SIGURÐSSON
Orkustofnun (National Energy Authority)
Grensásvegi 9,108 Reykjavík, Iceland.
abstract
The major glaciers of Iceland are, at least par-
tially, situated on permeable rock formations. These
conditions are favourable for the infiltration of
groundwater from the base of the glaciers, although
dependent on the permeability of the bedrock. From
the glacier Langjökull area (= 1,000 km2) 50-80 m3/s
are infiltrated but from the glacier Hofsjökull (of a
similar size) only 10 m3ls.
The total groundwater runoff from the glaciers
discussed in the present article (Langjökull, Hofs-
jökull, NW- and W-Vatnajökull, N-Mýrdalsjökull) is
estimated to be 130-220 rrv’/s. Groundwater from
the other glaciers and glacial groundwater flowing at
great depths wouldprobably increase the total glacial
groundwater runoffto 200-300 rrv’/s.
New maps ofthe distribution ofsome major chem-
ical components in the groundwater in lceland are
presented in the article. The glacial groundwater ap-
pears to be characterized by low temperatures and
low chemical content, especially in the mineral com-
ponents which are normally dissolved from the host
rock in the groundwater systems.
The glacial groundwater is demonstrated to con-
stitute a major component in some shallow aquifers
extendingfor some kilometres away from the glaciers.
In some fissure zones it can similarily be traced for
some tens of kilometres. The dilution of the glacial
groundwater is apparently the less the higher the con-
finityand the anisotropy ofthe aquifers are.
INTRODUCTION
Groundwater plays an important role in the hydro-
logical regime of Iceland and in the economical activ-
ities and prospects of the inhabitants of the country. It
supplies freshwater for most of the public water works
and for many industrial enterprises, as well as consti-
tuting the mainstay of the base flow of the numerous
rivers, which are potential sources of hydropower, or
even already hamessed for production of electricity.
Part of this groundwater is released tardily from
soils and rocks, often with considerable seasonal vari-
ations and at a low discharge rate per area unit, but part
of it is discharged in effluent springs, often grouped
together in narrow areas. The latter have usually a
rather constant flow, temperature and chemical com-
position, indicating a drainage from a larger area and
over a long time. (Fig. 1).
Some of this groundwater might originate from the
glaciers, covering more than one-tenth of the country
(Bjömsson, 1979). The precipitation is thought to be
exceptionally high on the glaciers (Einarsson, 1976)
and substantialparts of them are situated on permeable
rock formations, possibly permitting a considerable
infiltration into the bedrock. The ice mass of the
glaciers acts as a groundwater reservoir, although in a
way somewhat different from that of the rocks.
There are hydrological differences between the
glaciers and the icefree surroundings. On the glaciers
the composition of the precipitation is different from
the surrounding areas, due to the higher altitude of the
surface. The release of the water bound in ice and
snow on the glaciers occurs in a relatively short time,
compared to the lower surroundings. The hydrologi-
cal properties of the glaciers are different from those of
most Icelandic rocks. The chemistry of the circulating
water is influenced in a different way on the glaciers. It
is therefore of interest to consider whether the glacial
JÖKULL, No. 40, 1990 119