Jökull - 01.12.1982, Page 88

GEOTHERMAL ACTIVITY IN
THE EYJAFJÖRDUR AREA
Natural discharge of warm water is widespread
in the area around the bay of Eyjafjördur (see Fig.
1). The hot springs yield rather sparingly, on aver-
age less that 1 1/s. A yield less than 1 1/s is common
and 3 1/s is an absolute maximum.
Hot water has been used for a long time many
places in the region for house heating and bathing.
Geothermal drilling in the area started in 1933.
Before the 1974 oil crisis plans of general geother-
mal house heating in this region had been given up
as unprofitable. After 1974 geothermal prospecting
has been intensified in the area as the need of long
piping systems, expensive drillings and the use of
poor production areas are more feasible now than
previously. The town of Akureyri is now almost
totally heated by geothermal water. Water is how-
ever short and extensive research still goes on in the
area.
The temperature of the natural discharge is up to
90°C, but most commonly below 50°C. The max-
imum water temperature measured at depth is just
over 100°C in the Laugaland area. So far there are
four production areas in the region: Laugaland,
Ytri-Tjarnir, Botn and Glerárgil (Fig. 1).
'Fhe aquifer depths are difierent in each area, but
no major aquifer is found at greater depth than 1700
m. In the Laugaland area the main aquifer is cut at
600 - 1500 m depth with water temperature 92 -
96°C. A smaller shallow aquifer is encountered at
200 — 300 m depth with water temperature about
60°C. At Ytri-Tjarnir the main aquifer is cut at 800
— 1500 m and the water temperature is 75-82°C. A
shallow colder aquifer was also encountered in this
area. In Botn the water in the main aquifer is
around 85°C. A hotter aquifer, near to 100°C, is cut
belowatabout 1700mdepth. InGlerárgil thewater
temperature is about 55°C.
The geothermal water in Eyjafjördur is believed
to draw its heat from a regional heat source i.e. have
been slowly heated as the water flows through the
hot bedrocks. From the ð D map of Arnason (1976)
the water appears to have its origin in the north-
western part of Vatnajökull and the mountains
north of Vatnajökull. From there it is believed to
have flown northwards in permeable layers at
depths down to 3 km.
In the Eyjafjördur valley itself the rocks are Tert-
iary lava formations, 8—10 m.y. old (Björnsson et.al.
1978). Alteration at sea level in the valley corre-
sponds to the mesolite - scolecite alteration zone
and the rocks are therefore rather impermeable.
The nature of the aquifers is not known, but it is
believed that at least the upflow is governed by
tectonic features as crossing dykes or faults. The
7- /
loq NoVh+’^y5- +0,125 /
'/
*/v
-V
- •7 - •
• .V
• V.
-
/ ••
/ ’ b)
/
2.5 3.0 1000/ T
Fig. 2. a) Calcite saturation in geothermal water
from Eyjafjördur. b) Log. Na+/H+ against 100/T
in the geothermal water from Eyjafjördur.
Mynd 2. a) Kalkmettun jarbhilavatns í Eyjafirði. b)
Virknihlutfall natríum og vetnisjóna miðað við hitastig
(1000/T) íjarðhitavatni úr Eyjafirði.
84 JÖKULL 32. ÁR