Náttúrufræðingurinn - 1988, Page 51

SUMMARY
Geothermal activity
in the tidal zone and below
sea level around Iceland
by
Jón Benjamínsson
Marine Research Institute
Skúlagata 4
IS-101 REYKJAVÍK
Iceland
Geothermal activity in the form of hot
springs, steaming ground and gas vents is
common in Iceland but the geothermal ac-
tivity under the sea around Iceland has
not been accounted for. Geothermal gra-
dients in Iceland tend to be low in the ol-
dest rocks in Eastern and Western Iceland
but increasing towards the volcanic zones
in the central region. The geothermal wa-
ter, originally rainwater, sea water or a
mixture of these two, percolates through
the bedrock. It is warmed by the under-
lying large volcanic heat source and rises
through faults and cavities in the bedrock
because of the lowering of its specific
gravity.
This paper reports 53 locations where
geothermal activity is found or suspected
to be present below sea level or in the tid-
al zone. Most of these sites are in the
Western Fjord region. No submarine ac-
tivity has been proven to be present off
the east- and south coasts. Twelve of the
sites cannot be seen directly but are in-
ferred from indirect evidence. The deep-
est signs of geothermal activity are found
at Hörgárgrunn in Eyjafjörður at 97 m
b.s.l. and on the Kolbeinsey Ridge at 90
m b.s.l. The highest temperature mea-
sured, 100°C, was in Öxarfjörður. There,
as on the Kolbeinsey Ridge, the geother-
mal area is inferred to represent a high
temperature system. The others reported
are low temperature systems. One geo-
thermal site near Reykjavík seems to have
sunk to a greater depth over the years.
This finding is in agreement with the ob-
served trend in sea level changes in the
Reykjavík area.
169