Jökull - 01.12.1961, Blaðsíða 31

U. N. CONFERENCE ON NEW SOURCES OF ENERGY, ROME 1961:
Physical Characteristics of Natural Heat Resources in Iceland
BY
GUNNAR BODVARSSON
STATE ELECTRICITY AUTHORITY, REYKJAVIK, ICELAND
SUMMARY.
The present paper discusses the physical
characteristics of natural heat resources in Ice-
land on the basis of geophysical, geological and
geochemical data.
Iceland is, according to recent seismic studi-
es, built up of a layer of Tertiary basalts which
reaches a thickness of 2 to 3 km. The Tertiary
formations are in some regions, mainly in the
central ancl southern parts, covered by Quat-
ernary volcanics.
Tioo types of thermal areas can be distin-
guished. Firstly, the low-temperature areas
lohich are characterized by hot-water springs
and subsurface temperatures below 150° C.
These areas are located mainly in the Tertiary
districts. Secondly, the high-ternperature areas
which are located within the Quaternary dist-
ricts ancl are characterized by natural-steam
holes and large areas of hot ground. The subsur-
face temperature in these areas is above 200° C
at a relatively very shallow depth. The total
heat output of the low-temperature areas is
estimated. at 708 cal/sec whereas the high-temp-
erature areas appear to have an output of 109
caljsec.
In general, the thermal areas are controlled
by permeable contacts between lava-beds,
permeable dikes and faults. The circulation
base may be the bottom of the flood basalts,
that is, at a depth of 2 to 3 km. Recent hot
volcanic structures appear to supply the heat
in the case of the high-temperature areas. The
circulaling water appears to have a direct con-
tact with the source rock. The low-temperature
areas, on the other hand, appear to draw on the
natural heat content of the rocli in tlie lower
parts of the flood basalls. The temperature at
the circulation base may be 100° C to 150° C.
A considerable amount of surplus heat is
accumulated in the subsurface formations of
the large high-temperature areas. The time of
accumulation is of the order of several thousand
years. The surplus heat is a vast heat reservoir
which can be exploited by drilling. Some aspects
of the reservoir mechanics are discussed. Also,
exploration methods are reviewed briefly. The
integrated potential of the natural heat resour-
ces in Iceland is in terms of electric poiuer esti-
mated at the order of 500 megawatts.
1. INTRODUCTION
Tliermal activity is a very common pheno-
menon in Iceland. Hot-water springs and natur-
al-steam outlets are scattered over large parts of
the country and constitute a striking and unu-
sual natural phenomenon. In the course of the
past decades the thermal activity has become an
important natural resource which is now being
exploited on an increasing scale. Modern geo-
logical, geophysical and geochemial methods are
now applied in order to explore the characteris-
tics of the subsurface phenomena. Drilling for
hot-water and natural-steam is being carried out
on a relatively large scale.
The present paper is written for the purpose
of giving a brief report on the main results of
geological and geophysical exploratory work.
The paper is based mainly on results obtained
in the periocl after 1945. For further information
the reader is referred to other papers by the
present author. (Bodvarsson, 1949, 1950, 1951,
1956, and 1957).
Important contributions to the study of the
thermal activity in Iceland have been made by
Thoroddsen (1925) and Thorkelsson (1940, and
earlier works). The book by Barth (1950) con-
tains a wealth of descriptive material. More-
over, the work by Einarsson (1942) deserves a
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