Jökull - 01.12.1982, Blaðsíða 23

Glaciation and geothermal Processes in Iceland
GUNNAR BÖÐVARSSON
School of Oceanography,
Oregon State University, Corvallis, Oregon 97331, U.S.A.
ABSTRACT
An evaluation of the energy balance, the effects of the
Pleistocene glaciation combined wilh the rapid rate of de-
glaciation about 104 years ago suggests that the rock/water
heat transfer processes supplying the low-temperature acliv-
ity in Iceland are of a transient nature. Transient models
lead to plausible estimates of rock/water contact areas re-
quired to maintain the energy dissipation of the thermal
systems. Much of the low-temperature activity may have been
initiated at the end of the last period of glaciation about 104
years ago.
INTRODUCTION
According to views prevailing during the first
decades of this century, all thermal activity in Ice-
land is more or less associated with volcanism. Since
most of the high-temperature (HT) activity is ob-
viously generated by magmatic processes, it was
taken to be only reasonable to generalize the vol-
canic theory to the low-temperature (LT) activity
also (Barth 1950). This view was challenged in the
case of the LT systems in North Iceland by Einarsson
(1937, 1942), who concluded on the basis of his
work in the Eyjafjordur area that the LT systems
there are entirely of a non-volcanic nature.
Einarsson (unpublished report 1950, published
1966) later extended his theories to all LT systems
in Iceland. He envisions a general circulation of
meteoric water from the central highland out to the
coastal areas and assumes that the circulation base
is deep enough for the water to be heated by the
terrestrial conduction current to the temperatures
observed in the I.T areas. The heat conduction
processes are thus taken to be essentially ofa steady
state nature. Bodvarsson (1950, 1964) expressed
agreement with Einarsson’s opinion on the nonvol-
canic nature of the LT activity, but concluded on
the basis of energy balance consideration, that the
conduction processes involved in the heating must
be of a transient nature, that is, draw on the local
enthalpy of the formations through which the water
percolates. The postulate ofa steady state situation
appears untenable.
The gencral understanding of the thermal activ-
ity in Iceland, and of the LT activity, in particular,
was greatly advanced by the mapping of the deuter-
ium contents of natural waters in Iceland by Amason
(1976). His data indicate quite clearly that the re-
charge of the LT thermal systems is to a consider-
able extent derived from the central highlands of
Iceland. These results lend strong support to Einars-
son’s (1942) conclusions as to the origin of the ther-
mal water of the LT activity. Furthermore, al-
though the deuterium data íhrnish no clues as to the
mode of heating of the water, Amason{ 1976), never-
theless, claims that his results completely support
Einarsson’s views including the steady state nature
of the conduction processes. Bjomsson (1980) in-
vestigating the total energy balance of the LT activ-
ity in Iceland concludes that the steady state model
is a viable possibility.
The question of the time dependence of the heat
conduction processes is interesting and of quite
fundamental importance. Underlining that transi-
cnt heating processes are q uite diíferent from steady
state situations, the present writer remains of the
opinion that steady state conduction processes can
not be invoked as a basis for the energy supply of the
LT activity in Iceland. Below, we will elaborate on
this subject in some detail. First, by considering the
relevance of steady state oonduction processes in
the very dynamic environment of Iceland. Second,
by investigating the overall energy balance of the LT
thermal activity and, in particular, th'e specific case
of one of the major LT systems in the Borgarfjordur
area in VVestern Iceland.
JÖKULL 32. ÁR 21