Jökull


Jökull - 01.12.1982, Page 23

Jökull - 01.12.1982, Page 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 Einarsson (unpublished report 1950, published 1966) later extended his theories to all LT systems in Iceland.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
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