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SUMMARY
Heat, Groundwater
and Geothermal Systems
by Sveinbjörn Bjórnsson, Science lnshtute,
University of Iceland, Dunhagi 3, 107 Reykjavík.
Although the origin and nature of low-
temperature geothermal systems are gener-
ally understood, there remain many
questions to be answered. What is the age of
the geothermal water issued in hot springs?
How great is the total flow of hot ground-
water and where does the water go, that does
not find an outlet in the hot springs? fs the
regional conducted heat flow sufficient to
heat the groundwater current? What con-
trols the upflow of hot water in the hot
spring areas? Can the water convect in the
rock? Can we explain the high temperature
systems with the same model as the low-
temperature ones? What happens when the
upwelling water starts boiling in the rock?
Should we regard the high temperature
fields as finite mines of heat or as a con-
tinuous flux of heat from an infinite heat
source?
To deal with questions of this nature we
have to apply basic principles of ground-
water theory and thermodynamics. The
paper reviews these principles and gives a
riumber of examples that illustrate the
nature of geothermal systems. Accurate cal-
culations are hampered by inadequate
knowledge of many physical properties of
rock. Computer modelling will in the near
future greatly advance theoretical under-
standing of geothermal processes and
geothermal systems. The powerful tech-
nique of computer simulation will still be of
little use unless we gather reliable input data
on pressure conditions and natural heat loss
of the individual systems we want to simu-
late.
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