Rit (Vísindafélag Íslendinga) - 01.06.1967, Qupperneq 124

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Water convection in the upper part of the crust
It has long been considered that at least the low-tempera-
ture thermal areas in Iceland can be explained hy deep cir-
culation of meteoric water. This view was first advanced by
Einarsson (1942), who contended that rain water from high-
er elevations would flow toward the coastal areas and be
heated according to depth of penetration. Extensive studies
of isotopic composition of water from hot and cold springs
by Árnason and Sigurgeirsson (1967) tend to support this
hypothesis.
It is of interest to investigate whether conditions for free
convection of water are likely to exist in the upper part of
the crust in Iceland. This possibility was considered by Ein-
arsson (1950). Since then additional data have become avail-
able, which enable more definite conclusions to be drawn
about conditions in Iceland.
The problem of free convection in a homogeneous hori-
zontal layer of constant permeability and heated from below
has been treated by many authors, f. inst. Lapwood (1948),
Goguel (1953), Wooding (1957) and Elder (1965). It
has been found that a certain dimensionless convection para-
meter has to reach a certain critical value in order that a
sustained convection is possible. The parameter is given by
the following expression:
k • a • (Ti — T0) g • d
p = -----------------------
(Km/Kw) • x • v
where
k = permeability
a = coefficient of thermal volume expansion of liquid
g = acceleration of gravity
d = thickness of layer
x = thermal diffusivity of liquid
v = kinematic viscosity of liquid