Rit (Vísindafélag Íslendinga) - 01.06.1967, Page 128
124
land has been found to be in the range 103—104 darcy (H.
Tómasson, pers. comm.).
Although it is to he expected that the permeability of the
flood hasalts varies considerably from one area to another, this
result gives an indication of the order of magnitude to be
expected. Vertical permeahility can be expected to be lower,
with the possible exception of the neovolcanic zone which is
tectonically active with large systems of more or less verti-
cal fractures. As mentioned earlier all the high-temperature
thermal areas in Iceland are confined to this zone.
To investigate further the possibility of free convection,
this value of the permeability is substituted into the expres-
sion for the convection parameter p, together with the
following values for other quantities: a = 5X10-4 °C_1,
(Ti—T0)/d = 6X10-4 °C/cm, g = 980 cm/sec2, d = 2X105cm,
Km = 4.5X 10~3 cal/cm sec°C, o = 1 g/cm3, c = 1 cal/g °C,
v = 4.8X10'3 cm2/sec.
This gives for the convection parameter the value
r| = 190
which is well above the critical value 40. Considering that
these calculations are based on conditions outside the neo-
volcanic zone, and that 2 km is a low estimate for the thick-
ness of the permeable layer, the results tend to support the
hypothesis that conditions for free convection may exist in
the neovolcanic zone where vertical permeability is larger
and horizontal permeability along fault zones probably also
is greater than in the Tertiary districts.
Comparison with resulls elsewhere on the
Mid-Atlantic Ridge
A large number of heat flow measurements have been
made in recent years on the Mid-Atlantic Ridge by various
workers. Fig. 6 is reproduced from Lee and Uyeda (1965)
and shows the distribution of heat flow values as a function