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ridge. But in other respects Iceland is probahly a typical
ridge area. Tectonic phenomena and heat flow which are di-
rectly related to the crestal zone, may in Iceland he expected
to be typical of the ridge. The purpose of this paper is to
present data on surface heat flow and subsurface tempera-
ture conditions in Iceland and to compare them with heat
flow conditions studied elsewhere on the ridge.
Thermal conductivity
Only a few thermal conductivity measurements of Icelandic
basalts have been made. Bödvarson (1957) gives values of
0.0039 to 0.0045 cal/cm sec°C for 4 samples of unaltered basalt
from SW-Iceland. Recently measurements have been made
on several samples from a horhole in the Vestman Islands
off the south coast of Iceland. These were made in a divid-
ed-bar apparatus and the results are shown in Table I. From
the data available it appears that for holes which are drilled
in unaltered solid basalts in Iceland it is reasonable to assume
a thermal conductivity of 0.0045 cal/cm sec°C for estimat-
ing the heat flow, and this will be done here. The uncer-
Table I.
Therrnal Conductivity of Samples from the
Vestman Islands Borehole
Sample No. Depth m Thermal conductivity 10r3 cal/cm sec°C Rock type
1 .... 242 2.0 Sediment
2 .... 242 2.0 99
2U1) .... 242 2.7 99
3 .... 646 5.2 Basalt intrusion
4 .... 646 5.0 99
5 .... 1010 4.5 Basalt
6 .... 1010 4.5 99
!) Same as sample No. 2, but having been immersed in water for one
week.