Jökull - 01.12.1962, Side 54

A DV.

-7 ..
Z/s>+ of +Ýts/Z/6r/t//r7
/
/
/
/
/
/
/ x (/O)
/
/
PLOT OF /50 TOPF DA TA
/
/
*(//)
/ (6) /J)
/ (&„**(*)
' (7)x *<a)
/
/ X (9)
/
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x (O
A o,a v..
-S -6 -7
-9 -/o -// -/? ./3 ./4
Fig. 3. Plot of AD against AO18.
the raclioactive decay. In principle, it should be
possible to use the tritium-concentration of
ground water in order to derive the “age” of
water, that is, the time since it left the atmos-
phere.
An important fact is that tritium can be
produced in nucfear reactors ancl synthetic tri-
tium is, therefore, available.
GENERAL PATTERN OF THE USE OF
ISOTOPES IN HYDROLOGY
The stable isotopes. The fact that the pre-
cipitation is labelled by its isotopic concentra-
tion suggests an application along two lines.
Firstly, the ratio AD/AO18 in thermal water is
indicative of any intermixture with components
that are not derived from the oceanic-meteoro-
logical system. Many geologists believe that
thermal waters contain juvenife or volcanic
components. This theory can be tested on the
basis of data on AD/AO18.
Secondly, as thermal water, and ground water
in generaf, may percolate a long clistance under-
ground its isotopic concentration may differ
from the concentration in the local precipita-
tion at the springs. A systematic study of the
precipitation in the region may, therefore, lead
to the detection of the recharge areas. This
methocl should be applicable in geothermal
work as well as in grouncl-water hydrology in
general.
A corollary is that changes of flow into a
reservoir, either transitory or continuous, may
be detected on the basis of the isotopic con-
centration of the reservoir provided the re-
charge is a mixture of different components
of natural water. These aspects are of consider-
abfe importance in geothermal work.
The exploitation of natural heat resources by
drilling involves the danger of an infiltration
of cold ground water surrounding the thermal
area. The colcl water encroaches on the thermal
water and appears in wells after a certain lag
of time. In the case that the isotopic concentra-
tion in the cold water differs from that of the
52 JÖKULL