Jökull - 01.12.1978, Page 113

HYDROGEOLOGICAL MAPPING BY
VERTICAL ELECTRICAL SOUNDINGS
Freyr Thórarinsson, National Energy Authonty,
Kristján Agústsson, National Energy Authority
Repeated attempts have been made to in-
terpret vertical electrical sounding (VES)
curves from the Reykjanes peninsula in terms
of thickness of the freshwater lens which floats
there freely on seawater. This interpretation is
complicated by the inhomogenity in surface
resistivity of lavas and the extreme steepness of
the appropriate VES Q-curves.
These curves have now been interpreted
with the aid of a computer program, by which
a measured VES-curve is compared to a col-
lection of Q-mastercurves and the deviation
from each mastercurve plotted on the h2q2—
plane, the second layer being the freshwater
lens. This graph shows the regions of
equivalence with respect to the second layer,
being bounded by lines of iso-deviation from
the mastercurves. These computations are
very cheap.
The results are combined with the geologi-
cal information as groundwater height and
resistivity of aquifers. Thus, the hydrogeology
of the groundwater basin is mapped and then
used in mathematical modelling of the basin
with good results.
CHEMICAL AND ISOTOPE ANALYSIS
AND TEMPERATURE
MEASUREMENTS OF
GROUNDWATER AT LINDARBREKKA
IN KELDUHVERFI, N-ICELAND
Thóroddur F. Thóroddsson,
National Energy Authority
During the winter 1975—1976 the area
between Lake Mývatn and Axarfjördur was
seismically very active. At the same time the
temperature of groundwater from springs
around Lindarbrekka rose from 10—15°C up
to 50°C. The amount of dissolved solids
probably did change too, but reliable older
analysis are not available. Since December
1975 water samples for chemical and isotopic
analysis (deuterium and tritium) have been
taken and the temperature repeatedly
measured in many places. The isotope analysis
are not yet finished. The temperature has
decreased since April 1976 and the amount of
dissolved solids has decreased too.
Si02 Cl
Date T°C ppm ppm
Open fissure 76 01 16 46 104 320
200 m east 76 04 12 46 85 280
of farm Framnes 77 10 22 38.5 68 257
A spring 76 04 12 39.5 72 220
by farm Kelduneskot 77 10 22 32 57 183
COMPARISON OF SEDIMENT LOAD
TRANSPORT IN THE SKEIDARA
JÖKULHLAUPS IN 1972 AND 1976.
RESULTS
Fdaukur Tómasson, National Energy Authority,
Svanur Pálsson, National Energy Authority
In the jökulhlaup of 1976 a good
discharge/sediment rating curve and a fairly
uniform spatial distribution of sediment were
obtained. In 1972 the reverse was the case as
this relationship was then poor and the spatial
distribution uneven.
In the jökulhlaup of 1972 a layer of sand
and coarse silt was deposited in the flood
channel but not in 1976. The deposit is too
fine-grained to have been deposited in run-
ning water. Here it is explained as having been
deposited by way of anchor ice which is also
considered responsible for the divergence in
sediment concentration from one place to
another. Similarly, such deposition is sup-
posed to explain very fine-grained layers in
ancient alluvial sediments.
JÖKULL 28. ÁR 111