Jökull - 01.12.1967, Side 73

advancecl nearest to the mainland and in the
lowest part of the seclimentary pile.
BICARBONATE,
SULPHATE AND SILICA
The concentration of bicarbonate is much
higher in water from the well than in sea-
water but the sulphate concentration is much
lower. With increasing temperature the solu-
bility of calcium carbonate increases while that
of calcium sulphate decreases. It seems likely
that the amount of bicarbonate and sulphate
in the water is controlled by the solubility of
calcium carbonate and calcium sulphate. The
sediments contain considerable quantity of
Fig. 7. A cross section from Vestmann Islands
to Eyjaíjallajökull. The location is shown in
Fig. 8. See Fig. 6 for further explanation.
Mynd 7. Snið frá Vestmannaeyjum að Eyja-
fjallajökli. Lega sniðsins er sýnd á Mynd 8.
Sjá nánari skýringar með Mynd 6.
calcium carbonate, while gypsum and other
minerals containing calcium sulphate have not
been detected.
The mineralogical analysis of the sediments
is not precise enough to exclude the possibility
that minerals of calcium sulphate could be
present. In the sediments of the California
Basin the carbonate and bicarbonate in the
water originated from the breaking-down of
organic compounds (Emery ancl Rittenberg
1952).
Fig. 8. Location of cross sections in Figs. 6
and 7.
Mynd 8. Lega sniða i Myndum 6 og 7.
The silica content in the water samples from
the Vestmann Islands is fairly constant (90—
110 ppm) and is unaffected by the salt con-
centration. As already stated the sediments con-
tain great amounts of opaline gel, indicating
much solution of silica from the sediments.
According to Siever (1962) volcanic glass is un-
stable in sea-water. It hydrolyzes and releases
silica into solution at the same time. The
silicic acid is precipitated to a great extent as
amorphous silica, although some secondarv
quartz lias been observed. The water is some-
what undersaturated with respect to the solu-
bility of amorphous silica but oversaturated
with respect to the solubility of quartz. Thus
the composition of both sediment and water is
as may be expected in a sedimentary environ-
ment.
JÖKUl.L 17. ÁR 307