Jökull - 01.12.1978, Blaðsíða 110

MERCURY AND ARSENIC IN
NÁMAFJALL AND KRAFLA
DRILLHOLES
Jón Ólafsson,
Marine Research Institute
Mercury and arsenic in water, steam and
uncondensable gases were surveyed on two
occasions, in November 1976 and August
1977. Mercury was found chiefly to be associ-
ated with steam and gases but arsenic with the
liquid phase. Significant differences were
found in the mercury concentrations between
the Námafjall and Krafla regions. Large vari-
ations were also found within the Krafla
region. An increase in the mercury concen-
trations at Námafjall was noted and associ-
ated with volcanic events. The arsenic con-
centrations in the Krafla drillholes (except
one) are low but at Námafjall the concen-
trations are significantly higher. The concen-
trations calculated for deep water range from
6.3 to 126 ug As H and 40 to 1399 ng Hg l '.
The distribution of these elements will be dis-
cussed, their connections with other drillhole
parameters and their fate in the environment.
REGIONAL DIP AND DEPOSITION
RATE IN THE TERTIARY LAVA PILE
OF ICELAND, AND THEIR
RELATIONSHIP TO THE ACCRETION
PROCESS IN THE AXIAL ZONE
Gudmundur Pálmason,
National Energy Aulhority
On the basis of a physical model of crustal
accretion, characterized by total lava produc-
tion rate (q), width (standard deviations 0,
and 02) and drift velocity (vd) relationships
are derived between the lava deposition rate
and dip in the Tertiary pile on the one hand,
and the parameters q, 0,, 02 and vd on the
other. It is shown that the dip at a given depth
depends primarily on 02, and the deposition
rate depends primarily on 02/vd. Both dip and
deposition rate depend only slightly on q and
0j. Published data on dip and deposition rate
in eastern Iceland and western Iceland (Borg-
arfjördur) are used to estimate the width of the
accretion zone and the drift velocity when the
corresponding parts of the crust were being
generated. The results are 02 = 15 — 20 km
and vd = 0.8—l.Ocm/yr.
Finally, the influence of more complicated
models on these results is discussed.
THE LAST STAGES OF GLACIATION
IN BORGARFJÖRDUR AREA
Guttormur Sigbjarnarson,
National Energy Authority
1. In late pleistocene time, glacial move-
ment was mainly directed through the valleys
of Borgarfjördur from a glacier center to the
south of what is now the Langjökull glacier. As
the glaciers retreated, the center shifted north
and northwest, finally being confined in the
last stage of glacial advance to the eastern part
of the Snæfellsnes-peninsula and the Trölla-
kirkja-region.
2. This caused icedammed lakes to be
formed in the valleys Flókadalur, Lunda-
reykjadalur and Skorradalur, but the glacier
snout stretched south to Melasveit-region.
3. At that time glacier lobes extended from
the east down to Flókadalur and Lunda-
reykjadalur, but at the same time the valleys,
Skorradalur and Svínadalur, were ice-free.
4. In the Melasveit region, two stages of
successive advances of glaciers from the Borg-
arfjördur-region are indicated. The first one is
connected to a sealevel on 100— 110 m and the
latter one to a shore line of 60 m.
5. The C14-datings of marine shells so far
indicate that the lowland of Borgarfjördur
was submerged during the Alleröd and
Bölling interstadials, and the marine-deposits
in the region were formed during these
periods. The two previously mentioned stages
108 JÖKULL 28. ÁR