Jökull - 01.12.1953, Blaðsíða 20

Fig. 9. The liot springs at Vatnshamar 1 July
1953. The white spots near the lake surface are
lime deposits.
Laugarnar viö rætur Vatnshamars 1. júli 1953.
Hvítu sliellurnar nærri vatnsboröi eru kalkút-
felling.
Photograph by S. Þórarinsson.
or to 1460 m height, this would be equivalent
to an increase in volume amounting to ab. 2
km3, and it would take ab. 3 years from 1 Julv
1953 to fill the basin to that level. I think it
very unlikely that the level could now be raised
higher than to 1460 m height — although it
may be concluded from Wadell’s pictures and
sketch map from 1919, that the water level
must have been higher before the 1922 glacier
burst and that the barrier must be considerably
lower now than in 1922.
It is thus highly probable that the next Skeið-
arárhlaup will occur within three years, and
judging from the happenings in the 1940’s it
may happen at any time within these next few
years. It is also probable that the next glacier
burst will be bigger than the bursts occurring
in the 1940’s and more like a normal Skeiðarár-
hlaup.
Further observations in the Grímsvötn area. —
Although our stay in Grímsvötn was far too short
for a thorough investigation, some observations
besides those already mentioned were made dur-
ing the day we spent there. The two small nuna-
taks along the western border of the plain N of
Vatnshamar were found to consist of palagon-
ite breccia rich in small angular basalt frag-
ments. Vatnshamar seems to consist of the
same sort of breccia, but is cut through by two
nearly vertical basalt dykes, the southernmost
of which is very thick, the northernmost one
much smaller.
Stórkonuþil, the nearly vertical NW face of
Gríðarhorn, is also built up mainly of breccias
with interbedded nearly horizontal (but some-
what dislocated) layers of basalt and beds of
sediments which looked like moraine (viewed
through my fieldglasses). The whole formation
was cut through by irregular veins of very fine-
grained rock, a sample of which (analysed by
J. Jakobsson) contains 47.75% of SÍO2.
The hot springs at Vatnshamar. — At the foot
of Vatnshamar we found 7 hot springs
(Fig. 9) situated near to each other in 1 to 1 5
m height above the lake level. The total dis-
charge of these springs was estimated at 5—10
1 /sec. The biggest one gushed its water con-
tinuously ab. 40 cm high. The temperature in
this spring was 87.5° C. Beneath the biggest
springs the ground was coloured white by a layer
of calcium carbonate which was only ab. 5 mm
thick. A sample of water from the biggest spring
was analysed by B. Líndal. It contained 52 mg/1
soluble SÍO2 and 91 mg/1 CaC03. Ph was 7.3 and
the conductivity very high. The hot springs are
situated between the basalt dykes and are prob-
ably connected with them.
The thermal area SW af Svíahnúkur eystri. —
During the flight on 26 June we observed steain
rising from several spots on a small snowfree
area some 200 m SW of the cairn of Svíahnúkur
eystri. This area was visited by Steinþór Sig-
urðsson’s expedition on 18 Aug. 1942, and the
temp. of the steam was then estimated to be
nearly 100° C (acc. to an unpublished diary by
E. Pálsson, kindly placed at my disposal). This
thermal area was again visited by some ,mem-
bers of our expedition. Its height was found to
be 26 m less than Svíahnúkurs or 1676 m. A
small amount of steam was seen rising from 8
or 10 vents. It smelled very faintly of sulphur.
The highest temperature measured was 91° C.
Signs of solfatara activity within the Grims-
vötn depression. — During our stay in the west-
ern part of the Grímsvötn depression we now
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