Jökull - 01.12.1967, Page 11

bouring areu, Ragnar Thorsteinsson í'rom
Höfdabrekka and Sigurjón Bödvarsson froni
Bólstadur, in order to study the cauldrons that
formed simultaneously with the jökulhlaup.
The cauldrons were two. We managed to
climb into them and measure their dimensions.
The bigger was 1050 metres across at tlie top
and 80 metres deep. At the bottom there was
a circular lake 150 metres across on which
floated large ice fragments and cracks in the
ice radiated from it. (See Fig. 2 in Thorarins-
son and Rist (1955) and Fig. 1 in Thorarins-
son (1957)). The volume of this cauldron was
25 G1 ± 15% (Fig. 2).
The smaller cauldron lay northwest of the
larger one. It measured 700 metres across and
was 15 metres deep, volurne 2 Gl. Northwest
of Ytri-Kötlukollur ancl elsewhere in the
Katla depression fissures and minor cracks
formed, indicating some movement in the ice
cover and downwarping. If this regional down-
warping is estimated as 1 Gl, the total volume
will be 28 G1 ± 15%.
In the summer of 1960 the larger cauldron
could still be seen but shortly afterwards it had
completely disappeared.
The location of the ice cauldrons is in good
agreement with the location of crater of the
Katla eruption in 1918 as reported by Sveins-
son (1919). It also fits well with the directions
taken from the village Vík on the eruption
cloud in 1918 (Fig. 1 in the preceding article
p. 239). On the Icelandic topographic map nr.
68 Katla 'is erroneously located several kilo-
meters further SE.
JÖKULHLAUP FALLING ÍNTO THE
MÚLAKVÍSL ON JANUARY 20, 1956
Late in the year of 1955 the flow rate of
glacial melt water flowing into the Múlakvísl
was unusually high for that time of the year.
This was so because the Múlakvísl drained
now most of the melt water from Höfdabrekku-
jökull. On the contrary the flow in the Skálm
was very low. At the end of Dec. the flow
in the Múlakvísl fell suddenly and downstream
tliere was no sign of rnuddy glacial melt water.
No change was observed in the Skálm. These
conditions persisted until on Jan. 20, 1956,
when a jökulhlaup flowecl into the Múlakvísl.
Fig. 3. A view towards SE over the two ice
cauldrons which were formed in the Katla
glacier simultaneously with the jökulhlaup on
June 25, 1955. The cauldron in tlie foreground
is about 700 m in diameter and about 15 m
deep. The other is about 1050 m in diameter
and 80 m cleep.
Photo M. Jóhannsson June 27, 1955.
Mynd 3. Horft til suðausturs yfir ketilsigin i
Kötlujökli. Ketilsigið í forgrunni er um 700 rn
i þvermál og um 15 metra djúpt, en hið stærra
um 1050 m í þvermál og 80 m djúpt.
Ljósrnynd M. Jóhannsson 27. júní 1955.
This hlaup persisted for few hours only during
the day. When at maximum the flow rate was
only 50 m3/sec. In the evening of the same
day the flow rate liad become normal again.
At midday of Jan. 21 the flow rate increased
again but for a short while only.. The author
visited the area on Jan. 24 to study the effects
of the burst. Mr. Valmundur Björnsson, bridge
constructor, had observed all changes in the
Múlakvísl since the day of the burst and hacl
noticed that the muddy glacial water was dif-
ferent from that of the jökulhlaup in 1955.
From an aeroplane it was observed that this
hlaup was caused by the draining of two ice
dammed lakes in Huldufjöll and Rjúpnagil.
Tlie area was never visited for a closer study.
JÖKULL 17. ÁR 245