Jökull - 01.12.1982, Blaðsíða 67

Fig. 2. Hypothetical model of
a Katla flow.
Mynd 2. Þverskurður af Kötlu-
hlauþi. Hugmynd.
ations it is evident that the first flood wave passed
on top of the glacier, rushed over a part of the
ntoutain at Sker (Fig. 1), into the Remmdargilgorge
down to the sandur plain. This flow seems to have
emanated from the volcanic source area and drained
ofF on top of the glacier — supraglacially. The sec-
ond ílow pulse which was the most voluminous and
reached its maximum at 5,30 (see above) seems to
have advanced supraglacially, intraglacially and
subglacially. During the course of this event of the
flow the margin of the glacier was extensively frag-
mented and a great amout of gigantic iceblocks
carried away. Much the same occurred simultan-
eously at the northeastern part ofthe glacier at the
source of the eastern flow (Sveinsson 1930). From
records in Safn til Sögu Islands (1907-1915) it appears
that the course of events was similar during the
eruptions 1721, 1755, 1823, as 1918. This seems to
be normal.
Volume of the debrisflow.
The volume of the Katla debris flow of 12th Oct-
ober 1918 has been estimated by Hannesson (1934) to
300 000-400 000m3/sec, Thorarinsson (1957) >100
000 m3/sec, and Jónsson (1969) 200 000 m3/sec. All
these figures, however, are a mere guess work. On
my suggestion Professor Thorbjöm Karlsson at the
University in Reykjavík is now trying to calculate
the volume of this flow based on available inform-
ation and observations in the field. I will not antici-
pate his detailed results here as he will publish them
soon himself. His provisional figure for the peak of
the 1918 flow between Hafursey and Vestureggjaris
1.5 million m3/sec. Accordingly, when at its max-
imum, the total volume of the Katla flow of 1918
must have been considerably more thán 2 million
m3/sec. The depth of the flow there was estimated
by Jóhannsson (op. cit.) and his companions as hav-
ing been some 60-70 m.
Fig. 3. Pumice bed at Sandgil.
Mynd 3. Þverskurður af vikurlögum í Sandgili.
JÖKULL 32. ÁR 63