Jökull - 01.01.2021, Page 6

Larsen et al.
evening hours. Later in the evening a red glow was
seen at its base, lasting for some time (Skeggi, Oct.
12 and 18, 1918).
Figure 2. Eruption plume above Katla seen from north
of Vík village. The mountain to the right is Hatta,
504 m a.s.l. The eruption plume rises at least 15 km
a.s.l. See descriptions in main text. Photo: Þorlákur
Sverrisson, undated, but most likely from October 12.
– Gosmökkur yfir Kötlu. Myndin er tekin fyrir norðan
Vík í Mýrdal. Fjallið til hægri er Hatta, 504 m y.s.
Mökkurinn rís a.m.k. 15 km y.s. Ljósmynd: Þorlákur
Sverrisson, ódagsett en líklega tekin 12. október.
Lightning and accompanying thunder was ob-
served within the eruption plume from the beginning.
In the evening the arrow-like flashes were said to oc-
cur almost constantly, although “sometimes with a
few seconds in between” (Jóhannsson, 1919). Larger
flashes “that lit up the whole cloud” were also ob-
served, sometimes lasting for a while, and “booms”
were heard every now and then from the beginning
of the eruption. Around 9 PM a glow at its base was
noticed, lasting for a while (Jóhannsson, 1919).
The eruption plume was measured from Reykja-
vík on October 12 (Eggertsson, 1919), about 150 km
WNW from Katla at a time when the plume was head-
ing towards E or ESE in the direction of Álftaver.
The maximum plume height reported by Eggertsson
(1919) is 14.3 km a.s.l., but he does not give the timing
of this observation. The descriptions from Reykjavík
state that upwards-directed lightning strikes rose from
the plume reaching 20–25 km height (Figure 3). The
width of the eruption plume at its top was measured
to be about 8 km across (Eggertsson, 1919).
Eruption plume 13 October – 4 November
The photographs of the eruption plume shown in Fig-
ures 4a-d are examples of the several images that ex-
ist; some of which are not dated. However, they show
a plume as high as 15 km (a, most likely taken on Oc-
tober 12), as low as 4 km (b), and then there are two
showing height of 7–8 km (c and d).
No detailed descriptions exist from October 13
and 14. The weather was cloudy on the 13th and haze
caused poor visibility on the 14th. On October 15, the
visible activity fluctuated, with periods of ascending
and receding plume. On October 16, the plume was
definitely lower than before, and it was at its lowest
the following day (Jóhannsson, 1919). On October 18
no plume was observed. On October 20, two sepa-
rate eruption columns were spotted for the first time
(see Larsen and Högnadóttir, this issue), the western
column was much lower and weaker than the east-
ern one, each “apparently coming from several vents”
(Jóhannsson, 1919). The plume was now lower and
darker than during the first days and described as an
ash cloud.
On October 22 the eruption intensified and the
plume became more magnificent than ever before, and
the black, lower part of the plume had never been
as high as seen on this day (Sveinsson, 1919). The
following day the plume was referred to as “black
smoke”, but on October 24 the plume was described
as a “horrible black ash column” akin to that of Octo-
ber 22 but emanating from two sources (vent areas),
this time with the western one “blacker” (Sveinsson,
4 JÖKULL No. 71, 2021