Jökull - 01.01.2021, Page 5

The 1918 Katla eruption
A complementary paper (Gudmundsson et al., this
issue) presents the details on this isopach map, the
data used, analysis of tephra distribution and thickness
variations on Mýrdalsjökull ice cap, and estimates of
the volume of the tephra layer.
Lightning and thunder are an aspect of the 1918
eruption that is not attended to here although fre-
quently mentioned in contemporary sources.
PRECURSORS, ERUPTION PLUME AND
TEPHRA FALL:
CONTEMPORARY RECORDS
The 1918 Katla eruption was among the largest 20th
century eruptions in Iceland, despite being relatively
short-lived, lasting 23 days. The following account
of events from October 12 to November 4 is based
on contemporary observations published in an offi-
cial report to the authorities (Sveinsson, 1919), writ-
ten descriptions from neighbouring areas (Jóhanns-
son, 1919; Loftsson, 1930), and newspaper reports
from October and November 1918. Frequent men-
tion is also made of the farming areas or districts that
were greatly affected by the eruption and located to
the northeast, east and south of Katla, notably Skaftár-
tunga, Álftaver, Síða, Meðalland and Mýrdalur with
the small village of Vík (Figure 1).
Precursors
The precursors observed were earthquakes felt at the
village of Vík, about 20 km S of the eruption site
(Sveinsson, 1919; see also Einarsson, 2019). At about
1 PM, local time, on October 12 a strong earthquake
was felt in Vík, with frequent small quakes occurring
in the next 1/2 hour (Jóhannsson, 1919). Signs of un-
rest, however, were noticed earlier. At about 11:30
AM, small ripples were noted in a water basin used
for washing.2 This suggests that small earthquakes
and tremors had started at least 1.5 hours before the
strong earthquake.
Eruption onset
The eruption plume was seen from Vík village ris-
ing from Mýrdalsjökull at about 3 PM (Jóhannsson,
1919). It was described as a steam cloud or as an
ascending, winding smoke with a lower black part,
brightening upwards and extending slowly towards
east (Sveinsson, 1919). Figure 2 is most likely taken
on this first day of the eruption. Another account de-
scribed a fast ascending eruption column with uneven
upwind edge with ripples and puffs, and strange for-
mations within the plume, e.g. in the shape of an in-
verted funnel above a large horizontal ring, that re-
mained unchanged for an hour (Jóhannsson, 1919).
The plume extended eastwards towards Álftaver and
darkened in the hours that followed.
Farmers were herding sheep in Mýrdalur on Oc-
tober 12. This included the Hafursá canyon (Hafurs-
árgil), which cuts into the lower slopes of the Katla
volcano. The plume was seen rising from the glacier
where none had been earlier. This description is not
timed, but indicates the rapid ascent of the plume.3
An account from Vestmannaeyjar islands, about
65 km to the of WSW of Katla, described the begin-
ning of the eruption on October 12 as the appearance
of a dense, light-grey cloud among the clouds above
Mýrdalsjökull, rising slowly at first, soon accelerat-
ing and forming a tall, straight smoke column that
widened at the top and extended towards east. The
light-grey plume was noticed around 3 PM, but there
were also claims that some smoke had been spotted at
least an hour earlier. The column had a well-defined
point of origin as seen from Vestmannaeyjar. Flashes
of light were seen in the cloud soon after it appeared
and onwards. The “smoke” was extruded continu-
ously, the plume becoming more impressive in the
2Lilja Tómasdóttir (1906–1973), was 12 years old in 1918 and lived with her parents in Vík. On the morning of October 12 she had
been washing clothes with her mother (Margrét Eiríksdóttir, 1867–1950) by the small river that runs through the village. At about 11:30
AM she noticed that there were small ripples on the surface of the water in the tub they were using. Her mother then said: “Guð hjálpi
okkur, ætli Katla sé að koma?” (God help us, could this be Katla coming?) At 3 PM they had lunch. As the family sits by the table, a man
comes and shouts: “Katla er að koma” (Katla is coming). Lilja then ran up the slope above the house and looking east saw the jökulhlaup
burst forth carrying large blocks of ice, west of Hjörleifshöfði, 8–10 km away (Source: Erlingur Ísleifsson, son of Lilja, 30th of January
2001).
3This observation was made by Magnús Ingibergur Þórðarson (1895–1983) (Source: Þórður Eydal Magnússon, son of Magnús, 11th of
October 2018).
JÖKULL No. 71, 2021 3