Jökull - 01.01.2021, Side 10

Larsen et al.
eruption. The wind was blowing from the northwest
resulting in some tephra fall in Álftaver (Jóhannsson,
1919) and about 1/2 inch (1.3 cm) in eastern Mýr-
dalur (Sveinsson, 1919). In Álftaver, tephra fall re-
sumed around midnight and lasted with a short pause
until noon on October 23 when the total tephra fall
amounted to 5 cm (Jóhannsson, 1919). The wind then
shifted and carried the plume across Skaftártunga and
Síða. During 5 hours of tephra fall about an inch
(2.6 cm) of pumiceous ash was deposited in Skaftár-
tunga (25–35 km from source). Later in the evening
and the following night another inch of ash fell on
Skaftártunga, bringing the total, from the beginning
of the eruption, to 2.5 inches (6.5 cm). The Síða dis-
trict (40–60 km from source) received less tephra fall,
but the ground was covered by ash to such an extent
that it prohibited grazing (Sveinsson, 1919; Jóhanns-
son, 1919).
In the early hours on October 24, the wind was
from the northwest and tephra was carried across
Álftaver and Meðalland between 4 and 6 AM. In
Álftaver the accumulated tephra thickness was now
6–8 cm (Jóhannsson, 1919). This was the last sig-
nificant tephra fall in these districts. From Vík vil-
lage the eruption column looked as black as ever and
was apparently ascending from two separated “vents”.
Around 1 PM the wind had become more northerly
and carried ash and pumice over Mýrdalur and Vík
village (Figure 6a), causing total darkness around 2
PM. Electricity had to be turned off in the village and
use of telephones was forbidden due to the threat of
lightning (Sveinsson, 1919). Intense tephra fall lasted
until 5 PM, when there was a short break. Less in-
tense tephra fall continued until 2 AM on October 25,
and had by then lasted for 13 hours (including a one
hour break). After three hours of intense tephra fall
the tephra thickness was 1–2 cm on level ground and
after 13 hours 2–4 cm. Most of this time the darkness
in Vík was so complete that windows could not be
discerned from solid walls (Jóhannsson, 1919).
On October 25 the wind was southerly. Minor
tephra fall was reported in Skaftártunga and Síða in
the morning and later that day tephra fell in Reykjavík
(Figure 5) for the third time (Morgunblaðið, 26 Oct.).
The next day the eruption column was described as
mostly composed of steam. During the following 7
days the wind was southerly and the tephra was car-
ried towards the north (Sveinsson, 1919). Tephra fall
in the early hours and morning of October 26 was re-
ported from Akureyri and Húsavík in North Iceland
(Figure 5), in both areas footprints were traceable on
the ground (Morgunblaðið, 27 and 28 Oct.; Dagur,
5 Nov.), which indicates deposition of the order of
300 g/m2 (∼0.3 mm) of tephra (Thorarinsson, 1955).
Tephra fall was reported from the Skagafjörður dis-
trict on October 28, (Tíminn, 14 Dec.).
On October 30, with the wind blowing from the
southeast, tephra fall was reported in areas to the
west, in Rangárvallasýsla and Reykjavík (Morgun-
blaðið, 31 Oct.; Lögrjetta 27 Nov.). During the next
two days fallout was reported in northern Iceland; in
Skagafjörður and Siglufjörður “the greatest” tephra
fall occurred on October 31 and November 1, respec-
tively (Fram, 2 Nov.; Tíminn, 14 Dec.). This was
the last verified tephra fall from the Katla 1918 erup-
tion (Figure 5). Re-deposition of wind-blown ash was,
however, reported on several occasions during and af-
ter the eruption (e.g. Sveinsson, 1919; Jóhannsson,
1919; Lögrjetta 27 Nov.).
The 1918 tephra layer, preservation
The 1918 Katla eruption occurred in late autumn. The
tephra fall areas were grasslands and sandur plains in
the lowland areas, unvegetated highland areas and ice
caps. The preservation potential in the 1918 tephra
fall area is therefore generally low.
The Katla 1918 tephra is relatively fine grained
and was mostly in the ash size range (<2 mm) out-
side of the Mýrdalsjökull ice cap (Jónsdóttir, 2015).
The contemporary records mention that the tephra de-
posited during the first days was much finer than the
tephra deposited later in the eruption. The records
describe syn-and post-depositional erosion after each
tephra fall event. They also describe how the tephra
was eroded and redeposited by wind and water dur-
ing the following winter, in some places almost com-
pletely obliterated, and later on in springtime, when
the ground had become snow-free, how the dry tephra
was blown about “On a windy day an ash-storm blew
all over the neighbourhood” (Sveinsson, 1919, 38).
8 JÖKULL No. 71, 2021