Jökull - 01.01.2021, Page 17

The 1918 Katla eruption
Figure 10. b) Photo of the same area as Figure 10a, taken about a month later, during a trip on November 17,
1918. The hills and Kötlujökull are now partly snow-covered. Múlakvísl river has receded and the main flood
route is dry. A large amount of sediment has been removed by Múlakvísl, revealing the true size of the icebergs.
The largest one towers at least 45 m above the sandur plain. Photo Kjartan Guðmundsson. The top of the largest
iceberg on b) can also be seen sticking out of the sediment on a). – b) Ljósmynd Kjartans Guðmundssonar
af sama svæði og er á mynd 10a, dagsett 17. nóvember 1918. Kötlujökull og hæðarkollar eru hvítir af snjó.
Rennsli í Múlakvísl hefur minnkað mikið og ekkert vatn sést í farveginum við Hafursey. Múlakvísl hefur grafið
hlaupsetið frá jakahrönninni svo raunveruleg stærð ísjakanna kemur í ljós. Stóri upprétti jakinn til hægri rís
a.m.k. 45 m yfir sandinn. Aðeins efsti hluti hans stendur upp úr hrönninni á mynd a).
Tephra fall was reported somewhere in Iceland al-
most every day from October 12 to November 1, most
often to the northeast of Katla, in Skaftártunga and
Síða, or on 12 out of the 20 days of recorded tephra
fall. In Álftaver and Meðalland, east-southeast of
Katla, eight days of tephra fall were recorded. Areas
to the south, west and north experienced tephra fall
on five days or less. The tephra fall during the 1918
Katla eruption produced the most voluminous tephra
layer of the 20th century in Iceland (Gudmundsson et
al., this issue). The area within the 0.5 cm isopach
is considered to be about 20,000 km2 and it is likely
that traces of tephra were carried over most of Ice-
land although no reports exist from the extreme west
and northeast. Outside the Mýrdalsjökull glacier the
1918 Katla tephra layer is mostly in the ash size range
(grains ≤2 mm), which is in accordance with eyewit-
ness descriptions of the tephra fall (Jóhannsson, 1919;
Sveinsson, 1919). Bedding is not prominent (Fig-
ure 6a), which may in part be due to remobilization,
as described in the contemporary records (Jóhanns-
son 1919; Sveinsson 1919). However, tephra de-
posited within the accumulation area of Mýrdalsjökull
is buried by snow and preserved intact until it reap-
pears on the ablation area. This tephra is in the ash
and lapilli size range with distinct bedding preserved
(Figure 6b).
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