Jökull - 01.01.2021, Page 12

Larsen et al.
Table 1. Comparison of the Katla tephra thickness as reported in 1918 and as measured in the soil 50–100 years
later. – Samanburður á þykkt Kötlugjóskunnar samkvæmt heimildum 1918 og eins og hún mældist í jarðvegi
50–100 árum síðar.
The 1918 Katla tephra
Districts south and Tephra thickness Tephra thickness Comments
east Mýrdalsjökull on surface as measured in soil
reported in 1918 1970 and later
Mýrdalur 3.5-4.5 cm 0-2 cm Calculated from reports (GS, GJ)
Álftaver 6-8 cm 1.5-4 cm Accumulated tephra as reported (GJ)
Skaftártunga 6.5-10 cm 0.5-6 cm Accumulated tephra as reported* (GS)
Síða 3.5-4.5 cm 0.5-3 cm Estimated from reports* (GS, GJ)
*Thickness reported in inches
Figure 7. Map of the 1918 Katla tephra
layer within the 0.5 cm isopach, as
it is currently found in soil and ice
(compacted). It has three main sec-
tors, to the SE, NE and N, which corre-
spond reasonably well to contemporary
records of the tephra fall. Compiled by
M. H. Janebo, G. Larsen, S. Thorarins-
son, J. Gudnason, T. Thordarson, M. T.
Gudmundsson, T. Jónsdóttir and oth-
ers. – Þykktarkort af Kötlugjóskunni
frá 1918 eins og hún er í jarðvegi nú.
Helstu þykktarásarnir stefna SA, NA
og N sem er í samræmi við lýsingar í
samtímaheimildum. Byggt á gögnum
frá Mariu H. Janebo, Guðrúnu Larsen,
Sigurði Þórarinssyni, Jónasi Guðna-
syni; Þorvaldi Þórðarsyni, Magnúsi
T. Guðmundssyni, Tinnu Jónsdóttur og
fleirum.
tephra carried in that direction was mostly deposited
over unpopulated areas. The tephra badly affected
trout fishing in the Veiðivötn lakes up to 70 km to the
north of Katla (Guðmundsson, 2017), but caused only
minor tephra fall in populated areas.
The volume of the tephra is estimated in Gud-
mundsson et al. (this issue) as 0.95±0.25 km3. As-
suming ∼20% compaction since deposition this cor-
responds to 1.1–1.2 km3 as freshly fallen tephra.
THE 1918 JÖKULHLAUP ON 12
OCTOBER
All Katla eruptions described in contemporary
records have been accompanied by jökulhlaups,
floods of meltwater originating at the subglacial erup-
tion sites within the caldera. These jökulhlaups es-
cape subglacially through the deep subglacial pass in
the caldera rim on the eastern side (Björnsson et al.,
10 JÖKULL No. 71, 2021