Jökull - 01.01.2021, Blaðsíða 115

Ljósmyndir Þorláks Sverrissonar
Five photographs (Figures 10–13) show the melt-
water, icebergs and sediments that accompanied the
1918 Katla eruption. These were taken while the
eruption was ongoing and are the only such pho-
tographs known to the authors. Two (Figures 10–
11) show flood routes and deposits, two show the ice
canyon through which the main phase of the jökulh-
laup emerged (Figures 12a, b), and one a colossal ice-
berg (Figure 13). The photographs of Kjartan Guð-
mundsson of icebergs and sediments were taken in
mid-November, after the eruption had ceased.
None of the photographs were dated by Sverris-
son, except that he claimed to have photographed the
eruption from the beginning to the end. However, de-
tailed day to day descriptions exist of the eruption
cloud when the glacier was visible, of the weather
conditions, and the tephra fall in Vík village and vicin-
ity (Jóhannsson 1919; Sveinsson 1919). This infor-
mation has been crucial for constraining the most
likely dates for the photographs.
Figures 2 and 3, showing the Katla eruption cloud
on October 12, may be the first photographs ever
taken of a subglacial volcanic eruption, and are almost
certainly the first of an explosive basaltic eruption
through a glacier. Search for older photographs has
not revealed any photos of eruptions through glacier
ice prior to the 1918 eruption. An undated photograph
from Reykjavík by Magnús Ólafsson showing a sunlit
Katla eruption cloud may have been taken in the late
afternoon on October 12, 1918.
In addition to the historical value, the scientific
value of Sverrisson’s photos is considerable and the
examples detailed here are only a part of the informa-
tion they contain. The height of the eruption cloud
at various times can be calculated, the location of
source vents can be constrained, the photos contain
information on the response of the Kötlujökull outlet
glacier to the flood and the maximum flood level at
Hafursey can be estimated. Although peak discharge
for the 1918 main phase has been estimated (Tómas-
son 1993; Karlsson 1994) the additional information
may help to refine these estimates.
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