Jökull - 01.01.2021, Qupperneq 32

Gudmundsson et al.
Figure 5. Isopach map of the Katla 1918 tephra layer based on available data and the reconstructed thick-
nesses and locations within the Katla caldera. The frame marks the area shown in Figure 6. – Jafnþykktarkort
af gjóskulaginu frá 1918, byggt á öllum tiltækum mælingum og reiknuðum þykktum og staðsetningum innan
Kötluöskjunnar. Ramminn afmarkar kortið á 6. mynd.
DISCUSSION
When compared with published estimates of previous
eruptions (Óladóttir et al., 2018), the results obtained
demonstrate that Katla 1918 is among the largest of
the tephra layers produced by Katla in the last 1000
years. A previous estimate was made in 1919 by
Samúel Eggertsson (1919) using the approximation of
a stack of concentric vertical cylinders with Katla at
their axis and height equal to tephra thickness. Egg-
ertsson’s result was a total volume of 0.7 km3. Given
the scarce data available at this time this estimate must
be regarded as remarkably good. In Figure 7b the
layer is compared with other Katla layers that fell
mostly on land and have been mapped (Óladóttir et
al., 2018). The data from the older eruptions does
not include the thick proximal part, allowing compar-
30 JÖKULL No. 71, 2021