Jökull - 01.01.2021, Page 60

Magnússon et al.
Figure 10. A close up of the area around K16, K9 and K17 (shown with a blue box in a) showing 3D representa-
tion of the glacier surface (in September 2016) and bedrock (b). The magenta coloured cluster on the surface 3D
image, indicates location of traced bedrock reflections from the 3D migrated RES-data. The corresponding area
is outlined with a dashed black line on the 3D bedrock image. The RES-survey of K9 and K17 in 2019 focused
on the area considered in Björnsson et al., (2000) as the location of the 1918 eruption, orange dash lined circle
in (a) and (b). More recent study (Gudmundsson et al., 2021) however locates the eruption further east (orange
dot lined ellipse in a and b). Large part of that area was surveyed with dense RES-profiling in May 2021 (more
info on Figure 12). c) 3D migrated RES-profile crossing a mountain west of K9 (profile location from A to B
shown in b) revealing 250 m high cliffs on the west side of the mountain (dashed magenta line indicates traced
bed reflections). The RES-profile (c) and the 3D images (b) are without vertical exaggeration. – Nærmynd af
svæðinu nærri kötlum 16, 9 og 17 (afmarkað með bláu boxi á mynd (a)) sem þrívíddarmynd af jökulyfirborði og
botni (b). Purpurarauðu skellurnar á yfirborðinu sýna staðsetningar greindra botnendurkasta í íssjársniðum
unnar með þrívíðri staðsetningarleiðréttingu á endurkastsflötum. Tilsvarandi svæði er sýnt með svartri brota-
línu á botni. Íssjármæling umhverfis katlana vorið 2019 beindist að svæði sem talið var gosstöðvarnar 1918
(Helgi Björnsson o.fl., 2000) innan hringlaga appelsínugulrar brotalínu á myndum (a) og (b). Samkvæmt nýrri
rannsókn (Magnús T. Guðmundsson o.fl., 2021) voru gosstöðvarnar líklega að mestu bundnar við svæði nokkru
austar, innan sporbaugslaga appelsínugulrar punktalínu á myndum (a) og (b) en stór hluti þess svæðis var
mældur í maí 2021 (sjá 12. mynd). c) Íssjársnið með þrívíðri staðsetningarleiðréttingu, yfir fjall vestur af katli
9 (frá A til B á b), sýnir um 250 m háa hamra í vesturhlíðum fjallsins (purpurarauð brotalína afmarkar greind
botnendurköst). Bæði þrívíddarmyndin (b) og sniðið (c) eru án hæðarýkingar.
created by kriging interpolation from 2D migrated bed
traces is compared to the 3D migrated DEM, the dif-
ference is also on average ∼10 m higher with ∼20 m
standard deviation (Figure 5d). Most of this differ-
ence can be related to the previously mentioned lim-
itation of the 2D migrated data (see Data and Meth-
ods), caused by cross-track bed reflections interpreted
as being located directly beneath the radar, while the
actual bed at the same location is often tens of metres
lower (up to 100 m for the data shown in Figure 5).
The main exception, where the limitation of the 2D
migrated data does not explain this, is at the location
58 JÖKULL No. 71, 2021