Jökull - 01.01.2019, Síða 62

The 2011 unrest at Katla volcano
Figure 6. Schematic map of the main geological features observed in the Gvendarfell and Norðurgilshaus area.
The approximate location of the Gvendarfell seismic cluster is also drawn with a red box representing the uncer-
tainty of absolute location (Sgattoni et al., 2016a,c). – Kort af helstu jarðmyndunum svæðisins við Gvendarfell
og Norðurgilshaus. Upptakasvæði skjálftanna við Gvendarfell er einnig afmarkað með rauðum ferningi. Stærð
hans gefur til kynna óvissu í staðsetningu þyrpingarinnar.
jökull glacier and the exposed region is characterized
by flat-topped ridges bordered by steep ravines eroded
by the fast-retreating Hafursárjökull and Mosakambur
glacier streams (Figures 6, 7). We carried out a
geological field study and lithostratigraphic analysis
around the Stórihryggur ridge, whereas it was not pos-
sible to directly investigate the flanks of the Gvendar-
fell ridge. Moreover, we worked in the area around
the Gaesavatn lake, to the south-east of Gvendarfell.
No signs of recent volcanic or hydrothermal activity
have been seen in the whole area.
A hundred-meters thick pile consisting of pale-
grey rhyolitic lava lobes and domes (tens-of-meters
thick) was identified on the E side of the Stórihryggur
ridge. They show concentric to fan-shaped flow
bands (Figure 7a) and obsidian-rich margins, embed-
ded within pale fragmented (talus) material. The lavas
are characterized by pervasive prismatic, platy and
columnar jointing, which is arranged both subverti-
cally and in fan shapes, depending upon the overall
morphology of the lava. Where clearly seen, fracture
spacing appears to be narrow, on the order of cm to
JÖKULL No. 69, 2019 61