Jökull - 01.01.2016, Blaðsíða 19

The subglacial topography of Drangajökull ice cap, NW-Iceland
Further studies are required to confirm which, if
any of the above explanations is true for the forma-
tion of Langahraun.
Directional landforms beneath S-Drangajökull
The unusually dense RES-survey of Drangajökull re-
veals a detailed image of the bed topography. It shows
ridges and troughs beneath S-Drangajökull with a
dominant N-S strike, which in some cases can be
traced across the ice cap and are clearly visible outside
the glacier in the Lidar DEM from 2011 (Figure 14).
The same alignment in landforms in the area south
and east of Drangajökull is clearly revealed by aerial
photographs (see e.g. www.map.is). The alignment
of these is likely related to bedrock joints which have
been eroded more heavily than the less fractured rock
nearby. The subglacial ridges and troughs aligned in
this N-S direction likely effect the routing of glacier
water, particularly when the glacier becomes thinner
and eventually retreats from these landforms.
Surface depressions on Reykjarfjarðarjökull
In the accumulation area of Reykjarfjarðarjökull,
there are steep depressions in the glacier surface (Fig-
ure 15). These surface features have unique shape and
have not been observed in the surface of other Ice-
landic glaciers. Some of these features on Reykjar-
fjarðarjökull have been permanent in the glacier sur-
face for decades. They do however move down glacier
(Belart, 2013), which makes it very unlikely that these
depressions are ice cauldrons produced by subglacial
geothermal activity; the ice cauldrons would not move
unless the geothermal activity at the bed did likewise.
The locations of depressions D1–5, appearing in the
aerial photographs of 1946, were tracked (Figure 15a)
until October 2014 or when they were last detected.
It is known that D5 disappeared in 1993 (Jóhannes-
son, 1998). The tracked locations are based on or-
thorectified aerial photographs in 1946–2005 (Belart,
2013; Magnússon et al., 2016), the 2011 Lidar DEM
(Jóhannesson et al., 2013) and Pléiades orthorectified
image in 2014 (Belart et al., in open review, 2016).
Aerial photographs from July 2005 (Figure 15b) re-
veal several new depressions with similar shape. Two
of those (D6-7) still existed in July 2011 (Figure 15a).
The 2005 aerial photographs suggest that the new de-
pressions are parts of crevasse formations associated
Figure 14. Perspective view from S of the bedrock topography of Drangajökull ice cap with twofold vertical
exaggeration. The DEM of the area outside the ice cap and attached ice and snow patches are from the Lidar
DEM of 2011 (Jóhannesson et al., 2013). – Landið undir Drangajökli séð úr suðri.
JÖKULL No. 66, 2016 19