Jökull - 01.01.2016, Síða 40

Jonathan L. Carrivick et al.
Figure 7 (partly on previous page). Local relief as seen in the field in 2007, 2009 and 2010. The orientation
of the camera in 2007 and 2009 is near-identical and is depicted in Figure 3B, but the view in 2007 is more
distant from the glacier than in 2009. The view in 2010 is of the north-eastern part of the terminus. Note more
chaotic surface in 2009 with local relief in inset image of up to 20 m. Inset image view is directly up-glacier
and reveals exposed structure of ice with evidence of vertical compression in the form of stacked thrust planes.
In 2010, heavy crevassing is visible just back from the terminus, which shows no signs of advance at that time.
Image from 2010 is courtesy of Jónas Helgason. – Sporður Kverkjökuls 2007, 2009 og 2010. Stefna ljósmynda-
vélarinnar var svipuð 2007 og 2009, og er sýnd á mynd 3B, en myndin frá 2007 var tekin úr meiri fjarlægð.
Myndin frá 2010 er af norðaustanverðum sporðinum. Yfirborð jökulsins 2009 er meira brotið upp en 2007 og
hæðarmunur milli nærliggjandi staða er allt að 20 m. Minni myndin frá 2009 er tekin beint upp jökulinn og
sýnir ummerki um samkýtingu og hreyfingu á aðliggjandi, samsíða skriðflötum. Myndin frá 2010 sýnir mikla
sprungumyndun skammt ofan jökuljaðarsins en jaðarinn sjálfur hefur ekki gengið fram. Ljósmyndin frá 2010
er tekin af Jónasi Helgasyni.
labelled ‘L’ in Figure 5B, exists from the vicinity of
Gengissig towards the mid-reaches of the glacier.
The area of the glacier with negative surface el-
evation changes, i.e. thinning, between 2007 and
2011 was 7.4 km2, and this related to a volume de-
crease across this area of 0.05 km3. The area of the
glacier experiencing gains in elevation was 5.3 km2
and across this area there was 0.04 km3 more ice in
2011 than in 2007. Thus the surge was characterised
by a simple translation of mass from higher to lower
elevations. The 0.01 km3 discrepancy in reservoir and
receiving volumes is rather low to be due to normal
ice wastage due to negative glacier mass balance. Part
of the increased volume in the receiving area may be
due to the increased crevassing and this may in part
explain the relatively small reduction in ice volume
over the period 2008 to 2011.
Horizontal surface velocities of up to ∼80 m yr−1
were measured in the terminus area (Figure 8). How-
ever, whilst the direction of these surface velocities in
the terminus area was spatially concordant, the mag-
nitude of the velocities had no clear pattern. Whilst
most surface velocities had significantly reduced in
2012 to 2013, in comparison with 2011 to 2012 (Fig-
ures 8 and 9), the terminus was still advancing be-
tween 2012 and 2013, with horizontal displacements
40 JÖKULL No. 66, 2016