Jökull - 01.01.2016, Side 35

First documented surge of Kverkjökull, central Iceland
Figure 3. Difference in elevation at points measured for 3D position in 2008 with dGPS between those points
and the 2007 ALS (A) and the 2011 ALS (B). A vertical transect between X’ and Y’ is depicted in panel C.
All panels together evidence that the surge of Kverkjökull had not started, or at least reached the terminus, in
2008, and that by 2011 the north-eastern and south-western portions of the terminus were behaving differently.
– Hæðarmunur í mælipunktum sem staðsettir voru með dGPS-mælingum árið 2008 samanborið við leysimæl-
ingar 2007 (A) og 2011 (B). Lóðrétt snið mælinganna milli X’ og Y’ eru sýnd á mynd C. Mælingarnar sýna að
framhlaup Kverkjökuls var ekki hafið árið 2008, eða hafði a.m.k. ekki náð niður á sporðinn þá, og að árið 2011
voru áhrif framhlaupsins mjög mismunandi á norðaustur- og suðvesturhluta sporðsins.
where ρ is the density of ice, 900 kg m−3, g is grav-
itational acceleration, 9.82 m s−2, H1 and H2 are ice
thickness in time 1 (2007) and time 2 (2011), respec-
tively, and α1 and α2 are the corresponding surface
slopes. For this change in driving stress calculation,
we resampled surface slope from 5 m to 20 m grid
cell size to avoid locally high slope values due to
crevasses.
River discharge
River discharge data were gained via the Icelandic
Meteorological Office from continuous river stage
recorders on the Kreppa River at Lónshnjúkur, and
on the Jökulsá á Fjöllum at Upptyppingar. These
two rivers both originate from the northern margin of
Vatnajökull in the vicinity of Kverkfjöll so will both
reflect changes in glacier mass balance. However,
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