Jökull - 01.01.2016, Blaðsíða 96

Snævarr Guðmundsson and Helgi Björnsson
Figure 1. Breiðamerkurjökull outlet glacier
of the Vatnajökull ice cap. Surface map
based on LiDAR survey in 2010. Ice
divides (solid lines) of the three major
branches south of the Esjufjöll nunataks
are located along the Mávabyggðarönd and
Esjufjallarönd medial moraines. Carto-
graphy based on Guðmundsson (2014).
– Kort af Breiðamerkurjökli, gert eftir
LiDAR mælingum frá 2010.
to 60 m a.s.l. down to 200 m below sea level over a
distance of 1 km. The trench is parallel to the moraine.
In 2014 a peculiar bend on the Esjufjallarönd me-
dial moraine, near and upglacier of the Jökulsárlón
lagoon, was detected (Figure 2). This initiated our ex-
amination of its development.
MAPPING CHANGES IN THE
ESJUFJALLARÖND
We describe changes of the Esjufjallarönd me-
dial moraine by comparision of a high resolu-
tion SPOT satellite image of Breiðamerkurjökull,
taken in 2004 (SPOT 2004) and a set of georef-
erenced satellite images from 2006 to 2016 (Land-
sat 7 and Landsat 8, with pixel resolution of 15–30
m/px., downloaded from the Earth Explorer website
http://earthexplorer.usgs.gov/; Figure 4).
As early as 2006 the medial moraine started to be
shifted eastward (Figures 3 and 4). In 2007 it, how-
ever, became evident that the southernmost tip of the
terminus was stagnant where a solid bedrock covered
with debris emerged underneath the moraine. The
shift varied along the medial moraine, from ∼70 m
yr−1 were it moved at the fastest rate near the lagoon,
to ∼5 m yr−1 about 10 km up from the terminus of
the glacier (Figure 5). No translation of the moraine is
observed upstream from a subglacial hill, rising above
sea level, about 9 km above the calving front (Figure
5). The lower part of the medial moraine has been
shifted ∼900 m towards east, closest to the lagoon
(Figure 3). In 2016 the moraine ended in the lagoon
about 0.6–1.0 km above the location of the stagnant
moraine piece. The motionless southernmost part of
the moraine still contains large amounts of dead ice
which will melt over the next years and leave a low
ridge of debris.
96 JÖKULL No. 66, 2016