Jökull


Jökull - 01.01.2016, Side 96

Jökull - 01.01.2016, Side 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
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Jökull

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