Hvítárvatn is a proglacial lake adjacent to Langjökull, the second largest ice cap in Iceland. The lake is 422 m a.s.l. and 36 km2 with a maximum depth of 85 m (Fig. 1). Langjökull feeds two outlet glaciers, Suðurjökull and Norðurjökull, which both terminated in the lake during the Little Ice Age (LIA; AD 1300–1900). The LIA extent of both outlet glaciers is clearly defined by moraines visible on land and in high-frequency multibeam sonar bathymetric images of the lake bottom (Geirsdóttir et al. 2008). The multibeam sonar bathymetry, chirp bottom profiles and numerous sediment cores contain information on the sedimentary history of the lake and indicate that, following regional deglaciation 10 ka ago, glaciers entered the lake only during the LIA (Larsen et al. 2011, 2012). Suðurjökull remained in the lake until the mid-twentieth century, whereas Norðurjökull retreated from the lake in the summer of 2009. The multibeam sonar bathymetric data show large differences in the behaviour of Norðurjökull and Suðurjökull during the LIA that can be explained by both glacial processes and variations in the stability of the catchment.
Langjökull and Hvítárvatn glacier geological setting. (a) Topographic map of field site showing location of Hvítárvatn (HVT) adjacent to Langjökull's eastern margin (map gridlines are spaced 1 km). Lake surface is overlain with bathymetric map; maximum LIA extent (dashed lines) of outlet glaciers Norðurjökull (NJ) and Suðurjökull (SJ) are visible in lake bathymetry. Inset map highlights position of Langjökull in Iceland's central highlands. Other geographical features mentioned in text are Skriðufell (SK), Leggjarbrjótur (LB) and the Hvítárnes delta (HV). (b) Multibeam bathymetric map of Hvítárvatn's main basin showing detailed view of lake-floor morphology and position of seismic profile (dashed line) presented in (c). Multibeam acquisition system Seabat 8101. Frequency 240 kHz. (c) Chirp seismic profile (dashed line …
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