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.