An extensive late Holocene glacier advance of Kötlujökull, central south Iceland

This paper presents data on an extensive late Holocene advance of Kötlujökull, a southeastern outlet glacier from the ice cap Mýrdalsjökull, central south Iceland. During the advance, basal till was deposited on top of a volcanic ash layer resting on lava hummocks. Remnants of this landscape are now seen 3.5-5.5 km in front of Kötlujökull as a fragment surrounded by the Mýrdalssandur. Electron microprobe analysis of the volcanic ash shows that it is silicic and originates from the volcano Katla underneath Mýrdalsjökull. A ¹⁴C AMS date on a twig fragment sampled in the upper part of the volcanic ash layer provides a maximum age of the till of 1610±40 yr BP, and this is supported by tephrochronological and geochemical analyses of the volcanic ash. It is concluded that Kötlujökull must have advanced more than 5.5 km from its present position after 1.6 kyr BP. This advance is much more extensive than the Little Ice Age (LIA) advance and took place in a relatively cold period also identified in the Greenland ice cores and the diatom record in the seas surrounding Iceland. In the proglacial environment in front of the Icelandic ice caps, the preservation potential of older end-moraines is strongly restricted due to intense glaciofluvial erosion. Therefore, the LIA end-moraines have in many cases been interpreted as marking the outermost Holocene glacier front position. This study as well as other recent results stresses the fact that the "LIA glacial maximum" in Iceland may not be identical to the Holocene glacial maximum, and that far more case studies with well-constrained dating control are needed.