Timing and significance of mid-Holocene glacier advances in Northern and Central Iceland

Tephrochronology is used to date mid-Holocene moraines in Iceland. In the Grænavatn cirque (Tröllaskagi Peninsula) the H-4 tephra (ca. 3830 yr BP) lies within sediment accumulated against the distal slope of a lateral moraine, providing a minimum age for glaciation, and the absence of H-5 (ca. 5950 yr BP) provides a maximum age. By implication, the cirque was glaciated in the early Neoglacial period. A large rock glacier, the development of which post-dates the moraine, probably formed within the 'Little Ice Age' (LIA) of the sixteenth to nineteenth centuries AD. At Eystri-Loomundarjökull in central Iceland, frozen colluvium containing the H-3 (ca. 2900 yr BP) and H-4 tephras provides a minimum age of ca. 3830 yr BP for two terminal moraines, and a maximum age of ca. 2900 yr BP for a third. The older moraines are correlated with the Vatnsdalur I/Drangagíl advances (ca. 4700 yr BP and = 4500 yr BP respectively) and the Bægisárdalur I advance (ca. 4200 yr BP). They imply that early Neoglacial advances throughout Iceland were locally more extensive than those of the LIA. The apparent LIA Holocene glacial maximum may reflect (i) selective sampling of large ice-cap-outlet glaciers, where the preservation potential of pre-LIA deposits is low, and (ii) reliance on lichenometric dating, which has a restriced temporal range.