Proximal products of ~ 12 ka silicic explosive-effusive eruptions at Katla volcano: implications for volcano-glacier interactions and paleoenvironment

Abstract Eruptions from the Katla central volcano occur through the overlying Mýrdalsjökull ice cap, meaning proximal deposits are usually not well preserved or exposed. Two nunataks, Enta and Klakksfjöll, crop out above the ice cap close to the Katla caldera rim and offer exceptional exposure of proximal rhyolitic eruptive products from this predominantly basaltic volcano. Geological mapping of these nunataks reveals silicic tephra with synchronously emplaced rhyolite lava flows and intrusions. The physical characteristics of the deposits indicate that silicic explosive eruptions accompanied lava effusion from multiple englacial vents around the caldera. New 40 Ar/ 39 Ar ages for ice-confined lavas at Enta (11.9 ± 1.9 ka) and Klakksfjöll (11.7 ± 2.3 ka) indicate eruptions coincided with the Younger Dryas and that the ice surface at the time of eruption was 150–300 higher than at present. This inferred ice thickness concurs with independent estimates for the Younger Dryas glacier thickness at these locations, based on reconstructed southern and western margins. The lava ages and the major element geochemistry of the tephra are comparable with those of the ~ 12.1 ka Vedde Ash, a well-known Katla ash layer and an important stratigraphic marker in northern Europe and the North Atlantic. These nunataks may therefore preserve the proximal deposits of this significant eruption. At the end of the last glacial period, retreat of the Icelandic Ice Sheet was rapid and coincided with increased volcanic activity. It is possible that glacial unloading during deglaciation facilitated multiple silicic eruptions at Katla during the last glacial-interglacial transition.