Geological and geomorphic evidence for eruption style, paleoenvironment and landform modification at Katla and Eyjafjallajökull volcanoes, Iceland

Volcanic landforms and eruptive products can be effective proxies for paleoenvironment. The morphology of volcanic edifices can reveal whether they were constructed in subaerial or subglacial environments, while the physical characteristics of individual products indicate emplacement in wet or dry conditions. Polygenetic volcanoes with eruptive histories spanning glacial and interglacial periods therefore have the potential to record environmental change and it‘s influence on volcano evolution. The deeply dissected flanks of the ice-capped Katla and Eyjafjallajökull volcanoes expose a >55 ka sequence of edifice-forming volcanic products. We combine detailed characterisation and geological mapping of the sequence with airborne photogrammetry surveys, examination of the geomorphology, and dating to reconstruct the eruption and emplacement processes, landform modification and paleoenvironments that have shaped this dynamic glaciovolcanic landscape. For example, intercalation of subglacial and subaerial deposits at the base of the sequence indicates a fluctuating ice margin 57-55 ka. Other distintive landforms include a 795 m-high peak dominated by bedded tuff and intruded with lobate lava bodies with an 40Ar/39Ar age of ~19 ka. The peak acted as a partial topographic barrier behind which an englacial lake accumulated. A lava delta prograded into the lake from 13-11 ka. A subaerial lava flow caps the delta and indicates a miniumum ice surface level ~ 850 m a.s.l. at the time of emplacement. The lava delta now forms a flat-topped, steep-sided plateau standing several hundred metres high above the landscape. While these formations appear morphologically like volcanic vents or tuyas, detailed examination of the rock sequence, contact relationships and internal structures reveal they were once connected to the flanks of Katla and Eyjafjallajökull, and have been heavily modified by canyon incision. The lava ages reveal that canyon formation was rapid and likely faciliated by jökulhlaups associated with eruptions in a destabilising ice sheet. This is a crucial distinction for reconstructing the sequence of volcanic and glacial events, and the types of hazards that have occurred. These examples show how traditional geological mapping remains a fundamental tool for understanding volcanic landform evolution and hazard assessment.