Abstract
Volcanic landscapes, edifice morphologies, and environmental conditions influence the styles of eruptions at ice-capped and subglacial volcanoes, making glaciovolcanic products useful in reconstructing past environments and glacier characteristics. We use geological mapping and physical volcanology to determine eruption styles and emplacement processes of three glaciovolcanic formations on the flanks of the ice capped Katla volcano. We determine the volume of ice melted and thickness and extent of the glacier at each eruption, and we integrate these results with 40Ar/39Ar dating of lava to provide onshore constraints on the size of the glacier in the late Pleistocene.
One sequence, situated between Katla and Eyjafjallajokull volcanoes, is basaltic. Deposits of subaqueous pyroclastic currents adjoin a pile of pillow lavas and pillow breccia, indicating eruptions into a meltwater lake. Overlying lobate entablature-jointed to massive pahoehoe lava record a drying-up sequence as the formation emerged above lake level approximately 790 m above present-day sea level. Meltwater accumulation was facilitated by the setting between two volcanoes at the ancient confluence of three major glaciers. The interaction between glaciers and the subglacial topography directly influenced eruption style and volcanic products.
Two rhyolitic formations on the northwestern and eastern flanks of Katla comprise silicic fragmental material intruded or capped, respectively, by ice-confined rhyolitic lava. The glacier had a minimum surface elevation above present-day sea level of 1160 m in the northwest and 900 m in the east, at the times of eruption. These formations show no evidence for meltwater accumulation; meltwater probably drained from the eruption site as it was formed, indicating a leaky glacier and/or that glacial hydrology was controlled by subglacial topography rather than ice thickness.
Understanding the interplay among volcanic eruption styles, glacial hydrology, glacial characteristics and edifice morphology is becoming increasingly important as the climate and glacial-edifice configurations change at ice capped volcanoes.