Volcanic eruption styles in changing environments at Katla and Eyjafjallajökull volcanoes, south Iceland

It has been established through geochemical and geophysical models that, in Iceland, unloading of the Pleistocene ice sheet at the end of the last glacial period resulted in a peak in magma production and volcanic activity. Environmental differences are recorded in volcanic products, but mostly between discrete monogenetic glaciovolcanoes and postglacial lava flows. In areas of frequent and persistent activity, the way in which physical eruption styles evolved with changing ice thickness and glacial hydrology has received less attention. We examine a sequence of volcanic products exposed in the dissected flanks of Katla and Eyjafjallajökull, two ice-capped volcanoes that have been active beneath fluctuating glacial cover from the Pleistocene to present day. We use traditional geological mapping combined with photogrammetry surveys, major element geochemistry, paleomagnetic techniques and radiometric dating to determine how volcanic eruption processes have evolved with the eruptive environment throughout this period.

 

A wide diversity in the physical volcanology of deposits and major element geochemistry indicates a rich eruptive history alongside changes in glacial configuration and meltwater availability in this area. Volcanic products include pillow lavas, pillow breccias, tuff sheets 50-100 m thick, tuff mountains containing crystal-rich intrusions, lobate lava, entablature lava and compound pahoehoe lava. Evidence for glaciofluvial processes, including debris flow deposits, diamictite, and possible flood-formed canyons demonstrate additional processes that have shaped this landscape. Recognition of volcanic, constructive processes vs remobilisation and erosive processes is vital for accurately determining the distribution and source of products, particularly since edifice morphology is commonly used to characterise glaciovolcanoes.

 

Reliable dating from independent sources is necessary to determine the chronology of events and the timescale of volcano evolution. Identification of the Þórsmörk ignimbrite within the stratigraphy indicates a timescale spanning > 55 ka as well as a period of ice-free conditions. Additional age constraints from deposits in the area include a ⁴⁰Ar/³⁹Ar date from basaltic lava of < 20 ka and the identification of reworked Vedde-like pumice (< 12 ka). The sequence is capped by the 2010 Fimmvörðuháls lava. We are testing the use of paleomagnetic dating to refine the dates that have higher uncertainty and to provide additional ages for intercalated lavas that cannot be dated by radiometric isotope systems.

 

Given the ongoing changes in global glacier extent, it is critical to understand how glaciated volcanoes will behave physically. We are building an age-constrained eruptive history and record of eruptive environment from one of the most volcanically productive areas of Iceland to inform our understanding of the influence a changing environment has on volcanism.