Insights into volcanic hazards and plume chemistry from multi-parameter observations: the eruptions of Fimmvorouhals and Eyjafjallajokull (2010) and Holuhraun (2014-2015)

The eruptions of Eyjafjallajokull volcano in 2010 (including its initial effusive phase at Fimmvorouhals and its later explosive phase from the central volcano) and Baroarbunga volcano in 2014-2015 (at Holuhraun) were widely reported. Here, we report on complementary, interdisciplinary observations made of the eruptive gases and lavas that shed light on the processes and atmospheric impacts of the eruptions, and afford an intercomparison of contrasting eruptive styles and hazards. We find that (i) consistent with other authors, there are substantial differences in the gas composition between the eruptions; namely that the deeper stored Eyjafjallajokull magmas led to greater enrichment in Cl relative to S; (ii) lava field SO2 degassing was measured to be 5-20% of the total emissions during Holuhraun, and the lava emissions were enriched in Cl at both fissure eruptions-particularly Fimmvorouhals; and (iii) BrO is produced in Icelandic plumes in spite of the low UV levels.