Volcanic emissions of environmentally reactive trace elements at the Fagradalsfjall 2021-2023 eruptions, Iceland

Effusive basaltic eruptions are one of the most significant natural sources of trace elements to the atmosphere. Trace elements are transferred from deep within the Earth to the surface, where they can serve as essential nutrients for life or as harmful pollutants. Understanding the emission sources, downwind transport processes, and depositional mechanisms of volcanic trace elements is therefore vital for constraining and mitigating against potential environmental and health hazards, as well as for gaining deeper insight into fundamental volcanic and bio-geochemical processes.

This thesis explores the behaviour of volcanic trace elements at the Fagradalsfjall 2021-2023 eruptions on the Reykjanes Peninsula in Iceland. Cutting-edge UAV (Uncrewed Aerial Vehicle) sampling was used to collect in-situ samples of the at-vent and downwind volcanic plume, including major gases and particulate matter, which were analysed for an array of trace elements. Sampling above lava flows at discrete distances from the vent revealed that the composition of lava flow outgassing evolves downflow as the lava cools and ages, driven by fractional degassing of S, Cl, and F species, respectively. This has implications for understanding population exposure downflow and for re-evaluating total trace element degassing inventories for effusive eruptions. In-situ sampling of the downwind volcanic plume also demonstrated heterogeneous deposition of volatile trace elements depending on background meteorological conditions. The resulting mechanistic framework can be applied to interpreting ice core records of volcanic aerosols and raises the possibility of seasonally dependent delivery of trace elements to surface reservoirs. Mixing between volcanic and wildfire emissions during a compound volcanic-wildfire event was also explored, where scavenging and agglomeration processes generated “hybrid” particulate matter with altered physicochemical properties. Interactions between emissions therefore provide alternative depositional and transport pathways for trace elements compared to a standalone volcanic eruption. Continued global warming and growing urbanisation make compound volcanic air pollution events a clear direction for future work.