Lava flows from eruptions on Reykjanes peninsula in Iceland started burning urban structures on 14 January 2024. Volcanic emissions and urban fires, respectively, are known to contain many chemical compounds that are hazardous to health. While these distinct end member compositions are better known, lava-urban interface (LUI) emissions have not been studied. Key hypotheses: LUI emissions have unique chemistry due to the combination of volcanic and human-made compounds. The interaction impacts the combustion process, the composition of the emissions released into the environment, and the chemical reaction pathways in the atmospheric plume. The LUI interaction may also be modifying the degassing processes in the lava, and release of magmatic volatiles. Eruptions at the urban interface lead to higher human exposures than remote eruptions because of their proximity to communities; and small eruptions can cause severe air pollution in populated areas. Lava encounters urban space quasi-periodically, for example Kilauea, Hawaii 2018, Cumbre Vieja, La Palma 2021 and now on Reykjanes, Iceland (2024 - present). Despite the recognition of the importance of characterising chemistry of air pollution sources, LUI emissions remain unstudied, likely due to a combination of challenging sampling conditions, and the unpredictability and the short duration of each eruptive episode. Globally, the number of people exposed to LUI emissions is growing because of building expansion into previously uninhabited areas. For instance, the homes burned by lava in Iceland in January 2024 were newbuilds, the construction of which began when the volcanic system was already in unrest. We will use the ongoing activity in Iceland as a natural laboratory for the first ever characterisation of LUI emission chemistry at-source and in the near-field (1-40 km distance).

The ongoing eruption at Fagradalsfjall in Iceland presents an outstanding and rare opportunity to observe and model the behaviour of dense volcanic gases. Sulphur Dioxide (SO2) is the principal emission from lava-rich eruptions such as at Fagradalsfjall. With more than double the molecular weight of air, this is prone to exhibiting dense gas dispersion characteristics such as settling, with the potential to significantly affect the dispersion over scales of hundreds of kilometers. This can lead to enhanced concentrations at low levels with consequences for air quality and human health. This project aims to (a) collect a surface air quality and meteorological dataset and (b) produce a modelling framework capable of simulating dense gas and validate it against (a). Such a framework does not exist at present. This is a significant, time-limited and accessible eruption event which, if responded to now, can lead to major advances in both scientific understandings and in the management of future, possibly larger, eruptions from which there is a serious gas hazard. (A) We will enhance existing air quality observations in the vicinity of Fagradalsfjall, creating a network to provide a comprehensive assessment of dense volcanic gas dispersion on a scale of 50-100 km. This unique dataset will provide the first independent verification for a full meteorological prediction model with dense gas capability coupled with surface heating (see below). (B) Recent model development work has demonstrated effective volcanic gas dispersion predictions using an adapted version of the NCAR Weather Research and Forecasting (WRF) model. This system was used to successfully interpret aircraft measurements of CO2 dispersion from the (subglacial) Katla volcano in Iceland and to explain quantitatively, for the first time, the dense gas CO2 behaviour which led to the Lake Nyos disaster in 1986 that saw dense CO2 pooling and draining down valleys, causing ~1700 deaths. Neither of these applications considered (or required) a heated surface. However, the Fagradalsfjall eruption is now in a phase where lava fountains have been reported, and so the effect of surface heating will need to be considered in any modelling, to include the complex interactions and feedbacks between a dense gas, a heated surface, and the underlying meteorology. The model, after development and verification, will be available in the future as an operational hazard prediction system and and could lead to significant improvements in the UK national capability to respond to dense gas releases. This includes anthropogenic releases, for example industrial accidents and fires.