Volume, effusion rates and lava hazards of the 2021, 2022 and 2023 Reykjanes fires: Lessons learned from near real-time photogrammetric monitoring

At the time of writing (January 9, 2024) four basaltic effusive eruptions have taken place on the Reykjanes Peninsula, SW Iceland since 2021. This includes three eruptions within the Fagradalsfjall volcanic system (March 19–September 18, 2021; August 3–21, 2022 and July 10–August 5, 2023) and one eruption within the Svartsengi volcanic system (December 18–21, 2023). Near real-time photogrammetric monitoring was performed during all four eruptions and the results yielded eruption parameters such as lava volumes, thicknesses, and effusion rates, which are key for hazard assessments.   The 6-month long 2021 Fagradalsfjall eruption produced a bulk lava volume of 150 ± 3 × 106 m3 and the mean output rate (MOR) of 9.5 ± 0.2 m3/s with a fairly constant time-averaged discharge rate ranging between 1–8 m3/s in March–April and increasing to 9–13 m3/s in May–September. The 18 day long eruption in 2022 had a bulk volume of 11 ± 0.4 × 106 m3 with a MOR of ~7 m3/s, starting with a fairly high initial effusion (exceeding 30 m3/s a few hours from the eruption start) followed by an exponential declining phase of waning effusion. The 2023 eruption in the Fagradalsfjall volcanic system lasted 26 days and the effusion rate followed an exponential declining trend like the 2022 eruption with similar MOR of ~7 m3/s and a bulk volume of ~15 × 106 m3. The initial effusion rates observed in these three eruptions were comparable to the calculated inflow rates into the dikes prior to eruption onset, suggesting that the magnitude of effusion can be estimated prior to eruption onset. Furthermore, first order assessments of eruption durations were feasible from the exponentially declining effusion rate curves in 2022 and 2023. The eruption in the Svartsengi volcanic system yielded a bulk volume of ~11 × 106 m3 with a MOR of ~50 m3/s. The initial effusion rate was likely to have exceeded 300 m3/s and declined rapidly ending after 2.5 days. Here we discuss the different trends in the effusion rate curves for these four eruptions, what insight they provide regarding plumbing system dynamics, and their implications concerning associated lava hazards.