Quantifying explosive processes of the 2022 Meradalir eruption of the Fagradalsfjall Fires, Iceland

The 2022 Meradalir eruption at Fagradalsfjall, Iceland, provided an opportunity to study mildly explosive volcanic activity of a mafic volcano using video analysis. During a field campaign from 10 to 14 August 2022, we recorded high-resolution videos of explosive activity during the cone-building phase of the eruption. We analyzed 30-min intervals on two days with differing eruptive intensities—12 August (high intensity) and 14 August (low intensity)—to quantify particle exit velocities, particle size distributions, and mass eruption rates. Our results show significant variability in eruptive intensity on short (seconds to minutes) to long (hours to days) timescales. Instantaneous mass eruption rates fluctuated between 10² and 10⁵ kg/s, with average rates decreasing from 5.5 × 10³ kg/s on 12 August to 6.7 × 10² kg/s on 14 August. Correspondingly, particle exit velocities decreased from a range of 4.7–37.7 m/s on 12 August to 3.5–27.2 m/s on 14 August. Maximum particle sizes decreased from − 12.7 Φ (6.7 m) to − 11.8 Φ (3.6 m) and median from − 10.7 Φ (1.7 m) to − 9.7 Φ (0.83). The sustained yet pulsating activity suggests a complex interplay between coupled and decoupled gas–magma flows within the conduit, characteristic of unsteady Hawaiian-style eruptions. High-resolution video analysis proved valuable in capturing fine-scale eruptive dynamics often obscured in field deposits. By providing detailed measurements of eruption source parameters, this approach enhances understanding of explosive mafic volcanism and contributes to improved hazard assessment and risk mitigation strategies in volcanic regions.