Lava Lake Spattering Drives Seismic Tremor During the Geldingadalir 2021 Eruption, Iceland

Abstract Volcanic eruptions generate a continuous ground motion that is commonly referred to as tremor. Although tremor is used worldwide for real‐time monitoring of volcanoes, the mechanisms involved are generally poorly understood. Here, we study the episodic effusion during 2021 Geldingadalir eruption. We use photogrammetric data and videos acquired by drones hovering over the active lava lake on 8 June 2021, and compare them with volcanic tremor recorded by a seismometer at 1.8 km distance from the vent. This allows us to investigate the timing of tremor, eruption, and the rise and falls of the lava lake. We observe an episodic seismic tremor lasting about 5 min, followed by over 7‐min‐long repose times. A closer study of one effusion episode reveals that within these 12 min the lava lake rises and falls by 24.6 0.6 m. The rise time is about 10 min, while the lake level drops within 2 min, contrasting with the tremor observations. By combining tremor and video analysis, we show that the tremor amplitude is not related to the lake level, but peaks when the bubble bursting and spattering in the lava lake is at its maximum. We therefore suggest that the tremor is closely related to the bubble bursting activity and is thus indicative of near‐surface processes during an eruption. This study provides insights into tremor generation associated with the Geldingadalir eruption, leading to a conceptual model to assess its implications for the characterization and interpretation of dynamic lava lake evolution.