Linking volcanic tremor amplitude to drone records of lava lake level changes during the 2021 Geldingadalir eruption, Iceland

On March 19, 2021, an effusive eruption lasting for six months began in the Geldingadalir valley on the Reykjanes peninsula, in the southwest of Iceland. This eruption was characterised by episodic lava effusion from 2 May to 18 September and changing eruptive behaviour. Here, we analyse five of such effusion episodes of 8 June 2021 by using drone video data acquired over the active crater lake together with volcanic tremors that were recorded by a seismometer located at 5.5 km distance from the active vent. We are thus able to study each of the five episodes in terms of tremor amplitude evolution and its frequency spectrum, and compare it with the timing, height and dynamics of the lava lake, its bubbling and crater overflow. We observe a slow rise of the lava lake by 25.1 to 26.2 metres within 6.15 ± 2.35 minutes, followed by a rapid fall of the lava lake surface to its previous level within 1.6 ± 0.12 minutes. In contrast, the quiescence period in the tremor lasts ~ 10.12 ± 0.68 minutes followed by another 2.55 ± 0.2 minutes of tremor. Thus, the duration of tremor generation is shorter than the time required for the lava lake to reach its maximum height. Furthermore, the tremor amplitude reaches its maximum after the lava lake has started to sink. We discuss the volcanic tremor generation in relation to lava lake elevation and related processes.