Seismic Tremor Reveals Changes in Episode Duration throughout the 2021 Geldingadalir Eruption, Iceland

The Geldingadalir eruption on the Reykjanes peninsula, Iceland, lasted from 19 March to 18 September 2021. While it continuously effused lava in March and April, it transitioned to an episodic pattern from 2 May onwards. We based our analysis on seismometer data from stations NUPH and LHR located 5.5 and 2 km SE of the active vent, respectively.

From 2 May to 14 June the eruption featured minute-long episodes that were classified into 6 different periods based on the duration of the tremor, the repose time, and the seismic amplitude (Eibl et al. 2022, Bulletin of Volcanology).

Here we focus on the timespan from 14 June to 18 September and define another three periods with distinct patterns: (i) For most of June the tremor was continuous and transitioned on 6 July to a period with hour long effusion followed by minute-long episodic effusion, (ii) 19 July to 3 September which featured only hour-long lava effusion episodes, and (iii) from 11 September, a 2-day-long effusion was followed by several days of minute-long episodes.

We discuss these changes in the context of acoustic data, video camera data, geomorphological changes of the crater and the shallow subsurface. Overall, we find further indications for an evolving shallow magma compartment in July.