Seismic, acoustic, and visual observations of ash-rich plume events during the Geldingadalir eruption, Iceland

In 2021, an eruption began in the Geldingadalir valley in southwest Iceland, lasting six months. This eruption exhibited a constantly changing eruption dynamic recorded as volcanic tremor of varying duration and amplitude. In May 2021 a transition occurred, from continuous tremor in the early phase of the eruption, to minute-long tremor episodes. Throughout this period the vent featured an active lava lake. On 2 July, the lava lake drained and several ash-rich plumes rose from the crater between 3:00 and 5:00 am. The plumes were accompanied by several transient seismic and acoustic signals. Following these events, the volcanic tremor shifted from minute-long to hour-long episodes. Here, we use a multidisciplinary approach combining video footage with seismic and acoustic data to investigate the source process and its potential link to the observed tremor transition. We performed a source inversion of the seismically strongest event using seismometers within 6-8 km distance from the active crater. We tested different source models and compared the simulated waveforms to those that were observed to constrain the source. In addition, we calculated the Volcanic Acoustic–Seismic Ratio (VASR) using seismic and acoustic tremor recordings. The VASR reveals a decrease over time. The local webcam footage provides an insight into surface processes including inner crater collapses preceding several ash-rich plumes. This observation suggests a potential link between shallow collapses, plume generation and seismic and acoustic signals. These collapses may have modified the shallow conduit and caused the transition from minute-long to hour-long episodes.