Local infrasound monitoring of lava eruptions at Nyiragongo volcano (D.R. Congo) using urban and near-source stations

During eruptions, volcanoes produce air-pressure waves inaudible for the human ear called infrasound, which are very helpful for detecting early signs of magma at the surface. Compared to violent ash-rich explosions, recording more discrete atmospheric disturbances from effusive eruptions remains a practical challenge depending on the distance to the source. In contrast with powerful volcanic explosions, close-range deployment of instruments around the active vent (for instance < 15 km) is generally needed for continuously monitoring long-living lava effusion or degassing as observed at open-vent volcanoes, such as Kīlauea (Hawaii) or Nyiragongo (D.R. Congo). Nyiragongo, towering above a 1-million urban area, hosted the world’s largest lava lake up to 2021, which was drained during the third known flank eruption of this volcano on 22 May 2021. We analyzed local infrasonic records between January 2018 and April 2022. A persistent acoustic signature from the crater before and after the flank eruption was detected up to the volcano observatory facilities in Goma city center about 17 km from its crater. We also explore these records for characterizing the temporal and spatial evolution of the flank eruption on May 22, 2021. These ~4-year results show remarkable local recordings of eruptive infrasound from near-source and city-based stations and have significant implication for optimizing future monitoring efforts in a harsh field environment. Remote observations from space (ground deformation, gas emissions, thermal anomalies) can also provide essential information about the eruptive state of a volcano and were jointly analysed with infrasound records. The multidisciplinary approach with infrasound and space-based observations of the intra-crater activity leads to a comprehensive picture of Nyiragongo’s eruptive activity during this period.