The sequence of the 2017–2018 eruptions and seismo-acoustic activity at Kirishima volcano group

Abstract

Kirishima volcano consists of more than 20 eruptive centers. Among them, Shinmoe-dake had magmatic eruptions in October 2017 and March 2018. Subsequently, another active cone, Iwo-yama, had phreatic eruptions in April 2018. These events were unique in that the 2018 eruption was the first effusion-dominated eruption of Shinmoe-dake and the first simultaneous activity of two cones of the Kirishima volcanic group ever documented. We report the detailed sequence of the events by combining areal photos, satellite images, and seismo-acoustic data analyses with the other published information. The seismo-acoustic data clarify the eruption onset and the transitions of the behaviors in three stages for each of the 2017 and 2018 eruptions. For both eruptions, we present regularly repeated tremors or ’drumbeat’ earthquakes in the second stage, which interpret as gas separation from magma, leading to the ash-poor plume in the 2017 eruption or the effusive eruption in the 2018 event. We also propose that the 2017 and 2018 eruptions of Shinmoe-dake and the 2018 eruption of Iwo-yama are sequential events linked by the degassing of magma beneath Shinmoe-dake. An eruption like the 2017–2018 eruptions of Shinmoe-dake would leave few geological records and could be captured only by modern techniques. Although Shinmoe-dake has been believed to be an example of less-frequent eruptions, effusive eruptions like the 2018 case might have occurred more frequently in the past , but the following eruptions had obscured their records. The timelines summarized in this study will be useful in future studies of Kirishima volcanoes and world equivalences. Graphical Abstract

Precursory crater contraction associated with the 2017 eruption of Shinmoe-dake volcano (Japan) detected by PALSAR-2 and Sentinel-1 InSAR

“…Furthermore, no signi cant increase in volcanic earthquakes was identi ed for several months before the 2017 eruption (Yamada et al 2019). Ichihara et al (2023a) suggested that the increasing magnitude of the seismic background noise since early 2017 is due to the degassing from the magma within the conduit. Therefore, we have identi ed no robust supporting evidence for the material withdrawn preceding the 2017 eruption.…”

“…In contrast, the GNSS baselines turned to extension after the early stage of the eruption (Yamada et al 2019). The lava was ejected from the vent from the east side of the crater after the ash emission phase and covered the pre-existing lava dome, which was formed during the 2011 eruption (Additional File 1: Figure S1; Ichihara et al 2023a).…”

“…During the observation period of this study, Iwo-yama volcano, located 5 km to the northwest of Shinmoe-dake volcano, also experienced a steam blowout from the vent in April 2017 and a phreatic eruption in April 2018 (Narita et al 2020;Tajima et al 2020). These eruptions are related to the overpressure of the hydrothermal system beneath Shinmoe-dake and Iwo-yama volcanoes across the Kirishima volcanic complex (Narita et al 2020;Ichihara et al 2023a).…”

“…level(Ichihara et al 2023a). The geometry of the pipe-like deformation source has been employed to explain tilt changes and displacements associated with volcanic eruptions(Genco & Ripepe, 2010; Ripepe et al, 2021; Saballos et al, 2014).…”