Reconstructing Surface Eruptive Sequence of 2018 Small Phreatic Eruption of Iwo-Yama Volcano, Kirishima Volcanic Complex, Japan by Infrasound Cross-correlation Analysis

Abstract

The Iwo-yama volcano of the Kirishima Volcanic Complex in Japan had a small phreatic eruption in April 2018, which formed multiple vents. The activity was recorded by two infrasound sensors and two monitoring cameras which had been installed within 1 km of the vents. This study identified infrasonic signals from the multiple vents by a cross-correlation analysis between the two infrasound sensors. The analysis successfully revealed the signals from two main eruption craters and constrained the infrasound onsets at the individual vents in the two craters. We combined the results with the images from the cameras and reconstructed the sequence of the small phreatic eruption of Iwo-yama. Notably, the intense eruption accompanying remarkable infrasound delayed several hours to the eruption onset at each of the two craters. This study provides a sequence of the activities of the multiple vents in a phreatic eruption, which will be useful for understanding the phreatic eruption mechanism and hazard assessments.

An experiment to distinguish persistent infrasounds from two fumaroles at Kirishima Iwo-Yama

“…After the phreatic eruption of Iwo-Yama on 19 April 2018, the Iwo-Yama west crater (hereafter noted as IWC) started to be active. The infrasonic activities of ISC and IWC during the phreatic eruption in April 2018 were reported by Muramatsu et al (2021). They identi ed the simultaneous two signals: the major one from ISC and the moderate one from IWC, analyzing data from two microphones (Fig.…”

“…During the experiment of this paper (19-20 October 2020), the activities of the two craters were minor but still ongoing. The main purpose of this paper is to resolve the infrasonic signals from these two craters, particularly the Y2a and Y3 vents in ISC and the W4 vent in IWC (Tajima et al 2020;Muramatsu et al 2021). Hereafter, I refer to the Y2a and Y3 vents as the ISC fumarole and the W4 vent as the IWC fumarole.…”

“…Many volcanoes have multiple vents. In Stromboli, several vents are active simultaneously (e.g., Chouet et al 1997 (Fee et al 2011) and by phreatic eruptions like the 2018 eruption of Kirishima Iwo-Yama, Japan (Muramatsu et al 2021). In history, Sakurajima is known to have erupted at two places simultaneously (Iguchi 2013).…”

Multi-parametric observations of intermittent hydrothermal discharge in West Crater of Iwo-Yama volcano, Kirishima Volcanic Complex, Japan

“…1) at 4.3 ka (Tajima et al, 2014). Iwo-Yama volcano underwent a small phreatic eruption starting at 15:39 on 19 April in Japan Standard Time (JST: UTC + 9h), forming several new craters (Tsukamoto et al, 2018;Tajima et al, 2021;Aizawa et al, 2022), including (on 20 April) a new crater to the west of Iwo-Yama (Iwo-Yama West Crater; Muramatsu et al, 2021;Fig. 1).…”

Experiment to distinguish two fumaroles consistently emanating infrasound at Kirishima Iwo-Yama

“…In some volcanoes, flank eruptions formed multiple new vents emanating infrasound, like the 2006 and 2007 eruptions of Etna, Italy (Marchetti et al 2009;Cannata et al 2009) and the 2007 eruption of Kilauea, Hawaii (Fee et al 2011). Also, multiple new vents can open in phreatic eruptions, like the 2018 eruption of Kirishima Iwo-Yama, Japan (Muramatsu et al 2021). Historically, Sakurajima has erupted simultaneously at the eastern and western flanks in 1914 (Iguchi 2013).…”