Skip to content

Seismoacoustic analysis of possible vent-drying sequence during phreatomagmatic activity on 13 July 2021 at Semisopochnoi Island, Alaska

Dan Muramatsu 1,2, John J. Lyons2, Hannah R. Dietterich2, Mie Ichihara1, Alexandra M. Iezzi3

  • Affiliations: 1Earthquake Research Institute, University of Tokyo, Japan; 2Alaska Volcano Observatory, U.S. Geological Survey, U.S.; 3Cascades Volcano Observatory, U.S. Geological Survey, U.S.

  • Presentation type: Poster

  • Presentation time: Thursday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 108

  • Programme No: 2.1.18

  • Theme 2 > Session 1

Abstract

Semisopochnoi Island in the Aleutian Arc, Alaska, erupted from 2018 to 2021. The activity occurred at the north crater of Mount Young and was characterized by phreatomagmatic eruptions with low-level ash emissions (Orr et al., 2024). Here, we focus on small amplitude (up to 0.2 Pa at 5 km from the crater) pulse-like infrasound observed on 13 July 2021. Pulse-like infrasound sometimes suggests interaction with water at the vent, for example, shallow submarine eruptions (Lyons et al., 2019). Indeed, overflight observations confirmed a small, ephemeral water lake on the crater floor in June 2021. We examined temporal variations in seismoacoustic amplitudes and spectral characteristics to discuss transitions of the source dynamics. We also picked pulse-like infrasound events by template matching and investigated their waveform, spectra, and temporal change in event number. The seismoacoustic amplitude ratio decreased, and the infrasound frequency index (Fee et al., 2020) increased with time. With this change, pulse-like infrasound activity became intermittent and finally waned. These results suggest less interaction with water due to drying out of the vent. Satellite observations also show weakened steaming from the crater and increased ground surface temperatures inside the crater from 13 to 14 in July. The pulse-like infrasound exhibits different waveform and spectrum among stations, which are stable over time at each station. These features could not be explained by source characteristics alone. In the presentation, we discuss the possibility of topographic effects based on simulations and consider the source process of pulse-like infrasound.