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Title: Analysis of gas jetting and fumarole acoustics at Aso Volcano, Japan

The gas-thrust region of a large volcanic eruption column is predominately a momentum-driven, fluid flow process that perturbs the atmosphere and produces sound akin to noise from jet and rocket engines, termed “jet noise”. In this paper, we aim to enhance understanding of large-scale volcanic jets by studying an accessible, less hazardous fumarolic jet. We characterize the acoustic signature of ~ 2.5-meter wide vigorously jetting fumarole at Aso Volcano, Japan using a 5-element infrasound array located on the nearby crater. The fumarole opened on 13 July 2015 on the southwest flank of the partially collapsed pyroclastic cone within Aso Volcano's Naka-dake crater and had persistent gas jetting, which produced significant audible jet noise. The array was ~ 220 m from the fumarole and 57.6° from the vertical jet axis, a recording angle not typically feasible in volcanic environments. Array processing is performed to distinguish fumarolic jet noise from wind. Highly correlated periods are characterized by sustained, low-amplitude signal with a 7–10 Hz spectral peak. Finite difference time domain method numerical modeling suggests the influence of topography near the vent and along the propagation path significantly affects the spectral content, complicating comparisons with laboratory jet noise. The fumarolic jet has amore » low estimated Mach number (0.3 to 0.4) and measured temperature of ~ 260 °C. The Strouhal number for infrasound from volcanic jet flows and geysers is not known; thus we assume a peak Strouhal number of 0.19 based on pure-air laboratory jet experiments. This assumption leads to an estimated exit velocity of the fumarole of ~ 79 to 132 m/s. Finally, using published gas composition data from 2003 to 2009, the fumarolic vent area estimated from thermal infrared images, and estimated jet velocity, we estimate total volatile flux at ~ 160–270 kg/s (14,000–23,000 t/d).« less
Authors:
 [1] ;  [1] ;  [2] ;  [3] ;  [4]
  1. Univ. of Alaska, Fairbanks, AK (United States). Alaska Volcano Observatory. Wilson Alaska Technical Center. Geophysical Inst.
  2. Kyoto Univ., Minami-Aso (Japan). Aso Volcanological Lab. Inst. for Geothermal Sciences
  3. Univ. of California, Santa Barbara, CA (United States). Dept. of Earth Science. Earth Research Inst.
  4. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Publication Date:
Report Number(s):
LLNL-JRNL-729060
Journal ID: ISSN 0377-0273
Grant/Contract Number:
AC52-07NA27344; EAPSI-1515624; NSF-EAR-1113294
Type:
Accepted Manuscript
Journal Name:
Journal of Volcanology and Geothermal Research
Additional Journal Information:
Journal Volume: 340; Journal ID: ISSN 0377-0273
Research Org:
Univ. of Alaska, Fairbanks, AK (United States); Kyoto Univ., Minami-Aso (Japan); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org:
USDOE; Japan Society for the Promotion of Science (JSPS); National Science Foundation (NSF)
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES
OSTI Identifier:
1366922