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Master of Science (MS)
DeBari, Susan M., 1962-
Dziak, Robert P.
West Mata is a submarine volcano in the northeast Lau Basin. Hydroacoustic data from a 5-month period provide insight into the nature of eruptive behavior at this volcano. Previous studies have used acoustic data to estimate the eruption velocity at subaerial volcanoes (Woulff and McGetchin, 1976; Vergniolle et al., 2004; Vergniolle and Caplan- Auerbach, 2004, 2006; Caplan-Auerbach et al., 2010). In this study, the hydroacoustic data from West Mata are used to calculate eruption velocities and volumes (both lava and gas) for explosions during the 5-month hydrophone deployment. The method used in this study, developed by Vergniolle and Caplan-Auerbach (2006), was found to be most successful when events were hand-picked for a portion of the data during processing, and then extrapolated for explosions from the entire data set. However, there are two factors that contribute to an underestimation of the total eruptive volume. Only one signal type (explosions, representing discrete gas bubble bursts at the volcanic vent) could be used for estimating the eruptive velocities and volumes at West Mata, due to interference resulting from signal reflections. Another issue for accurately estimating cumulative eruptive volume resulted from raypaths reflecting on the sea surface, and arriving at the hydrophones 20 – 80 ms after the direct wave. This also caused hydroacoustic signals to overlap, limiting the calculations to the first 20 ms instead of the entire waveform.
Eruptive velocities for vent explosions recorded at West Mata’s four hydrophones were found to range from 2.4 – 24.8 m/s. Eruptive flux ranged from 1.9 – 9.7 m3/s for each event. The volumes erupted per explosion ranged from 0.03 – 0.15 m3. Yearly eruption rates were calculated to be 5.7 x 103 – 9.1 x 104 m3/yr for both gas and lava. However, if only lava is used (assumed to contain 25% vesicularity), then the yearly eruptive rate at West Mata is estimated to be 1.9 x 103 – 5.6 x 104 m3/yr. These results were compared to estimates determined from video imagery at West Mata and long-term bathymetric surveys at West Mata and another submarine volcano, NW Rota-1. Velocities estimated from video imagery compare well with velocities estimated from hydroacoustic signals in this study, ranging from 0.2 – 5.2 m/s, compared to a range of 1.0 – 31 m/s using hydroacoustic signals. Volumes estimated from hydroacoustic date are up to three orders of magnitude lower than those derived from bathymetric surveys at West Mata. Given that the results from this study are expected to be an underestimate of eruptive volume, these estimates are considered to be reasonable, suggesting that the hydroacoustic method of estimating eruptive flux is also viable for the submarine environment. It is recommended that future studies deploy hydrophone stations in the near-field (< 5 km) to reduce the effects of sea surface reflections, which would ensure the most accurate results.
Western Washington University
West Mata Volcano (South Pacfic Ocean)
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Mack, Chelsea J. (Chelsea Joy), "Quantifying submarine eruptive flux from interpretation of hydroacoustic signals, West Mata Volcano, Lau Basin" (2014). WWU Masters Thesis Collection. 378.