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Continuous sampling and investigation of volcanic ash to monitor eruption sequence at andesitic volcanoes in Japan

Taketo Shimano 1, Nanami Homma1, Atsushi Yasuda2, Masato Iguchi3,4, Michihiko Nakamura5

  • Affiliations: 1Graduate school of Science and Engineering, Kagoshima University; 2Earthquake Research Institute, University of Tokyo; 3Disaster Prevention Research Institute, Kyoto University; 4Kagoshima City Office, 5Graduate school of Science, Tohoku University

  • Presentation type: Poster

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

  • Poster Board Number: 227

  • Programme No: 1.6.7

  • Theme 1 > Session 6

Abstract

We carried out time-series sampling of ash fall at Sakurajima, Shinmoe-dake, and Suwanosejima volcano, southern Japan, to understand the mechanism of eruption sequence. At Sakurajima volcano, we collected daily samples for more than 10 years of vulcanian activity by an automatic apparatus. We also constructed systematics of volcanic ash by optical spectroscopy to elucidate how the mixtures of ash particles with different characteristics are generated and to compare with other observations such as seismicity, ground deformation, etc. Ash samples consist of several types of particles with different sizes that make a quasi-linear trend in color space, and drastic changes in eruption sequence have been recognized by monitoring these data variation, trend, and endmembers. At Shinmoe-dake, Kirishima volcano, we succeeded in collecting time-series samples during the waxing period of 2017-2018 eruption. Some spectroscopic methods are executed for different size fractions to elucidate that color of bulk ash samples changed systematically with eruption transitions whereas fine and coarse fractions have different colors that changed with time. These changes are interpreted to reflect appearance/disappearance of different particle types that changed with eruption style. Visible microspectroscopy was useful in quantifying color of single ash particles to classify objectively and to derive the componentry automatically. At Suwanosejima volcano, we carried out componentry and glass chemical analyses of two hundred years of ash layers in time-series in detail and found that the activation of eruptions is often preceded by mafic injections of short interval followed by crystallization at shallow depths resulting in alternative phenomena of eruptions.