三宅島2000年火山灰粒子の特徴と本質物の特定

概要

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Volcanic activity at the summit of the Miyakejima volcano, Japan has been ejecting volcanic ash without conspicuous magmatic event such as lava fountaining since 8 July, 2000. Ashes erupted on 8, 14 July, 10, 13, 14, 18, 29 August, and 9, 11, 12, 21-22 September, 2000 show that they are polymictic. Backscattered Electron Images (BEIs) of screened ash particles 0.25-0.15 mm across disclose a group of particles called Myk2000g-2 to be identified as essential material. The Myk2000g-2 particles are fresh and similar in texture and constitutes to the cauliflower-shaped volcanic bombs ejected at the most prominent event on 18 August, 2000. They constitute the majority in fresh ashes, especially in those of large eruptions. We conclude that some of the series of eruptions, at least those ashes erupted on July 14, August 10, 13, and 18, are phreatomagmatic. Based on our characterization, further geochemical and petrological studies are going on.
特定非営利活動法人日本火山学会の論文
2002-03-05