火山灰から見た2008年の桜島昭和火口の再活動過程

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We describe reactivation processes of the Showa volcanic vent at Sakura jima volcano, Kagoshima, Japan. The Showa volcanic vent is located on the east side hill of Minami-dake summit vent at Sakura jima volcano. While Minami-dake summit vent has been active intermittently for the past five decades, the Showa volcanic vent was dormant for an interval of about 58 years until 4 June 2005. Ash samples analyzed were obtained from volcanic explosions of both Showa and Minamidake summit vents from 1981 to 2009. The analyses and observations on the volcanic ash samples include (1) amount of water soluble chlorine and sulfur adsorbed on volcanic ash particles, (2) mineral identification using X-ray diffraction patterns, (3) color measurement, (4) simplified particle size analysis of volcanic ash, (5) micrographic observations of ash particles using an optical binocular microscope and a SEM, and (6) chemical analysis of minerals and glasses in ash particles with an EPMA. (1) and (2) suggested that the proportion altered/non-altered blocky particles in volcanic ash from the Showa volcanic vent was decreased from 2008 to 2009. (2), (3), and (5) indicated a gradual increase in temperature of the vent with time. We regard (1)-(5) features as results of a gradual reactivation process of the Showa volcanic vent since 4 June 2005 by May 2008.
2010-02-27