霧島・御鉢火山における2003年12月以降の噴気活動と明治〜大正時代の火山活動

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(3) . ,. . ,**/ 0 ,* ,**/ ++ 1 . Fumarolic Activity since December ,**- and Volcanic Activity during the Meiji and Taisho Eras (+22*ῌ+3,-) of Ohachi Volcano, Kirishima Volcano Group, Southern Kyushu, Japan Masaaki TSUTSUI῍, Katsutoshi TOMITA῍῍,῍῍῍ and Tetsuo KOBAYASHI῍῍ A new fumarolic activity at Ohachi Volcano of Kirishima Volcano Group started on December +-, ,**- after about 2* years of inactivity. Two small fumarolic vents, T2 and T3, were formed on the slope within the Ohachi crater. Ejected materials were mainly fine-grained mud (altered ash), that were distributed within the southwestern sector of the crater. Small accessory lapilli, which were coated by mud, were scattered within ,* meters of T2 vent. No essential material was found. Alunite, kaolinite, +* -halloysite were present as clay minerals. The volume of ejected material was very small, probably less than +* m-. At the time of this writing, the fumarolic activity at Ohachi crater is still going on. To understand the present activity, we investigated old documents of historic eruptions of this volcano, in particular those that occurred during the Meiji and Taisho eras (+22*ῌ+3,-), to determine the mode of eruptions during that time. The first stage of the eruption started with a fumarolic activity, which became more active. Then magmatic activities continued for about .* years. The early phase of magmatic activities was characterized by vulcanian eruptions generating a large volume of ash, while the latter phase was characterized by sporadic but strong vulcanian explosions accompanied by ejection of volcanic bombs and blocks. At present, it would be di$cult to judge whether the fumarolic activity will become more active, and proceed to magmatic stage. However, the results of our investigation of historical eruptions would still be useful to predict the nature of future eruption of this volcano. Key words : Ohachi Volcano, Kirishima Volcano Group, fumarolic vent, documents of eruption, Meiji and Taisho eras. +ῌ ῐ ῎ ῑ ῏. +1 + @23_Tàb c&3d Ief,=I. +/(,**-) +, +, +/ !"# *+,-. / )1. $%&'(!"#) &.02345,62378. ghAij4DEkl78mno)LMNp GPS 4D E'qrT78stuv,F@?Fmwx=>. 9: , ;<,=> ?@ 1 ABC+@23789. F?yI +- 4z{MI|'4}Ux=F?y. :4DEF +, ++ +. G4.0HIJKFLMN. .0~3mwE UM m*E,. EOPQ .* G@23RST +1 , + UM. n!I, 24,WN=n!UMn. VWN=STOPQ@X8YZ[\,]@^ ; . <I4,6=> ?mn<@. --+ῌ20-2 W=-

(4) ,ῌ,1,ῌ ¡¢£¤¥¦§¨©ª§« ¬®¯§ª° DIA Consultant Co., Ltd., Sabo and Disaster Prevention Center, ,ῌ,1,ῌ- Yoshino-cho, Kita-ku, Saitama --+ῌ20-2, Japan.. 23*ῌ**0/ $%&±² +ῌ,+ῌ-/ $%&³´´µ'¶·¸¹´¹ Earth and Environmental Sciences, Faculty of Science,. Kagoshima University, +ῌ,+ῌ-/ Korimoto, Kagoshima 23*ῌ**0/, Japan.. |º 23*ῌ*2*, $%&»¼ 1ῌ+. Present : 1ῌ+. Shimizu-cho, Kagoshima 23*ῌ*2*,, Japan.. =U 1 I M. Corresponding author : Masaaki Tsutsui e-mail : M. Tsutsui@diaconsult. co. jp.

(5) f+)gh¼i¢Vjk. 476. Fig. +. Location of fumarolic vents and distribution of ejected materials. a) Solid circles indicate new fumarolic vents (T2 and T3). b) Solid and dashed lines indicate the limit of distribution of ejected materials. Dotted part and gray area show the distribution of muddy ash and moist area, respectively. Maps are based on + : +*,*** volcanic map of “Kirishimayama” published by the Geographical Survey Institute. Contour interval is / meters..

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