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The ,**/ Activity and Products of Nakadake Crater, Aso Volcano, Japan
Yasuo MIYABUCHI῍, Shin-ichiro IKEBE῍῍ and Kazunori WATANABE῍῍῍
Small ash emissions were frequently observed from a crater lake, in which the amount of water decreased
considerably, at Nakadake, Aso Volcano, southwestern Japan, between April and August ,**/. During thisperiod, major ash emitting events, which produced mostly white aggregated ash, occurred on April +., June +*ῌ
+,, June ,+ (.., tons) and July ,/ (+., tons). Ash emissions at the Nakadake crater in ,**/ were classiﬁed as
three types : gentle release of white aggregated ash from fumaroles inside the crater lake (e.g. daytime of April +.,June +*ῌ+, and July ,/); short (ca. ,* seconds) gas-and-ash emission through the crater lake (April +. ,* : .+);and emission of black ash from an almost dry vent (June ,+). All products from these ash emissions werecomposed of ﬁne-grained (+ mm) glass shards, crystals and lithic fragments, and contained neither lapilli nor
blocks. Although the glass shards show varying degrees of crystallization and alteration, clear glass shards, whichappear fresh and are not altered, may be juvenile materials.
Key words : ash emission, clear glass shards, crater lake, Nakadake, Aso Volcano+ῌ ῐ ῎ ῑ ῏ + }~;+eQ[0C3 !"#$< (,**/)  %& '()*+,-./012+3 ,**-  1 '+@a]58

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 ©20*ῌ*20, ª#«¬& .ῌ++ῌ+0­'®¯°±²³´µ²
Kyushu Research Center, Forestry and Forest Products Research Institute, Kurokami .ῌ++ῌ+0, Kumamoto 20*ῌ*20,, Japan.
 ©203ῌ,,-, ª#¶«X· +3-*ῌ+¸¹(z )º
Aso Volcano Museum, +3-*ῌ+ Akamizu, Aso, Kuma-

moto 203ῌ,,-,, Japan.
 ©20*ῌ2/// ª#«¬& ,ῌ.*ῌ+ª#¨»¼»*Faculty of Education, Kumamoto University, Kurokami ,ῌ.*ῌ+, Kumamoto 20*ῌ2///, Japan.
Corresponding author : Yasuo Miyabuchi
e-mail : yasuo@a#rc.go.jp

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135

Fig. +. Records of earthquakes, tremor, temperature at the southern crater wall, rainfall, surface temperature andsize of Nakadake crater lake and weight of ash deposited at the crater rim. Data except for ash weight arefrom the Japan Meteorological Agency (JMA). Incandescent phenomena of crater bottom and southerncrater wall were observed by JMA and Aso Volcano Museum personnel.

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Fig. ,. Size variations of lake of the +st crater, Nakadake Volcano, in ,**/. Photographs taken from thesouthwestern crater rim. Arrow in each photo shows the northwestern edge of the crater lake. The craterbottom is about ,** m across.

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137

Major ash emission events at Nakadake +st crater, Aso Volcano in ,**/.

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138

Fig. -. Photographs of the ,**/ ash-fall deposits from the Nakadake crater. (A) +. April daytime whiteaggregated ash adhered to a wood fence at the SW crater rim. Scale in centimeters. (B) ,/ July ,**/ whiteash deposited on a solar panel at site A. Scale in centimeters. (C) +. April ,* : .+ muddy ash deposited nearsite MB. Scale in centimeters. (D) ,+ June ,**/ black ash adhered to a plastic pole at site D (NW craterrim). Top cylinder is about +/ cm across.

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139

Fig. .. Distribution of the +. April ,**/ ash-fall deposits from the Nakadake crater. Base map is + : ,/,***-scale
topographic map of the Asosan district published by the Geographical Survey Institute. The crater camera of
the Aso Volcano Museum (AVM) was installed at the site A. AWS : Asosan Weather Station (JMA).
Longitude and latitude are shown as Tokyo Datum.

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140°±²³´µ¦¶·¸´¹¦·ºFig. /. Distribution of the ,/ July ,**/ ash from Nakadake crater. Base map is + : /*,***-scale topographic mapof the Asosan district published by the Geographical Survey Institute. Broken lines indicate isopleths (g/m,).
AVM : Aso Volcano Museum. Longitude and latitude are shown as Tokyo Datum.

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Fig. 2. Photograph of a vent formed near thenorthwestern margin of crater lake probably on
June ,+, ,**/. The photo taken from the SW
crater rim on June ,., ,**/. The vent is about+/ m across.
Fig. 1. Distribution of the ,+ June ,**/ ash fromthe Nakadake crater. Base map is a + : /*,***scale topographic map of the Asosan district
published by the Geographical Survey Institute.
Broken lines indicate isopleths (g/m,). Longitude and latitude are shown as Tokyo Datum.

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(+33/) Ash eruption of the Naka-dake crater, Aso volcano, southwestern Japan. J. Volcanol. Geotherm. Res., 00,+-1ῌ+.2.
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Walker, G.P.L. (+31-) Explosive volcanic eruptionsµa
new classiﬁcation scheme. Geologische Rundschau, 0,,.-+ῌ..0.
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terminology of pyroclastic deposits. J. Volcanol. Geotherm.
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