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Quantitative Analysis of Geothermal Events at the Yoshioka Hot Spring,
Aso Volcano, in ,**0Akihiko TERADA, Yasuaki SUDO,, Shin YOSHIKAWA and Hiroyuki INOUENew geothermal activities occurred at the Yoshioka hot spring of Aso Volcano from June ,**0. We founda new fumarole named “a-” in a new steaming ground called “A”. The maximum temperature of the steams fromit exceeded 32 degrees centigrade. In August, a vigorous fumarole “b+” and new steaming grounds “B” and “C”
were formed. Vapor ﬂuxes from these fumaroles obviously increased in October, and the daily mean heat andwater discharge rates of the fumarole “b+” were estimated approximately to be +/ῌ-* MW and 0.1ῌ+- kg/s (/2*ῌ+,+** ton/day), respectively. Especially, “b+” ejected over +* tons of ash on +0 October. After November,**0, the temperatures of the steaming grounds fell, and heat and the water discharge rates of the fumarole “b+”decreased to be about ..0 MW and ,.* kg/s (+1* ton/day), respectively. The average heat discharge rate from “b+” is more than tens times higher than that of existing natural fumaroles in the Yoshioka, Yunotani, Jigoku andTarutama hot springs in the usual period. We infer that the vigorous geothermal events were caused by thetemporal increase of vapor ﬂux from the deep geothermal hot water.
Key words : Yoshioka hot spring, Aso volcano, fumarole, steaming ground+  ,**+ ; opq ,***C 0.'()'(*/ km !"#$%& 0** m !"#$%+*,'(.%.0&'( rstu567vw) gxyz{NO%|}*!"#$%i3  ~ ,**011>  +.0 km !"#$%-/ 12'(334! AQ89.ghEX'(M*_3 *

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!k=94 +*,'(X12 -/'(<[&'() +30* !WNO.(<'(1AA *lFmNO9=% je n&iO!<O.11>389* ¡ ¢)T £203ῌ+.*. ¤!¥¦§¨) /,2*©ª«¬«¬­ ¬ ¡®*¯1°¬ ¡±² ¡³´µ¶
Aso Volcanological Laboratory, Kyoto University, /,2*
Kawayo, Minami-Aso, Kumamoto 203ῌ+.*. Japan.
 c¯ ·¸+¹,-º£203ῌ,,-, ¤!¥»¼g +3-*ῌ+Aso Volcano Museum, +3-*ῌ+, Akamizu, Aso, Kumamoto 203ῌ,,-, Japan.
Corresponding author : Akihiko Terada
e-mail : terada@aso.vgs.kyoto-u.ac.jp

¶N·S<¸TU1<¹ º<N»¼V336

Fig. +. (a) Locality of Yoshioka hot spring at Aso volcano in central Kyusyu, Japan, and neighboring geothermalareas of Yunotani, Jigoku and Tarutama. Closed square indicates the Aso Volcanological Laboratory (AVL)
where the high sensitive camera is installed. (b) Localities of steaming ground where existing plants
completely died (gray areas), fumaroles (solid triangles) and a hot water pool (gray square). An open squareindicates the hot water source of the Yoshioka hot spring. Closed circles indicate the locations where the ashof +0 October ,**0 were sampled, and numerals represent the ash weights in g/m,. A black solid line andbroken lines represent vehicle-accessible roads and vehicle-inaccessible path, respectively.

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Fig. ,. (a) The photograph of vent “b+” with the small tu#-cone taken at . October ,**0 and (b) vent “b+”,taken just after the ash ejection events on +0 October ,**0. The three trees marked as +, , and - in (a) are,respectively, identical to the trees marked as +, , and - in (b). (c) A photograph of ash cloud emitted fromvent “b+” on ,+ October ,**0, taken from /** m south of AVL. (d) An aerial infrared photograph of
Yoshioka taken on +3 January ,**1 by the local government of Kumamoto Prefecture.

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338

Fig. -. Time-series variation of heat and water discharge rates from b+ (b,) (closed circles).
Open circles represent daily mean rates.

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Table +. Heat discharge rates from Yoshioka (this study) and neighboring geothermal areas of Yunotani, Jigoku and Tarutama(after Yuhara and Ushijima, +32*).

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x,'ayoDzῌ ῑ ῐ ῍Anderson, G.P., Berk, A., Acharya, P.K., Matthew, M.W.,
Bernstein, L.S., Chetwynd, J.H., Dothe, H., AdlerGolden, S.M., Ratkowski, A. J., Felde, G.W., Gardner,J.A., Hoke, M.L., Richtsmeier, S.C., Pukall, B., Mello J.
and Jeong, L.S. (,***) MODTRAN. : radiative transfer
modeling for remote sensing, In Algorithms for multispectral, hyperspectral, and ultraspectral imagery VI, Proceedings of SPIE, .*.3, +10ῌ+2-.
Hedenquis, J.W. and Henry, R.W. (+32/) Hydrothermal
eruption in the Waiotapu geothermal system, New Zealand : their origin, associated breccias and relation toprecious metal mineralization. Econ. Geol., 2*, 0.*ῌ+002.
pq{r (+30/) stMWHJK| &LH +0 /+ῌ/3.
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 (+312) 0p)P+H,O Plume rise 0  ,-+2-ῌ+31.
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jkl`$bYc (,***) E5%&'()+|}+W  ./ ,/ῌ-,.
Nakamura, T., Sugimoto, N., Tsuda, T., Abo, M., Hashimoto T. and Terada, A. (,**0) Observation of water
vapor with a portable Raman Lidar  Continuous
monitoring and ﬁled experiment over the forest and atthe volcano. Reviewed and Revised Papers, ,-rd International Laser Radar Conference ,**0, Part ll, 231ῌ3**.
EB (+32.) E5'()&ZI +311ῌ+32,
 E50]hZI  , / R 23ῌ32.
Sekioka, M. and Yuhara, K. (+31.) Heat ﬂux estimation ingeothermal areas based on the heat balance of the groundsurface. J. Geophys. Res., 13, +., ,*/-ῌ,*/2.
Sekioka, M. (+32-) Proposal of a convenient version of theheat balance technique estimating heat ﬂux on geothermal and volcanic ﬁelds by means of infrared remotesensing. Memoirs of the National Defense Academy Japan,,-, 3/ῌ+*-.
DP$,]h (+33/) E5(* vRz No. -2 +/*2p.
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B¦¡ (,**.) ¢ A §PlumeRise £@¨¤z)¥©¦ FYG%H
MWHJKR 01 -,1ῌ--/.
Terada, A., Hashimoto, T,. Kagiyama, T. and Sasaki H.
(,**1) Precise remote-monitoring technique of water
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