Evaluation of Total Ejected Ash in Volcanic Clouds Using Video Records: Application to the Eruption of Asama Volcano, Japan, on February 0,,**-

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1 /* (,**/) ,**-, 0,**. / -+,**/ - ++ Evaluation of Total Ejected Ash in Volcanic Clouds Using Video Records: Application to the Eruption of Asama Volcano, Japan, on February 0,,**- Akihiko TERADA, Taketo SHIMANO, Sei IIJIMA and Jun OIKAWA From February to April,**-, four small eruptions occurred in Asama volcano, central Japan. During these eruptions, movements of volcanic clouds were automatically recorded by video cameras. Based on these camera records, we studied the features of ascent processes of volcanic clouds. The volcanic cloud on 0 February,**- had mostly isolated symmetric shape and expanded linearly with height as it ascended. The squares of heights from virtual origin are proportional to time. These features are consistent with the characters of a thermal, which is well known from dimension analyses and experiments. To evaluate the masses of ejected ash we developed a simple model for volcanic clouds based on thermal assumption, and described the ascent velocity as a function of mean temperature and mass of ash in a volcanic cloud. In this model, a volcanic cloud is composed of ash and ideal gas, driven only by buoyancy. Any fall-out of particles was neglected. We compared the model with the video records of the volcanic cloud on 0 February,**-, and deduced that the volcanic cloud had less than about.** ton of ash. We found new vents at the bottom of the main crater. Volume of the most prominent vent is comparable with the ash volume derived from our model. Chemical compositions of the products resemble those of Maekake stage, the youngest stage of Asama volcano, suggesting that the ash were derived from the shallow part of the volcanic edifice. It is interpreted that the small explosion occurred at the shallow part beneath the main crater. We propose that high temperature of ejecta was responsible for the formation of unusual volcanic cloud. Key words : Asama volcano, thermal, volcanic cloud, camera recordings, mass of ash +,**-,.. +32* +31/,**- a *0* *2+* +* 2 Institute of Seismology and Volcanology, Graduate School of Science, Hokkaido University, North +* West 2, Kita-ku, Sapporo *0* *2+*, Japan. ++- **-, Earthquake Research Institute, University of Tokyo,,** Yayoi, Bunkyo-ku, Tokyo ++- **-,, Japan. -23 *++/ ++/+, Karuizawa Weather Station, Japan Meteorological Agency, ++/+, Oiwake, Karuizawa, Kitasaku, Nagano -23 *++/, Japan. Correspnding author: Akihiko Terada terada@eos.hokudai.ac.jp

2 184 Walker, +32* ; +32+ ; Hayakawa, +32/ ; Sparks, +320 Morton et al., +3/0 ; Wilson et al., +312 ; Sparks et al., +320 Briggs, +303 ; Graf et al., +333 Woods, +33- ;,**, ;,**- Wen and Rose, +33. ; +330,**-, 0,**-,, - - ASE + + Fig. + (TSB) +, + +, Fig. + WJM, TTN *3 -,**- - + Table,,*** 3 /** m, Fig km OWK TC -2+*..+ km ASE (VICTOR TK-+*1*) OWK +, ASE +0 01,. Table + OWK OWK.,-** m +,1** m OWK ASE Fig. +. Map of the area around Asama Volcano showing locations of the cameras with azimuth of fields, sampling site of ejected ash and stations of upper air observations. The arrow indicates the site from which the photograph was taken by TSB (TV. Shinshu Broadcasting Co., LTD) in Fig., (f).

3 185 Table +. Parameters of camera at OWK station. (,*** ;,**+ ;,**, ;,**- a),*** 3,**, / +*,**-,.,**-, +,***,,1** ton day,**, 2 +*,**- / 0., +* -,,**-, 0 -, + Fig.,,**-, 0,,2** m +, + -* A A (Fig., (a)) -* +,, (Fig., (b)) A +,, -* A (Fig., (c)) +, - (Fig., (d)) Fig., (f) TSB A A Fig., (c) (d) TSB, OWK ASE (Fig., (e)) A B +, +.2 Table,. The time sequence of noticeable activities of Asama volcano. The data are in part from Japan Meteorological Agency (,***;,**+;,**,;,**- a). Close circles in Fumaroic Activity denote that the monthly maximum heights were over /** m above the top of the summit. Tri-angles denote small eruptions reported by Japan Meteorological Agency. (Fig., (a)) B (Fig., (f)) A Fig. - A A Fig. - (a)-(g) +, - Hill, +23. (Fig. - (h))., Thermal Woodward, +3/3 ; Turner, +30.

4 G USVW ¹SXY ºS»Z ¼ 186 Fig.,. Photographs of the volcanic cloud on 0 Feb.,,**-. (a)-(d) A sequence of photographs taken from OWK. The times shown in the photographs are of - seconds slow relative to the Japan Standard Time. (e) The photograph taken from ASE. The time shown in the photograph is of + second fast relative to JST. (f) The photograph taken by TSB from Miyota town in Fig VD + q : 6J + ;< $d? %C : x C - 1 ' 5$d!" # $%& -ῌ,ῌ, -** m * +,Fig. + '() -./ ,**- / 8 0 9: ; <3 = > +, cm?@ A B %..ῌ+ Fig. / (a) =+ >?+ 7 :@A C$D 9: EF ;G -+* gῌm, H& t h 2 C?& X JA qi 7? i IJ%F KLMNOP,QR STU +32+/ VDEVW,,/** kgῌm- 3X;YC BZ[!\ "]'^_` a# H $b 2,% +12- &' ' 2 / 3V c =d (Fig.. (a)) e fe g!\ hd= Y i$ 3Y j(k lk!\3y )m n$ Y *o $d (Fig..(b), (c)) pq=rs t kuklm SiO, 1/ G ῌ H& -ῌ *. 8 1, +2 Yv.d-w '^}/# ~0%C, 8 0 'VD Yv 13 C =d, 2,**- b/ x C OWK Ed=! - 8 -* hi ditan,qi q*/ h* (+) 7<d= xx h* L%C e q* X JA qi =? L >Et di F H L A GSH (,**-) V # q di + 7<d IZ J #+ a 3'( >7K [ di 7X;Y& : $ ' -w x C ' yz { ' D %C t hi $d Fig. / (b) V,**- "]'^ BC7: L A q* % 3] q 4 56'. 8 1 ' 5 '7 & q # 8 Z 9 H e,,**-, 8 0 RSM #+ a LMN, 2 ª/ %C N +,*«E 3 x + ASE TSB 4 XC > 'O ^P%C! XC yz 3Q $d R> + >?7 (+) ±3,S + ²d ³ T x3 X;Y& Fµ7 q

º» H 8³ ¼ q 187 Fig. -. (a)-(g) A sequence of photographs magniﬁed around the volcanic cloud on 0 Feb.,,**-. Numbers point out the remarkable parts of volcanic cloud.

5 º» H 8³ ¼ q 187 Fig. -. (a)-(g) A sequence of photographs magniﬁed around the volcanic cloud on 0 Feb.,,**-. Numbers point out the remarkable parts of volcanic cloud. (h) Schematic of convection pattern at surface of cloud. ~.ῌ, ῐΐῌῑῒ Thermal Thermal Thermal 9 H tq % ', H% I GJ Turner, +30.K C + % ' Thermal 9 3 A A $ % I G J!" # $ %&' ( ) Scorer, +3/1 ; Saunders, +30+ ; Turner, +30.K!" *+ ',-./%01 2/ 3 C + 9 C :; %<= >=?@/ A B ^ 9 G% /% e ra g - D, -. / % co- e3f" ' 9 tq + /% ignimbrite ash cloud 9E, % FG, H% I G q 93 q/% 9 J Woods and Kienle, +33.K ;" " % 8C p q'] Scorer (+3/1) Thermal LM NOPQR S T # IUB -.T# VWK w Thermal `*., e3 f 3** hpa "1, gh!x 1., Kῌkm H% (,) 7 H% Thermal d ( YZ% [\]^D, w [ 3 9;0 M % 9 bca-.t# D, Thermal ª : ῌ ra`r +, rῒῐ ra ῑ w_c ῌ rῒ Thermal #«E % ' X % (,) "s@ ' P±79²,J P± 7 8³ µ p [ 3 9 % a!bc r ra Thermal dme3f!" gh # ῌ i jt# k % C lmn9op, %qr s' #t uvwxy z{ X% + } + nrt +`n _ ¹ r p s r gh # T (-) gh # R

6 188 Fig... Whole rock and mineral composition of the +12- and the,**- ejecta of Asama Volcano. (a) Whole rock composition. Composition ranges of the products in Maekake, Hotokeiwa and Kurofu stages are also shown (Aramaki and Takahashi, +33, ; Takahashi et al.,,**-). (b) Anorthite content of plagioclase compared with those of the +12- products (lower, middle, upper airfall pumice, lava ﬂow, and blast in ascending order). (c) Pyroxene compositions on the quadrilateral diagram of Lindsley and Anderson (+32-). Thick broken, solid, and thin broken lines are isotherms of 3**, +*** and ++**, respectively.

7 189 R,21 J K kg s -,,,,/** kg m - p p n M g, M t Mg n (.) M g M t r Fig. /. Method to estimate the locations of volcanic clouds from camera recordings. (a) Heights above sea level. (b) Horizontal locations. M. g M t - pr- r (/) r (,) r (-)-(/) z r, r, T M t r r (,) w w w obs M t T / Fig. 0 (a) A Fig. 0 (b) A B A +, + -*, pixel + sec A,/,,3-* m /1* m +* (Fig. 0 (b)) A (Fig. 0 (a)) +-* m,,3-* m A,,3-* m Fig. 0 (a) k *.00 *.,* *.,/ Scorer, +3/1 ; Woodward, +3/3 ; Turner, +30. * Virtual Origin, Scorer, +3/1,,1./ m A,. w obs m s, 0.2 m s B A 2,,2+* m./* m B B

8 , Thermal,**-, 0 Thermal Fig.,, - A Fig. /,3-* m A A Thermal Fig. 0 (c) A Z A t t * m (0) Fig. 0. Details of ascent process of volcanic clouds on 0 Feb.,,**-. (a) Correlation between top heights and maximum radius. (b) Top of height as a function of time. (c) Examples of Eq.(0) fits to the observation data with variances about m +, -/., +/, and +/.. Z is the top heights of volcanic cloud from virtual origin. See section 0 + for detail. (d) Z, as a function of time. Z t t * A m , +. A t * Thermal m +, Plume m -. A Thermal Fig. 0 (d) m +, (0) Thermal Scorer, +3/1 Fig. 0 (d),,3-* m A Thermal (Fig. 0),,2-*,,3-* m +

9 191 Woods, +322 ; Woods and Kienle, +33. A Thermal.2* m B 0, Fig. 1 (a),**-, 0 A T M t (-) (/) r a r r a Fig. 1 (a),,3** m 1* m.,,0* K Woods, * m 1** hpa -0- K Fig. 1 (a) r a r r a (,) r w obs 0 2 m s Fig. 1 (b) (,) w w obs, T, M t w obs T, M t Fig. 1 (b) T, M t w obs 0 2 m s M t -0- K -0*.-* ton * ton,2* K C C *.23 (Malkus and Scorer, +3//) +./ (Saunders, +30+) +.* +./ Scorer, +3/1 ; Turner, +30. Turner (+30.) C k k *.00 Turner +30. C C +.,, Fig. 1 (c) C *.23 +./ Fig. 1 (a) (,) w obs w M t C *.23 -+*.+* ton, C +././*.3* ton C +.* +* T A (,),**. +* m s Fig. 1 (b) M t M t B A B Thermal Thermal +. (Morton et al., +3/0) B A 2 B A.* ,,**- / 0,,

10 192 Fig. 1. Variations of parameters as a function of temperature T and mass of ash M t with radius of 1*m and height of,3** m a.s.l.. (a) Density ratio (r a-r)/r a.ineq.(,). (b) Velocity w in Eq. (,) with C of +.*. The stippled area is enclosed by uncertain of observation data. (c) Velocity w in Eq. (,) with C of *.23 and +./., 0 A +*.** ton,/** kg m - +/* m -. m, - m 0. Thermal Plume Shear A 1** m, 0, 0 Cone 0 /.** ton +32* + +** ton +31/ +32, ** + +*,*** + +* (Table,)

11 193 m 1,**-, 0 Thermal.** ton +/*m - +32* +** + +*,*** + (+32,) +32,,1,*-,+/. (+32-) ,2,-,/. Aramaki S. and Takahashi M. (+33,) Field Workshop at Asama and Kusatsu-Shirane Volcanoes, Japan. IAVCEI Commission on Explosive Volcanism, Workshop Guide Book, 0* p. Briggs, G. A. (+303) Plume rise. Critical Review Series, Rep. TID-,/*1/, At. Energy Comm. Washington, D. C., 2+ p. Graf, H. F., Herzog, M., Oberhuber, J. M. and Textor, C. (+333) E#ect of environmental conditions on volcanic plume rise. J. Geophys. Res., +*.,,.-*3,.-,*. Hayakawa, Y. (+32/) Pyroclastic geology of Towada Volcano. Bull. Earthq. Res. Inst., 0*, /*1 /3,. Hill, M. J. M. (+23.) On a spherical vortex. Philos. Trans. Roy. Soc. London, A+2/,,+-,./. (,***),*** +, +, 0* 03. (,**+),**+ +- +, 01 1/. (,**,),**, +. +, /0 0/. (,**- a),**- +/ +, (,**- b).2 -,3 --,. (,**-),**-, Lindsley, D. H. and Anderson, D. J. (+32-) A twopyroxene thermometer. J. Geophys. Res., 22, 221 3*0. Malkus, J. S. and Scorer, R. S. (+3//) The erosion of column towers. J. Meteor., +,,.- /1. Morton, B. R., Taylor, G. and Turner, J. S. (+3/0) Turbulent gravitational convection from maintained and instantaneous source. Proc. Roy. Soc., Ser. a.,,-., +,-. (,**+),*** :.0,3/ -*.. (+32+), Saunders, P. M. (+30+) An observational study of cumulus. J. Meteor., +2,./+.01. (+330) Scorer, R. S. (+3/1) Experiments of convection of isolated masses of buoyant fluid. J. Fluid. Mech.,,, /2- /3.. (+31/) +31- /* ++/ +/+. Sparks, R. S. J. (+320) The dimensions and dynamics of volcanic eruption column. Bull. Volcanol.,.2, - +/. Sparks, R. S. J., Moore, J. G. and Rice, C. J. (+320) The initial giant umbrella cloud of the May +2th, +32*, explosive eruption of Mt. St. Helens. J. Volcanol. Geotherm. Res.,,2,,/1,1.. (+32+),0 3,-. (,**-)

12 / 22. (,**,) -3 +,+ +,3. (,**-) Windows PC.2.././3. Turner, J. S. (+30.) The flow into an expanding spherical vortex. J. Fluid Mech., +2, +3/,*2. Walker, G. P. L. (+32*) The Taupo pumice: product of the most powerful known (Ultraplinian) eruption? J. Volcanol. Geotherm. Res., 2, Wen, S. and Rose. W. I. (+33.) Retrieval of size and total masses of particles in volcanic clouds using AVHRR bands. and /. J. Geophys. Res., 33, /.,+ /.-+. Wilson, L., Sparks, R. S. J., Huang, L. and Watkins, N. (+312) The control of volcanic eruption column heights by eruption energetics and dynamics. J. Geophys. Res., 2-, +2, Woods, A. W. (+322) The fluid dynamics and thermodynamic of eruption column. Bull. Volcanol. /*, Woods, A. W. (+33-) Moist convection and the injection of volcanic ash into the atmosphere. J. Geophys. Res., 32, +10, Woods, A. W. and Kienle, J. (+33.) The dynamics and thermodynamics of volcanic clouds: theory and observation from April +/ and April,+ +33* eruptions of Redoubt Volcano, Alaska. J. Volcanol. Geotherm. Res., 0,,,1-,33. Woodward, B. (+3/3) The motion in and around isolated thermals. Quart. J. Roy. Meteor. Soc., 2/, +.. +/+.

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