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 h t uStudy on Air Pressure Waves Induced by Volcanic Eruptions½Signals Recorded in Eruption Movies½
Akihiko YOKOO+    

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et al., ,**,

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Sakurajima Volcano Research Center, Disaster Prevention Research Institute, Kyoto University, Sakurajima-Yokoyamacho +1,,ῌ+3, Kagoshima 23+ῌ+.+3,

D'J[x7¼r /+, 10 +3-* @s
Japan
TEL : *33ῌ,3-ῌ,*/2
Corresponding author : Akihiko Yokooe-mail : yokoo@svo.dpri.kyoto-u.ac.jp

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44

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Fig. +. Selected snapshots of the Vulcanian eruption
on March ,-, +322, occurred at the Minamidake
summit crater of Sakurajima volcano. (a) : No
signiﬁcant clouds are seen above the crater
before the eruption. (b) and (c) : +./ s and ..1 s
after (a), respectively. Instantaneous formationand deformation of condensation clouds caused
by a rarefaction phase of strong air pressure
waves are recognized. These pictures are captured from the archived movies of Sakurajima
Volcanological Observatory.

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45

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processing applied to the movies of Aso +323
eruption (modiﬁed from Yokoo and Taniguchi,,**.). The set of darker-brighter-darker changes
in luminance (set of blue-red-blue colored clusters)
at lower center of the right image corresponds aphase change of H,O occurred within the plume,
which propagated upward with a velocity of ,1*
m/s. (b) Schematic relationship between pressurechange propagating through the plume, phasechange of H,O (shadowed and hatched areas), andthe resulting luminance change (curved arrows)that we can recognize.

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¸JZ&'8'qe V=E &'NfV5$Q/DBD Fig. . ; ºsW&`ab+= 678' :»[# ,**+ :e ¼ ? j % &' j{% W; 678'hM45>

hMZqe`½9 *.,  *.- ?@u%U9 ¢N¥¦2 xE-0% 

MQ/D:e 9 !"#$%&'()*"#+, -./0123#$%&'4547

Fig. -. Relationship among internal pressure of an explosion source (horizontal axis), mean velocity of pressure
wave at a range of ,/*ῌ0** m distance (vertical axis), and the radius of the gas pocket (r), calculated from an+D spherical explosion model (after Yokoo and Ishiahra, ,**1). The gas of the explosion source is assumed
to be composed of /** H,O vapor degassed from magma.

Fig. .. Infrasound waveforms observed by low frequency microphones deployed around Sakurajima volcano(January ,, ,**1 ; left). In zoom-up image at the beginning of the sharp onset at the stations (right), a
preceding phase (Sakai et al., ,**+ ; Yokoo et al., ,**2) associated with swelling of a lava plug at the craterbottom at the eruption is recognized. SVO, KUR and ARM are the stations’ names. This ﬁgure is modiﬁed
from Fig. , of Yokoo et al. (,**2) with permission from Springer-Verlag.

6789:3;<5= *./ >? (Fig. /) @9AB

guri et al., ,**,) 9CDEFGHI JK89 !GH

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5@YSf

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ῌ῍῏῎

48

Fig. /. Schematic sequential image for the surface phenomena at the explosive eruption of Sakurajima volcano on
January ,, ,**1 (after Fig. +, of Yokoo et al., ,**2 ; Springer-Verlag holds the copyright of this figure).

 '"#()"#*+
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AºGoto, A., Taniguchi, H., Yoshida, M., Ohba, T. andOshima, H. (,**+) E#ects of explosion energy and depth ,-./#0'1

49

to the formation of blast wave and crater : ﬁeld explosion
experiment for the understanding of volcanic explosion.
Geophys. Res. Lett., ,2, .,21ῌ.,3*.
>="#$?%@ (+33*) &' A()
,F*+ 
-./0,F  G12H*34 --B-+ +ῌ+,.
Ishihara, K. (+32/) Dynamic analysis of volcanic explosion. J. Geodyn., -, -,1ῌ-.3.
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$?%@>="#AB C (+320)&A  /    +-+ῌ+-2.
Johnson, J.B. (,**/) Source location variability and volcanic vent mapping with a small-aperture infrasoundarray at Stromboli Volcano, Italy. Bull. Volcanol., 01, +ῌ+..
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50

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