  /.  (,**3)
 -  ++-ῌ+,+ !"# 
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Dynamics of Caldera Formation During a Large-scale Silicic Eruption
Fukashi MAENO+    

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g84;L (,)

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/ x io %j M*+<=>?"@ £N2 R¤(f*8 VEI 0

r8%45R <=>?,g8/<`/¥! 1¦?O!'%§ig +* km- ¥! 

TUVWY0_'% ¨Pu©RaQªK

" ABCDED ['L «¬7

"#$%[RyiL­+%§*~ gS!1  +®TL¯+R°r8%( VEI 2  !

:'%()(R VEI 1  1.- ka lm<=>?

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and Simkin, ,**,ῌ,**2)

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4²)W ³X/YZ_'%(f*8

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'% 7%jtTUVWY0_"++-ῌ**-,  +ῌ+ῌ+ Earthquake Research Institute, University of Tokyo,+ῌ+ῌ+, Yayoi, Bunkyo-ku, Tokyo, ++-ῌ**-,, Japan.

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Corresponding author : Fukashi Maeno
e-mail : fmaeno@eri.u-tokyo.ac.jp

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114

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@A 0BCD9E (Pyle, +323 ; Carey and Sparks,+320) F)YG DRE M?N 2 km- >|H

4  (.*  .- km)
Fig. +. Schematic chronology and variation of massdischarge rate (dark colored) of a silicic calderaforming eruption, based on evidences from somehistorical eruptions and geological records.

 ;} I "6c, 0 _  h

3/ 6M. ~ @A9:" Walker et al.
J;:t)=>KxM^/ = |(+32.)

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9E (Woods, +322) F)L<3YRO ,1

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6R! S. . T / " !   
;,/ N/ "S" , V !

;=. WS":Q

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!

9AV#> C"() X;}I"6c,Y/ . /0  ,ῌ, ῏῎῏῔῍ῌΐῐῑῒ

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Maeno and Taniguchi (,**1) . 1.- ka klUE9A

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;%& Units

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115

Fig. ,. A time-distance plot showing eruptive sequences and lithofacies variations of pyroclastic deposits during
the 1.- ka Kikai eruption (Reprinted from J. Volcanol. Geotherm. Res., +01, Maeno, F. and Taniguchi, H.,
Spatiotemporal evolution of a marine caldera-forming eruption, generating a low-aspect ratio pyroclastic ﬂow,
1.- ka, Kikai caldera, Japan : implication from near-vent eruptive deposits, page ,--, Copyright ,**1, withpermission from Elsevier).

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F[W R hijHKLMO"*'klmnoNpNf ῌ x

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+^{|6^}~ (Coherent collapse) O fῌR

3qOAB)*rs t."uv+ P

and Sparks (+32.) m6+ w  PO)&rs+O{|6 ~T (Inco-S\'O7jHO Roche and Druitt (,**+) 6

herent collapse) Long Valley  Bishop Tuff 9 +t*O)*HwhT @@IJ!" 9m6+ R  f O!"xyh

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116
- km *(Saito et al., ,**+) +,-./! +/+* kmO#  R*.,*.- +6 ""  898
#JU3

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1*3* km- *_=><' "#?! Stage ῌ]8'=><#`  898

01

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! N)

NO6:d O5& "$)u L #

3:d;M&= Stage ῌ#Pf

and Taniguchi (,**1)

 9 "
=>O Maeno

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8# + O 1.- ka xy+,-. ) : 4

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+ :;5V+

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! 898#bc0898%c#H5bd
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

-ῌ+ 

14^X6+,-.N)'.S;5$Yh]& + iQ +,-.N)'kl6%G # 2 4.

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xy W< +,-.#dz0nH =5 (Global Volcano Program ; Siebert and Simkin, ,**,ῌ

*7; (Lipman, +331) F¡ 5M&=

,**2) B# 1 U/# )Z9[#fg-!

 +,-.N)Jp; 1#{zD¢£¡#" |# )Z9[#?] `9<¤v?<¤'V5y .1= N)nH! } )#¥ ¢¦F%~p3/ (6§6#0 ¨74%G '©;$6ª¨2«"

 (Carey et al., ,**+ ; Minoura et al., ,*** ; Waythomas# (Outward-dipping reverse faults) #$] W<

and Neal, +332) #?'@<45A ! B

453"'@= <(Acocella, ,**1 ; Cole et 

al., ,**/) Roche et al. (,***) ! D¢£9<¤ 

&"'(  +22-  Krakatau) (Nomanbhoy,CD%EFG (R)and Satake, +33/)  -.0 ka Aniakchak) (Waythomas

HI4 J!#"#K#$

 *7¬'FI"@=

45 ­0'®3c5 R '<5 A ! ­ FI "#'k }#] .] 4N)fW;a,P
J (Coherent/Subcritical collapse) 'Z"a and Watts, ,**-) 6g =45
Maeno et al. (,**0) Maeno and Imamura (,**1) !
1.- ka xy+,-.

)!#+,-.W 

& 1   S7  "=#­0'¯3 5 R '25 A ! v#"#'°± ! (a) +,-.N) (Maeno et al., ,**0) 898­0="y .] 4f}  (b) )uL##E (Maeno and Imamura, ,**1) #xyN )f '²; *, P

J (Incoherent/, ~#}y6$F+m³M& BSupercritical collapse) 'Z" "#898­0´#µ-,¬#¸¹ J#:d! N)²_#!Q%,

<º/ v?¦¶·  »¼< # / /½

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Maeno and Ima-mura (,**1) Z .-IJ 1.- ka 012:;< f2ghi#$ 2:;<Y+
Fig. -. Results of numerical simulation of tsunami
generated by a caldera collapse during 1.- ka
Kikai eruption, using a model with + hour collapse-duration. (a) A snapshot of 2*-minutes
after collapse started (Reprinted from Earth,Planets and Space, /2, Maeno, F., Imamura, F.
and Taniguchi, H., Numerical simulation oftsunami generated by caldera collapse during the
1.- ka Kikai eruption, Kyushu, Japan, page+*+1, Copyright ,**0, with permission fromTERRAPUB). (b) Refraction diagram of thenegative leading wave (/ minutes interval).
Upper right ﬁgures show a simple plunger modelused.

34aj XCkl:Z8mX 0 ]5n#Dopq67Z 

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C|)$ }D<#$~#a&-ῌ, ῑῐῒῌ῍῎῏ EF#2:;<Y+Ckl:
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fCl676 -  

8mRoche and Druitt (,**+) -\.&676Hj>{~# Fig. .a Z R  f  
Ic;l NOML!5PJ/<

Coherent collapse K Z Incoherent collapse c]L&mj W*./0,& c->{%MNa&E$

M&O~#$a&

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a&Maeno et al. (,**0) Z V -)= , Xj¢Y£D Z¤ ,/* m  2** m  , X
jY+[R ,/* m  /** m X#$¥\]¦- +,?lmj ,

0 

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Y+#\. 1.- ka 012:;< TU
#$v& +33+  Pinatubo

 0./  W¡ : Mori et al., +330  +22-  Krakatau
 , +, !"  : Self ^IR Y+_# .-P

and Rampino, +32+ ; Simkin and Fiske, +32- O*R`v/d§<flC;¨©ª# Ya&+¬Ja1*­`v®¯mj Y+°,. 

#$%&'()& (Fig. -)b&jI& (Fig. .a) m]

^1 _2F;:E$Z ¢Y£D£cd

O3 aj-Y+Ckl:*&±-5u<ef+,-.&- (+*²#$D& (-

1

2-+* m /s)+* km-) iR _q!j´ \d&]_§<flC;¨ (Maeno and Imamura, ,**1)opZ iO«3 (VEI 1)  +2+/  Tamobra/!"  : Self et al., +32. 

R  f  -gh\.&Y+­³* (Fig. .b) +,-.& Tambora/ 012:;< b f [\ Incoherent collapse
#MNa&f [\k\#$Z

xROGH&lmnF;:µ¶gl­ ·o%&P G,¸¹N

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118

 Pinatubo I

 " Krakatau #/7 Incoherent collapse ,=!

STU1 # VWXY'07Z[\Q]
'XY4eD f 4ef, &d Coherent
collapse =g# lm Fig. .a n !b(g7o

 "!`# 2 stH/uRvwlm !
 $7CDf : Wilson and

Hildreth, +331#'56# 77'898:; !

< Coherent collapse ,=1 # Fig. .a, b 7CD# EFD898:GH
0J K# R L f 7MN'OPQR,J< ?
^./ " _`# abcd#'OPQR,J< ?^I /(ghijkpqr012)"!# Long Valley' Bishop Tuff I /# Stage ῌ 3* ,?
/B

! /7>,?

!STU1 " Crater Lake, Santorini, Taupo I /. 



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&'()*+,-./'012) 34'w 8O0#  (Ring-ﬁssure conduit), /898z abL (Crater Lake, Druitt
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Fig. .. (a) Relationship between caldera-collapse duration
and DRE volume erupted for six caldera-forming
eruptions. Open circles : eruptions on condition ofcoherent-collapse ; closed squares : eruptions on condition of incoherent-collapse, as indicated in ﬁgure (b).
Broken lines show ranges of uncertainty. (b) Relationship between the chamber volume fraction withdrawn
before the onset of collapse (f) and the roof aspectratio (R) for eight caldera-forming eruptions. A
boundary of coherent-incoherent collapse for ringfault dips of 1*% and 3*% is shown as shaded region,
based on Roche and Druitt (,**+). Data of DRE
volume, caldera size, magma chamber depth, andcollapse duration were referred from the followings.
Long Valley : Hildreth and Mahood (+320), Wilson
and Hildreth (+331), Wallace et al. (+333) ; Crater
Lake : Bacon (+32-), Bacon et al. (+33,) ; Kikai :Saito et al. (,**+), Maeno et al. (,**0), Maeno andTaniguchi (,**1) ; Santorini : Cottrell et al. (+333),
Sigurdsson et al. (,**0) ; Taupo : Wilson and Walker(+32/), Dunbar et al. (+323) ; Tambora : Sigurdsson
and Carey (+323), Self et al. (,**.), Thomas et al.
(,**0) ; Krakatau : Self and Rampino (+32+), Simkin
and Fiske (+32-), Mandeville et al. (+330a), Mandeville et al. (+330b) ; Pinatubo : Scott et al. (+330),
Mori et al. (+330), Pallister et al. (+330).

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