ῒΐ  /-  (,**2)
 0  +1+῍+3+ ῕ ῔ +3,0
(   ,**2 H . I +0 *JK ,**2 H ++ I +* *JBRestudy of Stratigraphy and Paleomagnetic Characteristics of Taisho Lahar Deposit Associatedwith the +3,0 Eruption on Tokachidake Volcano, Central Hokkaido, Japan
Shimpei UESAWA῍
On May ,.th +3,0, the eruption of Tokachidake volcano, in central Hokkaido, e$ciently melted the snow packon the hill slope, triggering the Taisho lahar which killed +.. people in the towns of Kamifurano and Biei. A
geological survey and paleomagnetic and granumetric studies were conducted on the northwestern slope ofTokachidake volcano to reconstruct the sequence of the +3,0 eruption and decipher the triggering mechanism for
the Taisho lahar. The Taisho lahar deposits in the proximal area of the volcano are divided into ﬁve distinct units(unit L+, L,, and A through C, from oldest to youngest). Unit L+ is an older lahar deposit that underlies the+3,0 deposits. The +3,0 sequence consists of debris avalanche deposits (unit A and C), a laminated sandy debris
ﬂow deposit (unit B), and a lahar deposit including scoria clasts (unit L,). Each unit contains hydrothermallyaltered rocks and clay material with more than / wt.ῌ fragments smaller than , mm in diameter. The progressive
thermal demagnetization experiments show that the natural remanent magnetization (NRM) of all samples in unit
A, B and C have a stable single or multi-component magnetization. The emplacement temperatures are estimatedto be normal temperatures to 0,* for unit A, -** to ./* for unit B, and normal temperature to /** for unit
C. On the basis of geological and paleomagnetic data and old documents, a sequence for the eruption and themechanism of formation and emplacement of the Taisho lahar can be reconstructed. The ﬁrst eruption at +, :++ May ,.th triggered a small lahar (unit L,). Collapse of central crater at +0 : +1 May ,.th +3,0 then resulted
in a debris avalanche containing highly altered hydrothermal rocks with hot temperatures ranging from -** to0,* (unit A). The debris avalanche ﬂowed down the slope of the volcano, bulldozing and trapping snow.
Immediately following the collapse, a hot (approximately .**) hydrothermal surge (unit B) melted snow andtransformed into a lahar causing signiﬁcant damage and deaths in the towns downstream. Just after thegeneration of the lahar, another collapse occurred at the crater causing another debris avalanche (unit C).
Key words : debris avalanche, emplacement temperature, lahar, remanent magnetization, Tokachidake volcano+320 LMNO  PQRS T0 URVWX+ῌ ῐ ῎ ῑ ῏YZX[ RSU\]^S_ Z`ab

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



hall, +323)

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67 *0*῍*2+* 89:;&; +* <= 2 >?
;@A,-,-.B-.CDE3-FG
Graduate School of integrated Basic Siences, Nihon
University, -῍,/῍.*, Sakura-jyosui, Setagaya-ku, Tokyo+/0῍2//*, Japan.

^nomxjyz{ |xi }lV (Major and New-

(Present address Department of Natural History Sciences, Graduate School of Science, Hokkaido University, N+* W2, Kita-ku, Sapporo *0*῍*2+*)
Corresponding author : Shimpei Uesawa
e-mail : s-uesawa@mail.sci.hokudai.ac.jp



172

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+3,0

Fig. +. Distribution of the +3,0 deposit of Tokachidake volcano (A), and locality map of study area (B).
Numerals show locality numbers. Open square is position that the Motoyama O$ce (MO) was situated.
Shadow area is lahar ﬂowed area. Map A is modiﬁed after Tada and Tsuya (+3,1).

173

%

174
+3,0  3 3

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8X9':;<9' G87&A NOG(Katsui et al, +33*) YZ & [\ +30,  STU,/  ,0 #V Cm]=;< &A^ >9? +31+ M 7&@#ABCD_^AB)?

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  .,0** m

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(+3,1) eh

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(+3,0) 01 (+3,0)  ++ 2  (+3,0) ++ 2 ,* ' 7<Z >9? +31+-ῌ-+3,0  /,.  , 

+0 2 +1 }¹ p , mN Ke&&

p , mN

9dLLe  +0 2 +1

Cm 

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k»#Z4+R1¼½

 GH>9 !"# +3,0 $"%&'()*+,-./012345
Table +.

175

Correlations of stratigraphy for Cm deposit between this study and previous studies.

6 (+31+) 7 Cm /8 9:6 (,***a) 7 Cm+Cm,
;<=> (+3,1) 7?@A'/8B()
(Table +)  C*D

 L+, L,, A, B, C / E DF GHI1J *, D KLM

 L+, A, B, C NCO/P .

7QRS B  !TUV>WXYZ +,,1* m 1J+3 L+, A, B, C /[\]^ _ L , `ab

 L , 7QRS A

c (Fig. ,) CdE ]8

B()HI1J ,* ,+ ;<=> (+3,1) 7@e
A'/8BfgDh iK j**+ kl[\m4n]op_.ῌ, Cm ῔ΐ῕ῌῑῒ
.ῌ,ῌ+ ῐ῏῍῎ L+

 L+ YZ +,+**+,/** m qr1st
8 uv"w[]xy Hz{|D}~ 
~()Dh (Fig. ,) 5O %*
YZ +,.** m WXD , m Dh ~8B'~MC 8 
Cuv"w[/G8%[]4n G[
#[Dh

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B GMHC[¨4nxKuv"w[/©Dh *xm

 A
 A



ªS



.ῌ,ῌ, ῐ῏῍῎ L,

 L , 1J +3 WXYZ  +,,1* m  +,-**
Fig. ,. Schematic illustrations showing distribution andcross sections of Cm deposit. On the distribution
map, solid lines are *./ m isopach lines of Cm
deposit and broken lines are *.+ m isopach line ofunit L+. On the c-d cross section diagram of Cm
deposit, central crater lava surface is normalized *m.

m, « +* m fg

_*« m ¬­{|}~ ~()Dh ~~D®¯
~8B­|[];O

 L,



  + m im°±²P7¢8ONC B³´µ¶·¸¹]º ¶·¸¹3»¶M¼~8.ῌ,ῌ- ῐ῏῍῎ A

 A YZ 2/*+,/** m_½{|¬­{|}~ ~()Dh %*

176






.m

   (Fig. -a) 

!"#$%& '()*+,--./012 34*56 7  7
-*%8

7

9:;<=>8/

 ;<= ?@ABC DEFGDEFH
I. JK+ LMNO A P.Q7 .R=S$T
UNV=WXYZV[NV (Ui, +32-) \]Z^N_`abZV (Ui, +32/) 8c*+d5 - m  (Fig.
.a) \ efg=h8K+8ij*(Fig. .b) k-\l-m*Pn o*+pqr+* cm stTUNV8]NuvZVw1o$
(Fig. .d) xy *+ z +,..* m

7 pq /+* cm,z# +-* cm ]({w!|8}$ (Fig. /) ]({w!|7~B  p LMNO

$ ]({  7_O6f

* o+ xy */ z +,,,* m

7 LMNO

L+ CLMNO A P]Nuwf 

0 8J LMNO A 7z 2/* m xy ,*,+ 8

(Fig. - a) B[Zp 3 7 LMNO
A7

LMNO B C  *+.*

LMNO A 7!TUNVC*%LMNO B o$% (Fig. 0) LMNO A P

.QT

UNV7Cq d5q7xy *+7 , m, xy ,+7 /* cm C#0=

.ῌ,ῌ. ῏῎ῌ῍ B

LMNO B 7z 2/* m  +,/** m "*
l,-,-mB  J #
7 

7

%0= d+ m C0 $xy *+

7+*,* cm C

D¡[¢£8}$ (Fig. /) o+LMNO A C¤&'()*+,--./012 #7 

7 9:¥¦8Pf *   
C'§1(¨8©ª*¥¦8«0= (Fig. 0) L
MNO B 7z 2/* m xy ,* ,+ 8
(Fig. -a) B[Z\LMNO A p 3 7 LMNO B 7
LMNO A C  *+.* LMNO B
Fig. -. Isopach maps of Taisho lahar of unit A,B
and C. Numerals show the thickness of thedeposit in meter. Broken lines show distribution limit of Cm deposit. C represents central
crater.

7LMNO A !TUNV¬  (Fig.
0)  d ­*+pq *./  (*.1/ mm)+  (*./mm) ®P7 ;<=¯[° °±²³8 -ῌ ´

µijB 3°±²³%*%¶)? @A*+C3· ;<=^a[aFGDEFDEF
D¸F8}$+ °±²³ *¹BD¸Fº# *.+ mm 

=K%½8J

7 »

*+ ¼



 +3,0  !"#

177

Fig. .. Debris avalanche facies of Unit A and C. (a) A large debris avalanche block with -m in diameter inunit A. (b) A shearing joints block in unit A. (c) A percussion mark block in unit C. (d) Patchwork
structure in unit A.

$%&'() (Fig. 0) *+,-. ,*.ῌ,ῌ/  C/012 C -34 +,***+,/** m 56,7)

cm 89:;<= . + m >?="@ABCDE

FGE:H7)I J, KLJ=M) .

:HN OP2JBQJ

-V?W , =- , m = ?X'*,YXZ(S[\X'B]^_N=`aAbcBdE$RE, JNSTU

.:ef) (Fig. -c) -OP2gh]LQJ

ij:kKC Pm : lmn ,***b:N op JNSFGEREjij[:q(Fig. 0) $r%=s) Cm tuvwxP-

ykK ^_N>?-

.$ -* cm, OP2JL=z{U()|JB=

-FGERE,

JN}Z)$ ~-`aAbcB$qZ bcB

v$%&'() z{-op JNSDE:* 7) [=MRE[$<=M) W-S ",?=-x1OxSj

`aA$yLJ=v$%&'()^X':kK (Fig. .c) S *+/012 A /012 B

lmn (,***a)  Cm-s ,7)'()

: ]^¡ *=-/012 A, B ¢£7) Cm
    ¤¥¦]34 +,,** m ]?  =/ Cm - /012 C §?+, +322ῌ23 ¨vwxP/ῌ+ Cm 

$%&'()
.ῌ- Cm  

¶ZW ,, 34 /1* m · =-[+¸A"@X' Cm tuvwxP,7)

Cm  ©ª{:'X,7)S&«¬­®¯x°x ±²³´:Z} ©²:µS ²,- Cm ->* 2 mm >* QJ

]¹ºNS 3 »:¼NS ¹ºNS»- ½

1234

178

Fig. /.

Photographs and sketch of unit A, B and C at Loc. *+ (+,..* m in altitude).

567'8"9:;<=<5 >! ?@AB

C *0

#55N0 . #O@O< .  *.*0,/ mm 

PQ  RSGTU" (Fig. 2) IJKL L, #V DE1F.G1H#IJKL A #M%9

 # . 1 *.*0,/ mm 1 #WXY

Z +./ , *+,&G[\+]&^( 9<> . #_` a (,**/) #bcde

0. wt.ῌ fU  0 wt.ῌ ge IJKL A

h+i+jk lmc&ne>oph+i+Vqr#VZ ,  (*.,/ mm)  3  (*.**, mm) *+s tuv SALD--,**S =wq&xy> z,&{[\+]&^( (Fig. 1)  |} +,..* m  . 

F. +,+** m ~("#e +/ wt.ῌ F. 1 wt.ῌ  !" 2  ##$%&'(g("" (Fig. 2)

A##IJKL L+ #VZ9 -* wt.ῌ & !  . wt.ῌ &U KA##)*+,-!./0 *./  (+.. mm) +./  (*.-/

 , wt. ῌ ge IJKL B #VZ +./mm) F*+,&{[\+]&^( (Fig. 1) 

 (*.-/ mm), PQ*+,&{[#9 Fig. 0.

 +3,0  !"179Geological columnar sections of Cm deposit. Site of each column is shown in Figure +.

# $%& +,..* m '( *+ )*

+,-. / 012 345678/9 :;*<=>?@ AB * . wt.ῌ CDE> F-GH

IJ4  KJ4  LMJ4  0N OJ4 

P-QE

VWXY ZJ4  [\ - /9 AB R-STU# (Fig. 2) &+,*** m '( *0 )* ]^_` B *Fa]^_]^_` L+ ( *, *IJ4 > -.ῌ KJ4` A 6bcdefg/2<=>h@D# (Fig. 2) ]> -.ῌ 0N -,ῌ ?cD# 0NPi 3+ῌ *O^_` C  j *,  (. mm)+  (, mm) +J4 kl9 m9 OJ4 Pi +1ῌ *noDpq

 (*./ mm), -rst6RiuvHDwsxHyD

zq{ |}~{ }~{ }{\6 ]^_# AB` L , *IJ4

* ,  1 wt. ῌ CDE (Fig. 1) ( *0 )*  > 01 wt.ῌ STU#/ῌ,> -+ῌ KJ4> /3ῌ 0N>++ῌ ) 0N 2 >VWXY)

Cm 

# ]^_`

A ]^_` B *IJ4 > ,0.1ῌ KJ4 > .3

Cm :; 6F)l9

01vol.ῌ 0N> ,2ῌ )Hy--*( *+ ( *0 ( ,* ( ,,  Cm y :;;*/DE (Fig. 2)  Cm ?c/9 3 -E2 6l9zs  *IJ4

g> /0ῌ  ]¢£E (Fig. 2) ]*./  (*.1/ mm)+  (*./ mm)  36 /9 D¡^_` A ]^_` B  -*ῌ -]^_` A ( *+ - +  (2*./ mm) ^_` C *LMJ4 > 12ῌ IJ4 > +3ῌ KJ

3-E2 + ¤:; 6¥¢9¦§ ¨D

4 > -ῌ 0N> +ῌ ) #©G*ª«y¬DHl9 0¦) -**­%

3®6R *  (+ mm)+  (*./ mm)  j>1

0 Cm :; 6¯U#°8/ :;±®g6²³

0ῌ+ 

/9 ´8-µ/2*´8±®> -**Cm 

¶·-D#?P
6¸¹º»¼ ¸¹½

180



Fig. 2. Downstream changes of white lithic content(a), sorting (b), and clay content (c) of unit A
and B deposits and distal lahar deposit originatedfrom Cm deposit from central crater. The
degree of sorting is calculated by the method ofFriedman (+312).

! "#$%

&'()

 *+

,

Cm -./ /, 0120 +/ 345678 / 0 20+/ 9:;<= /1 9> ?*Cm -./

@ABC AC ,DE*FGHIJK LMN
OPN,@ABC A  C

Q2R*+9() 20 *+ N,@ABC A 3STUV /*  ,** mm MW

X8Y%Z[ +- \ ]^&'_`abc

d%Z[ - \9 @ABC B 3ST, @ABC B
eST -/ cm f 1 +*+, cm gf hi&'Ljkj 0 l<= +, \_`abcd%Z[9 @ABC C 3ST,MW X8Y%Z[ +, \9 20 *0 N, @ABC A @AB

C B NMWX8Y9 0 \l <= +, 9 M 8Y%Z[,%Z[mnBop qr +333

s)  tZ _`abcdN

,uvwv (,**.) Zp s)  xy z{|}Fig. 1. Grain size histograms of Cm deposit.
Samples of unit L+ was taken at Loc. ++, unit
A, B and C were at Loc. *+, unit L, was at
Loc. +3.

~!Z[~$%, 

=  SMD-22 $%hi+*.+*++ Am, 9 
0ῌ, ῑῌῒῐ῎῏῍
Cm -./Z[~9$%|}  //  

9

  ,  DEM- +3,0 ῏ !"#$

181

Fig. 3. Stereographic projections of the result of progressive thermal demagnetization experiments showing thedirections of single-component, low-temperature component, and high-temperature component in the layer ofunit A, B and C deposits and central crater lava. Solid and open circles are vectors projected onto lower andupper hemisphere, respectively. Triangles and Open triangles are matrix specimens. Square and oval in
low-temperature component indicate mean direction and 3/ῌ conﬁdence limit.

20*, %ῌ&' ()!*+, mo-./01234/5

6789:6;<=' (Table ,) )!>?, / @ῑAB @ῑCDE+0FGH!IJK, / nT LM;<N - @ῑO -**-/* PQ;RSTUV%WX , @H mo-./,(012Y!῎OZ[\]^H'_

ῑ O .** `a78bDcd;ef`TUV%WX

gh%ῒij012jῒX @ῑk(l,mno;pῒ0,* ;)!X'X' g@ῑqrsῐ!] (NRM) %CDX'l ptXu v῏w x *+ yz +,./* m 0FGH{"N;|}()!~% /* +** ,** -** -/* .** A 12X'./* /** /.* /2* 0,* 0/* 02*  +- |};=- @ῑO%

' TF ='!]/, 3./ K 

%' +, @ ῑ 0&u t:6% ῍ ,*** %='3 ¡0¢£^H :6O¤z¥¦O§^H!]:E¨b$%©ª^H'_

x +/ ;X' / @ῑN«¬­

@ῑ 3 @ῑ@ῑ@ῑ . @ῑO%WX'

¤2%WAT`=' %WX' . @ῑ,z¥0%3 ¡0¢£^H¤¤2%

&u|}()!®%=' ¯Ba@ῑ,&°B

WA° ±¥%9²0¢£^H³´µ1&¤¶·DX'%WX ¯Ba:6%3

¤2%WX' (Fig. 3a, Table ,) ¯±¥¸¨ ¡0 ^H / x¶¤¤2%WX'

!]:6,¹º »!IOW^:60Q& Aa0(Fig. 3c) t¸¨!]:6,¹º »!IW^:)!>?, @ῑ¼½ ++ @ῑO 0,*0/* ;R

182

ῌ῏῍῎

Fig. +*. Representative diagram of the result of progressive demagnetization analysis. Results of progressivealternating ﬁeld demagnetization (PAFD) and progressive thermal demagnetization (PThD) are shown inorthogonal demagnetization diagrams. Intensity decay curves are on the right side of the each diagram.
Solid and open circles represent projection on the horizontal and north-south vertical plane, respectively. (a)Example of single component. (b) Example of multi-component. (C) Example of aluminum-pipe sample.
RT : room temperature.

 !" +3,0 #!$%&'()*+ ,-./0 123

183

Table ,. Mean paleomagnetic data for Cm deposits and central crater lava (CL). N : number of specimens,
Dm : Declination of between-site mean direction, Im : inclination of between-site mean direction, k :precision parameter, a3/ : radius of 3/ῌ conﬁdence cone, R : Length of the vector.

456789 (Fig. +*a) ,: /.* ;< 0,* =JK;56789L CL MN -

>OP /**0/* =Y456789L B ]D^_L +**+cA]D^_L .

>G@A8 +:de=HI@AQ`ab>RI@A+ @A feLghi

j89L kcA]D^_L .
 + >G@A89

>RI@A:de=HI@AQ+ @AfeLghij89L w@A8xyzos/ bcA kcA/Bo> ?@A B >C/CD89EF G@A HI@
AQBRI@AQBSTUV W89E5;X

L (Fig. 3b) Z[\> ,:JK;56789 : ,/* .** =Y456789 ,,:/2*0,* =Y456789L
0ῌ- 

lZmno]XPp<qLghij:eLg@A=rs;t; CL u3vg (VRM){|8}~sLo Zmn8X

L Zo> -1

 `a

HI@AQ=C/CXLW89 RI@AQ=C/

 A



 C



CD:;XL (Fig. 3a) HI@AQ g

W

/

 A

 B



>  ]`obcA kcA/BoSTUV: .



+

*0

F

 B

*+

A

[\> 1

  DEM-20*+C 8 mn8XL 

: /** {=Y456789 +: ,**C=JK;56789L¡ 0,* =Y456789

F

 +-

bcA kc

9W/W=rXL (Fig. 3a, Table ,) Z
:JK;567[\8 (Fig. +* c) ,

MN +

*+

8 Z

Z> vg (NRM) 8L¡ / +* ,*-* .* /* 0* 1* 2* 3* +** mT++ =XLZmn8XL¢£ q<

L C ]D^_L  `a 1*+:?@A8 /

:G@A89L q< W@/ mT ]D$

8B

>OP

=rs/8}~

L CL lZmno]D , @A¤b ghij

A8xyz bos/ ?@:~<qL oP> Fq @ABeL

A B >C/CD89EF G@A B >HI@Aghij:~<qL (Fig. +*)  /;< Q=¥¦§C/CXLW89 RI@AQ=C/q< ghij>lvg (TRM) /P¨pE

CXLW89E5;XL HI@AQ

W>¥¦§]C/CD89L (Fig. 3a, Table ,) Z[\>2

: /2*0,* {=Y456789 (Fig.

+*b) -

: .**/2* =$¯67 +:²R +,+** m]D^_L  `a /= / mT

=Z¬sde

5ghij8­® :~<qL (Fig. +*b)
0ῌ.





lZmn °¡|l«o3±) N,**-** =Y456789LkQ

qLghij=rs/:}~EqL (Fig. +*) 5© Aª « 1

*0 o©³s

 A>?@A +>G@8}~sL 8XL o>lZ8XL //



`a

*0

+,

8

A89L xyz b=> ?@A  Bartington  MS,B-Susceptibility

B >C/CD89EF G@A HI@AQB RI

meter 8 L SI ?´= w= +@AQBSTUV W@A89E5;XL Z

[\>OPoP /2*0,* =Y456

789L
+ B => 0« /:?@A

:G@A89L xyz b=µ ¶

o /

·8¸¹L

lZmn °¡K|l«o©³s3±)
N8}~sL 8XL ºjz»¼>:½5L

*0

'

184

(
Deviation) ) +/* +, -. +333

/ 01 / mT  12,3 
1456789:  (VRM) 1; < );  6789=,>5?@==, A ,**+
B'CD5EF1G,HIJ8KC%& L
KM NOKC EPQR

Table - LS

 5K EPQ:TUL%&,=VW!$ 

1 %& (DRM)

VL$ :?/ X ) -/*Y1Z[5\] S Q)^_ @CD5Q!L:`abcR) -,*

1,d,d"Pe#1fg
ij< )Sk#$

$%h (Pyrrhotite)!l ,**. m, Q

NP:no5!pqr&N1 @$!6789:
Fig. ++. Variation diagrams showing change in magnetic
susceptibility during PThD. All specimens are taken
at Loc. *0.

A!pqr&NQ='(L)s1tuv_*w
x+y S @= ! &NLi/$ $%h:,z-5"PLC{>|#$*1:5?=VW!
$ !pqr&N: / Q}>))s S, @$ +, QL~?> tu +** =L.

!QR: /2* 0,* 1 

{  t= QL~?>.L/

6789:tuv_*wx+y S,/=/3*0{":5 !1  !LNC?@=

Q!Li/$  h "P:|>?5?=1

,=VW!$ #$ (Fig. ++)

Cm %&

: 

0ῌ/ ! !pqr&N: /2* 0,* B'1
D8 A :'2 *3 *+ 1
{NQ +- QD 3 Q=EP =Q"P#=

Q - Q)R1,@= S, NQ . Q

 4 L +,N"P) -/*0,* 1,=VW!$  / 

51, /L6, E)P5

S,7L[; *no } L:no1

2 *3 *0 1: 0 Q}>)R1,=VW!$  8 B :'2 *3 *+ 1: EPQ; )7)89,>? *¡"P s2E

3 Q)?¢$* -**./* 1,=VW!$2£:f)89,>? *!"P } L;8<¤-P5R= ¥~$m{=VW!$ L"P)>,?*

"P E} s2/ 2 *3 *0 1: 0 Q}>)R1

¦2); * = / ~L6,

,=VW!$  8 C :'2 *3 *+ 1





{N+§ ., QD

no ) / Q  ) - Q ¡"P ) ++ Q !"P ) +3 Q "P ) . Q1;{D) ,  ¥~*: "+, Q! 1 Q)R1,=VW!$ / Q) -/*/** 1,=VW!$ ¨ (,**-) :©?@ª (+3,1) *P«LE¬?
>­*®-¯A

{ B°±=¨ (,**-)P ) + Q !"P ) 0 Q ¡"P ) - Q<¤1 no :   < ¤ -" P,Q  )©

!+,Q *3 *0 HQ=DszE{,Q)$³$´µ(Table -)
0ῌ0 Cm = *3 *+ HQ=¨ (,**-) C²

Q L: ,     !"#$Cm %& =VW!$  *3 *+¥~Q ) F ¶^_, $!:-/*0,* 1, )s*:}>R1

R:A (,**+) L·{ 5K  !

,=VW!$



/2* B ' = ,  ¨  (,**-) = ¸ 5 Kirchvink(+32*) LC ¹G ?> X )Hº,>-

B' »Z¼½ (MAD ; Maximum Angular!+ @: C ²(,**-) )DszE: , ,@=:*3 *0 =sI  R  s + ¨ *~Q)^_=

 , , *3 *0 JR

+3,0

185



186













,,*.,* $&'() (,**-) &*+(  !"#$%
,-&./0,(12 (,**+)

1 
1ῌ+



34 ,., ka 356 

7+38 4 !"Cm 

9#$4 %, 4 %: ;< )BC(>D+E, *FD+E, +,&./ &?@A A, >?@A B, >?@A C &*+ -G3H

Cm &'(=8>?@A L +'(IJ,&./FK$+,;< LM0NO&./0,(PQRQ12 S132S1T4

D+E,&'($U(&./0,( >?@A A -4VWX5YZ67[LMJ& B&'

8 '(\]^9C:  I&I&4 !"8 (20;,(_< +3,0 =+ `>?+$+

@ ab2 4 2ABcd,C,ID6J&20 +3,0 =e+,

E2,f,&./0,( d .g[>&'&'($U(&./0,( FGHIJ?@A A KLU(M */ $  >?@A

; 3** m 20FGHNd$'(O ,** =hL+ &>?@A A ij"$kP(Q"l[ mR ,***b   >?@A L, &./ 2

J, Cno(STpD+E, CB

U1qVZ6+ -G3H0&WrPQRQ1

csE2@+, J@>?@A A &>LX2 S132S1T47[LM J,01?@A L+ ij,tkP(Qupv>?@A L , A  C 

1&wxY-0,+6 dy&;$( >?@A L+ & Ta-a &Z[\z{| ]^$U >?@A A}a_vy20~Q

(I Z>?@A A &Z6+t

`<$U(J&B1 za=8 1 `<$

 '&'(Y-0,+6J&20 >?@A L+ &6(J&20 b & `<$Up&./h 1.\c$U(&;, de .&0,( d z>?@A L+  cw$6(J'($U(fg;6& CUp"$ 9p; ,* m z>?@A A, C R@ +h 

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187

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188

ῌ῏῍῎

Fig. +,. Schematic illustrations showing the formation process of the Cm deposit. (a) Central crater before the+3,0 eruption. (b) First collapse of central crater at +0 : +1 May ,. +3,0 (unit A). (c) Large explosion andhydrothermal surge melting snow and generation of lahar at downstream (unit B). (d) Second collapse ofcentral crater just after the formation of unit B (unit C) and magmatic eruption producing volcanic bombs atthe central crater.

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189

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MENAOPQBR CSTCUV W?BXD
?-8ῌ ῏ ῎ ῍
Aramaki, S. and Akimoto, S. (+3/1) Temperature estimation of pyroclastic deposit by natural remnent magnetism. Amer. J. Sci., ,//, 0+3ῌ0,1.
Capra, L. and Macias, J.L. (,**,) The cohesive Naranjo
debris-ﬂow derived from the Pleistocene debris-avalanche deposit of Nevado de Colima Volcano (Mexico).
J. Volcanol. Geotherm. Res., ++1, ,+-ῌ,-/.
Crandell, D.R. (+31+) Postglacial lahars from Mount
Rainier Volcano, Washington. U.S. Geol. Surv. Prof. Pap.,
011, 1/p.
Friedman, G.M. and Sanders, J.E. (+312) Principles ofsedimentology. New York : Wiley, 13,p.
YZ]k[lmN\: (,**+) ,n]^_]^.`@opab,  , ,ka +, ,  .0 .
+21ῌ,*-.
Yqcderkfgh:Ni j (,**1) J^Kes, ka,  - -** *t+,l,  /, / ,/-ῌ,1+.
tcNyuv (+323) ka 0,ῌ+ ,z, {+x@ +322 *ka, +,y} z~DPKg789 ,-<:;2 (No.
0-++/*/.) 756:;@L 5:; (+) :; No. B-0--/ 9 :   01ῌ12.
Hoblitt, R.P. and Kellogg, K.S. (+313) Emplacement temperatures of unsorted and unstratifaied deposits of volcanic rock debris as determined by paleomagnetic techniques. Geol. Soc. Am. Bull., 3*, 0--ῌ0.,.
c   x\ Y i (+333) ]^_@opka z~ 
8 Qg -2 :;gn: %xqs (+31+) ka, L+,lDPK5 J^
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 p. -0.
n: (+32+) ²r l +Q_
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P9+,56v»:;
9 : ½¼ ½  3ῌ+-.

        (+320) !"#$%&'  ()  )*+,
 +32/ *+,456789:; ,-<:;2 (No. 0**,**/*) 345656:;756:;@L No. B-0*-1.
EY:FZGH[\]I (+323) J^K_`a, LM L 2 p.
Katsui, Y., Kawachi, S., Kondo, Y., Ikeda, Y., Nakagawa,
M., Gotoh, Y. and Yamagishi, H. (+33*) The +322ῌ+323
Explosive Eruption of Tokatidake, Central Hokkaido, Its
Sequence and Mode. Bull. Volcanol. Soc. Japan., -/, +++ῌ+,3.
Kirschvink, J.L. (+32*) The least-squares line and plane
and the analysis of paleomagnetic data. Geophys. J. Roy.
Astron. Soc., 0,, 033ῌ1+3.
NbcO (+333) dPe f QRg ,.2p.
STh (,***) PeM UiM ,*** * *V S
ThjWX B+-No. -/.
Lecointre, J.A., Neall, V.E., Wallace, R.C. and Prebble, W.
M. (,**,) The //-to 0* ka Te Whaiau formation : acatastrophic, avalanche-indeed, cohesive debris-ﬂow deposit from Proto-Tongariro Volcano, New Zealand. Bull.
Volcanol., 0-, /*3ῌ/,/.
Major, J. J. and Newhall, C.G. (+323) Snow and ice perturbation during historical volcanic eruptions and the formation of lahars and ﬂoods. A global review. Bull.
Volcanol., /,, +ῌ,1.
imCuvwnopqHrp xq s
pe : (+323) kaDA9 +322 * +, |w9+,r{|}~ +322 *ka, +,y} z~DPKg789 ,- <:; 2 (No. 0-++/*/.) 7 56  :; @L 5:; (+) :; No. B-0--/ 9 :  01ῌ12.
McClelland, E.A. and Druitt, T.H. (+323) Palaeomagnetic
estimateres of emplacement temperatures of pyroclastic
deposition Santrorini, Greece. Bull. Volcanol., /+, +0ῌ,1.
Murai, I. (+30*) On the Mud-ﬂows of the +3,0 Eruption ofVolcano Tokachi-dake, Central Hokkaido, Japan. Bull.
Earthq. Res. Inst., -2, //ῌ1*.
Murai, I. (+30-) A brief note on the eruption of theTokachi-dake volcano of June ,3 and -*, +30,. Bull.
Earthq. Res. Inst., .+, +2/ῌ,*2.
[ (+30/) kaSB  /3+.ῌ,-.
e (,**.) !+ PeP¢dPe@o AMS -¤ £¤ -. ¥©:;g +12p.
«   ]qp£¦®Y¬p ¢ (,**2) ka¯[DA9, z°789:; g± 0* / ,-ῌ-*.
op³H (+33-) ka B ,-<:;2345656:; :;²³ , 56´µ
45· 9 ¶¸¹ ¶µ¤ 31ῌ33.
¹qºc (+3,1) kaº» ¼`  -3,*.ῌ,+-.
¹qºc (+3,2) ka  .* -0/ῌ-00.

 +3,0  !"#$%&'() *+, -./ 01 2 3/?@AB (,**/) CD EF GHI0JKLNO ,**.  3 P ,- QRSTUVW`  /* 0 /-/ῌ//..
Porreca, M., Mattei, M., MacNiocaill, C., Giordano, G.,
McCelelland, E. and Funiciello, R. (,**2) Paleomagnetic
evidence for low temperature emplacement of the phreatomagmatic Peperino Albano ignimbrite (Colli Albani volcano, Central Italy). Bull. Volcanol., 1*, 211ῌ23-.
Satio, T., Ishikawa, N. and Kamata, H. (,**-) Identiﬁcation of magnetic minerals carrying NRM in pyroclasticﬂow deposits. J. Volcanol. Geotherm. Res., +,0, +,1ῌ+.,.
mnE op qr s (,***a) 
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mnE  op (,***b) 
R a UV (+1-3) U Q ] ,***  ] !¡D +//.
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deposits. J. Volcanol. Geotherm. Res., +2, +-/ῌ+/*.
Ui, T. (+32/) Debris avalanche deposits associated withvolcanic activity. Proc. IV International Conference andField Workshop on Landslides, Tokyo, .*/ῌ.+*.
Valentine, G.A. and Fisher, R.V. (+33-) Glowing avalanches : new research on volcanic density currents. Science, ,/3, ++-*ῌ++-+.
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