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Eruption Products and Structure of Katsuma-Yama Volcano,Okushiri Island, Hokkaido, Northern Japan
Kazuhiko KANOῌ, Yohei YOSHIMURAῌῌ, Daizo ISHIYAMAῌῌ,Geo#rey J. ORTONῌῌ and Takeshi OHGUCHIῌῌ
This paper describes the eruption products and structure of Katsuma-Yama volcano. Katsuma-Yama
volcano is located in the northern part of Okushiri Island o# the Oshima Peninsula, Hokkaido and has three
eruption centers : Horonai-Gawa caldera, Katsuma-Yama crater and west Katsuma-Yama crater. HoronaiGawa caldera is , km by +./ km in dimension, and is ﬁlled mainly with massive breccias to tu# breccias,
ﬁne-grained lacustrine sediments and bedded lapillistone to tu#. Massive breccias to tu# breccias are exposed
along the western wall of the caldera and have been recovered by drilling in the central portions of the caldera.
The breccias contain fragments mainly of dacite, dacite pyroclastic rocks, andesite, and granodiorite together withminor fragments of perlitic rhyolite. The majority of the rock fragments are quite similar in their constituentsand textures to the surrounding basement rocks. Perlitic rhyolite, however, is relatively fresh and cannot berecognized in the surrounding basement rocks. This rock is, therefore, thought to be juvenile, although noeruption products remain outside the caldera. The ﬁne-grained lacustrine sediments are wavy stratiﬁed with awavelength up to a few meters and locally contain sulfur deposits. Bedded lapillistone to tu# comprises mostly
fragments of glassy biotite-rhyolite, and projectiles derived from the direction of Mt. Katsuma Yama formed sag
structures in the beds. Katsuma-Yama crater occurs at Mt. Katsuma Yama. The crater has a diameter of 1.*
m across and is ﬁlled with bedded lapillistone to tu#. The constituents are mostly non- to poorly vesicularpolyhedral or platy fragments of glassy biotite-rhyolite and are thought to be phreatomagmatic in origin.
Although the outﬂow deposits partly remain on the western and southeastern ﬂanks of Mt. Katsuma Yama, mostof the expected pyroclastic ring or cone has been removed through later erosion. Katsuma-Yama lava of similar
composition occurs through the crater inﬁll, spreads over the eroded surface of the outﬂow deposits, and is
distributed mainly on the southwestern ﬂank of Mt. Katsuma Yama and further to Horonai-Gawa caldera. Thelava has a thickness of +** m at Mt. Katsuma Yama, thins to the downﬂow directions with a variable thickness of
ﬂow breccias, and is intruded into the inﬁll of Horonai-Gawa caldera, with plastic deformation of the caldera
deposits along the contact. West Katsuma-Yama crater opens through Katsuma-Yama lava at its western
margin, with a diameter of +2* m. The major inﬁllings comprise rock fragments mostly similar to those from the
Katsuma-Yama crater. A minor volume of pyroclastic surge deposits from this crater remains on KatsumaYama lava in the summit area of Mt. Katsuma Yama, and rests on the brown soil of a few centimeters that covers
the eroded surface of the western rim of Katsuma-Yama crater. The eruption volume from Horonai-Gawa
caldera is unknown but could be between + and +* km-. The eruption volume from Katsuma-Yama crater
perhaps slightly exceeds *.0 km-, and the eruption volume from west Katsuma-Yama crater is very small, perhaps
-*/ῌ2/01!"#$ + %& +ῌ+!"'( 1)*+,-./012345/067
Institute of Geology and Geoinformation, Geological
Survey of Japan, AIST, Tsukuba Central 1, +ῌ+,Higashi +-chome, Tsukuba -*/ῌ2/01, Japan.
*+*ῌ2/*, 89#:;<=> +ῌ+89<?<@A<6

Faculty of Engineering and Resource Science, Akita
University, +ῌ+, Tegatagakuen-cho, Akita *+*ῌ2/*,,
Japan.
Corresponding author : Kazuhiko Kanoe-mail : kazu.kano@aist.go.jp

5·6¸¹ 6º+¦6Geo#rey J. ORTON6+¬»¼

212-

less than *.*+ km . Katsuma-Yama lava is dated by ﬁssion-track methods to be *.,ῌ*.1 Ma, and no soil occurs
between the lava and the overlying pyroclastic surge deposits of the west Katsuma-Yama crater origin. A thinbrown soil between the pyroclastc deposits of Katsuma-Yama and west Katsuma-Yama craters represents a shortdormancy in volcanic activity. Lacustrine deposits in Horonai-Gawa caldera indicate a high wave-energy setting.
Sulfur precipitated in the deposits suggests fumarolic activity in the caldera lake. These facts likely demonstrate
post-caldera volcanism, and the plastic deformation of the caldera ﬁll by the intrusion of Kamui-Yama lava
suggests that the post-caldera volcanism was succeeded by the activities of Katsuma-Yama and west KatsumaYama craters.
Key words : Katsuma-Yama volcano, rhyolite, phreatomagmatic eruption, caldera, Pleistocene+ῌ ῏ ῍ ῐ ῎  

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Shiramizu Sawa, Horonai Gawa (River).

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Fig. 2. Ash grains of rhyolite glass in a thin lapilli
tu# bed in Horonai-Gawa caldera. Sample*-*1,/*,-*. collected from the upper stream ofHoronai Gawa.

Fig. 1. Thin section of a sulfur-bearing gravellytu#aceous mudstone in Horonai-Gawa caldera.
(A) Sulfur clasts and lithic clasts set in the
mudstone matrix composed mainly of sulfur andopaque materials, under crossed polarized light.
A tiny vesicle is visible in the sulfur clasts. (B)Pumice and sulfur clasts set in the mudstonematrix, under plane polarized light. A sulfur
spherule surrounded by opaque materials is
visible in the right upper part.

Fig. 3. Inter-bedded lapilli tu# to lapillistone andtu# in Horonai-Gawa caldera. Tu# is wavy toparallel laminated. Lapillistone to lapilli tu# isvaguely laminated with sparse block-sag structures. Lens cap is 0 cm across. Two sag structures are discernible above the lens cap. These
structures develop from upper right to lower
left, indicating blocks came from the right side.
Photo taken at a roadside cut along the Horonai
Gawa (River).

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+33.> ?@= 9A- .** m )<_ ,KA-;^ +,,** m # R12#BCDE$%&'( N.-OS-/ # =  #3)0N E= b$%&'FG!"#H!EI$!"

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KHN Kef[ = ?J

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9:;<= +33.> UV  A-=

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#J= $%&'(?L-EOPOQ

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219

Fig. +*. Geologic columns of bore holes N.-OS-/, N.-OS-0, N--OS-, and N,-OS-+, compiled after NEDO(+33.). The boring sites are shown in Fig. ,. Stratigraphic units in parentheses are those assigned in theoriginal description by NEDO (+33.), but are interpreted in this paper to be intra-caldera debris avalanche orrockslide deposits.



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Fig. ++. Bedded lapilli tu# and tu# inﬁlling Katsuma-Yama crater. Photo taken in a valley on
the north side of Katsuma Yama.

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Fig. +,. Polyhedral blocks and lapilli in lapilli tu#
of Katsuma-Yama crater. Prismatic joints develop on the surface of the block in the centerof this photo. Lens cap is 0 cm across. Phototaken in a valley on the north side of Katsuma
Yama.

Fig. +-. Pyroclastic surge deposits discordantly reston those from Katsuma-Yama crater, the surface of which has been turned into brown soil.
White arrows indicate the soil layer. Hammer
is -* cm long. Photo taken at the west quarryof Katsuma Yama.

µEFG¶·¸H:¶¹Eº¶Geo#rey J. ORTON¶E»¼

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 (Fig. +1) [(m C4!   (Fig.
+0)  7A<>
Fig. +.. Jigsaw-ﬁt glassy rhyolite plastically loadedon the lapilli tu# of Katsuma-Yama crater.
Photo taken in a valley on the north side of
Katsuma Yama. Hammer is -* cm long.

(m C45:67 @%p0C8h + mm
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into the surge thin-bedded lapilli tu# and tu#
erupted from Katsuma-Yama crater. The protrusion has jigsaw-ﬁt cracks. Photo taken at
the upper stream of Shiromizu Sawa, Horonai
Gawa (River). The source Katasuma-Yamacrater is on the left side.

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Fig. +0. Flow breccia (upper right side) and innercoherent, ﬂow-layered rhyolite lava (lower leftside) e#used from Katsuma-Yama crater. Phototaken at the west quarry of Katsuma Yama.

Fig. +1. Inner coherent ﬂow-layered and foldedrhyolite of Katsuma-Yama lava. Black layers
are dense and glassy and minor light grey layers
are vesicular or ﬁlled with secondary silica andfeldspar. Photo taken at the west quarry of
Katsuma Yama.

Fig. +2. Close-up of the inner part of KatsumaYama lava. Note light grey layers represent
ﬂow folds and vesicular portion of the lava.
Cracks develop normal to the ﬂow layers andnear parallel to the cracks. Photo taken at thewest quarry of Katsuma Yama.

Fig. +3. Light grey portion develops into and acrossdense dark layers along ﬂow-parallel joints
and brittle fractures in Katsuma-Yama lava.
Cracks develop vertically or slightly oblique tolight grey layers by ﬂow drag, and adjacentdense portion ﬁlls the cracks. Lens cap is 0 cm
across. Photo taken at the west quarry of
Katsuma Yama.

µ¶·¸¹·W9º·Geo#rey J. ORTON·9»¼

224

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@]A? %#^; -* cm  8 m`^; ,./ m n op,%#/#$8 F/ qr3stu -*v=lwxH?%#&yopabz]Ax<x{|} ~ (Fig. ,+),
 ^; 0* cm ?<Kx` $]A
%#&%#=>

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z

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,+) %#op, {|} ~8abz]Ax < x/ ufx` $]A~8 (Fig. ,,), m

Fig. ,+. Poorly-sorted pyroclastic breccia andoverlying pyroclastic surge deposit inﬁlling west
Katsuma-Yama crater. The surge deposit is 1*
m thick and has a down-sag structure (upper
right). Rock fragments produced from thequarry cover the surge deposit. Photo taken at
the west quarry of Katsuma Yama.

Fig. ,*. Outcrop crossing west Katsuma-Yama crater. Pyroclastic inﬁllings incline to the centerand abut the Katsuma-Yama lava. Photo taken
at the west quarry of Katsuma Yama.

Fig. ,,. Pyroclastic surge deposits from west
Katsuma-Yama crater, overlying the ﬂow breccia of Katsuma-Yama lava. Hammer is -* cm
long. Photo taken at the north quarry of
Katsuma Yama.

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225

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lmx^_n' 1_U,<0 ,-k´¢( 1e2ῌ ¶fcyzrsr-4567{^o|}/' (Heiken, +31. ; Heiken and Wohletz, +32/)³¢´, 1/e10ῌ 2 K,O , ../ῌ Pµ Q, <·R§CS (+300) T¸´¢=
8x¹U

2³¢´´¢U,112T¸ U^p(Fig. ,-. Mdf-sf plots for the eruption products of Katsuma-Yama and west Katsuma-Yama craters. Boundaries
for pyroclastic ﬂow, ﬁnes-depleted pyroclastic ﬂow and pyroclastic surge deposits are adopted from Walker(+32-). Boundary for pyroclastic fall is adopted from Walker (+31+).

Table +.
Bulk chemistry of eruption products from Katsuma-Yama and west Katsuma-Yama craters.

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  ;<;=>?">%@>A#
BCD E$'  !#$ Sato and Taniguchi (+331) "-
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9:;Y

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 :D n#%XY(Z  [\  TU>opCD qrst
%+  TU>uI vw*mDWu
I% F]xL 1> w*:yL^zFU+ *e fM 8J  {_`1>|a(bzc jdΐU+f(h S rῒ:ef(g}~(]Mh ij
k2=_a %$ lg} Q  Vg}m(n+h o pq r 3 _`Da z (+333) =>3 +333 Ver. +.*. =>
x (+321) < =>[ [ 
>¡¢£¤¥2 ` =!£¦ ` @ABlS§ 3- -21ῌ.*+.
`=lx (+33,)  ¨oB
©lY lS{ -1 ++ῌ,-.
 ª@``« (+32,) ¬ l­lS l­lS® _/  + n
a lSg}u 2-p.
Heiken, G. (+31.) An atlas of volcanic ash. Smithsonian
Contrib. Earth Sci., +,, +ῌ+*+.
Heiken, G. and Wohletz, K.H. (+32/) Volcanic Ash. Univ.
California Press, Berkeley, ,.0p.
¯` `EC° (+302) =>x*±{ + : ,,***,*** lSg}u lSn +²12p.
Jackson, R.G. (+310) Sedimentological and ﬂuid-dynamic
implications of the turbulent bursting phenomena in geophysical ﬂows. J. Fluid Mechanics, 11, /-+ῌ/0*.
AC  ` "³ ` vi ` ´ ` t (,**,) ]^ : < => @AB c1
.>S¡123  .1 -1-ῌ-30.
>|az{ _AC `Da z{ (,***) =>¡>|a Ver. +.*. ¢£lSn
G-. lSg}u CD-ROM , ¤I¥¦ (+33+) §¨[µ =>Rt© +0*ῌ+03.
Le Maitre, R.W., Streckeisen, A., Zanettin,B., Le Bas, M.
J., Bonin, B., Bateman, P., Bellieni, G., Dudek, A.,
Efremova, S., Keller, J., Lameyre, P.A., Sabine, P.A.,
Schmid, R., Sorensen, H. and Wooley, A.R. (,**,)
Igneous rocks : A classiﬁcation and glossary of terms.
Recommendations of the International Union of Geological Sciences Subcommission on the Systematics of Igneous Rocks. Cambridge Univ. Press, ,-0p.
Matsueda, H. (+33,) Globular sulfur in hot lakes of southwestern Hokkaido. ,3th IGC Field Trip Guide Book Vol.
0, A*., +3ῌ,,.
EC°`ª¶`«·| (+32+) => _ ,¬a lSg}uE¸­d`j®¯`C«¯°±`E¸²³` ´`µ¶´w (+32*) §¨[µ·¹1¸    ,/ -*3.
º¹@`[º´ (+300) ¨|»S>
(+)
|»0!;=>¼ // +0*ῌ+02.
Sato, H. and Taniguchi, H. (+331) Relationship between
crater size and ejecta volume of recent magmatic andphreatomagmatic eruptions ; Implications for energy
partitioning. Geophys. Res. Lett., ,., ,*/ῌ,*2.

%&'(1 klbob)~

 (+33.)  No. --,  ++*2p.
!  " #$ (+3-/) %&'()* +,-. /01 .11 /0-ῌ/10.
!  " #$ (+3-0) %&'()* +,2. /01 .21 ,-ῌ--.
3456 (+312) 789:;<=>?@ABC8?D
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defgShij (+333)  +klb. Lmnob
pqrstuKv1 IJ)Lmnobpqrs +333
Ver. +.*, IJob/K
Walker, G.P.L. (+31+) Grain size characteristics of pyroclastic deposits. J. Geol., 13, 030ῌ1+..
Walker, G.P.L. (+32-) Ignimbrite types and ignimbrite
problems. J. Volcanol. Geotherm. Res., +1, 0/ῌ22.
+vwxy z{|}.