eruption age and sequence of ogurayama lava dome at … ˘ˇˆ˙˝˛˚˜ˇ !" # $% &’...

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腏 腔腪腨腧 臟膯腤 臈腴膄腻膃膑 膆臊 腴膄腻膃膙臆膑 腇腁 腇腁 膉膾膝腜腓腥膰臝 臗膊臒 膮膖膒膷臍膩膜膔膹臔膳臀自膜膔臥臲 膭腣臨膌膎臟膯腤 膺膭 臑臕 臭臸腞臐膼腟腘腫膣臋膭臵膐腽腄膂 臡膴臤 臡膴臷 膑腮膲腘臛膿臌腮膕腟腗腝 臨膌腳腾腸腄腽 臮腢膘臧 膵臹臚膌膭腤臝臬臡臭膠臬臥腢膇臖腗 臘膚至 腖腬 膽膇腐腪 腣膸腢腱膄膀腰膁腹腼腮臶腍腝 腣腴膄腻膃腮致腘腫膎膌膭腞腌腫 膵臹臚膌 臰臯 臇臷腖腬腝腍腫 臗臉 腡腠腢腩腛腝 腙腣膻膫腑臱腪腐腢腖 膵臹臚膡臗臁臤膗腣膣臋臣臜臠臓臥腮膥臆腘腫腻腲 腬腝腍腫 腕腬腪腣膜膔腢腩腬腥 膵臹臚膌膭腣臨膌膎 腵腲腼膳腣臵膐腽腄膂腞腌腫 膵臹臚膌膭腣 臔膳膍臙膜膔腤腕腬腧腞臅臏腓膧腭腬腝腒腚腑 腙腣腦 膢腴膄腻膃膑 膞膬 腜腣腷腺腄 腟腯腠腤膣臋膭臵膐腽腄膂腮膵臹臚膌膭膪臂腣臨膶臦腞 腶腢膘臧腖腬腫 腧腚 腣臨膌腲膁膅腼腤臨膌膓膱 腌腫腟膦腎腝腍腫 膈膽 臫膋 ῒΐ ῐ῎ῑ῏ 腍腔腑腆腋 腊腐腋腓腇腃腀腄腂腉腏腌腈腁腒腆腎腅 ῌῌ ῌῌ UDO ( ) ka ( Hayakawa ( ) ( ) (Hayakawa, ) AIST, Institute of Geology and Geoinformation, Geo- Towada volcano is an active volcano located in the northern part of the Northeast Japan arc. Ogurayama Lava Dome (OLD), which is a dacitic lava dome located near the center of Towada volcano, has been regarded as a product of the latest eruptive episode A. In this paper, the author reports that the OLD is older than previously thought and that it was formed at the end of eruptive episode D . The OLD overlies pyroclastic deposits of the eruptive episode E and is overlain by pyroclastic deposits of the eruptive episode C. These stratigraphic relations restrict the eruption age of the OLD to . . cal kyr BP. Within this time interval, two eruptive episodes (D and D) are recognized as tephra fall deposits in the distal area. The distribution of Herai Ash from the eruptive episode D shows that the source vent is located in the vicinity of the OLD. Furthermore, the petrological features of the OLD closely resemble those of the Herai Ash. These observations indicate that the OLD is the product of the eruptive episode D (. cal kyr BP). The probable eruption sequence of the eruptive episode D is as follows. Intermittent phreatomagmatic eruptions occurred in the earliest stage. These eruptions produced the lower part of the Herai Ash. Subsequent lava eruptions formed the OLD and accompanied intermittent vulcanian eruptions produced the main part of the Herai Ash. The source vent of the eruptive episode A is not the Ogurayama, because the Ogurayama was formed before this episode. Since the only crater topography currently recognized in the Towada volcano is the Nakanoumi crater (NC), the source vent of the eruptive episode A is considered to be the NC. Since the NC has been the main crater throughout the post-caldera stage, future eruptions will probably occur in the NC. There is the current NC at the bottom of the lake of m in depth. A detailed examination of probable eruption style in the future will be required for predicting volcanic hazard of Towada volcano. : Towada volcano, Ogurayama Lava Dome, stratigraphy, eruption age, eruption sequence, eruptive episode D , eruptive episode A km A, B, C a, b (Hayakawa, ) ( ) a, c . ka) . ka Hayakawa, ; ; Tsukuba, Ibaraki , Japan. Corresponding author : Takashi Kudo logical Survey of Japan, Central , Higashi , e-mail : [email protected] Takashi K Eruption Age and Sequence of Ogurayama Lava Dome at Towada Volcano, Northeast Japan Arc Key words // ,*+* , 23 +*1 // // +32/ +320 +32/ ,**3 - ,1 ,*+* - ,- 3, 0, 1/ -,* ++ + +32/ +320 + +/ / +/ / - +32/ +30, -*/ 2/01 +++ 1 -*/ 2/01 1 +++ +

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Page 1: Eruption Age and Sequence of Ogurayama Lava Dome at … ˘ˇˆ˙˝˛˚˜ˇ !" # $% &’ ’( )*+,-./012 34-.56+,7 ˜ˇ58 9:; ?ˇ@a/ bc $defg )hiˆj klml 5nopqrst,+ +u/vw

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UDO

( )

ka (

Hayakawa ( ) ( ) (Hayakawa, )

AIST, Institute of Geology and Geoinformation, Geo-

Towada volcano is an active volcano located in the northern part of the Northeast Japan arc. Ogurayama

Lava Dome (OLD), which is a dacitic lava dome located near the center of Towada volcano, has been regarded

as a product of the latest eruptive episode A. In this paper, the author reports that the OLD is older than

previously thought and that it was formed at the end of eruptive episode D .

The OLD overlies pyroclastic deposits of the eruptive episode E and is overlain by pyroclastic deposits of the

eruptive episode C. These stratigraphic relations restrict the eruption age of the OLD to . . cal kyr BP.

Within this time interval, two eruptive episodes (D and D) are recognized as tephra fall deposits in the distal area.

The distribution of Herai Ash from the eruptive episode D shows that the source vent is located in the vicinity of

the OLD. Furthermore, the petrological features of the OLD closely resemble those of the Herai Ash. These

observations indicate that the OLD is the product of the eruptive episode D ( . cal kyr BP).

The probable eruption sequence of the eruptive episode D is as follows. Intermittent phreatomagmatic

eruptions occurred in the earliest stage. These eruptions produced the lower part of the Herai Ash. Subsequent

lava eruptions formed the OLD and accompanied intermittent vulcanian eruptions produced the main part of the

Herai Ash.

The source vent of the eruptive episode A is not the Ogurayama, because the Ogurayama was formed before

this episode. Since the only crater topography currently recognized in the Towada volcano is the Nakanoumi

crater (NC), the source vent of the eruptive episode A is considered to be the NC.

Since the NC has been the main crater throughout the post-caldera stage, future eruptions will probably occur

in the NC. There is the current NC at the bottom of the lake of m in depth. A detailed examination of

probable eruption style in the future will be required for predicting volcanic hazard of Towada volcano.

: Towada volcano, Ogurayama Lava Dome, stratigraphy, eruption age, eruption sequence, eruptive

episode D , eruptive episode A

km A, B, C

a, b (Hayakawa, )

( )

a, c

. ka) . ka

Hayakawa, ; ;

Tsukuba, Ibaraki , Japan.

Corresponding author : Takashi Kudo

logical Survey of Japan, Central , Higashi , e-mail : [email protected]

Takashi K

Eruption Age and Sequence of Ogurayama Lava Dome

at Towada Volcano, Northeast Japan Arc

Key words

// ,*+*, 23 +*1

// //

+32/ +320 +32/

,**3 - ,1 ,*+* - ,-

3 , 0 ,

1 /

-,*

++

+ +32/

+320

+

+/ / +/ / -

+32/ +30,

-*/ 2/01 + + + 1 -*/ 2/01

1 + + +

+

Page 2: Eruption Age and Sequence of Ogurayama Lava Dome at … ˘ˇˆ˙˝˛˚˜ˇ !" # $% &’ ’( )*+,-./012 34-.56+,7 ˜ˇ58 9:; ?ˇ@a/ bc $defg )hiˆj klml 5nopqrst,+ +u/vw

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1 2 390

Fig. . (a) Topographical map of Towada volcano showing the locality of outcrops. (b)

Location map of Towada volcano. (c) Topographical map of Ogurayama Lava Dome

showing a survey route and the locality of outcrops. A part of : , topographic map

“Towadako-toubu” published by the Geographical Survey Institute is used.

(a) (b) (c)

+

+ ,/ ***

+, /

+

Page 3: Eruption Age and Sequence of Ogurayama Lava Dome at … ˘ˇˆ˙˝˛˚˜ˇ !" # $% &’ ’( )*+,-./012 34-.56+,7 ˜ˇ58 9:; ?ˇ@a/ bc $defg )hiˆj klml 5nopqrst,+ +u/vw

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of Towada volcano. Ages : *Machida ( )

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; Kuno ; ;

; ; ;

kawa ( )

A

( ) ( )

;

Hayakawa,

Fig. . Eruptive history during the post-caldera stage

and Hayakawa and Koyama ( ) ; **Kudo and

Sasaki ( ) ; ***Kudo ( ) ; ****Kudo

( ) ; *****Horiuchi ( ).VEI

Hayakawa, ; ;: * ( ) ( ) ;

** ( ) ; *** ( ) ;

**** ( ) ; *****Horiuchi ( ).

cal kyr BP

. cal kyr BP (Horiuchi

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(Hayakawa, )

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Hunter and Blake, ;

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. cal kyr BP

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et al.

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et al.,

+331 ,**-

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+31* +320 +310

+32/ 3+/

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+32.

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++ 1

+33/ +333

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Table . Modal compositions of eruptive rocks from the eruptive episodes A to G in Towada volcano.

. A G

(Hayakawa, ) c

cal kyr BP G

; km km

A a

(Hayakawa, )

km G

a, c Hayakawa, (vol. )

; ;

(Hayakawa, )

A

B

g

+

+

+

+32/ +

++ ,**2

3+/ +332 ,2 ,,

+32+ 2 +

+32/

-

+

+32/ +320 +310

+32/

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- ,

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Table . Representative whole-rock major element compositions for eruptive rocks from the

eruptive episodes A to G in Towada volcano.

. A G

. mm . . mm

Lipman ( )

X PHILIPS PW

:

A B wt.

( )

JB- a

B D vol.

3.

,

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Fig. . A stratigraphic columnar section at the crater

wall of Nakanoumi (loc. ). Its location is shown

in Fig. c.

c )

TiO MnO

c B D

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Page 7: Eruption Age and Sequence of Ogurayama Lava Dome at … ˘ˇˆ˙˝˛˚˜ˇ !" # $% &’ ’( )*+,-./012 34-.56+,7 ˜ˇ58 9:; ?ˇ@a/ bc $defg )hiˆj klml 5nopqrst,+ +u/vw

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Fig. . Whole-rock TiO -SiO and MnO-SiO diagrams for eruptive rocks from the eruptive

episodes C, E and G. The other eruptive rocks during the post-caldera stage of Towada

volcano are plotted in the outside of these frames.

C, E G TiO -SiO MnO-SiO

E

L G

cm K cm

B D E I ;

mm cm

E H cm

F K I

F (Hayakawa, ) H

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Page 8: Eruption Age and Sequence of Ogurayama Lava Dome at … ˘ˇˆ˙˝˛˚˜ˇ !" # $% &’ ’( )*+,-./012 34-.56+,7 ˜ˇ58 9:; ?ˇ@a/ bc $defg )hiˆj klml 5nopqrst,+ +u/vw

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A stratigraphic columnar section at the southeast

96

h G

E cm

D cm

C

C cm

B m

A

cm

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F

A

C, D F

A

C

Fig. .

of Ogurayama (loc. ). Its location is shown in

Fig. c.

.

c

A

c e g cm C

m C

h

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Page 9: Eruption Age and Sequence of Ogurayama Lava Dome at … ˘ˇˆ˙˝˛˚˜ˇ !" # $% &’ ’( )*+,-./012 34-.56+,7 ˜ˇ58 9:; ?ˇ@a/ bc $defg )hiˆj klml 5nopqrst,+ +u/vw

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Fig. . Modal compositions of eruptive rocks from the eruptive episodes A to G in Towada volcano.

. A G

c

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cm

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Page 10: Eruption Age and Sequence of Ogurayama Lava Dome at … ˘ˇˆ˙˝˛˚˜ˇ !" # $% &’ ’( )*+,-./012 34-.56+,7 ˜ˇ58 9:; ?ˇ@a/ bc $defg )hiˆj klml 5nopqrst,+ +u/vw

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E . cal kyr BP ;

98

Fig. . Whole-rock TiO -SiO and MnO-SiO diagrams for the Ogurayama Lava Dome and related rocks.

. TiO -SiO MnO-SiO

. cal kyr BP

D . cal kyr BP

D

(Hayakawa, )

Fig. . A sketch of a fallen tree near the summit of D

D D.

c

D D

E

D D

C

C

D

C (Hayakawa, )

Hayakawa ( )

. cal kyr BP

C .

mm

D D

D

, , ,

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. +

0 + ,**-

1

1

2 , ,**1

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,

/

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Page 11: Eruption Age and Sequence of Ogurayama Lava Dome at … ˘ˇˆ˙˝˛˚˜ˇ !" # $% &’ ’( )*+,-./012 34-.56+,7 ˜ˇ58 9:; ?ˇ@a/ bc $defg )hiˆj klml 5nopqrst,+ +u/vw

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Fig. . Correlative stratigraphic columns for representative sections. Locations of each section are shown in Fig. a.

. a

3 +

3 +

Page 12: Eruption Age and Sequence of Ogurayama Lava Dome at … ˘ˇˆ˙˝˛˚˜ˇ !" # $% &’ ’( )*+,-./012 34-.56+,7 ˜ˇ58 9:; ?ˇ@a/ bc $defg )hiˆj klml 5nopqrst,+ +u/vw

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Houghton

Rock Equivalent) . km (Hayakawa,

100

Fig. . Stratigraphic columns for Nakanosawa Ash and Herai Ash at each type locality.

Locations of each section are shown in Fig. a.

. a

(Hayakawa,

)

)

( )

a

; Self and Sparks, ; Walker,

mm

mm

et al.,

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Page 13: Eruption Age and Sequence of Ogurayama Lava Dome at … ˘ˇˆ˙˝˛˚˜ˇ !" # $% &’ ’( )*+,-./012 34-.56+,7 ˜ˇ58 9:; ?ˇ@a/ bc $defg )hiˆj klml 5nopqrst,+ +u/vw

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345�6 7869:;�<=>?@��AB

Isopach maps for tephras from the eruptive episode D (upper) and D (lower). Numerals show

101

Fig. .

the thickness of tephra in centimeters. A part of thickness data for Oguni Pumice (marked by *) is

quoted from Hayakawa ( ).

. D D (cm)

* Hayakawa ( )

++

+32/

+++32/

Page 14: Eruption Age and Sequence of Ogurayama Lava Dome at … ˘ˇˆ˙˝˛˚˜ˇ !" # $% &’ ’( )*+,-./012 34-.56+,7 ˜ˇ58 9:; ?ˇ@a/ bc $defg )hiˆj klml 5nopqrst,+ +u/vw

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Relation between the area enclosed by isopachs

assuming a relation . presented by Haya-

(S) (T)

102

Fig. . Photomicrographs of grains in tephra samples. (a) The middle unit of Nakanosawa Ash. It contains

blocky and flaky glass fragments, spongy pumices and fresh dacite blocks. (b) Thin section of the middle unit

of Nakanosawa Ash (open nicol). (c) Herai Ash. Most grains are fresh dacite blocks. It contains small

amount of spongy pumices. (d) Thin section of Herai Ash (open nicol). All grains are fresh dacite blocks.

. (a)

(b)

(c) (d)

Fig. .

(S) and the thickness (T), for Nakanosawa Ash

and Herai Ash. Broken lines are iso-volume lines

kawa ( ) (see text in detail).

.

Hayakawa ( ) .

V TS

V TS

+, ,

+,

+,

+-

+32/

+-

+32/ +, ,

Page 15: Eruption Age and Sequence of Ogurayama Lava Dome at … ˘ˇˆ˙˝˛˚˜ˇ !" # $% &’ ’( )*+,-./012 34-.56+,7 ˜ˇ58 9:; ?ˇ@a/ bc $defg )hiˆj klml 5nopqrst,+ +u/vw

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106

A X

A

Kano ( )

( )

no. .

( )

.

Hayakawa, Y. ( ) Pyroclastic geology of Towada vol-Ecano. , .

C( )

E C ( . . cal kyr .

( )BP)

D.

Horiuchi, K., Sonoda, S., Matsuzaki, H. and Ohyama, M.

( ) Radiocarbon analysis of tree rings from a . -cal

kyr BP pyroclastically buried forest : a pilot study.D, .

. cal kyr BP DHoughton, B.F., Wilson, C.J.N., Smith, R.T. and Gilbert,

J.S. ( ) Phreatoplinian eruptions. In

D

Hunter, A.G. and Blake, S. ( ) Petrogenetic evolution

of a transitional tholeiitic - calc-alkaline series : Towada

volcano, Japan. , .

( )

p.

( )

.D

Kano, K., Yamamoto, T. and Ono, K. ( ) SubaqueousA

eruption and emplacement of the Shinjima Pumice, Shin-

jima (Moeshima) Island, Kagoshima Bay, SW Japan.

, .A( )

.

( )

no. .m

( ) E G

.

( )

.

( )

.

Kuno, H., Ishikawa, T., Katsui, Y., Yagi, K., Yamasaki,

Volcanoes

et al.

Bull. Earthq. Res. Inst.

Radi-

ocarbon,

Encyclopedia of

J. Petrol.,

J.

Volcanol. Geotherm. Res.,

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107

M. and Taneda, S. ( ) Sorting of pumice and lithic Morrissey, M.M. and Mastin, L.G. ( ) Vulcanian erup-

fragments as a key to eruptive and emplacement mecha- tions. In (Sigurdsson, H. ed.),

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silicic magma and water. , .

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