23
ῒΐ /, (,**1) 0 -++--- 腌腉腃腅: 腎腆腍腁腊腇腀腃腅腄腋腁腈腂 膞臏膇膿 ,**0 - -* ,**1 3 ,+ Stratigraphy and volcanic activities of Hijiori volcano, Northeastern Japan arc Isoji MIYAGI The volcanic activity of Hijiori volcano (N-2-0-/,E+.*3,*; WGS2.) is reported in detail as a case study to understand how a new felsic volcano commences the activity. Hijiori volcano, a small caldera with approximately , km in diameter, is an active volcano of Japan, which started a series of eruptions +,,*** years ago (in Calendar age), where no volcanic body had existed before. The eruptive history of Hijiori volcano was divided into four major stages (Stage +, ,, -, .) and the subdivisions (Stage +, Stage ,+, ,,, Stage -+, -,, -- [a, b], Stage .+ [a, b, c, d, e], .,, .-). Time span of each hiatus among the four major stages is shorter enough to produce no black soils, and no significant di#erence in the +. C age have been recognized between the stage + and stage -. The major eruptive product of Hijiori volcano turns out to be valley filling non-welded (Stage +, -- [a, b]) and partly welded (Stage ,,) pumice flow deposits with total maximum thickness of about +/* m and with a range / km to the southward and 3 km to the northward. The accompanying pumice fall (Stage +, ,,, -- [a, b]) and ash fall (Stage .,) are dispersed 0* km to the eastward. All the essential pumice from the eruptions were hypersthene-hornblende-quartz dacite. There are phreatic (or phreatomagmatic) eruptions at the beginning of Stage ,, -, and . which deposited lapilli falls and flows (Stage ,+, -+, .+ [ae]) in the proximity. The volume of the valley filling pyroclastic flow deposit and the air fall deposit are +.. and *.0 km - , respectively, and the caldera filling deposit is estimated to be *.- km - . Therefore, total eruptive volume of Hijiori volcano is estimated to be about ,.- km - . Key words : Hijiori, caldera, new volcano, pyroclastic flow +ῐ῎ῑ῏ 臥腓腤膕臵腢膍膹腲腎腮腄腗腟腥膾腤膍腣腎腞腢臄臝腪腑腢腖腯腞腌腮腎腦膎膠腤膍膕 腀腣腨膂腗臟腖腯腮臍腤膵膒腲腼腵腄腺腾腹 腽腟臆臭腘腮臺腤臄臝腪腟腋腮腕腤腬腍腣膙臢腤 膍膹臦腑臢膷腘腮臐膰腣腥腙腤膍膹腑臍腫腚腭腘膵 膒腲臟臡腘腮腕腠腥膓臵膄腟腋腮腕腯腣臧腗膪膷膍膹臦腤腢腌臮膆腣腏腌腞膹腑臑膚臉膪腘腮腕腠腲臟致腗腚臧膸腥腨腠腳腡臄腭 腯腞腌腢腌腗腐腗臂膶腣腥臇臶膧腤膈腻臻膋+3/3 ; Katsui et al., +313 ; Takahashi, +32*腆腀 膹膣膧腤臗膍膹 臙膬臣臎+33. ; 臔臣+3/- ; Ui, +31+腆腀 臘臨 腤膃臫膍膹 膑自+32/腆腀 腙腗腞腤臚膜膍膹 臬臙腧腚+30. ; +323腤腬腍腣腙腯腩腟 膩臱腢膍膹臦腤腐腜腚臮膆腣腏腌腞腈腉臵腢腑膛腒腚腥腌腓腝腫臢膷腘腮腫腗臍腘腅腣腱腚 腮膲臷腤腢腟腔腕腲膮腎腮臐膰腣腥臹臛腙腤臐臋腣膍 膹腑臑膚臉膪腘腮膌臕腣腝腌腞腗腢腔腯腦腢腭 腢腌腾腴腾腑腡腤腬腍腣臯臖腗腡腤腬腍腣膍腣膼腜 腚腐腲膏腘腮腕腠腥臑膚膍膹腤膍腧腤臧膸腲膮腎 腮腍腎腟臈腢膘臜腠腢腮腛腰腍腙腕腟膙臢腤膍膹臦腤腌臮膆腣膍膹腑臑膚腣臉膪腗 腚膴膢腤膽腠腗腞臃腥臸腖腄腗膫膹膣膧臗膍膹 腤腾腴腾腽膀腷腶腲膦膟臰腟腋腮膭腥腾腴腾腽膀 腷腶腤膥臼腤膘臜腠腗腞腤臞臌腠膍膕腤臒膅腣膗腘腮臭膨腲膱腘腮-*/2/01 膉臏膧腝腓腦膻臸 + + + 臰膊臩臀 膺膡膝臊臠膰膦膟臋臮臁臲膳臠膰腷膁腸腄 Geological Survey of Japan, AIST, Tsukuba Central 1, Tsukuba, Ibaraki -*/2/01, Japan. Corresponding author : Isoji Miyagi e-mail : miyagi.iso+.***@aist.go.jp

Stratigraphy and volcanic activities of Hijiori volcano ...Stratigraphy and volcanic activities of Hijiori volcano, Northeastern Japan arc Isoji MIYAGI The volcanic activity of Hijiori

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Page 1: Stratigraphy and volcanic activities of Hijiori volcano ...Stratigraphy and volcanic activities of Hijiori volcano, Northeastern Japan arc Isoji MIYAGI The volcanic activity of Hijiori

� �� ��� � /,� (,**1)

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,**0� - -*���� ,**1� 3 ,+���

Stratigraphy and volcanic activities of Hijiori volcano, Northeastern Japan arc

Isoji MIYAGI�

The volcanic activity of Hijiori volcano (N-2�-0�-/�, E+.*�3�,*� ; WGS2.) is reported in detail as a case

study to understand how a new felsic volcano commences the activity. Hijiori volcano, a small caldera with

approximately , km in diameter, is an active volcano of Japan, which started a series of eruptions +,,*** years ago

(in Calendar age), where no volcanic body had existed before.

The eruptive history of Hijiori volcano was divided into four major stages (Stage +, ,, -, .) and the

subdivisions (Stage +, Stage ,�+, ,�,, Stage -�+, -�,, -�- [a, b], Stage .�+ [a, b, c, d, e], .�,, .�-). Time span

of each hiatus among the four major stages is shorter enough to produce no black soils, and no significant

di#erence in the +.C age have been recognized between the stage + and stage -. The major eruptive product of

Hijiori volcano turns out to be valley filling non-welded (Stage +, -�- [a, b]) and partly welded (Stage ,�,) pumice

flow deposits with total maximum thickness of about +/* m and with a range / km to the southward and 3 km to

the northward. The accompanying pumice fall (Stage +, ,�,, -�- [a, b]) and ash fall (Stage .�,) are dispersed

0* km to the eastward. All the essential pumice from the eruptions were hypersthene-hornblende-quartz dacite.

There are phreatic (or phreatomagmatic) eruptions at the beginning of Stage ,, -, and . which deposited lapilli

falls and flows (Stage ,�+, -�+, .�+ [a�e]) in the proximity. The volume of the valley filling pyroclastic flow

deposit and the air fall deposit are +.. and *.0 km-, respectively, and the caldera filling deposit is estimated to be

*.- km-. Therefore, total eruptive volume of Hijiori volcano is estimated to be about ,.- km-.

Key words : Hijiori, caldera, new volcano, pyroclastic flow

+� � � ������������������ ������� �!"#$�%&�'�( ��)*+���� ���,-� �.%&�/��01�2345678�9:;�� <�!"#�=�( >�?@�� AB���C$BD;�EF��� G���$/�HIJ;01�.K;�>L�� �M��N�=�(>&�O-� PD��C��'QR�S'�� /���$TUVP;�>L�.W-IOX�� YLZ[!J&�'�'( -\-]^��� _`a�bc�d ef�+3/3 ; Katsui et al., +313 ; Takahashi, +32* � �ga��h�� ijklm� +33. ; nl� +3/- ; Ui, +31+ � op�qr�� st� +32/ � G-��u��vw�� xyik��� +30. ; ��kz� +323 �?@�� G&{�

|}���C��\~IQR�S'��������$��I��'��HBD;�( H-/������I���� !"#����EF����� G�E����$TUVP;��$���'�� �%-��&)�J�'( 6�6$[�?@���-[�?@����~I\���;�>L�� TU������OX����@���&���L����@(G>�AB���C��'QR���$TU�VP-I�����L-�� '��������ga�h���6�68�� �¡¢£�=�( �¤�� 6�68�� �¥¦���L-�� (�V)�§¨L����©ª�«;�:¬�*­;�(

�®-*/�2/01 ¯�a��)°� +� +� +£±�²³´µ¶·F¡¢��Q¸¹º·F�»¼4Geological Survey of Japan, AIST, Tsukuba Central

1, Tsukuba, Ibaraki -*/�2/01, Japan.

Corresponding author : Isoji Miyagi

e-mail : miyagi.iso+.***@aist.go.jp

Page 2: Stratigraphy and volcanic activities of Hijiori volcano ...Stratigraphy and volcanic activities of Hijiori volcano, Northeastern Japan arc Isoji MIYAGI The volcanic activity of Hijiori

,� � � � �,�+ ����� ����� ��� -2� -0� -/�� �� +.*� 3� ,*

� ; WGS2.��� �� ���� ���������� .* km� ������������ ����� ,**/�� ������������ !�"�� �������� �#��$��%�&'�����"��()*!�+,� -./��0�123 (Tamura

et al., ,**,)�4��5)*!��" (Fig. +)� �������������6. !7�"#�8$9&:+Vp�Vs�8$�%;< !�" (Nakajima et al., ,**+)�=<*� &> +/ km'��?;@��AB(<*!�"C D�E%���)�*!�"��F()�� +G*� ������"!�H�,I��-?JKLMN

A.O��'P�� �����/<QRS0�����,�, �������TUV1W234�������5� +./ km, 6�� , km, 7+#XYZ *., km�8[K$\]���� 94 (+3/-)9&::; (+30+)�<^ �07�@"_!*��������=>A`,?a@ �bA?�cd,?�eA?�"BC<Q�DfgEh (+31+)�XiLjN=>�CF�@"_!* 2,2**k+,2**=G"<Q� ���lHmnop�I$qr/s�Z=>�CJ�� ++,***

c+-,***=G��� �+KgL� ,**-�� MNOPQAR!Q=>�C��� tugL (+31-)� 3,12*c+*,1.*=B.P., Sg5T (+31/)� 3,/**k+1*= B.P."Uv<*!�� Vwg41 (+33.)�WX<Q�������x��� ��yYZ[A\�Zz2{ +� Zz2{ ,� Zz2{ .� � -]^��_()Q�a�|`Aa}�Q~Vwg41 (+33.)�&�]^�� -KM3 �b�A!}� RS�&��_"�c��� Miyagi (,**.)���KMZz2{ +9&:KMZz2{ .��Z�=>A�C<� ++,3,*c+,,--* cal B.P. (+s)"!'JAUv<Q� KMZz2{ +"KMZz2{ .���d� =>�CJ��!� �� �Q� ae��&'��������Zz2{���f�[A\�gh��i�j~�)�@��� kl ����) !� 1��� �����m=>�� +,,***=G���A��<� n�������2�A�PQ"�P�������o-\�'�yYZ[A\�� 94 (+3/-)

�&� -p�'

���

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yYZ3 "!'q�r�()Q� Sg�s (+300)�� �TUt�u�������� -t�uyY]3 �]���Av�� ���yY� ¡������"wC<Q� K$\]Txa� p�V9&:y

��!

V��

���z{�&�K$\]¢�Tx()Q�� =�a�8�

|�£

}¤�

!7�gh�&G*¢{�~�)Q"�P�)*!��?;���K$\]'����£*�K$\]¢�Tx()Q¢x[A\�&G*� ¥� -.*c-2* m��� �Tx()*!�� ?;�������o���� !�� I���B(<*!�� K$\]��¦"�§���,����� �§��¢x]��<!��A�}*!�� �Q� K$\]�6�¦��,¨r$©2gª«¬��­��®¯�+,p)����°A± GQ���K$\]�¯��� +,p)��RS ��P²� V³gL� ,**,� �Q~���#�¯����O��\2´���)QQ~� 7µ�����G*!����K$\]�¶�¯���·T����[A���w��A� '@��� ��K$\]'��¯��K$\]&�"v�� ���¸�¹���Q)*!� �,

Fig. +. Location. Hijiori volcano is located at the north-

eastern Japan arc. It is just on the edge of a mantle

hot finger (gray filled regions) proposed by Tamura

et al. (,**,).

º   » ¼312

Page 3: Stratigraphy and volcanic activities of Hijiori volcano ...Stratigraphy and volcanic activities of Hijiori volcano, Northeastern Japan arc Isoji MIYAGI The volcanic activity of Hijiori

�������� +32- ; ��� +33/ � ������������������ !"#$���� %� ����&�'()*+�,-./01�2345678�9:;<=)" >?@�AB� ,**- ; CD� +32- ; EF� +32- � G<HI(������6����&%��JK*+�,-./0LHMN(=)"�OP<"6 � Q56RSTUVWUX�5�YZ"[\3�

,�- ����������]^_`ab%cdbd�(=efg^hi^�

jkjTd6]^.lm� nopq% +/* mrs�tau<� vwx%������6yz / km{|� }z 3

km{|HP1" (Fig. ,)� ��~�6��H��`a(1]^_`ab6��% +.. km-rs�ta�u<">�� (+3/-)% +.. km-�Ui (+31+)% *.0�, km-� ����� (+300)% +.0�+*3TU��� � Ui (+31+)%��]^_. ,�6�pHv01� G6�� $���| (+33.)

%~�_`ab. -p�Hv�(1� c� %� $���| (+33.)H��;<=)�)� ���o�����

Fig. ,. Distribution of Hijiori pyroclastic flow deposits. Modified after Kawaguchi and Murakami (+33.).

The filled circles with identifier represent locations of outcrops referred in the text. Filled stars represent

the locations of boreholes by NEDO.

��~� :  ¡b6p��~���6�¢ 313

Page 4: Stratigraphy and volcanic activities of Hijiori volcano ...Stratigraphy and volcanic activities of Hijiori volcano, Northeastern Japan arc Isoji MIYAGI The volcanic activity of Hijiori

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,�. �������� �. /����� 0�12 /�� /*

km345��6�789:;�� ��12<=. >��?�� @���6 +,,***��A B�� �������CD�EFGHI�"J�0K�L��:�M�NO��;���PQ� (+323).��12<=�RS;�TU���VW����X�� YZ[��\�]^_���`���a�N�bc�� �P'd (+33,)

. ��12<=��e�!��f[U�YZ[��UJ:(��� �U��O� ���6."g#<=�O�� /��7��h��i�$j)��U.%&6kl��'m.��12<=��n���42(o�pqr_s)�<=��7��42(o�$j89����� �� �����*��+,��-���

,�/ �����+,-�� ��?��. .tu�v=O//8�:wx�yzv0OR���� {� |t1�2�vz�>�}2O~3��� /�4�yzv0�5������l: � ��h����}2�6vO//8��U ""�>�7�TJ���O6�����@8�� �9 ,**,A� �������� �6.b�

v:,;�HI��c�����%O�'{���:" @Fig. ,4���A �:<2��=v�vz��>-�}2O?��Ul:;�� >��z� @�� +31.A"�#'��q���@ (+32-)�������%r����E� ��pqr_"�#>�t1��zAB������ (Fig. -)� ������ �� �t1�C?�:;��=v. ������c�� h¡;� ����.��pqr_�6{D��:" pqr_���=}2.��E6.�}�F¢E.�£;� >��c k��i�}2. ��pqr_ @<¤ , kmA�Gu�6{ .**¥0** m{(o)�� {�{�� ���?|�¦HO%&�� � ���yzv0O{��8��}2.IJ6��;� 'm .�.§6. � ���yzv0O{��8��}2�T;:E¨)�O>���.� |�¦H�T;:{ 0�©K)�� 32� '��q���@ (+32-)�&ª�{�«;:��pqr_�� SKG--�¬�LMs�"J��=�vz��>-�}2�X�)���=v� ���­��=.gN®Ov6k �� �26.¯B2 +,1** m3}��!)�� ���=gN®Ov�°7)�v:O�>�C?��{�. ��pqr_�F¢P 1 kmMs��!)�±

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S�� ��.�=�gN®Ov��<ºTU�

Fig. -. Geological section of Hijiori volcano. Ko: Kodake granite, Ga : Gassan F. (altered basalt and andesite),

Ty : Tatsuyazawa F. (mudstone and tu#), As : Aosawa F. (basalt), Ok : Ookura acidic tu#, Ts : Tsunokawa

F. (mudstone), Ks : Kusanagi F. (shale), Fu : Furuguchi F. (mudstone), No : Noguchi F. (silty sand and

tu#ceous sandstone), Hj : Hijiori pyroclastic deposits.

Y Z » ¼314

Page 5: Stratigraphy and volcanic activities of Hijiori volcano ...Stratigraphy and volcanic activities of Hijiori volcano, Northeastern Japan arc Isoji MIYAGI The volcanic activity of Hijiori

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Page 6: Stratigraphy and volcanic activities of Hijiori volcano ...Stratigraphy and volcanic activities of Hijiori volcano, Northeastern Japan arc Isoji MIYAGI The volcanic activity of Hijiori

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determined by previous works and this study.

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Page 7: Stratigraphy and volcanic activities of Hijiori volcano ...Stratigraphy and volcanic activities of Hijiori volcano, Northeastern Japan arc Isoji MIYAGI The volcanic activity of Hijiori

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Page 8: Stratigraphy and volcanic activities of Hijiori volcano ...Stratigraphy and volcanic activities of Hijiori volcano, Northeastern Japan arc Isoji MIYAGI The volcanic activity of Hijiori

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Table +. Characteristics of Hijiori eruptive stages.

¹ º » ¼318

Page 9: Stratigraphy and volcanic activities of Hijiori volcano ...Stratigraphy and volcanic activities of Hijiori volcano, Northeastern Japan arc Isoji MIYAGI The volcanic activity of Hijiori

Fig. 0. Backscattered Electron Images of typical essential materials from Hijiori volcano (data from Miyagi ,**0).

A: stage +, B : stage ,�,, C : stage -�-a.

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Page 10: Stratigraphy and volcanic activities of Hijiori volcano ...Stratigraphy and volcanic activities of Hijiori volcano, Northeastern Japan arc Isoji MIYAGI The volcanic activity of Hijiori

��� ,�+����� +�������� ������ ,������������ �� -��������� �� + cm� ���� ,�+���� !"#�$����� ,�,��% �% ��&#��'(���� ,�+����� ,�,�)**+,���-.' "� /&( 0123�' 4� 2., km��� . ��5-2� -0� /..-0�( 6 +.*� +.� /0.,0�� ����,( ���� +�789:������ ,�,�789:��*�;' "���� +<=�>? "@A�����BCD��EB�8�FG�H ���IJ�KG( #�D������ ,�+���L"�-.' "��/G���� +�@A�������$&������ ,�+��$&#��MN% "� OD�PQ�'(���� ,�+�RST�9,���� +�����U,�( ��VWX*�YZ[�C��@�UK"�\�]!&����� ,�,���� ,�,,�^_�D (+33.)� `KM���� ,

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Fig. 1. Constituent of pyroclastic particles (,.2 to ..*mm in size) from Hijiori volcano. For the erup-

tive product of stage -�+, discrimination among

the essential, accessory, and reworked particles

was not possible.

¹ º » ¼320

Page 11: Stratigraphy and volcanic activities of Hijiori volcano ...Stratigraphy and volcanic activities of Hijiori volcano, Northeastern Japan arc Isoji MIYAGI The volcanic activity of Hijiori

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Page 12: Stratigraphy and volcanic activities of Hijiori volcano ...Stratigraphy and volcanic activities of Hijiori volcano, Northeastern Japan arc Isoji MIYAGI The volcanic activity of Hijiori

Fig. 2. Isopachs in centimeters for fallout deposits of Hijiori volcano. The locations of outcrops are shown by cross

marks. Thickness of fallout at a location is shown by a figure on the right of each cross mark, or expressed as “nd”

if no data available. The origin of these plot corresponds to the center of Hijiori caldera. Valley-filling pyroclastic

flow deposits are not included. A: stage +, B : stage ,�,, C : stage -�,, D : stage -�-a, E : stage -�-b, F : stage .�+,

G : stage .�,, H (solid curves) : Hj-O from Machida and Arai (+33,), H (dotted curves) : Hj-O from Yonechi and

Kikuchi (+300).

� � � �322

Page 13: Stratigraphy and volcanic activities of Hijiori volcano ...Stratigraphy and volcanic activities of Hijiori volcano, Northeastern Japan arc Isoji MIYAGI The volcanic activity of Hijiori

Fig. 2. Continued

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Page 14: Stratigraphy and volcanic activities of Hijiori volcano ...Stratigraphy and volcanic activities of Hijiori volcano, Northeastern Japan arc Isoji MIYAGI The volcanic activity of Hijiori

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Page 16: Stratigraphy and volcanic activities of Hijiori volcano ...Stratigraphy and volcanic activities of Hijiori volcano, Northeastern Japan arc Isoji MIYAGI The volcanic activity of Hijiori

Fig. 3. Typical occurrences of Hijiori eruptive products. A : Stage -�-a pyroclastic flow deposit at “Warabi-no”,

bearing 0+ degrees and /.* km from the caldera center. B : Close up of photo A. C: Flat floor of the Hijiori

caldera covered with lake deposit and circular pit with ,/* m in diameter and �.* m of relative height (center

of this photo) at “Kan-kane-no”. D: Proximal faces of the stage .�, pumice flow deposit at the eastward of

“Mogami-tai”, bearing +-3 degrees and -./ km from the caldera center. E : Distal faces of the stage -�-a

fallout and .�, pumice flow deposit at “Yakurai-san”, bearing 3/ degrees and .1., km from the caldera center.

F : Unconformity between the stage -�-b pyroclastic flow deposit and stage .�+ lapilli fall at “Yuno-tai”, +*,degrees and -., km from the center.

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Page 17: Stratigraphy and volcanic activities of Hijiori volcano ...Stratigraphy and volcanic activities of Hijiori volcano, Northeastern Japan arc Isoji MIYAGI The volcanic activity of Hijiori

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ufgv (+32-) w�x_:.yA'L�hi�� !�12� z{|� /� ++0�+,+.

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