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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

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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

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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

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%~�_`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.

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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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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.

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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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Fig. .. Comparison of the stratigraphy of Hijiori volcano

determined by previous works and this study.

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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

������������ ���� ���� +���������������������� � ������!��"#��"��$ %���&'(���� +���)�* +���,�-���.�� ���� +�/����0�12 Fig. 0A�#3����� +���45� ��6�78 ,.2�..* mm

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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

���������� ������� ��� ��*� +* cm������� .3.1 km,���� / cm, ��+*� -* cm����� -*.* km,� ,* cm��� ����� -* cm��� +..3 km,� .* cm����� ������ *.*+. km-� !"��� -�#��$%&' ,�+� ,�,��(�� )*�+,��� �-������ ������ +1.0 km� 1 .�/ -2� -,� +1.//�� �0 +.*� ,*� 2.3+

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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).

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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.

� � � �326

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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Page 18: 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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Hijiori stage +, ,�,, -�,, -�-a, -�-b, .�+ and .�,.

¹ º » ¼328

Page 19: 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 20: 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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