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Eruptive History of Satsuma Iwo-jima Island, Kikai Caldera,
after a 0./ ka Caldera-forming Eruption
Fukashi MAENO�and Hiromitsu TANIGUCHI��
Kikai Caldera, +1 km wide and ,* km long, is a Quaternary volcano located, nearly submerged, in the East
China Sea, southern Kyushu. Two volcanoes, Iwo-dake (a rhyolitic volcano) and Inamura-dake (a basaltic
volcano) on Satsuma Iwo-jima Island at the marginal part of this caldera, were formed after the great
caldera-forming eruption of 0./ ka known as the Akahoya Eruption. We made a geological study to understand
the eruptive history of Satsuma Iwo-jima Island after the caldera formation.
The volcanic activity in the island after the Akahoya Eruption is divided into three main stages and ten
sub-stages based on volcanic edifice development and tephra deposits ; the old Iwo-dake stage (stage OIo-�-�),the Inamura-dake stage (stage In-�-�), and the young Iwo-dake stage (stage YIo-�-�). The old Iwo-dake
stage was initiated by phreatomagmatic eruptions and pumice fallout (stage OIo-�), followed by the e#usion ofrhyolitic lava with continuous ejection of ash and lithic fragments, resulting in building up an old volcanic edifice
(stage OIo-�). In the stage OIo-�, intermittent explosive eruptions also occurred. The Inamura-dake stage is
characterized by the e#usion of basaltic lava flows and scoria-cone building (stage In-�-�). After that, at the
western foot of the cone, phreatomagmatic explosions occurred (stage In-�) and andesitic lava flow e#used (stageIn-�). In the young Iwo-dake stage, the explosive eruption occurred at the beginning (stage YIo-�), followed bythe e#usion of multiple rhyolitic lava flows from the summit crater and the formation of hyaloclastite in shallow
sea that made up the marine terrace (stage YIo-�). During the past +*** years, the volcanic activity changedto intermittent ones with pumice and bomb fallout (stage YIo-�-�). Total phenocryst contents of the Iwo-dake
lavas increased up to 2 vol.� through the young stages. The magma of the young Iwo-dake stage is di#erentfrom that of the Akahoya Eruption and the old Iwo-dake stage, bordered by the Inamura-dake stage.
Key words : Kikai Caldera, Iwo-dake volcano, rhyolite lava, eruptive history, bimodal volcanism
+� � � �������� �� !"#$%&'() .* km!*+,-.� /'(01234� 56� 7%89#:;����<=>?@ABC#!DEFG+,-HIJKL� ������#:MN�OP.QRS� TUVWA� XA89<����YZ.Q[G+K\Q]I^_`aI<� b* ,* km, !/ +1 km+Rc>:;����`aI (Matumoto, +3.- ; Figs. +a, b)J d#�����
efg +*h�i+jkIlgm#:nopq+cSrst\� 0./ ka+� uv�wxqyz{`|(\I }#����pq<~�.k ���}�� +312 ; 3���+32, ; Kitagawa et al., +33/ ; ��� ,**,�J TUVWAVW� ������� ��� ������� ��VWA ��������.Q[O��+�LHI��q���<�v�wxpq��+sF.k}.]qy�`aIJ 3�� (+32,)� ��� (,***)� Kawanabe and Saito (,**,)
��32*�2/12 ���� ¡¢�£� b/:¤:¤¥�¤¦§¨B¤©ªInstitute of Mineralogy, Petrology, and Economic
Geology, Graduate School of Science, Tohoku Uni-
versity, Aramaki-Aza-Aoba, Aoba-ku, Sendai 32*�2/12,Japan.
���32*�2/10 ���� ¡«¬b/:¤b/vv¦§®¯°±Center for Northeast Asian Studies, Tohoku Uni-
versity, Kawauchi, Aoba-ku, Sendai 32*�2/10, Japan.
Corrsponding author : Fukashi Maeno
E-mail : [email protected]
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Fig. +. Maps showing the location (a) and topo-
graphy (b) of the Kikai Caldera. Figure (c)
shows the topography with outcrop distribution
in Satsuma Iwo-jima. For the abbreviations in
(c), see the text.
�C ¹�Tº»¼72
��� ������� ����������K-Sk-l, K-In, K-Sk-u����� ������ ,�� ,��.��� 2�������� ���� ! "#� $%&'(���������� K-In-+)*+ ,� ,��,���� ! -.�/0�*1� 2�������34�5���6��� 7��� ���� 89&�:;<=> ?@A��BC�D��5��E��! FE�� 89GGH�IJK�����L�?@A�LMBC;5����� 2�;7����NOPQRSTU�VWX;Y��# (Table +)!���L�Y��� Z [�\]S�^;_���`�� ���5a�bcdefgh" ij��� 2�;_���VWXk����L"#��������lm�Y��#! def�� nop;q�rs2���� etguv�#2�� >�wxyz[{�RSVW�|}"#�~�Xg��#2�;�>!���L�?@A�LM;7��> �� VWX��"�lm�� NOPQRS (Akahoya Eruption)� �X89&�VWX (Old Iwo-dake stage)� $%&�VWX
(Inamura-dake stage)� �X89&�VWX (Young Iwo-
dake stage)�Y�Em ! 2��;6��� �X89&���������� stage OIo-�,�� ,����� $%&���������� stage In-���� .����� �X89&���������� stage YIo-���� .�����Y��# (Table +, Figs. -, .)!�VWX����L�� �X89&������ stage
OIo-�� ����> �X89& +a�+b, ,a�,b (OIo+a�+b, OIo,a�,b)� .�� $%&����� stage In-������> $%& +, ,, - (In+, In,, In-)� -�� �X89&����� stage YIo������> �X89& +, ,a�,e, -a�-c, .a�.b (YIo+, YIo,a�,e, YIo-a�-c, YIo.a�.b)� ++�g��6� ! ���������E�� �������Lg����� #�� ,a, ,b� ��*��Y��#! "#� In,� In-������ i��*���� ��5a�f�g������2�g� !
,�- ���89&�� ��O���� S¡¢��£¤�¥� ¦"1�§¦¨©�ª«�� ¬¦ 1**m�®¯��:
Fig. ,. Geological map of Satsuma Iwo-jima (modified from Ono et al., +32,).
°±89G�)² O���³=XTU�RS´ 73
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�o���� �SK����N @�m (IoL) ���L� NL� �SK������� M�� ; 0�++P �� IoL
��k��.L�,������D� >����4=�l ���L�4=N�� �SK������ y=������ ��������� MO��5� +32,P f=�pL!� � �iD� 6��r���F��tu������¡���� ¢£¤¥¦§¨©£ª (Pichler, +30/) M�SK¢£¤¥¦§¨©£ª� ; IoHyP � y=���«¬��� M�SKt�«¬�� ; IoTeP !)X�4 !�����.L (Figs. /, 0)� ¢£¤¥¦§¨©£ª��$%��®�Ap�¡�� (IoHy-l) ��� (IoHy-u)
�o��p�� �SK�+,���J� ^���F�=�!� ()>��¯?�p��SK�������1°�� M¢£¤¥¦§¨©£ª�±²P �� �³´ab
Table +. Geological units in Kikai Caldera area
µ��S¶�CF�·¸¹§���º»��1¼ 75
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-� �������-�+ ����� +a, +b (OIo+a, +b)
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!� ��2��wx�����7�]�j��� ����7��*�����n]M�� ��� cm���� x�� ¡�¢£� /�v�F�� ¤0� p�¥
Fig. .. Photograph of the outcrop at Sakamoto (ST). OIo+a>,b, In+>-, and YIo+>.a are derived from the
Old Iwo-dake volcano, the Inamura-dake volcano, and the Young Iwo-dake volcano, respectively.
Fig. /. Geomorphological map of Iwo-dake volcano.
Shaded area at the western foot of Iwo-dake
shows the distribution of volcanic bombs (YIo.a, b) ejected from the Kintsuba crater in stage
Io-�.
¦§ ¨©ª3«¬76
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-�, ����� ,a, ,b (OIo,a, ,b)
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.� �����
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cm��,-�klmn�� "#By,�>?�B>Ci# -$����� ��� !� (ST),� ,$�Y� klmn"z:�)� - cm��,{|%&� u?�}?"<"�efa� In+�9dG +* cm"'~�B>��T��6��
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����"z+N��f� �S�{ZQ*�"��j+klmnCiJ��� �/,� InSLC In+�0� stage In-�"1������
.�- ��� , (In,)
Kawanabe and Saito (,**,)"K-In-,"+� +� Kj+klmn�L �g�d�� /01234,� ,$"j+klmn��h��iO>?�B>�, .� !a� �9� "#By, ,m, ���, -* cm��,-� �|� "#By,� =N"klmn��+mC�� ���qr2s� z<9�� klmn)� +�,� + cm*+,-� =�,�z: - cm�Pa� ��� !�,�� ,�- cm"9d,-� In,
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�"1��,-�.�/ ��� - (In-)
Kawanabe and Saito (,**,)"K-In-,"=� ,�K�������j+klmn�L �g�d�� �5����"#By4,"�9�z: +./m�Pa� ���z+�"9d ,�- cm"j+klmn� ��"9dG +*
cm�� + m*="�������� [{�z=�"9d� +* cm"j+klmn���Y� =��+�"j+klmn�6 E,%&��5�� =�"j+klmn�� ��������="RSC¡W¢X����5�-� ���������Gmm�G cm"7�"£O\, D� , cm*+"klmn �B> ����Y� O��) +* cm��"M89��� sag
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/�, ����� ,a�,e (YIo,a�,e)
Kawanabe and Saito (,**,)K-Sk-u-,�234��56789:;��� /��<=>?@AB���� (YIo,a, ,b, ,c, ,d, ,e)C�D�� EFG (HJ)� HI(ST)��� JK�L� - m���� stage YIo-�MNOP�QRSTUV�LWXY8Z�[�� XY8�\]�^�C�_�`� ab�c@d efghi���`]jk'�� ���U��0lmm,m�no�� pq�rs'�t]�[�� V_��L4l +* cm
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/�- ������� ������ (IoHy-l)
�QR�<����� '�¡¢�£?8}¤¢¥��� ,q¦§¨© (0�-) �]�'�]� stage YIo-�og��MNSTPª+��[�� ^�� (IoHy-l)
V«�L� +/ m��'��t���:¬�®8}���#� E¯D°±� �²� D³�i�,m.l cm<l +* cm��1 ]� ´|���<³� .lmm<l cm��1 µB�¶"4�� t����K]
Fig. 0. A marine terrace (a) consists of volcanic conglomerate (IoTe) and hyaloclastite (IoHy-l) at south-coast of
Iwo-dake. A volcanic conglomerate (b) covers a hyaloclastite layer including a block of pseudo-pillow lava
(c) with radial cracks due to rapid cooling. Figure d shows a sketch of the pseudo-pillow lava.
·� ¸v¹º»¼78
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and Katsui, +310)�0()12��� (3,�-&4����� pseudo-pillow1$567�/� 8�9���:;��<�=>?@��-A>B)�CD��67�� �E� +32, ; 8�F�E� +330# )GH��� � � IJ�K�� (IoTe)��L�()M�� N�OPQ���� )RS3�T��0� !"3UV�W)XY� (367�1=>?@��-A>B) !� �Z3"�� [#\&���� �$� %]3����%[3^�_&1W`���� [#\&')a]b.'M��^�_&1W`���1$c� (��W%&1d�������� =>?@��-A>B3e1����()If3e ISD*+# �/� =>?@��-A>B),g3��� hmmih cm-.# M��/j0k��1lm�
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/�0 ����������� (IoSP)
(3�Q�\�/ ISC*+�3c���� (Fig.
-)� �� -* cm-.�� E� +* cm!Q3%]<}�^�3�\M��� Q=>?@��-A>B�(IoHy-l)3E"�0k�� �����M��IJ�K�� (IoTe)�W(3�),�^��\�$��()
M�� IoTe�J3EFM� � /��,��32noG��) !�Y� (3���/����H�I32no����)/JK�Y���
/�1 ��������� (IoTe)
��/h +* cmi+m-.�� Q=>?@��-A>B�1L����~�K0k��0 (Figs. 0a, b)���.� 2no�g3���s�_J��� 45� W��/'M��$� r]���� %]�\� ^��\� .:&� ���M���¡>v/E�h cmihm�� (��/¢�£NN¤1d��¥������
/�2 ������ B, C (IoLB, C)
2no��7 B, C (IoLB, C)/� �o�yM�7���7O����� 2no(M�)I3¦31�m�P��)W� �IN3Q�� ��� IoLB/� ISA*+�y3If�2no=>?@��-A>BQ��2no��7 A (IoLA)1L������ (Figs. 1
a, 1b)� �D -*m!"345���7�� Q����� ��� �§M��/ IoLA)/¨�z� ©R�7�/������ %@� />?����Sh3������ �� e/4�.���
/�3 ������ D, E (IoLD,E)
2no(ªT��������0� �T�/UV���7*�1W«��W33� �6"�/pq�¬c� xg/���Y�� 2no��7D (IoLD)
/� )X (HO)�y�®YoG��� YIo+, YIo,a1���I� �� (Figs. 1c, d)��¯M������H"3 YIo, ����),��3G��)RS���2no��7 E(IoLE)/� IoLD}zWZ°[� . vol.
�!"\±�� IoLD)/¨���7�0�/�+* ������ F (IoLF)
s�E*B<}�ªi]I3�^�'Dm7O����� IoLAiE<}�²³0k�1�~�W´����0� �6"�/pq� .:&�¬µ��� _h`3 flow lobe/� ¶�W�� /*m1|S� ��45�·&�0�
/�++ ����� !" (IoTa)
2no�^M��T�'Dm²³0k� Fig. ,�3 l# �� ¸¹�}��/�� -*m!"� m� E�h cmM�h +* cm345�r]���� �$� r]���1$5� %&/��r��M��� 2no(If�/��Qº��$.3}�\ �h cm-.# �$��� 8&�&1$c� 2no��7)abM����0()M�� ��7��3cd4��) !�Y� ef�M�®Yo� �T�/� IoTa1�g)mg�*0k� Fig. ,�3 k# ������
»h2n��<������J�!�3G�¼ 79
/�+, ����� -a�-c (YIo-a�-c)
YIo-a�-c�� ������� �������������������� !"#$%&�K-
Sk-u-- (Kawanabe and Saito, ,**,)�'(�)�� YIo-a
�� + cm*+��,-./0mm�0 cm�1�2�345�6728-9:� 8��;<� 0* cm=>���� +?��@AB8C-DEF� �?�GH�IJK�LMNOP�� ���QR�STUV (HJS)��� 6W���XBYI��� Z�6W����� �[ +
m=>�� \]�^ -* cm�_P�`abc-de�.:� fg�2�672���� ���hR (IOW)���0 cm�`abcijB�6W���Fkljm��Z�6W�� ���7n�opP�`abcijB�K-Iw-P+ (Kawanabe and Saito, ,**,)�'([m�� qr� ���stuvw (IOT)��� 8� -* cm=>�x
+6728X�Ikljm��Z�0 +* cm�y��� ,
z�@AB2��345�{g6728 (YIo-b, -c)F��P�� |m}m�yM~�:-���GH672�NOP�D��� @AB����9p�kljmB��l� Zmj�;I stage YIo-�� �X�����
/�+- ����� .a, .b (YIo.a, .b)
����h7�ij7R�i�I���IJK� bcJ��67�� ��-�<X�� ,z*���8ijB�F� +y� ,z (YIo.a, .b)�:F@AB8X�Ik��)�� ���w���� YIo.a, .b|m}m�� sag
structure-���\]^ 2* cm�_P��4�a67�Fkljm��67��������#�g��?���2�bcg��S�B����m�d�<a���� Sag
structure�� ��2��bc� ���,� �g���������[mIJK� ���S����� 67��
Fig. 1. Figures a and b show a photograph and a sketch of the outcrop at south-coast of Iwo-dake (ISA),
respectively. Iwo-dake hyaloclastite (IoHy-l) and Iwo-dake lava A (IoLA), which is a feeder of IoHy-l, are
covered by Iwo-dake lava C (IoLC). Figures c and d show a photograph and a sketch of the outcrop at
Higashi Onsen (HO), respectively. Inamura-dake East lava (InEL), YIo+ and YIo,a are covered by
Iwo-dake lava D (IoLD), talus and fan deposits. Locations of outcrops are shown in Fig. /.
¡¢ £�¤¥¦�80
��������������� (Fig. /) ��������������������������� �!�" YIo.a, .b� #��$�� cm%&���'()*�+,-���.����./ 0123��45$� ���678�9:$� ;�+<=;>" ?@AB�C� D@�E��FG H� +*
cmI8����JK/L>� (K-Iw-P, ; Kawanabe
and Saito, ,**,)"
0� �������MN��� OP� QN����RSR�TU ��.V>LWX��� Y;Z[N��\��*�]^+_`�" %& a�bc��]^*�dbTU+]8 (Fig. 2, Table ,)"
0�+ �� ����OIo+b�e&�� (stage OIo-�)� fgh��ih���*$ j0kl�\� mnTU+<8" oH +
mm9:�pq;ro��Ys$ Fe-Tit.��,���" u� OIo,a���F (stage OIo-�)� stage OIo-
� mnv�wxyz{$!�� ���|}~ �����|+�8�ro���� - mm�+Ys /�fgh��ih�2����$!� (Figs. 2a, 2b, Table ,)"ro����� j0kl�\� stage OIo-�$ /�1
vol. �$!���/ stage OIo-�$�� ,* vol. �I8� (Fig. 3)" fgh��)�ih���V>L# j0kl�\�$���$!���/ stage OIo-��\�$��� ;�"
0�, ������OP��Y;�\�� OP�� * (InSL)'()
OP�� * (InEL)$a�=���ih�������!* (Fig. 2e, Table ,)$ oH +�- mm�ro����+��,-" e&���j�� ���ro�����y/�����G ����+,-�"#:������������y�!�" �� *� oH .
mmI8�ro���+�8� �����fgh��ih�¡�*$!� (Fig. 2f, Table ,)" pq;ro��$¢b�£ InSLG InELTUb;ro���������;>"OP��\�� j0kl��¤�¥¦§�\�
�fgh��ih�¡�* ; Fig. 2d� ,��� %�¨E}~+#Vro�&'�������;>"
0�- ��� ����QN���©N����ª�j«¬3���� ���ro��� �+ mm9:� +�8�®��� (1�3vol. �)�fgh��ih���*$!�" Q/>�\�¯°����±'()²7$�³´µ¶/ �#Q
Fig. 2. Microphotographs (cross nicol) of volcanic rocks. Scale bar indicates + mm. Pl : plagioclase, Cpx :
augite, Opx : hypersthenes, Ol : olivine. (a) Two pyroxene rhyolite with clear plagioclase (pumice in K-Tk at
HJ), (b) two pyroxene dacite with dusty plagioclase (ballistic bomb in OIo,a at HJ), (c) two pyroxene
rhyolite with clear plagioclase (lava flow in IoLE at IOW), (d) two pyroxene andesite with large dusty
plagioclase (banded pumice in K-Tk at TK), (e) olivine two pyroxene basalt with plagioclase aggregates (lava
flow in InSL at INS), (f) two pyroxene andesite with dusty and clear plagioclase (lava flow in InIL at IM).
For the abbreviations of sampling locations, see Fig. +c.
·(��¸'¹�0123º»N%e���¼ 81
�� YIo.a (stage YIo-�)��� ������ -./
mm��� ���� +,�+- vol. ���� (Figs. 2, 3,
Table ,)� ��� +3-.�-/��������� +1
vol. ����� � ��� �������� ���� !����"#$� %��������&�'�(���)*�+ �������",� � -./����/����0�1��234�5� 6����������7���8�+���
1� � � �9:;<=>��?�@�A��0�1� B+�����CD�� +.C�E��F��G " HI�JK�+32, ; L�JK� ,*** ; Kawanabe and Saito, ,**,M� %���N�����OP=>��A��Q� ��R�ST�0�1�U��V��+1���� �W��� XY<N�� �Z[� OP =� ����0�1!�+��"\]6���1� ���CD��^A�_X`a�b* ��#c�de�0�1f�gh�1�$�
1�+ ������%����A��� /., ka HL�JK� ,***M �ij��� stage OIo-�k��A����l2`a"$m���%no�pq�� (OIo+a)� B�pq��� rsrtuv&$�'wx`_2`apq��gy�+ � z�{�|���� OIo+b"pq��{� A���
}�$~�� �stage OIo-��%����@� A��� (�)�
pq���O�Z (OIo,a, ,b)�*+,�� HOIo,a�-M ���)*�+ ��.� �`��s/���� H�0JK� +310M ��� ��OP�O12��� ����� "�&34q����]60 HI�JK�+32,M� B�B��� A�ij�5� OP�-����� �]@���A��=>�+� z+�'�� ��)�&$)��"$m��B�]���1� � �����O��9:;<6��� OIo,a, ,b��1pq���gy�+ ���JK (,**+)�� �9�����?����"� n����> HTiO,, K,O, Zr, Rb�QM ��8�+ ����,����9�����%���s:`��CD�s:`�� ����s:`������ B�]���� %�������� �9������ 6���" +* vol. ���5¡� "� �>)���9�����7¢s:`��£�+� �9�����¤¥rsr�85� A��G¦��gy�+ �§¨����©�9��¥¨� %�2��� ����� (IoLAªIoLC)�� «��� ����¬�:��6%�� ���� B+���� � IoLD����CD�A��]®¯°±� ��²³´;�µ���N��¶��·]��°±��$¸¹(���
Table ,. Model Compositions of Representative Samples from Satsuma Iwo-Jima
�� ºJ<©»¼82
IoLD������ �������� ����� YIo+, YIo,a�� �� (Figs. 1c, d)� ���������������� IoLC�� �!"#� �� IoSP
$�%��&'� SiO,&�� 0+�1+ wt ������()*�+,� � -.��� /0123&�4� 5��6�7� �8�91�:� ;< =>���IoLA?IoLC�� -.�@� A�>BC� DE��FGH�OIo,a, ,b �I�"JK@� sag structure �L
M���� N.��OP -.�>QR ST!3"P,�>#$U4�D� %VWX@� YZ�&���W��
1�, ���������� -.3 ka[��\'D]�^� YIo-� \'D]�� ,., ka 5_�6(� ,*** ; Kawanabe and Saito,
,**,: ��3� )`a .b \'.�c L U4��stage In-������ K@d����ef� �>@*�� +!,>�H\'-g�./hi�4��stage In-���� jk�ef�>>l3� �01��2HKmn1o��� (In-)D3'�4�=>���p/p4qr56D67,�l >89U4�� ���Kmn1o��� IU� :;��� = s K7���@� <=3"P,�t>?DV�� stage In-���� @�<= =K7��uvw+!D,, ���stage In-� K7> stage In-� K7D A l �F���XH��@&�F�D� xWa>l� stage In-
�;j� �� \'Ay�� <=3z{,�>BC�4������ �!"#� �� �|}~�K �B�p/p>��W^ 5��6(� +320 ; ��6(� ,**+:�Sr T�C�V�D�+� (Notsu et al., +321)� =4� =>��� �� \'�l��,�p/p�� �|}~�K;j3��|09�k3��U4�-,�p/p t>?DF��
1�- ������-.� \'�� �� \'���� ,., ka[5_�6(� ,*** ; Kawanabe and Saito, ,**,: 3�],�� stage YIo-��� �E (ST) YIo+3��4��H3� !��1��56��K�./hi�4�� YIo+
���4 �F�lGa� <k3�I�H�ID6J, ��=>��� stage YIo-��� K���.�3���L6�W\'>89U4�� � � stage
YIo-��� -.� ���\'.�� �+!(IoLA?IoLF) ,3�^� OP @� )�:DL U4��stage YIo-����OP�^lM3T!��K7 5N
N�: ��+!D,,�� @� O���+!,D�A3,4������������� (IoHy-l)�L ,�� �� 1***P� �4��' 5)Q� ,**,: ��BC�>� � R� "P�� � � �M��AS T��+�, ��� +!, IoLA?IoLC�,,�N \'�� �K7�OT! z',� �<?U=�M �� IoLD?IoLFD,,�� =4��+! VW¡��� �lN����������� (IoHy-l)
� 3 vol. �� NN���,,�+! (IoLA?IoLC)
� 3�+* vol. �� � � \'�,,�+!� ++�+0
vol.��F^� \'¢£>¤3� IoLA��¢3X¥, �� (Table ,, Fig. 3)� =4��+!¦>|09�Y§= YIo,a?,e> @��Z� YZW[C��` �W�D� YIo,a?,e�� -.� ¨©�¦>, ��lIa� \.�3]^b3ª�� ,,��+!32H¨©�¦>BC�4��stage YIo-��� YIo-a 5$�%��&«�@* Km,>� |09�Y§=3��4�jkK@d: ��]��� kT3�I�H�I¬D"P��=>��� +!,���>,� stage YIo-�;j� K���.�c�� \'>BC�4�� ��� �@_3"P��$�%� (K-Iw-P+ ; Kawanabe and Saito, ,**,)
�� stage YIo-� �+!, IoLF�� �^�YIo-a3[CU4�� |09�Y§= ¨©�D 3.*.* yBP (Kawanabe and Saito, ,**,)� @_ ¨©�D++-*.* yBP (Kawanabe and Saito, ,**,)� @* Km,���D +***2* yBP 5_�6(� ,***: �F�=>��� YIo-a �P`���� +***P�>BC�4�� = Km,�K;j�� ^b K@dJa�1���KDF��l � ®b )`W56��K��=, �W��stage YIo-���¯)c�K@�J%�WX� jk¨©� ��./Ni�4�\'.�F�� �W¨©��� ,d (YIo.a, .b)"P��D� X°�l:;�QR�<*3±�4 (Fig. /)� |09�Y §=3�Q>²X:;³�� C´�µ®bW�K�F��� = \'�e /**�0**P� 5_�6(� ,*** ; Kawanabe and Saito,
,**,: >U4 ��� YIo.aA �� VW¡�� +/�+1 vol. ��� stage YIo-� +!, VW¡� �">fg�3X¥, ��� ��� +3-.�-/P ¶g�h�K�,,�,i!�+! VW¡�� +1 vol. ��·C� = W¡� ¸j��"��P��¹k, ���-.�,i! �!"#� �� �|}~�K>�W�/012�ºa^ 5��6(� ,**+:� ��� Sr T�C��|}~�K ,i!�p/p�^lVaW�
»l�h3�i�|09�L .;j �K¼ 83
(Notsu et al., +321)� ������ ���� � ��������������� �������������� �!"�#$����%�&���'� � ��(��%)*+,��
2� � � �-.�/01���� �!23����$����
(stage OIo-�4�)� ��� (stage In-�4�)� ����� (stage YIo-�4�)������5+,��$������ � 678��%9:�! (stage
OIo-�)�;� <=>��>�!�?� @��AB��!CD��(��CE�F@GH� (stage OIo-�)������ I�'� '��(%JKL�M�NF
(stage In-�4�)� OC��� � 678��%PC'� '��( (stage In-�4�)%?Q���R���������� �ST�� +***�<���>�!%
'��(��BCE�F@GH�� (stage YIo-�4�)� UV +***�<� '��(��"+W� <=>�XY�9:�!�Q����Z�� (stage YIo-�4�)� ����������� ��� �!"�#$����%�&���'� � ��(�� ����[S�� \�]��^_�`a��?��
� ��bc�dT��e�B� f�ghf��i�bcjklm�n� op��qr�s����tu� vwx�tuy��� �g�hbcz�{|�}~�� ������~�� g� �p� f��i�bcjklm�;���p� ����\�bc������p����>v���tuy��� ��������p� �� �p� !��"�����p�vwx�� ���� �g�#¡���� ¢£¤¥¦¤��$_��� %§¨��©�g�"ª&�By��� 2«�$_�¬+®¯�w�'�y°�
� �
����±²³´µ (+330)¶·¤��'� '��x+,�(¸!³%)(*� !C� .+� +1+�+13.
Kawanabe, Y. and Saito, G. (,**,) Volcanic activity of theSatsuma-Iwojima area during the past 0/** years. Earth
Planets Space, /., ,3/�-*+.Kazahaya, K., Shinohara, H. and Saito, G. (,**,) Degass-ing process of Satsuma-Iwojima volcano, Japan : supply
of volatile components from a deep magma chamber.
Earth Planets Space, /., -,1�--/.Kitagawa, H., Fukusawa, H., Nakamura, T., Okamura,
M., Takemura, K., Hayashida, A. and Yasuda, Y.
(+33/) AMS +.C dating of the varved sediments from
Lake Suigetsu, central Japan and atmospheric +.C change
Fig. 3. Variations of modal abundance of phenocryst in volcanic rocks for the past 0/** years. The rock of the
stage OIo-�is more crystal-rich (¹,* vol.�) than that of other stages (º,* vol.�). In the Young
Iwo-dake stage, the modal abundance increased gradually with decreasing age.
»% ¼±²³´µ84
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in and around Japan : recent progress. Quatern. Res., -2,+3.�,*+.�� ������ (+312)������� �������������������� !"# +1#+.-�+0-.�� ������ (+33,)����$�%� �&'(��)# ,10 p.
�� ��*�+�,-.�/� ��01234,**+5� 678 1 9����:;�<��&'(��)# -// p.
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(+33.)����# �`���aEbcdH�e�6fgh +.C�R� ij�'(�(� � 47(�k�(5# ,1# +23�+31.\� D (+330)���6�� ����6fgh +.C
�R 4��5�lm'(fghn��opqr�st4�5# 23�+*3.\� D� �'!�^�_� (,***)���6��uvuwuMx�yz +*"�{6����� |#L!
"# +,# 3�,-.\� D (,**,)���E�$dHyz% -"�{6���6�R(U!"� �� !"# .+# ,,/�,-0.^�}~��m&'���(. (+32,)�)*��7�67n� 7�7n!"�s 4/"�6 +�+5# 7n���# 2* p.
',�- (,**,)ij�.S/�0�����EFGH�1O6��2�� �� !"# .+# ,-1�,/+.
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¬�S®� �¯# 2+# +*/�++/.Watanabe, K. and Katsui, Y. (+310) Pseudo-pillow lavas in
the Aso Caldera, Kyusyu, Japan. Petr. Econo. Geol., 1+,..�.3.°�_:�;B±-�<²³´ (+310)�)*��67=K�EFGH�µ62n¶>E·¸�� 7=# +-#+-+�+.+.
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