/+ (,**0) / -,1 --2 3,,**0 / 3,**0 2,3 Frequent and Intensive Eruptions in the 3th Century, Izu Islands, Japan: Revision of Volcano-Stratigraphy Based on Tephras and Historical Document Masashi TSUKUI, Koichiro SAITO, Kouichiro HAYASHI, Based on the study of tephra deposits and historical documents concerning with Izu islands, we reexamined the volcano-stratigraphy in and around Izu islands. We reconfirmed that Kozushima Tenjosan erupted in A.D. 2-2 and Niijima Mukaiyama erupted in A.D.220. Eruptions from both volcanoes were big throughout their eruptive histories. Dispersed tephras from these eruptions covered most of the Izu islands, thus are good time-markers. Our results revealed that the several eruptive events occurred in between the A.D.2-2 and A.D.220 major volcanic episodes. In Izu-Oshima, the later stage of N -.*, N,.* and N +.* eruptions took place. In Niijima, a series of eruptions started with phreatomagmatic eruption of basaltic composition at Kudamaki and ended with the formation of Atchiyama rhyolite dome. In Miyakejima, lavas were e#used from Oyama central vent which spilled over Hatchodaira caldera. A lateral fissure extended from the eastern flank to Miike and resulted in a phreatomagmatic eruption around A.D.2/*. We concluded that the volcanism during the middle of the 3th century in and around Izu islands was unusually high compared with the eruptions of both the preceding and the following periods. Key words : Izu Islands, 3 th century, historical eruption, historical documents, volcano-stratigraphy + +3.+ ; +3+/ ; +3+2a +32, +32. +321 ; +330 ; +32. ; Nakamura, +30. ;,0-2/,, + -- Department of Earth Sciences, Faculty of Science, Chiba University, Inage-ku, Chiba, Japan,0-2/,,,0-2/,, + -- Graduate School of Science and Technology, Chiba University, Inage-ku, Chiba, Japan,0-2/,, 2++ +-*,,,+ -0,**+ ; +33* ; +332 ; +330 3 2-2 +0 N -.* + 220, 2-2 220 Present address. Kyushu Headquarter, OYO Corporation,,,+ -0 Ijiri, Minami-ku, Fukuoka, Japan 2++ +-*, Corresponding author: Masashi Tsukui e-mail: tsukui@faculty.chiba-u.jp
328,**/ ;,**/ ;,**/ 3 3 2+2 (M 1./) 2.+ (M 1.*) 212 (M 1..) 221 (M 2.* 2./) +322 ; +333 ; +32- ;,**- Fig. +. Map showing the Izu Islands. (+3+2b; 2 3 ) 3 (+330) (,**+) 2-2 220 2** 20. 2-2,, + 3 +3-/ +3-. ;,**- +3-. +3-. +31. ; +320 +3-- +3,3 +3-,b +3-,a 3 + Nakamura (+30*) (+330), (+33-)
3 329 Table +. Records related to eruption and unrest in historical documents. Table,. Promotion of rank in the Imperial list of shrines located on the Izu islands. +, (,**,) 3,1 +31, -+-, 3,.0 +3.- 0, 0/ p +330 01 p,**, +/0 p,, +.2+ +32* ;,,0,,1 p; +301 0*+ p;, +303 20 p +301,23,3. p, -*- p (/2. p, /23 p) +3.-,3 -* (+32+) (+33., ++2/ p)
330 Fig.,. View of Niijima Island from Tsumekizaki, Izu Peninsula. 3,1 - - + 2-2 220, 2-2 220, 2-2 2 ++ ; - 2 +- ;. +*,+ ; / +0, 2.*, +32, ; +32+ 220 220 3 / 0,3 -/ 1 +, - (0 3 cm) -0 220 1 + -1-2 ; ; +32+ /1 p 221 ++,* -3 -* m, (+3+/) -/ (+330) 220 N,.*
3 331 Table -. Chemical compositions of A.D.2-2 Kozushima Tenjosan tephra and A.D.220 Niijima Mukaiyama tephra. Total iron is shown as FeO. Analytical results are normalized to +**. Sampling localities are indicated in WGS2.., 220 +321 ; +3+/ N,.* / 220 +,2 +* -. JSM/0** LINK ISIS--** EDS - - SiO, Al,O - (,**/) FeO* CaO K,O,**+ ;,**/,**+ -, 3 Nakamura (+30*, +30.) N - N -.* 2-2 220 +32. ; +332 (+32.) (+330) / 2.+ +32- (+33.) N +.* Y 0.* N +.* Y 0.* *./ + mm N -.* N +.* Y 0.* N -.* - 220-0 N +.* Y 0.* N,.* N +.* N -.* N,.*,,**+ +++, ++ ++.*.+ N +.* Y 0.* ++2/ +--- Y 0.* +- +32. p20 ; Nakamura, +30*, p+., 220 N +.* 2-2 220.2 N -.* N,.* N +.* +1 +2 +3,*,. -+ - +/ kv, 2.* +* +* A + +** 0.- mm..1 mm, ZAF 32.. +.+ 3+.. *.3 +**
332 -, --,0,2 Y 0.* Y 0.* N +.* 3 +++, Y 0.* N +.* (Nakamura, +30*) N +.* +330 N +.* Y 0.* - - 2/0 2/1 ; 2/0 3 +* +0 2/1 1,2 ; +1 1 -* ; +2 2 + ; +3 - ;. A 2-2 / cm +/ cm 0 cm +, mm,/ cm +- cm (+330),. (KdB) A + cm. (AtL) +330 (AtP) 2/0 3 + cm +0 2/1 1 2 +1 +3 -. 2-, 2/* 2-, 0,- +.* (,**-) +,,*** ha,* km,, - (,**-), ; +332
3 333 +332 AMS AD 0+* 01* Beta-+-1/+2 ;,**, +. C 2-2 220 (+31/), + (+31-) 2/* 20* (+31/) (+31-), 2-2 +, +3.-.-.2 p; +330 0, 01 p 2.* +*,+ ++ ++ 0 (+3+2a) + (+3.+) (+330) +- (,**+) +.**.* +31*,.3 p (,**-) + (+31-) (+31/) (+330) ; 2/* +* 1 2 +332 3 +* 2/* +, 1 ++ - (+332) 2/0 2/* 2/0 (+332),**, /* p, 2/* 2/- 2/. +/ +, +332 - / +.21 +/+2 / +/,, +/,-
334 Fig... Map showing thickness of Kudamaki tephra (KdB) and Atchiyama tephra (AtP)(in cm). AtL : Atchiyama lava dome. Fig. -. Stratigraphic columnar section at an outcrop on Miyatsukayama. Locality of the section is shown at point A, in Fig... *: Age estimation by Yoshida (+33,). +0*/ +332 ; +33* 3 +33+ +. 3 (,**/) 2-2 +. C 2** +*** 2** 2-2 20. 2** 3** +- +. 2/- 2 2/3 -,, 20.,1 / 3 / 2-2 220 N -.*
3 335 B (+1/.*.-*) 3 Fig. /. Diagram showing the eruptions and earthquakes those occurred in and around the Izu islands in the 3 th century. N,.*, N+.* 220 ; +330 S,.* N +.* 3, kg s N +.*,/ kg s N -.* N +.*,2* /* 2-2 220, 2-, 2/*,/** 221 +330 ; +333 3 /* 3 (+31-) -1 +*. +++. (+3.-) +21 p, -.. p. (+32,) / + 1/ p, (+32.) / + +-- p. (+321) / + 2/ p. (+33-) +-+- p, +/./ p. (+332) +* (,**,),**, +,0. (,**/),**/ V*// P*+1. (+333) +*2 -.0-03. (+330) +*/ +-- +0,. (+322) 1***, 0- +./ +2,. (+32.),3 S+ S+/. (+3.+) + +31/ 3.- p. (+31/) 1/ 13 -+3 --.. Nakamura, K. (+30*) Stratigraphic study of the pyroclastics of Oshima Volcano, Izu, deposited during the last fifteen centuries. I. Cyclic activity of Main craters and the absolute chronology of the pyroclastic sediments. Sci. Pap. Coll. Gen. Education, Univ. Tokyo, +*, +,/ +./. Nakamura, K. (+30.) Volcano-stratigraphic study of Oshima Volcano, Izu. Bull. Earthq. Res. Inst. Univ. Tokyo,.,, 0.3 1,2.
336 (+3+/) 13-2 /0. (,**,).-. p. (+31*) -2, p. (+32+) +* /11 p. (+3+2a) 20 +32,,-0 p. (+3+2b) 21 +32, ++0 p. (+33.) + +,*/ p. (+330), 2*2 p, +-+ p. (+333) -3/ p. (+32.) 0 +1+ +11. (+332),,/** +*1 03/ 1+,. (,**+) ++* 3. +*/. (,**/) 2-2 220 2** +*** -/ +-- +-.. (,**/) 2** +*** +.C,**/ V *//-P*+/. (+32-) /2 131 2-*. (+33*) + 1. (+33+) +,,- p. (+332) 1***.- +.3 +00. (+33.) -- +0/ +21. (,**-).+0,**+ 0*/ p. (+33,) +33,, 0-. (+330) 3 :,,+. (+303), + +*2 (+301) 0,3 p. (+303), //+ p. (+3,3) +* /.0 p. (+3-,a) 2,*0 p, -/0 p, -12 p. (+3-,b) +, --0 p,./0 p. (+3--) / /.0 p. (+3-.) - +-2 p,,.0 p, +,0 p. (+3-/), /0+ p. (+31,),0 -,- 032 033 +*-, (+31.). + -,0 -,1 0.- (,**-) +-3, p. (+32*),,*,.* +0 (+320) ++2. p. (,**+) +, -23 p. + 2-, 0,-, 2-2 1,3 2-2 1,3
3 337-2-2 2 ++. 2-2 2 +- / 2-2 +*,+ 2-2 2 0 2.* ++ ++ 1 2/* 1 +0 2 2/* +* - 3 2/* ++ +. +* 2/* ++ +/ ++ 2/* +, 1 +, 2/- +,1 +- 2/- 2 +- +. 2/- 2,+ +/ 2/. 1,. +0 2/0 3 +* +1 2/1 1,2 +2 2/1 1 -* +3 2/1 2 +,* 2/2 /,1,+ 2/2 1,-,, 2/3 - /,01,- 20+ /,1,. 20,. +2,/ 20- -,.,0 20. - +0,1 20. 1,,2 202 2 +2,3 21- + + -* 22* -,/ -+ 22*. 0 -, 22+ +,, -- 22+ +,. -. 220 +,2 -/ 220 0,3 220 3 / 220 3 / -0 220 1 + -/ 220 3 / -1 220 1 +
338-2 220 +,,. -3 221 ++,*.* +++, ++ +-.+ +++, +, +1