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ÍCn\ÅÏ@³êéÅà_Ci~bNÈn¿»ÛÌêÂÅéBÎR¬ÎÍCÉCn\Å¶·éäXlÞÌ¶½ðº©·æ¤È­I»ÛÆÈèC»Ì®l®âÚiÎR¬ÎÌ½l«jÈÇð\ª·é±ÆÍÐQy¸Ì½ßÉKvsÂÅæêàÍCnéB®l®âÚð\ª·é½ßÌàÅÌ}O}­¶Cnà©çn\ÖÌÚ®C»µÄn\ÖÌ¬oJjYÌðÅ

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àÌjðÌæµÄC»Ì»wg¬âÜÜêé»âAÌ÷×\¢©çAv[`·éû@âCÎRßTÉÝuµ½nkvâXÎvÈÇ©ç¾çêén¨IÈÏªf[^ðàÆÉAv[`·éû@ÈÇªéiFig. 1jBÜ½CÀÛÉnàÌððÀ±ºÅÄ»µC}O}Ì­¶CÚ®C¬oJjYðð·éû@àéiFig. 1jB±Ìæ¤ÉlXÈè@ÉæÁÄ¯¶ÎR»ÛÉAv[`·é±ÆªÂ\ÅéCÂÜèñíÉwÛIÈ¤ªìÅé±ÆÍCÈwIÈ»¡ÌÎÛÆµÄàÎRwð£ÍIÈàÌÆµÄ¢éB{_¶ÅÍCn\ÖÌ}O}Ìã¸ðÀ±ºÅÄ»µC»±©çÎR¬ÎÌ½l«Ì´öðð¾·éÝÉÂ¢ÄÐî·éB}O}ªn\Öã¸µ¬oÉéÅåÌì®ÍÍC}O}ÉÜÜêÄ¢éö­«¬ªÌ­AÅéiFig. 1jB}O

Fig. 1(Color online) A schematic illustration of volcanic erup­
tions. Petrographic analysis of volcanic materials, geophysi­
cal observation, and laboratory simulation have been carriedout to understand the mechanism of volcanic eruptions andto predict intensity, magnitude, and duration of volcaniceruptions. A scanning electron microscopic (SEM) image ofthin section of pumice from the 1707 eruption of Fuji volca­
no and X­ray computed tomography (CT) image of ex­
perimentally decompressed magma in laboratory are shown,in which the black parts represent pores; both magmas show
spongy texture. The white bars in SEM and X­ray CT images
represent 500 mm long.

222  úËõ July 2012 Vol.25 No.4(C) 2012 The Japanese Society for Synchrotron Radiation ResearchgsbNX ¡ úËõ X üðp¢½¬®·é}O}Ì»ÌêÏ@FÎR¬ÎÌ½l«Ì´öð¾Öü¯ÄéB±Ìâñ_»YfÌ}O}ÉÎ·énðxÍ³ÍÉ­­Ë¶µCnàÅÍ[És­ÙÇ³ÉÈé½ßC}O}ªn\Öü¯Äã¸µ¸³³êéÆCr[âY_ù¿Ìæ¤Én¯«êÈ­ÈÁ½ö­«¬ªª­A·éB­Aµ½}O}ÍKXðÜÞ½ßC}O}SÌÌ§xÍ}É¸­µCå«ÈÍð¾é±ÆÅã¸Ìì®ÍÆÈéBÀÛÉÎR¬ÎÅ¬oµ½âÎðÏ@·éÆC½­ÌêCX|WÌæ¤ÈóðÜÞiFig. 1 Ì SEM im­
agejBµ©µC±Ìæ¤È­A»ÛÌð¾¯ÅÍÎR¬ÎÌ½l«ðà¾Å«È¢Bá¦ÎCö­«¬ªð¯öxÜÞ}O}ªÙÈé¬Îl®ðæèCÜ½\ªÈÊÌö­«¬ªðÜñ¾}O}ªärI¸â©É¬o·éP[XªxXÏª³êÄ¢é1_2) B³çÉCö­«¬ªðÜñÅ¢½Í¸ÈÌÉC¬oµ½}O}ÉÍÙÆñÇóª©çêÈ¢êàéBÈãÌæ¤ÈÏ@À©çC­AÉÁ¦Ädv¾Æl¦çêÄ¢éÌÍC­AÉæÁÄ`¬³ê½KXÌÎROÖÌ¬oiEKXjÅéBÂÜèCEKXÌöxÌá¢ÉæÁÄC}O}ã¸Ìì®ÍªÏ»·éÆ¢¤l¦ÅéiFig. 1jBÎRÌüÓÅÍC}O}Ì

¬oðºíÈ¢ärIÃ¸ÈúÉ¨¢ÄàCÎRKXÌ¬oâÎR«Ì¬ªðÜÞ·òÌNoª
EKXªN±ÁÄ¢é±ÆÍ¾ç©ÅèC}O}©çFig. 2 (Color online) A timescale of buoyant migration of bubbles
in magma. The rise speed (v) of a spherical bubble with a di­ameter of d is estimated from Stokes' law (vd2rg/18 m,where r and m are magma density and viscosity). The timenecessary to ascend 1000 m in a volcanic conduit depends onmagma viscosity and bubble size. When we assume bubble
size 1 mm on the basis of the observation of volcanic
materials, bubble migration takes more than 103 days. This ismuch longer than the timescale of magma ascent; hence, thebuoyant migration of individual bubbles is negligible for thedegassing during magma ascent.

éBEKXÌJjYÆµÄÍC}O}É`¬³ê½ÂXÌCAªÍÅ}O}©çª£·éÂ\«ÆC}O}ÅCA¯mªA¾ç©ÉÈÁÄ«½ÎR¬ÎÌ­«ðxz·évöÉÂµÄCAlbg[Nð`¬µ½ãC»Ìlbg[N¢Äc_·éB2 ÍÅÍCÀ±VXeÌTvÉÂ¢ÄCàðZ§¬ÆµÄKXªÚ®·éÂ\«ÈÇªñÄ³êÄ3 ÍÅÍ¬®·é}O}ÅÌ­AÆEKXðÂ»µ½¢é1)B}O}ÍS«ª­iã\IÈ}O}Å102`106ÊÉÂ¢ÄÐî·éB4 ÍÅÍÏ@³ê½Ê©çÎRPaÉs öxjÍÉì®³êéª£ÌÔXP[iCA¬ÎÌ½l«Ì´öÉÂ¢Äl@·éB{_¶ÅÐî·éÌ¼að1 mm Æ·éÆ1000úÈãjÍ}O}ã¸Ì·³Ï`À±uÆ X ü§ß@ÉRsÔXP[i¢êÅÔjæèà·¢½ßiFig. 2jCwBe@iX ü CTjðgÝí¹½À±ÍC»ÝC¢E}O}ã¸ÉN±éEKXÌJjYÆµÄÍZ§¬EKXªLÍÈóâÅé1)Bµ©µÈªçC}O}ªãðTµÄà SPring­8 ÅÌÝÂ\Å[^[fèC¡ã±ÌVXeðp¢½Vµ¢­©ªúÒ³êéB¸·éðºÅZ§¬EKXÉæÁÄKXÌª£ªN±
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10|6 _10|2 s|1 öxÅé3)B±êÍ¼a10 m ÌÎ¹i}O}ªn\Öü¯Äã¸·éÊè¹jðzè·éÆC}O}ª¨¨æ»10|5_0.1 m s|1 Ì¬xÅã¸·é±ÆÉÎ·éBc¬xÉÁ¦ÄÏ`ÊifcCÂÜèc¬xÆÔÌÏjàC}O}ã¸Ì­A©çEKXÜÅÌêAÌßöðð·éãÅdvÈp[^[ÆÈéBá¦ÎC2008NÉ­IÈÎR¬Îðµ½`Ì`CeÎRÅÍnº 5 km È[Ì}O}¾Üè©ç 4 Ôöx©¯Ä}O}ªã¸µ½Æl¦çêÄ¢Ä4)CãLÌc¬xð¼è·éÆ}O}É­¶µ½fcÍ1.44~10|2 _144öx
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èC{_Fig. 3(Color online) (a) A photograph of high temperature­pres­sure deformation apparatus installed in the synchrotron
radiation X­ray system of SPring­8 (BL20B2). (b) A cell as­
semblage inside of the furnace. A sample can be observed athigh temperature and high pressure conditions because only
a graphite cylinder and the sample exist on the X­ray path.
(c) A schematic illustration showing the rotational parts(black) and the xed part (white) of the deformation ap­
paratus during the X­ray CT. The furnace is xed by thestage.

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Ä¾Ä¢éobNOEh§ßÌBeû@ðüÇ·éKvªë¤BBeµ½æÍCGPU Rs[^[ðp¢Ä¬Ä\¬ðsÁ½ãCæðÍðs¤Bá¦ÎÈºÉÐî·éÀ±ÅÍCÏ@Ép¢½ X üGlM[i25 keVjÆ}O}Ì»wg¬©ç\z³êé_IÈ X üzûWð
vZµC}O}ÆCAðª¯é½ßÌñl»ðsÁ½Bñl»µ½æ©ç­AxâeCAÌTCYCCA¯mÌAxÈÇÌp[^[ðªè·é±ÆÅC}O}Ì­AÉEKXßöÉ¨¯éCAgDÌi»CÂÜè}O}ªã¸·éÉÂêÄ­AªiÞÌ©EKXªiÞÌ©ðèÊI
É¾ç©É·é±ÆªÅ«éB3. ·³ºÅ¬®·é}O}ÌÏ@Fig. 4Radiographic images obtained every 100 seconds duringmagma vesiculation. Because the X­ray attenuationcoecient of gas bubbles is smaller than that of magma, thelighter part corresponds to the bubbles. The tip of a lower
piston is found as black parts (convexo­concave shape) in
the lower portion. Every panel is 4.9 mm wide and 3.43 mm
high.

Fig. 5

Radiographic images obtained every 0.5 rotations (oneminute) during magma deformation. Every panel is 4.9 mm
wide and 3.43 mm high.

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Fig. 6Three dimensional images obtained by X­ray CT. The graypart represents magma and the black parts in the magma cor­
respond to gas bubbles. Before the rotation, bubbles showedspherical shape, and they were deformed and elongated afterone rotation. After the six rotations, the bubbles were highly
deformed and some parts in the magma have low vesicularity
due to degassing and subsequent compaction.

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k§»Ì½ßáó¦ÈÌæª}O}ÉsÏêÉ¶ÝµÄ¢é±ÆÈÇªª©éBÜ½C§ßÅàÏ@³ê½æ
¤ÉÏ`ªiÞÉÂêÄCCAªÏ`ÉÌµCAlbg

Fig. 7(Color online) A simulation of magma ascent in a volcanicconduit. Shear strain yielding in the magma is inversely
proportional to the ratio of the radius of the conduit (R) tothe conduit length (L) when the steady state Newtonian ow
is assumed in a cylindrical conduit (Poiseuille ow). The
shear strain also depends on the radial position in the conduit(y), and it is larger at the outer part of the conduit. When weassume R/L0.002_
0.02 (see text), almost all the magma inthe conduit experiences the shear strain `10, which islarge enough to induce the degassing and subsequent com­paction.

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çÌ»¡¾¯ÅÈ­C¬ÎÌ½l«ððÉ\ªµÐQðy¸·é½ßÉàKvsÂÅéB­I¬ÎðU­·éJjYÌêÂÆµÄÍCã¸É¬®·é}O}ÅÌÏ`Wª°çêéBÏ`WªN±é±ÆÅC»ÌÏ`WÑÈOÅÌCAÌÉÏ`ª}§³êCEKXæèà­AªisµC­I¬ÎÉéÆ¢¤l¦ûÅéBÀÛÉC{eÅÐîµ½À±uðp¢½À±©ç1)
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úËõ July 2012 Vol.25 No.4  227ÒÐîº kåwåw@w¤ÈnwêUn f¯¨¿ÈwÈ ³E0mail: sokumuram.tohoku.ac.jpêåFÎRwmªðn
2005N 3 HÆåwåw@Hw¤ÈmÛöC¹iwm)C2005N 4
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E­mail: nakammm.tohoku.ac.jpêåFâÎwÉÎRwmªðn
1993N 3 åwåw@w¤ÈmÛöC¹miw) CHÆåwåw@Hw¤ÈèCZ[HÈåwqõ¤õCkåwåw@w¤È³öÉy³öðoÄC2012N 1 æè»EB

Laboratory simulation of volcanism:
In situ observation of owing magma bysynchrotron radiation X­ray radiography andcomputed tomography
Satoshi OKUMURA

Division of Earth and Planetary Materials Science, Department of EarthScience, Graduate School of Science, Tohoku University,Miyagi 980_8578, Japan

Michihiko NAKAMURA

Division of Earth and Planetary Materials Science, Department of Earth
Science, Graduate School of Science, Tohoku University,
Miyagi 980_8578, Japan

Kentaro UESUGIJapan Synchrotron Radiation Research Institute, Hyogo 679_5198, Japan

Abstract

Understanding the mechanisms that control intensity, magnitude, and duration of volcanic erup­
tions is a central issue in volcanology; it is indispensable to eruption forecasting and volcanic haz­ard mitigation. The eruption mechanisms have been investigated on the basis of multidisciplinary
approaches including experimental approach. This paper introduces newly developed high tem­
perature­pressure deformation apparatus installed in the synchrotron radiation X­ray imaging sys­
tem which makes it possible to observe in situ magma owing at high temperature and high pres­sure conditions within volcanoes. On the basis of in situ observation of owing magma, we dis­cuss the mechanisms of foaming and outgassing of magma during its ascent in a volcanic conduit,
which may control eruption explosivity.

228  úËõ July 2012 Vol.25 No.4