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Eruptive Style and its Temporal Variation through the +3+.῍+3+/ Eruptionof Sakurajima Volcano, Southern Kyushu, JapanMaya YASUI῍, Masaki TAKAHASHI῍, Kazuhiro ISHIHARA῍῍ and Daisuke MIKI῍῍The +3+.῍+3+/ Sakurajima eruption was the largest eruption in Japan in the ,*th century and erupted
andesitic magma was about +./ km- DRE (Dense Rock Equivalent) in volume. Pumice fall and lava ﬂows weregenerated from the ﬁssure vents on the western and the eastern ﬂanks of the volcano and pyroclastic cones wereformed around the vents. Eruptive style changed with time. It is divided into three stages. After the initial,
vigorous, Plinian eruption of about -0 hours (Stage +), extrusion of lava associated with intermittent ash-emitting
eruptions with or without detonations lasted for about ,* days on both sides (Stage ,), followed by an outﬂow oflava for more than +./ years on the eastern side (Stage -). Consequently, the vast lava ﬁelds, which consist of anumber of ﬂow units formed on both sides of the volcano. Some units of lava show evidence of welded
pyroclastic origin, suggesting clastogenic lava. In the western lava ﬁeld, surface blocks characteristically consistof pyroclastic materials which show variable degrees of welding even within a single block. Typical eutaxitic
textures and abundant broken crystals are also recognized under the microscope. Some ﬂow units can be traced
upstream to a pyroclastic cone. These features indicate that many ﬂow units of lava on the western ﬂank areclastogenic, which were generated by the initial, Plinian eruption of Stage +. In the eastern lava ﬁeld, evidenceof pyroclastic origin is rarely discernable. However, the content of broken crystals varies widely from ,*ῌ to
2*ῌ in volume. Most lava ﬂows, which were erupted in Stage , associated with frequent ash-emitting eruptions,contain broken crystals more or less than /*ῌ. This fact indicates that magma in the conduit experienced
repetitive fragmentation and coalescence due to intermittent explosions prior to outﬂow. Lava ﬂows of Stage contain much smaller amounts of broken crystals indicating gentle outﬂow of coherent lava. Relatively
large-scale lava deltas developed toward the sea in the eastern lava ﬁeld. Eyewitness account at that time reportsthat ocean entry of lava from several points started several months after the beginning of Stage -. Althoughsmall-scale breakouts formed at the ﬂow fronts of some lava on both sides, a large volume of the deltas can not be
accounted for by secondary breakouts of ponded lava within the precedent ﬂow lobes. It is considered that lava
tube system fed lava to form the lava deltas.
Key words : Sakurajima Volcano, Taisho eruption, eruptive style, clastogenic lava+ῌ ῐ ῎ ῑ ῏UVW-XYZ< [$\4  \4 8]9:X!"#$ %" +3+.&+3+/  '()*#+$!8^_!`abCANc;=` %"de 2 fgh,-."/0123 +./ km- $#456768%9:

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Department of Geosystem Sciences, College of Humanities and Sciences, Nihon University, -῍,/῍.* Sakurajosui, Setagaya-ku, Tokyo +/0῍2//*, Japan.
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Sakurajima Volcano Research Center, Disaster Prevention Research Institute, Kyoto University, SakurajimaYokoyama, Kagoshima-shi, Kagoshima 23+῍+.+3, Japan.
Corresponding author : Maya Yasui
e-mail : yasui@chs.nihon-u.ac.jp