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Quaternary Volcanoes > Active Volcanoes > Kuju
Kuju Volcano   textGeologicMap3DgeologicMap
　Date 　Main activities
AD1995 11 Oct. 　Erupted with a chain of craters opening near Iozan, northeast Hosshozan.
　Ash falls and mudflows lasted until March of the following year.
AD1803   　 (error in interpreting old records. )
AD1777    　(changes in fumarole activities. )
AD1742 12 Feb.  　(clerical error in ages. )
AD1738 13 Aug. 　Protrusion of fumaroles or surface explosion of geothermal fields.
AD1675   　Protrusion of fumaroles or surface explosion of geothermal fields.
AD1663   　 (clerical error in ages. )
AD1662 26 Feb. 　Protrusion of fumaroles or surface explosion of geothermal fields.
　Slightly larger scale (?)

ZOOM
Table 1　Historical eruption records of Kuju Volcano.Almost reffered from Imura and Kamata(1996)
fig9
ZOOM
Fig.9　Location of the craters of the 1995 Kuju eruption
a1, a2, a3, b, c1, c2, c3, c4, d, e: eruption fissure and craters.
f: Steaming ground.
Hatched area: Fumarole area of Io Zan.
Contour interval is 20m.
4: Historic eruptions

4.1: Eruptions of historic times
   In the historical documents, volcanic activities of Kuju Volcano are recorded in 1662, 1675, 1738, and 1777. However, these were all protrusion of fumaroles or surface explosion phenomena of geothermal fields, and no deposits correspond to these eruptions (Imura and Kamata, 1996; Table 1).

4.2: 1995–1996 eruption
   During the evening of October 11, 1995, volcanic ashes were ejected from Iozan in the northeast region of Hosshozan. The height of the plume reached about 1,000 m, and ash fall was confirmed in the western direction Minamioguni town, Kumamoto Prefecture and even in Kumamoto City about 70 km away. The ejection of volcanic ash almost stopped by the early morning of October 12. The craters were lined up at N80°W nearly in an east–west direction extending about 400 m. In detail, fissures forming a hatch-mark shape developed to include craters a1–a3, b, c1–c4, d, and e ( Figure 9). The westernmost a1 and a2 craters produced small-scale mudflows. Near craters, ejecta dozens of centimeters thick were deposited that consisted of wet clay volcanic ash and altered lapilli; no pumice was visible (Hoshizumi et al., 1996). On December 18 and 22, volcanic ash was released including a small ash fall at Naoirimachi, Taketa City in Oita Prefecture about 14 km away. From the evening of January 13, 1996, to the morning of January 14 and into mid-March, small amounts of volcanic ash falls were reported. At the same time, many earthquakes occurred near Sujiyu to the west of Kuju Volcano and the Hosshozan area, some of which could be felt. In addition, contraction of volcanic edifices in northern Hosshozan area was observed. Volcanic tremors were observed occasionally until 1997 (Japan Meteorological Agency, 2013).

   This eruption contained very little fresh vesiculated glass in the beginning, but since December 1995, a small amount of fresh vesiculated glass was reported (Nakata et al., 1996; Hatae et al., 1997). Therefore, the eruptions likely changed from phreatic to phreatomagmatic. .


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