Volcanic history of Kuchinoerabujima Volcano in the last 30,000 years is reconstructed based on tephra stratigraphy. Kuchinoerabujima is a volcanic island which is a cluster of at least nine volcanic edifices; Gokyo, Jyogahana, Ban-yagamine, Takadomori, Noike, Kashimine, Hachikubo, Furutake and Shintake. Eruptions within the last 30,000 years occurred from Noike, Hachikubo, Furutake and Shintake volcanoes. Two major pumice and scoria eruptions occurred between 15 and 11 ka after an inactive period since ca. 30ka. NoikeYumugi tephra (15-14ka, DRE＞0.06km³), erupted from the summit of Noike Volcano, consists of Yumugi pumice fall deposit and Nemachi pyroclastic flow deposit. Furutake-Megasaki tephra (12-11 ka, DRE ca. 0.8km³) erupted from Furutake Volcano and consists of Furutake agglutinate, Furutake scoria flow deposit and Megasaki scoria fall deposits. Volcanic edifice of Older Furutake was built during the 12-11 ka eruption. Eruption style changed around 10ka, after the collapse of Older Furutake Volcano. Activities of Yougner Furutake and Shintake Volcanoes are characterized with effusion of lava flow and no major pumice eruption is recognized. Lithic tephra erupted from Younger Furutake and Shitake Volcanoes within the last 10,000 indicates repetitive Vulcanian-type and phreatomagmatic eruptions. All historical eruptions since 1841 occurred at and around Shintake crater and were Vulcanian-type explosions with emission of magmatic materials and phreatic explosions.

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Kuchinoerabujima, located in southwestern Japan, is an andesitic volcano where explosive eruptions have repeatedly occurred. Seismicity increased in 1996 and 1999, and inflation of the volcanic body was detected by GPS surveys during the period from 1995/96 to 2000 (Iguchi et al., 2002). We established a continuous GPS observation network in April, 2004 to study the relation between seismicity and ground deformation. Vertical component of a baseline with a particularly large elevation difference is influenced by water vapor in the atmosphere. In this study, a simple atmospheric correction method is proposed to detect an upheaval component of 1 cm order. After the correction, ground deformation starting at the beginning of January, 2005 is clearly recognized at an observation site near the summit crater. The ground deformation has progressed at a rate of about 1 cm per 100 days, and it may be caused by a presumed pressure source at a depth of 300m beneath the summit. The deformation corresponded to increase in seismicity of high-frequency events at depths shallower than 500m. It is inferred that these phenomena were caused by hydrothermal activity.

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Kimpo volcano is a distinct volcano in central Kyushu, western Japan, and is located 30km west of the active volcanic front of Ryukyu arc. In order to determine the growth history of the volcano, systematic K-Ar dating has been performed. The activity of Kimpo volcano has been divided into three stages. The oldest activity formed the andesitic stratovolcano in the southern part (Older stage). Six ages are concentrated between 1.38 and 1.15 Ma. The horseshoe shaped caldera was formed before the middle stage activity. The middle stage activity formed the andesitic volcano in the northern part (Sannotake-Ninotake). Ages between 0.58 and 0.50 Ma are obtained from six samples. The youngest activity formed a dacite lava dome (Ichinotake), which is located within the caldera of the first stage activity. Two samples gave consistent ages of 0.2 Ma. The total duration of the volcanism at Kimpo volcano exceeds one million years. However, long periods of repose existed between each active stage: about 600,000 years between the first and the second stages, and about 300,000 years between the second and the third stages. These inactive periods are much longer than the durations of volcanic activities of each stage. It is therefore important to determine the duration of each active and inactive period of the volcanoes that have longer than a few thousand years of growth history.

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Flow properties of volcanic fluids beneath the Kusatsu-Shirane volcano have been studied at the Volcano Fluid Research Center, Tokyo Institute of Technology, by using geochemical methods. A novel seismic observation system, in which seismic signals from two borehole stations newly constructed at the summit are continuously acquired with the data from our previous observation system, started to monitor the activity of the Kusatsu-Shirane volcano in November 2001. The seismic signals are digitized with a 20 or 22bit A/D resolution and a sampling time of 0.01s, and are integrated with the seismic data from the Earthquake Research Institute, University of Tokyo. As a result, the detection capability of earthquakes and the accuracy of hypocenter determination are significantly improved especially in the Yugama region. Volcanic earthquakes in excess of 100 occurrences per month -5 to 10 times the number of earthquakes observed by the Japan Meteorological Agency - were observed by the new system. The observed volcanic earthquakes are tectonic type, with distinct P- and S-waves. A total of 602 earthquake hypocenters were determined between November 2001 and March 2003. The regions of Yugama and north Motoshirane are seismogenic regions in the vicinity of the Kusatsu-Shirane volcano. Seismic activity in north Motoshirane, which was unknown in the past, is equivalent to the activity in Yugama.

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The September 2004 eruptions of Asama volcano, central Japan, ejected essential materials such as pumice with bread crust on September 1st and scoria on September 23rd. The textural and chemical analyses on the materials reveal the crystallization processes in a deep magma chamber and a shallow vent. Two distinct stages of crystallization can be recognized in size distributions and morphology of plagioclase phenocryst and microlite both in the pumice and scoria. First stage (range I ): In a deep magma chamber, pyroxene phenocryst began to crystallize out at 1150℃, and then pyroxene and plagioclase continued to nucleate and grow slowly. Second stage (range II) is divided into two sub-stages for pyroxene or three (range IIa-c) for plagioclase. II a: Magma left the chamber and rose slowly through the vent with ever increasing nucleation rate. II b-c: In a shallow vent beneath the crater, numerous plagioclase microlites like swallow-tailed shape precipitated rapidly under a high undercooling condition induced by decompression. Plagioclase microlite in the pumice and scoria developed a characteristic population density like a bell with a peak at the grain size of 0.003mm, which is interpreted to reflect a decrease in nucleation rate of plagioclase, in response to crystallization and establishment of equilibrium during the time duration when the magma stayed in the vent. Magmatic temperatures estimated from plagioclase-glass equilibrium decreased to 850℃ before the September 1st eruption. The similarity in crystal size distribution of the pumice and scoria implies that they had a common ascent history, although groundmass in the scoria has lower crystallinity than that in the pumice, suggesting that the magma of the Sept. 23rd eruption stood lower in the magma column than the Sept. 1st magma.

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Asama volcano erupted on September 1, 2004, and volcanic bombs, lapilli, and volcanic ash were ejected, The distribution of the volcanic bombs was investigated by using IKONOS high-resolution satellite imagery. IKONOS imagery with one-meter ground resolution enabled us to identify the distribution of the impact craters greater than three meters in diameter. Many impact craters are distributed northwestward, according to the distribution density chart of the impact craters. The crater shape of Asama volcano was analyzed by using DEM created from airborne laser scanner data, and the result shows that there is no obstruction in the crater area to prevent volcanic bombs to be projected at an angle of 63 degree that gives the maximum attainment distance (Iguchi et al., 1983). It suggests that the shape of the crater did not affect the distribution pattern of the impact craters. The outline of the eruption can be understood based on the distribution pattern of the impact craters larger than three meters in diameter, which can be interpreted from IKONOS imagery.

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Asama Volcano had a series of eruptions from September 1 to November 14, 2004. We have carried out infrared observation at the eastern foot of the volcano since August 2002, and have succeeded in capturing successive plume imageries. We examined long term and short term variation in volcanic plumes related with the 2004 Eruptions. We examined long term variation of the plume height from January to November 2004, and found two different kinds of correlation between the plume height and other volcanic activities; the increase in plume height followed by the eruption with a long time delay, and that followed by the eruption promptly. The plume height turned to increase gradually in March and May with the increase of the A-type earthquakes and gradual inflation suggesting supply of magma in the deeper part, and the height increased anomalously from July 25 with rapid inflation suggesting magma migration to the shallower part. These anomalies were followed by the first eruption on September 1 about 40 days after. Erupted products included some juvenile materials, but the major part of the products were lithic materials. The plume height became lower just after the eruption, but turned to increase from September 12 following the increase of A-type earthquakes. The second eruptive stage started from September 14,2 days after the increase of the plume height. Three small eruptions occurred on September 14, and many small eruptions occurred successively from September 16 to 17. The erupted products were mostly well vesiculated juvenile materials. This evidence suggests that the eruptions in the second stage occurred with much volcanic gas, while the first eruption occurred after degassing from magma. We examined short term variation of the volcanic plume during the developing stage of the successive minor eruptions; from 00:57a.m. to 08:00a.m. on September 16. We got time series data of the average temperature on the certain vertical line segment, which is crossed by moving volcanic plume, and examined spectrums. As a result of analysis, some power peaks were confirmed at the multiples of 0.0025 Hz until 4a.m. And this peak was found to move to higher frequency according to the eruptive activity; 0.0032Hz at 7a.m. One possible reason is that Asama Volcano has some resonance beneath the crater (conduit), and the characteristic length of the conduit changed to be shorter during the successive minor eruptions. Japan Meteorological Agency reported the number of eruptions increased from 4a.m., and Geographical Survey Institute found a lava cake within the crater about 11a.m. These evidences suggest that magma ascended within the conduit around 4 or 7a.m., and may be consistent with our analytical results.

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The eruptive activity of Asamayama Volcano started at the summit crater on September 1, 2004. The first eruption was explosive and accompanied with very strong air shock. Before the explosion, significant tilt change was detected by a tiltmeter installed at the northeastern flank of the volcano by JMA. Tilting direction of the signal was in the sense of ground-up toward the west side of the station. BH-type volcanic earthquakes drastically increased at the same time as the start of the precursory tilt change. Including the first one, four remarkable explosive eruptions occurred. In all the cases, significant tilt change and the BH-type volcanic earthquake swarms were observed before the explosive eruptions. The starts of the precursory signals were about 3.5-29 hours before the explosions and the amounts of tilt change were 0.03-0.11μ radian. These features suggest that the prediction of explosion may be possible at Asamayama volcano. We estimated the crustal deformation source using the tilt data associated with the explosive eruption occurred on November 14. The location of the estimated dike intrusion source was about 1 km below sea-level at the summit area. The volume of dike was 4.6×10⁴m³.

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