A paleomagnetic study was carried out on four historic and three pre-historic lava flows at Sakurajima volcano, Kyushu, Japan. Measured directions of natural remanent magnetizations and paleointensities indicated good concentration for each lava flow with a few exceptions. The directions and paleointensities from historic lava flows are concordant with those expected from known geomagnetic secular variation in Japan. This suggests that they correctly reflect the ancient geomagnetic field and such comparison is applicable for the age estimation. The Nagasakibana, Kamonzaki, and Miyamoto lava flows were paleomagnetically corresponded to the late 8th century, about 3 ka, and about 4 ka, respectively. These ages are consistent with lava stratigraphy. The paleointensity determination combined with directional measurement was much helpful to reduce possible candidates of those erupted ages.

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We have applied FT-IR remote sensing to the measurement of the volcanic gases of Aso volcano, central Kyushu, Japan, which has inaccessible fumaroles in an active crater. The observations were carried out three times between August 1996 and August 1997. As a result, in all observations, CO, CO₂, SO₂ and HCl were remotely detected and those column concentrations were estimated by comparison between theoretical and observed spectra. The observed CO/CO₂ and CO₂/SO₂ changed accompanying with the fumarolic temperamre. The observed CO₂/SO₂ decreased from August 1996 to April 1997 and increased from April 1997 to August 1997. As the variation of CO₂/SO₂ may attribute to the depth of magma degassing, the depth of magma degassing may have become shallow from August 1996 to April 1997 and deep from April 1997 to August 1997. The observed HCl/SO₂ showed low values (0.02 to 0.04) during the period. They are typical values at the quiescent stage of this volcano.

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The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), which will be launched on EOS AM-1 platform in 1999, is a high spatial resolution imaging spectro-radiometer in the visible to near-infrared, shortwave-infrared and thermal infrared regions. ASTER can be used for volcano observations from the viewpoints of topographic and geologic analyses, mapping volcanic products, eruption plume analysis, discolored sea water and crater lake monitoring, generating digital elevation models, surface temperature mapping and sulfur dioxide emission analyses. The ASTER allows continuous temperature measurements ranging from amibient temperature to 460℃ and from 670℃ to 910℃. The TIR instrument can be used to make estimation of sulfur dioxide content of volcanic plumes. The authors propose the global volcano monitoring plan by using the ASTER data, in which over 900 volcanoes will be monitored periodically according to their volcanic activity. The volcanoes to be monitored are divided into three classes, A, B and C. Volcanoes in the Class A, which had several eruptions during last 10 years, will be observed every 48 days in day time and every 32 days in night time. Volcanoes in the Class B, which had several eruptions during last 100 years, will be observed every 3 months in day and night time. The other volcanoes classified to the Class C will be observed every 6 months in day and night time.

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Taiheizan pyroclastic deposits (3,710+130y.B.P.) are the youngest pyroclastics of Sambe Volcano, southwest Japan. The deposits are distributed mainly on the southwestern and eastern flanks of the volcano. We preliminary report the depositional process of the deposits on the southwestern flank, and quantitative perspective on the flow properties of block-and-ash flow. Depositional processes suggest that more than 6 times block-and-ash flows associated with small-scale pyroclastic falls and surges occurred during the youngest volcanic active stage (Taiheizan stage). These block-and-ash flows are considered to have derived from partial collapse of growing lava dome, which exits on the present main part of Sambe Volcano. Dacite block-and-ash flow type pyroclastic flow deposits are distributed along the Hayamizu River up to 9 km from the source area. A typical flow unit is composed of four depositional subunits which are (1) the poorly sorted boulder-sized blocks with normal to reverse grading, (2) poorly sorted boulder-to cobble-sized blocks with gas segregation pipes, (3) well sorted plane stratified lapilli and ash, and (4) well sorted ash with normal grading, in ascending order. The fomer two subunits can be interpreted as the main body deposits of block-and-ash flow, in which grains must be supported mainly by grain collide dispersion and fluidization, respectively. The third subunit of stratified lapilli and ash indicates the deposits of ash cloud surge with turbulence grain support mechanism. Depositional facies of the fourth subunit suggests the suspension fallout deposits from ash cloud. The flow viscosity is quantitatively estimated by assuming possible flow velocity. The visccsity of the upper main body of the block-and-ash flow was about 0.72 to 4.7 poise, and that of ash cloud surge was about 0.18 to 0.75 poise.

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