The activity of Towada Volcano started about 200,000 years ago and more than 20 eruptive episodes are geologically recognized. Ninokura scoria group is collective name of the series of pyroclastic fall deposits which erupted just after the latest caldera-forming Hachinohe pyroclastic flow (13,000 y. b. p.). On the basis of field investigation, systematic sampling and analysis of Ninokura pyroclastic fall deposits, we divided Ninokura scoria group into 11 tephra layers in descending order ; NK-a～NK-k. Each eruption mass of the layer is about 1.2〜35.9×10¹⁰ kg. Total mass of Ninokura scoria is about 1.74×10¹² kg. Ninokura scoria group eruption starts without long dormant time after Hachinohe pyroclastic flow eruption. The mean interval of Ninokura scoria group eruptions is about a few hundred years.

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The Nigorikawa Caldera in southwest Hokkaido, Japan, is 3 km in diameter at the outer rim. Drilling data from 42 geothermal wells of up to -3,000 masl (m above sea level) has been used to study the internal structure of the caldera. Interpretation of the data shows an angular funnel shape, with a wide upper region (3×2.5 km) tapering to a narrower lower region (0.7×0.5 km). The shear zone is the same shape as the caldera, that is, rectangular with a NE-SW elongation. The caldera is infilled with vent-fill material, lake and alluvial deposits, landslide deposits, and post-caldera intrusions. The vent-fill material is a gray, non-welded lapilli tuff and tuff breccia, which homogeneously includes accidental lithics and shattered fragments, which were sheared during pyroclastic eruption, as well as accretionary lapilli occurring up to -824 masl. The vent-fill is intercalated with many lithic bands or lithic dominant zones that dip toward the caldera center. No large fault displacement can be recognized around the caldera wall. The Nigorikawa Caldera was formed ca 12,000 years ago by violent pyroclastic flow eruption, fall-back, and the following subsidence by compaction with degassing.

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Soon after the beginning of the 1995 eruption from the south of Iwoyama in Kuju volcano, GPS and EDM instruments were set around the newly opened craters and fumarolic zone around Iwoyama to observe ground deformation. The data of repeated measurements of GPS and the continuous automatic EDM clearly show the deflation around the fumarolic zone on Iwoyama and no significant deformation around the new craters. Volume changes and locations of Mogi models were calculated for every two years from 1995 to 2001. They were estimated to be around 500～600 meters in depth from the surface and 250 thousand cubic meters of deflation, respectively for the entire monitoring period. The deflation is likely to occur by over effusion from the upper middle part of the geothermal convection system. This type of deflation would cause contraction of the peripheral area of the geothermal field to make new cracks to introduce eruption in this area.

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Ground deformation around Iwate and Mitsuishi-yama volcanoes was monitored by Electro-optical distance measurement (EDM), global positioning system (GPS), and leveling from 1998 to 2002. Repeated GPS observation data, which showed a four to six centimeter eastward movement of the summit of Iwate volcano in 1998 and 1999, are concordant with the interferometry SAR analysis by the NASDA, which showed the expansion around the Mitsuishi-yama in 1998. The leveling on the north side of Iwate and Mitsuishi-yama volcanoes also showed the upheaval around the Mitsuishi-yama between 1998 and 1999, and depression between 1999 and 2000. The automatic continuous GPS observation and data transfer system was developed in this study, and the data showed the depression of the Mitsuishi-yama area from 2000 to 2002. The direction of the depression was not straight downward, but the south or south-south-east at the rate of one to three centimeters a year. According to the extent of the deformation area, their source is thought to be at a depth around eight kilometers. A higher temperature granitic body of five hundred degrees centigrade or more has been already detected directly by drilling in the Kakkonda geothermal field, just south of Mitsuishi-yama. The addition of new magma to the granitic body or separation of gas from the magma possibly caused the expansion in this area in 1998 and 1999, but it may be difficult to explain the depression of this area from 2000 to 2002.

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A three-dimensional seismic velocity structure in the edifice of the central cones of Aso Volcano is obtained from a tomographic inversion to seismic data of a controlled source experiment ASO98. The three dimensional Pwave velocity structure with dimensions of 12 km × 9 km × 2 km is derived from 1207 P-wave first arrivals at 296 temporary stations for six explosions. The entire velocity structure obtained includes higher velocities than those of any previous velocity models down to 0.5 km of altitude above sea level. A high velocity zone and a low-velocity zone are revealed in the obtained velocity structure. The high velocity zone lies toward WSW direction from the active crater. The strike of this high velocity zone is coincident with the general alignment of the central cones and with a trend of the high gravity anomaly in this area. The high velocity zone is inferred as dykes or volcanic deposits with dense materials from its coincident location with the high gravity zone and drilling core samples in the vicinity. The low velocity zone is located in the northwest flank of the central cones. The low velocity zone implies deposits with low density and low velocity material beneath the northwestern flank.

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Yumuta tephra layers 1～9 (Yum 1～9) in ascending order are recognized in tephric loess between Aso-3 (110～123 ka) and K-Tz (90～95 ka) widespread tephras on the Yumuta plateau, west side of Yufudake volcano, Kyushu. Ata (95～110 ka) widespread tephra is also seen between Yum2 and Yum3. Therefore, eruptive age of Yum3～9 is ca. 100 ka. Yum3, 7, 8 are correlated with Tsukahara 3, 2, 1 pumice layers (TP-3, TP-2, TP-1) at the north foot of Yufudake Volcano on the basis of shape of volcanic glass shards, the refractive indices of glass, orthopyroxene and hornblende. Mineral assemblage and refractive indices of minerals show that Yum8 is the tephra erupted from Kuju Volcano above Kuju-Shimosakata pyroclastic flow deposites and that Yum3 through 8 are correlated with a part of Aso-ABCD airfall pumice erupted from Aso Volcano.

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