Several heat flow values observed in the granitic rock regions of Japan show anomalously high ones amounting to 150 mW/m² (3.6 HFU), compared to the geologic age-heat flow dependency. As origins of such anomalously high heat flow values, the following were investigated: (1) anomalous concentration of radioactive heat elements, (2) residual heat of intrusive granitic bodies, (3) upheaval and denudation of granitic bodies, (4) deep volcanic activity in more recent ages, and (5) hydrothermal circulation in the deeper crust. As a result, the possibility of the deep volcanic activity in more recent ages is suggested. This means that even if recent volcanic activities are not observed at the surface, there may exist a high temperature state in the deeper crust and the upper mantle at present.

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Remarkable infrasonic waves from the eruptions of Izu-Oshima Volcano in 1986 and 1987 were recorded by a tripartite array of low frequency capacitor microphones installed in Kariya, 215 km west of the volcano. The signals from the 1986 eruptions were recorded intermittently from Nov. 17 through Nov. 23, despite somewhat unfavorable propagation conditions, the infrasonic rays being reflected only in the thermosphere. The dominant frequency of the observed waves was around 0.5 Hz until Nov. 19, but it was as low as 0.1 Hz by the evening of Nov. 21. Also, the signal amplitude became considerably larger on Nov. 21 and the strongest signals were recorded from the evening of Nov. 21 through 0100 JST on Nov. 22. These facts are in accordance with the change in the mode of eruption at the summit crater from the early stage to eject lava spring continuously to a highly explosive stage. Although intensive fissure eruptions took place simultaneously on the evening of Nov. 21, the observed strong signals are mostly attributable to the eruptions at the summit crater. The infrasonic waves from the 1987 eruption arrived as two distinct wave packets with duration of 1 to 2 minutes, and this fact indicates that the eruption was of a nature of single intensive explosion, rather than a continuous or repetitive ones as in the case of 1986 eruptions. The separation into two packets is explained by the difference in the reflection heights in the atmosphere, the former being in the upper stratosphere and the latter in the thermosphere. Judging from the signal amplitude, the strength of the 1987 explosion is estimated to be comparable to the most intensive one that took place in the series of 1986 eruptions.

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Distitribution of the melt phase in a partially molten system is controlled by the interfacial energy ratio between the melt and solid phases under textural equlilbrium and hydrostatic condition. In case of multiphase solids system, the melt phase distribution is not homogeneous at grain boundaries due to the different dihedral angles (i.e. interfacial energy ratios). By using a newly proposed model of the the multiphase grain control percolation (MGCP), critical modal composition and critical melt fraction, at which the melt network is connected extensively over the system, for a natural spinel Iherzolite are estimated to be 63 and 0.8 vol.%, respectively. Petrological and geophysical implications are discussed for the partial melting and cumulate forming processes. It is likely that a partially molten layer would remain at critical state where the melt network becomes connecting thoroughout the system.

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The Kannabe monogenetic volcano group is situated in the back-arc region of southwest Japan and is composed of six scoria cones (Nishiki, Yamanomiya, Buri, Otsukue, Kiyotaki and Kannabe) and one scoria bed (Nishibashi-kita). Stratigraphic relationships between various groups of ejecta are inferred from the tephrochronology of fall scoriae and widespread tephra. With the exception of Yamanomiya and Kiyotaki, the volcanic activity began with the formation of scoriae and ended with a phase of lava flow extrusion. No such lava flows are developed in either Yamanomiya or Kiyotaki. The volcanic activity of the Kannabe volcano group mainly took place prior to 21,000-22,000 y. B. P. with the exception of the Kannabe scoria cone itself, which was active before 6,000-6,500 y. B. P. In the vicinity of the Yamanomiya scoria cone, a new debris avalanche deposit has been discovered. This consists mainly of blocks of the Yamanomiya scoria cone, which preserve their original stratification defined by preferential alignment of scoriae and spatters.

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About 50 volcanoes are active each year, threatening the lives and property of millions of people. The highest risk volcanoes are those which are likely to erupt explosively within decades or less, that are not presently well studied or monitored, and that are surrounded by a large population. Volcanic disasters since 1700 A.D. have killed more than 260,000 people (a number that would be much higher with today’s population), destroyed whole cities and forests, and severely disrupted local economies for months and even years. One of IAVCEI’s main goals is to prevent losses from volcanic eruptions. The International Decade for Natural Disaster Reduction (IDNDR) has a similar goal for all natural hazards. In support of the IDNDR, this Task Group urges a package of new projects for volcanic disaster prevention during the 1990’s. Activities in this package would supplement a considerable body of volcanic hazards work that is already in progress; new projects would take advantage of the excellent climate during the IDNDR for international cooperation. Volcanic hazards need not, and must not, become volcanic disasters. The package of suggested projects includes: ○Hazard and Risk Mapping: reconnaissance mapping of hazards and risks at previously unmapped volcanoes ○Volcano Surveillance: new, rudimentary volcano surveillance where little or none exists today ○Public Education: improved education about volcanic hazards ○Dialogue with Public Officials: scientists helping civil defense officials and community leaders on questions of emergency planning, land use planning, and other risk-reducing activities ○“Decade Volcano” Demonstration Projects: in-depth, multi-disciplinary, multi-national demonstration work on all phases of the hazards mitigation process, at about 10 selected "Decade Volcanoes" ○IAVNET: an electronic mail and voice network for rapid, long-distance communication between vofcanologists ○Reference Materials: development of national volcanological archives ○Volcano Training: training in volcanology and mitigation techniques ○Low-cost Equipment: development of new, reliable, low-cost monitoring equipment ○Satellite Monitoring: remote sensing and satellite-relayed monitoring that could not be accomplished at lower cost by conventional means ○Crisis Assistance: both national and international ○Seed money: grants for volcano mitigation projects, to be matched by local or national governments, or private interests ○Publications: publication and wide dissemination of lessons learned during volcanic hazards mitigation work of the IDNDR. Approximately US$ 10 million/year will be needed to fund this package of activities. These costs must be borne in part by international organizations, in part by bilateral cooperation agencies, and in part by national and local governments.

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