A computer-communication system has been developed in order to collect geophysical data from remote volcanoes via a public telephone network. The system is composed of a host personal computer at an observatory and several personal computers as terminals at remote stations. Each terminal acquires seismic, infrasonic, ground deformation or other pertinent geophysical data. Seismic and infrasonic events are recorded at a sampling rate of 100 Hz by a triggering algorithm. The absolute value of amplitude of seismic waves is averaged over one minute and the hourly numbers of minor events are counted. Ground deformation data are recorded at time intervals of 1-60 minutes. These data are stored in the terminals temporarily, and transmitted to the host computer upon command from either the host computer or terminals. Experimental monitoring has been conducted between Sakumjima Volcanological Observatory and several stations in the Satsunan and Kyushu Islands. The seismic and eruptive activities of Suwanosejima volcano have been monitored by this system since May 1989. At the volcano. earthquakes and air-shocks accompanied by explosive activity have been observed over the two periods, June 22-26 and September 16-November 6, 1989. B-type earthquakes occurred prior to the relatively prolonged eruptive activity from September to November. Intermittent occurences of volcanic tremors were also clearly recognized from the change in mean amplitudes of seismic waves.

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Hachijo island, located 300 km south of Tokyo, consists of two Quaternary volcanoes; Higashiyama in the southeast, and Nishiyama in the northwest. The eruptive history of the Higashiyama volcano was investigated. The volcanic edifice of Higashiyama is composed of Early stratovolcanoes I,II, Middle stratovolcano, and Late volcano. A series of dacitic pumice fall and flow eruptions took place ca. 22,000 yBP, at the end of the Middle stratovolcano, Sueyoshi stage. Evacuation of a large amount of magma in this stage caused formation of Mihara caldera of 1.4 km×0.9 km. The history of the Late volcano can be further subdivided into the Nakanogo and Mitsune stages. In the former stage, basaltic scoria-fallout eruptions frequently took place inside the Mihara caldera and east to south flank of the volcano. While in the latter stage, eruptive vents were restricted on the flank of the volcano. The major erupted magma type changed to differentiated andesite and dacite. The last eruption of Higashiyama which covered the whole volcano was estimated to be 5,000-4,000 yBP. Beside tephras from Higashiyama, at least seven hydromagmatic-eruption deposits from northwest of Higashiyama volcano are detectable. They are most likely the products resulted from the submarine to the earliest subaerial eruptions of the Nishiyama volcano, in 10,000-8,000 yBP.

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The recent progress of physical volcanology is reviewed focusing on studies on volcaniclastic flows and their deposits. Pyroclastic flows are high-particle-concentration, laminar currents with gas as a continuous phase. Pyroclastic surges are low-particle-concentration, turbulent currents with gas as a continuous phase. Lahars are flows of debris with liquid water as a continuous phase. Debris avalanches are catastrophic landslides in which a continuous phase is absent or plays no role for the motion. Owing to the upward gas flow, fluidization processes operate in pyroclastic flows. Flow behavior and resultant deposits are remarkably different depending the degree of fluidization, because it effectively reduces the yield strength of the flow. However, the distance traveled is slightly affected by the degree of fluidization. It is determined mainly by the mass incorporated at the source or by the velocity acquired when it wes initiated.

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The optical detection of fission-track in minerals and glasses in the early 1960's was subsequently utilized in dating geological matehals. Fission-track dating technique has had a rapid growth in its application from the dating into a successfull themotectonic analytical tool in the realm of geochronology. Recent fission-track length studies have shown that thermal overprints can also be detected and dated by this technique.

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