The tomographic inversion of Fuji, using both artificial and natural earthquake data, suggests the existence of a super-critical water region at around a 10 to 15km depth and magmatic fluid at deeper than 20km.
A precise chemical evolution model of magma including timings of magma mixing and eruption was proposed for the Usu volcano. The temporal change of volatile components in the shallow rhyolite reservoir of Satsuma-Iwojima was interpreted as being linked to the process of depressurization in the magma reservoir, degassing due to convection in conduit, and the supply of volatile components from basaltic magma in the deeper part.
Eruptive history analyses were carried out for many volcanoes to make plans for long-term prediction of volcanic eruptions. For Fuji, there was an active period that formed a volcanic edifice “Sen Komitake” with basaltic ejecta, preceding the well-known Shin-Fuji, Ko-Fuji and Komitake active periods. In addition, the details of flank eruptions in the last 10,000 years, especially eras of flank eruptions in the last 2,000 years, became clear. The diversity of magma of Fuji volcano results from mixing between the differentiated magma in the shallow reservoir and magma being episodically supplied from a deep (10 to 20km) reservoir, the location of which was inferred from seismic tomography. The Unzen volcano activity that started about 0.5 million years ago was classified into three periods with distinct characteristics.
SO2 gas emission at Miyakejima volcano was observed by satellite and airborne multi-spectral scanners (MSSs), both of which provided data coincident with those of COSPEC. The airborne MSS also employed a technique to reduce the eruptive column effect. In-SAR analyses using the data acquired by the new satellite DAICHI (ALOS) have detected overall ground deformation of many active volcanoes.
A new emission quantity observing instrument, Differential Optical Absorption Spectroscopy (DOAS), was developed. This is one-third to one-fifth the weight and size of COSPEC instruments. The development of the sensor for the chemical components of volcanic smokes enabled observation near the gas-emitting field. A system for visualizing the SO2 distribution in an eruptive column revealed the detailed temporal variation.
3. National Project for Predicting Volcanic Eruptions
The seventh 5-year plan of the national project was proposed by the Council for Science and Technology in 2003 after reviewing the achievements of the project since 1974. The proposed plan consists of three parts: (1) Enhancement of volcano monitoring and observational research, (2) Promotion of basic research for more accurate predictions of volcanic eruptions, and (3) Improvement of the scheme for predicting volcanic eruptions.
Based on this project, universities conducted comprehensive joint volcano observations at Kusatsu-Shirane, Ontake, Asama and Usu and dense seismic-array observations at Fuji, Kuchinoerabu and Asama. Detailed structures in terms of seismic wave velocity were developed at Hokkaido-Komagatake, Fuji, Kuchinoerabu and Asama volcanoes using active seismic sources. Analyzed results suggested a high-velocity region upheaval beneath the volcanic centers. At Iwate volcano, analysis using receiver functions of far-field seismic data suggested a low S-wave velocity zone at about 30km depth. Analysis of later seismic phases in Unzen volcano seismic data revealed the magma plumbing system with magma pockets.
The temporal movement of the activity source toward the western region in Iwate volcano was detected by analyzing data of seismicity and ground deformation. A model of the magma system was inferred to consist of an intruded dyke and hydrothermal system. A magma system was indicated by seismic and geodetic data analyses at Miyakejima volcano.
University researchers conducted a challenging project incorporating observation, field and laboratory experiments, and modeling, entitled “Dynamics of Volcanic Explosion,” based on a