Volcanic gas plays key roles in various volcanic activities. Thus, measurements of volcanic gas chemistries and its fluxes are important for understanding volcanic activities. Although, UV spectrometers have been used in conventional volcanic sulfur dioxide flux measurements, visualization technique of sulfur dioxide in volcanic plumes are now used for understanding behaviors of volcanic plumes and for high temporal resolution flux measurements. The technique uses two UV sensitive CCD cameras with bandpass filters which are within and outside the UV wavelength range of sulfur dioxide absorption, respectively. By using the visualization technique, volcanic gas observation has been improved extensively and is now able to link with geophysical observations. In this article, the method for the visualization technique and its application in volcanic gas measurements are described.

Weakening process of the crust is an important key for understanding of crustal dynamics. Earthquake faulting is a phenomenon of inelastic deformation taking place within seismogenic zone and its occurrence is affected by stress condition of the crust. High-resolution hypocenter distribution, fault orientation of small earthquakes, and structure of seismic wave propagating velocity illuminate present condition in the crust. Therefore, we are carrying out seismic observation by one thousand stations in an aftershock area of the 2000 Western Tottori earthquake (M7.3). It is expected that the detectability of earthquake is smaller than magnitude of minus 1 and accuracy of the fault orientation is less than several degrees. These observation enable us to visible the crustal activity.

  Recently, “Muography” technique for probing inner structure using cosmic ray muons is making progress remarkably. Visualization of density structure of inner volcano is one of the remarkable results. However, this technique could be applied to only the structure above the detector, because of its technical characteristic. Therefore, most of former studies using muography technique target object which are above the ground, such as mountain. We developed new observation system to extend observational target to underground, especially seismic fault.

The observation system has been installed at Atotsugawa, Kamioka, Hida, Gifu prefecture where the part of Atotsugawa fault zone. We performed structural survey of the fault zone to depth of 100 m. Then, we observed a sign of average density change caused by the fault zone which exists around the borehole.

  In near future, we extend the observation depth to 300 m and perform for detail investigation.

As a water-rich magma ascends upwards, it vesiculates into bubbly foam as a result of solubility decrease due to decompression. Further ascent results in magma fragmentation into a mixture of high-temperature gas and pyroclasts. On the other hand, the same water-rich magma often erupts non-explosively, producing bubble-less lava. For the non-explosive eruption, it is considered that open-system gas loss works efficiently to reduce the gas content. However, little is known about the mechanism of the gas loss, because evidence for gas transport is rarely found in volcanic rock. In this paper we review previous researches on the gas transport in the magma. We also discuss a new method to visualise the gas transport pathways that may be preserved in volcanic rock.

  Recent experiments conducted at sub-seismic to seismic sliding velocities (mm/s to m/s) show the dramatic weakening in the friction coefficient for a wide variety of rock types due to mechanochemical effects by frictional heating. Consequently, several weakening mechanisms have been proposed depending on the type of rock specimens. Some of them are based on the sample observation and analysis after experiments. Direct observation of frictional contacts during an experiment is indisputable to constrain an elementary process at frictional contacts during slip. In this paper, we show the direct visualization of temperature distribution of frictional interface during the high-velocity friction experiment at slip velocity of 1m/s.

Laboratory experiments help visualizing subsurface volcanic processes of which direct observation is difficult. We have explored "fragmentation wave" that has been believed to occur in magma during an explosive eruption. Shock-tube apparatuses are used to apply rapid decompression to specimens made of silicone compound and volcanic rocks containing bubbles. We successfully visualized propagating fragmentation fronts, which were exactly like the image of the volcanic processes. However, applying the results to magma fragmentation was found difficult, because of significant effects of adhesion of the specimen to the tube wall and difference in viscoelastic properties between flowing magma and the specimens. The difficulties have overcome by the experiments using porous syrup specimens. We have found a particular fragmentation behavior characterized by significant time delay after decompression and by successive explosions. Combining the fragmentation experiments with X-ray radiography and computed tomography, we are now approaching ductile processes inside the specimen that may control the speed of fragmentation.