VLF-EM method and radioactivity prospecting were carried out in Bandai-san Caldera. The distribution and characteristic of fault system in Bandai-san Caldera occurred in 1888 eruption were made clear.
The results of these prospecting show that the fault systems is divided into three directions; north-south direction, northeast direction and east-northeast direction. The most prominent fault identified by this study was the north-south fault located within the central portion of the caldera. The northern extension of this fault appeared to be connected to the eastern scarp of Avalanche valley and the southern extension appeared to be under the peak of Kobandai-san which was destroyed by a volcanic eruption in 1888. Northeast and east-northeast faults cut across the caldera.
Considering the results of this study and other geological informations, it may be inferred that the northsouth fault was formed by intrusion of north-south dike. The directions of northeast and east-northeast fault are concordant with the ridge direction of Kobandai-san. The feature suggests that the northeast and the east-northeast fault are gravity fault caused landslide plane.

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This paper presents the changes of physical properties of inside slope of the decomposed granite soil, MASA, on the basis of the results of four tests, namely specific surface, X-ray diffraction, pore content and pFmoisture content.
According to the results of these tests, the authors have recognised that the soil at the upper layer of natural slope composed of the Masa are influenced very much of the granulation and the alteration of constituent minerals and that soil texture of the upper layer changes from sandy soil to clayey soil.
Moreover, we can think that the generation and development of the fine pores in soil particles are deeply concerned in the changes of soil texture from coarse to fine soil.
With the change of soil texture, the soil of upper layer of MASA slope has been higher water retention comparing with lower one. It can be considered that there are deeply the effect of the total content and distribution of fine pores for high water retention of upper layer soil.

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Downward infiltration of rainwater within the Quaternary pyroclastic plateau have been studied by using continuous and automatical survey of electric prospecting and chemical analysis of seepage water from the foot of the plateau.
Reduction of apparent resistivity and its downward extension are recognized within the plateau just after the heavy rain. This means the existence of downward infiltration of rainwater.
However, the style of infiltration is various, and it seems to be strongly influenced by rainfall condition and surface humus soils.
Downward velocity of the infiltration is estimated to be 60 meters/12 hours, and this value is too rapid compared with the well-known value of 1-3mm/day. Probably, two types of downward infiltration may co-exist because of cooling joints or pipe structures within the pyroclastic flow deposits.
On the other hand, chemical analysis of seepage water shows that the concentration of ions may change depending on that of rainfall. This may support the result mentioned above of the rapid velocity.

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Serpentines occur in ultrabasic dykes, ophiolitic complexes, melanges, etc.
The author has classified serpentinization, based on the above occurrences, into 4 types. Type A is the Serpentines that occurs in dykes, type B occurs in complexes, type C occurs in serpentine melanges, and type D occurs in the sedimentary melanges.
Further classification established 3 alteration grades of serpentinization. Alteration grade-I is the forming serpentinite (massive serpentine), alteration grade-II is forming of foliation or shearing by the tectonic movement, and alteration grade-III is the talc-chlorite alteration by the regional metamorphism.
It might be shown that hard constructions in the serpentine areas are owing to the alteration grade-II zone.
Chrysotile and antigorite in serpentinite causes serious unsymmetrical pressures and deformations in rocks, since they have the peculiar characteristics of swelling and viscosity, and that causes land-slides near land cuttings in Serpentine areas. Talc and Mg-chlorite, as clay minerals belong to the same Phyllosilicates, also show similar characteristics to Serpentinite. Mg-chlorite has characteristics of swelling. The axis perpendicular to the foliation plaine of the serpentinized rock is considered to be maximum principal axis of swelling pressure.

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