Since 1917, especially after the World War II, many investigations has been carried on to clarify the hydrology of Fuji Goko (five lakes) and hydrogeology of volcano slope with relation to groundwater development. Mt. Fuji, the highest peak of 3776 meters in Japan, is one of the largest and the most typical strato-volcano of basaltic rocks with gentle slope on all sides. It is noticed that this volcano has many large springs, five lakes with abundant water and some characteristic rivers on and around volcano.
Within past ten years, groundwater has been developed or is about to be developed in quantities ranging from 1, 400, 000m³ per day on southern part to 24, 000m³ per day on northern part. An extensive development of ground water for industrial use as well as for agricultural one has caused many troubles, such as abrupt decline of groundwater pressure, stopping or decreasing of spring discharge and groundwater contamination by sea water invasion.
Volcano body is a big reservoir which absorb and store rain water in its body as ground-water and release it over a long enough period. Hydrologic knowledges involving mode of occurrence of water, storage capacity of groundwater and water balance on volcano make it possible to evaluate the water potentiality of volcano as reservoir.
The author reviewed the results of past studies of hydrology of this area and collected all data useful for further study. (Tab. 1, 2, 3) (Fig. 2, 3) Mt. Fuji consist of three parts, Komitake, Old Fuji and New Fuji, errupted successively in descending order. (Tsuya 1940) The author and his collaborator, assumed that Komitake was impermeable in the previous studies. But, Machida's (1964) tephrochronological study of the pyroclastic fall deposit of this area supplied them new knowledges about permeability problemes. (Tab. 5) He collected all data about lakes (Tab. 6), river discharge (Tab. 7), spring discharge (Tab. 8) (Fig. 4) and permeability coefficient of different rocks. (Tab. 10) He also cheked data of geophysical explo-ration such as electric, seismic and radio active prospecting (Fig. 7) and that of deep well. (geologic column, electric logging, water level and specific discharge) Among these Ochiai's (one of his collaboraters) quantitative data about the velosity of groundwater through lava and porosity, using iso-topic materials
By these data above mentioned, he simulated groundwater body in Mt. Fuji as shown in Fig. 8 for mathematical analysis. He proposed the differential equation (1), transforming this by Bessel's function and obtained following equation which showed discharge amount of springs around Mt. Fuji.
Q=-2παTmAJ₁(ma)e-m²T/S t
Here, a:radius
T:transmmissibility coefficient
S:storage coefficient
v:time
Time dependant decresing factor is expressed as τ=τ₀e-m²T/S t. The result obtained from this calculation has fairy good coincidence with actual measurements.
He also proposed a diagramatic division on hydrologic structure of Mt. Fuji, classifying volcano body into three zones, as upper recharging zone, middle recharging zone, spring zone and gave brief explanation about these. (Fig. 9)

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Insolation depends on latitude and time. Under natural conditions, it is reduced by absorp-tion or diffusion of water vapor, clouds, dust and air molecules. It is approximately a function of cloud amount and the percentage of possible sunshine. The natural balance has, however, been changed by man's discharge of pollutants throughout the world. This phenomenon is particularly evident within cities, where an urban climate is created which differs from that in rural areas.
The object of the research outlined in this report was to consider Insolation from an urban-clima tological standpoint, by considering such problems as:
Why does any difference in Insolation occur within the compass of a city;ought it not to be constant?
By how much does it differ?
What influence does this difference have?
To solve such problems the author required the selection of suitable observation instru-ments. The Eppley pyrheliometer which has been used in Japan since the International Geo-physical Year is regarded as the most suitable, and was used for the research, taking contin-uous observations in central Tokyo and in the suburbs (Fig. 1). Observation stations were at the Joto Health Center and Asaka High School. In addition, solar radiation values avail-able at the Aerological Observatory (Tateno) and at the Japanese Meteorological Agency were used.
Observations were made from August 1, 1967 to July 31, 1968. Days were considered cloudless when insolation was not shut off by the clouds and when neither clouds nor altost-rati were present in the hourly observations at the Japanese Meteorological Agency. Only such cloudless days were considered for this report. Wind data at Seikei, Nishigahara, Haneda and Kawasaki and wind and temperature data at the Tokyo Tower were also used.
Based on the reduction of insolation, it became evident that cloudless days were best re-lated to three classes of wind direction: sea breezes, northerly winds and southerly winds. The reduction of insolation in Tokyo was shown to be
R=I_o-I_i/I_o×100
(I_o; Insolation at Tateno, I_i; Insolation a.t each location in Tokyo) It was decided to call R the “reduction index”.
Initially the seasonal change of cloudless days was investigated. The number of such days increased in winter and decreased in summer (Table 1) . The insolation at each locality was then compared with the value at the top of the atmosphere (Fig. 2) The dotted lines in Fig. 2 indicate transmission ratios of 0.6, 0.7 and 0.8. The insolation at Tateno and at Asaka reached about 70 per cent of the solar radiation on a horizontal surface at the top of the atmosphere, and the insolation at Joto and the Japanese Meteorological Agency did about 60 per cent.
The investigation then turned to the daily total insolation and the reduction index for the wind direction type: sea breeze, northerly and southerly. Typical days experiencing these wind directions were selected, and in 1967 these were October 31 (sea breeze), December 11 (northerly wind) and December 16 (southerly wind) (Figs. 3-5). Average daily total of insolation and reduction indices are given in Table 2. The reduction index appears largest during the sea breeze, while for the southerly wind large reductions are not found. It must therefore be assumed that the reduction of insolation becomes marked during sea breeze because sus-pended particles blown over the sea by the northerly wind are driven back again to the land by the sea breeze, without being diffused.
Differences in insolation between Sundays, holidays and weekdays were also investigated (Table 3). If the wind type and wind velocity were substantially the same, certain differences could be noted.

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Erosional processes of youthfully dissected strato-volcanoes in Japan have been studied quantitatively by physical and morphometrical analysis. The result may be applied to the study of slope development at general slope.
The amount of detritus eroded by tracting force of overland flow is given by a simplified function of slope length l and the sine of slope angle θ as follows;
E=Kl^msinⁿθ (1)
where K is a function of climatic, vegetational and geologic factors. K is supposed to be con-stant at each mountain slope assuming the mean condition in the long geological time. The value of m and n obtained by formulas on tractional load proposed by Brown, Shields, Du Boys and so on approximately ranges from 1.0 to 1.7. The amount of detritus eroded by secondary action of mass movement such as landslide and debris flow is given by the same equation. In this case, the value of m is larger than the above value. At actual mountain slopes, values of m and n are supposed to be smaller than theoretical ones, and to vary with slopes related to mainly the sorts of erosional phenomena there occur. The above equation of erosion may be applicable to fairly short and steep slopes.
Averaged profiles of initial landforms and altitudinal changes of average amounts of ero-sion were obtained by morphometric measurement at seven slopes of Iwaki, Haruna, Nantai, Takachiho and Yotei volcanoes. Gradients of the lower ends of the measured slopes where the amounts of erosion come to nearly zero are 15-20 degrees. The gradients approximately coincide with the critical angle of slope surface deposited by debris flow. Then, by introduc-ing the critical angle θ_c, equation (1) is modified as follows;
E=Kl^m(sinθ-sinθ_c)ⁿ(2)
By the method of least squares, multiple regression coefficients, log K, m and n were obtained with each slope. Substituting l, θ and θ_c obtained from the averaged profiles for the equation with determined coefficients, theoretical values of erosion are obtained at any place of each slope, and agree quite well with measured values. As Mt. Iwaki has long and gentle slope, equation (2) is applicable only to the upper slope, but Horton's equation on erosion can be ap-plied with success at the lower slope. Curvature of slope is infered to have only a little in-fluence on erosion.
From simplifying equation (2), partial differential equation on slope development is lead,
∂y/∂t=Kx(∂y/∂x+I_c)

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From 17th to 18th of August, 1968, very active fronts passing through the southeastern part of Gif u Prefecture, central Japan, brought about extraordinarily heavy rainfall, and disastrous floods and landslides resulted. The authors investigated the relation of the distribution and form of the landslides to rainfall, landf orm and geology. The results are summarized as follows:
(1) After intermittent rain which had continued from the morning of 17th, downpour started by midnight. At the time of the maximum intensity, more than 80 mm of rainfall were recorded during one hour and a half. It was after this time that most of the landslides occurred.
(2) All the landslides are of a small-scale, and only the weathered material 0.5_??_2 meters thick lying on the top has slided.
(3) The area of the most frequent landslides nearly coincides with the area where the maximum hourly rainfall exceeds 60 mm.
(4) The area where few landslides occurred in spite of hourly rainfall exceeding 60 mm has a landf orm composed mainly of gentle slopes.
(5) Between the area of palaeozoic rocks and that of rhyolitic rocks, no difference is found in the density or in the form of landslides.

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