Vapour temperature in the steam well bored in thermal area rises generally with the depth, but the temperature gradient is various. This refers to the difference of flow rate, temperature of vapour and geothermal condition of surrounding rock. If the ground temperature around the well is nearly to the vapour temperature in the well, the vapour is not cooled by thermal conduction but only by adiabatic change. While, if the ground temperature is lower than that of the vapour, cooling by the surrounding rock may be chief factor for the vertical temperature distribution. As an example of the former, we give Geyser Well-4, discussing the temperature distribution with the adiabatic equation. Beppu-Hakuryu Well is cited as an example of the latter in which the temperatures at each depth are calculated by an approximate solution taking both coolings into account. The results were compared with observed values. Kuzyu-Otake Well-3 was bored to 900m in 1956, but at present, it is clogged by the scale at 65m below the ground surface and the mass of issuing gas is little. The vapour temperature is 98.4℃ at 65m depth, 97.2℃ at the upper end of the well. This little difference of the temperature is due to the condensation of the vapour, that is, the heat taken by the cooling may be compensated by the condensation.

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Systematic sampling in the lava flow erupted in 1950～1951 from Volcano O-sima was carried out in order to ascertain whether such a large lava flow has uniform chemical composition or a certain regularity in it. After the error of chemical analysis was determined, the sampling and the preparation of sample for chemical analysis from it was criticized by the iron content of 159 samples collected from the lava flow and the following conclusion was obtained. 1) This lava flow has very uniform total iron content, Fe₂O₃^* = 14.2～14.4, average 14.3%, and distinct difference of the total iron content from other lava flow or rocks erupted in other ages. Any distinct regular difference could not be found among their total iron contents of each part of this lava flow regardless their appearance of rocks samples such as red coloured, porous, scoriaceous, etc. 2) Fe₂O₃/FeO ratio in this lava flow varies distinctly owing to the degree of oxidation during the solidification of it and is larger in the samples of red colour, porous structure, and scoria, or stalactitic structure than normal compact samples. Any regular difference in the Fe₂O₃/FeO ratio could not be found among the 159 samples collected in this lava flow and other rocks erupted in other ages. 3) About 4g of rock sample was sufficient for the determination of the total iron content in this lava flow when about 4g of rock sample was completely pulverized. 4) One or two samples of about 10g is sufficient for the determination of the total iron content of this lava flow.

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Variation of chemical composition during magmatic differentiation is quantitatively calculated based upon assumptions of ideal solution and strong fractionation. The distribution coefficient k defined by [concentration in solidified rock/concentration in residual melt] is an essential parameter. The results are illustrated in a form of fractionation diagram which shows the variations of concentration versus solidification stage. (1) A model path for a simple crystallization differentiation of the Skaergaard-like magma is obtained and plotted in a FeO+Fe₂O₃-MgO-Na₂O+K₂O triangular diagram (Fig. 3). A model path for a contamination differentiation is also obtained in Fig. 4. (2) Based upon experimentally determined phase diagrams of FeO-Fe₂O3-MgO-SiO₂ system, a path for simple crystallization differentiation is traced. These model paths are useful to estimate physical conditions prevailing the differentiation of H. Kuno’s hyperthenic and pigeonitic rock series.

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The volcanic activity is on intimate relation with the variation of the volcanic micro-tremors and the deformation of the local crust in the volcanic area. It may be thought that these phenomena occur in the process of accumulating of magma beneath the crater and erupting of ejecta. The volcanic micro-tremors at Volcano Aso were divided into four classes by Prof. K. Sassa, according to their periods. Expecting that the volcanic activity will be accompanied with some phenomena having longer period than the volcanic micro-tremors of short period found by Prof. K. Sassa, the author has begun the observation of the long-period volcanic micro-tremors at Aso Volcano-logical Laboratory since March 1958, using a long-period horizontal seismometer having T₀ = 180sec. h₀ = 1, T_g = 100sec., h_g = 1 and V_max = 780. The long-period volcanic micro-tremors were observed before the eruption, June 24, 1958, of which the energy was estimated at nearly 10¹⁷ ergs. The nature of these long-period volcanic micro-tremors are: - 1) the period of the long-period volcanic micro-tremors is of 40〜55 seconds, 2) about twenty hours before the eruption the wave-trains are composed of three or four crests and troughs, then about five hours before they are composed of six or seven crests and troughs and finally about one hour before they decay, 3) and it is thought that these long-period volcanic micro-tremors are not induced by the volcanic micro-tremors of shorter periods, but due to the state of magma beneath the crater.

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