Sakurashima Volcano which erupted in October 1956 after a long quiescent period is still active accompanying more than one hundred explosions since then. From August 1956, we began observations of crustal deformations at Hakamagoshi, western part of the volcano, by means of a sillica tube extensometer. Results of the observation from August to October were compared with daily mean sea level, rainfall, air temperature etc. Although we have experienced several times of volcanic eruption during the period of our observation, it seems that there is no marked correlation between the deformation of the earth’s surface and the eruption. But there is a very interesting and important fact which seems to be relevant to the structure of the volcano. The fact is that the time lag between the oceanic tide and the crustal deformation is about 4 hours and a half, which is abnormally larger than those hitherto observed at several other places. Furthermore, when visited by three typhoons during the period the time of the maximum extension of the earth’s surface was from 10 to 20 hours after the time of the highest high water of the sea. Thus the observed time lag of the earth’s deformation takes place in depending on the period of external disturbances. We shall not enter in detail the mechanism of such observed phenomena but discuss in the forthcoming paper.

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The growth of bubbles in natural glasses was investigated, and it was found that (1) The growth of bubbles increased remarkably at aprox. η = 10⁸C.G.S. (2) The velocity of the growth (U_obs) showed varying values. For example U_obs = 4.4 × 10^-6cm/sec. This value is not always in accord with Verhoogen’s. (3) The nucleation of bubbles was completed almost immediately. A decrease in number of bubbles was noted in the process of the growth due to coalesence, which is also responsible for the size distributions.

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The purpose of the present study is to make clear the mechanism of pumice formation in order to investigate the thermodynamical conditions at volcanic eruption. J. Verhoogen investigated theoretically the mechanism of ash formation in the conditions of expansion of gas bubbles on the basis of hydro- and thermodynamical point of view. For the present purpose, the formation of gas bubbles in the molten magma would become to be essential. From this stand point, the conditions of pressure and temperature for bubble formation were calculated by using the homogeneous nucleation theory, which was justified by the laboratory experiment. A thin plate of pitchstone was heated in several ways in the electric furnace from room temperature up to 1100℃. At almost 900℃, gas bubbles began to form in the specimen, which are photographed at various stages. Nucleation rate of such gas bubbles was calculated on the basis of the experiment, and as the result, it agrees quite well with that derived from the theory. In reality, the pumice would be formed by the sudden decrease of pressure and temperature from the molten magma, however, the present experiment was made in one atmospheric pressure. Therefore, it is necessary to expose suddenly the specimen from the state of considerable pressure and temperature to one atmospheric pressure.

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From a few statistical investigations of the seismic phenomena accompanying Hawaiian volcanic activities, the following inferences were drawn. 1. The Ishimoto-Iida formula NA^m = C holds for Hawaiian earthquakes. The value of m was found to be 1. 9. 2. The aftershocks of strong earthquakes do not follow the Omori hyperbolic distribution except for rare cases. 3. During those years when the volcanoes are inactive earthquakes have a preference for occuring in the winter months. The same does not hold for those years when the volcanoes are active. 4. In the last sixty years the eruptions of Mauna Loa have alternated systematically between the summit ones and flank ones. The hypothesis that a flank eruption will follow a summit one within three years cannot be dismissed lightly.

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An attempt was made to discover any statistical relation of earthquakes as premonitory phenomena to volcanic eruptions on the basis of reports of the Hawaiian Volcano Observatory. The results seem to be negative. However certain factors must be kept in mind. First, seismic activity was tabulated according to the method of weekly local seismicity, an unique method employed in Hawaii. Secondly, the data used were obtained from low-powered seismometers. Hence, the possibility of seismic activity serving as premonitory phenomena of eruptions is still not excluded. It is then inferred that for further investigations seismometers of higher magnifications are necessary and consonantly a better way of tabulating seismic activity must be devised. It has also been found that there is a definite statistical relation between the frequency of earthquakes and their strength.

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