During the recent active period, from Apr. 1965 to Mar. 1966, of the Volcano Aso, a swarm of volcanic earthquakes was observed at the Hondo observation room of Kyoto University. By analysing the data, the locations of origins are determined and the source mechanism is discussed. The main results obtained are as follows : (1) the distribution of volcanic earthquakes is varied with the volcanic activity, that is, the origins are located in comparatively narrow region before the eruption, but scattered in wide region gradually after the eruption ; (2) the characteristic earthquakes regarded as derived from rarefaction origin are observed, that is, the first-motions are all "pull" around the epicenter. These rarefaction type earthquakes are observed in the earlier and active stage, but not in the later stage.

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Some considerations are presented on the origin of granitic magmas, based mainly on the recent advances in strontium isotopic geochemistry and experimental petrology. Several possibilities are examined on the derivation of granitic magmas from the crustal and upper mantle materials. It is assumed that the granitic magmas might have been derived currently from certain peridotitic or eclogitic materials of the upper mantle, although the real physicochemical mechanism concerned have remained uncertain. It is hoped that the experimental investigations on the phase equilbria of mafic and ultramafic rock substances under very high pressure conditions (＞100 kb) may throw a new light on the solution of the problem under consideration.

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The vertical deformations of the earth's crust in the vicinity of Aira Caldera were studied from the results of precise levelling surveys and observations of the sea level by means of tide gauges. Relative vertical deformation of Volcano Sakura-jima in recent years were obtained from the continuous observation data of the mean sea level between Kagoshima and Hakamagoshi. Upheaval movements of Volcano Sakura-jima were also revealed from the results of precise levelling surveys around Kagoshima Bay run in 1960 and repeated in 1962. Those two results were not so contradictory to the amount of the vertical displacements between Kagoshima and Volcano Sakura-jima. The great Sakura-jima eruptions in 1914 was followed by abnormal changes in the height of the mean sea level of Kagoshima Bay. In recent years, the relative elevation of B. M. 2474 was recovering as high as that had been in 1891 before the great eruptions in 1914. Those facts may suggest the gradual accumulations of the powerful volcanic tension under the center of Aira Caldera.

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