The 1914 eruption of Sakurajima volcano, Japan was one of the largest volcanic eruptions in the history of this country. Hitherto, numerous papers have appeared discussing this eruption from various standpoints. Nevertheless, there still remain many data not fully analyzed from viewpoints of increased volcanological knowledge. In the present paper, its eruption processes are interpreted utilizing the observational data with relation to subsurface structure. Benchmark (BM) 2469 near the Kagoshima harbor proved to have upheaved approximately 12cm relative to 1891 elevation before the 1914 eruption based on precise leveling surveys and the temporary sea level observations at the Kagoshima harbor. This was a part of the precursory upheaval around the volcano. BM. 2474 about 10km northwest of the center of the volcano subsided approximately 80cm by the eruption relative to the 1891 elevation, and 5cm more during subsequent 7 months. Such subsidence was common to the other benchmarks around the volcano. This means that the subsidence was rheological: we may assume that a part of the subsidence was elastic and the rest was viscoelastic. Such movements can not be attributed to lava effusions that continued for only 1 month. Considering the sequences of the volcanic activity in connection with the subsurface structure of the volcano, one can surmise the magma movements: The lava flows began to effuse 36 hours after the first outburst of a column of white smoke from the summit crater. The first outburst may have been caused by contact of magma with the aquifer at a depth of 2.5km below sea level based on analyses of the gravity anomalies there. If we adopt that the magma reached the first craterlet at 0.5km above sea level after 36 hours, we may calculate magma ascent velocity of 2km/day. Prior to the 1914 eruption, the first precursory shock of volcanic origin was observed 4 days prior to lava effusion. Thus, the starting point may be about 8km below the sea level. This is the depth of a short lived pressure source which is interpreted as the cause of surface subsidence.

抄録全体を表示

The isotopic composition of ¹⁶O-enriched oxygen was measured based on the negative thermal ionization mass spectrometry of ReO^-₄ ion. The resulting values are 0.00245, 0.00605 and 99.9915%, respectively, for ¹⁸O, ¹⁷O and ¹⁶O. This composition endorses that the use of this oxygen gas to form the negative oxide ion enables us to dispense with the correction for the isobaric interferences due to oxygen isotopes ¹⁷O and ¹⁸O. Also it is exhibited that the logarithm of relative depletion factor is a nearly linear or rather parabolic function of the difference in mass number.

抄録全体を表示

Although helium is generally quite insoluble in metals, large amounts of this element can be stored within a highly deuterated host metal such as Pd-black as a result of deuterium nuclear reactions continuously generated over long periods. However, since it is almost impossible for these helium atoms to then escape from the Pd-black host to the surrounding environment at ambient temperature, to confirm their presence it is absolutely essential that Pd-black samples be heated to high temperatures to expel whatever helium they may contain. Therefore, to confirm the existence of helium atoms generated from deuterium in samples of Pd-black, we simply employed the“Sample Heating”process (room temperature _??_1500°C), but carried it out using both a“QMS”system and a super-high vacuum favorable“Getter pump”inside a totally sealed vessel. We termed this methodology“closed QMS”, and developed a related discrimination method which applies an opportunely changing voltage to the anticipated elements present inside the“closed QMS”environment. Measurements were then taken as the applied voltage was both increased and decreased between 70_??_20[V] (here, range being determined by the ionization potential Vi[eV] for helium series elements). Using this principle, which we call the“Vi-effect”, in brief, we were able to conclusively confirm the presence of both ⁴₂He and ³₂He atoms, as well as their relative ratio. It is evident that development of both the“closed QMS”system and the“Vi-effect”methodology were vital to finally prove the presence of helium generated by deuterium nuclear fusion within highly deuterated Pd-black.

抄録全体を表示