16. 櫻島噴火に伴ふ鳴動及び噴煙
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概要
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In March 1946, Sakura-jima erupted with a large detonation, and smoke shooted up in the sky. Detonation in the end of March was the most intense ones, it became feeble gradually. The change in volume ejected smoke was nearly equal to the intensity of detonation. There was a distinct shortperiod of variation, 4～6 minutes in average period. Comparing the result of observation of tilting motion of ground by means of the spirit level with the strength of detonation, we found that there were some correlation between those two quantities. On the other hand, we observe 1 that the ejected smoke consistes with two斌inds of vortex. One of them is the horizontal vortex caused by the .Corioll's force of the earth, while the other is the vertical one which is hydrodynamically caused. From the observed values of vorticities of the latter type, we estimate the initial velocity of ejection of smoke from the crater, the result being that it was about 55m/sec. On the other hand, the initial velocity of ejection of volcanic bombs was also estimated from its flying pathes, the result just agreeing with that estimate from the vorticites. Then, the pressure of gas at the time of ejection was estimated to be about 18 atm., under the assumption "momentum conservation" in the case of ejection, of bombs. While from the pressure equation of compressible fluid, we can observe relation between the gas pressure into the above-mentioned equation and its density. Putting P 18 atm., we get that the density of volcanic smoke at the crater is about 0.05.
- 東京大学地震研究所,Earthquake Research Institute, University of Tokyo,地震研究所,地球物理學敎室の論文
- 1948-06-30