THE GREAT ERUPTION OF SAKÜRA-JIMA IN 1914. 121) 



ulated by G. K. Gilbert*^ to show the quantitative relation between 

 local variation of depth of compensation and the resulting variation 

 of gravity. The nature of the disturbance in the present case is 

 expressed in the relief through the concentric settling of terrene in 

 a cauldron -shape with a centre off the northern shore of Sakura- 

 jiraa (PI. XIII.). 



The subsidence of the present area involves a problem of 

 isostasy, caused directly by a mass defect produced in the out- 

 pouring of lava of 3,012,240 million kilogrammes or 3,012 million 

 metric tons (p. 108), besides an indefinite quantity of éjecta 

 hurled up from the vents and distributed within a distance of 

 more than 1,200 km. (to the northeast of Tokyo). 



H. Nagaoka, of the International Geodetic Committee, has 

 made known in a series of Annual Reports the anomalies of 

 gravity at Oita, Nobéoka, and Myazaki on the eastern coast, and 

 at Shibushi, Kagoshima, and Hitoyoshi oa the south, and in the 

 interior of southern Kyûshù, the former 3 with negative and the 

 latter 3 with positive values. These sets'"^ of values show that the 

 region has been, in general, out of isostatic equilibrium, and this 

 has been accentuated by the recent efiusion of lava at Sakura-jima, 

 w^hich lies, so it seems to the writer, on the borderland of positive 

 and negative anomahes. The borderland is as a general rule apt 

 to be subject to unbalanced stress accumulation, as in Central 

 Japan, where the great earthquake of 1891 devastated the stretch 

 between the t0^vns of negative Gifu and positive Nagoya. 



Assuming that the zone of compensation lies below 122 or 



1) •Interpretation of Anomalies of Gravity.' Prof. Paper 85 C. U. S. Geol. Sun:, 1913. 



2) Oita î7"o-7'o -0.032| ShibiisM g'\,-y'„ +0.034 



Nobéoka „ - 0.008 [ ^^^* Kagoshima „ +0.045 



I const 

 Myazaki „ -0.029' Hitoyoshi „ +0.000 J 



'Ergebnisse der relativen Schweren messungen in Japan in den Jahren 1909-1911 und 1912.' 



South 



and 



inland 



