H. Simotoinai — Tarumai Dome in Japan. 97 



5. The vent through which the lava rose is probably at the 

 most 60"" in diameter, because the lower part of the crater pit 

 measured that width before the eruption. According to this 

 supposition, the lava must have consolidated more rapidly in 

 the narrow vent than the nucleus of the dome, so that the 

 connection of the viscous lava between the dome and the sub- 

 terranean deep chamber was cut off. This accounts for the 

 fact that the settling of the lava-mass of the dome (20,000,000 

 cubic meters), due to consolidation, was comparatively less than 

 in the case of Usu after its eruption in 1910, when connection 

 with the subterranean chamber was probably not so quickly 

 cut off. 



It is impossible to calculate exactly the diminution of the 

 lava mass by settling, but a rough estimate gives about 5-10 

 per cent of the whole volume. 



6. The principal fissure formed on May 15th, 1909, on the 

 inner crater-wall just at the foot of the dome, and it opened a 

 way for the gas which issued from the consolidating lava in 

 the central part, thus tending to remove the danger of the 

 dome's destruction through gas explosion. The endogenetic 

 development of the dome was completed in about one month. 



7. The formation of the rock talus continues slowly and the 

 principal epigenetic cause is wind action. 



8. During seven years, some plants have migrated to the 

 dome on the still-fuming surface of lava. 



9. Tarumai is the representative type of this kind of dome. 



Literature of the recent eruption of the Tarumai volcano. 



Immanuel Friedlander: Ueber einige japanischen Vulkane, II 

 Teil, Mitteilungen der Deutschen Gesellschaft fiir Natur- 

 und Voelkerkunde Ostasiens. Bd. XII, Tokyo, 1910. 



Ueber den Usu in Hokkaido und ueber einige andere 



Vulkane mit Quellkuppenbuldungen, Petermann's Geo- 

 graphische Mitteihingen, Juni Heft, 1912. 



Bunjiro Koto: On the volcanoes of Japan II, Journal of the 

 Geological Society of Tokyo, vol. xxiii, No. 269, 1916. 



Synkusuke Kozu: Preliminary notes on some igneous rocks of 

 Japan, Journal of Geologj^ xix, No. 7. 



Yositika 6inoue: Report on the Tarumai eruption (Japanese), 

 Publications of Imp. Earthquake Investigation Comm., 

 No. 64. 



Sidney Powers: Volcanic Domes in the Pacific, this Journal,, 

 xlii, No. 249, Sept., 1916. 



Denzo Sato: Report on the Tarumai eruption (Japanese), Publi- 

 cation of the Imp. Geological Survey of Japan, No. 14, 

 Tokyo, 1909. 



Hidezo Simotomai: Der Tarumai Ausbruch in Japan 1909, Zeit- 

 schrift der Gesellschaft fur Erdkunde zu Berlin, Heft 6, 

 1912. 



