S. Powers — Volcanic Domes in the Pacific. 201 



Art. XXIX. — Volcanic Domes in the Pacific; by 

 Sidney Powers. 



Introduction - . 



Since the famous dome and spine rose on the summit of 

 Mont Pelee on Martinique in 1902-3, five domes of a some- 

 what similar nature have appeared on volcanoes in the Pacific 

 Ocean. Three spine-like domes have risen on the summit of 

 Bogoslof volcano in Bering. Sea, and two of them have been 

 destroyed by explosions. The other two domes have appeared 

 in Japan, one on the summit of Tarumai, in Hokkaido (Yezo), 

 during the spring of 1909, the other on the side of Usu, also 

 in Hokkaido, during 1910. It is the purpose of this paper to 

 describe the latter two domes, which were seen by the writer 

 in 1915, together with the other domes in Japan, those at 

 Bogoslof, and those which formerly existed at Kilauea, Hawaii. 

 A list of the known volcanic domes is appended with a brief 

 discussion of the theory of origin of spines and domes in gen- 

 eral. A portion of this material has not previously been 

 published and a full list of known domes has never appeared. 



Volcanic domes and spines are either masses of new, viscous, 

 lava pushed out from the top or sides of volcanoes, or masses 

 of material already on the volcanoes which are elevated by the 

 push of newly injected magma from below. In every case 

 described below, new lava has appeared at the surface either 

 comprising the greater part of the elevated mass or in the form 

 of volcanic bombs. Spines differ from domes in the form of 

 the extruded mass: Spines (aiguilles, Beloniten, 1 Felszahne) 

 are monolithic needles of new lava, such as the one on Mont 

 Pelee, which may form the centers of domes as was seen in 

 Perrj'- Peak, Bogoslof Island, after the explosion of 1906-7 ; 

 domes (Staukuppen, Quellkuppen, Tholoiden, 1 cumulo-vol- 

 canoes) are more rounded masses of new lava such as the 

 trachyte "Puys" of the Auvergne region or portions of older 

 lava or ejectamenta elevated by new lava beneath, as in the 

 Usu uplift of 1910 and in the Kilauean domes. 



Examples. 

 Tarumaidake. 2 The volcano Tarumai is situated on Hok- 

 kaido (Yezo), the northern island of Japan, 30 miles north 



1 The terms Beloniten and Tholoiden were introduced by K. Schneider, 

 Die vulkanischen Erscheinung der Erde, Berlin, 1911; but F. v. Wolff 



(Der Vulkanismus, vol. i, Stuttgart, 1914, p. 492) points out that the 

 former term has been previously used with another meaning. 



2 Dake signifies hill or mountain in Japanese. 



