412 



F. A. Perret — Volcanic Vortex Itings. 



It will be seen that this hypothesis does not in the least 

 degree invalidate the division of the eruption into a " Strom- 

 boTian." and a "Yulcanian" phase — on the contrary, it supplies 

 a cause for the great and continued dynamism of the "Yul- 

 canian " phase and explains the identity of its ash with the 

 co-eval lava. 



Fig. 7. 



It is interesting to note that the "Yulcanian" phase, as far 

 as actual, external eruption is concerned, is cooler than the 

 "Strombolian." This is due, in part, to the downward removal of 

 the furnace, i. e., the lava column, but also, most certainly to the 

 enormous absorption of heat in the process of gaseous expan- 

 sion in the deeper magma and the subdivision of the latter into 

 minute particles which quickly assume the temperature of the 

 gas which surrounds them. During the "Strombolian" phase 



