F. A. Per ret — Volcanic Vortex Rings. 41 8 



the incandescent lava in the crater is thrown into the air in 

 large masses by great gas bubbles rising through the liquid, 

 without material alteration of its temperature, but the magma 

 of the depths, if our theory be true, is atomized, so to speak, 

 into a gaseous emulsion whose temperature, although initially 

 above that of the crater lava in the " Strombolian " phase, will 

 be very quickly lowered by the enormous expansion — a degree 

 of extension which can only be fully appreciated by one who, 

 like the present writer, witnessed at close range the great 

 emission of April 8th, 1906, whose volutes of vapor, even at 

 the height of two kilometers, still expanded with an incredible 

 acceleration in all directions. No witness of that great, con- 

 tinuing, trepanning blast could ever be persuaded that there 

 remained in the throat of the volcano any broken solid materials 

 whose trituration should furnish the ash of that and the follow- 

 ing days, according to the ordinary conception. 



We must accept the absorption of heat by gaseous expansion 

 as the cause of a lower temperature or else admit for the 

 depths of the volcanic conduit and the magmatic pocket or 

 fissure a temperature inferior to. that of some intermediate 

 zone, as is often the case with geysers. The " Vulcanian " 

 phase needs study. 



Considering this principle of direct ash production as it may 

 obtain in the phenomena of volcanoes of different types, it 

 would seem that the highly viscous lavas of andesitic and 

 trachytic nature might explode subaerially, upon sudden 

 relief of pressure, into gas and divided solid material, causing 

 such effects as the "JSuees Ardentes" of Mt. Pelee. At the 

 other extreme, the ultrabasic Kilauea shows ash strata several 

 meters in depth and ash fields many kilometers in extent, and 

 there seems no reason to doubt that a sufficiently rapid outflow 

 at a low level will cause even the Hawaiian subjacent lavas 

 to froth up and be ejected as ash. 



In this connection it may be noted that Dana,* writing of the 

 thread-lace scoriae of Kilauea, suggests that a further subdivi- 

 sion or frothing of the material might produce ash, and claimed 

 for such a process an explanation of ash formation more 

 reasonable than the trituration of rocks. Taking this with the 

 many comments on the identity of ash and co-eval lava, it 

 would seem that only a dynamic theory was required for the 

 rounding out of a complete hypothesis. May not this conception 

 of a subdi visional, intermolecular gaseous development and 

 expansion in subjacent magma, upon relief of pressure from 

 above, be accepted as a plausible explanation of the observed 

 facts % 



Naples, July, 1912. 



* " Characteristics of Volcanoes." (Page 166.) 



