F. A. Perret — Lava Eruption of StromboU. 463 



volcano of saturated air from without. The great cloud of 

 wafer vapor is not an emanation of the volcano, but a conden- 

 sation from the atmosphere upon nuclei furnished by the 

 stream of dust particles emanating from the volcano, aided, 

 particularly in its initial stages, by direct ionization (electrons) 

 in case the volcanic gases are escaping from liquid lava or 

 through incandescent conduits. The well-known experiment, 

 at solfataras, of holding a lighted torch near a fnmarole to 

 produce a condensation of the emanating water vapor, may be 

 cited as an illustration of the phenomenon with, however, the 

 conditions exactly reversed — at the more active vent the water 

 is supplied by the atmosphere and the volcano is the torch. 



This atmospheric condensation will not always take place. 

 Too high a temperature — as over a crater full of incandescent 

 lava — will often prevent it, and even at a solfarata if the walls 

 of a small fnmarole are sufficiently heated artificially it will be 

 found impossible to condense the issuing vapor by nucleation 

 with a torch ; but these cases are due solely to excessive heat- 

 ing of the saturated air which then returns to an unsaturated 

 condition. The importance of an understanding of this phe- 

 nomenon lies mainly in avoiding erroneous impressions of a 

 volcano's state of activity based on the apparent emission of 

 great volumes of steam from a crater which may really be 

 almost quiescent at the time. Reports of this kind are con- 

 stantly being made, and the dynamic record is often corre- 

 spondingly faulty. 



Precipitation of salts from gas emanations was not marked, 

 during this eruption, excepting in the fumarolic area, towards 

 the end. This is perhaps but natural, considering that gaseous 

 emanation was not the salient feature of this almost wholly 

 effusive activity. There was evidence during the eruption of 

 response to the influence of favorable luni-solar combinations. 



In conclusion it may be pointed out that this last eruption 

 offers further proof of the view already expressed elsewhere* 

 that this volcano has, since 1907, entered upon a new period 

 of increased activity which has been characterized by powerful 

 explosive and effusive eruptions having a greater resemblance 

 to the processes of other volcanoes than to what has been 

 generally considered to be the normal Strombolian form of 

 action. There can be no doubt that Stromboli, to-day, is a 

 mine of wealth for the direct observation of volcanic pheno- 

 mena, and every effort should be made to provide for a more 

 continuous study of it. 



Geophysical Laboratory, 



Carnegie Institution of Washington, 

 Washington, D. C, Sept. 29, 1916. 



* Perret, F. A., Bull. Brooklyn Inst., i (1), p. 313, 1907; Ann. Uff. Cent. 

 Met. Ital., xxx (1), p. 27, 1910 ; Smithson. Reports (1912), p. 285, 1913. 



