278 H. S. WASHINGTON PERSISTENCE OF VENTS AT STROMBOLI 



The evolution of heat through the chemical interreactions of magmatic 

 gases and their consequent competence to "blow-pipe" their way, and thus 

 form a conduit, to the surface has also been suggested and discussed by 

 Day and Shepherd.^^ 



Daly applies this action to the revival of activity after a period of dor- 

 mancy. He supposes that the gas "blow-pipe" melts its way up through 

 the solidified plug which fills and obstructs the conduit (figure 135, page 

 276). But it may be pointed out that as this plug will consist of very 

 solid and tough rock, as he himself says, the vertical fluxing action would 

 probably take place not through, but alongside, of the plug, thus slightly 

 shifting the vent at the surface. If, however, the conduit remains open, 

 or only slightly obstructed, or if the solid plug be not too long, the exact 

 location of the vent will persist. 



It will be noted that certain important features of such a "gas-fluxing" 

 process are its quietness of operation, the boring being due to simple 

 fusion and not to explosion (except when the surface is reached) ; the 

 dominantly vertical direction and slight lateral extension of action; the 

 localization and independence of the several bore holes (if there are more 

 than one), due to their initiation at separate cupolas; and the possibility, 

 by continuance of this action, of the persistence in location of the vent. 



These features fully meet the requirements of the characters of the 

 Stromboli and Etna vents, and so it must be regarded that the "gas-flux- 

 ing" hypothesis of Daly is competent to explain their origin, characters, 

 and (at Stromboli and Kilauea) their persistence in location. 



This hypothesis is especially well fitted to explain the formation of the 

 vents on the Stromboli crater terrace, if it be true, as seems most prob- 

 able, that this occupies the top of an unsunken portion of the earlier Van- 

 cori cone, back of a steep fault-scarp. It would be precisely under this 

 portion of the mass, after the subsidence of the northwestern fault-block, 

 that the magma reservoir would be expected to preserve its original upper 

 level, so that this portion would serve as a locus of accumulation for the 

 magmatic gases. It is conceivable, also, that the number of vents and 

 their contiguity over a comparatively small area is due to the same cause 

 and the consequent areal restriction of the reservoir roof without com- 

 mensurate diminution of the gas supply. 



It may be added that the applicability of the gas-fluxing h3^pothesis to 

 Stromboli has indeed been suggested by Daly (op. cit., page 268) ; but he 

 would seem, possibly through lack of acquaintance with the volcano, to 

 have misunderstood the character of its crater terrace and to have over- 

 looked the features of its vents, as well as those of the Etna ones men- 

 tioned, which tell most strongly in favor of his own hypothesis. 



Day and Shepherd : Op. cit, pp. 599-601. 



