496 Mr. R. Mallet on the 



" On the Mechanism of Stromboli." By ROBERT MALLET, M.A., 

 F.R.S. Received May 17, 1874 *. 



Stromboli and Masaya stand alone, so far as observation Has yet gone, 

 amongst the volcanic vents of our planet, in the remarkable characteristic 

 of having a distinctly rhythmical interim ttence and recurrence in their 

 eruptive action. Masaya, though known for about 300 years, has been 

 but little observed, so that some doubt may exist as to whether its action 

 be truly intermittent and recurrent or not ; and if we leave it aside for 

 future observation, Stromboli stands unique amongst terrestrial volcanoes 

 in the rhythmical character of its eruptions, more or less accurate obser- 

 vations as to which are upon record for above 2000 years. Every vol- 

 canic vent is indeed intermittent, and often recurrent, in its action, which 

 has been properly denominated paroxysmal, but no law can be traced in 

 the intervals of time elapsing between the paroxysms. A vent may sud- 

 denly open and a cone be thrown up, as in the case of Monte Nuovo, and 

 after this burst volcanic effort may cease there, perhaps permanently ; or, 

 as in the case of Vesuvius, prior to A.D. 79, a period of repose may exist 

 in a volcanic cone already formed, exceeding human local tradition, to be 

 succeeded by paroxysmal efforts, varying enormously in intensity, and 

 with intervals in time between successive eruptions varying from hours to 

 centuries. In all these there is no rhythmical recurrence, or at least none 

 that, upon the narrow scale open to our observation, can be viewed as 

 such. In Stromboli, on the contrary, there is a distinctly rhythmical inter- 

 mittence and recurrence, so regular in time, and preserving for centuries 

 such a general uniformity in energy, and of such slight violence, as to 

 point to some distinct train of mechanism as producing it that me- 

 chanism, whatever be its nature, being comprehended within a moderate 

 distance from the surface, and not referable to the more mighty and deep- 

 seated forces which determine the uncertain and altogether unpredictable 

 paroxysms of volcanoes generally. Not that the rhythmic intervals of 

 Stromboli are precisely the same at all times, as has been erroneously 

 stated by many travellers, nor the violence of its outbursts at all times 

 alike ; but both vary within narrow limits during the immense historic 

 period that it has been observed. No satisfactory explanation has yet 

 been given, so far as the author is aware, of the physical and mechanical 

 condition constituting the mechanism upon which this extremely curious 

 rhythmical action depends ; and it is the object of this paper to point out 

 what appears to be its real nature. It is the more worthy of attentive 

 study, as Stromboli is in reality the link that connects two widely different 

 phenomena namely, the ordinary cone of eruption and the geyser. 

 Stromboli is, in fact, a volcano and a geyser united and acting together 

 in the same vent, the rhythmical action which characterizes the geyser 



* Eead June 18, 1874. See ante, p. 473. 



