On the mechanism stromboli

Abstract 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 intermittence 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 observations as to which are upon record for above 2000 years. Every volcanic 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 suddenly 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 intermittence 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 mechanism, whatever be its nature, being comprehended within a moderate distance from the surface, and not referable to the more mighty and deepseated 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 being thus communicated, within certain limits, to the otherwise irregular and accidental activity of the volcano. Passing ancient accounts, Stromboli has been visited in modern days, amongst men of science, by Spallanzani, Dollomieu, Hoffman, Scrope, Daubeny, and several others; but no very full or exact description of the crater and its adjuncts, much less any adequate explanation of the curious mechanism of its action, has been given by any of these writers.