538 G. Poulett Scrope — The Mechanism of StromhoU. 



column of melted matter reaching up to its lip; for iu that case, 

 -whatever be the mechanism of the volcano, at each outburst the 

 whole of this immense column of melted matter must be blown 

 completely out of the tube, which actually is emptied, at the end of 

 each outburst, of everything but gases and vapours, and these at 

 a tension not greatly exceeding that of the atmosphere." May we 

 not, however, ask Mr. Mallet on what ground he asserts so positively, 

 that the tube (which, in the case of Stromboli, he speaks of as 

 400 feet in depth, but which, by rectification of his measurements, 

 must really be, if it exists at all there, about five times as much, 

 viz. from the bottom of the crater to the level of the sea, whence 

 the water of his geyser is supposed by him to be supplied) "must be 

 actually emptied at every outburst" ? He admits that he was unable 

 to see the bottom of the crater where he places the mouth of his 

 geyser tube. Those who have been more fortunate certainly 

 saw nothing corresponding to Mr. Mallet's idea, but, on the con- 

 trary, the usual phenomena of a volcanic vent in moderate activity, 

 as described above. There is nothing, then, in the phenomena of 

 Stromboli so exceptional as to make it necessary to refer them to 

 any mechanism different from that of ordinary volcanos under 

 similar conditions. Intermittent, recurrent, or (if Mr. Mallet prefers 

 the word) rhythmical explosions are not peculiar to Stromboli. Dana, 

 as we have seen, and other trustworthy authorities, speak of those 

 of Vesuvius, when the volcano is but moderately active, as taking 

 place every three" or ten minutes, — as nearly as possible, the average 

 interval between the outbursts of Stromboli, — though of course, in 

 more violent paroxysmal eruptions, the intervals are reduced to 

 seconds or less, the explosions following one another too rapidly 

 to be counted. 



It is, then, evident that if Stromboli is to be supposed to have a 

 geyser under its eruptive lava-vent, on account of the intermittence 

 of its explosions, we must believe the same to be the fact in the case 

 of Vesuvius, and every other volcano when in activity — an absurdity 

 Avhich no geologist can be brought to countenance, and which even 

 Mr. Mallet would (perhaps?) hesitate to affirm. 



The peculiarity of Stromboli really consists, not in the more or less 

 rhythmical recurrence of its explosions, — which, as we have seen, is 

 common to all volcanos in the phase of moderate eruptive activity, — 

 but in the permanence of this phase in its instance. This is evi- 

 dently due to the slow and equable i-ate at which increments of heat 

 are communicated from beneath, together with fresh lava rising up 

 the chimney, and to the similarly equable dispersion of the matter 

 thus brought up, beyond the circumference of the crater. This equi- 

 librium of supply and waste is an unquestionable fact, since the 

 eruptive phenomena are, as a rule, equable within short periods, 

 and the crater remains always empty to about the same level, not- 

 withstanding the constant return into it of a large proportion of 

 the lava fragments ejected from its bottom. That other portion 

 of fragmentary lava which is carried off as ash by the wind, or 

 falls in larger masses outside the crater lip, evidently balances in 



