VOIP. 



VOLCANO. 



hi* organ*, as the singer does on his, and he will be rewarded wit] 

 ebMrfulness and health. 



Vil|I> 'V.i. 1-l-H.J 



I US. [Oiw.] 



' - >. The situations on the globe where subterranean fire* 

 hare made or found channel* to the surface of the land or to the bet 

 :' the sea, are termed volcanoes. A volcano u merely the channel < 

 upward communication from the subterranean fires; the mountain in 

 which the volcano acts, and the extensive mound) and mnntim of ashes 

 lava, Ac. (aubstancea hereafter described), which surround it. are the 

 effect and the measure of the expansive mechanical force* which are 

 relieved by the pouring forth of the streams of melted or flowing and 

 plastic rocks, the showers of ashes, torrents of steam mingled with 

 gases, and of water, which constitute the eruptions, lly considering 

 the nature of these solid, liquid, and gaseous substances, their mutua 

 relations and respective functions in volcanic phenomena, and the 

 circumstances of their ejection, some progress may be made towards i 

 chemical theory of the nature and origin of the subterranean fires ; bu 

 to gain a proper notion of the mechanical forces set in action during 

 volcanic excitement, we must enter upon a larger inquiry : the con 

 nection of earthquakes and volcanic eruptions, the relations of on 

 volcanic district with another, especially as to coincidence or reciprocity 

 in the times of their violent activity or remarkable repose ; and th 

 history not only of volcanic phenomena which are now in progress 01 

 have formerly happened in particular situations, but the general his 

 tory of the effects of the disturbance of the internal heat during al 

 geological periods and over all parts of the globe. Those mechanic.! 

 forces, It must be remembered, are simply the correlates of this heat 

 and come into action, primarily, in consequence of the antagonistic 

 action of the sun's rays upon the surface of the earth, and its more 

 immediate results in changing the position of the matter constituting 

 that surface. 



Has this extensive inquiry been followed out so completely am 

 methodically as to justify a belief that the true theory of volcanoes is 

 reduced, as several other branches of the great theory of nature have 

 been, to a plain process of induction T That many geologists suppose 

 so is evident from the decision with which their general speculations 

 are advanced ; but the student who desires to possess clear and 

 systematic inferences without being troubled with contending hypo- 

 theses will find it necessary to class the phenomena as if the inquiry 

 were very far from completion. The following views may aid his 

 researches into this large and interesting subject : 



Saectuion of Volcanic Phenomena. A complete history of any one 

 volcano, by showing us its origin, its alternations of rest and activity, 

 its progress to decay, and its final extinction, would furnish a sufficient 

 base for a general theory of volcanic action ; for the analogies among 

 all burning mountains, as to form, structure, composition, and asso- 

 ciated phenomena, are such as to warrant the application of a few 

 general laws and one theory to them all. But we know not completely 

 the succession of phenomena which have happened in any one volcano. 

 We hare indeed examples in abundance of new islands and new moun 

 tains being raised in our own days and giving forth fire ; we have 

 the hist >ry of Vesuvius as an Intermitting volcano for nearly eighteen 

 hundred, and that of jEtna for above two thousand three hundred, 

 Tears ; and we may contemplate on the banks of the Khine, in Hun- 

 gary, and in Auvergne, the aspect of a country from which the subter- 

 ranean fires appear to have withdrawn their forces before (though in 

 the country last named probably not long before) the origin of history 

 The birth, continued activity, decay, and extinction of volcanoes are 

 r.iena seen in separate parts of the earth's surface, and acquire 

 unity and consistence only by being rightly combined into a correct 

 general view of volcanic action. 



KarihiiHalxt. Previous to volcanic eruptions trenerally, whether 

 there happen in old craters or burst up in new situations, earthquakes 

 prevail, sometimes for a considerable period, in the vicinity of the 

 volcano, and extend their terrors to considerable distances from it. 

 Near to the centre of future violence springs have been known to fail 

 and others to burst forth, and unusual noises have been heard. 

 Previous to the year 1838 the Neapolitan shore bad been disturbed by 

 earthquakes for two years; and these symptoms of subterranean dis- 

 turbance were succeeded by the production of the Monte Nuovo (on 

 and over the ancient site of the Lucrine Lake) in the space of forty-eight 

 hours. 



Among the effects of great earthquakes are natures In the crust of 

 the earth, both in volcanic regions and in distant situations. In 1811 

 and 1812 the movements of the ((round In the valley of the Mississippi 

 ni.l in Csracas caused vast depressions and elevations, some of whirh 

 remained, so as permanently to affect the drainage and change the form 

 of the surface. .Some of the numerous fissures produced in Calabria 

 by the earthquake of 1783 aatumed a radiating form, and It is con- 

 jectured by Lyell that in these situations the ground was perma- 

 nently raised. In 1649 the flanks of .Ktna were fissured, and through 

 tin- "inning the Monte Rossi was raised, by ejection of ashes, Ac., to 

 the height of 450 feet. In 1 7'8 the new volcano of Jorullo was formed 

 un the plains west of Mexico by the accumulation of ejected materials 

 (as 1s now known) Into a mountain 10!' 5 feet high. 

 By these Instances, taken from situations far from other volcanoes 

 , t points in the ridnity of active and extinct volcanoes (the 



Monte Nuovo), and on the elopes of a freq 

 Monte Rossi), it appears that generally the 

 the history of volcanic phenomena is the opei 

 line of fissure. 



frequently burning none (tha 

 the earliest observable fact in 

 opening of the ground. 

 ' . In a system of intersecting fissure*. 

 Such openings, when happening on land, constitute subacrial volcanoes; 

 and whan occurring in tha bed of the sea they produce submarine 

 volcanoes. 



The preceding statements relative to the connection of earthquakes 

 and volcanoes, and the alleged deration of land by the former, are in 

 agreement with the inferences generally drawn from both rlssnm of 

 phenomena prior to the publication of the recent inductive researches 

 on earthquakes, of which, and of their results, we have given 

 account in the articles KAKTBQI'AKE and SM-MKI.O<;V. Soismic and 

 volcanic energy are evidently the same in origin, manifested in the 

 former in a manner purely mechanical, and in the latter in a thermal 

 (if not chemical) and also mechanical manner. But we must now admit 

 that these phenomena are not related as cause and effect Earthquakes 

 do not produce or commence volcanoes, or initiate, though they may 

 be simultaneous with, volcanic eruptions; nor do volcanoes, causa 

 earthquakes, though there is a common cause, or chain of causes, for 

 both. Mr. K. Mallet has shown that fissures even are never produced 

 by the direct passage of the wave of shock in an earthquake, but are a 

 mere secondary effect, conformed to and determined by the dip or 

 slope uf the subjacent beds of rock, and are no more than in 

 landslips. The movements of the ground in Caracas and in tlj. 

 of the Mississippi, mentioned above, were in nil probability of this 

 description. In like manner, having deduced from theory, as v 

 inferred from observation, that earthquakes cannot produce elevations 

 (although the latter have been known to have taken place about the 

 same time as earthquakes and in the same region), he examined with 

 care more than 150 miles of sea-coast, as well as river-courses, for 

 evidence of any permanent elevation of land having taken place even 

 concurrently with the earthquake of the I6th of December, 1857, the 

 greatest that has occurred in Italy since that of 1783, referred to 

 above, but found none. 



The production of elevations and true fissures appears in fact to be a 

 third great effect, or class of effects, of the common chain of causes of 

 earthquakes and volcanoes, to be a distinct consequence from tl.- 

 "the tendency of the globe to swell into froth at the surface," to use 

 the emphatic and comprehensive expression of Sir K. W. II. ruchel 

 That a volcano begins by the production of a fissure, through which 

 the ejections constituting an eruption are subsequently to be discharged 

 by the continuance of the force originating the fissure, is most probable; 

 though it may often happen that the elevation of such material)* from 

 below falls short of an eruption, and merely fills the fissure (afterwards 

 to be observed as a dyke), or that the materials elevated are of a 

 different description, and are not otherwise related to volcanic pheno- 

 mena than as being effects of a common primary cause subterranean 

 beat. We shall again have to notice the light thrown upon the 

 philosophy of volcanoes by the recent investigations of earthquake- 

 phenomena. 



Eruutiuni. When by some movement of the ground a channel is 

 opened from the interior to the surface of the earth, a paroxysm of 

 volcanic excitement follows, and an eruption happens through the new 

 opening. There may be a slow outpouring of melted rock, pressed 

 i). wards against gravity by an internal force; or a violent upburst of 

 clouds of scoria: and ashes, mixed with larger stones ; or a torrent <>f 

 .he same materials mixed with water, and constituting mud ; or 

 volumes of steam and gases of different sorts ; but permanently gaseous 

 matter appears to be much inferior in quantity to aqueous vapour, and 

 requently, if not generally, to be the least important pnxluct or 

 of an eruption. These are exactly the products, singly or in >,.;. 

 ion, which are delivered by long-established vents, and, as far as we 

 uui judge, the same have been yielded by volcanoes which probably 

 >ecamo extinct before the historic era of the human race; moreover, 

 he volcanoes of all regions agree generally .in this respect. Evidently, 

 herefore, the condition of the interior parts of the earth, which are 

 mder the influence of volcanic excitement, is of a general and 

 continuous nature, and must be supposed capable of int.i;.? 

 >y examination of the products and the circumstances of their 

 'xtrication. 



The enormous flashes of lightning which accompany volcanic erup- 

 ions, issuing from the ascending column of steam ana solid ejeoi 

 .nd which are equally characteristic of eruptions originally 

 when they rise into the atmosphere, have been celebrated from the 

 ime of Pliny ; but they had not been account.'. I for in any satisfactory 

 manner, having only been vaguely referred to an i-voluti..n .if electricity 

 connected with the intense actions of various kinds taking place in the 

 ruption. After Mr (now Sir William <!.) Armstrong had observed 

 he electricity of effluent steam, Mr. Brayley pointed out the precise 

 nalogy of the sparks given by it, to this volcanic lightning. ( PhiL 

 (ag., Series 8, vol. xviii. p. 94.) l>r. Karadsy subsequently ascertained 

 that the electricity of effluent steam is produced, in reality, by tin ft 

 f the globules of water, resulting from its partial condensation, and of 

 articles of foreign matter, both merely driven onward by the steam as 

 mechanical agent, upon tha substance of the tube from which it 

 ssues. In tha eruption of a volcano we have all thasa elements in 

 , and on n Immense scale, the foreign particles being supplied 



