SUBMARINE ERUPTIONS. IOC 



contrary, the rent forms a permanent conduit at once, or after seve 

 rai shocks in the same place. In this case there is sometimes 

 established a continuously active furnace, from which gaseous 

 matter in abundance is disengaged, or from which lava continu- 

 ously boils, and from which there is an incessant projection of 

 scoriae ; this has been the case at Stromboli from the remotest 

 antiquity. At other times the conduit is temporarily obstructed at 

 Us upper part ; but the least effort is sufficient to remove the ob- 

 struction, or to produce a new opening in 

 the vicinity, through some fissure which 

 communicates with the principal conduit 

 (Jig. 187). In all cases, the result is a 

 centre of easy communication between 

 the interior and exterior of the earth, and 

 it is this which is called a volcan or vol- 

 cano. Fig.181. Volcanic conduits. 



This facility of communication is probably a preservative against the vio 

 lence of earthquakes ; indeed it has been observed that, from the moment an 

 eruption takes place anywhere, the shocks which had been felt up to that 

 time, become fewer and weaker, and even cease altogether. The earthquake 

 of Caraccas, in 1812, terminated by the eruption of the volcan of Saint- 

 Vincent, in the Antilles; the eruption of Jomllo, and that of Monte-Nuovo, 

 terminated the earthquakes which desolated the surrounding countries. Oil 

 the contrary, when a volcano becomes in .ctive, it seems to announce earth- 

 quakes; in 1797, when the volcan of Purace, near Popayan, had ceased to 

 emit flarne and smoke, the valley of Quito v/as agitated by violent shocks. 

 Volcans, therefore, seem to be natural vents, designed by Providence to pre- 

 vent a complete destruction of the globe, and its inevitable rupture into frag- 

 ments, which, launched into space, might there describe new orbits. 



12. Submarine eruptions. It is not only on land that volcanic 

 phenomena occur; they also take place under the sea, as might 

 be naturally anticipated. In our own times, we have had formed in 

 this manner the island of Julia,in 1831, on the south-west of Sicily ; 

 Bogoslaw, in 1814, in the Aleutian Archipelago ; Sabrina, and 

 another one not named, in 1811, in the Azores, where, previously, 

 at different epochs, others were formed, according to the most 

 authentic histories. The same thing occurred, at different times, 

 around Iceland : and various accounts indicate that in the islands 

 of Sunda, the Philippines and Moluccas, throughout the Pacific, in 

 the Kuriles, Kamtschatka, &c., similar phenomena took place. 



Volcan of Unalaska. One of the most striking examples is furnished by 

 the island, which arose in 1796, about ten leagues from the northern point 

 of Unalaska, one of the Aleutian islands. At first a column of smoke rose 

 above the surface of the sea; then a black point appeared, the smmit of 

 which launched forth sheets of fire and stones with violence. This pheno- 

 menon continued for several months, during which the island grew succes- 

 sively in extent and height ; later, smoke only issued, which ceased altoge- 

 ther four years afterwards. Still the island continued to enlarge, and to rise 



12- Do volcanic eruptions take place on land exclusively ? 



