VOLCANO. 



Cixly miles, and alfo other volcanic ranges of great extent, 

 have probably been formed by enormous chafms, partially 

 choaked up in the fame manner. Indeed the new volcanic 

 range, of which Jorullo forms a part, is placed in the diredl 

 line of a volcanic range of vatt extent, which this erup- 

 tion appears to have partially re-opened. Humboldt ob- 

 ferves, that in New Spain there is a narrow zone placed 

 between latitude i8° 59' and 19° 12', in which the lofty 

 volcanoes that dill continue to burn, or which from their 

 form and the nature of the rocks may be inferred to have 

 been once volcanic, are fituated. In receding from the At- 

 lantic, we find in the fame line, ranging eaft and well, the 

 Pic d'Orizaba, the two volcanoes of Le Pucbla, the Ne- 

 vada de Toluca, and the volcano of Colima. The parallel of 

 their grcatell elevation ranges nearly at right angles with the 

 chain of mountains that form the Cordillera of Anahuac ; 

 and it is worthy of obfervation, that the volcano of Jorullo 

 forms a prolongation of that line, on the fame parallel with 

 the ancient Mexican volcanoes. Do not thefe analogies, he 

 adds, entitle us to fuppofe that in this part of Mexico there 

 exifts, at a great depth in the earth, a chafm, extending in 

 a direftion from eaft to welt one himdred and thirty-feven 

 leagues, along which the volcanic lire, at different epochas, 

 has burft through the porphyritic crull, from the gulf of 

 Mexico to the South fta ? This chafm may alfo extend to 

 the group of iflands called the Archipelago of Revellegedo, 

 placed in the fame parallel of latitude, around which pumice- 

 itone has been feen floating. 



For an account of the volcanic eruption which formed 

 Monte Roii'o on Etna, fee ^txa. 



A tremendous noife and violent concufBons of the earth 

 preceded the repeated difcharges of fcorije and fand in this 

 eruption ; yet during all thefe convulfions, the fummit of 

 Etna was perfeftly quiet, and only emitted a light fmoke, 

 which had ifTued with the fame tranquillity before the 

 eruption. A range of volcanic hills was formed in a fimilar 

 manner near the foot of Vefuvins, in 1760. After repeated 

 concudions of the earth, which were felt fifteen miles round 

 the mountain, a vaft opening was made in the territory of 

 Torre del Greco, from which fifteen volcanoes arofe ; eight 

 of thefe were foon covered by a torrent of lava, which 

 rufhed from one of them ; the other feven remaining entire, 

 and inceffantly ejecting from tluir mouths vaft quantities of 

 ignited fubftances, which falling almolt perpendicularly 

 round the new volcanoes, produced in ten days feven fmall 

 mountains of various heights, difpofed in a right line. 

 During the eruption, the iioifcs fometimes refembh-d violent 

 thunder, at others the difchargc of artillery ; large ftones 

 were thrown to the height of nine hundred and fixty feet. 

 After tile tenth day, the eruption ceafed, and the newly- 

 formed mountains gradually cooling, permitted a nearer ap- 

 proach'; fome of them had at their fummits a cavity 

 refembling a funnel, others a hollow of greater or lefs 

 depth. 



The J^ipari iflands extend in a right hne about fifty miles 

 from eaft to weft, except Vulcano, which makes a fmall 

 angle. Thefe iflands, as well as the volcanic ifles of the 

 Moluccas, which form a chain in the Indian ocean, pro- 

 bably originated from enormous chafms, hke thofc which 

 formed Jorullo, and the ranges on the fides of Etna and 

 Vefuvius. Thefe chafms were in all probability firil opened 

 under the ocean. 



When a volcano opens in a new fituation, the commo- 

 tions which precede it will be greater than when the erup- 

 tion takes place from craters already formed. The rc- 

 fiftance occalioned by the congelation of lava in the mouth 

 and paflages of the principal crater, may be greater than 



from other parts of tl:e furface, in which cafe the liquid 

 lava, confined and compreffed by the expanfive force of heat 

 and elaflic vapour, may be driven laterally to a great 

 diftance between the feams and fiffures of the ftrata, up- 

 heaving the furface in fome parts, and foftening it or melt- 

 ing it in others, producing earthquakes in countries far re- 

 mote from the principal crater, which will continue till a 

 new opening is made. 



It is related by Strabo, that the ifland of Euboea had 

 been for a long time violently agitated by earthquakes, 

 when a large rent opened in the plain of Lelantum, 

 from which was ejetted a river of fiery mud ; after this the 

 earthquake ceafed. Other inftances of violent earth- 

 quakes, felt at the diftance of many hundred miles from the 

 place of eruption, arc not uncommon, as we (hall foon have 

 occafion to notice. The lateral prefi'ure occafioned by a 

 column of lava two miles in lieight, inuft be enormoufly 

 great, and from this caufe alone we might expeft, that in 

 very lofty volcar->*5, like Etna, the eruptions ftiould be 

 more frequent fi^m the fides than the fummit, which is 

 found to be the faft. The fuddcn retiring of the fea from 

 the fliore before an eruption has frequently been noticed. 

 This can only be fatisfaftorily explained by the upheaving 

 of the foftened furface of the ground ; and during violent 

 earthquakes, the anchors let down at a diftance from the 

 fiiore have been oblerved to be heated, proving the ftate of 

 the ground below. 



Siihmarinc Voliniwes. — When a volcano breaks out under 

 the furface of tlie fea, the phenomena attending the erup- 

 tion vary confiderably from thofe obferved on land, owing to 

 the oppofition of conflicting elements, the refiftance made to 

 the eruption, and the more fudden cooling of the matter 

 ejefted. It is the opinion of Humboldt, that in all fub- 

 marine volcanoes, the cruft of the earth is foftened and 

 fwelled by fubterranean heat, till it rifes above the furface 

 of the ocean even from great depths, before any eruption 

 takes place. From the narrative of eyc-witneffes, we have 

 reafon to believe that in many inftances the opinion of Hum- 

 boldt is correct. There are, however, volcanic eruptions which 

 undoubtedly take place at the bottom of the fea, and the ap- 

 pearance of new land is caufcd by the ftones and fcori;c thrown 

 up from thence : the more rapid cooling of the cruft of the 

 lava may alfo accelerate the formation of a new ifland. We 

 have alio inftances of Immenfe quantities of pumice floating 

 in the ocean fome hundred leagues from land, which could 

 oiily proceed from the eruption of volcanoes at fo great a 

 depth under the fea as to prcfent no other volcanic phe- 

 nomena on its furface. The fubmarine volcanoes which 

 have been obft rved fince the records of authentic hiftory are 

 not very numerous, nor will this appear furprifing, when we 

 confider that the ocean has not been cxtenfively traverfed by 

 civilized men more than a few hundred years. The nu- 

 merous volcanic iflands fcattered over the globe, which are 

 evidently formed by fubterranean fire, may however con- 

 vince us, that the phenomena of fubmarine volcanoes have 

 been not unfrequent in a former condition of tlie globe. 

 The fubmarine volcanoes of which we have the earlieft ac- 

 count, are thofe in the Grecian Archipelago, near the ifland 

 of Santorini. This ifland forms a triangle with the ifland 

 of Melo, which is volcanic, and with Paros, fo celebrated 

 for its marble. The fides of the triangle are about fifteen 

 leagues each. 



Santorini, formerly Thera, and afterwards St. Irene, was 

 furnamed by the Greeks Kaij.mi, or burnt, and fo in fadl the 

 foil is. There is a tradition, fays Pliny, (hb. ii. cap. H7.) 

 " that it rofe out of the fea in a very remote but unknown 

 period." The fea i< very dee]) near Santorini, there being 



no 



