Volcanos and Earthquakes. 5f^ 



Skaptar Jdkul comrtiewced. On the 13th June 1 830, a simi- 

 lar submarine eruption was repeated.* 



The immense masses of lava ejected from a single volcano, 

 and the enormous extent in which volcanic actions are felt at the 

 same time, scarcely leave room to doubt that every active vol- 

 cano is in immediate communication with the whole melted 

 matter in the interior. In this manner alone can it be conceived, 

 how, for instance, the masses ejected at different times from 

 Vesuvius vastly exceed the whole bulk of the mountain,-f* while 

 tlie latter seems upon the whole to undergo no diminution, 

 for the falling in of its cone at one period appears to be ba- 

 lanced by the accumulation of ashes at another. 



If a rent reaching from the surface to the melted matters in 

 the interior be of great length, but not open throughout its 

 whole extent, the first eruption will take place where there is 

 the least resistance. 



If this channel become obstructed, the volcanic fire will seek 

 another vent.. I Violent concussions may open new fissures § 

 and close old ones, by which frequent changes may be produced 

 in the channels of the lava and water. Fissures obstructed by 

 lava are closed so firmly as to be incapable of being re-opened ; 

 new ones, therefore, are formed. Thus it is, at least, if a vol- 

 cano produce eruptions from its sides. If it happen that a wide 

 and lasting vent be formed, all partial workings in the neigh- 

 bourhood will cease. A similar combination, although on a 

 somewhat limited scale, is presented by groups of mineral 

 springs, especially of hot springs. In such groups new channels 



* Joimi. de Gc^ologie, t. i. 



t This was remarked even by the ancients ; and Seneca, Letter 7&, after 

 stating the difficulty, solves it by remarking-, that the fire of the volcano, 

 *' in ipso monte non alimentum liabet, sed viam." — Daiibeny on Volcanos, 

 p. 155. 



:J: Thus the interior of the crater of the Peak of Tenerife shews it to be u 

 volcano, which for thousands of years has thrown out fire only from its 

 sides. V. Humboldt, Reise, t. i. p. 105. 



§ According to the inhabitants of JVew Audahmay the soil in various dis- 

 tricts in their pro\4nce has become more and more arid, in consequence of 

 the frequent earthquakes with which they are visited from time to time. 

 V. Humboldt, Reise, t. ii. p. 21. 



