216 J. D. Dana — History of the Changes in Kilauea. 



canic igneous eruptions and nearly all other geological opera- 

 tions, the results are pericentric. Overflows and outflows, 

 aerial discharges and their depositions, fissure-making, subsi- 

 dences, elevations, everywhere illustrate this fundamental prin- 

 ciple in volcanic action. As the volcanic mountain with its 

 crater is its emphatic expression, so is almost every little 

 heap of lavas, or cinders, that may form within the crater or 

 over the mountain slopes. 



A. The work done by vapors. 



Only part of the work of vapors is of the permanent kind,, 

 carried on, as above described, by the vapors rising through the 

 lavas of the conduit. Another efficient part, but most efficient 

 in times of eruption, is dependent on vapors generated out- 

 side of the conduit. In addition, there are the chemical effects 

 of vapors. The work includes : 



(1) The effects of the expansive force of vapors in their 

 escape from the liquid lavas : projectile action and its results. 



(2) The effects of the expansive force of vapors within the 

 liquid lavas : vesiculation and its results. 



(3) The effects of vapors generated outside of the conduit : 

 fractures, displacements, etc. 



(4) The chemical action of vapors ; which is considered only 

 as regards certain metamorphic effects, in connection with the 

 account of the Summit crater. 



1. THE VAPORS CONCERNED : THEIR KINDS AND SOURCES. 



The vapors of Kilauea have not yet been made a subject of 

 special investigation. Still, there is no question that the chief 

 working vapor is the vapor of water ; besides which there is a 

 little sulphur gas, and probably some atmospheric air. In- 

 vestigations elsewhere have shown the vast predominance of 

 water-vapor among aerial volcanic products proving that less 

 than 1 part in 100 is vapor of any other kind. The state- 

 ment of Mr. J. S. Emerson (xxxiii, 90) that on the west 

 margin of Halema'uma'u, at one of his surveying stations in 

 April of 1886, to leeward of a " smoke-jet," he continued his 

 work " without regard to the smoke which the wind carried over 

 him within a few feet of his head," is proof that the air held 

 little sulphurous acid. Great volumes of vapors were constantly 

 rising from Halema'uma'u in August, 1887. 



Mr. Brigham was led "to conclude from his seeing so little 

 vapor rising from the Great Lake during his visit, that too 

 much influence had been ascribed by others to water ;* and 

 this view is presented also by Mr. W. L. Green, of Honolulu, 



* Brigham, Memoir, p. 450, and this Journal, xxxiv, 24. 



