J. D. Dana — History of the Changes in Kilauea. 219 



sometimes take place for eruptive effects, but of these we are 

 not speaking. The facts from the vesiculation of some lava- 

 flows of Mt. Loa brought out beyond (page 195) give further 

 evidence as to the quiet molecular occlusion of the waters. 

 Moreover, the possibility of this method of imbibition appears 

 to be demonstrated by Daubree's experimental work, which 

 proves that the process will go on through capillarity or mo- 

 lecular movement, against the opposing pressure of vapors 

 within.* He uses the fact to explain the origin of volcanic 

 vapors. 



The water seeking entrance in the depths below, more- 

 over, is under pressure from above, and, whatever the temper- 

 ature, the forcing of it back against this pressure and friction 

 is impossible ; the expansive force generated by the heat only 

 forces it into the rising lava of the conduit, as urged by Mallet, 

 and sustained by Prof. PrestWich. 



I proceed now with the consideration of 



2. THE EFFECT OF THE EXPANSIVE FORCE OF VAPORS IN THEIR ESCAPE 

 FROM THE LIQUID LAVAS : PROJECTILE ACTION. 



All the lava-lakes of the crater, whether one alone exists or 

 many, and the smaller vents over fires that are concealed but 

 not at too great depths, send forth vapors, which, in their 

 effort to escape as bubbles through a resisting medium, that 

 is, the lavas, do projectile work. The vapors thus produce 

 the play of jets over lava lakes with the muffled sounds and 

 tremor of ebullition ; and also the splashing and the throwing 

 of spray from open fire-places in the crusted lakes. They dash 

 up the melted fragments from a blow-hole with a rush and 

 roar " rivalling sometimes a thousand engines," thus introduc- 

 ing the coarser effects of gunnery into Kilauea. They make 

 the thin crust of the crusted lake to heave and break, press into 

 rope-like folds the lava along the red fissures, or start a new 

 play of fiery jets, high or low, and frequently several in alternate 

 play ; or, they make openings and push out a flood of lava ; 

 and occasionally, when rising in unwonted volume, they make 

 lava-fountains of unusual heights over the lakes, with at times 

 loud detonations. 



The projectile force required to throw up jets of lava to the 

 ordinary height they have in times of brilliant activity, thirty 

 feet or so (see pages 31, 32), is even less than a calculation from 

 the height, diameter and density would make it, because the 



*G-eologie Experimentale, 2 vols., 8vo, Paris, 1879, p. 235. 



The temperature of the liquid lava is nearly that of the dissociation tempera- 

 ture of water — 1985° F. to 2370° F. according to M. H. St. Claire Deville, — and 

 higher than this no doubt at depths below. But that dissociation takes place 

 within the conduit, under the pressure there existing, is not satisfactorily proved. 



