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



report on the Henry Mountains, gave the first intelligible idea 

 of its power. 



But there is nothing in the action that leads us to suppose 

 that it can, under any probable conditions, make jets or foun- 

 tains of lavas, or work in blow-hole style. Each jet over a 

 lake, and each large jet in a lava-fountain, has its local 

 projectile cause beneath the projected column of lava, and 

 cannot be produced by any general upthrnst movement in the 

 great conduit. The imperceptibly slow uplift and fountain- 

 making are incompatible effects. There seems to be, therefore, 

 no foundation for the comparison of the lava fountains to the 

 projectile effect in an " artesian boring made to a stratum of 

 molten rock which had only been awaiting an opportunity to 

 overflow."* 



The source of the ascensive movement I have stated to be 

 undetermined. It is most commonly referred to the pressure 

 of the earth's crust on the lava reservoir beneath, arising from 

 subsidence in the earth's crust from secular refrigeration. 

 Another explanation appeals to vapors from the deep source 

 of the lavas. The possibility of some addition to the force 

 through ascending vapors is referred to on page 195 of this 

 volume. 



C. Effects of Heat, 



1. From change of temperature. — Contractional effects from 

 cooling, that is fractures and changes of level, should be com- 

 mon in the crater; for each stream has passed from a tempera- 

 ture of 2000° F. or more to 70° or 80° F. and the upper 

 surface of a stream rapidly so. Besides ordinary shallow frac- 

 tures, the cause produces also an imperfectly columnar structure 

 in the cooled lava-stream below the upper foot. The cracks in 

 the floor often expose quite good basaltic columns even when 

 the thickness of the layer is hardly a dozen feet. 



There should be also larger effects in the Kilauea region 

 arising from change of temperature between periods of great 

 and little activity, or from periodical variations in the heat 

 below, and changes of level in the lava of the conduit. But 

 we have no special facts to report in illustration, although 

 there are cracks innumerable in view that probably have this 

 source. 



2. The dissolving action of the liquid lavas. 



(1.) The refusion of the crust over the surface of a lava- 

 lake by the liquid lavas is — as the history has shown — one of 

 the common occurrences in Halema'uma'u and other lava-lakes. 



* Mr. W. L. Green, Vestiges of the Molten Globe, pp. 163, 272. Mr. Green's 

 examples are taken from action in the summit crater, and when speaking of that 

 crater this point will be again considered. 



