HEAT. 279 



to a height of only 8 or 10 yards, as in Kilauea, — a height so small that 

 the projected drops or masses of lava fall back unsolidified, and the jets 

 dance in a lively and brilliant way over the surface of the lava-basin. The 

 scene is a brilliant one, when a lake of lava 500,000 square feet in area is 

 covered throughout with the playing jets, as at Kilauea in 1840. 



It is a mark also of such extreme liquidity, that where the escaping vapors throw up 

 the lavas in half -covered places under the rocky sides of a lake, the lavas in the recoil dash 

 out in fiery spray much like the spattering of breaking waves. In the pulling apart of the 

 rising lava-jet dividing it into drops, the glassy material in fusion is drawn out into hairs, 

 and forms the "Pele's hair " of Kilauea. 



In cases, outside of the lava-lakes, where the bubbles are bursting beneath an open- 

 ing in the bottom of the crater, the vapors and lava driblets escape from the aperture with 

 a riish and a roar, " as if all the steam engines of the world were concentrated in it." 

 (Douglas.) The driblet-cone, thus made, is sometimes called a hlovjing-cone. 



Now and then the regular ebullition is interrupted by larger throws, even to 200 feet. 

 At other times the lake becomes crusted over with a glassy scum, or with a crust of more 

 solid lava, and so remains for a while ; and then — at intervals of minutes, or hours, q~ 

 longer — it breaks anew into activity, attended with a remelting of what had solidifiecv^ 

 and the throwing up of jets asbefore. 



In the Mount Loa crater, situated 13,675 feet above the sea (10,000 feet 

 above Kilauea), the jets generally rise 200 feet or more, and instead of the 

 quiet ebullition of Kilauea there is the play of a great fiery fountain. One 

 of the describers states that in 1873 the " fountain of fire," 150 feet broad, 

 played in several united but independent jets to a height of 150 to 300 feet. 

 At one time the jets suddenly became low, and continued thus for a few 

 seconds, then " with a roar like the sound of gathering waters, nearly the 

 whole surface of the lake was lifted up, and its whole radiant mass rose 

 three times in one outburst to a height, as estimated by the surrounding 

 cliffs, of 600 feet. After this the fountain played as before with jets of 300 

 feet." (I. L. Bird, 1876.) Others report heights of 600 to 800 feet in the 

 playing fountains. These are the conditions in the Mount Loa crater only 

 when eruptions are imminent. 



The cause of this high projection of the lavas in fountain-like form in a summit crater 

 can be no other than the escaping vapors ; and the difference between such fountains 

 and the gentler ebullition of Kilauea must depend on their amount and rate of supply. 

 Such moisture, if the deep subterranean region of lavas were its source, would be most 

 abundant in the equally large but 10,000 feet lower crater, Kilauea. But if supplied by 

 the fresh v^aters from the rains over the region, the 10,000 feet of greater altitude are a 

 suflBcient reason for the difference. 



The idea was put forth by Scrope that the fusion in the lavas of a volcano was aqueo- 

 igneous fusion, or a mobility due in part to the water-vapor present. Such vapor must 

 increase the liquidity, but facts show that it is not dependent on it. The white light 

 which the lavas of Kilauea often display in their "ebullition" is evidence of heat suf- 

 ficient for fusion. Bartoli, on Etna in 1893, found the temperature of a lava stream, at 

 its exit, 1910° F. 



