DALY. — THE NATURE OF VOLCANIC ACTION. S3 



magmatic heat throughout the known history of Kilauea. In 1909, at 

 average intervals of about thirty-hve seconds, the surface of the lava 

 lake in this area was domed up to maximum heights of a few meters. 

 These fountains are not due to the rise and explosion of great gas 

 bubbles, the collapse of which could have been readily observed. No 

 appreciable amount of gas or va{)or was given off at the moment of 

 doming or immediately afterwards. The outbursts are best explained, 

 in part, on the principle illustrated in the upspringing of a log of light 

 wood freed at the bottom of a lake. Through its momentum the log 

 may jump clear out of the lake. In i)art, the outbursts of " Old Faith- 

 ful " are due to true explosive dilation of the gas bubbles in the "log." 

 The latter process is doubtless the chief cause of the smaller " foun- 

 tains " playing over the surface of Ilalemaumau, and of those which 

 played over the surface of Dana Lake or New Lake twenty-five years 

 ago. The draining of each of these two lakes has shown that it was 

 saucer-shaped and very shallow over most of its area, and the writer 

 believes this is true of Ilalemaumau to-day. (Compare Plate III.) 

 The depth is generally much too small to allow of such momentum 

 in magmatic " logs " that they might leap to the heights actually 

 observed. 



The site of "Old Faithful" is, thus, the place where the juvenile 

 gases rise from the depths in two-phase mixture with liquid lava. 

 With the collapse of each dome, the gas-charged magma finds its level 

 and runs under the semi-solid or solid " scum " on the lake surface. 

 (Figure Ct.) There the gas is slowly freed and accumulates beneath 

 the "scum " until the tension produces a true explosion, that is, one 

 of the many smaller " fountiiins " so constantly appearing on the lake. 



The incessant streaming in Ilalemaumau, the nature of the " Old 

 Faithful fountains," and the ceaseless vortical motion in the lake, as 

 well as the similar phenomena in the active Mokuaweoweo, are so 

 many direct evidences of two-])hase convection, which calculation shows 

 must be rajiid, j)rovided slight variations in vesicularity occur in tiie 

 depths of the lava column. Though it is not possible to prove abso- 

 lutely that the Kilauean column is vesiculated in depth, itcertiiinlyisso 

 at the surface to a remarkable degree. At many jxiints, the lower j)art 

 of the wall of Halcniaiiinau was found, in 1!MI9, to be covered with 

 thin ctjatings of black glass which represented splashes of lava from 

 the adjacent lake. This lava almost instantly " froze " to the wall. 

 In every ca.se it was extremely porous, so as to be (piite spongy in 

 appearance. The vesiculation was almost if Jiot (piito complete be- 

 fore the " sjila-sh " struck thn wall, and it is sini))lest to supi)ose that 

 the surface lava of the lake is a froth. There is no known reason why 



