73 



In 1909 the present writer used a Ft^ry pjTometer to determine the 

 average temperature of the non-incandescent scum which regularly 

 covered at lea.st two thirds of the lava lake. The average temperature 

 for this part was estimated to be about 450° C. ; the corresponding heat 

 loss is computed to be 0.277 cal. per square centimeter per .second. 



At the best points of observation in 1909, the area of the hottest 

 lava was not large enough to cover the " black spot " of the pyrometer 

 for a time long enough to give a reading for its full temperature. It 

 was clear, however, from the behavior of the galvanometer needle dur- 

 ing the brief exposures of the very hot lava in the "Old Faithful 

 fountains," that its temperature was well above lOOO" (J. Froui the 

 color the temperature of the hottest lava visible in the lake was esti- 

 mated to be somewhat over 1200° C. The third of the lake relatively 

 free from scum was estimated to have an average temperature of 

 1000° C, corresponding to a heat loss of 2.8 calories per square centi- 

 meter per second. 



With radius of 100 meters the circular lake would lose in heat about 

 375,000,000 calories per second. The actual lake of 1909 probably 

 lo.st more than 230,000,000 calories per second. 



We may conclude that heat was then being lost by radiation more 

 than fifty times faster than by conduction into the walls of the 

 Kilauean pipe, if it be assumed as two kilometers deep. It would .seem 

 that radiation at the crater must be the dominant one of these two 

 phases of heat loss in any strongly active volcano. 



Mi'thoih of Ilmt Tnin^jh: — ^The upward transfer of lu'at into a 

 volcanic j)ipe might conceivably take place in five dilferent ways : 

 (1) by explosive removal of nuiterial from the ui)per part of the vent, 

 followed by ni)rise of magma from the still Huid chamber; (2) by sim- 

 ple overflow of magma at the lip of the crater ; (3) by thermal convec- 

 tion in the lava column ; (4) by a process which may be called, for 

 convenience, "two-pha.se convection " ; and (5) by the jiassago of free 

 juvenile ga.s throiKjh the lava column, thus bringing al»yssal heat to 

 the upper j)art of the vent. 



The first and .second proce.s.ses have obviously played no essential 

 nMes in keeping up the heat supply in Kilauca siuco 1823, when do- 

 tailed records of its activity began. 



