170 Jaggar — Yolcanologic Investigations at Kilaiiea. 



Variable surface Radiation. 



It has been said that the maintenance of the lava lake in a 

 fluid condition is product of an incessant struggle with cold.^ 

 The two-phase convection hypothesis imagines a lagged system 

 like a hot-water heating plant with circulation evenly main- 

 tained by rising of hot fluid to the radiator (crater) and un- 

 obstructed sinking of cooler fluid to the furnace. Daly has 

 not discussed the possibility, which seems to me a certainty, 

 that uneven radiation of the system at the surface is what 

 builds the ami alar bench around the lake and the semi-solid 

 hot lava column within the pit and under the lake, with per- 

 forations through it at the wells of uprising foam. The 

 uneven radiation is due to shifting and changing radiators, the 

 craters, which vary continuously in size, shape and debris 

 accumulation as the lava rises, overflows, falls or shifts its 

 vent ; and which themselves occasionally by gas reaction 

 become localized heaters. 



In other words, the downflow material of the convection 

 becomes very viscous near the surface and actually hardens at 

 the surface in the form of overflow benches and islands. When 

 the net effect for a given period is a rising in a crater which 

 widens upward, the downflow column, plastic but stiff within, 

 may build by accretion under and around the hot froth column, 

 and either encroach on the latter or the reverse accord- 

 ing as the heat supply and the cooling are balanced or not 

 (Plate I and flg. 2). 



It is evident that if this view is correct, then a profound 

 subsidence of the entire lava column, induced at Kilauea by 

 an extraneous cause, like rock tide stress or the relief by over- 

 flow of connecting tubes at Mauna Loa, should carry down the 

 semi-solid lava body as well as the more liquid lava lake. This 

 is just what happened at the time of the great sinking in 

 Halemaumau which took place June 5, 1916, simultaneously 

 with the conclusion of the lava flows on Mauna Loa. The 

 lake for two days resolved itself into a shallow streaming 

 puddle, and remained so for 100 feet (122 meters) of sub- 

 sidence. The supporting floor of the liquid lake and the 

 islands which protruded through the lake, sank steadily and 

 undermined the peripheral bench, which tended to cling to the 

 outer funnel walls of the rock pit, so that the bench and lower 

 walls crashed inward in great avalanches. The bench rock was 

 incandescent and semi-solid; the old walls of the encompassing 

 pit were not. For two days of subsidence, the talus slopes 

 from such tumbling were always supported by the sinking lake 

 bottom. When avalanches fell into the lake its shallowness 

 was instantly revealed by the wave which carried all of the 

 liquid up the far slope and by distribution congealed it. The 



■>^Daly, loc. cit., pp. 68, 71 and 92. 



