200 Jaggar — Yoleanologic Investigations at Kilauea. 



along the line and so liberate imprisoned oxygen for union 

 with the magmatic gas. 



Rhythmic fountains like " Old Faithful " have commonly 

 at Kilaiiea intervals between explosions of from thirty to 

 ninety seconds and occnr immediately over sinkholes in the 

 bottom of the liquid lake some 50 feet (15 meters) below the 

 surface. They are particularly in evidence during a term of 

 prolonged and continuous subsidence when the sinkhole is 

 steadily acting as such, but their regularity may continue dur- 

 ing rising. The crust material which founders at the lake 

 margins of the cove in question sinks to the bottom and on 

 being drawn into the sinkhole is broken up in contact with the 

 gases of the lava. The reaction is continuous in supply of 

 materials. The excess of combustion products and localized 

 heat effect extend to the surface of the lake vertically in 

 spasmsj instead of continuously, because the excess of un com- 

 bined oxygen is insufficient to maintain a continuous stack or 

 furnace through the 50 feet (15 meters) or so of liquid melt 

 above. Such central fountains occasionally become continuous. 

 What factors are dominant in contributing to the rhythm of 

 the surface explosion is as yet unproved, but it seems probable 

 that the sinkhole itself acts rhythmically in its downtiow, 

 becoming clogged at intervals. The greatest amount of oxygen, 

 heat, expansion and local convection would be produced during 

 its more rapid downsuckings, and these times would surely 

 upset the surface equilibrium of the pool above and produce a 

 fountain. 



Continuous fountains, at the lake margin especially, form 

 grottoes of spatter glass in beehive, or half-dome, form, open 

 as glowing caverns on the side toward the lake and frequently 

 perforated with small flaming crevices, the walls of which are 

 incandescent (figs. 1-^a, 16/^, 10 right center). Usually such 

 grottoes surmount border sinkholes of some permanency as 

 revealed by sudden subsidences, and there is reason to suppose 

 that the mechanism of a prolonged building up of the bench 

 lava, with persistence of such a grotto, constructs such a sink- 

 hole by upward growth of the cavern in the bench and of the 

 floor of the lake % accretion (fig. 2, section) under the cavern's 

 mouth. Towards such a grotto there is continuous suction, 

 within there is continuous but variable fountaining and spray- 

 ing from outrush of gas, through the apertures and above the 

 entrance cavern there are continuous but variable spears and 

 banners of flame. Still higher appears the bluish fume which 

 retains its heat for hundreds of feet above and to leeward and 

 is painfully acrid with SO, and SOg in its effect on the human 

 mucoTiS membrane. The temperatures in these grottoes are 

 very high as shown by their luminosity, the magma within 

 them is at minimum viscosity as shown by its mobility, and the 

 glassiness and freedom from vesicles of the spatter product are 



