Jaggar — YolcanologiG Investigations at Kilauea. 197 



This is the case with "Old Faithful," a rlijthinic foniitaiii 

 which, w^itli occasional lapses, has been frequently seen in 

 Kilaiiea. The fountaininii: border grottoes are places where 

 there is conflict of a current or currents with the resistant 

 shore, and commonly also these are over submerged sinkholes. 

 The meaning of a conflict of streaming currents will be 

 apparent when we remember that convection is the motive 

 power. At x holes a lighter fluid is rising ; at y holes below a 

 shallow lake a denser fluid is sinking ; atmospheric cooling, 

 radiation and gas expansion change the x fluid into the ij fluid ; 

 and a more viscous, partially cooled magma descends. Such is 

 normal convection, and some such convection progresses in 

 Halemaumau. Solidification increases weight. The lighter 

 fluid rises through the conduits w^est : crusts form rapidly over 

 it : these are drawn toward the several sinkholes east : they are 

 heavy and founder in the lighter magma just beneath them, 

 when two currents, developed by this sinkhole distribution, 

 bring crusts together and rend them or bend them so as to 

 release the gas accumulated beneath and start an engulf men t, 

 which progresses rapidly edgewise when once a portion of a 

 sheet of crust is submerged. This engulf ment is often a 

 flexible downfolding (fig. IGa). The result is to draw away 

 along a fissured line a wide sheet of crust, and hot magma 

 wells up the fissui-e and itself quickly crusts over. This crack- 

 ing and foundering process is seen in flexible skins, heavy 

 blankets and hard brittle crusts according to their thickness, 

 the supporting power of the fluid next below, and the length of 

 time that the crusts are allowed for solidification without dis- 

 turbance. The surface streaming is maintained as a part of 

 the convection by this mechanism, with accelerations at the 

 fountains. Maximum speed of surface streaming is attained 

 during general subsidence, when sinkhole mechanism is 

 dominant over conduit mechanism; when the x holes lose 

 pressure of rising magma and the y holes themselves subside 

 and downflow through them is at a maximum, uncompensated 

 by any tendency of inflow to add y holes to the x group. 



Problems of Fountain Mechanism. 



Why should fountains burst at all, and why at points of in- 

 terference of currents? Furthermore why should accelerated 

 streaming rush centripetally with engulfment to the fountains? 

 Why should continuous fountains emit banners of flame? And 

 why should the fountains be places of highest incandescence 

 and highest apparent liquidity? (Fig. 18.)' This is evidenced 

 by their spatter which is a perfect glass, often drawn into flla- 

 mentous floss. (See glisten of fresh 'lava, Plate la, upper view.) 



