194 Jaggar — Yolcanologic Investigations at Kilauea. 



Distribution Crusting and Fountaining. 



On the lake surface over or near the inlet conduits, and 

 hence at the points of departure of the surface streaming, a 

 very marked cooling effect is generally observed in the form of 

 dark crust which remains stationary over the uprising gas- 

 charged melt (figs. 5^, Qa^ 15(?, on the right, 3 on the right, 18 

 on the left). Effervescence and incandescence are both at a 

 minimum at the locus of fresh rising lava. Radiation cooling 

 and expansion cooling both achieve their maximum immedi- 

 ately over the inlet vents. This was profoundly puzzling to 

 the writer during several years of continuous record and close 

 observation, when he supposed that rising juvenile gas was the 

 main source of heat, and hence the inlet wells should yield high 

 incandescence and much bubbling. Such multiple bubbling 

 of bright luminosity occurs in fact (1913) over the inlet region 

 only when the lava is subsiding, and convectional outletting is 

 greatly dominant over inletting — when a shallow rapid circula- 

 tion mixes air with tlie volcanic gases. During rising periods 

 the whole lake surface is apt to be quiet and crusted. (Con- 

 trast tig. 10 rising, with hg. 15 sinking.) These facts imply 

 that the rising magma aud gas from deep sources are only 

 moderately hot, the gas is evenly distributed in small bubbles, 

 and such lava is quickly solidified and crusted on exposure to 

 atmospheric temperatures. 



Let us now watch what happens as the crusts form, thicken 

 and stream across the lava lake to founder with sudden tearing, 

 downsucking, flaming and violent effervescence at a border 

 grotto, or to be engulfed at a central fountain. Such a foun- 

 tain forms, first, by conflicting currents tearing a crust asunder ; 

 then a spurt of flame appears, followed by a little bubbling ; 

 then a general downsucking of skins takes place toward a 

 point, frequently tearing a symmetrical hexagonal opening in 

 the crust, flfty feet (15"') across or more {^^. 12, a and l). The 

 crusts are heavy, tough, membraneous bodies like a doormat 

 (flg. IQa) and when they rift, the stiff vesicular slag below 

 wells up in the wake of the block which is foundering and 

 drawls out variously cooling shreds of its own substance from 

 the solid jagged edge of the mother crust, a glassy, veined 

 membrane of great toughness forming instantly over the newly 

 exposed lava through shades of cherry red to purple and black 

 (fig. 11, ^, G and cl). 



Cool air is incessanth^ circulating in contact with the crusts 

 to replace the hot uprush from the whole lake. The crusts are 

 three to four inches (eight to ten centimeters) thick (fig. 17«), 

 vesicular above, frequently folded or festooned and so involv- 

 ing large cavernous space, and their under sides, when they 

 are seen to turn up edgeways and sink, are covered with 



