Jaggar — Yolcanologic Investigations at Kilauea. 199 



gases of the melt including hydrogen, carbon monoxide and 

 sulphur at high temperature, explosive reactions are inevital)le, 

 and these will be a local, temporary and incomplete oxidation, 

 or a general, definitely situated, prolonged and flaring blast- 

 furnace effect, according as the supply of oxygen is temporary 

 and inadequate, or continuous and effective. The conflict of 

 streaming convection currents which determines foundering, 

 will thus produce subsurface oxidation of gas, more or less 

 complete, according as the downrush of air and air-filled crusts 

 is rapid or slow, general or sporadic, localized or shifting, con- 

 tinuous or temporary. 



It must be borne in mind that the only significance of cur- 

 rent conflict is as an observable and measurable evidence of 

 crust breaking ; and that this breaking of crusts by convec- 

 tional interference is not limited to the surface, but takes place 

 where vei* the glazed and air-charged blocks are subjected to 

 fracturing or erosion, as when they are drawn down sinkholes 

 in the bottom of the lake. 



On this analysis it will be seen that fountains should burst 

 where violent oxidation is produced by contact at high 

 temperature of magmatic gas and air. 



Thus central fountains may commonly be attributed to such 

 accumulation of air-filled crust beneath the surface, as to start 

 the oxidation reaction ; this involves violence and a consequent 

 further breaking up of the air-filled block ; the reaction may 

 involve condensation and devesiculates the melt, consequently 

 downsucking from the surface ensues, which supplies more 

 oxygen ; localized heat is liberated, inducing localized convec- 

 tion and expansion, and vertical escape of combustion products. 

 The two processes are opposed and produce the opposed effects 

 seen at a normal lava fountain, namely violent upward dis- 

 charge of more or less burned gas and convulsive downward 

 indraft of crusted magma. 



It will be seen that when two surface currents of different 

 velocity come together at an oblique angle and along the line 

 of meeting continuous downfolding of huge blankets of crust 

 ensues, the two currents merging hito one and carrying along 

 the submerged foundered skin in the new direction, the con- 

 dition is ideal for generating a line of travelling fountains 

 (tig. 13). And just such travelling fountains are there gen- 

 erated, the explosions migrating with the line of meeting, 

 accelerating the inrush of the skins along the line, sucking 

 down free air with them in the violence of the reaction, and 

 increasing in vehemence of fountaining until raw glowmg air- 

 free melt has been exposed on both sides, the fountain usually 

 ending its career at some permanent grotto on the bank. The 

 two currents streaming at different speeds in this case furnish 

 erosion mechanism to break up the crusts under the surface 



