DALY.— THE NATURE OF VOLCANIC ACTION. 91 



panied by the ejection of gas, as it is actually seen to emanate dur- 

 ing the crystallization of artificial slags. That process might cause 

 local supersaturation in the still liquid magma, with the forma- 

 tion of bubbles, (e) Chemical reactions in the magma, such as the 

 generation of hydrogen from dissolved primary water vapor — a reaction 

 to be expected witli a slight fall of temperature — might produce gases 

 insoluble in the magma at the pressure reigning at the place of the 

 reaction. 



Among so many possibilities, it seems legitimate to assume the gen- 

 eration of free gas in the main magma chamber. Irrespective of their 

 origin, the bubbles must rise with great slowness through the magma 

 chamber, because, first, they are of small size ; and, secondly, because 

 the viscosity of magma under great pressures must be relatively high. 

 Even in the case of supersaturation in all parts of the new abyssal in- 

 jection, the entire freeing of the bubbles may occupy many thousands 

 of years. 



As the bubbles rise, the gas tends to be concentrated in the volcanic 

 conduit. There the laws of mass-action and of the degradation of 

 energy seem to enforce exothermic reactions of the gaseous constituents 

 among themselves and with the elements of the liquid magma. It is 

 most probable that the heat so generated is very great when compared 

 to the mass of matter participating in the reactions. The conduit is 

 thus a furnace where the potential energy of the accumulating gases 

 is converted into heat energy. 



Other sources of heat which aid in prolonging the activity of the 

 volcano are: (a) the conversion of the potential energy of the liiju id 

 components of the magmatic system when thrown out of chemical 

 equilibrium by the change of pressure and subsequent lowering of 

 temperature ; (b) the liberation of latent heat in the slow crystalliza- 

 tion at the walls of the magma chamber ; and (c) some degree of 

 initial superheat in the magma, perhaps of the order of 1<)()° or '2i)()° 

 Centigrade. 



Since the loss of heat at an active vent is chiefly due to radiation 

 at the crater, the continuance of activity is controlled by the efficiency 

 of the mechanism by which the heat of the main chamber and the heat 

 chemically generated in the conduit are transferred to the earth's sur- 

 face. Field observations at Ivilauea and elsewhere, along with a priori 

 deduction.s, have suggested the general dominance of two-phase con- 

 vection (or, more generally, convection due to systematic, local changes 

 in gas-concentrati(jn) in making this transfer. 



Juvenile gas is thus conceived to act in a two-fold cai)!U'ity — as a 

 positive heater and as the agent enforcing convection. Its net eflect 



