DALY. — THE XATURE OF VOLCANIC ACTION'. 85 



On the other hand, the thermal conditions are different in craters 

 floored with highly viscous lava. There the emanating ga.ses com- 

 monly issue at pressures of more than one atmosphere, and they are 

 thus kept hot and endowed with some fluxing power. The small blow- 

 holes in Kilauea, as in most other basaltic districts, have long been 

 kept open through this action. It is quite possible that such hot- 

 blasting is operative on a greater scale in larger openings like the crater 

 of Stromboli. Yet even at Stromboli that cannot be the chief method 

 of heat transfer from the depths, and again no other method than that 

 of two-phase convection seems competent to keep the lower and greater 

 part of the lava column fluid. At Kilauea, at the wonderful Mokua- 

 weoweo (the vent of a main abyssal injection), at Matavanu in Savaii, 

 we seem compelled to exclude all other agencies for heat transfer except 

 this type of convection. The same explanation seems to apply also to 

 Vesuvius and Stromboli, for their craters in times of strong activity 

 have been observed at close quarters and, like Halemaumau, they show 

 lava " fountains " and other features of this convection. 



The Volcanic Furnace. — So far, no assumption has been made 

 that the hejTt transferred to the top of the volcanic conduit is other than 

 primary in origin, that is, heat due to the initial temperature of the 

 parent abyssal injection. Such is the orthodox view of volcanic heat. 

 The rough estimate made in the discussion of thermal convection sug- 

 gests the difficulty of understanding how the mere primary heat suf- 

 fices to explain the long life of many volcanoes. 



It may well be questioned, however, that all the heat at a volcanic 

 vent is primary.^* That due to the radioactivity of magma during 

 the fluid stage of an abyssal injection is too small in amount to afiect 

 the rate of heat loss to any sensible degree. More promising is the 

 idea that heat-producing chemical reactions in the conduit may have 

 powerful effect. Since the day when Sir Humphry Davy renounced 

 his own explanation of magmatic heat as due to the oxidation of alka- 

 line metals contacting with water, most volcanic theories have regarded 

 magma as inert so far as exothermic reactions are concerned. On the 

 other hand, recent studies of gaseous emanations from active volcanoes 

 and from artificially heated rocks and meteorites clearly suggest the 

 po.ssibility of such reactions. 



Analysis of any i)erfectly fresh igneous rock shows the presence of 

 water to a considerable i)ercentage by weight. This is true of in- 

 trusive gabbros and diabase as well as of ba.saltic lavas. Must of 



" Cf. G. Tschcmiak, SitzunRsbcr. .\kjul. WisM. Wicn, 76. ltJ2 (1.S77), where 

 a brief statcracut is given, showiug u dear uuticipatiuu uf this hypothesis. 



