VOLCANOS AND RADIOACTIVITY 543 



VOLCANOS AND RADIOACTIVITY 



By Major C. E. DUTTOX, U. S. A. 



/~\NE of the commonest and perhaps the most impressive of natural 

 ^-^ phenomena, the volcano, has hitherto been without any explana- 

 tion of its cause, though it has been before the world a subject of theory 

 for many centuries. The reason for this is quite apparent. We per- 

 ceive the action of the volcano upon the surface and we know what it 

 does. But the theater of its origin and the development of its energy 

 are far below the surface of the ground, out of reach of inspection or 

 direct observation. Human ingenuity has been baffled in its efforts to 

 explain the phenomenon because of the want of observed facts and the 

 impossibility of obtaining them. But while we are, and probably 

 always shall be, unable to directly inspect the seat of origin of the vol- 

 cano, there are certain inferences in connection with them which have 

 attained a degree of probability which entitles us to use them as facts 

 which may limit speculation and confine it within very narrow bound- 

 aries. I purpose to mention these inferences in order to see the gen- 

 eral nature of the solution to which they point ; for unless I am greatly 

 mistaken, they will show us that we are close upon the verge of a 

 solution. 



1. The first fact to be mentioned is the solidity of the earth. It is 

 so well known that I shall not dwell upon it and merely mention it in 

 order to bring it, together with other facts, into the same series or 

 group. 



2. The second fact is the comparative smallness of the extravasated 

 masses in any single volcanic eruption. In order to obtain an idea of 

 the relative magnitude of an erupted mass, let us draw upon a true 

 scale a segment of one degree of the earth's surface, of an arbitrary 

 thickness — say thirty miles. Upon this segment draw the profile of 

 Vesuvius. About a mile below the surface, beneath the volcano, draw 

 the reservoir of lava, having the same mass as the volcano itself. It 

 may have any thickness and any form, and is subject only to the condi- 

 tion that the capacity of it is the same as the mass of the erupted 

 material. Xow Vesuvius is built of I know not how many individual 

 eruptions, but let us say one hundred, though I presume that there 

 were, in reality, very many more. A single average eruption would be 

 the hundredth part of the volume of this reservoir. But there are 

 eruptions known which are many times greater than the average of 

 those of Vesuvius. The largest known in the United States are in 



