THE RELATION OF RADIOACTIVITY TO VULCANISM 



GEORGE DAVIS LOUDERBACK 

 University of California 



Within tiie last year or two those working in the rapidly growing 

 science of radioactivity and sub-atomic systems have discovered a 

 number of properties and relations that bear strongly on earth pro- 

 cesses and theories, and that are of daily increasing interest to the 

 geologist, many of whose problems are being made to assume a new 

 light. Very recently (April, 1906) Major Button^ presented a paper 

 to the National Academy of Sciences in which the results of the in- 

 vestigators of radioactivity have been brought into relation with 

 geological phenomena to construct a definite explanation of volcanic 

 action. 



In discussing the competency of radioactivity to produce the local 

 high-temperature effects which are essential to volcanic action, it is 

 desirable to consider first the relationship of radioactivity to the 

 general thermal condition of the earth's interior. Since Major 

 Button 's paper was prepared, R. J. Strutt^ has published an account 

 of some tests made on various igneous rocks from different parts 

 of the world, with the result that the earlier conclusions as to the 

 relation of earth heat to radioactivity are made much more secure 

 and definite. In general it may be said that all the igneous rocks 

 examined (they were selected to represent different parts of the earth 

 and different rock types) show distinct radioactivity, the most active 

 being the more acid granites and syenites; the least active, basalts 

 and various ultrabasic rocks. Division into more active and less 

 active specimens does not correspond absolutely to rock types, but 

 very generally so. The range in content is calculated at from 1.84X 

 io~""to25.5Xio~''^ grams of radium per cubic centimeter of rock, ot 



I See Popular Science Monthly, June 1906, pp. 542-50; also Journal of Geology, Vol. 

 XIV, pp. 259-68 (June, 1906). 



= R. J. Strutt, "On the Distribution of Radium in the Earth's Crust, and on the 

 Earth's Internal Heat," Proceedings of the Royal Society, Ser. A, Vol. LXXVII (1906), 

 pp. 472-85- 



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