THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



.Aet. XXXVI. — Volcanic Vortex Hings and . the direct con- 

 version of Lava into Ash ; by Feajsjk A. Peeeet, K.I.C. 

 Volcanologist of the Volcanic Research Society. 



The vortex rings projected from cannon, locomotives, the 

 mouth of a smoker, etc., are familiar to all. Sudden puffs from 

 any smoke-filled cavity will produce, by interference at the 

 edges of the orifice, visible annular vortices having a certain 

 stability of form due to the persistence of the vortical move- 

 ment. It is obvious, therefore, that the conditions necessary 

 for the production of these rings must often obtain at 

 volcanic craters and, in fact, such volcanoes as Vesuvius and 

 Stromboli, during the prolonged periods of moderate activity 

 which may be said to constitute their normal condition, project 

 large, thin rings of vapor which frequently attain diameters 

 of five hundred meters or more. Generally speaking, these 

 are somewhat difficult to photograph because of their delicacy 

 and lack of photographic contrast with the sky, and it was not 

 until the Etna eruption of 1910 that the present writer observed 

 volcanic vortex rings having a sufficient degree of solidity to 

 permit of satisfactory photography. Figs. 1 and 2 show the 

 type of rings projected at that time and of which the diameters 

 were approximately 150 and 200 meters. It is not, however, 

 with the purpose of discussing vortex rings, as such, that I have 

 here referred to this phenomenon but because of the fact that 

 these particular rings of the Etna eruption illustrate a principle 

 of volcanic action which is of such importance as to merit 

 attention at this time. 



What impressed me most in observing these rings was the 

 fact that they were composed almost entirely of ash and 

 yet had been projected from a crater yielding liquid lava. 

 This was the lowermost of the seven principal groups into 

 which the twenty or more vents of this eruption were con- 



Am. Jour. Sci.— Fourth Series, Vol. XXXIV, No. 203.— November, 1912. 

 27 



