Perret — Representation of Volcanic Phenomena. 51 



are here represented in six diagrams showing the development 

 and progressive variations of that important event. 



It may be of interest to note that any volcanologist could, 

 from these diagrams alone, mentally construct and vividly and 

 correctly describe the eruption. This is evidently working in 

 the wrong direction and is not to be recommended, but the 

 fact is mentioned as showing the effectiveness of the method. 



Considering now the characteristics constituting the key of 

 the diagram, the reader will at once perceive their emplace- 

 ment to be that which is most in accord with the nature of the 

 phenomena. Thus, the upwardly diverging radiants represent 

 the explosive phases, the vertical being devoted to volatile and 

 aerial products and phenomena, with the fragmental ejecta 

 adjacent on either side. The lower perpendicular indicates 

 degradation and deformation of the volcanic edifice by the 

 general phenomena of descent. The effusive line is horizontal, 

 on the right, while the left-hand corresponding radiant repre- 

 sents electrical effects, and is adjacent to the ash and detritus 

 which are essential to their development. Seismic phenomena 

 are placed at the lower right, while the so-called solfataric, i. e. 

 fumarolic, phase of activity is represented at the lower left. 



Speaking in the most general terms, the right-hand divisions 

 present the more direct products and phenomena, while those 

 at the left are of an accompanying or resultant nature. These 

 will be seen to correspond in some degree — especially as regards 

 the ejectamenta — with certain terms which have been proposed, 

 and in part adopted, for distinguishing the principal classes of 

 phenomena and products, but which, however convenient for 

 general descriptions, either fail in consistency under the test of 

 the diagrammatic method or are inapplicable because of the diffi- 

 culty of observational classification. They invariably constitute 

 an imperfect and limiting terminology, and are here best 

 avoided. 



We shall now examine in detail the various subdivisions of 

 the analytical key, beginning with the "Explosive" phase. 



The gases issuing from active lava on its first coming to the 

 surface — and even under other conditions — will frequently 

 burn with the production of true flame, which is sometimes 

 lost to view in the glare of the lava. At Etna in 1910 the 

 flames were ten meters in length, and at Kilauea in 1911 each 

 lava-fountain jet emitted a flash of burning gas. 



Apparently a product of this combustion, but possibly also 

 formed without it, the transparent bluish vapor constitutes one 

 of the commonest of volcanic exhalations. It is the bane of 

 the photographer in inter-crateric work, where its transparency 

 deceives the eye and its actinic color veils the photographic 

 image. The white "panache" is a characteristic feature of 



