May 6, 1909] 



NATURE 



THE ERUPTION OF VESUVIUS OF APRIL, 



1906.' 

 T7OR thirty years Dr. Johnston-Lavis has devoted much 

 of his life to the investigation and elucidation of 

 volcanic phenomena as illustrated by the classical type- 

 volcano Vesuvius. To him we owe the great geological 

 map of Vesuvius and Somma, and a detailed memoir in 

 which he wofked out the geology of that very complex 



Nasone on M. Somm 

 October, 1903, taken 

 at the extreme summ 



seen from the Punta del 

 t looking due south. The dotted line is that of the outHne of Vesuvius in 

 vith the same camera and lens, and represents, except for a faint variation 

 t, the actual outhne of the cone before it was truncated by the late eruption. 



well 



papers upon 



Neapolitan volcano, 

 several eruptions. 



In a monograph lately issued by the Royal Dublin 

 Society we have a careful vulcanological study of the great 

 paroxysm of 1906, and an attempt to read from the re- 

 corded phenomena and the ejected materials the physics of 

 such an eruption. 



.\ quarter of a century ago, and in frequent communica- 

 tions since. Dr. Johnston-Lavis has 

 pointed out that in the ejecta, and 

 especially in the fragmentary materials, 

 we have a key for interpreting the 

 physical causes and phases of an erup- 

 tion. 



He holds that the aqueous and other 

 vapours of an igneous magma are 

 derived from materials acquired and 

 dissolved by the igneous paste on its 

 way towards the surface. There is 

 evidence that the H.O and other vola- 

 tile elements really exist in the form of 

 a solution of gases in a liquid, and that 

 variations in the phases of an eruption 

 are due to the separation of such vola- 

 tile materials from solution and the 

 expansion to the gaseous state on the 

 relief of pressure or the increase of the 

 amount and resulting tension of them. 

 He maintains that the same physical 

 laws that govern the solution of CO, 

 in water under varying pressure and 

 temperature are identical with those 

 which govern the solution of H„0, 

 volatile chlorides and sulphates in a 

 mixture of fused silicates. 



This is the thesis that the author 

 follows in the description of the last 

 great outburst of Vesuvius, and still 

 further claims his old favourite as the 

 type-volcano of the world. 



In the first chapter is a review of the changes that have 

 occurred at Vesuvius since 1872, the date of the last 

 important eruption. Next follows a diary of the daily and 

 hourly changes at the volcano during its great paroxysm, 

 partly from Dr. Johnston-Lavis's own observations and 

 partly from those of other observers. The observations 

 are then analysed in a chapter on general considerations 

 and a scheme of grades and varieties of the activity of 

 1 .Scientific Transactions of the Royal Dublin Society, vo'. ix. (Series ii.), 

 part 8. (Dublin: University Press.) 



NO. 2062, VOL. 80] 



volcanoes is given, in which .the -eruption of April is classed 

 under the paroxysmal vcsuvian type, as distinguished from 

 ordinary Vcsuvian type. A protest is made against the 

 application of the terms vulcaiiian and pelean to this out- 

 burst, the term being considered to be mjore applicable to 

 acid volcanoes, in which the higher viscosity of an acid 

 inagma gives rise to a very different series of phenomena, 

 namely, (a) amount of lava above the lateral outlet ; 

 (6) the secular output oi lava; (c) -the 

 rise of magma due to its expansion 

 from increased vesiculation after the- 

 relief of pressure from the fluid column 

 above it has drained or blown away. 

 The different phases of the eruption are 

 studied, and the varying output of lava 

 examined from these points of view. 



The lava in this eruption was of the 

 usual aa type of Vesuvian rapid out- 

 flows, and differs from the pahoehoe 

 type of slow dribblings such as built up 

 the great lava cones of 1891 and 1895. 

 JK coinparison of inicroscopic characters 

 shows that the felspars are mote de- 

 veloped in the slow outflows, whilst the 

 leucites doininate in the rapid floods of 

 lava. A series of excellent photographs 

 taken by the author exhibit many 

 striking phenomena of lava flows on 

 the open slopes, along narrow ravines, 

 and amidst streets, houses, railroads, 

 bridges, &c. 

 The so-called bombs which are frequent on the surface 

 of lava streams were shovi/n by the author some years 

 ago to be due to the fragments of solid materials caught 

 in the lava stream and floated to the surface by the vesi- 

 culation on their surface, which latter acts in a catalytic 

 manner. They have condensed on their surface a crust 

 derived from the fluid rock which gives them their bomb- 

 like appearance. A photograph is given in which the 



it. 





2 — I he great cor 

 due east across th( 

 barrancos formed < 



I on May 3, igo6, to show the trun 

 iides by the slipping of loose fragn 



e Colle Umberto, looking 

 top and the remarkable 



nucleus is composed of a piece of wall, thus indicating 

 their true origin. The author aptly compares them to a 

 dumpling, and proposes in future to call them by that 

 name to distinguish them from other so-called bombs. 



Several reasons are given for the slight variations in 

 the composition of the lavas, scorias, and dusts, such as 

 the effect of aerial sorting, loss of chloride and sulphates, 

 or the acid radicles of such salts leaving the bases behind, 

 fumarolic exhaustion, &c,, which are each reviewed iri 

 turn. 



